GP 47-10 - Glycol Dehydration and Regeneration - 0900a86680328157

Document No.

GP 47-10

Applicability

Group

Date

29 February 2008

GP 47-10

Glycol Dehydration and Regeneration

Group Practice

BP GROUP ENGINEERING TECHNICAL PRACTICES

29 February 2008

GP 47-10 Glycol Dehydration and Regeneration

Foreword This is the first issue of Engineering Technical Practice (ETP) BP GP 47-10. This document is technically identical to the former GP 60-35 dated 16-December-2005. This Group Practice (GP) is based on parts of heritage documents from the merged BP companies as follows:

British Petroleum GS-140-1

Glycol Dehydration Unit.

This GP was written by an external engineering contractor using heritage material and did not have internal BP review before publishing. The ETP Working Group has approved a revision programme using a new external contactor with greater global reach, which is now underway. The updated GP will have BP internal review prior to re-issue. In the meantime TAs and EAs should ensure clear guidance is given over implementation of this GP.

Copyright  2008, BP Group. All rights reserved. The information contained in this document is subject to the terms and conditions of the agreement or contract under which the document was supplied to the recipient’s organization. None of the information contained in this document shall be disclosed outside the recipient’s own organization without the prior written permission of BP Group, unless the terms of such agreement or contract expressly allow.

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Table of Contents Page Foreword.......................................................................................................................................... 2 1.

Scope...................................................................................................................................... 4

2.

Normative references.............................................................................................................. 4

3.

Symbols and abbreviations.....................................................................................................5

4.

HSE......................................................................................................................................... 5

5.

General design considerations................................................................................................5

6.

Mechanical design.................................................................................................................. 6 6.1. Heat Exchangers.......................................................................................................... 6 6.2. Filtration....................................................................................................................... 6 6.3. Relief Valves/Systems..................................................................................................7 6.4. Contactor Tower........................................................................................................... 7 6.5. Pumps.......................................................................................................................... 8 6.6. Surge Drum.................................................................................................................. 8 6.7. Reboiler........................................................................................................................ 8 6.8. Piping........................................................................................................................... 8

7.

Chemical injection................................................................................................................... 9

8.

Insulation................................................................................................................................. 9

9.

Instrumentation....................................................................................................................... 9

10.

Electrical................................................................................................................................. 9

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1.


Scope This Group Practice gives guidelines for the design and installation of Glycol Dehydration and Regeneration Systems. This document takes into account health, safety and environmental legislation, good design practice, and technical and economic considerations for designing the system.

2.

Normative references The following normative documents contain requirements that, through reference in this text, constitute requirements of this technical practice. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this technical practice are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies.

American Petroleum Institute (API) RP C RP E RP-520

Design, Installation and Testing of Surface Safety Systems for Offshore Production Platforms. Design and Installation of Piping for Offshore Production Platforms. Appendix D Fire Relief Devices

American Society of Mechanical Engineers (ASME) Section VIII, Sect IX.

Boiler and Pressure Vessel Code

BP Group GP 12-15 GP 12-20 GP 12-25 GIS 12-201 GIS 12-202 GP 18-01 GP 30-25 GP 30-35 GIS 34-00 GIS 34-202 GIS 34-203 GIS 34-211 GIS 46-010 GP 60-50

Wire and Cable Motors Earthing/grounding Low Voltage Motors (IEC) Low Voltage Motors (NEMA) General Requirements for Welded Fabrication Field Instrumentation General Control Valves and Pressure Regulators Rotating and Machinery Equipment Horizontal Centrifugal Pumps (API) Vertical Centrifugal Pumps (API) Reciprocating Pumps (API) Pressure Vessels General Issues –Equipment Packages

National Electrical Manufacturers Association (NEMA) Standards for Enclosures for Electrical Equipment

National Fire Protection Association (NFPA) NFPA 70 NFPA 493 NFPA-496

National Electrical Codes Standards for Intrinsically Safe Apparatus Purged and Pressurized Enclosures for Electrical Equipment Page 4 of 10

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3.


Symbols and abbreviations For the purpose of this GP, the following symbols and abbreviations apply:

4.

5.

MSDS

Material Safety Data Sheet

PPE

Personal Protective Equipment

TEG

Tri-Ethylene Glycol

HSE a.

In the design and operation of the Glycol Dehydration and Regeneration System, precautions shall be taken to minimise human exposure to the glycol.

b.

Appropriate action shall be taken to avoid the loss of glycol due to leakage to the environment.

c.

Precautions shall be taken to ensure only essential and properly trained personnel equipped with the proper PPE are allowed in areas where glycol is being transferred or being drained from the system.

General design considerations a.

All rotating equipment shall comply with: 1.

GP 34-00,

2.

GIS 34-202,

3.

GIS 34-203,

4.

GIS 34-211.

b.

BP shall determine the applicable requirements in GP 60-50 and include them in the procurement documentation.

c.

In general, the contractor's normal standards shall be used for the design and construction of the unit, except where overridden by standards referred to in this document or associated project documentation.

d.

The contractor shall explicitly refer in his documentation to all applicable standards used.

e.

All pressure vessels shall comply with American Society of Mechanical Engineers (ASME) Section VIII, Sect IX., Boiler and Pressure Vessel Code and BP GIS 46-010.

f.

API Standard RP-E shall be applied during the design and installation of piping if intended for use on offshore production platforms.

g.

Welding shall comply with GP 18-01.

h.

The regeneration unit layout shall permit safe and efficient operational access to all valves and instruments, e.g., without having to step over small-bore piping or by providing walkways over piping.

i.

Reasonable separation shall be maintained between major vessels, to permit operator access. Where this applies, a minimum of 1.0 m (3.38 ft) horizontal clearance must be provided at the narrowest point of passage between the fittings on the vessels.

j.

The unit layout shall permit access for the following operations/maintenance activities without the need to dismantle piping or cabling on adjacent subsystems: 1.

Withdrawal of exchanger plates/tubes for cleaning,

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2.

Replacement of filter cartridges,

3.

Removal of glycol pumps for overhaul,

4.

Removal of instruments and automatic valves for overhaul,

5.

Removal of other individual equipment items for overhaul

k.

The turndown requirement stated within the data sheets shall be achieved in addition to meeting the other unit performance requirements.

l.

The regeneration unit design shall be such as to minimise glycol losses, and in any case not to exceed the levels defined in the data sheets. The temperature of the regenerator still column exit gas shall be cooled to minimize glycol losses.

m.

The absorbent for water removal from gas shall be tri-ethylene glycol (TEG) unless the contractor can demonstrate that an alternative medium offers significant advantages. This specification is based on the use of TEG. If the gas composition contains aromatics then account must be taken of this in the design. Aromatics are absorbed by the glycol and emitted as vapour from the reboiler stripping column, which causes a hazard to platform personnel when it emerges from the atmospheric vent. If the aromatic compounds are at trace level, it may be sufficient to include a condenser and recovery vessel in the glycol regeneration unit. If the levels are more significant, an alternative drying process such as DRIZO (TM) may be required. The presence of aromatics does not adversely affect dehydration performance - in fact, it enhances it.

n.

The lean glycol temperature at entry to the contactor shall be such that the glycol in the contactor is at least 10°C (18ºF) above the process gas inlet temperature, in order to avoid condensing any of the gas and cool enough to minimise glycol losses.

o.

The contacting medium for absorption of water from the process gas should normally be structured packing. This is capable of high efficiency and low turndown rates. Experienced contractors of structured packing currently include Glitsch, Koch, Muntz and Sulzer. The packing should achieve a glycol flow density of 17 m 3/h per m2 of tower cross-sectional are. A turndown to 10% of design flow without uneven distribution of either gas or liquid may also be achieved.

6. 6.1.

6.2.

Mechanical design Heat Exchangers a.

Maximum economic use shall be made of heat exchange between the rich and lean glycol.

b.

A cleanliness factor of no more than 85% shall be applied to the calculation of the required surface area for the glycol heat exchangers.

Filtration a.

b.

In order to reduce foaming in the contactor, the unit shall include filtration units to remove: 1.

Solid particulates,

2.

Glycol degradation products

The filters operate best warm, and shall be placed downstream of the glycol heat exchanger unless the contractor can demonstrate overriding benefits for an alternative location. Some contractors put the filters upstream of the exchanger, because the hot stream may have metallurgical implications in the design of the filter vessels. However, this slightly reduces the filter effectiveness.

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c.


The solid particulate filters shall include two full sized units, arranged so that the cartridge can be changed on the off-line filter without affecting unit operation. Single-cartridge type filters are preferred, for ease of cartridge replacement.

d.

Particle removal performance shall be determined by the need to prevent blockage or build-up in downstream equipment.

e.

Ten micron absolute rated filters should be utilized in the filter vessels.

f.

The filter for degradation products should operate on a slipstream of at least 10% of the glycol flow. Solid particles in the glycol tend to block the carbon filter and it is believed that they also promote degradation of the glycol by acting as nucleation sites.

6.3.

6.4.

Relief Valves/Systems a.

Fire relief devices shall be sized as per API RP 520.

b.

The phase change in the fluid subjected to fire heat input, and the phase of the fluid passing through the relief valve, should be considered when determining the relief rate.

c.

Relief facilities in the lower pressure-rated parts of the unit shall be sized to take account of the maximum possible rate of gas blow-by from areas of higher operating pressure, and if necessary to take two-phase flow at this rate.

d.

The relief system design basis must take account of the dynamics of the system.

e.

All relief calculations must be available for inspection by BP.

Contactor Tower a.

The contactor tower height and diameter shall be the minimum required for the duty, taking into account the best available data on the performance of structured packing.

b.

For correct functioning of the contactor, the inlet gas shall be free of liquid, either in bulk form or in droplets. A liquid scrubbing section shall be included in this package. Design of the inlet device, the liquid coalescing device, and certain internal dimensions in this scrubbing section, which have been developed with the aid of both laboratory and fullscale site testing should be incorporated in this package. The essential parameters of the liquid scrubbing section should therefore be given in the project data sheet.

c.

A contactor inlet vapour distributor will normally also be required, and will generally take the form of a perforated pipe. Even where this is not needed, tangential inlets shall not be used, because they cause uneven distribution of vapour in the packing.

d.

The contactor tower design shall be such as to minimise glycol losses. In particular, the contactor column liquid distributor should be designed so that the drip tubes extend to within approximately one meter above the packing surface (not the hold-down plate surface). This is to minimise the free fall of liquid glycol and hence the entrainment of liquid droplets into the outlet gas stream. Acceptable losses of 25 litres per million sm3 of gas processed (0.2 gal per MMSCF) have been quoted in the North Sea, but lower figures may be achievable. Contactor tower demister pads and catch pots have traditionally been specified, but when using structured packing with a properly designed liquid distributor, these should not be necessary.

e.

The liquid distributor shall be hydraulically tested by the contractor before delivery. The variance between the liquid outlet flows shall be less than 8% of the mean value. Distributor level tolerances shall be the maximum acceptable (vertical out-of-level is 2 mm).

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6.5.


f.

Qualified contractor supervision shall be provided for installation of the contactor tower packing and for on-site levelling of the liquid distributor.

g.

Where the preferred double-acting glycol pumps are not used, and the draw-off is therefore not from the liquid gas interface, then a separate draw-off point with manual valve should be provided for periodic disposal of any condensate which collects on the glycol surface. The draw-off nozzle should be a minimum of 40 mm (1.5 inch O.D.) bore.

Pumps a.

Double-acting, rich glycol driven pumps are preferred for glycol circulation, where contactor pressure makes this feasible.

b.

One fully operational spare glycol pump shall be provided

c.

The contractor must state the minimum gas pressure required in the contactor tower to operate the pumps, both with and without glycol in the tower. These pumps can be supplied by Kimray (USA), and offer the following advantages: no electric power supply to pump motors, no need for level controls or alarms/trips at base of contactor tower, reduced gas blow-by flow for relief design. When no process gas pressure is available to maintain circulation, nitrogen can be used.

6.6.

d.

The glycol pumps/drivers shall be capable of achieving a reasonable circulation rate with cold glycol at start-up, taking into account the viscosity of TEG at temperatures down to -5°C (23ºF).

e.

The contractor shall carry out a dynamic analysis of the glycol pumping system to identify any need for pulsation dampers.

Surge Drum a.

The glycol surge drum volume shall be no greater than that needed to contain volume changes due to thermal expansion (from the ambient shutdown condition to maximum gas throughput) and glycol inventory changes in the contactor as gas flow increases.

b.

High and low level alarms should be set to maximise the useful volume of the drum for a given diameter. Glycol inventory should be minimised, to reduce regeneration time after an upset.

6.7.

Reboiler a.

Reboiler high level instrumentation shall be set high enough to avoid spurious trips caused by the effect of stripping gas on reboiler level.

b.

The regeneration unit shall be designed to minimise glycol degradation. In particular, the reboiler temperature controller must be capable of holding the glycol temperature steady to within ± 1°C (1.8 ºF). This is because the optimum TEG regeneration temperature is 204°C (399ºF), but chemical degradation of TEG starts to become significant above 206°C (403ºF).

c. 6.8.

The still column will normally be provided with random packing.

Piping a.

On-unit flanging should be minimised, but shall be provided on all equipment items and automatic valves.

b.

Tapping points shall be provided at the lowest point on the regeneration unit (normally the surge drum) for drawing off or filling with glycol.

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7.


c.

Rich and lean glycol sampling points shall be provided adjacent to the contactor. Where piping from the contactor to the regeneration unit is provided by the Purchaser, these sampling points will also be provided by the Purchaser.

d.

The appropriate piping and gasket materials shall be used downstream of the depressurizing valves to handle the low temperatures due to auto-refrigeration.

Chemical injection a.

The unit shall include provision for injection of the following chemicals: 1.

Antifoam (emergency use only),

2.

Corrosion inhibitor, and pH control. The latter two functions may be combined in one chemical.

b.

8.

The degree of on-skid chemical injection provision (tanks, pumps, etc.) will be projectspecific and shall be described as necessary by BP in data sheets.

Insulation a.

Insulation for heat conservation purposes should be confined to vessels only. Insulation for personnel protection should be provided only where absolutely necessary and where other means of operator protection are not practicable.

b.

In general, insulation of small-bore piping should not be carried out by the contractor, unless instructed otherwise by the purchaser. Lagging tends to obstruct commissioning activities, and is frequently removed anyway at this stage.

9.

Instrumentation a.

All instrumentation shall comply with: 1.

GP 30-25,

2.

GP 30-35.

b.

The unit shall be designed for automatic operation and automatic safe shutdown without operator intervention.

c.

Facilities (push-button) shall be provided for shutting down the whole unit safely from a remote location.

d.

The contractor shall provide all local instrumentation which is necessary for normal operations, start-up and shutdown, plus those extra sensors or sensor insertion points which in his judgement are necessary to perform common diagnostic tests, in the event of operating upsets of the plant, without shutting down the plant. No detailed stipulations are made in this Specification as to the instrumentation required within the regeneration unit, on the basis that the selected contractor is competent and experienced in the design of glycol dehydration plants. Any instrumentation which is needed beyond the contractor's standard provision will be discussed with the contractor upon receipt of the P&ID at the quotation stage, however additional instrumentation is generally to be discouraged on cost grounds.

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10. Electrical a.

Electrical and instrumentation design of the unit shall be in accordance with the general Project requirements for contractor packages.

b.

The following electrical standards shall be adhered to: 1.

GP 12-15,

2.

GP 12-20,

3.

GP 12-25,

4.

GIS 12-201,

5.

GIS 12-202,

6.

NFPA 70,

7.

NFPA 493,

8.

NFPA 496,

9.

National Electric Manufacturers Association (NEMA) Standards for Enclosures.

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GP 47-10 - Glycol Dehydration and Regeneration - 0900a86680328157

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