System Designing

Post Graduate Diploma in Piping Design

Semester I

System Designing

This book is a part of the course by uts, Pune. This book contains the course content for System Designing.

© uts, Pune First Edition 2011 The content in the book is copyright of uts. All rights reserved. No part of the content may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without the prior permission of the publisher. uts makes reasonable endeavours to ensure content is current and accurate. uts reserves the right to alter the content whenever the need arises, and to vary it at any time without prior notice.

Published by

uts

Bavdhan, Pune - 411021 Website : www.utsglobal.edu.in Tel : +91-20-41034800, +91 9011067684

Index Content................................................................................................................................................................... II List of Figures........................................................................................................................................................ V List of Tables.........................................................................................................................................................VI Abbreviations.......................................................................................................................................................VII Case Study.......................................................................................................................................................... 131 Bibliography....................................................................................................................................................... 135 Self Assessment Answers.................................................................................................................................... 138 Book at a Glance

I/uts

Contents Chapter I........................................................................................................................................................ 1 Role of Piping Engineering and Needs of Various Process Industries..................................................... 1 Aim................................................................................................................................................................. 1 Objectives....................................................................................................................................................... 1 Learning outcome........................................................................................................................................... 1 1.1 Introduction............................................................................................................................................... 2 1.2 Piping Design............................................................................................................................................ 3 1.3 Piping Engineering.................................................................................................................................... 3 1.4 Piping Engineer: Roles and Responsibilities............................................................................................ 3 1.5 Design Planning........................................................................................................................................ 4 1.6 Basic Engineering Documents . ............................................................................................................... 4 1.7 Detailed Engineering Documents............................................................................................................. 7 1.8 Miscellaneous Documents........................................................................................................................ 7 1.9 Review of P and IDs................................................................................................................................. 8 1.10 Review of Other Documents................................................................................................................... 9 1.11 Pipe Stress Analysis ............................................................................................................................. 10 1.12 Piping Designing Tools......................................................................................................................... 13 Summary...................................................................................................................................................... 17 References.................................................................................................................................................... 17 Recommended Reading.............................................................................................................................. 17 Self Assessment............................................................................................................................................ 18 Chapter II.................................................................................................................................................... 20 Interdepartmental Interactions and Plot Plan......................................................................................... 20 Aim............................................................................................................................................................... 20 Objectives..................................................................................................................................................... 20 Learning outcome......................................................................................................................................... 20 2.1 Introduction............................................................................................................................................. 21 2.2 Information Sharing................................................................................................................................ 21 2.3 Stages of Data Generation ..................................................................................................................... 22 2.4 Nature of Problems in Interface Areas.................................................................................................... 23 2.5 Mitigation of the Problems in Interface Areas........................................................................................ 24 2.6 Guidelines for Plot Plan ......................................................................................................................... 25 2.7 Criteria for Facility Location.................................................................................................................. 31 Summary...................................................................................................................................................... 33 References.................................................................................................................................................... 33 Recommended Reading.............................................................................................................................. 33 Self Assessment............................................................................................................................................ 34 Chapter III . ................................................................................................................................................ 36 Process Piping and Instrumentation Diagram (P and ID)...................................................................... 36 Aim............................................................................................................................................................... 36 Objectives..................................................................................................................................................... 36 Learning outcome......................................................................................................................................... 36 3.1 Introduction............................................................................................................................................. 37 3.2 Piping and Instrumentation Diagram (P and ID) ................................................................................... 37 3.2.1 Operation................................................................................................................................ 37 3.2.2 Start-Up................................................................................................................................... 38 3.2.3 Maintenance............................................................................................................................ 38 3.2.4 Safety...................................................................................................................................... 38 3.2.5 Aesthetics................................................................................................................................ 39 3.3 Process P and ID Preparation.................................................................................................................. 39 3.4 Basic Instrument Symbols...................................................................................................................... 42 II/uts

Summary .................................................................................................................................................... 48 References.................................................................................................................................................... 48 Recommended Reading.............................................................................................................................. 48 Self Assessment............................................................................................................................................ 49 Chapter IV................................................................................................................................................... 51 Steam Tables and Mollier Diagram........................................................................................................... 51 Aim............................................................................................................................................................... 51 Objectives..................................................................................................................................................... 51 Learning outcome......................................................................................................................................... 51 4.1 Introduction............................................................................................................................................. 52 4.2 Steam: Formation and Properties............................................................................................................ 52 4.2.1 Formation of Steam................................................................................................................ 52 4.2.2 Properties of Steam................................................................................................................. 53 4.3 Steam Tables........................................................................................................................................... 53 4.4 Mollier Diagram...................................................................................................................................... 56 4.4.1 Dryness Fraction Lines........................................................................................................... 56 4.4.2 Constant Specific Volume Lines............................................................................................. 56 4.4.3 Constant Pressure Lines.......................................................................................................... 56 4.4.4 Constant Temperature Lines................................................................................................... 56 4.5 Piping for Steam Distribution................................................................................................................. 57 4.6 Heating Media......................................................................................................................................... 63 4.6.1 Steam Utilisation in the Large Complex................................................................................. 64 4.6.2 Steam Quality......................................................................................................................... 65 4.7 Selection of Steam Pressures.................................................................................................................. 69 4.8 Pressure Drop Factor ............................................................................................................................. 69 4.9 Steam Pipe Sizing and Design ............................................................................................................... 70 4.10 Thermal Insulation................................................................................................................................ 72 Summary .................................................................................................................................................... 75 References.................................................................................................................................................... 75 Recommended Reading.............................................................................................................................. 75 Self Assessment............................................................................................................................................ 76 Chapter V..................................................................................................................................................... 78 Slurry Piping Systems................................................................................................................................ 78 Aim............................................................................................................................................................... 78 Objectives..................................................................................................................................................... 78 Learning outcome......................................................................................................................................... 78 5.1 Introduction............................................................................................................................................. 79 5.2 Slurry Piping Systems............................................................................................................................. 79 5.3 Line Sizing and Pressure Drop............................................................................................................... 80 5.4 Special Considerations............................................................................................................................ 84 5.5 Pump for Slurry...................................................................................................................................... 85 5.6 Instrumentation....................................................................................................................................... 87 Summary...................................................................................................................................................... 88 References.................................................................................................................................................... 88 Recommended Reading.............................................................................................................................. 88 Self Assessment............................................................................................................................................ 89

III/uts

Chapter VI................................................................................................................................................... 91 Pumps........................................................................................................................................................... 91 Aim............................................................................................................................................................... 91 Objectives..................................................................................................................................................... 91 Learning outcome......................................................................................................................................... 91 6.1 Introduction............................................................................................................................................. 92 6.2 Centrifugal Pumps.................................................................................................................................. 92 6.3 Applications of Centrifugal Pump.......................................................................................................... 93 6.4 Calculation of Flow Required................................................................................................................. 94 6.5 Calculation of Pump Head...................................................................................................................... 95 6.6 Classification of Centrifugal Pump......................................................................................................... 96 6.7 Specific Speed......................................................................................................................................... 96 6.8 Power and Efficiency ............................................................................................................................. 97 6.9 Shut in Pressure...................................................................................................................................... 99 6.10 Expanding the Pump Capacity.............................................................................................................. 99 6.11 Importance of Low Discharge Flow................................................................................................... 100 6.12 NPSH (Net Positive Suction Head).................................................................................................... 101 6.13 Importance of Low NPSH.................................................................................................................. 104 6.14 Pump Safety Tips................................................................................................................................ 104 Summary.................................................................................................................................................... 106 References.................................................................................................................................................. 106 Recommended Reading............................................................................................................................ 106 Self Assessment.......................................................................................................................................... 107 Chapter VII............................................................................................................................................... 109 Pneumatic Conveying Terms CEMA Standard No. 805....................................................................... 109 Aim............................................................................................................................................................. 109 Objectives................................................................................................................................................... 109 Learning outcome....................................................................................................................................... 109 7.1 Introduction............................................................................................................................................110 7.2 List of Pneumatic Conveying Terms......................................................................................................110 7.3 Material Characterisation.......................................................................................................................111 7.4 Basic Terms and Definitions..................................................................................................................115 Summary.....................................................................................................................................................117 References...................................................................................................................................................117 Recommended Reading.............................................................................................................................117 Self Assessment...........................................................................................................................................118 Chapter VIII.............................................................................................................................................. 120 Cross – Country Pipe – Line.................................................................................................................... 120 Aim............................................................................................................................................................. 120 Objectives................................................................................................................................................... 120 Learning outcome....................................................................................................................................... 120 8.1 Introduction........................................................................................................................................... 121 8.2 Pipeline System..................................................................................................................................... 121 8.3 Limitations of Modes of Transport....................................................................................................... 122 8.4 Advantages and Disadvantages of Cross-Country Pipe-Lines.............................................................. 122 8.5 Preliminary Work for a Cross-Country Pipe-Line Project.................................................................... 123 8.6 Salient Steps in Detail Engineering...................................................................................................... 127 Summary.................................................................................................................................................... 128 References.................................................................................................................................................. 128 Recommended Reading............................................................................................................................ 128 Self Assessment.......................................................................................................................................... 129

IV/uts

List of Figures Fig. 1.1 Large-scale piping system ................................................................................................................ 2 Fig. 1.2 Piping engineering factors................................................................................................................. 4 Fig. 1.3 Process of piping system design........................................................................................................ 9 Fig. 1.4 Object diagram of piping system..................................................................................................... 10 Fig. 1.5 Stress-strain curve.............................................................................................................................11 Fig. 1.6 Stress analysis tool.......................................................................................................................... 15 Fig. 1.7 Routing process of main pipes......................................................................................................... 16 Fig. 2.1 Interaction between different departments in an industry............................................................... 21 Fig. 2.2 Data transfer from piping to other departments / clients / agencies................................................ 23 Fig. 2.3 Plot plan........................................................................................................................................... 26 Fig. 2.4 Plot plan and road............................................................................................................................ 27 Fig. 2.5 Location map of project site ........................................................................................................... 29 Fig. 2.6 A typical plot plan drawing.............................................................................................................. 30 Fig. 3.1 Process and instrument symbols...................................................................................................... 42 Fig. 3.2 Process and instrument symbols (continued).................................................................................. 43 Fig. 3.3 Process and instrument symbols (continued).................................................................................. 44 Fig. 3.4 Use of P and ID symbols................................................................................................................. 45 Fig. 3.5 Tag descriptors................................................................................................................................. 45 Fig. 3.6 Tag numbers..................................................................................................................................... 46 Fig. 3.7 Process flow diagram (PFD)............................................................................................................ 47 Fig. 4.1 Mollier diagram............................................................................................................................... 57 Fig. 4.2 Resistance of valves and fittings to flow of fluids........................................................................... 59 Fig. 4.3 Recommended take-off point with branch drainage........................................................................ 60 Fig. 4.4 Drain and vent................................................................................................................................. 61 Fig. 4.5 Relaying to higher level................................................................................................................... 61 Fig. 4.6 Ineffective and proper drainage point.............................................................................................. 62 Fig. 4.7 Steam line reducer........................................................................................................................... 62 Fig. 4.8 Automatic air vent located opposite the steam inlet on the jacketed pan........................................ 67 Fig. 4.9 Steam separator................................................................................................................................ 68 Fig. 4.10 Pressure reducing valve................................................................................................................. 69 Fig. 4.11 Pressure drop in stream pipes........................................................................................................ 70 Fig. 5.1 A typical graph for slurry specific gravity....................................................................................... 81 Fig. 5.2 A typical graph to calculate NRec................................................................................................... 82 Fig. 5.3 Slope of line..................................................................................................................................... 84 Fig. 5.4 Wear Prone Zone............................................................................................................................. 84 Fig. 5.5 Centrifugal pump............................................................................................................................. 85 Fig. 5.6 Piston and plunger pump................................................................................................................. 86 Fig. 6.1 Liquid flow path inside a centrifugal pump..................................................................................... 92 Fig. 6.2 Components of centrifugal pump.................................................................................................... 93 Fig. 6.3 Efficiency relative to different blade shapes................................................................................... 97 Fig. 6.4 Types of impeller............................................................................................................................. 98 Fig. 6.5 Shut in pressure............................................................................................................................... 99 Fig. 6.6 Low discharge flow....................................................................................................................... 101 Fig. 6.7 Effect of NPSH on pump............................................................................................................... 102 Fig. 6.8 NPSH............................................................................................................................................ 103 Fig. 6.9 Design of vortex braker ................................................................................................................ 104 Fig. 8.1 Typical mode-wise transportation of petroleum products............................................................. 121 Fig. 8.2 Modes of transportation of petroleum-A comparison.................................................................... 122 Fig. 8.3 Product transportation.................................................................................................................... 124

V/uts

List of Tables Table 2.1 L:B ratios and actual area relationship.......................................................................................... 28 Table 3.1 Major steps for the preparation of any process P and ID.............................................................. 39 Table 3.2 Details of the documents for preparation of P and ID................................................................... 41 Table 4.1 Example of saturated water and steam (temperature) table.......................................................... 54 Table 4.2 Saturated water and steam (pressure) tables................................................................................. 55 Table 4.3 Approximations of equivalent length of fittings........................................................................... 58 Table 4.4 Steam pipe sizing (carrying capacity in kg/h)............................................................................... 63 Table 4.5 Comparison of heating media with steam..................................................................................... 65 Table 4.6 Pipe NB according to different surface temperatures................................................................... 73 Table 4.7 Heat loss from fluid inside pipe (W/m)........................................................................................ 73 Table 6.1 Different types of impellers and their rotative speed.................................................................... 97 Table 6.2 Multiplication factor and absorbed power for pump motor.......................................................... 98 Table 7.1 The individual particle shape descriptions...................................................................................112 Table 7.2 The general compositions found in a bulk material.....................................................................113

VI/uts

Abbreviations ACFM API BHP BOM CEMA DG ETP FAD HAZOP HVAC ICFM MCC MTO NB NPSH NPSHa P & IDs PCC PFD ROW SCFM UFD WHP

- - - - - - - - - - - - - - - - - - - - - - -

Actual Cubic Feet per Minute Active Pharmaceutical Ingredients Brake Horsepower Bill of Materials Conveyor Equipment Manufacturers Association Diesel Generating Effluent Treatment Plant Free Air Delivered Hazard and Operability Heating, Ventilating and Air Conditioning Inlet Cubic Feet per Minute Motor Control Center Material Take Off Nominal Bore Net Positive Suction Head Available NPSH Piping and Instrumentation Diagrams Power Control Center Process Flow Diagram Right of Way Standard Cubic Feet per Minute Utility Flow Diagram Water Horsepower

VII/uts

VIII/uts

Chapter I Role of Piping Engineering and Needs of Various Process Industries Aim The aim of this chapter is to: •

define piping system

•

explain concept of piping engineering

•

illustrate the role of piping engineers

Objectives The objectives of this chapter are to: •

describe the pipe stress analysis

•

explain the piping designing tools

•

state the advantages of system designing software

Learning outcome At the end of this chapter, the students will be able to: •

examine various statutory bodies involved in piping system design

•

analyse the stress analysis process

•

describe the documents in piping system design

1/uts

System Designing

1.1 Introduction Piping is an asset for any project. Piping is a system of pipes (hollow, cylindrical tubes) used to pass on liquids, gases and other materials often under pressure and thermal loads, from one location to another within industrial facilities such as petroleum refineries, chemical and petrochemical manufacturing, natural gas processing, electricitygenerating power plants and many others. Industrial plant piping and the accompanying in-line components can be manufactured from various steel alloys, titanium, aluminium, copper, glass or various plastics. These in-line components are known as fittings and valves. Process control systems use in-line sensors and control valves installed in the piping to monitor and regulate the desired temperatures, pressures, flow rates and process vessel liquid levels of the fluids being transported and processed. Piping and control systems are referred to as piping and instrumentation diagrams.

Fig. 1.1 Large-scale piping system (Source: http://www.equityeng.com/piping.php)

2/uts

1.2 Piping Design •

Piping system includes: ‚‚ pipe ‚‚ fittings (e.g. elbows, reducers, branch connections, etc.) ‚‚ flanges, gaskets, bolting ‚‚ valves ‚‚ pipe supports

•

The routing and layout of the pipes fittings in a complex piping system is known as piping system design. This is typically done by experienced piping draftsmen known as piping designers.

•

Piping system design constitutes a major part of the design and engineering effort in any facility. The discipline of piping design requires good technical skills such as: ‚‚ the principles and practice of drafting and creating isometric drawings ‚‚ familiarity and experience with computerised drafting programs ‚‚ the ability to visualise and develop an industrial facility plot plan ‚‚ a basic understanding of fluid flow, piping materials and piping specifications ‚‚ an extensive knowledge of piping standards and codes as well as process safety codes and practices ‚‚ a knowledge of the various types of pipe connections such as threaded, welded and flanged connections ‚‚ a knowledge of the various types of valves and their use ‚‚ a good understanding of pipe stress analysis

1.3 Piping Engineering •

Piping engineering is a specialised branch of engineering dealing with design & layouts of piping network along with the equipments in a process plant. These layouts form a complete blue print of the plant & are used for plant construction at site.

•

The most important factors to be considered are process requirements, safety, operations, maintenance, compliance with statutory requirements & economy.

1.4 Piping Engineer: Roles and Responsibilities A piping engineer is a mechanical engineer who specialises in disciplines which deal with the design, planning and installation of various plumbing and piping systems for a wide variety of industries. The responsibilities of piping design engineer begins with: •

preparation of plot plan, equipment layouts piping studies, piping specification

•

review of process package

•

giving inputs to civil, vessel, electrical or instrumentation groups for various purposes

Goes through: •

preparation of piping layouts, isometrics, support drawings

•

stress analysis

•

procurement assistance

•

preparation of drawings for statutory approvals

•

preview of vendor drawings

•

coordination with various engineering groups & site

3/uts

System Designing

Ends with: •

completion & commissioning of plant Process Equipments Operations

Safety

Economy

Piping Engineering

Statutory requirements

Process Package

Plant Designs and Layout

Maintainence

Fig. 1.2 Piping engineering factors

1.5 Design Planning Following information is required for planning the various design activities: •

contract instructions

•

project design basis & scope of work

•

basic engineering documents

•

site design data including facilities around the plot

•

contour & survey drawing

•

applicable codes, standards & statutory regulations

•

project schedule & network

1.6 Basic Engineering Documents The main documents covered by design engineer are: Equipment layout •

4/uts

These include the documents showing layout of all equipments satisfying the process requirements, safety & statutory regulations, operations, ease of maintenance and economy.

•

Equipment layout including tanks, vessels, process pumps and other rotating machinery, must show the following: ‚‚ package items ‚‚ pipe racks ‚‚ electrical & instrument cable trays ‚‚ control rooms ‚‚ A/C ducting ‚‚ offices & maintenance areas ‚‚ building features including columns, beams, walls, floor openings, staircases, passages etc. ‚‚ show tube removal space for heat exchangers ‚‚ show monorails lifting bays & hoists etc.

•

Consideration must be given to the following while ‚‚ developing equipment layouts ‚‚ process requirements ‚‚ operations & maintenance requirements ‚‚ hazardous area classification ‚‚ safety requirements ‚‚ factory inspector’s requirements ‚‚ civil requirements ‚‚ erection / dismantling requirements ‚‚ future provisions

Piping layouts •

These include documents showing layouts of piping network to carry fluids from one equipment to another in a process plant.

•

Piping layouts is required by site for construction to prepare isometrics.

•

Piping layouts must consider process requirements, operations and maintenance requirements, area classification, safety requirements, factory inspector’s requirements, civil requirements, erection or dismantling requirements, future provisions etc.

•

Document required while developing piping layout are: ‚‚ equipment layouts ‚‚ process piping and instrumentation diagrams (P & IDs) ‚‚ utility piping and instrumentation diagrams (P & IDs) ‚‚ line designation list ‚‚ piping specification ‚‚ equipment data sheets or vendor drawings ‚‚ civil drawings ‚‚ inline instrument details ‚‚ insulation requirements

5/uts

System Designing

•

Following points should be kept in mind while developing piping layouts ‚‚ process requirements, e.g. slopes, vents & drains, barometric leg for vacuum lines ‚‚ instrument requirements e.g. straight length for flow measurement ‚‚ location of control valves, safety valves ‚‚ safety requirements ‚‚ operations & maintenance ‚‚ accessibility ‚‚ service stations, safety showers

Plot plan It includes arranging all plant units in a logical manner to take care of material flow, statutory requirements and good engineering practices. •

Plot plan shows overall areas & locates the co-ordinates of: ‚‚ process unit ‚‚ raw material storages ‚‚ finished product storage ‚‚ utility generation areas ‚‚ pipe racks ‚‚ electrical receiving and distribution substation ‚‚ facility blocks e.g. work shop ,weigh bridge, canteen ‚‚ administration lock, security, car or lorry park etc. ‚‚ flare system ‚‚ effluent treatment ‚‚ green belt ‚‚ future requirements etc.

•

Following documents are required to develop the plot plan: ‚‚ plot boundary and contour survey ‚‚ access by transportation modes (road, rail ) ‚‚ incoming utilities e.g. electrical, power, water ‚‚ feed stock etc. ‚‚ wind direction ‚‚ facilities around the plot etc.

•

The following factors should be kept in mind while developing the plot plan: ‚‚ Statutory requirements, e.g. factory inspector, chief controller explosives, tariff advisory committee, pollution board, local bodies, aviation authorities, hazardous area classification. ‚‚ site contour, drainage, effluent disposal, plant roads, space for pipe rack, underground lines etc. ‚‚ process & clients requirements ‚‚ material movement & workers management

•

The following should be ensured while developing the plot plan: ‚‚ utilities are closer to process plant to cut down the length of pipes & cable racks ‚‚ raw material and finished product warehouse are closer to access road or rail ‚‚ utility areas are kept near to each other as utility operators are common ‚‚ wind direction is taken care of while locating chimneys cooling tower etc. ‚‚ effluent disposal is towards natural plot gradient ‚‚ hazardous tank ages are at safe distance from process plant

6/uts

Pipe rack study sketches These are prepared taking into account requirements of piping, electrical & instrument cable trays to be routed between various plant areas. These documents are used by civil, piping, electrical and instrument group to prepare detailed construction drawings. Study piping layouts These are prepared to show routing of critical process lines which could affect functioning of plant. This document is reviewed by process licensor and forms basis of detailed piping layout drawings. Piping specifications These documents specify in detail all piping items required for the plant. Various piping items required for a particular duty condition, depending on type of fluid such as line pressure and temperature, are listed under one specification class. •

Utility flow diagram (UFD)

•

This document is similar to P&ID’s

•

Prepared based on utility summary

•

Prepared based on utility summery furnished by process group

•

Shows utility generation and distribution in the plant.

Line numbering and line list All process and utility lines appearing in P&IDs and UFDs are given unique serial numbers on these documents. The operating, design and test conditions, insulation and painting requirements are listed on line list. Critical line list All line requiring stress or vibration analysis etc. are listed in this document.

1.7 Detailed Engineering Documents These mainly cover the following documents: •

piping layouts drawings

•

material take off (MTO) or bill of materials (BOM) for piping items

•

nozzle orientation for fabricated equipments

•

stress analysis

•

piping isometric drawings

•

piping support drawings

•

fire fighting specification

•

drawings for statuary approvals

1.8 Miscellaneous Documents These mainly cover the following documents: •

review of drawings for machinery & other brought-outs

•

review of drawings for special piping items

•

specifications for bellows, spring, hangers etc.

•

specification for insulation and painting of equipments & piping items

•

updating of P&IDs based on detailed engineering

•

scheme for the erection of equipments in consultation with site engineer

7/uts

System Designing

1.9 Review of P and IDs •

A piping and instrumentation diagram (P and ID) is a schematic illustration of functional relationship of piping, instrumentation and system equipment components.

•

P and ID shows all of piping including the physical sequence of branches, reducers, valves, equipment, instrumentation and control interlocks.

•

The P and IDs are used to operate the process system.

•

Following information should be available in P and IDs: ‚‚ legends, notes, abbreviations ‚‚ location of change in piping specification ‚‚ specific requirements like slope, elevation difference , minimum running length, process drains and vents ‚‚ type of heating (jacketing, steam or electric heating) ‚‚ proper symbols for piping items ‚‚ equipments and nozzle numbers ‚‚ all instrumentation and control valves ‚‚ continuation sheet numbers ‚‚ instrumentation and designations ‚‚ mechanical equipment with names and numbers ‚‚ all valves and their identifications ‚‚ process piping, sizes and identification ‚‚ miscellaneous - vents, drains, special fittings, sampling lines ‚‚ permanent start-up and flush lines ‚‚ flow directions ‚‚ interconnection references ‚‚ control inputs and outputs, interlocks ‚‚ interfaces for class changes ‚‚ seismic category ‚‚ quality level ‚‚ computer control system input ‚‚ vendor and contractor interfaces ‚‚ identification of components and subsystems delivered by others ‚‚ intended physical sequence of the equipment

•

A P and ID should not include: ‚‚ instrument root valves ‚‚ control relays ‚‚ manual switches ‚‚ equipment rating or capacity ‚‚ primary instrument tubing and valves ‚‚ pressure temperature and flow data ‚‚ elbow, tees and similar standard fittings ‚‚ extensive explanatory notes

8/uts

1.10 Review of Other Documents These include: •

Utility summary: This document reflects the various utilities consumed by each of the equipment with conditions like pressure, temperate, flow, state of fluid and critical factor like freezing point etc.

•

Conceptual equipment layouts: This document gives the general arrangement of the equipments considering the process requirements like inter-distances and approximate elevations of the equipments.

•

Piping material specification: Basic material for piping items, valve specifications, special flanges & gaskets required etc.

•

Type of storage required: This document shall mention the state of the fluid and type of equipments to be used for the storage like active pharmaceutical ingredients (API) tank, dehumidified atmosphere (warehouse) etc.

•

Hazard classification: This document mentions the type of hazard for the fluids being handled (e.g. class a/b/c, flammability toxicity etc.) and the special precautions to be taken care of.

•

Future expansion requirements: These are to be mentioned by the client and to be taken care for the space requirement during the layout stage.

Building Spec.

System Design

Basic Design

Design Modification

Design Modification

Design Modification

3-D Modeling

3-D Model

2-D Drawing

Production Drawing

Detail Design

Functional Design

2-D Arrangement Drawing

Production Design Hull Structure Information

Production/ Installation Technology

Outfitting Information

Empirical Knowledge

Maritime Regulation

Fig. 1.3 Process of piping system design (Source: http://icad.kaist.ac.kr/~msh/ARS/cad-ars.htm)

9/uts

System Designing

Piping_Systems a_kind_of

Aux_Piping_Systems

Main_Piping_Systems consist_of

reference_to

consist_of

reference_to Equipments

Pipe_Lines

connected_with consist_of Connectors

reference_to

reference_to connected_with

Points reference_to Pipe_Routes consist_of

Catalogs

reference_to

Piping_Components a_kind_of

reference_to

Str_pipes Valves Elbows Reducers Flanges Sleeve_Joints Loops Sliding-Joints

Fig. 1.4 Object diagram of piping system (Source: http://icad.kaist.ac.kr/~msh/ARS/cad-ars.htm)

1.11 Pipe Stress Analysis •

Stress of a material is the internal resistance per unit area to the deformation caused by applied load.

•

Strain is the unit deformation under applied load.

•

Stress – strain curve is a curve in which unit load or stress is plotted against unit elongation, technically known as strain.

10/uts

‚‚ O – A represents the stress is directly proportional to strain, and point A is known as proportional limit. ‚‚ Point B represents elastic limit beyond which the material will not return to its original shape when unloaded but will retain a permanent deformation called permanent set. ‚‚ Point C is called yield point and is the point at which there is an appreciable elongation or yielding of the material without any corresponding increases of load. ‚‚ Point D is ultimate stress or ultimate strength of material. ‚‚ Point E is the stress at failure known as rupture strength.

Ultimate strength D

S T

E S

E

Rupture strength

Yield point

R B

Actual rupture strength

C

A

Elastic limit

S Proportional limit

O

STRAIN Fig. 1.5 Stress-strain curve (Source: http://civil-engg-world.blogspot.com/2008_10_01_archive.html) •

Stress analysis is a critical component of piping design through which important parameters such as piping safety, safety of related components and connected equipment and piping deflection can be addressed.

•

Piping stress analysis is a term applied to calculations, which address the static and dynamic loading resulting from the effects of gravity, temperature changes, internal and external pressures, changes in fluid flow rate and seismic activity.

•

Codes and standards establish the minimum requirements of stress analysis.

•

The objective of pipe stress analysis is to prevent premature failure of piping and piping components and ensuring that piping stresses are kept within allowable limits.

11/uts

System Designing

•

Why stress analysis? ‚‚ Stress analysis is carried out for all lines covered in critical line list. ‚‚ This is to ensure flexibility of lines operating at elevated temperatures and also to ensure that load on equipment nozzles is within remissible limits due to expansion of piping. ‚‚ Stress sketches are prepared in isometric form on stress sheet showing location of all supports.

•

Stress analysis ensures ‚‚ integrity of pipe and piping components against pressure and dead weight (fixed weight of a structure or piece of equipment on its supports) ‚‚ flexibility of pipe from thermal expansion ‚‚ safety of nozzles to the connected critical equipments ‚‚ proper supporting against dead weight, thermal expansion & occasional loads ‚‚ proper selection and specification of special supports like spring hangers and expansion joints

•

Stress categories The major stress categories are primary, secondary and peak stresses. ‚‚ Primary stresses These are developed by imposed loading and are necessary to satisfy the equilibrium between external and internal forces and moments of the piping system. Primary stresses are not self-limiting. ‚‚ Secondary stresses These are developed by the constraint of displacements of a structure. These displacements can be caused either by thermal expansion or by outwardly imposed restraint and anchor point movements. Secondary stresses are self-limiting. ‚‚ Peak stresses

Unlike loading condition of secondary stress which causes distortion, peak stresses cause no significant distortion. Peak stresses are the highest stresses in the region under consideration and are responsible for causing fatigue failure.

•

The piping engineers can provide protection against some of the failure modes by performing stress analysis according to piping codes. There are various failure modes that could affect a piping system such as: ‚‚ Failure by general yielding: failure is due to excessive plastic deformation. ‚‚ Yielding at sub elevated temperature: body undergoes plastic deformation. ‚‚ Yielding at elevated temperature: after slippage, material re-crystallises and hence yielding continues without increasing load. This phenomenon is known as creep. ‚‚ Failure by fracture: Body fails without undergoing yielding. –  Brittle fracture: Occurs in brittle materials. – Fatigue: Due to cyclic loading initially a small crack is developed which grows after each cycle and results in sudden failure.

•

How Stress analysis is carried out? ‚‚ Stress analysis is carried out using softwares. ‚‚ Output data is tabulated on stress sketch. ‚‚ A typical stress sketch giving input and output data is enclosed. ‚‚ Nozzle loadings on equipments are transmitted to mechanical group for approval if it exceeds permissible limit. ‚‚ Piping stress analysis process includes: ‚‚ stress sketch report ‚‚ support arrangement ‚‚ design conditions ‚‚ material code ‚‚ pipe size, insulation thickness

12/uts

‚‚ ‚‚ ‚‚ ‚‚ ‚‚ ‚‚ •

nozzle displacements loadings code compliance stress nozzle loads loads on supports piping movements

Statutory approvals Various statutory bodies whose approvals are necessary in piping system designing are: ‚‚ Chief inspector of factories ‚‚ Chief inspector of boilers ‚‚ Chief controller of explosives ‚‚ Petroleum act & rules ( for storage tanks) ‚‚ Gas cylinder & static & mobile pressure vessel rules ‚‚ Oil industry safety directorate ‚‚ Tariff advisory committee ‚‚ Pollution control board ‚‚ Local bodies (municipal or district authority, port authority, aviation authority, highway authority etc.) ‚‚ electrical inspection ‚‚ town planning authority

•

Responsibility of piping engineering onsite List of the major activities onsite includes: ‚‚ supervision of fabrication & erection of equipments and piping ‚‚ co-ordination with clients, contractors, & detail engineering office ‚‚ planning & monitoring the work for timely completion of the project ‚‚ conduct welding procedure & performance qualifications ‚‚ assure the quality of work done by contractors ‚‚ maintain QA or QC records ‚‚ assure the lifting equipments tools & tackles are in proper condition ‚‚ check the alignments of equipments ‚‚ assure the work is carried out as per P & IDs, layouts drawings & isometrics ‚‚ check critical pipe supports ‚‚ check visual inspection & radiography of weld joints ‚‚ check insulation & painting as per the specifications

1.12 Piping Designing Tools •

Advances in computer technology are providing better tools to simplify the tasks faced by engineers, especially those responsible for designing and managing process lines that handle fluids and gases.

•

Tools such as spreadsheets can be used to reduce errors in calculations. Spreadsheets, however, are generally tailored for very specific problems. Software tools help to avoid such engineering errors.

•

Computer-aided design (CAD) is the use of computer technology for the process of design and designdocumentation.

•

CAD softwares provide the user with input-tools for the purpose of streamlining design processes; drafting, documentation, and manufacturing processes.

•

CAD output is often in the form of electronic files for print or machining operations.

13/uts

System Designing

•

Software tools used for piping design are: ‚‚ 2D design tools like Microstation, AutoCAD etc. ‚‚ 3D design tools like PDS (Plant Design System), PDMS (Plant Design and Management System) ‚‚ CAESAR II ‚‚ CAEPipe ‚‚ AFT IMPULSE

•

AutoCAD or Micro Station are useful for piping applications: ‚‚ P&IDs ‚‚ Plot plans ‚‚ Equipments layouts ‚‚ Piping plans ‚‚ Isometrics ‚‚ Piping support drawings

•

Salient features of 3D design tools are: ‚‚ 3D software inputs data via forms and menu ‚‚ 3D model, easy conceptualise ‚‚ ing of plant layouts ‚‚ On line clash detections ‚‚ Various information obtained through PDS/PDMS are: –  Piping layouts –  Ducting layouts –  Cable tray layouts –  Isometrics and material take-off ‚‚ Customisation ‚‚ Ability to get inputs from various engineering disciplines ‚‚ Piping specification in users format

•

The advantages of piping design tools are: ‚‚ replacement of drawing board ‚‚ neat drawings ‚‚ fast modifications ‚‚ copying of identical parameters ‚‚ time saving ‚‚ accurate results ‚‚ fast problem solving – can solve problems with number of anchors and number of piping branches which by manual method is unimaginable –  can solve problems of occasional loads and various combinations of loads

14/uts

Fig. 1.6 Stress analysis tool (Source: http://www.cadalyst.com/aec/aec-from-ground-up-plant-and-piping-software-2867)

15/uts

System Designing

START

(1)

Set Design Environment

(2)

Decide Design Procedure of Piping Sys. Decide Typical Section

(3)

Decide Main Pipes Based on Priorities

Modification of Design Factors NO

All the Main Pipes Designed

YES

(4)

Visualization of the Design

NO Design Rules Satisfactory?

END Fig. 1.7 Routing process of main pipes (Source: http://icad.kaist.ac.kr/~msh/ARS/cad-ars.htm)

16/uts

Summary •

Piping is an asset for any project.

•

Piping is a system of pipes (hollow, cylindrical tubes) used to pass on liquids, gases and other materials often under pressure and thermal loads, from one location to another within industrial facilities.

•

Piping engineering is a specialised branch of engineering dealing with design & layouts of piping network along with the equipments in a process plant. These layouts form a complete blue print of the plant & are used for plant construction at site.

•

Piping layouts include documents showing layouts of piping network to carry fluids from one equipment to another in a process plant.

•

Plot plan includes arranging all plant units in a logical manner to take care of material flow, statutory requirements and good engineering practices.

•

Equipment layout include the documents showing layout of all equipments satisfying the process requirements, safety & statutory regulations, operations, ease of maintenance and economy.

•

Stress of a material is the internal resistance per unit area to the deformation caused by applied load. Strain is unit deformation under applied load.

•

Stress –strain curve is a curve in which unit load or stress is plotted against unit elongation, technically known as strain.

•

Piping stress analysis is a term applied to calculations, which address the static and dynamic loading resulting from the effects of gravity, temperature changes, internal and external pressures, changes in fluid flow rate and seismic activity.

•

Codes and standards establish the minimum requirements of stress analysis.

•

Advances in computer technology are providing better tools to simplify the tasks faced by engineers, especially those responsible for designing and managing process lines that handle fluids and gases.

•

Tools such as spreadsheets can be used to reduce errors in calculations. Spreadsheets, however, are generally tailored for very specific problems. Software tools help to avoid such engineering errors.

•

CAD softwares provide the user with input-tools for the purpose of streamlining design processes; drafting, documentation, and manufacturing processes.

References •

Fundamentals of Pipe Stress Analysis with Introduction to CAESAR II [Online]. Available at: < http://www. idc-online.com/pdf/training/mechanical/SA.pdf>. [Accessed 5 April 2011].

•

Stress analysis for process piping [Online]. Available at: . [Accessed 5 April 2011].

•

P&ID - Piping and Instrumentation Diagram [Online]. Available at: . [Accessed 5 April 2011].

Recommended Reading •

Kellogg, 1964. Design of Piping Systems, 2nd ed., John Wiley & Sons Inc.

•

Nayyar, M. L., 2000. Piping Handbook, 7th ed., McGraw-Hill.

•

Towler, G. P., & Sinnott R. K., 2008. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design, Butterworth-Heinemann.

•

Weaver, R., 1986. Process piping drafting, 3rd ed., Gulf Pub Co.

17/uts

System Designing

Self Assessment 1. Piping system does not include __________. a. pipe b. flanges c. valves d. logical gates 2. Piping system design is typically done by experienced piping draftsmen known as __________. a. piping designers b. administrators c. managers d. chemical engineer 3. Which of these is not an important factor to be considered in piping engineering? a. process requirements b. safety and operations c. social ethics d. maintenance 4. The responsibilities of piping design engineer does not begin with ________. a. preparation of plot plan, equipment layouts piping studies, piping specification b. review of process package c. giving inputs to civil, vessel, electrical or instrumentation groups for various purposes d. stress analysis 5. The responsibilities of piping design engineer end with ________. a. procurement assistance b. completion & commissioning of plant c. preparation of drawings for statutory approvals d. preview of vendor drawings 6. Equipment layout does not show___________. a. package items b. pipe racks c. future provisions d. A/C ducting 7. Which of the following statements is FALSE? a. Piping layouts is required by site for construction to prepare isometrics. b. Piping layouts must consider process requirements, operations and maintenance requirements. c. Piping layouts include documents showing layouts of piping network to carry fluids from equipment to another in a process plant. d. Piping layouts include the documents showing layout of all equipments satisfying the process requirements, ease of maintenance and economy.

18/uts

8. Which point is not included while developing piping layouts? a. process requirements b. instrument requirements c. aesthetics d. safety requirements 9. _______ are prepared taking into account requirements of piping, electrical & instrument cable trays to be routed between various plant areas. a. Pipe rack study sketches b. Piping layouts c. Piping specifications d. Utility flow diagram 10. Critical line list includes ____________. a. all line requiring stress or vibration analysis etc b. all process and utility lines appearing in P&IDs and UFDs c. documents specifying in detail all piping items required for the plant d. piping layouts drawings

19/uts

System Designing

Chapter II Interdepartmental Interactions and Plot Plan Aim The aim of this chapter is to: •

define plot plan

•

describe interaction between different departments in an industry

•

state the role of information sharing

Objectives The objectives of this chapter are to: •

describe the mitigation of the problems in interface areas

•

explain the major roles of plot plan

•

enlist the guidelines for plot plan or layout engineering

Learning outcome At the end of this chapter, the students will be able to: •

examine various criteria for facility location

•

illustrate the steps involved in preparation of a plot plan

•

explain the nature of problems in interface areas

20/uts

2.1 Introduction In general, every activity or work, whether big or small, personal or social, urgent or routine, is successfully executed by a team. The teamwork includes the co-ordinated efforts of all the participants. In particular, engineering of a project is a task of a team. The success of a project depends on various factors. Knowledge, skills and resources can not be beneficial for successful completion of the project, if it lacks proper co-ordination. In any task, there are two categories of the responsibilities resting with each individual member of the team and interface areas. Individual responsibilities are solely to be executed by the individual, using his own knowledge, skills, efforts, data resources. Responsibilities in interface areas are those where each individual has to interact with one or more of the other team members or departments. This is done by sharing of the information, understanding each other’s problems and resolving or arriving at the best compromise on conflicting requirements to achieve the best results. But there should not be any compromise in product or process quality, requirements and schedule. In order to achieve the common goal of the team, there has to be appropriate and efficient interaction between various departments, agencies, clients and technology licensors. As a result, the transfer of data, documents and information between individual team members can be made in very comprehensive, rational and effective manner. The diagram below shows how the departments at a typical manufacturing company interact with each other during production. The product is developed by the three departments. The researchers gather information on the new and improved materials that can be machined. Then, the new product system is developed using complex engineering software such as AutoCAD. The products are tested on the computer system. The designers take the findings from the research and development stage. All three departments work very closely together and meet at least on a daily or weekly basis. Sometimes they work in teams made up of researchers, development managers and designers. PRODUCT DEVELOPMENT RESEARCH PRODUCTION

DEVELOPMENT

PRODUCTION PLANNING

DESIGN PRODUCTION CONTROL

QUALITY CONTROL MARKETING HANDLING AND DISTRIBUTION

STORAGE

CUSTOMERS

Fig. 2.1 Interaction between different departments in an industry (Source: http://www.technologystudent.com/vocat/intact1.htm)

2.2 Information Sharing Broad responsibilities of piping engineer are to: ‚‚ receive or study basic engineering package ‚‚ receive or study equipment layouts, P&IDs, specifications ‚‚ prepare general plot plan of all facilities ‚‚ prepare layouts of each individual units ‚‚ prepare underground coordination plan ‚‚ prepare piping study drawings 21/uts

System Designing

‚‚ prepare piping plans or layouts ‚‚ prepare piping specifications ‚‚ prepare piping design or stress analysis or support systems ‚‚ prepare MTO or BOM for pipes or pipe fittings or valves etc. ‚‚ prepare piping isometrics ‚‚ prepare or co-ordinate material handling systems with the designers or suppliers ‚‚ prepare or co-ordinate fire- fighting system •

For the purpose of execution of the above responsibilities, piping engineer has to send as well as receive lots of data. This data-exchange forms the interface area.

•

In order to enable other departments to execute their individual responsibilities, piping has to initiate certain documents and send to others, so as to receive the required inputs from them.

2.3 Stages of Data Generation •

Generally, it is neither possible nor necessary to generate all design data in one stroke. The data gets built up as the engineering, ordering and detailing are in progress. Hence piping engineer must know : ‚‚ What data is required? ‚‚ In what sequence it is required? ‚‚ Which data is required by whom? ‚‚ At what stage a particular data is required? ‚‚ What is preliminary data? ‚‚ What is final data?

•

For the above purpose, the following guideline should be followed: ‚‚ preliminary data for overall knowledge of everyone ‚‚ data for preliminary estimates (may be with ± 30% accuracy) ‚‚ data for obtaining comments/mark- ups etc. from others ‚‚ data for preliminary design ‚‚ data for sending enquiries or tenders to suppliers or contractors ‚‚ data for approval of clients or licensors ‚‚ data for design and detail engineering ‚‚ data for construction ‚‚ data for final documentation

22/uts

Process Project Manager Planning

Control loops /On-line Instruments / Cable Routing

Piping Department

i ec

.F m r + e m TO eco ord M e R h. as ng pi ec urch i T P + P Sp

ns co f eo fic as ngs ci e l e i p s Re raw /S nt ut me D o y re La qui re Equipment Loads Nozzle details

n

Is

or

n

tio

c tru

tio

a fic

su

D

ra

Vendors

Instruments

P & ID’s /Spec.

Co Iss -o & ue rd i pr of ob co nati on lem ns /S s o truc ch n d tio ed ela n d ys raw ule in gs

Process description

Clients

w

eo

fc

in

g

&

on

str

M

TO

uc

Mechanical

tio

Contracts Procurement cost Estimation

n

Construction Vendors

Fig. 2.2 Data transfer from piping to other departments / clients / agencies

2.4 Nature of Problems in Interface Areas •

The efficient and effective engineers depend on the co-ordinated team efforts.

•

Hence any problem in interaction areas can be a serious issue to the project. The problems within the departments can be resolved quickly as they are seen or noticed in day-to-day work by the working and supervising persons.

•

But the problems in interface zone go concealed or hidden many times until some serious situations arise. This can create crisis, hasty actions and decisions and can lead to many more problems, delays and mistakes.

•

Hence all must know what are the likely problem areas and their nature in the interface zone.

•

Piping engineer, being at the focus of engineering data coordination must carefully avoid these problems, by using proper systems, data banks, communication methods and timely action.

•

The nature of problems arising in the interface areas can be listed below: ‚‚ Acceptance and use of incomplete or unapproved data can lead to incorrect down-stream activities which can lead to unprofitable work or redoing, and thus wastage of time and efforts. ‚‚ Incomplete study of data received from others and sending incomplete comments to others can mislead others who proceed with their work and return incomplete data for piping engineering, resulting in many more to -and- fro communications on the same topic and delaying everyone’s work. ‚‚ Sending data in inappropriate sequence will disturb the sequence of work to be executed by others. ‚‚ Not sending the revisions in frozen data that is already transferred to others for detail engineering, will erase the part or entire work done by others in office.

23/uts

System Designing

‚‚ Not incorporating the comments or mark-ups sent by others will lead to incomplete or incorrect engineering and also delays, at a very late stage of the project. ‚‚ Hasty action on data generation to meet the stipulated schedule dates will involve mistakes or errors leading to wrong data. ‚‚ Undefined or grey areas are certain portions of the project which are not found covered in the scope of any department. If this is not identified at a very early stage by project manager or not brought to anybody’s notice by the noticing individual, it can lead to a very serious situation. Due to its omission, ordering and the material, equipment or building required for project completion will be delayed. A small thing not executed on account of this reason can hold up the commissioning of the whole or part of the plant. ‚‚ Long delivery items are some of the critical equipments that take long period (10 to 18 months) for delivery by the supplier. Such items have to be tackled at a very early stage of the project. Hence, data for such items have to be generated much earlier and transferred to the concerned disciplines for their early actions. If there is delay on such matters then the entire project can be delayed. ‚‚ Not transferring the data in written form, sketches or drawings can be problematic. Sometimes, a telephonic conversation becomes essential between the two engineers interacting on a particular data. Certain clarifications, dimensions or details are clarified or communicated on telephone. This is acceptable as far as immediate actions are concerned. But the same should be instantly put in writing or on drawing and sent by the piping engineer to the others to use the data. ‚‚ Bad written communication is also a serious issue in interaction between departments. If the hand-drawn sketches or hand-written notes are used for transfer of data, then they should be neat and clear for reading and interpretation by the receiver. ‚‚ Not signing and getting an approval is another issue. Whenever experienced or inexperienced engineer works and prepares data, it should be signed and got approved by the seniors who can point out and correct the mistakes caused by the misconceptions or ignorance of the juniors. If this is not done, serious mistakes will lead to further chain reaction through all others concerned and using the wrong data that has been received. ‚‚ Bye-passing the QA system can be error-prone. Specific or contract related quality assurance procedures are made for each project. While transferring the data, if the steps are omitted or the procedures are violated by taking shortcuts, then such non-compliance can result in use of wrong data or outdated information.

2.5 Mitigation of the Problems in Interface Areas •

The problems in interface areas can be either mitigated or prevented. The above mentioned problems arise due to different sources listed below: ‚‚ improper and/or lack of communication ‚‚ casual approach to the serious nature and importance of the interaction ‚‚ not understanding the QA procedures ‚‚ notion that QA procedures are an unnecessary burden and bye-passing it ‚‚ conflicting situations, difference of opinions leading to no acceptable solution ‚‚ not following the priorities or not prioritising the work and generating data in wrong sequence ‚‚ not bothered of others’ problems, disciplines, norms, codes or practices ‚‚ likes and dislikes for persons and type of work ‚‚ lack of cost consciousness or knowledge ‚‚ ignorance or tendency to hide ignorance ‚‚ shyness to interact with the superiors or colleagues

24/uts

•

To prevent or minimise the problems in interface areas, following points should be considered by the engineer: ‚‚ Clear thinking ‚‚ Clear and complete communication ‚‚ Studying or understanding the job under execution ‚‚ Habit of listing down the doubts or queries while studying the basic data received ‚‚ Making a checklist of the data or information required by and to be received from others ‚‚ Following the QA and other departmental and interdepartmental procedures strictly ‚‚ Checking the correctness and completeness of the data by the receiver and rejecting or returning to the sender for completion. Incompleteness can be in respect of bad non-readable documents or no signatures and approval or missing dimensions or details, no revision numbers on the documents etc. ‚‚ Full preparation in co-ordination meetings to sort out most of the mutual problems ‚‚ Understanding the problems of others whenever there is difference of opinions on technical matters; resolving and arriving at common decision ‚‚ Awareness of the fact that all future problems, delays, mistakes, errors, re-doing, dismantling and extra unnecessary costs to clients and consultants, have their root causes deeply burred in the interaction phase of the project. If interaction is made in rational or serious manner, most of the future problems can be prevented at the root-level. ‚‚ Therefore, during interactions, the individual should be prompt, correct, neat, clear, precise, brief, timely, compromising and serious while generating, sending and receiving the data, documents or information.

2.6 Guidelines for Plot Plan •

A plot plan is a scale drawing that gives an overview (top view) of the entire plant.

•

Plot plan is the drawing of land detail with adjacent reference points, where project is to take or taken place. This is dimensional drawing.

•

Plot plans are considered to be the key documents of projects and are normally initiated in the pre-contract, conceptual and development stages of a proposal.

•

After the contract is awarded for engineering, plot plans are developed at a rather rapid pace with very limited information. This early stage plot plan usually is very limited in information, containing only enough dimensional data to define the outer limits of the available property selected for plant development.

•

The equipment sizes and shapes are pictorially positioned in a rough manner, along with anticipated pipe rack configurations, structure shape and rough sizes.

•

The plot plan at this level is then used for constructability evaluation and submitted to the client for approval.

Major roles of a plot plan •

Plot plans are essential for obtaining permits and determining environmental and personnel safety. They are the key documents used in assessing fire protection.

•

During the engineering and construction phases, many owners use the plot plan as a basis for evaluating the level of completeness of work agreed upon. The document can be used as a measure of the progress payments.

•

Prevailing winds and tower and structure heights must be considered in developing a plot plan. Although wind direction is never constant, prevailing wind is used as a basis to evaluate safety.

•

Climatic considerations also play a major role in plot plan development.

•

Thus, for preparation of plot plan of any plant, the concerned engineer has to proceed in a logical and sequential manner, before actually putting the unit-blocks on the drawing sheet.

25/uts

System Designing

The basic steps involved in preparation of plot plan are: Preparation of preliminary plot plan •

preliminary equipment layout or arrangement

•

preliminary arrangement of structures, building & other facilities

Study on preliminary plot plan •

study on safety instances

•

study on pipe rack width

•

study on routing for main piping & cables

•

study on construction & maintainability

•

study on operation accessibility & operability

•

study on underground obstruction

Completion of plot plan •

determination of dimension between equipment, structures etc.

•

modification as a result of piping layout

Fig. 2.3 Plot plan (Source: http://www.epcpj.com/preparation-of-plot-plan/)

26/uts

Fig. 2.4 Plot plan and road (Source: http://www.epcpj.com/preparation-of-plot-plan/) Elaborating the steps involved in preparation of a plot plan: STEP1: The list of all units and the sizes of the plots to accommodate each unit is prepared. The information can also be made available from process engineer. STEP 2: The total area occupied by the present and future facilities is ‘A’ sq. m. The area required for general facilities like roads, drains, underground services (cable trenches, drains, storm water pipes, chambers, manholes, parking places etc.) has to be added. Unit plot plans are generally defined by imaginary lines called battery limits. Thumb-Rule: For total space requirement to accommodate all facilities, double the area calculated i.e., (2A) sq. m. STEP 3: Having known that the total plot size required to accommodate all the facilities including process plant, off sites, utilities, non-plant buildings general facilities, is ‘2A’ sq. m, we can now approximately calculate, the project-plot size. •

For square plot, size is 2A ×2A

•

For rectangular plot and different ratios of L: B (length : width) can be calculated by assuming L:B-ratio like 1.25, 1.50, 1.75, 2.

•

e.g. if, L:B= 1.25: 1 and L x B = 2A, then (1.25) B2 = 2A

L= 1.25 B =

And the plot size is

27/uts

System Designing

Sl. No.

L:B ratio

L (m)

B (m)

Actual area

Check

1

1

245

245

60025

√

2

1.25

274

219

60006

√

3

1.5

300

200

60000

√

4

1.75

324

185

59940

√

5

2

347

173

60031

√

Table 2.1 L:B ratios and actual area relationship STEP 4: Next step is to select the portion of the entire land belonging to the owner, which will be developed to accommodate the proposed plant facilities. For this purpose, first the ‘green belt zone’ is demarcated. Minimum width of green belt differs according to different states and countries. For selecting the most optimum portion of the total land, following check- list of governing factors can be used. •

Preferably rectangular (or square) shape should be chosen near one of the corners of the land.

•

It should be nearest to the following public facilities, e.g. ‚‚ approach road (state or district highway) ‚‚ water-supply line or other water-sources such as well ‚‚ power-supply transmission line (or the location where it can enter the land from the nearest source) ‚‚ disposal channel for storm-water disposal

•

Proximity to ideal locations for main switchyard or substation, effluent treatment plant and water storagetanks.

•

Wind-direction

•

Existing tree-plantation

•

Suitability for future expansion of the same plant or other projects in the land

•

Land configuration: Based on above criteria, if the best location selected happens to be a very low lying area needing 4 to 6 m filling, to bring it to the safe level above high flood level, then another area adjacent to it is selected, which involves minimum cost of filling work.

•

Suitability of access road location from main adjacent state-road

28/uts

E'

C' C

277 m

.

D 217 m P PR PR OP OJ OSE EC D TS IT E

D' 300 m

KM 66

0m 10

E

m 500 m 440

A A'

m 470

ON SSI I M NS A .TR O.H

S. E N LI

. ER V I R

B'

Q

B

WATER LINE .

STATE HIGHWAY .

Fig. 2.5 Location map of project site •

Total Boundary of owners’ land ABCDE

(say, 2,50,000 m2)

•

Green Belt width, all around 30 m

(say, 57,600 m2)

•

Plot available for locating the proposed project A’B’C’D’E’

•

Total Land area within A’B’C’D’E’ = (ABCDE) - Green Belt Area = 2, 50,000 - 57,600 = 1, 92,400 m2

•

Total area required for the proposed plant = 60,000 m2

•

Balance available for future projects = 1,92,400 - 60,000 = 1,32,400 m2

•

Plot selected for the project C’D’PQ = 277 * 217 = 60,109 m2

29/uts

System Designing

N = 30 .

STEP 5: Having located the portion of the land based on the factors in Step 4, the area ‘C’D’PQ’ (277 x 217 m) can be blown up to a suitable scale, generally 1:331/3, or 1:50 or 1:100 for a very big-plot on sheet as given below:

. UE TR

W = 277

W = 250

LIST OF UNITS & SIZES . NO .

W = 200

UNIT .

SIZE .

PLANT .

NOTES :-

1) 2)

REFERENCE DRAWINGS :W = 150

W = 100

W = 50

KEY PLAN .

N = 217 .

N = 200 .

N = 150 .

N = 100 .

N = 50 .

N=0.

W=0

REV.TABLE .

NAME PLATE .

Fig. 2.6 A typical plot plan drawing •

Draw grid-lines on 100 m * 100 m spacing as shown in STEP 4.

•

Draw grid- lines on 50m * 50m spacing as shown in STEP 5.

•

Draw Name-plate, key-plan, N- lines, table for list of unit no., unit - name and plot-size.

•

On key plan, hatch the portion of whole land, selected for plot-plan as in STEP 4.

•

Show all other features as indicated above.

STEP 6: •

For locating different units (blocks onto the scaled-drawing as in STEP-5, the best way is to use a CAD facility. If not available, pieces of cardboard can be cut and used to required size and shape, drawn to the same scale as the plot drawn on drawing as in STEP 5. Also, the strips for roads between adjacent plots can be cut.

•

Approximately, width of the strips will be: (Road=6m) + (Shoulders (2×2) = 4m) + (Drain (l×2) = 2m) + (Additional space (4m×2) = 8m) Total = 20 m

•

The pieces within the specified plot is arranged, (277 × 217 in the STEP 5 example), giving consideration to following points ‚‚ Approximate main road spacing ‚‚ Locating main-process-plant at appropriate place, away from front boundary- line of the plot. ‚‚ Imposing the constraints on the layout and locating the respective units accordingly. - Vastu constraints (e.g. water body near N-E-corner, fire body near S-E corner etc.) as specified by clients - Access roads from main roads - Gate house, admin or canteen block - Flare-stack as per wind-direction - Closeness of certain units like (main substation-incoming line, water -tank – incoming water line, process-plant-control building room etc.)

30/uts

- Keeping the blocks and road strips adjusted until all blocks are arranged, satisfying all conditions of space requirements, space-constraints, mutual relationship etc.

- Finalising the locations and drawing the plot boundaries, roads, drains (double lines) etc.

‚‚ Number of units in each plot with reference to the table in the above figure. Number the roads, preferably as given below - All N-S roads are numbered by odd no. 1,3,5,7 ... etc. with Rd. 1, closest to the boundary - All E-W roads are numbered by even no. 2, 4, 6 ... etc. with Rd. 2 closest to south boundary which forms part of project boundary too - Sub -roads or in-plant roads to be suffixed by A, B, C etc. e.g. roads 4 and 6 to be numbered as Rd. 4A, Rd. 4B..... etc. - Roads between 3 and 5 to be numbered as 3A, 3B etc. ** While preparing plot-plan, due consideration to the following should be given to avoid interference of unitareas. •

road turning radius

•

storm-water, cables and underground pipe-crossings near the junction area

•

statutory & safety requirements, safe distance etc.

2.7 Criteria for Facility Location Following are the criteria for facility location: Utilities boiler house •

roads(6m minimum) close to process plant, at least from two sides

•

minimum pipe run to avoid excessive steam condensation high temperature lines

•

downwind to non plant process plant fire hazardous tank farms should be located

•

proper ventilation and light should be provided

•

sufficient space or access ( building opening height and near by pipe rack height) for boiler erection should be provided

•

space for future boiler house and erection space or access for boiler should be provided

•

sufficient space or access (near by pipe rack height) for chimney erection should be provided

•

other facilities like water treatment plant, furnace oil storage or coal storage, effluent treatment plant etc. should be located as per good engineering practices

Water treatment plant •

near to boiler house

•

space for acid , alkali storage or separate acid, alkali tank farm should be considered

•

minimum pipe run (of bigger water lines) should be taken into account

•

road (minimum 4.5m) on one side is sufficient, but fire fighting space needs to be provided

Utility building (with compressor, chillers etc) •

close to process plant but location away from admin ,office, residential complexes (to avoid noise trouble)

•

air (pressure) vessels outside the building in open area

•

if required noise dampening should be provided

•

road (minimum 4.5m) on one side is sufficient, but fire fighting space to be provided

31/uts

System Designing

Cooling towers •

located close to end user to have minimum pipe run

•

downwind to process plant; other plant buildings should be located in open (ventilated) area

•

water drift should not obstruct visibility on roads and corrode the adjacent plants

•

crosswind direction should be located to avoid suction discharge mixing and efficiency reduction

•

cooling water headers should be preferably run underground

•

road (minimum 4.5m) on one side is sufficient but fire fighting space to be provided

2 Pole/4 Pole structure •

close to the plot boundary and incoming HT cable (HT means more than 500V)

•

away from fire prone areas like fire hazard tank farm coal / bagasse storage

•

pathway (1m or 1.5m) should be provided if required (road is not required)

Mitch-yard /MCC (motor control center), PCC (power control center) room/ DG (diesel generating) room •

close to process plant or utility area (can be combined with utility block)

•

minimum cable run

•

provide sufficient space, pipe rack height road (min 4.5m) for DG panel erection

•

location at higher grade and above flood level

•

DG room should be located away from admin, office or residential complex; if required noise dampening should be provided

Raw water/ Fire water storage and pump house •

close to plant entry, in safe area near to water battery limit or tube well

•

location at higher grade elevation and high flood level

•

minimum pipe or cable run, fire fighting lines normally underground

•

road (min 4 m) on one side is sufficient, but fire fighting space to be provided

•

sufficient erection and maintenance space should be provided

Effluent treatment plant •

location in low lying area at remote place away from process (main) plant ,non plant building ensure proximity to industrial estate ETP line

•

minimum pipe or cable run pipes or cables are run underground

•

pathway on one side is sufficient but fire fighting space to be provided

32/uts

Summary •

The teamwork includes the co-ordinated efforts of all the participants. In particular, engineering of a project is a task of a team.

•

In order to achieve the common goal of the team, there has to be appropriate and efficient interaction between various departments, agencies, clients and technology licensors.

•

For the purpose of execution of various responsibilities, piping engineer has to send as well as receive lots of data. This data-exchange forms the interface area.

•

Generally, it is neither possible nor necessary to generate all design data in one stroke. The data gets built up as the engineering, ordering and detailing are in progress.

•

The efficient and effective engineers depend on the co-ordinated team efforts. Hence any problem in interaction areas can be a serious issue to the project.

•

Piping engineer, being at the focus of engineering data coordination must carefully avoid the problems, by using proper systems, data banks, communication methods and timely action.

•

Hasty action on data generation to meet the stipulated schedule dates will involve mistakes or errors leading to wrong data.

•

Not transferring the data in written form, sketches or drawings can be problematic.

•

Bye-passing the QA system can be error-prone. Specific or contract related quality assurance procedures are made for each project.

•

While transferring the data, if the steps are omitted or the procedures are violated by taking shortcuts, then such non-compliance can result in use of wrong data or outdated information.

•

Plot plan is the drawing of land detail with adjacent reference points, where project is to take or taken place. This is dimensional drawing.

•

Plot plans are considered to be the key documents of projects and are normally initiated in the pre-contract, conceptual and development stages of a proposal.

•

For preparation of plot plan of any plant, the concerned engineer has to proceed in a logical and sequential manner, before actually putting the unit-blocks on the drawing sheet.

•

As a result, the transfer of data, documents and information between individual team members can be made in very comprehensive, rational and effective manner.

References •

Wormer, R. V., Plot plan design [Online]. Available at: . [Accessed 6 April 2011.]

•

Preparation of Plot Plan [Online]. Available at: < http://www.epcpj.com/preparation-of-plot-plan/>. [Accessed 6 April 2011.]

•

Basic and Detailed Engineering [Online]. Available at: . [Accessed 6 April 2011.]

•

Design Guide for Layout and Plot Plan [Online]. Available at: . [Accessed 6 April 2011.]

Recommended Reading •

Bausbacher, E., & Hunt R. W., 1993. Process plant layout and piping design, PTR Prentice Hall.

•

Weaver, R., 1986. Process piping drafting, 3rd ed., Gulf Pub. Co.

•

Parisher R. A., Rhea, R. A., 2001. Pipe Drafting and Design, 2nd ed., Gulf Professional Publishing.

33/uts

System Designing

Self Assessment 1. Which of these do not include the responsibilities in interface areas? a. sharing of the information b. understanding each others’ problems c. resolving or arriving at best compromise on conflicting requirements d. compromising in product or process quality 2. Product development process does not include ________. a. production planning b. research c. development d. design 3. Long delivery items are some of the critical equipments that take long period of _______ for delivery by the supplier. a. 10 to 18 months b. 20 to 30 months c. 1 week d. 1 year 4. The data shared by piping engineer between departments should not be in form of _______ until immediate actions are concerned. a. written form b. sketches c. telephonic conversation d. drawings 5. Which of these is not problematic in interface areas? a. improper and/or lack of communication b. casual approach to the serious nature and importance of the interaction c. not understanding the QA procedures d. checklist of the data or information 6. Which of these describe the activities in completion of plot plan? a. determination of dimension between equipment, structures etc. b. study on routing for main piping & cables c. study on construction & maintainability d. study on operation accessibility & operability 7. For total space requirement to accommodate all facilities, _____ the area is calculated. a. triple b. double c. half d. one-fourth

34/uts

8. All _______roads are numbered by odd no. 1,3,5,7 ... etc. with Rd. 1, closest to the boundary a. N-S b. E-W c. N-E d. S-E 9. Which of the following is FALSE? a. Acceptance and use of incomplete or unapproved data can lead to incorrect down-stream activities b. Acceptance and use of incomplete or unapproved data can lead to unprofitable work or redoing, and thus wastage of time and efforts. c. Sending data in appropriate sequence will disturb the sequence of work to be executed by others. d. Not sending the revisions in frozen data that is already transferred to others for detail engineering, will erase the part or entire work done by others in office. 10. Which of the following is FALSE? a. Individual responsibilities are solely to be executed by the individual, using his own knowledge, skills, efforts, data resources. b. Responsibilities in interface areas are those where each individual has to interact with one or more of the other team members or departments. c. Knowledge, skills and resources are beneficial for successful completion of the project, if it lacks proper co-ordination. d. The transfer of data, documents and information between individual team members can be made in very comprehensive, rational and effective manner.

35/uts

System Designing

Chapter III Process Piping and Instrumentation Diagram (P and ID) Aim The aim of this chapter is to: •

define piping and instrumentation diagram

•

describe operational sequence of the process P and IDs

•

explain the steps in preparation of process P and IDs

Objectives The objectives of this chapter are to: •

describe the process flow diagrams

•

explain the use of P and ID symbols

•

discuss the importance of maintenance during process P and IDs

Learning outcome At the end of this chapter, the students will be able to: •

examine various aspects during the preparation of process P and ID

•

explain the importance of safety in process P and IDs

•

analyse basic instrument symbols

36/uts

3.1 Introduction The successful conversion of a conceptual idea into actual execution of process industry is the basic aim of any process engineer. Normally, a project passes through various phases, viz. basic engineering, detailed engineering, equipment fabrication or procurement, civil or structural work, erection and commissioning. The conceptual idea, either from the process development cell (for new processes) or from the marketing engineer (as per the customer’s requirement), is converted to executable documents during basic engineering stage, and thus governs the successful completion of the project.

3.2 Piping and Instrumentation Diagram (P and ID) •

P and ID is one of the important and basic engineering documents in the form of drawing, which truly represents the process plant.

•

It shows the pipelines, interconnecting all equipments, instruments, control systems, valves, etc. for the completeness of the process plant.

•

Since detailed engineering work for any process plant depends more on the P and ID, its correctness and completeness is very much essential. Any wrong information provided in the P and ID at the initial stage may bring a big disaster or may entail heavy expenses later on. Hence, great attention is required for the preparation of error-free P and ID.

•

Good quality P and ID may cut the engineering main hour requirement for the successful completion of a project.

•

Normally process plants have static equipments like storage tanks, columns, heat exchangers etc. and rotating equipments like pumps, blowers, etc. These equipments are connected to each other by a complicated pipeline network for the completeness of the process.

•

Measuring instruments like thermocouple for temperature measurement and controlling devices like temperature control valves are mounted on the equipments or pipelines for operating the plant at desired conditions.

•

Although a single step process like blending of two compounds can be represented in a single piping & instrumentation diagram (P and ID), a process having a large number of processing steps like reaction, filtration, drying, etc. would need to have many P and IDs for the complete representation of the process plants.

•

For an ease of understanding, the complete process plant is functionally divided into various units. For example, a reactor with the other related equipments, pipelines and instruments required for carrying out a reaction process may be covered in one unit while filtration operation may be specified with another unit number, according to the individual units.

•

In a big chemical process industry, the processing units are spread over a large area. Although two different units far away from each other, are connected by pipelines or the continuous flow of fluid from one unit to another.

•

Interconnection between two units is represented by interconnecting P and IDs.

•

Similarly, another engineering document, utility P and IDs, provides information regarding the distribution of utilities like water, steam, fuel etc. in the required locations.

•

Process P and ID provides detailed information of the process plant like type of equipment, the details of pipelines i.e., size of material, identification number, types of instruments, controlling devices etc.

•

Operation, start-up, maintenance, safety and aesthetic aspects are mainly considered during the preparation of process P and ID.

3.2.1 Operation •

Process P and ID is prepared by following the operational sequence of the process. For example, a process needs step like chemical reaction, followed by filtration and drying of the product. Process P and ID shows the corresponding equipment like reactor, filter and dryer in the same order.

•

All equipments are to be shown connected with pipelines, fittings and instruments necessary to carry out the process.

•

Clear understanding of the process is very much essential for the preparation of a good quality process. 37/uts

System Designing

•

Process P and ID provides detailed information of the process plant like type of equipment, the details of pipelines, i.e., size material, identification number, types of instruments and controlling devices, etc.

•

P and ID elevation of all equipment are normally fixed in the prior stage. Equipment in the process P and ID are shown at different levels with marked elevations. For example, head tank for reactant is shown above the reactor in process P and ID for representing the gravity flow of reactant from head tank to the reactor. Similarly, other equipments like critical pipelines, instruments, control valves etc. are shown at the appropriate elevations. Normally, heavy rotating equipments like pumps, compressors etc. are located at lower elevation i.e., ground floor. Therefore, rotating equipment is placed at a lower in the process P and ID also.

3.2.2 Start-Up •

Start-up of any process plant may need some additional steps which are not required for the normal run.

•

Special care should be taken for such steps at the initial stage of P and ID preparation. For example, safety seals in the critical gaseous lines need to be filled with liquid before installation of the plant.

•

Valve with connections should be shown in the process P and ID for liquid seal filling.

•

Critical equipment is bypassed using temporary pipeline connections during water test run to avoid contamination. Thus, process P and ID is marked with such types of requirements for the plant start-up.

3.2.3 Maintenance •

Maintenance is an important aspect during the preparation of process P and ID. For example, electric elevator required for lifting heavy equipment is shown in it.

•

Regulating valve in bypass line of control valve is provided for maintenance without affecting the running plant.

•

Sometimes, it is marked in the P and ID to provide sufficient room for cut-out in the floor above the vertical tube bundle from the heat exchanger body. If such type of information is not provided initially, it may be missed out in the various engineering stages and may lead to problems at the later stages.

•

To avoid such possibilities, process P andID, should be critically examined from the maintenance point of view during preparation stage.

3.2.4 Safety •

For the successful operation of any process plant, safety measures cannot be ignored. Hence, the preparation of process P and ID needs the attention of safety aspects too.

•

Hazard and operability (HAZOP) study is carried out keeping in view, each and every safety and operation step.

•

A hazard and operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.

•

For example, the exhaust of obnoxious gases near the plant operators is harmful to their health. Such gases are diffused in the atmosphere at a higher elevation. These safe elevations are normally marked in the process P and ID.

•

Safety interlocks are provided to ensure safe operation of the process plant. For example, failure of a running pump for a critical operation may disturb the complete process plant. To avoid this situation, the stand-by pump should be started without any time lag.

•

Necessary interlock is shown in the process P and ID. Some metallic pipelines and the equipments handling hot fluids are insulated for body protection. Here, heat saving may not be an important criteria for the selection of insulating, but it is essential for the operator’s safety. Such safety requirements are clearly marked in the P and ID.

•

Requirement of safety valves in pressurised system, minimum flow lines for centrifugal pumps, high and low alarms etc. are to be critically seen during the preparation of process P and ID.

38/uts

3.2.5 Aesthetics •

Though it is not concerned with the plant operation, aesthetic look of process P and ID is important for better presentation of the document and ease of understanding for the user.

•

Complex presentation of the pipelines i.e., lots of cross-crossing, may even lead to wrong pipeline routing and hence due attention should be paid to the aesthetic aspect during the preparation of process P and ID.

3.3 Process P and ID Preparation •

Although experience plays a major role, systematic approach is equally essential for producing error-free process P and ID. Table 3.1 highlights the major steps for the preparation of any process P and ID.

STEP No.1: Show all equipment as per equipment list and layout. STEP No.2: Connect all equipment with necessary pipings to carry out process. STEP No.3: Show all required valves and fittings. STEP No.4: Show all required instruments. STEP No.5: Mark size fluid code, material code & identification number of all pipelines. STEP No.6: Mark interlock number as per interlock description. STEP No.7: Review P& ID considering all operational steps. STEP No.8: Review P& ID considering start-up requirements. STEP No.9: Review P& ID for safety considerations following HAZOP analysis. STEP No.10: Review P& ID in reference to the maintenance. STEP No.11: Review P& ID for its aesthetic look. Table 3.1 Major steps for the preparation of any process P and ID Following documents are essentially required for the preparation of any process P and ID: •

Process Flow Diagram (PFD)

•

Equipment list

•

Fluid list

•

Equipment layout

•

Interlock description

•

Vendor information (for related equipment)

39/uts

System Designing

Details of these documents are given in Table 3.2 below. TYPE: SHELL - Cylindrical/Spherical/Rectangular/ Other ENDS - Flat /Conical/ Spherical /Other ORIENTATION - Vertical/Horizontal/Other NOZZLE: SIZES – Inlet/ Outlet/Vent/Drain/Overflow / Instrument /Spare LOCATION – Shell/Top/Bottom ELEVATION: As per equipment layout AGITATION: Is agitation required? Type of Agitation – Air/ Mechanical HEATING/ COOLING: Is heating or cooling required? Arrangement – Internal coil/Jacket/Limpet coil /other INSULATION: TYPE – Cold/Hot/Body Protection; Thickness INSTRUMENTATION: Necessary for parameters like pressure, level, temperature, etc. TYPE: Centrifugal/Reciprocating /Positive displacement DRIVE: Electric Motor/Steam Turbine /Pneumatic Drive QUANTITY: Working + Standby FLUSHING PLAN: Necessary piping as per flushing plan recommended by pump vendor PIPING: Sizes of suction and discharge lines Requirement of reducers at suction and discharge ports of pump Venting, drawing, degassing arrangements Ant vibration bellows; Suction line strainer especially for gear, screw pumps Pulsation dampener for positive displacement pumps Pulsation dampener for positive displacement pumps (if required) SAFETY: Minimum bypass line for centrifugal pumps Pressure safety valve /switch for positive displacement pump Non-return valve discharge line of auto start of centrifugal pump PROCESS LINES

40/uts

All process lines are correctly connected to equipment. UTILITY LINES Required utility line are shown. LINE DETAILS Size, fluid code, material code, identification number insulating thickness (if required). HEATING PURPOSE – Process requirement / Freeze protection TYPE – Steam /Electric / Thermal/ Fluid /Other Requirement of line Jacket VALVES AND SPECIAL PARTS Type of valve – Regulating /Isolating /Check /Other Special parts – Strainer /restriction orifices /insert tube spray nozzle IMPORTNT INFORMATION Slop in the lines; critical elevation differences; required liquid seal in gas lines Pipe class breakage as per the suitability of fluid to material; Flushing connection for slurry fluids, etc. TYPE OF MEASUREMENT Fluid pressure /temperature /flowers/pH /other TYPES OF INSTRUMENT Suitable instrument for selected variable, for example: rota meter for flow rate measurement. INTERLOCKING For representing control action, alarm, switch, operation CONTROL VALVE Type –Flow /Level/Temperature /Other Fail Safe Position – Failure to close /Open/ last status Bypass valve or hand wheel requirements Size of control valve, reducer requirement SIGNAL TYPE Field /PLC/DCS/Local panel NECESSARY INSTRUCTIONS Tap connection size for mounting transmitter; ensure proper contact of fluid to the analyzer probe, e.g. for pH measurement, etc. Table 3.2 Details of the documents for preparation of P and ID

41/uts

System Designing

3.4 Basic Instrument Symbols •

Process technicians use P and IDs to identify all of the equipment, instruments and pipings found in their units.

•

Knowing and recognising these symbols is important for an engineer. The chemical processing industry has assigned a symbol for each type of valve, pump, compressor, steam turbine, heat exchanger, cooling tower, basic instrumentation, reactor, distillation column, furnace, and boiler.

•

There are symbols to represent major and minor process lines and pneumatic, hydraulic, or electric lines.

HEAT EXCHANGERS

LINE SYMBOLS Future Equipment Major Process

Hairpin Exchanger

U-Tube Heat Exchanger

Shell & Tube Heat Exchanger

Minor Process Pneumatic L L L

Hydraulic Capillary Tubing

Single Pass Heat Exchanger

Reboiler

Electromagnetic Signal Heater

Condenser

Drum or Condenser Mixer

Tank

Forced-Draft Cooling Tower

Tower

Bin

Furnace

Induced-Draft Cooling Tower

Tower with Packing

TI

Te mp Indicator

TT

Te mp Transmitter

TR

Te mp Recorder

LI

Level Indicator

LT

Level Transmitter

LC

Level Controller

FI

Flow Indicator

FT

Flow Transmitter

FR

Flow Recorder

PI

Pressure Indicator

PT

Pressure Transmitter

PRC

Pressure Recording Controller

Fig. 3.1 Process and instrument symbols (Source: http://webtools.delmarlearning.com/sample_chapters/1418030678_ch12.pdf)

42/uts

X

Electric

VESSELS

Mixing Reactor

X X XXX

VALVES H

S Gate Valve

Needle

Four-Way

Diaphragm

Manual Operated Valve

Gauge

Solenoid Valve CLOSED

Hydraulic

Back Pressure Regulator

Back Pressure Regulator

Pneumatic Operated

Three-Way Valve

Globe Valve

Ball

Angle

Check Valve

Plug

Bleeder Val ves

COMPRESSORS

Reciprocating Compressor

Pneumatic Operated

M

Motor

Rotameter

Relief PRV

Safety PSV

PUMPS & TURBINE

Compressor & Silencers

Centrifugal Compressor

Vacuum Pump

Centrifugal Pumps

Ve rtical

T Rotary Compressor

Liquid Ring Compressor

Centrifugal Compressor (Turbine Driven)

Gear Pump

Screw Pump

Turbine

Fig. 3.2 Process and instrument symbols (continued) (Source: http://webtools.delmarlearning.com/sample_chapters/1418030678_ch .pdf)

43/uts

System Designing

I

TI

Temp Indicator

FI

Flow Indicator

TT

Temp Transmitter

FT

Flow Transmitter

PIC 105

Pressure Indicating Controller

TR

Temp Recorder

FR

Flow Recorder

PRC 40

Pressure Recording Controller

TC

Temp Controller

FC

Flow Controller

LA 25

Level Alarm

LI

Level Indicator

PI

Pressure Indicator

FE

Flow Element

Level Transmitter

PT 55

Pressure Transmitter

TE

Temperature Element

LR 65

Level Recorder

PR 55

Pressure Recorder

LG

Level Gauge

LC 65

Level Controller

PC 55

Pressure Controller

AT

Analyzer Transmitter

LT 65

V

What It Does

Measured

P

Transducer

Instrument

F IC 55 Control Loop

ariable Being Remote Location (board mounted)

Field Mounted Remote Location (behind control panel)

Fig. 3.3 Process and instrument symbols (continued) (Source: http://webtools.delmarlearning.com/sample_chapters/1418030678_ch12.pdf) •

The P and ID use symbols and circles to represent each instrument and how they are inter-connected in the process.

44/uts

Temperature Controller and Recorder

Temperature Transmitter Thermometer

Temperature Sensing Bulb

Pneumatic Control Valve Fig. 3.4 Use of P and ID symbols (Source: http://www.lle.rochester.edu/media/omega_facility//documents/P&ID.pdf) Tag Descriptors Tag “numbers” are letters and numbers placed within or near the instrument to identify the type and function of the device.

The first letter is used to designate the measured variable X Y Z

The succeeding letter(s) are used to designate the function of the component, or to modify the meaning of the first letter.

123

Pressure

Indicator

Level

Recorder

Flow

Controller

Temperature

Transmitter

Fig. 3.5 Tag descriptors (Source: http://www.lle.rochester.edu/media/omega_facility//documents/P&ID.pdf)

45/uts

System Designing

Temperature Recording Controller Temperature Transmitter

TRC 206

TI 206

TT 206

Temperature Indicator Temperature Sensing Bulb

FCV 206

Fig. 3.6 Tag numbers (Source: http://www.lle.rochester.edu/media/omega_facility//documents/P&ID.pdf) Process Flow Diagrams (PDF) •

Process flow diagrams typically include the major equipment and piping path which the process takes through the unit.

•

Some symbols are common among plants; others differ from plant to plant.

•

The symbols used in this chapter reflect a wide variety of petrochemical and refinery operations.

•

The PFD given below shows the basic relationships and flow paths found in a process unit. The flow diagram is broken down into sections: feed, preheating, the process, and the final products. This simple left-to-right approach allows a technician to identify where the process starts and where it will eventually end.

•

The feed section includes the feed tanks, mixers, pipings and valves.

•

In the second step of preheating, the process flow is gradually heated for processing. This section includes heat exchangers and furnaces.

•

In the third section, the process is included. Typical examples found in the process section could include distillation columns or reactors. The process area is a complex collection of equipment that works together to produce products that will be sent to the final section.

46/uts

Cooling Tower

Vacuum Pump

Product Tank 1

Drum

Furnace Feed Tank

Column Reactors

Product Tank 2

Bottoms Tank

Boiler

Fig. 3.7 Process flow diagram (PFD) (Source: http://webtools.delmarlearning.com/sample_chapters/1418030678_ch12.pdf)

47/uts

System Designing

Summary •

Normally, a project passes through various phases, viz. basic engineering, detailed engineering, equipment fabrication or procurement, civil or structural work, erection and commissioning.

•

In a big chemical process industry, the processing units are spread over a large area. Although two different units far away from each other, are connected by pipelines or the continuous flow of fluid from one unit to another.

•

Clear understanding of the process is very much essential for the preparation of a good quality process.

•

Process P and ID provides detailed information of the process plant like type of equipment, the details of pipelines i.e., size of material, identification number, types of instruments and controlling devices, etc.

•

Complex presentation of the pipelines i.e., lots of cross-crossing, may even lead to wrong pipeline routing and hence due attention should be paid to the aesthetic aspect during the preparation of process P and ID.

•

A hazard and operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.

References •

Design guide for layout and plot plan [Online]. Available at: . [Accessed 6 April, 2011].

•

Process diagrams [Online]. Available at: . [Accessed 6 April, 2011].

•

P&ID - Piping and Instrumentation Diagram [Online]. Available at: . [Accessed 7 April, 2011].

•

Symbols for Process Flow Diagrams and Engineering Line Diagrams [Online]. Available at: . [Accessed 7 April, 2011].

•

Interpreting Piping and Instrumentation Diagrams [Online]. Available at: < http://chenected.aiche.org/plantoperations/interpreting-piping-and-instrumentation-diagrams-part-2-of-5/>. [Accessed 7 April, 2011].

Recommended Reading •

Goettsche, L. D., 2005. Maintenance of instruments & systems: Practical guides for measurement and control, 2nd ed., ISA.

•

Blevins, T. L., 2010. Mark Nixon Control Loop Foundation: Batch and Continuous Processes, 2nd ed., ISA.

•

Thakore, 2008. Introduction to Process Engineering and Design, Tata McGraw-Hill Education.

48/uts

Self Assessment 1. What cannot be at all ignored for the successful operation of any process plant? a. Safety measures b. Maintenance c. Operations d. Aesthetics 2. What is not concerned with the plant operation? a. Maintenance b. Aesthetics c. Operations d. Start-up 3. ________of the process is very much essential for the preparation of a good quality process. a. Clear understanding b. Equipments c. Identification number d. Controlling devices 4. _______with connections should be shown in the process P & ID for liquid seal filling. a. P and ID b. Valve c. Instrument symbols d. Instrument size 5. __________ study is carried out keeping in view, each and every safety and operation step. a. Hazard and operability b. Equipment layouts c. Plot plan d. Piping specifications 6. Which of these is the final step for the preparation of any process P and ID? a. Show all equipment as per equipment list and layout. b. Show all required valves and fittings. c. Review P and ID considering start-up requirements. d. Review P and ID for its aesthetic look. 7. Which is not the necessary parameter of instrumentation? a. Pressure b. Level c. Temperature d. Light

49/uts

System Designing

8. Which of these is not a method of heating in a manufacturing industry? a. Steam b. Solar c. Electric d. Thermal 9. Which of these is not a type of valve used in piping? a. Regulating valve b. Isolating valve c. Check valve d. Rotating valve 10. Which of the following statement is FALSE? a. Process technicians use P and IDs to identify all of the equipment, instruments and pipings found in their units. b. There are symbols to represent major and minor process lines and pneumatic, hydraulic, or electric lines. c. The P and ID use symbols and circles to represent each instrument and how they are inter-connected in the process. d. P and ID are letters and numbers placed within or near the instrument to identify the type and function of the device.

50/uts

Chapter IV Steam Tables and Mollier Diagram Aim The aim of this chapter is to: •

define steam tables

•

describe properties and formation of steam

•

explain the Mollier diagram

•

discuss the steam distribution piping system

Objectives The objectives of this chapter are to: •

describe the typical steam distribution system

•

explain the use of P and ID symbols

•

understand the steam main and branch lines

Learning outcome At the end of this chapter, the students will be able to: •

examine various heating media used in industries

•

highlight the importance of steam quality

•

get an overview of steam tables and Mollier diagram

51/uts

System Designing

4.1 Introduction In oil and chemical plants, of all types and sizes, energy is used for process heating. It may also be used for space heating and for power, generating electricity and driving pumps and compressors. Process applications include product heating in stills, evaporators, feed heaters, boilers, reaction vessels and dyers. Maintenance of product temperature is often required in storage tanks, tracer lines jacketed pipes and valves. Particularly in the large complex, steam remains an obvious choice for heating. Although steam is the traditional means of conveying heat, there are now a number of alternatives. These include high or medium pressure hot water and heat transfer oils. In some cases, it is more convenient to use electricity, especially for tracing and for the mechanical agitation for storage tanks. Where electric power is generated, exhaust steam is an essential component of the overall heat balance. It is use directly as a constituent in many chemical reactions and it provides, though waste heat boiler, an obvious way of recovering heat from many exothermic reactions. In many refineries, primary steam is obtained by burning waste products in the boiler and thus, it costs low. Steam is usually generated in a central boiler used and distributed around the site, often at a number of different pressures, by a network of steam mains which plays a vital part in the efficient running of the plant. It has the advantage that it can be used for power and heating but its main virtue is its flexibility. Though many chemical plants may have a limited life, their overall cost will be reduced if they are applied from steam services on a permanent basis. Another great virtue of steam is that it can be regulated to give varying heat levels through reducing valves or to give temperature control through simple two-way valves.

4.2 Steam: Formation and Properties Steam is the vapour form of water. It does not obey the laws of perfect gases, until it is perfectly dry. When the dry steam is further heated, it behaves more or less like a perfect gas. The steam is generally used as a working substance in the operation of steam engines and steam turbines. 4.2.1 Formation of Steam i.

When any liquid is heated at constant temperature, it starts changing in vapour condition. A vapour is a mixture of gas and liquid particles in suspension and it can be liquefied by moderate changes of pressure or temperature.

ii.

The process of vapour formation from liquid state has some definite characteristics to follow in steam engine.

iii.

The heat supplied during the process of vaporisation changes its state gradually from liquid to gaseous state.

iv.

The vapour is said to be dry saturated when the process of vaporisation takes place at constant pressure and temperature or when the liquid is completely evaporated.

v.

The vapour is called superheated when the heat is added to the dry saturated vapour state. At superheated state, the temperature will rise gradually.

vi.

During the process of superheating, the volume of vapour at constant pressure increases approximately in proportion to the absolute temperature, which indicates that the vapour is approaching the state of perfect gas.

vii. The temperature at which the evaporation process is taking place increases when the pressure on the liquid surface is increased. The latent heat of vaporisation decreases with the increase of pressure and temperature but the enthalpy increases under this condition.

52/uts

viii. The total heat (enthalpy) of dry saturated vapour increases with increase in saturation temperature. After certain saturation temperature, the rate of increase in enthalpy is less than the rate of decrease in latent enthalpy and hence, the enthalpy of dry saturated vapour decreases. This will continue to happen until the saturation temperature is reached when the latent enthalpy becomes zero and the enthalpy of dry saturated vapour becomes equal to the sensible heat. This saturation temperature is called as critical temperature and the corresponding pressure is called critical pressure and the state of substance is called its critical state. ix.

Steam can not exist as saturated vapour above its critical temperature. At any temperature higher than the critical temperature (374.14°C), the vapour can only exist as a gas without any effect of pressure. At critical temperature, the specific volume of dry saturated vapour becomes equal to the specific volume of the liquid from which it is being formed.

4.2.2 Properties of Steam The followings properties of steam are always needed for the calculations of its various parameters, which are required in the operation of steam engines and steam turbines. Specific volume of steam •

It is the volume occupied by the steam per unit mass at a given temperature and pressure.

•

It is expressed in m/kg and is the reciprocal of the density of steam.

•

The specific volume of steam increases with the increase in temperature and decrease with the increase in pressure.

Specific enthalpy of steam •

It is the total heat absorbed by the steam per unit mass from the freezing point of water (0°C or 273 K) to the saturation temperature (100°C or 373K) plus the heat absorbed during evaporation.

•

It is expressed in kJ/kg.

•

The specific enthalpy of steam increases with the increase in temperature and pressure.

Specific entropy of steam •

It is a theoretical value of heat energy, which can not be transformed into mechanical work under the given conditions of temperature or pressure.

•

It is also called degree of disorder of the system.

•

It is expressed in kJ/kg K.

•

The specific entropy of steam decreases with an increase in temperature and pressure.

•

The most common term used is the change of entropy, which is mathematically given as:

4.3 Steam Tables •

Steam tables are tables of thermodynamic data for steam, used often by engineers and scientists in design and operation of equipment where thermodynamic cycles involving steam are used.

•

The various properties of steam (such as specific enthalpy and entropy) of dry saturated steam and superheated steam vary with the variations of temperature and pressure.

•

These values were carefully determined by observations and calculation first in (Foot Pound System) F.P.S. system and were made available in tabular form known as steam tables. Later on, these values were converted in to M.K.S. units and then in to S.I. units.

53/uts

System Designing

•

It is a general practice to give the following tables for some important values: ‚‚ Saturated water and steam (temperature) table ‚‚ Saturated water and steam (pressure) table ‚‚ Superheated steam table ‚‚ Supercritical steam table

Saturated water and steam (temperature) table •

It contains values of : ‚‚ absolute pressure (in bar) ‚‚ specific volume (in m3/kg) ‚‚ specific enthalpy (in kJ/kg) ‚‚ specific entropy (in kJ/kg K) from 0ºC to 374.15ºC (critical temperature)

•

A sample of this table is given below: Temperature in 0C (t)

Absolute pressure in bar (p)

Specific volume in m3/kg Water Steam (vƒ) (vg)

0 5 10

0.006 11 0.008 72 0.012 27

0.001 0.001 0.001

206.16 147.16 106.43

Specific enthalpy in kJ/kg Water Evaporation Steam (hƒ) (hƒg) (hg) 0.0 21.0 42.0

2501.6 2489.7 2477.9

2501.6 2510.7 2519.9

Specific entropy in kJ/kg K Water Evaporati Steam (sƒ) on (sƒg) (sg) 0.000 0.07 0.151

9.158 8.951 8.751

9.158 9.027 8.902

Table 4.1 Example of saturated water and steam (temperature) table The use of this table is given in the following example. Example 1: Calculate the specific enthalpy and specific entropy of 1 kg of steam at 100ºC when its dryness fraction is 0.8. Solution: •

Given: ‚‚ Mass of steam (m) = 1 kg; ‚‚ Temperature of steam (t) = 100ºC and ‚‚ dryness fraction of steam (x) = 0.8

•

From steam tables, corresponding to a temperature of 100ºC, we find that ‚‚ hƒ = 42.0 kJ/kg ‚‚ hƒg = 2477.9 kJ/kg ‚‚ sƒ = 0.151 kJ/kg K

‚‚ sƒg = 8.751 kJ/kg K. •

Specific enthalpy of steam We know that specific enthalpy of steam is, ‚‚ h = m [hƒ + x hƒg] = 1 × [42.0 + (0.8 × 2477.9)] = 2024 kJ

•

Specific entropy of steam We also known that specific entropy of steam is, ‚‚ s = m [sƒ + x sƒg] = 1 × [0.151 + (0.8 × 8.751)] = 7.1518 kJ/kg K

54/uts

Saturated water and steam (pressure) tables •

It contains the values of temperature (in ºC), specific enthalpy (in kJ/kg) and specific entropy (in kJ/kg K) from 0.0061 bar (critical pressure).

•

A sample of this table is given below: Specific volume in m3/kg

Specific enthalpy in kJ/kg

Specific entropy in kJ/kg K

Absolute pressure in bar (p)

Tempera ture in 0C (t)

Water (vƒ)

Steam (vg)

Water (hƒ)

Evaporation (hƒg)

Steam (hg)

Water (sƒ)

Evaporati on (sƒg)

Steam (sg)

0.010 0.020 0.030

6.98 17.51 24.10

0.001 0.001 0.001

129.21 67.012 45.670

29.3 73.5 101.0

2485.0 2460.2 2444.6

2514.4 2533.6 2545.6

0.106 0.261 0.354

8.871 8.464 8.224

8.977 8.725 8.578

Table 4.2 Saturated water and steam (pressure) tables The use of this table is given in the following example. Example 2: What is the specific enthalpy and specific entropy of 1.5 kg of steam at a pressure of 0.030 bars, when its dryness fraction is 0.6? Solution: •

Given: ‚‚ Mass of steam (m) = 1.5 kg ‚‚ Pressure of steam (p) = 0.030 bar and ‚‚ Dryness fraction of steam (x) = 0.6

•

From steam tables, corresponding to a pressure of 0.030 bars, we find that

•

hƒ =101 kJ/kg

•

hƒg = 2444.6 kJ/kg

•

sƒ = 0.354 kJ/kg K and

•

sƒg = 8.224 kJ/kg K

•

Specific enthalpy of steam We know that specific enthalpy of the steam, ‚‚ h = m [hƒ + x hƒg] = 1 × [101 + (0.6 × 2444.6)] = 1567.76 kJ

•

Specific entropy of the steam We also know that specific entropy of the steam, ‚‚ s = m [sƒ + x sƒg] = 1.5 × [0.354 + (0.6 × 8.224)] = 7.9326 kJ/kg K

Superheated steam tables •

These tables contain values of specific volume, specific enthalpy and entropy of superheated steam from an absolute pressure of 0.02 bar (critical pressure) at various temperatures from 100ºC to 800ºC.

•

The value of specific volume, specific enthalpy and specific entropy of steam are directly read from the concerned tables.

•

However, the value at any other pressure or temperature (not mentioned in the tables) is obtained by interpolation.

55/uts

System Designing

Supercritical steam tables •

These tables also contain the values of specific volume, specific enthalpy and specific entropy of super critical steam from an absolute pressure of 250 bar to 1000 bar at various temperatures from 400ºC to 800ºC.

•

In these tables also, the values of specific volume, specific enthalpy and specific entropy of steam are directly read from the concerned tables.

•

However, the value at any other pressure or temperature (not mentioned in the table) is obtained by interpolation.

4.4 Mollier Diagram •

The Mollier diagram is a graphic representation of the relationship between air temperature, moisture content and enthalpy, and is a basic design tool for building engineers and designers.

•

It is a graphical representation of steam tables, in which specific entropy (s) is plotted along the coordinate (Y-axis) and specific enthalpy (h) along the abscissa (X axis).

•

It is sometimes known as the h-s diagram.

•

The diagram is divided into two portions by a somewhat horizontal line termed as saturation curve.

•

The lower portion (i.e., wet steam region) contains the values of wet steam, whereas the upper portion (i.e., superheated steam region) contains the values of superheated steam.

•

A Mollier diagram has the following lines. ‚‚ Dryness fraction line ‚‚ Constant specific volume lines ‚‚ Constant pressure lines ‚‚ Constant temperature lines

4.4.1 Dryness Fraction Lines •

These lines are drawn in the wet steam region. i.e., only below the saturation curve (which represent dryness fraction equal to unity).

•

These lines represent the condition of wet steam between various values of enthalpy and entropy.

•

The dryness fraction lines are slightly curve in horizontal direction.

4.4.2 Constant Specific Volume Lines •

These lines are drawn in both the wet steam region and superheated steam region.

•

These lines represent the specific volume of steam between the various values of enthalpy and entropy.

•

The lines are straight in the wet steam region, i.e., below the saturation curve, but are curved upward in the superheated region i.e., above the saturation curve.

4.4.3 Constant Pressure Lines •

These lines are also drawn in both the wet steam region and superheated steam region.

•

These lines represent the pressure of steam between various values of enthalpy and entropy.

•

The pressure lines are also straight in the wet steam region, i.e., below the saturation curve, but are curved slightly upwards in the superheated region i.e., above the saturation curve.

4.4.4 Constant Temperature Lines •

These lines are drawn only in the superheated steam region i.e., above the solution curve.

•

These lines represent the temperature of steam between various values of enthalpy and entropy.

•

The temperature lines are slightly curved in the horizontal direction.

56/uts

Specific volume line Pressure line

H

Enthaply

Temperature line Superheated steam (x = 1) H2 Dryness fraction line

Saturation line

Dry saturated steam (x = 1) Wet steam (x < 1)

H1

x Fig. 4.1 Mollier diagram (Source: http://www.transtutors.com/university-yale/mollier-diagram-application-6.htm)

4.5 Piping for Steam Distribution In large size plants, steam is used for one or more of applications such as power generation (steam turbine), process heating in vacuum device (steam ejector) etc. Typical steam distribution system A typical steam distribution system consists of: •

Boiler, for steam generation.

•

Steam using equipments such as turbine, evaporator, reaction vessel, ejector etc.

•

Interconnecting pipelines.

•

Pressure reducing station (PRS) with desuperheater (PRDS) or without desuperheater.

•

Condensate return piping system with or without flash steam recovery system.

Heating or space heating applications For process or space heating options, other forms of steam are available viz. water (sometimes at high pressure) and thermic fluids (including high temperature oils) are used. Line size for steam pipe The line size for steam distribution is decided by the steam flow rate and permissible pressure drop. However, in case of steam piping, a few things are to be considered such as: •

quality of steam (dry saturated / wet exhaust / superheated)

•

main supply line (often referred to steam header) or branch line (pipeline form steam header to user equipment)

57/uts

System Designing

Unwin equation (using metric units) Unwin equation is used for calculation of pressure drop for steam service. The equation is given below:

where, the units for steam flow rate (W), internal pipe diameter (d) and density (ν) are: •

W - Kg / hr

•

d - mm

•

ν- Kg /m3

Equivalent length of fitting Pressure drop through fittings such as bend, reducer, valve etc. Fluid suffers pressure drop as it passes through fittings. The resistance offered by fitting can be correlated to length of straight pipe offering same resistance in terms of pressure drop. Such length of straight pipe is designated as equivalent length of the fitting. For any segment of pipeline, total equivalent length is the total of length of straight pipe plus equivalent length of all fittings. Nomograph is used for finding equivalent length of fittings. Some approximations can be seen as below. Fitting

Equipment length in m (d-pipe NB in mm)

Gate valve-full open

0.01

Globe valve-full open

0.35

Long radius bend

0.03

Tee connection

0.07

Table 4.3 Approximations of equivalent length of fittings Equations for pressure drop based on rigorous mathematics are available for isothermal as well as adiabatic flow conditions. However, certain empirical equations based theoretical consideration has proved adequate for the practical purpose. For steam applications, Unwin equation is widely used.

Where, •

W = steam flow in lbs/min v = sp. vol. in cub ft /lb

•

d = pipe ID in inches

•

Dp= actual pressure drop (psi per 100 ft pipe)

Conversion in metric units is:

Various units of pressure measurement are: 1 atm - 1.033 Kg / cm2 = 1.013 bar = 14.7 psi - 1.02 Kg / cm2 = 1 bar = 14.5 psi - 1 Kg / cm2 = 0.981 bar = 14.23 psi

58/uts

SHORT RADIUS 900 BEND

LONG RADIUS 0 90 BEND

Fig. 4.2 Resistance of valves and fittings to flow of fluids (Source: http://www.pipingguide.net/2010/01/piping-for-steam-distribution.html) Economic Velocity for deciding line size For given mass or volume, increasing pipe diameter (ID) would reduce the velocity. The effect of change in pipe size could be seen as below: Pipe size (ID)

Velocity

Pressure drop

Higher

Lower

More

Lower

Higher

Higher

Heat-loss

Less 59/uts

System Designing

A compromise has to be reached between these opposing factors of initial cost, pressure drop and heat loss. Velocity of steam which offers optimum solution is referred to as economic velocity. For standard steam service, the recommended velocities are: •

Exhaust wet steam 15 - 25 m /s

•

Dry saturated steam 25 - 35 m/s

•

Superheated steam 35 - 45 m/s

At these velocities the pressure drop would be about 1 psi /100 ft or about 0.2 bar / 100 m.

where, •

m = mass flow rate of steam in kg / hr

•

EV = economic velocity m/s

•

SPV = specific volume cub m/kg

•

d = pipe diameter ( ID) in mm

For purpose of deciding pipe sizes for steam service, the steam pipe lines could be broadly grouped into two categories viz. steam main and branch lines. •

Steam mains are large size line spanning considerable distance. They have to deliver steam of required quantity to various steam using devices. The pressure drop is, therefore, an important consideration. The design procedure, therefore, involves selecting steam velocity closest to, if not within economic range, which gives pressure drop within permissible limits.

•

Branch lines are much shorter in length. Thus, the pressure drop is not of substantial magnitude. Therefore, branch lines are sized on the basis of velocity of 25 - 35 m/s.

Main Shut-Off Valve

Trap Set Fig. 4.3 Recommended take-off point with branch drainage

60/uts

Vent Steam Main

Drain Fig. 4.4 Drain and vent

Foll 1/70

steam

Relay to higher level

30-50 m

drain points Fig. 4.5 Relaying to higher level

61/uts

System Designing

Correct Steam Condensare Incorrect

Steam Trap

Pocket

Steam

Steam Trap Fig. 4.6 Ineffective and proper drainage point

Correct Steam Condensare Incorrect

Fig. 4.7 Steam line reducer

62/uts

Pressure Bar 0.4 0.7 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 10.0 1 4.0

Velocity m/s 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40 15 25 40

15 mm 7 10 17 7 12 18 8 12 19 12 19 30 16 26 41 19 30 49 22 36 59 26 43 71 29 49 76 32 54 84 41 66 104 50 85 126

20 mm 14 25 35 16 25 37 17 26 39 25 43 64 37 56 87 42 63 116 49 81 131 59 97 157 63 114 177 70 122 192 95 142 216 121 195 305

25 mm 24 40 64 25 45 68 29 48 71 45 70 115 60 100 157 70 115 197 87 135 225 105 162 270 110 190 303 126 205 327 155 257 408 205 331 555

32 mm 37 62 102 40 72 106 43 72 112 70 112 178 93 152 250 108 180 295 128 211 338 153 253 405 165 288 455 190 320 510 250 405 615 310 520 825

40 mm 52 92 142 59 100 167 65 100 172 100 162 275 127 225 375 156 270 456 187 308 495 225 370 595 260 450 690 285 465 730 372 562 910 465 740 1210

50 mm 99 162 265 109 182 298 112 193 311 182 295 475 245 425 595 281 450 796 352 548 855 425 658 1025 445 785 1210 475 810 1370 626 990 1635 810 1375 2195

65 mm 145 265 403 166 287 428 182 300 465 280 428 745 385 632 1025 432 742 1247 526 885 1350 632 1065 1620 705 1205 1865 800 1260 2065 1012 1530 2545 1270 2080 3425

80 mm 213 384 576 250 430 630 260 445 640 410 656 1010 535 910 1460 635 1080 1825 770 1265 1890 925 1520 2270 952 1750 2520 1125 1870 3120 1465 2205 3600 1870 3120 4735

100 mm 394 675 1037 431 716 1108 470 730 1150 715 1215 1895 925 1580 2540 1166 1980 3120 1295 2110 3510 1555 2530 4210 1815 3025 458 5 1990 3240 5135 2495 3825 6230 3220 5200 8510

125 mm 648 972 1670 680 1145 1712 694 1160 1800 1125 1755 2925 1505 2480 4050 1685 2925 4940 2105 3540 5400 2525 4250 6475 2765 4815 7560 3025 5220 8395 3995 6295 9880 5215 8500 13050

150 mm 917 1457 2303 1006 1575 2417 1020 1660 2500 1580 2520 4175 2040 3440 5940 2460 4225 7050 2835 5150 7870 3400 6175 9445 3990 6900 10880 4540 7120 12470 5860 8995 14390 7390 12560 18630

200 mm 1606 2806 4318 1708 2816 4532 1864 3099 4815 2814 4815 7678 3983 6779 10476 4618 7866 12661 5548 8865 13761 6654 10629 16515 7390 12288 19141 8042 13140 21247 994 15966 26621 12921 21720 35548

250 mm 2590 4101 6909 27911 4629 7251 2814 4869 7333 4545 7425 11997 6217 10269 16470 7121 12225 19663 8586 14268 23205 10297 17108 27849 12015 19377 30978 12625 21600 33669 16172 25860 41011 20538 34139 54883

300 mm 3678 5938 9500 3852 6204 10323 4045 6751 10370 6277 10575 16796 8743 14316 22950 10358 17304 27816 11947 20051 32244 14328 24042 38697 16096 27080 43470 17728 33210 46858 22713 35890 57560 29016 47218 76534

Table 4.4 Steam pipe sizing (carrying capacity in kg/h)

4.6 Heating Media There are a number of heating media used in industries. Water systems •

Water systems find only limited application in the chemical industry but they are used particularly where the high temperatures associated with steam will damage the product.

•

They involve relatively large pipes and large heating surfaces.

High temperatures oils •

The oil and chemical industries were among the first to utilise high temperature fluids as heat transfer media.

•

These are extremely useful where high process temperatures are required and where the high pressure associated with steam would cause difficulties.

•

Most of these fluids are very expensive, but recently hydrocarbon oils have provided a more viable answer.

•

Hydrocarbon oils are used increasingly for the medium range temperatures associated, for example, with bitumen plants.

•

However, the inflexible nature of high temperature oil system suggests that it will take time to be considered as a complete alternative to steam. 63/uts

System Designing

Electric heating •

Whether electricity is generated or purchased from the national grid, electric heating is almost invariably more expensive than other forms of heating.

•

Therefore, it is rarely used for build heating but can sometimes be usefully employed on the heat loads associated with tracing.

•

Electric tracing is a system used to maintain or raise the temperature of pipes and vessels.

•

Electrical heat tracing may be described as an insulated electrical heating cable, which is spiralled around the process fluid pipe, after which the pipe and tracing is insulated with the appropriate type and thickness of insulation lagging material.

•

It is useful for overcoming cold start up conditions before steam is available or perhaps at remote points where there is no steam service.

•

On the other hand, an electric supply system is frequently less flexible than a steam system.

•

Although, the old tapping from a steam system can usually be used to provide steam tracing, the random use of electric tracing can soon produce overloading of supply cables and switchgear, and produce unsatisfactory load factors.

•

Electric heating is often avoided on sites where fire or explosion risks call for special flame-proofing.

Mechanical agitation •

From time to time, steam heating coils are used in storage tanks, not to maintain temperature, but simply to provide convection currents and thereby avoid the settling out of various fractions.

•

As an alternative, mechanical agitators or stirrers are sometimes used, powered by electric motors. The electric motors used on large tanks are sizeable.

4.6.1 Steam Utilisation in the Large Complex •

In a refinery chemical complex, there is a great demand for electrical power. This is largely met by generating electricity on site, utilising turbines fed by superheated steam from a central boiler plant.

•

Saturated steam will condense rapidly on any surface which is at lower temperature, giving up a large proportion of its total heat content. On condensation, the change in volume encourages the flow of steam towards the heat exchange surfaces and enables-high heat transfer rates to be maintained.

•

On the other hand, with superheated steam, the flow of heat from the core of the steam to the heat transfer surface is only by conduction and thus, much slower.

•

The dry gas acts as insulating film, resisting the flow of heat.

Sl. No.

Steam

Hot Water

High Temperature Oils

1

High heat content. Latent heat approximately 2100 kJ / kg 900 Btu /b

Moderate heat content. Specific heat – 4.19 kJ/ kg°C, 1 Btu/lb°F

Poor heat content Specific heat often 1.69 – 2.93 kJ/ kg°C, 0.4 -0.7 Btu/lb°F

2

Cheap but some water treatment cost

Cheap .Only occasional dosing

Expensive

3

Good heat transfer coefficients

Moderate heat transfer coefficients

Relatively poor heat transfer coefficients

4

High pressure required for high temperatures

High pressure required

Low pressures only to get high temperatures

5

No circulating pump required

Circulating pump required

Circulating pump required

64/uts

6

Small pipes

Large pipes

Large pipes

7

Easy to control with 2-way valves

Less easy – 3 way valves or differential pressure valves may be required

Less easy – 3 way valves or differential pressure valves may be required

8

Temperature breakdown easy through reducing valve

Temperature breakdown less easy

Temperature breakdown less easy

9

Steam traps required

No steams traps

No steams traps

10 Condensate to be handled

No condensate handlings

No condensate handlings

11 Flash problems

No flash problems

No flash problems

12 Blow down loss

No blow down loss

No blow down loss

13 Corrosion problems

Less corrosion

Negligible corrosion

Searching medium, welded or flanged joints usual

Very searching medium, welded or flanged joints usual

15 No fire risk

No fire risk

Fire risk

16 System flexible

System less flexible

System inflexible

14

Reasonable pipe-work required

Table 4.5 Comparison of heating media with steam 4.6.2 Steam Quality •

For most process applications, dry saturated steam is required.

•

An ideal condition could be achieved by distributing the steam from the boiler house, with sufficient superheat to cater mains losses, so that the steam arrived at the point of usage having lost its superheat, be in a dry state. In practice, such a condition is difficult to achieve.

•

Variations in lengths of travel and ambient air conditions make it impossible to reach the extract ideal of having dry saturated steam at each and every point of usage. Therefore, steam quality varies around the industrial complex.

•

This can even be the case where very high-pressure and high temperature superheated steam is being used.

•

On the start-up of such a system, the superheated steam enters the cold steam pipe work and gives up its superheat, until it condenses rapidly at the saturated steam temperature.

•

For such start-up conditions, it is a conventional practice to blow down the steam main through valves so that this condensate is removed. As the steam main comes up to the final working pressure and temperature, these values are closed.

•

However, depending upon the superheat temperature, the travel length of the steam main, the quality of insulation, weather conditions and the quantity of steam flowing under certain conditions, it is possible for the steam to give up its superheat and begin to condense.

•

Therefore, at these remote points, provisions should be made for automatically draining out such condensate using a steam trap. This is absolutely essential for the batch process applications, where for short periods, there is no steam demand and hence no flows of steam down the pipe. Under such circumstances, operators should not rely upon opening and closing drain valves.

•

Steam at the point of usage is seldom dry and unsaturated.

65/uts

System Designing

•

In chemical plant, steam is being generated within a boiler and thus, is in contact with water. Further, it leaves water through a surface which is turbulent, throwing up droplets of water into the steam space and producing wet steam. It depends on factors such as water level below the off-take (point of beginning of water channel), pressure on water surface, solids content of water and effect of peak loads.

•

Any of the factors, one or in combination, can make it possible for droplets of water to be carried over with the steam into the distribution system. These droplets entrained with the steam, carry no latent heat.

•

They add to the thickness of the resistant film of water on the heat exchanger surface and slow down the rate of heat transfer.

•

The problem lies to improve steam quality by removing these moisture particles. The solution can be achieved, simply by installing a steam dryer or separator into the pipe line.

•

A steam separator is an in-line piece of equipment that is used to remove entrained condensate particles.

•

Any moisture particles carried along with the steam will impinge on a plate, and drain to bottom of the unit leaving the dry steam to pass on to the processing plant.

•

The water is finally separated out and drained off by means of a steam trap. It is a good thing to fit separator on the branch line to every steam user, thus ensuring a dry steam supply.

•

The efficiency of separators is a big question. A generally high figure may be quoted suggesting that almost all free water is removed. Such figures are misleading on two counts.

•

Firstly, the performance of the separator varies with the conditions such as total moisture content, droplets size and particularly, the steam velocity.

•

Secondly, the measurement of results is the main tentative block. Although calorimeters are available for measurement of dryness fraction, it is almost impossible to take representative sample from the steam pipe either upstream or downstream of a separator. Steam at the centre of a pipe will travel at the highest velocity and will be relatively free of water droplets. Towards the pipe wall, the velocity will be lower. This part of the steam flow will carry more moisture while the pipe wall may be covered by a film of water being dragged along at some lower velocity. Results will depend on the point from which the sample is taken. It is, therefore, difficult to get any clear view.

•

Upon traditional experience of installations, particularly those with wide variations in conditions, the baffle plate type of separator, provides better plant performance by supplying steam using equipment with high quality dry steam.

•

Moisture, either being carried along in the steam flow or present as a film of condensate on the walls of steam pipe, is not the only factor affecting steam quality. There are factors like air and incondensable gases.

•

Consider a plant which has been shut down for a period of time. The steam trapped in the pipe is condensed and its place taken by air drawn in through flanged joints, unions, valve glands, etc. When the time comes to re-start the plant, this air has to be pushed out of the pipe work by the incoming steam acting like a piston.

•

This applies once a year for some plants which are in continuous operation, when the plant is restarted after annual shutdown.

•

If, because of lack of provision for air venting, 50 plant operators are waiting for minimum half an hour for their plant to warm up, then 25 valuable man hours are lost to production.

•

In such cases, the operator will invariably open the steam inlet valve to plant during this period. Air pushed along the steam mains, is now passed into the steam spaces of the plant.

•

So, particularly in those cases where steams distribute systems are shut down at frequent intervals, adequate provisions for air venting on start up is a must.

•

Coupled with air, there can be presence of other incondensable gases which enter the steam system, especially from decomposition of carbonate and bicarbonate ions from salts in the boiler feed water. These ions release carbon dioxide within the boiler, and this gas as well as the oxygen and nitrogen are carried by the steam into the distribution system.

66/uts

•

Even where desecrators are in use, very small amounts of gases remain in solution in the feed water and over moderate periods of use, it accumulates in the steam lines and in the heat exchangers. Only when the partial pressure of the gases has built up to a sufficient high level, they dissolve in the condensate. When this happens, corrosion problems usually occur swiftly and in the meantime, the gases form an insulating barrier between the steam and the heat exchanger surfaces, reducing the plant output.

•

Even if the appropriate chemicals are added to the boiler feed water to deal with oxygen and carbon dioxide, the nitrogen dissolved in the water is usually ignored.

•

Automatic air vents are the simple way of dealing with these problems.

Steam in

Air

Air

Air pushed along by steam Condensate

Steam in

Steam in

Air vent located opposite steam inlet

Air

Condensate Condensate

Condensate return line

Float-thermostatic trap set

Fig. 4.8 Automatic air vent located opposite the steam inlet on the jacketed pan (Source: http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-traps-and-steam-trapping/airventing-theory.asp)

67/uts

System Designing

Fig. 4.9 Steam separator (Source: http://arab-training.com/vb/t8022.html)

68/uts

4.7 Selection of Steam Pressures •

Steam should be distributed at high pressure because it occupies less space and this in turn means that smaller, less costly mains can be used. The smaller mains have less heat-losing surface and better quality steam is likely to result.

•

For process or space heating purposes, steam should be used at the lowest possible pressure. Low pressure steam offers the maximum amount of latent heat per pound and the problems of flash steam from the condensate are reduced. This means less back pressure in condensate systems and less wasteful vapour at collecting tanks or from trans-discharging to atmosphere. This vapour can also be dangerous if it reduces visibility or freezes in cold weather. But there are factors that limit how far pressure can be reduced.

•

The amount of heating surface in the plant will usually determine how low the pressure can be before the corresponding reduction in temperature head adversely affects outputs.

•

Some products must be processed at a particular temperature and this will require a certain steam temperature and pressure. The choice of pressure is a compromise and can only be decided in the light of all the factors.

•

When the steam pressure required in the distribution system, a reducing valve must be used to break down the pressure from a high pressure main and a good quality valve should be chosen providing a consistent supply of steam, regardless of load changes.

•

A reducing valve of the self-contained relay type is more than adequate for many applications, but it is to provide accurate control.

•

The use of a reducing valve will not normally convert wet steam into a superheated condition but will simply dry out some of the entrained water and give drier and, therefore, better quality steam reaching the reducing valve.

High pressure steam in

Separator

Pressure reducing valve

Safety valve

Low pressure steam out

Condensate

Fig. 4.10 Pressure reducing valve (Source: http://www.spiraxsarco.com/resources/steam-engineering-tutorials/control-applications/pressurecontrol-applications.asp)

4.8 Pressure Drop Factor •

Steam may be thought of as a medium to convey heat from the boiler to the point where it is needed.

•

As the temperature of saturated steam is fixed in relation to the pressure, the required temperature in any process can be controlled by the steam pressure. But, for instance, a 20% reduction in designed steam pressure to a calorifier may result in a 15% drop in output.

•

Therefore, while producing steam at the correct pressure and quantity in the boiler house is important.

•

While distribution pipework cannot be too big, the extra capital cost would not be acceptable. If pipework is too small, then the increased steam velocity will cause noise and erosion and the excessive pressure drop may starve the equipment of steam. Velocity should be designed to be below 15 metres/sec or 50 ft/sec.

•

In practice, sizing the pipework to produce a known pressure drop, works best. There are many programs, graphs and tables available that make use of the simplified formula: F= (P1 - P2)/ L 69/uts

System Designing

where, F P1 P2 L

= = = =

Pressure drop factor Factor at inlet pressure Factor at a distance of L metres Equivalent length of pipe (m)

4.9 Steam Pipe Sizing and Design Any modification and alteration in the existing steam piping, for supplying higher quality steam at right pressure and quantity must consider the following points: Pipe Sizing •

The objective of the steam distribution system is to supply steam at the correct pressure to the point of use. Pressure drop through the distribution system is an important feature.

•

Proper sizing of steam pipelines helps in minimising pressure drop.

•

The velocities for various types of steam are: ‚‚ Superheated : 50-70 m/sec ‚‚ Saturated: 30-40 m/sec ‚‚ Wet or Exhaust: 20-30 m/sec

•

For fluid flow, there must be more energy at Point 1 than Point 2.

•

The difference in energy is used to overcome frictional resistance between the pipe and the flowing fluid.

hf h1

h2

Pipe Diameter (D)

Flow Velocity (u)

Length (L) Point 1

Point 2

Fig. 4.11 Pressure drop in stream pipes This is illustrated by the equation:

= Where, hf = Head loss to friction (m) f = Friction factor (dimensionless) L = Length (m) u = Flow velocity (m/s) g = Gravitational constant (9.81 m/s²) D = Pipe diameter (m)

70/uts

It is useful to remember that: •

Head loss to friction (hf) is proportional to the velocity squared (u²).

•

The friction factor (f) is an experimental coefficient which is affected by factors including: ‚‚ Reynolds Number (which is affected by velocity)

The Reynolds Number is a non dimensional parameter defined by the ratio of dynamic pressure (ρ u2) and shearing stress (μ u / L) and can be expressed as Re = (ρ u2) / (μ u / L)    = ρ u L / μ    = u L / ν            Where, Re = Reynolds Number (non-dimensional) ρ = density (kg/m3, lbm/ft3) u = velocity (m/s, ft/s) μ = dynamic viscosity (Ns/m2, lbm/s ft) L = characteristic length (m, ft) ν = kinematic viscosity (m2/s, ft2/s) ‚‚ Reciprocal of velocity² •

Because the values for ‘f’ are quite complex, they are usually obtained from charts.

Example - Water pipe Determine the difference in pressure between two points 1 km apart in a 150 mm bore horizontal pipework system. Given: the water flow rate is 45 m³/h at15°C and the friction factor for this pipe is taken as 0.005.

= = = 3.43

0.34 bar

•

In practice, whether for water pipes or steam pipes, a balance is drawn between pipe size and pressure loss.

•

The steam piping should be sized, based on permissible velocity and the available pressure drop in the line.

•

Selecting a higher pipe size will reduce the pressure drop and thus the energy cost. However, higher pipe size will increase the initial installation cost. By use of smaller pipe size, even though the installation cost can be reduced, the energy cost will increase due to higher-pressure drop.

•

It is to be noted that the pressure drop change will be inversely proportional to the 5th power of diameter change. Hence, care should be taken in selecting the optimum pipe size. 71/uts

System Designing

Pipe redundancy •

All redundant (piping which are no longer needed) pipelines must be eliminated, which could be, at times, up to 10-15 % of total length.

•

This could reduce steam distribution losses significantly.

•

The pipe routing shall be made for transmission of steam in the shortest possible way, so as to reduce the pressure drop in the system, thus saving the energy.

•

However, care should be taken that, the pipe routing shall be flexible enough to take thermal expansion and to keep the terminal point loads, within the allowable limit.

4.10 Thermal Insulation •

Piping plays a central role in many industrial processes in chemical or petrochemical installations such as power plants, as it connects core components such as appliances, columns, vessels, boilers, turbines etc. with one another and facilitates the flow of materials and energy.

•

Pipe insulation is thermal or acoustic insulation used on pipework.

•

There are many reasons for insulating a pipeline, most important being the energy cost.  

Purpose of pipe insulation •

The functions of correct thermal insulation for piping includes: ‚‚ Condensation control ‚‚ Reduction of CO2 emissions ‚‚ Reduction of heat losses ‚‚ Frost protection in pipes ‚‚ Process control: ensuring stability of the process temperature ‚‚ Cost savings ‚‚ Energy saving ‚‚ Protection against extreme temperatures ‚‚ Noise reduction

•

Adequate thermal insulation is essential for preventing both heat loss from hot surfaces of ovens/furnaces/piping and heat gain in refrigeration systems.

•

Inadequate thickness of insulation or deterioration of existing insulation can have a significant impact on the energy consumption.

•

The material of insulation is also important to achieve low thermal conductivity and also low thermal inertia. Development of superior insulating materials and their availability at reasonable prices have made retrofitting or re-insulation a very attractive energy saving option.

•

The simplest method of analysing whether you should use 1” or 2” or 3” insulation is by comparing the cost of energy losses with the cost of insulating the pipe.

•

The insulation thickness, for which the total cost is minimum; is termed as economic thickness.

•

However, in plants, there are some limitations for using the results of economic thickness calculations. Due to space limitations, it is sometimes not possible to accommodate larger diameter of insulated pipes.

•

By optimum pipe thickness, heat loss can be reduced to 5- 10 % of heat loss from bare surface or brought down to 50 -100 k cal / hr m3.

72/uts

•

According to Petroleum Conservation Research Association (PCRA) recommended thickness of pipes are given in the table below: Pipe Nominal bore (NB)

Surface temp (°C)

25

50

80

100

Recommended thickness (inch) 100

1.0

1.5

1.5

2.0

200

2.0

3.5

3.5

3.5

300

3.0

4.5

4.5

5.0

Table 4.6 Pipe NB according to different surface temperatures Heat loss from 1/2” to 12” steel pipes at various temperature differences between pipe and air can be found in the table below. Nominal bore

Temperature Difference (o C)

(mm)

(inch)

50

60

75

100

110

125

140

150

165

195

225

280

15

1/2

30

40

60

90

130

155

180

205

235

280

375

575

20

3/4

35

50

70

110

160

190

220

255

290

370

465

660

25

1

40

60

90

130

200

235

275

305

355

455

565

815

32

11/4

50

70

110

160

240

290

330

375

435

555

700

1000

40

11/2

55

80

120

180

270

320

375

420

485

625

790

1120

50

2

65

95

150

220

330

395

465

520

600

770

975

1390

65

21/2

80

120

170

260

390

465

540

615

715

910

1150

1650

80

3

100

140

210

300

470

560

650

740

860

1090

1380

1980

100

4

120

170

260

380

5850

700

820

925

1065

1370

1740

2520

150

6

170

250

370

540

815

970

1130

1290

1470

1910

2430

3500

200

8

220

320

470

690

1040

1240

1440

1650

1900

2440

3100

4430

250

10

270

390

570

835

1250

1510

1750

1995

2300

2980

3780

5600

300

12

315

460

670

980

1470

1760

2060

2340

2690

3370

4430

6450

Table 4.7 Heat loss from fluid inside pipe (W/m) (Source: http://www.energymanagertraining.com/CodesandManualsCD-5Dec%2006/BEST%20PRACTICE%20 MANUAL-FLUID%20PIPING.pdf) • Factors influencing performance The relative performance of different pipe insulation on any given application can be influenced by many factors. The principle factors are: ‚‚ Thermal conductivity (“k” or “λ” value) ‚‚ Surface emissivity (“ε” value) ‚‚ Water vapour resistance (“μ” value) ‚‚ Insulation thickness

73/uts

System Designing

‚‚ Density ‚‚ Other factors, such as the level of moisture content and the opening of joints, can influence the overall performance of pipe insulation. •

Insulating material ‚‚ Calcium silicate ‚‚ Fiber glass ‚‚ Mineral wool or fibre ‚‚ Polyethylene ‚‚ Perlite ‚‚ Silica Aerogel ‚‚ Phenolic foam ‚‚ Flexible elastomeric foams

•

Condensate load occurs when heat loss after insulation leads to condensate formation in lines carrying saturated steam.

74/uts

Summary •

Though many chemical plants may have a limited life, their overall cost will be reduced if they are applied from steam services on a permanent basis.

•

Another great virtue of steam is that it can be regulated to give varying heat levels through reducing valves or to give temperature control through simple two-way valves.

•

Steam is the vapour form of water. It does not obey the laws of perfect gases, until it is perfectly dry.

•

The steam is generally used as a working substance in the operation of steam engines and steam turbines.

•

Steam can not exist as saturated vapour above its critical temperature.

•

At critical temperature, the specific volume of dry saturated vapour becomes equal to the specific volume of the liquid from which it is being formed.

•

Steam tables are tables of thermodynamic data for steam, used often by engineers and scientists in design and operation of equipment where thermodynamic cycles involving steam are used.

•

The Mollier diagram is a graphic representation of the relationship between air temperature, moisture content and enthalpy, and is a basic design tool for building engineers and designers.

•

The temperature lines are slightly curved in the horizontal direction.

•

The line size for steam distribution is decided by the steam flow rate and permissible pressure drop.

•

Steam mains are large size line spanning considerable distance. They have to deliver steam of required quantity to various steam using devices.

•

Branch lines are much shorter in length. Thus, the pressure drop is not of substantial magnitude.

•

Steam should be distributed at high pressure because it occupies less space and this in turn means that smaller, less costly mains can be used. The smaller mains have less heat-losing surface and better quality steam is likely to result.

•

The relative performance of different pipe insulation on any given application can be influenced by many factors.

References •

Important Characteristics in formation of Steam [Online]. Available at: . [Accessed 7 April 2011].

•

Piping for Steam Distribution [Online]. Available at: . [Accessed 7 April 2011].

•

Pipes and Pipe Sizing [Online]. Available at: . [Accessed 8 April 2011].

•

Steam Pipe Sizing and Design [Online]. Available at: . [Accessed 8 April 2011].

Recommended Reading •

Bel l, A. A., 2007. HVAC equations, data, and rules of thumb, 2nd ed., McGraw-Hill Professional, ISBN0071482423, 9780071482424.

•

Singh, O., 2007. Engineering Thermodynamics, New Age International, ISBN8122417507, 9788122417500.

•

Sawhney, 2009. Fundamentals of Mechanical Engineering: Thermodynamics Mechanics Theory of Machines and Strength of Materials, 2nd ed., PHI Learning Pvt. Ltd.

75/uts

System Designing

Self Assessment 1. The vapour is said to be ________when the process of vaporization takes place at constant pressure and temperature or when the liquid is completely evaporated. a. dry saturated b. supersaturated c. wet steam d. dry steam 2. Critical temperature is _________. a. 374.14°C b. 227.14°C c. 273°C d. 100°C 3. The freezing point of water is _________. a. 100°C b. 273°K c. 213°K d. 4°C 4. The SI unit of specific enthalpy of steam is _______. a. J/kg b. kJ/kg c. kJ/g d. kJ/mg 5. Specific entropy of steam is expressed in ________. a. kJ/kg K b. m3/kg c. kJ/kg d. bar 6. Which of these statements is TRUE? a. Steam tables are tables of thermodynamic data for steam. b. Specific enthalpy of steam is degree of disorder of the system. c. The specific entropy of steam increases with an increase in temperature and pressure. d. The specific enthalpy of steam decreases with the increase in temperature and pressure. 7. Which of these statements is FALSE? a. The Mollier diagram is a graphic representation of the relationship between air temperature, moisture content and enthalpy. b. The Mollier diagram is a basic design tool for building engineers and designers. c. The Mollier diagram is sometimes known as the h-s diagram. d. The Mollier diagram is divided into two portions by a somewhat vertical line termed as saturation curve.

76/uts

8. ________ lines are drawn in the wet steam region. i.e., only below the saturation curve. a. Constant specific volume b. Dryness fraction c. Constant pressure d. Constant temperature 9. In Urwin equation, pressure drop is measured in _________. a. Kg / hr b. mm c. bar∕100m d. Kg /m3 10. The equivalent length of fitting of gate valve-full open is ________. a. 0.01 b. 0.35 c. 0.03 d. 0.07

77/uts

System Designing

Chapter V Slurry Piping Systems Aim The aim of this chapter is to: •

define pressure drop

•

describe slurry characteristics in system design

•

explain the method to calculate critical velocity

Objectives The objectives of this chapter are to: •

describe the pumps used in slurry piping system

•

explain the restrictions on instrumentation use in slurry piping system

•

illustrate the concept of design velocity

Learning outcome At the end of this chapter, the students will be able to: •

examine various considerations determining the behaviour slurry

•

discuss the parameters in slurry piping system

•

highlight the special considerations in slurry piping system

78/uts

5.1 Introduction Liquid-solid suspensions, called slurries, are produced and handled in many processes throughout the chemical process industries. Layout and mechanical design considerations are as important as hydrodynamic aspects, such as line sizing, pressure drop and critical deposition velocity, when designing piping systems to handle slurries. Because of the nature of slurries, proper layout and mechanical design are critical to prevent operational problems, such as pipeline plugging and erosion. The different slurry piping systems are found in chemical, petrochemical and pharmaceutical plants. Slurry pipelines are widely used in industrial and mining operations. However, slurry pipeline systems are frequently characterised by operational problems and high running and maintenance costs. This is often due to inadequate design associated with a lack of understanding of the flow behaviour of two phase solid liquid mixtures. The implementation of a reliable slurry pipeline system requires that all parties involved have a sound understanding of the underlying flow mechanisms of the slurries.

5.2 Slurry Piping Systems •

A suspension of solid particles in a liquid, as in a mixture of cement, clay, coal dust, manure, meat, etc. with water is often called slurry.

•

Slurry can be described as liquid with solids suspended therein.

•

Slurry piping system, like any other system, consists of slurry pumps, pipelines and valves.

•

Special considerations relevant to these systems are introduced by the fact that slurry is not a homogeneous phase (unlike gas or liquid).

•

Typical industrial instances of slurry handling are as follows: ‚‚ coal practices suspended in water (in coal washeries) ‚‚ crystals suspended in solvent in crystallization (wax manufacturing process) fed to any filtration equipment ‚‚ pulp suspension encountered in papermaking ‚‚ sludge encountered in effluent treatment etc.

•

Various considerations determine behaviour of slurry such as: ‚‚ solid concentration (usually expressed in weight % of solid) ‚‚ practical size of solids ‚‚ nature of solids (soft, hard, abrasive) ‚‚ properties of liquid (density, viscosity, chemical nature) etc.

•

The design of the system (including selection of proper materials) is governed by following general considerations: ‚‚ no solid deposition in system ‚‚ no change in slurry composition from inlet to outlet of the system ‚‚ minimum wear and tear or erosion

•

The design and engineering of the system components is discussed in the following order: ‚‚ line sizing and pressure drop ‚‚ special consideration ‚‚ pumps for slurry ‚‚ instrumentation

79/uts

System Designing

5.3 Line Sizing and Pressure Drop The basic steps in design are as follows: 1. Identify slurry characteristic 2. Select slurry concentration 3. Select trial pipe size 4. Calculate critical velocity 5. Compare design velocity with critical velocity 6. Calculate design friction loss 7. Calculate system pressure gradient and pump discharge pressure Explanations and / or clarifications relevant to each of above steps are discussed below. Step 1: Slurry characteristics The type of slurry (whether homogeneous or heterogeneous) dictates rheological (the study of the deformation and flow of matter) properties and therefore its characterisation is important. Slurries can be classified into broad categories as homogenous or heterogeneous. Homogeneous slurry In this type of slurry, solid particles are uniformly distributed in liquid medium. Such slurries are characterised by high concentration of solids having small (fine) particle size .Typical examples include sewage sludge and clay slurry. Cement kiln feed slurry Such slurries usually exhibit non-Newtonian flow behaviour (effective viscosity changing with shear rate). Majority of them show behaviour like Bingham plastic (no shear rate up to yield stress and Newtonian behaviour for stress beyond yield stress). Heterogeneous slurry The solids are not uniformly distributed in liquid in such slurries. In a horizontal pipe the concentration of solids is higher at lower levels and lower at upper levels. Such slurry is characterised by low concentration of large size particles. Phosphate rock slurry is typical example of this type. Mixed behaviour of slurry Many types of slurry encountered in industry may show behaviour in between homogeneous and heterogeneous states, especially when particles of different sizes constitute the slurry. In such a situation dominant characteristics have to be identified and proper design procedure should be adopted to arrive at safer design. A typical example of this type is slurry of coal particles in water. Step 2: Slurry concentrations (Solid content of slurry) Solid concentration of slurry becomes an important factor for following reasons: •

Solids concentration governs the slurry specific gravity (and hence pumping cost) and sometimes, the rheology of the slurry.

•

At certain solid concentration, slurry may be difficult to transport or unstable. In such situation, solids concentration would have to be selected for proper transportation. Solids concentration in static settled slurry would be a useful guidance in this respect. Generally solid concentration of 10-15 % below static settled slurry concentration would prove stable and convenient for handling.

•

Solid concentrations in settled slurries depending on nature of solid, vary over a wide range (10-50%). Generally solids with particle size of 0.4-0.5 micron may form stable slurry for solid concentration up to 40%.

80/uts

2.0

Solid volume fraction

1.8 1.6 1.4 1.2 80

0.1 30

Slurry special gravity

0.70

Solid weight %

Fig. 5.1 A typical graph for slurry specific gravity Step 3: Trial pipe size selection Selection of pipe size (particularly pipe inner diameter) will determine the velocity of slurry through the pipe. The velocity calculated is referred to as design velocity. Volume flow rate = velocity × area of cross section Example: Given, •

Flow rate of slurry 3000 litres/min

•

Trial pipe size 200 mm ID

= 1.60 m/s The design velocity is significant with reference to the critical velocity .Critical velocity is an important parameter for slurry. When slurry flows at velocity below the critical velocity, solids in slurry may start separating out and setting in a horizontal pipe. The critical velocity is analogous to transition velocity in flow of homogeneous fluids, the velocity at which laminar flow ceases to exist. Tendency of solids in slurry to settle or separate out will be reduced in pressure of turbulence .The critical velocity for given slurry will be determined by different parameters such as size and specific gravity of solids, solids concentration viscosity of liquid and degree of turbulence. Step 4: Calculation of critical velocity Calculations of critical velocity for homogeneous slurry are described as below: For heterogeneous slurries the procedure is little complex. For homogeneous slurry, the procedure for calculating critical velocity is as follows: A. If the slurry shows the Newtonian behaviour, then critical Reynolds No. NRec is considered to be 2100 and critical velocity is calculated. Example: Given, ‚‚ Slurry flow rate = 3000 litres / min, V = 1.60 m/s ‚‚ Apparent viscosity of slurry or coefficient of rigidity (μ)= 60 ‚‚ NRec = 2100 ‚‚ Pipe ID = 200 mm, D=0.2 m ‚‚ Slurry specific gravity (e) = 1.61 81/uts

System Designing

B. I f the slurry is non-Newtonian type and exhibits Bingham plastics type behaviour, then the procedure adopted for calculating critical velocity is as follow: Referring to example above, Calculate design Reynolds No. NRe

Calculate plasticity no. PL

To= 50dynes/ sq.cm. = 5 N/sq.cm. V for NRe = 1.60 m/s D = 0.2 m

Calculate Hedstom No. NHe

NHe = NRe × PL = 8586 × 10.417 = 89440

Critical Reynolds Number (LOG) NRe

Use chart as shown in the figure below to calculate NRec. Enter the chart with value of NHe, to find the value of critical Reynolds No. NRec.

(log)NHe Headstorm Number Fig. 5.2 A typical graph to calculate NRec

82/uts

Calculate critical velocity (Vc) If, say NRec = 6400, critical velocity can be calculated by using one of the following relationships:

Since, •

NRec = 6400

•

NRe= 8586

•

V= 1.60 for NRe

Step 5: Compare design velocity with critical velocity Vc = 1.193 m/s V = 1.60 m/s V-Vc = 1.6 – 1.193 = 0.417 m/s The trial pipe size selected, should be such that (V-Ve) should be 0.3 m/s or more. In the calculations above, (V-Vc) = 0.417 m/s, therefore selected pipe size is satisfactory. Step 6: Calculate design friction loss Once the selected trial pipe size is satisfactory, the pressure loss can be calculated by usual equation i.e.

For this calculation, the numerical value off is to be selected from “f vs NRe” charts. Since f depends on roughness of pipe, as considered (Hazen William factor =100). Secondly, it is a common practice to express the friction loss per say 10m of piping. For this purpose, equivalent lengths of fittings etc. have to be taken into account.

Example,

Considering, f = 0.008, Friction loss per 10 m equivalent pipe length

= 3297.3 N/m = 3.297 kN/m2 Since, •

slurry specific gravity = 1.61

•

6.4 m of slurry column = 1 atm (101.3 kN/m2)

Friction loss per10 m of equivalent piping =  = 0.208 m of slurry column

83/uts

System Designing

Step 7: Calculate pump dish charge pressure For transport of such slurry, consider •

elevation change = 10m

• total equivalent length =200m Total head to be developed by pump, =10 +

× 0.208 = 10.416 m (of slurry)

Since 1 atm =6.4 m slurry Pump discharge pressure required (for flooded suction condition)

= =1.63 atm

Slope of line

Fig. 5.3 Slope of line

5.4 Special Considerations •

Slope of pipe lines: Slopes of horizontal lines should not exceed angle of repose for slurry.

•

Provisions for flushing and draining of pipe lines and manual cleaning.

•

Selection of wear resistance materials or higher thickness.

•

Identification of wear prone points ‚‚ downstream of weld ‚‚ joints for easy replacement of worn out positions

Fig. 5.4 Wear Prone Zone •

Use of long radius bends

•

No dead spaces

•

General observation: Wear /erosion is higher for velocities more than 2.1 m/s whereas critical velocity may dictate minimum velocity as 1.2 m/s.

•

Use valves with maximum port size ‚‚ Use full part ball valves. ‚‚ Avoid use of globe value (seat may be plugged by solid deposition) ‚‚ Provide flushing connections for valves

84/uts

5.5 Pump for Slurry Different types of pumps used for slurry are as given below: Centrifugal •

For very dilute slurries with solids concentration up to 10 litres, sump type pumps could be used.

•

Impeller may have to be replaced frequently due to erosion; therefore split casing type design is preferred.

•

Low efficiencies are to be expected.

•

Rubber lining may prove useful in many situations.

•

Special wear resistant materials should be used.

•

Flushing connection for shaft sealing arrangement is to be provided.

Fig. 5.5 Centrifugal pump (Source: http://www.savinobarbera.com/english/pump-basics.html) Positive displacement (Plunger/piston type) •

Used for high discharge pressure (about 40 bar)

•

Plunger type design is preferred for abrasive slurries.

•

Flushing arrangement for plunger packing is desirable.

•

Liners of wear resistant materials inside the cylinder can yield longer trouble free services.

85/uts

System Designing

Piston Pump

Plunger Pump

Fig. 5.6 Piston and plunger pump (Source: http://en.wikipedia.org/wiki/File:Piston_VS_Plunger_Pump.png) Lock-hopper system It is a useful system for slurry of coarse particles. Surge pump Surge pump is the lock-hopper system concept used in conjunction with a positive displacement pump. A chamber filled with clear liquid is interposed between piston and pump valves. Movement of piston creates pressure sludge in clear liquid chamber which is utilised to discharge the slurry. Such designs have been used for abrasive slurries. Diaphragm pumps These types of pumps are common choice when lower through puts are to be handled for low delivery pressure (Typically up to 3 bar). Moyno pump It is a proprietary type design incorporating “advancing cavity” concept. It is used for moderate flows and pressure, the discharge in obtained at a steady pressure, well suited for thick slurries.

86/uts

5.6 Instrumentation Pressure of solids and possibilities of erosion put many restrictions on instruments to be used. Some relevant observations are as below: •

For measuring slurry concentration, use of radiation density meters is convenient. However, periodic calibration may be necessary.

•

When a side stream is drawn and then returned conveniently, measured by magnetic flow meters (which are rather expensive).

•

Flow rate of slurry can be conveniently measured by magnetic flow meters (which are rather expensive).

•

When positive displacement pump is used for slurry transfer pump speed and displacement can be used to calculate slurry flow rate.

•

Pressure gauges and other instruments mounted on pipe line are susceptible to damage due to vibrations.

•

For measurement of pressure, diaphragm type gauges are recommended which should be provided with back flushing arrangements, connected to pipeline with capillary. Moreover the gauges should be separately supported and not mounted directly on pipe line.

87/uts

System Designing

Summary •

Liquid-solid suspensions, called slurries, are produced and handled in many processes throughout the chemical process industries.

•

Because of the nature of slurries, proper layout and mechanical design are critical to prevent operational problems, such as pipeline plugging and erosion.

•

The different slurry piping systems are found in chemical, petrochemical and pharmaceutical plants.

•

The implementation of a reliable slurry pipeline system requires that all parties involved have a sound understanding of the underlying flow mechanisms of the slurries.

•

A suspension of solid particles in a liquid, as in a mixture of cement, clay, coal dust, manure, meat, etc. with water is often called slurry. Slurry piping system, like any other system, consists of slurry pumps, pipelines and valves.

•

Special considerations relevant to these systems are introduced by the fact that slurry in not homogeneous phase (unlike gas or liquid).

•

The design velocity is significant with reference to the critical velocity .Critical velocity is an important parameter for slurry.

•

The critical velocity for given slurry will be determined by different parameters such as size and specific gravity of solids, solids concentration viscosity of liquid and degree of turbulence.

•

Solid concentrations in settled slurries depending on nature of solid vary over a wide range (10-50%).

•

For measuring slurry concentration, use of radiation density meters is convenient. However, periodic calibration may be necessary.

References •

Grossel. S., Improved Design Practices for Slurry Piping Systems [Online]. Available at: . [Accessed 8 April 2011].

•

Pump basics [Online]. Available at: . [Accessed 9 April 2011].

•

Slurry characteristics [Online]. Available at: . [Accessed 9 April 2011].

Recommended Reading •

Aude, T.C., Cowper N.T., Thompson, T.L., & Wasp, E.J., 1971. Slurry Piping System: Trends, chemical Engineering.

•

Abulnaga, B. E., 2002. Slurry systems handbook, McGraw-Hill Professional, ISBN0071375082, 9780071375085

•

Brown, N. P. & Heywood, N. I., 1991. Slurry handling: design of solid-liquid systems, Springer, ISBN 1851666451, 9781851666454.

88/uts

Self Assessment 1. Which of these is not a hydrodynamic aspect? a. Line sizing b. Pressure drop c. Critical deposition velocity d. Light 2. Slurry piping system, like any other system, does not consist of __________. a. slurry pumps b. pipelines c. valves d. hazardous materials 3. Crystallisation occurs in _________. a. wax manufacturing process b. coal washeries c. papermaking d. effluent treatment 4. Which of these is not a property of liquid? a. Density b. Rigidity c. Viscosity d. Chemical nature 5. Sewage sludge is an example of ___________. a. homogeneous slurry b. cement kiln feed slurry c. heterogeneous slurry d. mixed behaviour of slurry 6. Phosphate rock slurry is typical example of _________. a. heterogeneous slurry b. homogeneous slurry c. cement kiln feed slurry d. mixed behaviour of slurry 7. Generally solid concentration of _____ below static settled slurry concentration would prove stable and convenient for handling. a. 0-5 % b. 10-15 % c. 1-1.5 % d. 50-75 %

89/uts

System Designing

8. Generally solids with particle size of 0.4-0.5 micron may form stable slurry for solid concentration up to_______. a. 40% b. 0% c. 10% d. 20% 9. Volume flow rate = __________× area of cross section. a. flow volume b. specific gravity c. π d. velocity 10. NHe = NRe × _________ a. PL b. D c. η d. μ

90/uts

Chapter VI Pumps Aim The aim of this chapter is to: •

define centrifugal pump

•

describe components of centrifugal pump

•

explain the applications of centrifugal pump

Objectives The objectives of this chapter are to: •

describe the pump head and net positive suction head concept

•

explain the specific speed and its calculation

•

discuss the concept of suction head

Learning outcome At the end of this chapter, the students will be able to: •

examine various considerations determining the behaviour slurry

•

state the importance of low NPSH

•

discuss the calculation of flow required

91/uts

System Designing

6.1 Introduction Pump is important rotating equipment used in industries. Pump installation and performance is very important for piping engineers. The classification, working and standard engineers’ practice of pump should be known. Selection procedure for the pump There are several things we must know before we attempt to select a proper pump: •

How many litres per min. are it is going to be pumped?

•

How high is the pump above water?

•

How high must the water be pushed after it leaves the pump?

•

What is the total length of pipe to be used?

•

Is water merely to be dumped at the end of the discharge run, or will it to be used?

6.2 Centrifugal Pumps •

A centrifugal pump is one of the simplest pieces of equipment in any process plant.

•

Its purpose is to convert energy of a prime mover (electric motor or turbine) first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped.

•

The energy changes occur by virtue of two main parts of the pump, the impeller and the volute or diffuser.

•

The impeller is the rotating part that converts driver energy into the kinetic energy.

•

The volute or diffuser is the stationary part that converts the kinetic energy into pressure energy.

Discharge Volute Casing

Impeller

Vanes

Suction Eye

Fig. 6.1 Liquid flow path inside a centrifugal pump (Source: http://www.maintenanceworld.com/Articles/engresource/centrifugalpumps.pdf) 92/uts

Components of centrifugal pump •

The centrifugal is like the ‘WORK HORSE’ in a process industry. The following figure shows major components in a centrifugal pump. DISCHARGE .

IMPELLER . SHAFT . SUCTION . COUPLING TO MOTOR . BEARINGS .

SEAL .

PUMP CASING .

Fig. 6.2 Components of centrifugal pump •

Liquid is pressured into the suction pump where the impeller imparts a centrifugal velocity to the fluid. As the liquid discharges from the pump its velocity head converts to pressure head because of typical shape of the casing.

•

Pumps are usually specified early in the process schedule, when lines are located and sized in sketches, when control valves have not been sized and when pump performances must be estimated rather than established.

•

A complex relationship exists between the system head, pump head and valve drop characteristics.

•

Methods of selecting control valve drop and impeller performance are not readily systematised.

•

API 610 is a standard that covers the minimum requirements for centrifugal pumps for use in petroleum, heavy duty chemical and gas industry services. It includes pumps running in reverse as hydraulic power recovery turbines.

•

A system design engineer must consider two characteristics of a centrifugal pump, the discharge pressure and volumetric flow rate. The designer’s heat and material balance will give the required flow rate hydraulic.

•

All of the forms of energy involved in a liquid flow system are expressed in terms of feet of liquid i.e., head.

6.3 Applications of Centrifugal Pump Pumps can be used in various settings and to pump different types of liquids. Pumps can be used in the following applications: •

Residential - Small pumps serve many purposes in home. Potable water may enter house after being pumped from the well or through the municipal system. The heating and/or cooling units use pumps to move fluids and air through those systems. High rise apartment buildings must maintain constant water pressure to ensure residents on the top floors receive the same pressure as those at street level.

•

Industrial - Fire pumps protect buildings and people during the work day. These systems stand primed and ready in case of fire. Pumps generate high water pressures for de-scaling and boiler feed applications. Some food and drink preparation requires pumps to insert the finished product into packaging.

•

Agricultural - Pumps support food production and agriculture by irrigating arid lands and areas with little rainfall. Wells and vertical pumps offer life supporting water to live stock as well as people.

93/uts

System Designing

•

Scientific and medical - Pumps are used in scientific arenas in the manufacturing of pharmaceuticals, toothpaste and medicine. Chemicals require special pumps, called process pumps that seal the processed liquids from the outside environment preventing contamination. Blood and bodily fluids are moved with pumps and pumping systems when in surgical or medical settings.

•

Marine - Naval ships and other marine going vessels use pumps to de-water bilges, provide boiler feed, stabilize ballast systems, support weaponry and to turn sea water into potable water. Pumps are a very important component of a marine vessel’s safety and security system.

6.4 Calculation of Flow Required The flow rate in kg/hr of liquid to be pumped is calculated from heat and material balance. Case-1 Suppose we have a simple equation HCL+ NaOH = = > NaCL + H2O = = => (1 mole + 1 mole = = => 1 mole + 1 mole) Molecular weight = = => 36.5 kg + 40 kg = = => 58.5 kg+18 kg Hence, for manufacturing 100 kg of NaCL, 62.40 kg of HCL & 68.37 kg of NaOH have to be pumped. Case -2 Sometimes, to take away the reaction heat, excess reactant is added. It may be as high as 5 to 6 times the actual requirement. Case – 3 For some reactions, to ensure completion of (100 %) reaction, some excess reactant is added. Case – 4 As a design engineer, about 20% flow as re -circulation is considered to avoid cavitations problems in the pump. •

Hence designed flow rate shall be 20% more than the actual flow rate.

•

Referring to the discussion above, pump flow ratio is calculated by following equation:

where, Q = pump flow ratio (m3/hr) For example, if one has to pump 1000 kg/hr of H2SO4 (which has specific gravity 1.8 (98% H2SO4) , the required m3/hr is m /hr.

=

94/uts

0.56 m /hr

6.5 Calculation of Pump Head The basic calculation consists of five steps: •

Differential pressure between two vessels

•

Head to lift the liquid

•

Friction head loss in the piping

•

Pressure drop allowed to control flow

•

Net Positive Suction head (NPSH) for the pump

Differential pressure between two vessels •

To calculate the differential pressure, the following formula should be used: using specific gravity of the liquid pumped at the process temperature.

Pump head to lift the liquid •

This is simply the difference between the liquid level in the first & second vessels.

Friction head loss •

Actually a design engineer does not lay the piping. Considering that 0.3kg/cm2 pressure drop for each 100 m of piping is allowed and the approximate distance run by the piping is estimated.

•

The calculated pressure drop is doubled to allow for elbows, bends, valves and other pipe fittings.

•

The friction pressure drop into head is converted by same formula given above.

Control valves / instruments •

As a thumb rule, the loss across a control valve is equivalent to half the friction loss of pipe line or 1.50 kg/cm (whichever is greater).

Net Positive Suction head (NPSH) required by pump •

Net Positive Suction head (NPSH) required by a pump is normally given in the manufacture’s pump curve which is normally 0.5-4 m.

Example:

100 m 2

20 m

2

1.5 Kg/cm

5m

5 Kg/cm

Lc

95/uts

System Designing

H = 88 m

6.6 Classification of Centrifugal Pump A pump can be classified depending where the impeller discharges the liquid as: ‚‚ axial flow ‚‚ mixed flow ‚‚ radial flow •

An axial flow pump discharges the liquid in the axial direction compared to the pump shaft centreline

•

A radial flow pump discharges the liquid in the radial direction.

•

A mixed flow pump is one that is a combination between a radial and an axial flow pump design.

6.7 Specific Speed •

Specific speed is defined as the speed in revolutions per minute (rpm) at which an impeller would operate if reduced proportionately in size so as to deliver a unit of capacity against a unit of total head.

•

The performance of a pump can be determined by stating its speed, the head it generates and the rate of discharge.

•

Different types of impellers and flow patterns can best be compared by means of the specific speed.

•

Pumps have to be selected with the right specific speed impellers in order to operate satisfactorily in the desired application.

•

High specific speed impellers (as fitted in axial flow and mixed flow pumps) are for high flow and lower head applications (such as ditch drainage, water supply operations, lift stations, flood control etc.) where huge amounts of water need to be moved quickly.

•

Low specific speed impellers (such as those installed in radial flow pumps) produce higher heads (pressures) at moderate flow rates, typically this type of pump is used to move liquids to much higher elevation levels (e.g. water well pumps, process pumps, boiler feed pumps etc).

•

Specific speed is one of the first parameters that a centrifugal pump designer looks at when evaluating a pump application. Specific speed may be used to rapidly determine the most feasible designs for the service conditions.

•

Specific Speed (Ns) is often treated as a dimensionless number that represents the physical design of an impeller regardless of pump size. The equation for specific speed is:

where, ‚‚ Ns = rotative speed in revolutions per minute (rpm)

‚‚ Q = pump flow or quantity of flow in m3/s (at the best efficiency point) ‚‚ H = pump differential head at the best efficiency point

96/uts

Type of Impeller

Ns

D2 (outlet diameter)/D1 (inlet diameters)

Slow speed radial flow

10-30

3.5-2

Normal speed radial flow High speed radial flow Mixed flow impeller (screw) Axial flow (propeller)

30-50 50-80 80-160 110-500

2.0-1.5 1.5-1.3 1.2-1.1 1.0

Table 6.1 Different types of impellers and their rotative speed •

Pumps having a specific speed less than 12 are generally not recommended. Infact, the pump efficiency falls drastically if the specific speed is less than 20. This is because impeller becomes disproportionate, the diameter being too large relative to width.

•

It results in leakage and higher disc friction and fluid friction losses owing to narrow passage of fluid.

•

It is therefore advisable to use impellers of small diameters consequently high specific speed. This will reduce the disc friction losses which vary with the radius, increase efficiency and decrease cost.

•

Thus, using higher stage pumps came in to picture. If we select higher stages, H will be divided for that many stages and single impeller head reduce and Ns increases.

•

Depending on the blade shape, the efficiency changes and it can have one of the following different shapes. >90ᴼ

90ᴼ

A

B

C

Shape

Approx. efficiency (η) %

Blades bent backward

85-90

Straight blades

~80

Blades ending radially

80-85

Blades bent forward

N 75

D

Fig. 6.3 Efficiency relative to different blade shapes •

In order to have high efficiency, the blades bent backward shall be selected. Straight blades can be used for small pumps where economy is important. Blades bent forward yield very low efficiency and hence rarely used.

6.8 Power and Efficiency •

The work performed by a pump is a function of the total head and the weight of the liquid pumped in a given time period.

•

Pump input or brake horsepower (BHP) is the actual horsepower delivered to the pump shaft. Pump output or hydraulic or water horsepower (WHP) is the liquid horsepower delivered by the pump.

97/uts

System Designing

Selecting a pump’s impeller •

Design of the pump impeller (the main internal moving part in a centrifugal pump) determines the pressure-flow operating characteristics of the centrifugal pump.

•

Impellers of pumps are classified based on the number of points that the liquid can enter the impeller and also on the amount of webbing between the impeller blades.

•

Impellers can be open, semi-open, or enclosed.

•

The open impeller consists only of blades attached to a hub.

•

The semi-open impeller is constructed with a circular plate (the web) attached to one side of the blades.

•

The enclosed impeller has circular plates attached to both sides of the blades. Enclosed impellers are also referred to as shrouded impellers.

Open impeller

Semi-open impeller

Closed impeller

Fig. 6.4 Types of impeller Selecting a pump motor •

An experienced design engineer shall usually select a motor for centrifugal pumps based not on the size of impeller used but on the maximum impeller diameter that will fit in to the pumps.

•

The reasons for selecting higher Kilowatt (KW) rating motors are : ‚‚ it doesn’t trip for higher initial torque ‚‚ to expand the pump capacity

•

Otherwise the motor shall be selected at the end of the curve power OR with the following correlations as per normal practice depend on the absorbed power. Absorbed Power (KW)

Multiplication Factor

upto 3.7

1.5

5.5 to 18.5

1.25

22 to 55

1.15

75 or above

1.10

Table 6.2 Multiplication factor and absorbed power for pump motor

98/uts

6.9 Shut in Pressure •

Shut in pressure is the pressure the pump will put up at zero flow. The larger the impeller size, the larger the shut in pressure.

•

The maximum shut in pressure which is allowed is the critical variable when selecting the size of an impeller.

•

The design engineer shall be assured that eventually the operator will block in a pump down stream.

•

The importance of shut in pressure is given in the figure below. If operator accidentally closes this valve, the shell of heat exchanger is subjected to shut in pressure of the pump.

•

In case, heat exchanger shell is not designed for shut in pressure, there can be following options: ‚‚ use small impeller ‚‚ install relief valve on shell ‚‚ eliminate valve

TANK .

OPEARTOR ACCIDENTLY CLOSES THE VALVE.

HEAT EXCHANGER PUMP . Fig. 6.5 Shut in pressure •

Often, a design engineer ignores the consequences to downstream equipment when expanding the capacity of pump.

•

The need to design all process equipment between pump and a block valve for the pump shut in pressure is a legal requirement.

6.10 Expanding the Pump Capacity There are two inexpensive methods to expand pumping capacity: •

reduce down stream pressure drop

•

increase size of impeller

Reducing downstream pressure drop The typical causes of excessive pressure drop and suggested remedies identified by many practical experiments are listed below: •

High tube side pressure drop through a shell & tube heat exchanger. ‚‚ reduce no. of tube side passes ‚‚ if the side passes are decreased in number from 4 to 2, 7/8 of drop is cut-off

• •

High shell side pressure drop in a shell‐and‐tube heat exchanger ‚‚ A new tube bundle with larger spaces between baffles (expensive choice)

High pressure drop through a wide open control valve ‚‚ change control valve port size or trim to the maximum size permitted in the control valve body, e.g. 3” control valve can accommodate 2 port size

99/uts

System Designing

•

Excessive piping losses ‚‚ increase diameter of piping or parallel piping runs

Large impeller •

The trick to select a larger impeller when expanding a pump capacity is to match the impeller size to the capacity existing motor drive.

•

The changing of impeller is easy and cheaper when compared to changing the motor and its associate compounds.

•

The changing of the diameter of impeller is done through following empirical relations.

where, ‚‚ Q2 = flow rate with larger impeller

Q2 = Q1 (D2/D1) h2 = h1 (D2/D1)2 P2 = P1 (D2/D1)3

‚‚ Q1 = flow rate with existing impeller ‚‚ D2 = Diameter of larger impeller

‚‚ D1 = Diameter of existing impeller

‚‚ h2 = Head delivered by larger impeller

‚‚ h1 = Head delivered by existing impeller

‚‚ P2 = Power drawn by motor with larger impeller

‚‚ P1 = Power drawn by motor with existing impeller •

To decide on the maximum size impeller that can be used existing motor, it is best to observe following in field. ‚‚ The control valve position should be placed “wide open.” ‚‚ The amperage drawn by motor should be measured.

•

The rated capacity of the motor (in amps) is multiplied by its service factor (typically 10-15 %) to calculate maximum size of impeller that can be used with existing motor.

6.11 Importance of Low Discharge Flow •

When discharge of pump is closed, pump will overheat.

•

The motor’s electric power is converted to heat as the pump churns the trapped liquid. The pump’s case and bearings become hotter and hotter and eventually the bearings will burn out also damage the pump seal.

•

In addition, many large head pumps are subjected to a phenomenon called internal recirculation, which damages pumps internal parts when the pump is operated at reduced rate.

•

A simple modification in the process as shown below will automatically prevent pump damage due to low flow.

•

The designer should consider whether the minimum flow bypass is necessary, considering the process variables of the plant designed .Never tie the minimum flow disc line in to the suction of pump. This defeats the purpose of line; it must be routed back to a point in the process where the pumping heat is dissipated .

100/uts

RE - CIRCULATION.

Ro TO PROCESS.

Fig. 6.6 Low discharge flow

6.12 NPSH (Net Positive Suction Head) •

The margin of pressure over vapour pressure, at the pump suction nozzle, is Net Positive Suction Head (NPSH).

•

NPSH is the difference between suction pressure (stagnation) and vapor pressure. In equation form: NPSH = Ps - Pvap

where, ‚‚ NPSH = NPSH available from the system, at the pump inlet, with the pump running ‚‚ Ps = Stagnation suction pressure, at the pump inlet, with the pump running ‚‚ Pvap = Vapor pressure of the pumpage at inlet temperature •

Low pressure at the suction side of a pump can encounter the fluid to start boiling with ‚‚ reduced efficiency ‚‚ cavitations ‚‚ damage

•

To characterise the potential for boiling and cavitation, the difference between the total head on the suction side of the pump, close to the impeller, and the liquid vapour pressure at the actual temperature, can be used.

101/uts

System Designing

pd ps

vapor pressure NO bubble formation Discharge Suction

Eye

Discharge pd

ps

Suction

vapor pressure Bubble Formation Suction

Eye

Discharge

Fig. 6.7 Effect of NPSH on pump (Source: http://www.techpedia.in/uploads/8dcbccda736a01969106b71b90a4c49b.pdf? PHPSESSID=28646d66d12ea7c61dd41478a181830b) Suction head Based on the energy equation, the suction head in the fluid close to the impeller can be expressed as the sum of the static and the velocity head:

hs = ps / γ + vs2 / 2 g ................(1) where, ‚‚ ‚‚ ‚‚ ‚‚

hs = suction head close to the impeller ps = static pressure in the fluid close to the impeller γ = specific weight of the fluid vs = velocity of fluid

‚‚ g = acceleration of gravity Liquids vapour head The liquids vapour head at the actual temperature can be expressed as: hv = pv / γ .......(2) where, ‚‚ hv = vapor head ‚‚ pv = vapor pressure The vapour pressure in a fluid depends on temperature. Water, the most common fluid, starts boiling at 20°C if the absolute pressure in the fluid is 2.3 KN/m2. For an absolute pressure of 47.5 N/m2, the water starts boiling at 80°C. At an absolute pressure of 101.3 KN/m2 (normal atmosphere), the boiling starts at 100°C. The net positive suction head can be also be expressed as the difference between the suction head and the liquids vapor head and expressed like 102/uts

NPSH = hs - hv......... (3a) Or, by combining (1) and (2)

NPSH = ps / γ + vs2 / 2 g - pv / γ.......... (3b) Available NPSH (NPSHa) The Net Positive Suction Head made available the suction system for the pump is often named NPSHa. The NPSHa can be determined during design and construction, or determined experimentally from the actual physical system.

he

ho

he Fig. 6.8 NPSH (Source: http://www.techpedia.in/uploads/8dcbccda736a01969106b71b90a4c49b.pdf?PHPSESSID=28646d66d1 2ea7c61dd41478a181830b) The available NPSHa can be calculated with the energy equation. For a common application where the pump lifts a fluid from an open tank at one level to another, the energy or head at the surface of the tank is the same as the energy or head before the pump impeller and can be expressed as: h0 = hs + hl............. (4a) where,

‚‚ h = head at surface ‚‚ h = head before the impeller ‚‚ h = head loss from the surface to impeller - major and minor loss in the suction pipe 0 s l

In an open tank the head at surface can be expressed as: h0 = p0 / γ = patm / γ.......... (4b) For a closed pressurized tank the absolute static pressure inside the tank must be used. The head before the impeller can be expressed as: hs = ps / γ + vs2 / 2 g + he.......... (4c)

he = elevation from surface to pump - positive if pump is above the tank, negative if the pump is below the tank

103/uts

System Designing

Transforming (4a) with (4b) and (4c) patm / γ = ps / γ + vs2 / 2 g + he + h1.......... (4d) The head available before the impeller can be expressed as: ps / γ + vs2 / 2 g = patm / γ - he - h1.............. (4e) or as the available NPSHa: NPSHa = patm / γ - he - hl - pv / γ............ (4f)

6.13 Importance of Low NPSH •

When a centrifugal pump loses suction due to low NPSH, the pumped fluid begins to flash at the eye of impeller .This results bubbles of vapours which when carried towards discharge are compressed and collapse. This phenomenon is called cavitations, which is a common cause for failure of pump.

•

A designer can prevent damage to many pumps by applying a few simple ideas. ‚‚ Location of the coolers on suction side of pumps. The decreased pump suction pressure will be usually more than offset by the reduction in the fluid’s bubble point. ‚‚ Providing vortex breakers in bottom of all vessels regardless of the anticipated liquid level in vessel. ‚‚ Provide adequate liquid hold in process vessels acting as surge drums. As a thumb rule 5-15 min. hold up is a typical range.

4D

0.5 D

D

VORTEX BRAKER

Fig. 6.9 Design of vortex braker

6.14 Pump Safety Tips Maintenance personnel should be aware of potential hazards to reduce the risk of accidents. The following are the safety tips for pumps operation: •

Safety apparel ‚‚ Insulated work gloves when handling hot bearings or using bearing heater. ‚‚ Heavy work gloves when handling parts with sharp edges, especially impellers. ‚‚ Safety glasses (with side shields) for eye protection, especially in machine shop areas. ‚‚ Steel-toed shoes for foot protection when handling pants, heavy tools, etc. ‚‚ Other personal protective equipment to protect against hazardous/toxic fluids.

104/uts

•

Couplings guards ‚‚ Never operate pump without a coupling guard properly installed. ‚‚ Flanged Connections: ‚‚ Never force piping to make a connection with a pump. ‚‚ Use only fasteners of the proper size and material. ‚‚ Ensure there are no missing fasteners. ‚‚ Beware of corroded or loose fasteners.

•

Operation ‚‚ Do not operate below minimum rated flow, or with suction/discharge valves closed. ‚‚ Do not open vent or drain valves, or remove plugs while system is pressurized.

•

Maintenance safety ‚‚ Always lockout power. ‚‚ Ensure pump is isolated from system and pressure is relieved before disassembling pump, removing plugs, or disconnecting piping. ‚‚ Use proper lifting and supporting equipment to prevent serious injury. ‚‚ Observe proper decontamination procedures. ‚‚ Know and follow company safety regulations. ‚‚ Never apply heat to remove impeller.

105/uts

System Designing

Summary •

Pump is an important rotating equipment used in industries. Pump installation and performance is very important for piping engineers.

•

A centrifugal pump is one of the simplest pieces of equipment in any process plant.

•

Its purpose is to convert energy of a prime mover (electric motor or turbine) first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped.

•

The energy changes occur by virtue of two main parts of the pump, the impeller and the volute or diffuser.

•

The impeller is the rotating part that converts driver energy into the kinetic energy.

•

The volute or diffuser is the stationary part that converts the kinetic energy into pressure energy.

•

API 610 is a standard that covers the minimum requirements for centrifugal pumps for use in petroleum, heavy duty chemical and gas industry services. It includes pumps running in reverse as hydraulic power recovery turbines.

•

A system design engineer must consider two characteristics of a centrifugal pump, the discharge pressure and volumetric flow rate. The designer’s heat and material balance will give the required flow rate hydraulic.

•

All of the forms of energy involved in a liquid flow system are expressed in terms of feet of liquid i.e., head.

•

Fire pumps protect buildings and people during the work day. Pumps generate high water pressures for descaling and boiler feed applications.

•

Wells and vertical pumps offer life supporting water to live stock as well as people.

•

Pumps are used in scientific arenas in the manufacturing of pharmaceuticals, toothpaste and medicine. Pumps are a very important component of a marine vessel’s safety and security system.

•

The maximum shut in pressure which is allowed is the critical variable when selecting the size of an impeller. The design engineer shall be assured that eventually the operator will block in a pump down stream.

•

Maintenance personnel should be aware of potential hazards to reduce the risk of accidents.

References •

Centrifugal Pumps [Online]. Available at: . [Accessed 9 April 2011].

•

Fluid mechanics pumped pipe systems [Online]. Available at: . [Accessed 9 April 2011].

•

Centrifugal Pumps [Online]. Available at: . [Accessed 10 April 2011].

Recommended Reading •

Lobanoff,V. S., & Ross, R. R., 1992. Centrifugal pumps: design & application, 2nd ed., Gulf Professional.

•

Bachus, L., & Custodio, A., 2003. Know and Understand Centrifugal Pumps, Elsevier.

•

Munson, 2007. Fundamentals of Fluid Mechanics, Wiley-India.

106/uts

Self Assessment 1. ______ is important rotating equipment used in industries. a. Valves b. Bolts c. Pumps d. Gauges 2. Centrifugal pump converts energy of a prime mover (electric motor or turbine) first into _______. a. kinetic energy b. electricity c. light energy d. heat energy 3. Which is the rotating part that converts driver energy into the kinetic energy? a. Impeller b. Suction eye c. Vanes d. Volute casting 4. Flow rate is measured in _________ S.I unit. a. kg/hr b. kg/sec c. g/sec d. kg/min 5. The SI Unit of pump flow ratio is _____________. a. kg/hr b. m3/hr c. m3/min d. kg/min 6. Pumps having a specific speed less than ______ are generally not recommended. a. 20 b. 12 c. 40 d. 55 7. Blades bent backward have approximatr efficiency of ________. a. 85-90 % b. 90-95 % c. 10-20 % d. 13-18 %

107/uts

System Designing

8. In the equation, Q2 = Q1 (D2/D1), Q2 is ______________. a. flow rate with larger impeller b. flow rate with existing impeller c. head delivered by larger impeller d. head delivered by existing impeller 9. The _______impeller consists only of blades attached to a hub. a. semi-open b. open c. closed d. semi-closed 10. Specific speed is the speed in ____________. a. km/sec b. m/sec c. revolutions per minute d. revolutions per sec

108/uts

Chapter VII Pneumatic Conveying Terms CEMA Standard No. 805 Aim The aim of this chapter is to: •

describe pneumatic conveying terms

•

explain the basic terms and definitions

•

state the material characterisation

Objectives The objectives of this chapter are to: •

describe the individual particle shape descriptions

•

explain the general compositions found in bulk material

•

discuss the importance of pneumatic terms

Learning outcome At the end of this chapter, the students will be able to: •

examine various bulk density terms

•

describe the different gas velocity terms

•

get an overview of CEMA

109/uts

System Designing

7.1 Introduction One of the most popular methods of moving solids in the chemical industry is pneumatic conveying.  Pneumatic conveying refers to the moving of solids suspended in or forced by a gas stream through horizontal and/or vertical pipes.  Pneumatic conveying can be used for particles ranging from fine powders to pellets and bulk densities of 16 to 3200 kg/m3 (1 to 200 lb/ft3). The Conveyor Equipment Manufacturers Association (CEMA) has developed industry standard safety labels for use on the conveying equipment of its member companies. The purpose of the labels is to identify common and uncommon hazards, conditions and unsafe practices which can injure, or cause the death of, the unwary or inattentive person who is working at or around conveying equipment. The labels are available for sale to member companies and non-member companies. A full description of the labels, their purpose, and guidelines on where to place the labels on typical equipment has been published in CEMA’s Safety Label Brochure No. 201. The Brochure is available for purchase by members and non-members of the association. Safety labels and safety label placement guidelines, originally published in the Brochure, are also available free on the CEMA web site at http://www.cemanet.org/CEMA_Safety_Pg.htm **Should any of the safety labels supplied by the equipment manufacturer become unreadable for any reason, the equipment user is then responsible for replacement and location of these safety labels. Replacement labels and placement guidelines can be obtained by contacting equipment supplier or CEMA.

7.2 List of Pneumatic Conveying Terms The list of pneumatic conveying terms is given below: ‚‚ Abrasiveness ‚‚ Actual gas velocity ‚‚ Adhesiveness ‚‚ Aeration ‚‚ Air retention ‚‚ Angle of repose ‚‚ Average gas velocity ‚‚ Bulk material composition ‚‚ Choking velocity ‚‚ Cohesiveness ‚‚ Conveying pressure ‚‚ Corrosiveness ‚‚ Dense phase conveying ‚‚ Dilute phase conveying ‚‚ Explosiveness ‚‚ Flotation velocity ‚‚ Flowability ‚‚ Fluidised ‚‚ Fluidised bulk density ‚‚ Friability ‚‚ Hardness ‚‚ Hygroscopicity ‚‚ Loose bulk density ‚‚ Material mass flow rate 110/uts

‚‚ Material temperature ‚‚ Material temperature sensitivity ‚‚ Material to air ratio ‚‚ Material velocity ‚‚ Maximum particle size ‚‚ Median particle size ‚‚ Minimum conveying velocity ‚‚ Packed bulk density ‚‚ Particle density ‚‚ Particle shape ‚‚ Particle size distribution ‚‚ Permeability ‚‚ Saltation velocity ‚‚ Terminal gas velocity ‚‚ Two-phase flow ‚‚ Volumetric gas flow The terms have been grouped into two sections: ‚‚ Material Characterisation ‚‚ Basic Terms and Definitions

7.3 Material Characterisation The terms are described below: Loose bulk density •

The loose bulk density (sometimes called the poured bulk density) of a bulk material is the weight per unit of volume (usually pounds per cubic foot) that has been measured when the sample is in a loose, non-compacted or poured condition.

•

The loose bulk density may be close to the “as conveyed” bulk density and is preferred for the purposes of pneumatic conveying system design.

Packed bulk density •

The packed bulk density of a bulk material is the weight per unit volume (usually pounds per cubic foot) that has been measured when the sample has been packed or compacted in, for instance, a silo or bin or after containerised transportation.

•

The packed bulk density does not compare to the conditions that would be found in a pneumatic conveying system.

•

It is for this reason that the loose bulk density is preferred for the purposes of conveying system design.

Fluidised bulk density •

Fluidised bulk density is the apparent bulk density of a material in its fluidised state.

•

It is generally lower than either the packed or loose bulk density due to the air absorbed into the voids.

Particle density •

Particle density is the mass of a particle divided by its volume.

•

For a bulk material, average particle density is used, found by dividing the mass of the material by its volume, excluding the voids.

111/uts

System Designing

Particle size distribution •

The particle size distribution of a bulk material is a tabulation of the percentage of particles by mass in each particle size range.

•

The percentage described is either that passing or being retained on a specific screen size. In the United States, the screens used are “U.S. Standard Screens” or “Tyler Test Screens”.

•

Other methods of size analysis may be used, particularly in the case of very fine and/or cohesive powders.

•

These methods include photo sedimentation, optical microscopy, electrical sensing zone techniques (such as the Coulter counter), and laser diffraction spectrometry.

Maximum particle size •

Maximum particle size is the maximum dimension in inches (in the case of lumpy materials) or the maximum sieve size (in the case of powders and granules) of the largest lump or particle in the bulk material.

•

Maximum particle size can be critical in the design of pneumatic conveying systems.

Median particle size •

The median size is the mid-point of the particle distribution.

Particle shape •

The shape and form of the particles of a bulk material can vary considerably.

•

The following table specifically describes the individual particle shape only and not the bulk material as a whole.

Term

Definition

Needle-like

Long, thin, rigid, straight and pointed

Angular

Sharp edged or having a multi-faced, irregular shape

Crystalline

Of geometric shape or multi-faced regular shape

Dendritic

Having a branched, crystalline shape with the branches extending from the faces of the body

Fibrous

Regularly or irregularly thread like with a flexible structure

Flaky

Plate-like

Spherical

Globe-like

Out-of-Round

Similar to Spherical but being somewhat deformed or elongated

Cylindrical

Cylinder-shaped

Agglomerated

Several individual particles bended together Table 7.1 The individual particle shape descriptions

112/uts

Bulk material composition The following table describes the general compositions and the shapes that may be found. Term

Definition

Uniform

A single bulk material whose particles possess the same size and shape.

Non-uniform

A single bulk material whose particle size : and shape may vary

Granular

A bulk material comprised of individual particles which can be visibly discerned.

Powder

A bulk material comprised of individual particles which cannot be visibly discerned.

Mixed

Two or more different bulk materials which have been combined. Table 7.2 The general compositions found in a bulk material

Flow ability •

Flow ability is the case where a bulk material flows under the influence of gravity only.

Cohesiveness •

Cohesiveness is described as the tendency of a material to adhere to itself.

•

The cohesiveness of a bulk solid material can be caused by any and sometimes by all of several factors.

•

These include electrostatic charging, surface tension effects, and interlocking of certain particle shapes, particularly fibrous types of materials.

•

Cohesiveness in bulk solids causes erratic flow from bins, pipeline feeding problems and adverse effects in certain kinds of valves.

Adhesiveness •

Adhesiveness can be described as “external cohesiveness” i.e., the ability of a material to adhere to other surfaces.

Fluidised •

Fluidised describes the state some bulk materials achieve when a gas has been entrained into the void spaces between the particles of the material.

•

Material in a highly fluidised state ends to behave more like a fluid (as the term implies) than a solid bulk material.

Aeration •

Aeration is the action of introducing air (or gas) to a bulk material by any means.

•

Aeration may cause the material to become fluidised or agitated.

Angle of repose •

The angle of repose of a bulk material is the angle between the horizontal and the sloping surface of a heap of the material which has been allowed to form naturally without any conditioning, usually by gravity flow from a funnel or other similar device.

Hardness •

Hardness is a property of a solid material which contributes to its overall abrasiveness.

•

The harder a material is, generally, the greater the erosion for a given velocity on a pipeline.

•

Hardness is difficult to quantity and is somewhat subjective when described. Moh’s scale of hardness is used to describe the materials when designing pneumatic conveying systems. 113/uts

System Designing

Abrasiveness •

The abrasiveness of a material is determined by its hardness factor and the shape of its particles.

•

A material which has, for instance, a high Moh’s hardness factor and its sharp, angular-shaped particles will be considered highly abrasive.

Material Temperature •

Generally, most bulk materials are handled at ambient temperature conditions.

•

However, in some cases, the material may be at an elevated temperature.

•

Elevated temperature can affect both the condition of the material it sell and its surroundings, particularly, the equipment that is being used to convey it.

•

Care should be taken, when considering high temperature.

•

Elevated temperature range is clearly and accurately stated, and any effects on the material (particularly its handling characteristics) should be noted.

•

The temperature of the bulk material, measured in °F or °C, for purposes of pneumatic conveying design, is the material temperature taken at the point of entry to the system.

Material temperature sensitivity •

Material temperature sensitivity is the temperature at which a bulk material changes its characteristics.

Hygroscopicity •

Hygroscopicity is the ability of a material to absorb moisture from its surroundings.

•

Moisture may be absorbed from either the ambient air (especially during high humidity conditions) or the conveying air of the pneumatic system.

Explosiveness •

In certain conditions, some bulk materials can form potentially explosive mixtures when combined with air.

•

These conditions depend on (a) the nature of the material itself, which would include its ignition temperature, its chemical reaction with oxygen, its particle size distribution, and so on; and (b) the nature of the operation involving the material.

•

Details of explosion risk, reactivity, and fire hazard are now required by law in most states in the U.S. to be listed on the Material Safety Data Sheet (MSDS).The MSDS must accompany any material which is transported stored or tested.

•

In all cases involving explosive materials, reference should be made to National Fire Protection Association (NFPA) classifications.

Corrosiveness •

Some materials have chemical properties which will, when combined with other materials such as moisture and air, cause chemical deterioration to materials of construction.

Friability •

Friability describes a bulk material where particles are crumbled or pulverised.

Permeability •

The permeability of a bulk material is the degree to which air (or other gas) may be passed through the void spaces between the particles of the material.

114/uts

Air retention •

Air retention is the ability of a material to retain air (or other gas) in the void spaces of the material after the air (for gas) supply to it has been terminated.

•

Air retention capability can vary between almost zero and several days, depending upon the material’s other physical characteristics.

7.4 Basic Terms and Definitions The terms are described below: Material mass flow rate •

The mass of material conveyed over a specified period of time, usually expressed in tons/hour or lbs./minute. Material mass flow rate is also called conveying rate or system capacity.

Actual gas velocity •

Actual gas velocity is the volume flow rate at pressure and temperature conditions per unit cross-sectional area of the empty pipe, normally expressed in distance/time.

•

Actual gas velocity varies throughout the entire length of the pipeline.

Saltation velocity •

The saltation velocity of a material is the actual gas velocity in a horizontal pipeline at which particles in a homogeneous mixture with the conveying gas will begin to fall out of the gas stream.

Chocking velocity •

The chocking velocity of a material is the actual gas velocity in a vertical pipeline at which particles in a homogeneous mixture with the conveying gas settle out of the gas stream.

Minimum conveying velocity •

The minimum conveying velocity is the lowest gas velocity that can be used to insure stable conveying conditions.

•

Since the minimum conveying velocity occurs at the material feed point in the system, it is also known as the “pick-up” velocity.

•

These terms are generally applied to dilute phase systems.

Terminal gas velocity •

The terminal gas velocity in a pneumatic conveying system is the velocity of the gas as it exits the system.

•

It is also known as the ending gas velocity and conveying line exit velocity.

Average gas velocity •

The average (also called mean) gas velocity of a system is usually defined as the mean of the beginning (or pick-up) gas velocity and the terminal gas velocity.

Material velocity •

The material velocity is the velocity of the material itself, which is somewhat lower than the gas velocity.

•

Material velocity is usually specified as either average (or mean) velocity or terminal velocity.

•

There are no reliable means, at the present time, for measuring the actual material velocity, and only an estimate can be made.

115/uts

System Designing

Volumetric gas flow •

The user should be aware that there are several different terms used when considering volumetric gas flow.

•

The volumetric gas rate during conveying is expressed as free air delivered (FAD).

•

Most air movers, such as blowers and compressors, are specified in terms of FAD, measured in standard cubic feet per minute (SCFM).

•

FAD is the volumetric gas flow at the suction port of a positive pressure blower or compressor or at the discharge port of a vacuum blower or vacuum pump.

•

SCFM is the gas flow rate at standard atmospheric conditions (i.e., barometric pressure at sea level, 680°F, and 36% relative humidity).

•

Actual cubic feet per minute (ACFM) or inlet cubic feet per minute (ICFM) is the volumetric gas flow at the actual conditions that will be experienced where compressor or blower is located.

•

The ACFM or ICFM must be calculated from the SCFM, taking into account elevation of the location and maximum summertime ambient conditions.

•

In the case of vacuum systems, the pressure drop of the system must also be taken into account when calculating the gas at the inlet of the blower.

Conveying pressure •

The conveying pressure for any system is required to overcome resistances in the system caused by interactions between the conveying gas, the material being conveyed, the pipeline, and other system components.

•

It is also referred to as “pressure drop”.

•

The conveying pressure is the difference measured between the beginning and the end of the pneumatic system and is applicable to both positive pressure and vacuum (negative pressure) systems.

Two phase flow •

All bulk solid materials pneumatic conveying systems operate on a two-phase flow principle, i.e., a solid phase (the materials being conveyed) and the gaseous phase (the conveying gas).

Dilute phase conveying •

A dilute phase system is any pneumatic conveying system for which the conveying gas velocity is generally equal to or above the saltation velocity of the material being conveyed.

Dense phase conveying •

A dense phase system is any pneumatic conveying system for which the conveying gas velocity is generally below the saltation velocity of the material conveyed.

Material to air ratio •

A parameter used by pneumatic system designers.

•

It is the ratio of the mass of material conveyed to mass of conveying gas used.

•

It is also referred to as “phase density”, “solids loading ratio”, and “mass flow ratio”.

Flotation velocity •

The flotation velocity is the velocity at which material will be suspended in air.

•

Knowing flotation velocity is critical to determining “enclosure velocity”, which is the upward velocity of gas in a filter receiver or bin vent.

•

This term is typically used in the design of bag-houses and dust collection systems.

116/uts

Summary •

Pneumatic conveying refers to the moving of solids suspended in or forced by a gas stream through horizontal and/or vertical pipes. 

•

The Conveyor Equipment Manufacturers Association (CEMA) has developed industry standard safety labels for use on the conveying equipment of its member companies.

•

The purpose of the labels is to identify common and uncommon hazards, conditions and unsafe practices which can injure, or cause the death of, the unwary or inattentive person who is working at or around conveying equipment.

•

The terms have been grouped into two sections: material characterisation and basic terms and definitions.

References •

Glossary of Pneumatic Conveying Terms [Online]. Available at: >http://www.cemanet.org/publications/previews/ CEMA%20Standard%20805pv.pdf>. [Accessed 10 April 2011].

•

Conveyor Equipment Manufacturer’s Association Publications [Online]. Available at: . [Accessed 10 April 2011].

•

Tekchandaney, J. Material Properties Affecting Solids Blending and Blender Selection: Bulk Density [Online]. Available at: . [Accessed 10 April 2011].

Recommended Reading •

CEMA Standard No. 805, “Glossary of Pneumatic Conveying Terms - 2005”.

•

Yang, 2003. Handbook of Fluidization and Fluid-Particle Systems, 2nd ed., CRC Press.

•

Tekchandaney R. Jayesh, Material Properties Affecting Solids Blending & Blender Selection.

117/uts

System Designing

Self Assessment 1. A _________is any pneumatic conveying system for which the conveying gas velocity is generally below the saltation velocity of the material conveyed. a. dense phase conveying b. dilute phase conveying c. conveying pressure d. two phase flow 2. Pneumatic conveying terms are described as CEMA standard no. ________. a. 805 b. 806 c. 808 d. 803 3. What is sometimes called the poured bulk density? a. Fluidised bulk density b. Loose bulk density c. Packed bulk density d. Particle density 4. Which is the apparent bulk density of a material in its fluidised state? a. Fluidised bulk density b. Loose bulk density c. Packed bulk density d. Particle density 5. What can be critical in the design of pneumatic conveying systems? a. Material Velocity b. Maximum Particle Size c. Median Particle Size d. Minimum Conveying Velocity 6. Which of these is a method for particle size distribution? a. photo sedimentation b. optical microscopy c. electrical sensing zone techniques d. Nuclear magnetic resonance spectrometry 7. What is similar to spherical but being somewhat deformed or elongated? a. Fibrous b. Flaky c. Spherical d. Out-of-round

118/uts

8. Which is a bulk material comprised of individual particles which cannot be visibly discerned? a. Powder b. Granular c. Uniform d. Non-uniform 9. __________ is a single bulk material whose particles possess the same size and shape. a. Uniform b. Mixed c. Powder d. Non-uniform 10. ___________ is the ability of a material to absorb moisture from its surroundings. a. Abrasiveness b. Explosiveness c. Hygroscopicity d. Corrosiveness

119/uts

System Designing

Chapter VIII Cross – Country Pipe – Line Aim The aim of this chapter is to: •

highlight the main features of the detailed engineering

•

explain construction of cross- country pipe-lines

•

analyse the advantages of cross- country pipe-lines

Objectives The objectives of this chapter are to: •

describe the route survey and analysis

•

enlist the data on the product to be carried out

•

state the limitations of transport modes

Learning outcome At the end of this chapter, the students will be able to: •

examine the implementation and planning in detail engineering

•

explain the project schedule concept

•

state the disadvantages of cross- country pipe-lines

120/uts

8.1 Introduction In the modern age of industrial word, the oil refineries, petroleum products and petrochemicals form the major part of the industrial set-up all over the world. It is often economical and practical to carry the liquid and gaseous products through pipe-lines rather than by tankers over long distance. A pipe-line has to carry products like crude oil, refined oil, chemicals like naphthalene, ethylene, propylene etc. over long distance ranging from 10 km to even 1000 km. Passing through land, rivers, sea, mountains, marshy areas, private and public land rivers, sea, mountains, marshy areas, private and public land and crossing other services like roads, railways, transmission lines, underground pipes or cables etc, such a pipeline is called “cross-country pipe-line”. As the name suggests it transfers the liquid or gas products from one place to another at far distance. Engineering and installation of cross-country pipe-lines form a special branch of piping design and engineering, as it involves many aspects and parameter which are normally faced in plant piping system within the boundaries of refinery or a chemical or petrochemical plant. Special techniques have to be adopted for design, laying, welding or joining, corrosion protection, testing, commissioning etc. The most common line familiar to all is, water-line from reservoirs to different consumption points like, water-main from dams to city of Mumbai. Unlike water line, the hazardous chemical conveying pipelines, involves many more stringent precautions in their design and installation. This is mainly due to fire and explosion hazards associated with the oils and chemicals.

8.2 Pipeline System •

Pipeline systems are the safest and the most environment friendly mode of transportation of crude petroleum, refined products and natural gas.

•

Being a closed system, there is minimal handling and transit losses as compared to other means of transportation, hence it is considered to be most efficient.

•

The safety and reliability ensure minimum disruptions.

•

High grade steel pipes (API 5L international code) are used for constructing cross country pipelines.

•

The typical sizes of pipes are: ‚‚ diameter: 4 - 56 inch ‚‚ pipe thickness: 0.219 – 1 inch

•

These pipelines are designed to handle pressures upto 120 kg/cm2 to achieve throughput.

Rail 30%

INDIA*

Pipelines 39%

Road/ Coastal 31%

USA** Coastal 25%

Rail 3%

Road

4%

68%

Pipelines

Fig. 8.1 Typical mode-wise transportation of petroleum products (Source: http://petrofed.winwinhosting.net/upload/26-28July10/BDYadav.pdf) 121/uts

System Designing

8.3 Limitations of Modes of Transport •

The most common modes of transport known to all includes trucks running over roads, railway goods train and ships, launches, boats, barges on waterways.

•

The transport by airway or by cargo air-crafts is also another way of bulk-transport.

•

These modes of transport have the following limitations: ‚‚ availability of sufficient roads, rail-tracks and port-harbour facilities to take up the traffic load. ‚‚ condition of tracks ‚‚ hurdles and conditions of the vehicles ‚‚ maintenance and conditions of the vehicles ‚‚ procedures and control involved in the transport operation (permits/ licenses/octroi/toll/RTO etc) ‚‚ manpower to run and maintain the transport system ‚‚ availability of fuel and power required to run the system ‚‚ effect of nature on the system like rains, storms, earthquakes, thundering, mist etc. ‚‚ pollution generated by the transporting vehicles ‚‚ safety, insurance and security of the transported goods and materials ‚‚ time taken for transportation and delays ‚‚ overall efficiency of the system

•

While transportation by roads, railways, water and air-ways is widely used all over the world, it has its own limitations due to the features used all over the world.

•

These limitations especially restrict or forbid their use when large quantities of oil, petroleum, water, chemicals are to be continuously supplied from the source to the consumption point at user’s end.

•

Hence, the most reliable and efficient system can be provided only be cross-country pipe-lines. Head

Road

Rail

Pipeline

Energy cost

Very High

High

Low

Operating cost

Very High

High

Low

Pollution

High

Low

Nil

Movement congestion

High

Low

Nil

Handling loss

High

Low

Negligible

Safety Hazards

High

Low

Negligible

Reliability

Low

Low

100%

Fig. 8.2 Modes of transportation of petroleum-A comparison (Source: http://petrofed.winwinhosting.net/upload/26-28July10/BDYadav.pdf)

8.4 Advantages and Disadvantages of Cross-Country Pipe-Lines •

The advantages of cross-country pipelines are given below: ‚‚ Continuous un-interrupted transport is ensured. ‚‚ No dependence on availability of roads, railways, bridges etc. ‚‚ Least manpower requirement to operate the transport system except for inspection and maintenance of minimum required level. ‚‚ No hindrances on way due to any reasons for surface transport, air or water ways. ‚‚ Possibility of crossing any odd areas like seas, oceans, rivers, mountains and underground space.

122/uts

‚‚ Safety and purity of the product is ensured. The product reaches exactly in the same condition from source to the supply point, with minimal loss of quality or quantity. ‚‚ Once laid down, the system works automatically especially with the help of modern instrumentation, safety devices, interlocks, communication system and remote control devices. ‚‚ Minimum or no tampering on the way. ‚‚ Cost of transport per unit of the product conveyed is far less than the transport by trucks, railways, water or airways. ‚‚ Fastest mode of transport even between two countries or continents. ‚‚ Comparatively much less hazardous than surface transport and minimum dependence on human factors. •

There are of course certain disadvantages but they are offset by the advantages to a large extent, so as to make them ignorable as far as safety and techno-economic aspects are concerned.

•

These disadvantages are listed below: ‚‚ Right of way acquisition to run the pipeline, especially through private and agricultural land and habitat areas. ‚‚ High fire and explosion hazards potential. ‚‚ Problem of corrosion and leakages and repair work involved ‚‚ Daily on-route inspection, testing and quick arrangements for attending to repairs and rectification work ‚‚ Possibility of laying other services in future (like other pipelines due to ignorance of its existence, among other agencies) causing damage ‚‚ Special techniques and agencies are required to design, engineer, install and operate the pipeline system. ‚‚ Expensive cathodic protection required for the protection of underground lines running in close proximity of overhead high tension electrical transmission lines which induce the currents in the metallic pipelines, causing the corrosion by stray-currents.

•

The modern techniques are well developed to offset the effects of the above disadvantages. Even if a line has to shut-off for a day or two, the storage facilities at the users end take care of such stoppages even for 15 days to 1 month.

8.5 Preliminary Work for a Cross-Country Pipe-Line Project The following necessary work on planning and collection of information or data is required to be for pre-project activities, once it is decided to install a cross-country pipe-line. Data on the product to be carried •

name, quantity per day, properties of the product

•

source of supply and location details

•

names and location of consumers

•

quantity per day to be supplied to each consumer

•

storage facilities at supplier’s end and consumer end

•

pumping facilities at supplier’s end

•

unloading facilities at receiver’s end

•

safety requirements for the product

•

risk and hazards associated with product

•

interruptions in supply at supplier’s end and at receiving end

123/uts

System Designing

REFINED PRODUCT FROM UNIT OF REFINERIES

IMPORTED/ OTHER PRODUCT IN SHIP/OIL JETTY

REFINERY’S PRODUCT TANKAGE

TANKAGES

PUMPING STATION CROSS COUNTRY PIPELINE PUMPING CUM DELIVERY STATIONS DELIVERY TERMINAL

Fig. 8.3 Product transportation (Source: http://petrofed.winwinhosting.net/upload/26-28July10/BDYadav.pdf) Route survey and analysis There may be many alternatives for routing the pipeline from supplier to the consumer. It is necessary to study the techno-economic comparison of the alternative routes. This survey includes the following activities: •

Spot-level survey at every 50 to 100 metres and atleast over 10 m on either side of the probable route.

•

Soil conditions in the form of bore-logs, trial pits, chemical tests on subsoil and ground water etc.

•

Alignment map with lengths, bearings, angles etc. to know the exact route and the total length of the pipeline.

•

Details on the route and their location dimensions etc sea, roads (crossing and along side the route) rivers, Nallas, pipe-lines, bridges, rail-tracks, transmission lines, underground services including cables or pipes etc, hills and mountains, buildings, plantation, forests, agricultural land etc.

•

Cadestral survey –The route may be passing through so many lands belonging to private owners, farmers, govt. authorities, defence wings etc. En-route information and data has to be collected for such land pieces. Such data will include: ‚‚ Type of land and the owner’s name ‚‚ Length of the route through the land ‚‚ Problems in acquiring Right of Way (ROW) ‚‚ Authority which will permit or grant ROW ‚‚ Survey maps for the land available from the local land authorities (such as collector, Tahasildar, GramPanchayat etc.) ‚‚ Land records regarding the title and ownership of the land ‚‚ Approximate compensation required for acquiring the ROW ‚‚ Status of habitation on the land ‚‚ Similar information of the adjacent plots on 50 to 100 m on either side of the route. ‚‚ Plans for future installations by others on the proposed route and/ or in the vicinity such as roads, rail-tracks, buildings or pipe-lines etc.

124/uts

•

Availability of construction materials, labour and facilities ‚‚ Since the pipe-line has to pass through different areas and over a long distance, it is essential to know the availability of construction labour and materials on the way. ‚‚ Such as excavation labour, transport facilities, access roads, construction material like stones, aggregates, sand, cement, steel, structurals, etc., workshop facilities. ‚‚ This information will be useful in working out project schedule and cost estimates and assessing the problems in construction.

•

Soil resistivity survey ‚‚ It is required for design of cathodic protection system. ‚‚ Names and addresses of the statutory and public bodies required to be contacted for acquiring ROW, construction permission, blasting licences, excavating the public facilities (Roads, rivers, rail-tracks etc.) and cathodic protection work, power supply/water supply etc. ‚‚ Such authorities include the following but not limited to the listed ones. i.

Local land authorities – distr. Collector, Municipal Corporation, Tahsildars, etc.

ii.

Owners of the respective land

iii.

PWD authorities – local office

iv.

Irrigation department

v.

Electricity supply agencies, bodies or boards

vi.

Water-supply and public health department

vii.

Controller of explosives and use of hazardous chemicals

viii. Industrial development corporations ix.

Railway authorities

x.

Marine and port authorities

xi.

Salt-commissioner and controller

xii.

Competent authorities for land and row acquisition.

xiii. State and central government for necessary permissions, licences, clearances etc. xiv.

Import, export rules or regulations authorities

xv.

Controller of quarrying and mining

xvi. Navy, army or air force (defence authorities) xvii. Plants for future installations. xviii. Forest authorities Project schedule •

Based on various data collected and the cost estimates, over all project schedules has to be prepared based on past experience and specific problems unique to the project under consideration.

•

This schedule should cover only broad activities to serve as a guideline for preparation of detail activity schedule.

•

This will establish the overall completion time for the entire project work.

•

This should generally include: ‚‚ preliminary survey or data collection ‚‚ finalising the route ‚‚ cost estimates / budget sanctions ‚‚ acquisition of ROW and land ‚‚ basic engineering package 125/uts

System Designing

‚‚ detail engineering work ‚‚ construction work (Civil, mechanical, piping, electrical or marine crossing, river crossing etc or cathodic protection) ‚‚ testing, flushing or pigging ‚‚ commissioning and hand over Finalising the most optimum route •

This involves the comparison of alternative router surveyed.

•

The analysis should include various parameters which are tabulated in the following format: Sr. No.

Parameter

Values for Alt-routes

Remarks

Alt. 1

Alt. 2

Alt. 3

1. 2. 3. 4 Under parameter columns, following minimum items should be included: 1. Estimated cost • • • • • • • • • • • • • • • • 2. 3. 4. 5.

row acquisition land acquisition statutory permission basic engineering detail engineering material procurement (pipes/valves/equipments) construction cost civil piping mechanical electrical cathodic protection on line buildings marine or river crossings testing commissioning cathodic protection

Overall completion - Time Total length Cost per km Other features ‚‚ rock area ‚‚ marine zone ‚‚ no. of road crossings ‚‚ no. of railway crossings ‚‚ no. of nallas crossings ‚‚ underground portion lengths

126/uts

‚‚ above ground portion lengths ‚‚ no. of isolation valves ‚‚ pipe-line diameter ‚‚ no. of rectifier stations ‚‚ no. of diode stations 6. cost of operation or year 7. cost of maintenance or year 8. hazard classifications 9. risk-factor 10. disaster management category 11. stoppages or shut down due to external factors 12. threat to security and safety etc. Value analysis should be done for each alternative routes considering appropriate weightage assigned to these parameters and costs of the same. Thus final and most optimum route can be selected.

8.6 Salient Steps in Detail Engineering After deciding the final route, cost estimates, broad project schedule and engineering, the detail engineering involves the following main steps: Detail design of each system •

Civil works including trenching, sand filling, back filling, buildings, concreting, river weights, valve-chambers, test points, markers and construction infrastructure like site office, construction water, power, site godown/open yards etc.

•

Construction equipment required for transport, laying, welding, erection testing etc.

•

Piping: stringing, welding, laying or testing pipe support system

•

Cathodic protection system design, diode stations, sacrificial anodes, UPS installations, on-line test-points, insulation flanges

•

Specific designs for submarine portions and river-crossings

•

Designs of all crossings, pipe-bridges, supports

•

Preparing detail design and fabrication drawings for all systems

•

Quantity calculation for materials and work items.

Implementation, planning and organising •

selection and appointing agencies/contractors/suppliers for various activities and materials

•

division of work among the staff on the project

•

progress monitoring and reporting system

•

mobilising planning (manpower deployment planning), resource-planning

•

implementation work packages

•

payment to subcontractor system

•

inventory-control-planning

•

safety/security guidelines

•

organising revisions/change/alternatives/improvements in system design/drawing during the project-process

•

preparation of as-built construction drawings and final costing

•

databank for the executed project, useful for future project

127/uts

System Designing

Summary •

A pipe-line has to carry products like crude oil, refined oil, chemicals like naphthalene, ethylene, propylene etc. over long distance.

•

Passing through land, rivers, sea, mountains, marshy areas, private and public land, and crossing other services like roads, railways, transmission lines, underground pipes or cables etc, such a pipeline is called “cross-country pipe-line.”

•

Engineering and installation of cross-country pipelines form a special branch of piping design and engineering, as it involves many aspects and parameter which are normally faced with in plant piping system within the boundaries of refinery or a chemical or petrochemical plant.

•

Special techniques have to be adopted for design, laying, welding or joining, corrosion protection, testing, commissioning etc.

•

The most common modes of transport known to all includse trucks running over roads, railway goods train and ships, launches, boats, barges on waterways.

•

The transport by airway by cargo air-crafts is also another way of bulk-transport.

•

Based on various data collected and the cost estimates, over all project schedules has to be prepared based on past experience and specific problems unique to the project under consideration.

•

Value analysis should be done for each alternative routes considering appropriate weightage assigned to these parameters and costs of the same. Thus final and most optimum route can be selected.

References •

Cross-Country Pipeline: A National Asset [Online]. Available at: . [Accessed 18 April 2011].

•

Yadav, B. D. Cross-Country Pipelines: An Overview [Online]. Available at: . [Accessed 18 April 2011].

•

Transportation of Flammable and or Toxic Solvents [Online]. Available at: . [Accessed 18 April 2011].

Recommended Reading •

Day, N. B., 1998. Pipeline Route Selection for Rural and Cross-Country Pipelines: Issue 46 of ASCE Manuals and Reports on Engineering Practice, ASCE Publications.

•

Orszulik, S. T., 2008. Environmental technology in the oil industry, 2nd ed., Springer.

•

Jacques V. G., 1984. Fundamentals of Pipeline Engineering, TECHNIP.

128/uts

Self Assessment 1. What should be the typical diameter of pipes in cross-country pipelines? a. 4 - 56 inch b. 51 - 56 inch c. 25 - 56 inch d. 56 - 96 inch 2. Spot-level survey should be done at every 50 to 100 metres and atleast over ___________ on either sides of the probable route. a. 20 m b. 10 m c. 30 m d. 40 m 3. Pipelines cover___________ of modes of transport in India. a. 39 % b. 75 % c. 50 % d. 89 % 4. Being a ________ system, there is minimal handling and transit losses in pipelines as compared to other means of transportation, hence it is considered to be most efficient. a. closed b. open c. partially-open d. crude 5. Which survey includes the type of land and the owner’s name? a. Spot-level survey b. Cadestral survey c. Soil Resistivity Survey d. Routes detail 6. Which of the following is an advantage of cross-country pipelines? a. Right of way acquisition to run the pipeline, especially through private and agricultural land and habitat areas. b. High fire and explosion hazards potential. c. Problem of corrosion and leakages and repair work involved. d. Fastest mode of transport between two countries or continents. 7. Pipelines have ________. a. low energy cost b. high energy cost c. high operating cost d. nil pollution

129/uts

System Designing

8. Pipelines have _________ reliability. a. 100 % b. 30 % c. 86 % d. 70 % 9. Railways have ________. a. low energy cost b. high energy cost c. low operating cost d. high pollution 10. Estimated cost in pipelines is stated as ______________. a. cost per km b. cost per m c. cost per inches d. cost per mm

130/uts

Case Study I Check Valve Failures The piping system is normally considered to be the safest part of the plant. However reviews of catastrophic accidents show that piping system failures represent that largest percentage of equipment failures. Check valves are important safety devices in piping. Check valves have been utilized in the process industry for many years to keep material from flowing the wrong way and causing operational or safety concerns. One common mistake is installing the check valve backwards and blocking the process flow. An arrow on the check valve designates the proper flow direction, indicating the proper installation position. In December 1991, a chemical plant in Saudi Arabia experienced a release of propane gas due to a check valve shaft blowout. The incident followed a process upset in the facility’s ethylene plant, where the unintentional shutdown of a cracked gas compressor resulted in downstream flow instabilities and surging in the unit’s propane refrigeration compressor. During this period, the check valves installed in the propane refrigeration compression system slammed closed repeatedly. The shaft of the compressor’s third stage discharge valve eventually separated from its disk and was partially ejected from the valve. Propane gas began to leak out of the valve around the gap between the shaft and its stuffing box until operators discovered the leak and shut down the compressor. The facility was fortunate that an adjacent steam line kept the shaft from being fully ejected from the valve, thus limiting the leak rate and preventing an accident of potentially greater severity. A subsequent investigation and analysis of the check valve’s internal components revealed that the dowel pin, which secured the drive shaft to the valve flapper, had sheared, and the shaft key had fallen out of its key-way. The investigation report also revealed that facility maintenance records indicated a long history of problems with the check valves installed there. The valves were installed in 1982, and due to continuing valve malfunctions, underwent repair or modifications in subsequent years. These repairs and modifications included replacement of damaged counterweight arms, replacement of seals and gaskets, replacement of dowel pins and internal keys, and installation of external shaft “keepers”. Questions: 1. How check valves in the piping system is an important safety concern? 2. Explain the accidental case at the chemical plant in Saudi Arabia? 3. Give the details of the report of the investigation carried out. Answers: 1. Check valves are important safety devices in piping. Check valves in the process industry is used to prevent material from flowing the wrong way and causing operational or safety concerns. Installation of the check valve backwards and blocking the process flow is a common mistake done by the process designers. An arrow on the check valve designates the proper flow direction, indicating the proper installation position.

131/uts

System Designing

2. In December 1991, a chemical plant in Saudi Arabia experienced a release of propane gas due to a check valve shaft blowout. An unintentional shutdown of a cracked gas compressor resulted in downstream flow instabilities and surging in the unit’s propane refrigeration compressor. The check valves installed in the propane refrigeration compression system slammed closed repeatedly. Propane gas began to leak out of the valve around the gap between the shaft and its stuffing box until operators discovered the leak and shut down the compressor. 3. A subsequent investigation and analysis of the check valve’s internal components revealed that the dowel pin, which secured the drive shaft to the valve flapper, had sheared, and the shaft key had fallen out of its key-way. The investigation report also revealed that facility maintenance records indicated a long history of problems with the check valves installed there. The valves had continued malfunctions, repair or modifications. These repairs and modifications included replacement of damaged counterweight arms, replacement of seals and gaskets, replacement of dowel pins and internal keys, and installation of external shaft “keepers”.

132/uts

Case Study II Bulk Storage and Piping Case Study Ohio is a major steel manufacturer which established the first R & D department in the steel industry in 1910. It grew through the development of specialty steels and new technology. This company holds more U.S. patents than any other specialty steel company. The development of continuous rolling technology was among the first. As measured by production and shipped tons, the company is the largest specialty steel company in the US. However, the environmental and safety concerns grow with the company. As part of its efforts to reduce its environmental expenses and maintain a high level of safety in its manufacturing facilities, it had Mech-Chem inspect to test and certify its waste acid storage tanks. Four bulk storage systems ranging in size from 10,000 gallons to 40,000 gallons were inspected and certified. Mech-Chem then went on to design a new waste acid bulk storage facility and related piping system to handle their waste acid production. The testing and inspection of the waste acid storage tanks included visual internal and external inspection, spark testing of the tank liners and non-destructive ultrasonic thickness survey tests of the tank shell and heads. An engineering report was prepared to submit to the Ohio EPA, including a CAD drawing for each tank showing results of the non-destructive ultrasonic thickness survey and tests. The inspection, structural analysis and certification of the secondary containment systems also included materials of construction and structural-mechanical review of the design for compliance with Ohio EPA waste management regulations. Mech-Chem was contracted to engineer and design a waste acid bulk storage facility and related piping systems. The waste acid bulk storage facility consists of eight process and storage tanks varying in size from 5,000 gallons to 40,000 gallons. The waste acids piped and stored in this system include Hydrofluoric Acid (HF), Nitric Acid (HNO3), Hydrochloric Acid (HCl), and Sulfuric Acid (H2SO4). The handling of these various acid mixtures presented unique material of construction requirements. The bulk storage facility and piping systems are designed to handle 20,000 gallons per day of various hot (160 °F) waste acid mixtures. The facility design provides for secondary containment for the process tanks, storage tanks, pumps, piping, and loading-unloading of tank wagons. The company not only ensured that its existing tanks met all the necessary OSHA codes and EPA regulations, but it also acquired a new, fully automated bulk storage and piping system designed by Mech-Chem. Questions: 1. Why Ohio needed Mech-Chem support for its bulk storage tanks? 2. What were the activities included in testing and inspection of the bulk storage tanks? 3. What was the contract given to Mech-Chem?

133/uts

System Designing

Case Study III Pipeline Asset Management System (PAMS) Pipeline is the heart-line of oil and gas transportation. There is an increasing demand for sophisticated and advanced tools to cater to the pipeline project implementation, asset management, operation and maintenance. There was a great challenge to efficiently manage 850 km of existing pipeline network and 840 km of proposed pipeline network across India. With limited resource availability, it was an uphill task for Gujarat State Petronet Limited (GSPL) to manage. Secon, an ISO 9001:2000 certified firm, provides end-to-end services on geospatial & engineering including data capture, processing, design & drafting, GIS based customization and application development. It used Pipeline Asset Management System (PAMS) for day-to- day easy management of pipelines from inception to commissioning. Pipeline Asset Management System (PAMS) was a one-stop solution for the cross-country pipelines. PAMS database was designed to handle complete data corresponding to the pipeline, and also a powerful tool for disaster management. PAMS included pre-engineering, engineering, construction, health, safety & environment and operation & maintenance. It provided the general benefits of managing the master database of entire pipeline information for ease of use, accessibility through LAN/ WAN/ WEB, customized report generation and faster & efficient data access with better decision making platform. The pipeline project execution gave stage wise benefits. Prior to construction, survey and land acquisition processes were monitored. Inter-connecting of all zonal offices using applications for project monitoring & acquisition management was implemented. The PAMS database was centralized to connect all station offices for operations and management purpose. Disaster management tools & web enabled maintenance system were also installed. Overall, this resulted in manpower reduction requirement for land acquisition process by 55% and time was saved by 48%. Efficient and accurate data management was achieved. Web enabled system provided efficient processing and management details. Questions: 1. What was the challenging task given to Gujarat State Petronet Limited? 2. What are the features of PAMS? 3. What was the final outcome of the efforts by Secon?

134/uts

Bibliography References •

Basic and Detailed Engineering [Online]. Available at: . [Accessed 6 April 2011].

•

Centrifugal Pumps [Online]. Available at: . [Accessed 9 April 2011].

•

Centrifugal Pumps [Online]. Available at: . [Accessed 10 April 2011].

•

Conveyor Equipment Manufacturer’s Association Publications [Online]. Available at: . [Accessed 10 April 201].

•

Cross-Country Pipeline: A National Asset [Online]. Available at: . [Accessed 18 April 2011].

•

Design Guide for Layout and Plot Plan [Online]. Available at: . [Accessed 6 April 2011].

•

Design guide for Layout and Plot Plan [Online]. Available at: . [Accessed 6 April, 2011].

•

Fluid mechanics pumped pipe systems [Online]. Available at: . [Accessed 9 April 2011].

•

Fundamentals of Pipe Stress Analysis with Introduction to CAESAR II [Online]. Available at: < http://www. idc-online.com/pdf/training/mechanical/SA.pdf>. [Accessed 5 April 2011].

•

Glossary of Pneumatic Conveying Terms [Online]. Available at: . [Accessed 10 April].

•

Grossel. S., Improved Design Practices for Slurry Piping Systems [Online]. Available at: . [Accessed 8 April 2011].

•

Important Characteristics in formation of Steam [Online]. Available at: . [Accessed 7 April 2011].

•

Interpreting Piping and Instrumentation Diagrams [Online]. Available at: < http://chenected.aiche.org/plantoperations/interpreting-piping-and-instrumentation-diagrams-part-2-of-5/>. [Accessed 7 April, 2011].

•

P&ID - Piping and Instrumentation Diagram [Online]. Available at: . [Accessed 7 April, 2011].

•

Pipes and Pipe Sizing [Online]. Available at: . [Accessed 8 April 2011].

•

Piping for Steam Distribution [Online]. Available at: . [Accessed 7 April 2011].

•

Preparation of Plot Plan [Online]. Available at: < http://www.epcpj.com/preparation-of-plot-plan/>. [Accessed 6 April 2011].

•

Process diagrams [Online]. Available at: . [Accessed 6 April, 2011].

•

Pump basics [Online]. Available at: . [Accessed 9 April 2011].

•

Slurry characteristics [Online]. Available at: . [Accessed 9 April 2011].

135/uts

System Designing

•

Steam Pipe Sizing and Design [Online]. Available at: . [Accessed 8 April 2011].

•

Stress analysis for process piping [Online]. Available at: . [Accessed 5 April 2011].

•

Symbols for Process Flow Diagrams and Engineering Line Diagrams [Online]. Available at: . [Accessed 7 April, 2011].

•

Tekchandaney, J. Material Properties Affecting Solids Blending and Blender Selection: Bulk Density [Online]. Available at: . [Accessed 10 April 2011].

•

Transportation of Flammable and or Toxic Solvents [Online]. Available at: . [Accessed 18 April 2011.]

•

Wormer, R. V., Plot plan design [Online]. Available at: . [Accessed 6 April 2011].

•

Yadav, B. D. Cross-Country Pipelines: An Overview [Online]. Available at: . [Accessed 18 April 2011].

Recommended Reading •

Abulnaga, B. E., 2002. Slurry systems handbook, McGraw-Hill Professional, ISBN0071375082, 9780071375085.

•

Aude, T.C., Cowper N.T., Thompson, T.L., & Wasp, E.J., 1971. Slurry Piping System: Trends, chemical Engineering.

•

Bachus, L., & Custodio, A., 2003. Know and Understand Centrifugal Pumps, Elsevier.

•

Bausbacher, E., & Hunt R. W., 1993. Process plant layout and piping design, PTR Prentice Hall.

•

Bel l, A. A., 2007. HVAC equations, data, and rules of thumb, 2nd ed., McGraw-Hill Professional, ISBN0071482423, 9780071482424.

•

Blevins, T. L., 2010. Mark Nixon Control Loop Foundation: Batch and Continuous Processes, 2nd ed., ISA.

•

Brown, N. P. & Heywood, N. I., 1991. Slurry handling: design of solid-liquid systems, Springer, ISBN 1851666451, 9781851666454.

•

CEMA Standard No. 805, “Glossary of Pneumatic Conveying Terms - 2005”

•

Day, N. B., 1998. Pipeline Route Selection for Rural and Cross-Country Pipelines: Issue 46 of ASCE Manuals and Reports on Engineering Practice, ASCE Publications.

•

Goettsche, L. D., 2005. Maintenance of instruments & systems: Practical guides for measurement and control, 2nd ed., ISA.

•

Jacques V. G., 1984. Fundamentals of Pipeline Engineering, TECHNIP.

•

Kellogg, 1964. Design of Piping Systems, 2nd ed., John Wiley & Sons Inc.

•

Lobanoff,V. S., & Ross, R. R., 1992. Centrifugal pumps: design & application, 2nd ed., Gulf Professional.

•

Munson, 2007. Fundamentals of Fluid Mechanics, Wiley-India.

•

Nayyar, M. L., 2000. Piping Handbook, 7th ed., McGraw-Hill.

•

Orszulik, S. T., 2008. Environmental technology in the oil industry, 2nd ed., Springer.

•

Parisher R. A., Rhea, R. A., 2001. Pipe Drafting and Design, 2nd ed., Gulf Professional Publishing.

•

Sawhney, 2009. Fundamentals of Mechanical Engineering: Thermodynamics Mechanics Theory of Machines and Strength of Materials, 2nd ed., PHI Learning Pvt. Ltd.

136/uts

•

Singh, O., 2007. Engineering Thermodynamics, New Age International, ISBN8122417507, 9788122417500.

•

Tekchandaney R. Jayesh, Material Properties Affecting Solids Blending & Blender Selection.

•

Thakore, 2008. Introduction to Process Engineering and Design, Tata McGraw-Hill Education.

•

Towler, G. P., & Sinnott R. K., 2008. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design, Butterworth-Heinemann.

•

Weaver, R., 1986. Process piping drafting, 3rd ed., Gulf Pub Co.

•

Yang, 2003. Handbook of Fluidization and Fluid-Particle Systems, 2nd ed., CRC Press.

137/uts

System Designing

Self Assessment Answers Chapter I 1. d 2. a 3. c 4. d 5. b 6. c 7. d 8. c 9. a 10. a Chapter II 1. d 2. a 3. a 4. c 5. d 6. a 7. b 8. a 9. c 10. c Chapter III 1. a 2. b 3. a 4. b 5. a 6. d 7. d 8. b 9. d 10. d Chapter IV 1. a 2. a 3. b 4. b 5. a 6. a 7. d 8. b 9. c 10. a

138/uts

Chapter V 1. d 2. d 3. a 4. b 5. a 6. a 7. b 8. a 9. d 10. a Chapter VI 1. c 2. a 3. a 4. a 5. b 6. b 7. a 8. a 9. b 10. c Chapter VII 1. a 2. a 3. b 4. a 5. b 6. d 7. d 8. a 9. a 10. c

Chapter VIII 1. a 2. b 3. a 4. a 5. b 6. d 7. a 8. a 9. b 10. a

139/uts