chapter 26 safety, health, and the environment
TRANSCRIPT
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Chapter 26 Health, Safety, and the
Environment
Department of Chemical Engineering
West Virginia University
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Outline
• Risks
• Regulations and Agencies
• Worker Exposure
• Process Safety Management
• Fires and Explosions
• Inherently Safe Design
• Pollution Prevention
• Life-cycle Analysis
• HAZOP Copyright - R.Turton and J. Shaeiwitz 2012 2
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Risk Assessment • Statistics
OSHA incidence rate
Injuries and illnesses/100 worker years
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200,000 hrs @ 2000 hrs/yr
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Risk Assessment • Statistics
FAR (fatal accident rate)
Fatalities/1000 worker lifetimes
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108 hr
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Risk Assessment • Statistics
Fatality rate
Fatalities/yr/applicable population
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e.g., smokers
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Risk Assessment Activity OSHA Incident
Rate
(injuries & deaths
per 200,000 h)
Fatal Accident
Rate
(deaths per
100,000,000 h)
Fatality Rate
(deaths per person
per year)
Working in Chemical
Industry 0.49 4
Staying at Home 3
Working in Steel
Industry 1.54 8
Working in
Construction 3.88 67
Traveling by Car 57 170 x 10-6
Rock Climbing 4000 40 x 10-6
Smoking (1 pack per
day) 5000 x 10-6
Being struck by
Lightning 0.1 x 10-6
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Risk Assessment
• Accident statistics - Table 22.1
• Worst case scenario HAZOPS
• Role of CHE – to communicate risks to employees, employers, clients, public – Important Public Relations
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Regulations and Agencies • Rules and regulations arise from governmental (OSHA,
NIOSH, EPA, DOT, MSHA) and non-governmental agencies (AIChE, API, ASTM, NFPA, etc.)
• Federal government rules are published in the Federal Register (FR) and the Code of Federal Regulations (CFR).
• Important Standards include – OSHA Act and Air Contamination Standard – give exposure limits
– Hazard Communication Standard – “worker right to know” or HazCom. Specifies proper labeling of containers and availability of Material Safety Data Sheets (MSDS).
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Worker Exposure
• Workers OSHA
Permissible Exposure Limit Threshold Limit Values (ACGIH)
NIOSH – Recommended Exposure Limits Short Term Exposure Limit – 15 minute exposure
• Public EPA – CAA, CWA, SARA DOT
• MSDS Sheet See Table 22.3
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Time weighted average over 8-hr day
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Process Safety Management
• Process Safety Management
– See 13 components of PSM in Table 22.4
• Process Hazards Management
– See video – API 750
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Fires and Explosions
• Combustion - rapid oxidation – At room temp rate usually low
– Increases rapidly with temperature
– Below auto-ignition temperature – remove heat and returns to room temperature
• Auto-ignition temperature – Above this temperature, combustion is sustained when
heat source removed.
– Energy to heat small region to above A-I temp is called the ignition energy – very small
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Fires and Explosions
• Flammability (or explosive) Limits LFL (LEL) – min concentration of fuel in
oxidant (usually air) that will support combustion
UFL (UEL) - max concentration of fuel in oxidant (usually air) that will support combustion
MOC – relates to “inerting”
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Fires and Explosions
• Explosion – rapid combustion in which the pressure waves formed propagate the combustion. Waves compresses and heats flammable mixture to its AI temperature.
Deflagraton (< speed of sound)
Detonation (> speed of sound)
• Vapor cloud explosion
• BLEVE (boiling-liquid expanding vapor-cloud explosion – rapid expansion of vapor can cause a massive shock wave)
BLEVE + VCE =
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Fires and Explosions
• Runaway reaction
– Insufficient heat removal from exothermic reaction LOCA (loss of cooling accident)
– Use a small or large DT for cooling medium?
• Over-pressure
– Pressure-relief valves
– Bursting discs
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Inherently Safe Design
• Substitution – avoid
• Intensification – use less
• Attenuation – less hazardous conditions
• Containment – do not let out
• Control Leaks – emergency isolation
• Survive Leaks – fire protection, etc.
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Pollution Prevention
• Source Reduction
• Recycling – “mass integration” – In process
– On-site
– Off-site
• Treatment
• Disposal
• Release
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Life-cycle Analysis
• “Cradle-to-grave”
– Raw materials acquisition
– Manufacturing
– Use, reuse, maintenance
– Recycle and waste management
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Life-cycle Analysis
• Inventory analysis
– Material and energy inputs to environment
• Impact analysis
– Environmental consequences
• Improvement analysis
– Opportunities to improve environment
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HAZOP
• Hazard and Operability Study
• Ask: What if?
• “A modified brainstorming technique for identifying and resolving process hazards by considering seemingly unusual occurrences.”
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HAZOP • Guide words used to describe possible
deviations in the process – No, none, not
– More of
– Less of
– More than, or as well as
– Part of
– Reverse
– Other than
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HAZOP
• No, none, not
– Design intention does not occur
• More of
– Beyond design intention
• Less of
– Below design intention
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HAZOP
• More than, or as well as – In addition to design intention
• Part of – Only some of intention present
• Reverse – Opposite of design intention
• Other than – Other than intended by design
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HAZOP • Intention
– How process is designed to operate
• Deviation – From operating specifications
• Cause – How deviation might occur
• Consequence – Of deviation with reasonable causes
• Hazard – Consequences that could cause dangerous situation
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HAZOP Algorithm • Pick unit and establish design intention
• Pick streams entering
• Apply all guide words – does possible cause exist for given deviation
• For deviation – determine consequences and suggest remedy
• Repeat for all equipment
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HAZOP Example
• See Table 26.5
– Shows example of each guide word
– Shows “correct” tabular form for presentation of results
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Table 21.5. HAZOP for the Feed Heater of the Hydrodealkylation (HDA) Process Process Unit: H-101, Feed Heater, Figure 1.3
Intention: To provide feed to the Reactor (Stream 6) at 600ºC.
Guide
Word
Deviation Cause Consequence Action
No No flow (Stream 4) blockage in line Fluid in H-101
overheats
Consider an interlock on
fuel gas flow
No O2 in
combustion
products
Rich fuel:air mixture Unburned fuel and
CO in combustion
products
None. O2 analyzer with
self-checking circuit
controls ratio reliably
O2 analyzer
malfunction
Potentially rich
fuel:air mixture
No flow (Stream 6) Heat tubes burst Explosion Interlock with sudden P
drop alarm and shutdown
No benzene in
Stream 6
C-101 not working Hydrogen:Toluene
ratio off to R-101 and
loss of hydrogen to
fuel gas
Maintain spare
compressor C-101
No fuel gas flow Supply pipe rupture Cold shot to R-101,
quenching reaction
Interlock with process
shutdown
No flame Momentary loss of fuel
gas
Explosive mixture Automatic flame
detection with re-ignition
cycle
4
6
fg air
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Summary
• Risks
• Regulations and Agencies
• Worker Exposure
• Process Safety Management
• Fires and Explosions
• Inherently Safe Design
• Pollution Prevention
• Life-cycle Analysis
• HAZOP
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