Different Types of HAZOP
Transcript of Different Types of HAZOP
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Different Types of HAZOP Appendix II - 1
A P P E N D I X I 1
Different Types of HAZOP A. Parametric Deviation Based HAZOP
Parametric Deviation Based HAZOP relies on establishing sets of commonly applied deviations by establishing typical parameters/properties/operations and assigning Guide Words (such as High, Low, No, Part of, Other than, As well as, etc.).
The resultant deviations effectively form a "library of deviations" which can be repetitively used, depending on the equipment type being HAZOPed.
It is the most widely used form of HAZOP in the world today
Advantage of Parametric Deviation Based HAZOP
It has the advantage of giving reasonably consistent results and is simple to use. It also adds a certain degree of quality assurance.
Disadvantage of Parametric Deviation Based HAZOP
It has the disadvantage that certain interactions and special case deviations may be overlooked. In addition, more deviations than are really required may also be processed, thus consuming excessive time and effort.
Furthermore the basis for using such established deviations is experience as opposed to a basic methodology based on logic1 reasoning.
An ultra conservative approach would be to use a very extensive list of deviations, say around 20 (or even more), for every node reviewed. However, such an approach is very time consuming.
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Different Types of HAZOP Appendix 11 - 2
This could lead to frustration, boredom and lack of co~iviction, by team members, that any specific deviation is particularly relevant; this can compromise quality.
The key to efficient HAZOPs is:
1. Making node sufficiently large to minimize repetition 2. Using correct deviations (not too many, not too few) 3. Control of HAZOP sessions (See Chapter 19)
The following table, Table 11-1, shows typical Deviations for Various Items of Equipment.
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Different Types of HAZOP Appendix 11 - 3
Parametric Deviation based Methodology
Table 11-1: Examples of Equipment Types and Assigned HAZOP Deviations
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DEVIATION
High Suction Pressure
High Pressure
High Discharge Pressure
High Temperature
High Discharge Temperature High Flow
High Bonoms Level
High Concentration of Impurities Low Pressure
Low Suction Pressure
Low Flow, Low1 No Flow Low Temperature
Low Bottoms Level
Low Tray Level
Reversel Misdirected Flow Column Flooding
Contaminants Enter Equipment Leakage
Rupture
Cavitation
Maintenance Hazards
Startup1 Shutdown Hazards Loss of Performance
CENTRIFUGAL COMPRESSOR
X
X
X
X
X x x
CENTRIFUGAL PUMP
x
x x X
COLUMN
x
X X X
x X X
X
x x
X X
FURNACE HEATER
X
x
X
X
X X
X
X x x
HEAT EXCHANGER
X
x
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X
X
X (Tube 8 Shell) X (Tube 8 Shell)
X
LINE
X
X
X
X
X
X
X x x
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Different Types of HAZOP Appendix I1 - 4
B. "Creative Identification of Deviations & Disturbances" Methodology for Performing HAZOPs
Ref "A Manual of Hazard & Operability Studies - The Creative Identification of Deviations and Disturbances" by R. Ellis Knowlton, published by Chemetics International Ltd., 1992
Example:
Consider a kettle, operating on a batch basis, into which are fed several liquids - X and Y - for mixing and emulsification. Consider that X is being pumped from a supply drum to the kettle via a feed line.
The process intention can be described in the following words: "Transfer X from the supply drum to the kettle via supply pump and feed line." The design intention is analyzed in terms of 5 specific components: Node, Material handled, Activity undertaken, Source, and Destination. See the following table.
Advantages
Node Material Activity Source Destination
Thorough Good for batch type operations
Supply Pump and Feed Line X Transfer Supply Drum Kettle
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Different Types of HAZOP Appendix 11 - 5
Disadvantages
Not all deviations may be valid or could be hard to interpret.
May be cryptic and hard to audit unless very well documented. Can be hard to apply to continuous operations.
The deviations are obtained by applying Guide Words to Material, Activity, Source, and Destination, as follows:
Table 11-2: Deviations derived by applying Guide Words to Material, Activity, Source, and Destination
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Material Activity
Source
Destination 7
MORE
More X Transfer more
More from supply drum
More to kettle
LESS
Less X Transfer less
Less from supply drum Less to kettle
REVERSE
Reverse X Reverse transfer
Reverse from supply drum Reverse to
kettle
AS WELL AS
As well as X As well as
transfer As well as from
supply drum As well as to
kettle
PART OF
Part of X Part of transfer
Part of from supply drum
Part of a kettle
OTHER THAN
Other than X Other than
transfer Other than from
supply drum Other than to
kettle
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Different Types of HAZOP Appendix 11 - 6
C. Procedural HAZOP
Batch processes are often used to produce various kinds of materials in the chemical
industry. Continuous operations are also operated in batch modes, e.g. during startup, shutdown, maintenance, etc.
In such cases the HAZOP can be performed by sequentially analyzing the operating
procedures of the particular batch process.
The operating instructions of the batch process are divided and simplified and rewritten, if necessary, so that each instruction represents the design intention.
For e.g., one instruction might be "Fully open valve V-101 to transfer 4500 kg of reactant X to the reactor R-201." This can be broken into more elemental actions; "Fully open V-
101" and "Transfer 4500 kg of X into R-201". Each can then be combined with Guide Words to establish deviations, as follows.
Not / Fully open V- 10 1 As well as / Fully open V- 10 1 More / Transfer 4500 kg of X into R-201 Less / Transfer 4500 kg of X into R-201, and so on.
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Different Types of HAZOP Appendix 11 - 7
Procedural HAZOP Example
Procedure Description
The start-up operations of the light ends column C-101 is used to illustrate the hazard and operability technique used in batch processes. The following steps illustrate the procedures followed during the startup of the column. (See Figure 11-1 for reference)
1. Put cooling water on light ends condenser EX- 102 to condense light ends flashing from feed.
2. Open bypass around PV-106 to allow non-condensibles to pass to flare without pressure build-up in light ends stripper, C-101.
3. Set FRC-101 on feed supply to minimum setting (after opening up battery limit valve on feed from feed drum V- 10 1).
4. When level in base of column reaches normal liquid level on LIC-110 crack open manual by pass around TV- 126.
5. Observe level in reflux drum V-102 on LIC-107 and close manual bypass around PV-106 ensuring that setpoint of PIC-106 is set for normal design when low level is reached on LIC- 107.
6. Start reflux pump P- 10 1 and ensure total reflux with FRC- 1 16 set for design flow. 7. Increase steam on reboiler to design flow by setting TRC-126. 8. When medium high level is almost reached in column bottoms, LIC-119, start
bottoms pump P- 102. With LV- 1 19 fully closed maintain minimum flow conditions on P- 102.
9. Stop feed to column, maintain reflux but do not export distillate or bottoms. Keep reboiler running and maintain check on overheads composition.
10. When overheads material is fully up to specification introduce more feed at reduced flowrate and export distillate and bottoms to maintain equilibrium.
1 I. Increase feed flow to design flowrate over duration of shift.
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Different Types of HAZOP Appendix 11 - 8
Figure 11-1: P&ID of Light Ends Process
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Different Types of HAZOP Appendix 11 - 9
Procedural Step Evaluation In the above example, each of the startup procedures was considered to be a node and the deviations associated with each of these nodes were evaluated. The procedure is illustrated using the first procedure. Startup Procedure: Put cooling water on light ends condenser EX-102 to condense light ends flashing fiom feed.
Assigned Node: Cooling water on light ends condenser EX- 102
Deviations:
No cooling water on light ends condenser EX-102 SoonerILater cooling water on light ends condenser EX- 102 More cooling water to EX-102 Less cooling water to EX-102
Reverse cooling water to EX-102 Other than cooling water to EX-102 As well as cooling water to EX-102
Deviation: No Cooling water on light ends condenser EX- 102 Cause: Frozen pipeline in winter Consequence: Can't startup Safeguards: %" Bypass line which is electrically traced Recommendations: Ensure that there is a low point drain and a high point vent
Similar evaluation is conducted on each of the above nodes. The above procedural step methodology can be conducted to evaluate batch operations, operating procedures, operating manual instructions etc.
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Different Types of HAZOP Appendix I I - 10
Table 11-3: Example of Procedural HAZOP Worksheet for Light Ends
10:33:09 AM 512210 1 Node: 1. Cooling water on light ends condenser EX-102. Drawing: Type: Procedural Step
drain and a high point vent.
(1.3. More cooling water to EX-102 T l l c o n s e q u e n c e s ImSafegllardsmkIIRR(I~ecolnmendations
1 1.4. Less cooling water to EX- 102
1 1.5. Reverse cooling water to EX- 102 m l c o n s e q u e n c e s l l S a f e g l l a r d s ~ ~ ~ ~ ~ R e c o m m e n d a t i o n s l [ ~ e s ~ o n s i b l e I I . N o c a u s e s n n n - 7 1
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Different Types of HAZOP Appendix II - 11
lternatively provide extended
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Different Types of HAZOP Appendix 11 - 12
r2.5. Reverse Bleed non condensibles to flare via bypass around PV-106 1 ~esponsible
12.6. As well as Bleed non condensibles to flare via bypass around PV- 106
T l l ~ o n s e q u e n c e s I m S a f e g u a r d s m E l l R e c o m l n e n d a t i o n s fl~esponsible p i Z K i q ~ l n n n ~ ~ 1
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Node: 3. Minimum feed supply fiom V- I0 I to the column C- 10 1 Type: Procedural Step
Drawing: Fig A 2.1
3.1. No Minimum feed supply from V- I 0No l to the column C-101
13.2. More Minimum feed supply from V-101 to the column C-101 ' ~ f l ~ [ ~ [ i l e s p o n s i b l e ,
1. Operator 1.1. Rapid start- 1. I. None 1 3 3 10. Update operating instructions Operations sets setpoint up and possible to manually crack open steam on on FRC- I0 I loss of control. reboiler at start prior to feed
1 3 3
~ ~ ~ ~ ~ ~ ~ z ; ~ i ~ r ~ ; t h e o p e r a t i n g vaporization in the column during start-up earl hase.
13.3. Less Minimum feed supply from V- 10 l to the colu~nn C- 10 1 v l l ~ o n s e ~ u e n c e s l l S a f e g L l a r d s ~ ~ ~ / l ~ e c o m m e n d a t i o n s
1
1 1 . Start-up at 25% feed rate to be Operations ri 2003 by CRC Prcss LLC
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Different Types of HAZOP Appendix 11 - 13
Advantages of Procedural HAZOP
include checking of level of liquid in upstream feed from V- 10 1.
1. Good for HAZOPing batch operations.
2. Good for HAZOPing Operating Manuals, including Start-up, Shutdown etc.
Disadvantages of Procedural HAZOP
drum V-101
1. Limited for HAZOPing continuous operations.
2. Can be time consuming.
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3 13. Ensure that there is a vortex breaker in the upstream vessel V- 10 1 bottoms.
Eng. Dept.
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Different Types of HAZOP Appendix 11 - 14
D. Knowledge Based HAZOP
This methodology typically is sometimes applied in place of the Guide Word Methodology. Some assumptions are:
Extensive design standards and procedures are in place. HAZOP team has experience with similar designs. Process being HAZOPed is well established.
Basis is to use detailed Knowledge Based Checklists and brainstorm process for possible I
deficiencies.
Table 11-4: Example of Knowledge Based Checklist for Centrifugal Compressor
TYPE = COMPRESSOR (CENTRIFUGAL) COMPRESSOR SUCTION
QUESTION = Suction side overpressured from backflow/ leakage of recycle valve on compressor shutdown?
QUESTION = Interstage equipment overpressured from backflow/,leakage of recycle valve on compressor shutdown?
QUESTION = Suction side overpressured from backflow or recycle leakage with parallel compressors?
QUESTION = Interstage equipment overpressured from backflow or recycle leakage with parallel compressor?
QUESTION = Does suction side have permanent strainer with local pressure indication downstream?
QUESTION = Does suction side have low-pressure alarm and, possibly, trip at low pressure?
QUESTION = Do suction/ interstage knockout drums have high liquid level alarms and trips at high high liquid level?
QUESTION = Will the compressor be shut down at low suction pressure?
QUESTION = Are air compressors intakes protected against contaminants (flammables, carbon monoxide, etc. ) ?
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Table 11-5: Applicability of Different Types of HAZOP
Note: More ticks are better -
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PARAMETRIC DEVIATION BASED HAZOP
GUIDE WORD (ELLIS KNOWLTON METHOD) PROCEDURAL STEP
KNOWLEDGE BASED HAZOP
EXISTING PROCESS
J J J (If Continuous)
JJJ (If Batch)
JJJ (If Batch)
JJJ
OPERATING MANUAL
STARTUP & SHUTDOWN
J
1/44
JJJ
J
BATCH
J
JJJ
1/44
J
CONTINUOUS
1/44
d
J
JJJ
NEW PROCESS
JJJ (If Continuous)
JJJ (If Batch)
J (If Batch)
J
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Different Types of HAZOP Appendix 11 - 16
SUGGESTED READING (Note: URLs current at date of publication) "Apply the HAZOP Method to Batch Operations" by R.L.Collins, Chemical Engineering Progress, April 1995, pages 48 to 5 1 www.che.com/ "Guidelines for Hazard Evaluation Procedures" by AIChE, CCPS, 2"d edition, 1992 plus "Guidelines for Hazard Evaluation Procedures" by AIChE, CCPS, 1st edition, 1985 u~w~~~.aichc.org/p~L~cat/s~ac1tl.as~~?Act~~C~&Catcgor~~=~Scct4&M in=20 "A Manual of Hazard & Operability Studies - The Creative Identification of Deviations and Disturbances", published by Chemetics International, 1992 www.kvaerner.con.~~companics/co1n~~~1niesdt-.tail.as~:'id=796 "DOE Handbook - Chemical Process Hazards Analysis", (Website) http:!~tis.el~.doe.~ov/techstdsistandi~rd/11dbl1 100/htlbk I lOO.~?dt'
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Guidelines for Process Hazards Analysis, Hazards Identification & Risk AnalysisTable of ContentsAPPENDIX II: Different Types of HAZOPA. Parametric Deviation Based HAZOPB. "Creative Identification of Deviations & Disturbances" Methodology for Performing HAZOPsC. Procedural HAZOPD. Knowledge Based HAZOP