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1 Chemical Process Safety Read Chapter 24: Turton’s Design Book (Crowl & Louvar) Chapter 11: Hazard Identification Chapter 12: Risk Assessment Guidelines.

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Presentation on theme: "1 Chemical Process Safety Read Chapter 24: Turton’s Design Book (Crowl & Louvar) Chapter 11: Hazard Identification Chapter 12: Risk Assessment Guidelines."— Presentation transcript:

1 1 Chemical Process Safety Read Chapter 24: Turton’s Design Book (Crowl & Louvar) Chapter 11: Hazard Identification Chapter 12: Risk Assessment Guidelines for Hazard Evaluation Procedures, 3 rd Ed., CCPS (John Wiley), 2008: 5.3; ; ch 9

2 2 Introduction Micro and mini scale reactors Adiabatic calorimeters Kinetics, modelling, simulation Design reappraisal, relief systems, dump and quench tanks Desktop studies Objective is to move from the earliest phases of research and development through to full scale production in a confident, safe and cost effective manner Automated Calorimeters and reactors HAZOP, HAZAN, HAZID Synthetic organic chemistry ideas Desktop screening, databases, calculations Discovery research and multiple experiments Automated laboratory reactors. Process optimization Pilot plant studies Scale up and design Industrial production. Debottlenecking. Optimization of mature processes. Retrofits. SAFE PROCESS DEVELOPMENT C H E M I C A L P R O C E S S L I F E C Y C L E D. Crowl, notes

3 3 Figure 11-1 Hazards identification and risk assessment procedure. (Adapted from Guidelines for Hazards Evaluation Procedures (New York: American Institute of Chemical Engineers, 1985), pp. 1–9.)

4 4 Process Hazard Analysis – Many Options 1. What-If 2. Checklist 3. What-If/Checklist 4. FMEA – Failure Mode & Effects Analysis 5. FTA – Fault Tree Analysis 6. Hazards Surveys 7. HAZOP – Hazards & Operability study

5 5 Process Hazard Analysis – Many Options 1. What-If 2. Checklist 3. What-If/Checklist 4. FMEA – Failure Mode & Effects Analysis 5. FTA – Fault Tree Analysis 6. Hazards Surveys 7. HAZOP – Hazards & Operability study

6 6 1. What-If Analysis Unstructured method for considering results of unexpected events Uses questions beginning with "what-if“ Not concerned with "how" failures occur Purpose is to identify problems that could lead to accidents Results in a list of potential problem areas and suggested mitigation methods

7 7 What-If Example LNG Vaporizer What if: (a) Water flow is stopped? (b) LNG flow is stopped? (c) Natural gas temperature is too low? (d) Water flow is too low? (e) Water pressure is too high? (f) A tube leaks into the shell? (g) Inlet water temperature is too low? D. Crowl, notes

8 8 What-If Example LNG Vaporizer too low? flow alarm. What-IfConsequence/ HazardRecommendation Water flow is stopped?Water in shell freezes and may rupture shell; natural gas temperature too low. Automatic interlock to stop LNG flow if water flow is stopped. LNG flow is stopped?Not HazardousNone Natural gas temperature is Downstream piping may become embrittled. Monitor gas temperature; low temperature alarm. Water flow is too low? Natural gas temperature may be too low; water may freeze in tubes. Monitor flow rate; low D. Crowl, notes

9 9 6. Hazards Surveys Can be simple like inventory of hazardous chemicals More rigorous procedures: - Dow Fire & Explosion Index - Dow Chemical Exposure Index

10 10 6. Hazards Surveys: Dow Fire & Explosion Index Complex and detailed procedure carried out by an individual Rates relative hazards of storing, handling, processing flammable and explosive materials Systematic approach independent of judgmental factors Break the process down into units or sections, e.g. the reactor, storage tank or a pump Use experience to select the units or sections that have the highest likelihood of a significant hazard (too many to cover all); may use checklist approach to choose Define the material factor (what chemicals are being used); in general, higher the value the more flammable / explosive Adjust this with various penalties based on conditions such as storage above normal boiling point, exothermic reaction, etc Then take credits for safety procedures and safety systems Finally arrive at a number that rates the hazard; compare with table / experience

11 11 6. Hazards Surveys: Dow Fire & Explosion Index Dow Fire & Explosion Index standard form; C&L Fig 11-3 Penalties Material factor Penalty factors Special Process Hazards Factor MF F1F1 General Process Hazards Factor F2F2 D. Crowl, notes

12 12 6. Hazards Surveys: Dow Fire & Explosion Index Dow F&EI - Determining the degree of hazard, Table 11-2 F&EI index valueDegree of hazard 1 – 60 Light 61 – 96 Moderate 97 – 127 Intermediate 128 – 158 Heavy > 158 Severe D. Crowl, notes

13 13 7. Hazard and Operability (HAZOP) Study HAZOP is a Structured "What If" Type of Study Objectives - Identify Hazard s - Identify Operability Problems HAZOPs Use Team Approach Multi-Disciplinary Guide word based Structured and Systematic

14 14 Hazards and Operability Study Investigative Process Select study nodes –Major process vessels –Major process lines connected to process vessels –Pumps and compressors –Heat exchangers –Major support systems Pick a process parameter - Flow, level, temperature, pressure, volume, pH, concentration, agitation, etc

15 15 Hazards and Operability Study Investigative Process (Cont’d) Apply guide words to process parameters –Determine deviation from design –Determine consequences of deviations –Evaluate consequences Typical causes of deviations –Hardware failures –Human error –Outside forces –Unanticipated process state

16 16 Hazards and Operability Study Investigative Process (Cont’d) Suggested actions –Change in design –Change in equipment –Alter operating procedures –Improve maintenance –Investigate further HAZOP Follow-up –Assign responsibility for carrying out recommendations with agreed timetable –Refer recommendations to appropriate managers –Evaluate and review Record keeping –Copy of all data used –Copy of all working papers –HAZOP worksheets

17 17 Hazards and Operability Study Guide Words and Their Meanings Simple words or phrases used to qualify the intention and associated parameters in order to discover deviations.

18 18

19 19 HAZOP Example Chemistry is such that concentrations of B must not exceed that of A First Study Node - pipeline from suction side of pump that delivers A to the reaction vessel First Guide Word - No to design intent of transfer A Causes of Deviation –Supply tank is empty –Pumps fail to run –Pipeline is fractured –Isolation valve is closed Consequences –Excess of B over A could lead to an explosion Recommendation –Install interlock device on pump B into reactor

20 20 HAZOP Example Worksheet D. Crowl, notes

21 21 W. Buck, SDSMT Seminar, 2012

22 22 Risk Matrix B.K. Vaughen, PSM Overview, SACHE, 2012 Frequency Consequence Unacceptable Undesirable Marginal Risk =F x C Acceptable

23 23 Risk Equation B.K. Vaughen, PSM Overview, SACHE, 2012 Frequency How often the event may occur - its likelihood is a “probability” Consequence How severe the event may be - an undesired result of the event

24 24 Operational Discipline B.K. Vaughen, PSM Overview, SACHE, 2012 The personal commitment of everyone to ensure their personal and process safety by 1) performing their tasks correctly, and 2) recognizing, responding to and seeking help, as needed, to unanticipated situations or conditions. OD

25 25 Operational Discipline B.K. Vaughen, PSM Overview, SACHE, 2012 “Organizational” OD Leadership Focus Employee Involvement Practice Consistent With Procedures Excellent Housekeeping “Personal” OD Awareness Knowledge Commitment

26 26 Risk Reduction B.K. Vaughen, PSM Overview, SACHE, 2012 FFrequency Engineering and Administrative Controls CConsequence Inherently Safer Processes Emergency Response Design Phase: the best time to use ISP

27 27 Risk Reduction B.K. Vaughen, PSM Overview, SACHE, 2012 ODOperational Discipline Safety Culture Organizational OD Safety Behaviorand Personal OD Commitment Characteristics

28 28 Effect of Poor OD on Risk B.K. Vaughen, PSM Overview, SACHE, 2012

29 29 Risk Matrix W. Buck, SDSMT Seminar, 2012

30 30 PSM Systems B.K. Vaughen, PSM Overview, SACHE, 2012 Designed to minimize process safety risk: There is always some level of risk Our PSM-related risk reduction efforts are compared and evaluated against other potential business risks (i.e., environmental, operational, maintenance, quality and financial)

31 31

32 32 B.K. Vaughen, PSM Overview, SACHE, 2012

33 33 Questions?


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