CHAPTER 8
HAZOP STUDY OF STRIPPER
SUMMARY
In this chapter, it reviews about the hazop study of stripper. It describes the parameters need to be used and control during the process begins. HAZOP is a formal procedure that offers a great potential to improve the safety, safet y, reliability and operability of process plants by recognizing and eliminating potential problems at the design stage. It is not limited to the design stage, however. It can be applied anywhere that a design intention (Perry’s ( Perry’s Handbook, 1998). 1998) . When using the operability study technique to vet a process design, the action to be taken to deal with a potential hazard will often be modification to the control system and instrumentation, the inclusion of additional alarms, trips or interlock. If major hazard are identified, major design changes may be necessary, alternatives processes, material and equipment. In order to have a safe process successfully producing to specification to the required product, a sound control system is necessary but not sufficient(Coulson sufficient (Coulson & Richardson’s, 1999).
8.1 INTRODUCTION
In this project, the safety procedure will be used to study the safety of the plant designed. 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. This procedure is preferred since it is a formal systematic examination of a processing plant for identifying hazards, failure and operability problems and assessing the consequences. This leads to fewer lapses in safety, quality and production provided that the plant is installed according to the design and maintained in appropriate condition. A HAZOP is carried out as a team activity. The HAZOP can also be used as a check on the operability of an existing plant. The procedure for a HAZOP study is to apply a number of guide words to various parts of the process design intention, which tells us what, the process is, expected to do. The advantages of HAZOP study to the design application:
Early identification of problems areas when conceptual design stage.
Identifies need for emergency procedures to mitigate.
Provide essential information for safety case, such as on the hazards identified and effectiveness of safety systems.
Through examination of hazard and operability problems when applied at detailed stage.
Meets legislative requirements. Identifies need for commissioning, operating and maintenance procedures for
safe and reliable operations.
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8.2 Parameters and guide words
The key feature is to select appropriate parameters which apply to the design intention. These are general words such as flow, temperature, pressure, level, time, concentration and reaction. It can be seen that variations in these parameters could constitute deviations from the design Intention. A set of guide words to each parameter for each section of the process was applied in order to identify deviations. These guide words are given below and are applied to the stripper unit operations to be considered. Guide Word
Meaning
The complete negation of
No or Not
these intentions
Comment
No part of the intentions is achieved but nothing else happens. These refer to quantities
More or Less
Quantitative increases or and properties such as flow decreases
rate and temperature as well activity likes “HEAT” All
As well as
A qualitative increases
the
design
and
operating
intentions
are
achieved
together
with
some additional activity. Part of
A qualitative decrease
Only some of the attention achieved; some are not.
The following words are used in a special way, and have the precise meanings given below: i.
Intention: the intention defines how the particular part of the process was intended to operate and the intention of the designer.
ii. Deviations: these are departures from the designer’s intention which are detected by the systematic application of the guide words.
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iii. Causes: reasons why, and how, the deviations could occur. Only if a deviation can be shown to have a realistic cause is it treated as meaningful. iv. Consequences: the results that follow the occurrence of a meaningful deviation.
The table below shows the typical HAZOP process parameter that could be considered during the measurement of the HAZOP study.
Typical Hazop Process Parameter Pressure
Addition
Temperature
Data
Flow
Information
Level
Separation
Time
Viscosity
Composition
Voltage
pH
Frequency
Reaction
Speed
Heating
Density
Cooling
Solubility
Mixing
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Type of vessel: Stripper Temperature: 180⁰C Pressure: 2.75Pa Guide
Deviation
Possible Causes
Consequences
Actions
Word
None
Required
No Flow
-
-
No flow in
Quality
and
stream
amount
of
coming to
product
will
the column
suffer.
Line
-
-
fracture
Accidental discharge
-
Install low level alarm
-
to
Plant shut down.
the environment (aromatics are flammable material). More
Flow
-
of
LCV
fails
-
Overfills
open
in
-
Incomplete
high level
separation of
alarm and
non-
check
aromatics
sizing.
error
-
Install
from solvent + aromatics Pressure
-
Isolation
-
valve close
Full
pump
-
delivery
Isolation valve
in error
close
in
error Temperatu re
-
Higher
-
Degradation
-
High
pressure in
of the solvent
Temperat
transfer
quality
ure Alarm
will
5
line
become
(HTA).
significant ms.
Less of
Flow
-
Leaking flange
-
of
discharge
valve
Others
Maintenan ce
-
Equipment Failure
Material
-
to
-
Isolate
-
that
the
of
environment
plant
Line
cannot
be
-
part the
Install alarms.
completely drained
or
purged
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REFERENCES
Charles A.Wentz, Safety, Health, And Environmental Protection, McGraw Hill, 1998 Coulson and Richardson’s. Chemical Engineering Design, Volume 6. Butterworth Heinemann. 2000. Green W. Don & Perry Robert H. Perry’s Chemical Engineers’ Handbook. Seventh Edition Kansas. McGraw Hill, 1997.
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