CHAPTER 8 CHAPTER 8
HAZOP STUDY OF STRIPPER HAZOP STUDY OF STRIPPER
SUMMARY SUMMARY
In this chapter, it reviews about the hazop study of stripper. It describes the In this chapter, it reviews about the hazop study of stripper. It describes the parameters need to be used and control during the process
parameters need to be used and control during the process begins. HAZOP is a formalbegins. HAZOP is a formal procedure that offers a great
procedure that offers a great potential to improve the safetpotential to improve the safety, reliability and operabilityy, reliability and operability of process plants by recognizing and eliminating potential problems at the design 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 stage. It is not limited to the design stage, however. It can be applied anywhere that a design intention (
design intention (Perry’s Handbook, 1998)Perry’s Handbook, 1998). When using the operability study. When using the operability study technique to vet a process design, the action to be taken to deal with a potential hazard 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 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 additional alarms, trips or interlock. If major hazard are identified, major design changes may be necessary, alternatives processes, material and equipment. In order to 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 have a safe process successfully producing to specification to the required product, a sound control system is necessary but not sufficient
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.
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 Comment
No or Not The complete negation of these intentions
No part of the intentions is achieved but nothing else happens.
More or Less Quantitative increases or decreases
These refer to quantities and properties such as flow rate and temperature as well activity likes “HEAT”
As well as A qualitative increases
All 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.
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 Temperature Flow Level Time Composition pH Reaction Heating Cooling Mixing Addition Data Information Separation Viscosity Voltage Frequency Speed Density Solubility
Type of vessel: Stripper
Temperature: 180⁰C
Pressure: 2.75Pa
Guide Word
Deviation Possible Causes Consequences Actions Required None No Flow - No flow in
stream coming to the column - Quality and amount of product will suffer. - Install low level alarm - Line fracture - Accidental discharge to the environment (aromatics are flammable material). - Plant shut down. More of Flow - LCV fails open in error - Overfills - Incomplete separation of non-aromatics from solvent + aromatics - Install high level alarm and check sizing.
line become significant ms.
(HTA).
Less of Flow - Leaking
flange of valve - Material discharge to the environment - Isolate - that part of the plant Others Maintenan ce - Equipment Failure - Line cannot be completely drained or purged - Install alarms.
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.
