CHAPTER 8 Hazop Study

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.

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Through examination of hazard and operability problems when applied at detailed stage.

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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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