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ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
1
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
1/63
Overview of Process Safety, Green Engineering, and Inherently Safer Design
Harry J. Toups LSU Department of Chemical Engineering with significant material from SACHE 2003 Workshop presentation entitled: Inherently Safer Design, byDennis HendershotRohm and Haas Company
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Three Elements of Process Safety
Behavior
Systems Process
ProcessSafety
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
2
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
3/63
Process Safety Milestone Practices
Performance-, risk-based standards, regulations; ‘green’ and ‘inherent’ designs
1980’s +
Development of risk assessment techniques and systematic approaches
1970’s, 80’s
Find breakdown in, and fix man-machine interface
Pre-1970’s
Identify who caused the loss and punish the guilty
Pre-1930’s Behavior
Process
Mgmt Systems
Comprehensive
4/63
Causes of Losses in Large Plant Accidents
44
22
12 11
5 51
Mechanical OperatorError
Unknown ProcessUpsets
NaturalHazards
Design Sabotageand Arson
Acc
iden
ts (%
)
ProcessDesign
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
3
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
5/63
Green chemistry and engineering –A Definition
The design, commercialization, and use of chemical processes and products, which are feasible and economical while minimizing:
1) generation of pollution at the source, and
2) risk to human health and the environment.
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New paradigm for the environment
• Traditional environmental approach
– “End of pipe” waste treatment– “Waste minimization” – an advance,
but we can go further
• Green chemistry and engineering
– Eliminate or dramatically reduce hazards to the environment
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
4
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
7/63
– “Once you get something dirty, the only way to get it clean is to make something else dirty.”
– The best way to keep the world clean is to not get it dirty to begin with.
Many of us learned this as children
• Dr. Suess –The Cat in the Hat Comes Back
8/63
Inherently Safer Design –A Definition
The design of chemical processes and products with specific attention to eliminating hazards from the manufacturing process rather than relying on the control of these hazards
Notice the common philosophy to Green Engineering?
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
5
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
9/63
New paradigm for safety
• Traditional safety approach– “Add on” safety features
• Prevent - alarms, safety interlocks, procedures, training
• Mitigate – sprinkler systems, water curtains, emergency response systems and procedures
• Inherently safer design– Eliminate or significantly reduce
process hazards
10/63
Inherently safer design, green chemistry, and green engineering
Green Chemistryand Engineering
InherentlySafer
Design
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
6
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
11/63
Why are we interested in inherently safer design?
12/63
Flixborough, England (1974)
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
7
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
13/63
Flixborough, England (1974)
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Henderson, Nevada, (1988)
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
8
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
15/63
What is inherently safer design?
• Inherent - “existing in something as a permanent and inseparable element...”– safety “built in”, not “added on”
• Eliminate or minimize hazards rather than control hazards
• More a philosophy and way of thinking than a specific set of tools and methods– Applicable at all levels of design and
operation from conceptual design to plant operations
• “Safer,” not “Safe”
16/63
Hazard
• An inherent physical or chemical characteristic that has the potential for causing harm to people, the environment, or property (CCPS, 1992).
• Hazards are intrinsic to a material, or its conditions of use.
• Examples– Phosgene - toxic by inhalation– Acetone - flammable– High pressure steam - potential energy due
to pressure, high temperature
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
9
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
17/63
To eliminate hazards:
• Eliminate the material• Change the material• Change the conditions of use
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Chemical Process Safety Strategies
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
10
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
19/63
Inherent
• Eliminate or reduce the hazard by changing to a process or materials which are non-hazardous or less hazardous
• Integral to the product, process, or plant -cannot be easily defeated or changed without fundamentally altering the process or plant design
• EXAMPLE– Substituting water for a flammable solvent
(latex paints compared to oil base paints)
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Passive
• Minimize hazard using process or equipment design features which reduce frequency or consequence without the active functioning of any device
• EXAMPLE– Containment dike around a
hazardous material storage tank
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
11
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
21/63
Active
• Controls, safety interlocks, automatic shut down systems
• Multiple active elements– Sensor - detect hazardous condition– Logic device - decide what to do– Control element - implement action
• Prevent incidents, or mitigate the consequences of incidents
• EXAMPLE– High level alarm in a tank shuts automatic feed
valve• Caution: Even protective systems can cause
incidents! (See Hendershot et al handouts)
22/63
Procedural
• Standard operating procedures, safety rules and standard procedures, emergency response procedures, training
• EXAMPLE– Confined space entry procedures
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
12
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
23/63
Batch Chemical Reactor Example
Hazard of concern
• Runaway reaction causing high temperature and pressure and potential reactor rupture
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Passive
• Maximum adiabatic pressure for reaction determined to be 150 psig
• Run reaction in a 250 psig design reactor
• Hazard (pressure) still exists, but passively contained by the pressure vessel
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
13
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
25/63
Active• Maximum adiabatic pressure for
100% reaction is 150 psig, reactor design pressure is 50 psig
• Gradually add limiting reactant with temperature control to limit potential energy from reaction
• Use high temperature and pressure interlocks to stop feed and apply emergency cooling
• Provide emergency relief system
26/63
Procedural
• Maximum adiabatic pressure for 100% reaction is 150 psig, reactor design pressure is 50 psig
• Gradually add limiting reactant with temperature control to limit potential energy from reaction
• Train operator to observe temperature, stop feeds and apply cooling if temperature exceeds critical operating limit
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
14
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
27/63
Inherent
• Develop chemistry which is not exothermic, or mildly exothermic– Maximum adiabatic exotherm
temperature < boiling point of all ingredients and onset temperature of any decomposition or other reactions
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Which strategy should we use?
• Generally, in order of robustness and reliability:– Inherent– Passive– Active– Procedural
• But - there is a place and need for ALL of these strategies in a complete safety program
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
15
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
29/63
Inherently Safer Design Strategies
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Inherently Safer Design Strategies
• Minimize• Moderate• Substitute• Simplify
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
16
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
31/63
Minimize
• Use small quantities of hazardous substances or energy– Storage– Intermediate storage – Piping– Process equipment
• “Process Intensification”
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Benefits
• Reduced consequence of incident (explosion, fire, toxic material release)
• Improved effectiveness and feasibility of other protective systems – for example:– Secondary containment– Reactor dump or quench systems
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
17
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
33/63
Semi-batch nitration process
Batch Reactor~6000 gallons
Organic Substrate andsolvents pre-charge
Nitric acid gradualaddition
Catalyst (usuallysulfuric acid) feed
or pre-charge
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How can Process Intensification be used in this reaction?
• Mixing – bringing reactants into contact with each other
• Mass transfer – from aqueous phase (nitric acid) to organic phase (organic substrate)
• Heat removal
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
18
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
35/63
CSTR Nitration Process
Product
RawMaterialFeeds
Organic substrateCatalystNitric Acid
Reactor ~ 100 gallons
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One step further:Do this reaction in a pipe reactor?
RawMaterialFeeds
Organic substrateCatalystNitric Acid
Cooled continuousmixer/reactor
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
19
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
37/63
Scale up
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Scale out
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
20
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
39/63
On-demand phosgene generation
• Continuous process to produce phosgene• Phosgene consumers are batch processes• No phosgene storage• Engineering challenges
– Rapid startup and shutdown– Quality control – Instrumentation and dynamic process
control– Disposal of “tail gas” and inerts
40/63
Moderate
• Dilution• Refrigeration• Less severe processing conditions• Physical characteristics• Containment
– Better described as “passive” rather than “inherent”
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
21
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
41/63
Dilution
• Aqueous ammonia instead of anhydrous
• Aqueous HCl in place of anhydrous HCl
• Sulfuric acid in place of oleum• Wet benzoyl peroxide in place of dry• Dynamite instead of nitroglycerine
42/63
Effect of dilution
0 10
10,000
20,000
Cen
terl
ine
Am
mon
iaC
once
ntra
tion,
mol
e pp
m
28%AqueousAmmonia
AnhydrousAmmonia
(B) - Release Scenario:2 inch transfer pipe failure
Distance, Miles
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
22
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
43/63
Less severe processing conditions
• Ammonia manufacture– 1930s - pressures up to 600 bar– 1950s - typically 300-350 bar– 1980s - plants operating at pressures
of 100-150 bar were being built• Result of understanding and
improving the process• Lower pressure plants are cheaper,
more efficient, as well as safer
44/63
Substitute
• Substitute a less hazardous reaction chemistry
• Replace a hazardous material with a less hazardous alternative
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
23
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
45/63
Substitute materials
• Water based coatings and paints in place of solvent based alternatives– Reduce fire hazard– Less toxic– Less odor– More environmentally friendly– Reduce hazards for end user and
also for the manufacturer
46/63
Simplify
• Eliminate unnecessary complexity to reduce risk of human error– QUESTION ALL COMPLEXITY! Is it
really necessary?
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
24
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
47/63
Simplify - eliminate equipment
• Reactive distillation methyl acetate process (Eastman Chemical)
• Which is simpler?
Reactor
SplitterExtractiveDistillaton
SolventRecovery
MethanolRecovery
Extractor
AzeoColumn
Decanter
FlashColumn
ColorColumn
FlashColumn
W ater
W ater
Heavies
MethylAcetate
W ater
CatalystMethanolAcetic Acid
Re acto rCo lumn
ImpurityRe mov alCo lumns
Wate r
He av ie s
Ace tic Acid
M e thano l
Su lfu r icAcid
M e thylAce tate
48/63
Modified methyl acetate process
• Fewer vessels• Fewer pumps• Fewer flanges• Fewer instruments• Fewer valves• Less piping• ......
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
25
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
49/63
But, it isn’t simpler in every way
• Reactive distillation column itself is more complex
• Multiple unit operations occur within one vessel
• More complex to design• More difficult to control and
operate
50/63
Single, complex batch reactor
Condenser
DistillateReceiver
RefrigeratedBrine
LargeRupture
Disk
A
B
C
D
E
Condensate
Water Supply
Steam
Water Return
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
26
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
51/63
A sequence of simpler batch reactors for the same process
A
B
C
D
E
DistillateReceiver
Condenser
Water Supply
Water Return
RefrigeratedBrine
Steam
Condensate
Large RuptureDisk
52/63
Inherent safety conflicts
• In the previous example– Each vessel is simpler
• But– There are now three vessels, the
overall plant is more complex in some ways
– Compare to methyl acetate example• Need to understand specific hazards
for each situation to decide what is best
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
27
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
53/63
Conflicts and Tradeoffs
54/63
Some problems
• The properties of a technology which make it hazardous may be the same as the properties which make it useful:– Airplanes travel at 600 mph– Gasoline is flammable
• Any replacement must have the ability to store a large quantity of energy in a compact form
– Chlorine is toxic
• Control of the hazard is the critical issue in safely getting the benefits of the technology
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
28
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
55/63
Multiple hazards• Everything has multiple hazards
– Automobile travel• velocity (energy), flammable fuel,
exhaust gas toxicity, hot surfaces, pressurized cooling system, electricity......
– Chemical process or product• acute toxicity, flammability,
corrosiveness, chronic toxicity, various environmental impacts, reactivity.......
56/63
What does inherently safer mean?
• Inherently safer is in the context of one or more of the multiple hazards
• There may be conflicts– Example - CFC refrigerants
• low acute toxicity, not flammable• potential for environmental damage,
long term health impacts• Are they inherently safer than
alternatives such as propane (flammable) or ammonia (flammable and toxic)?
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
29
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
57/63
Inherently safer hydrocarbon based refrigerators?
• Can we redesign the refrigeration machine to minimize the quantity of refrigerant sufficiently that we could still regard it as inherently safer?– Home refrigerators – perhaps (<120
grams)– Industrial scale applications –
probably not, need to rely on passive, active, procedural risk management strategies
58/63
Multiple impacts
• Different populations may perceive the inherent safety of different technology options differently
• Example - chlorine handling - 1 ton cylinders vs. a 90 ton rail car– A neighbor two miles away?– An operator who has to connect and
disconnect cylinders 90 times instead of a rail car once?
• Who is right?
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
30
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
59/63
Inherently safer = safer• Air travel
– several hundred people– 5 miles up– control in 3 dimensions– 600 mph– thousands of gallons of
fuel– passengers in a
pressure vessel– .........
• Automobile travel– a few people– on the ground– control in 2 dimensions– 60 mph– a few gallons of fuel
– might even be a convertible
– .........
l Automobile travel is inherently saferl But, what is the safest way to travel from
Washington to Los Angeles?l Why?
60/63
At what level of design should engineers consider inherently safer design?• Selecting Technology? Plant Design?
Equipment Details? Operations?
• Best answer?– All levels!
• Inherently safer design is not a meeting.
• Inherently safer design is a way of thinking, a way of approaching technology design at every level of detail – part of the daily thought process.
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
31
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
61/63
Questions a designer should ask when he has identified a hazard
In this order1. Can I eliminate this hazard?2. If not, can I reduce the magnitude of the
hazard?3. Do the alternatives identified in questions 1
and 2 increase the magnitude of any other hazards, or create new hazards?
4. At this point, what technical and management systems are required to manage the hazards which inevitably will remain?
62/63
The Future: Inherently safer design
• Some hazardous materials and processes can be eliminated or the hazards dramatically reduced.
• The useful characteristics of other materials or processes make their continued use essential to society for the foreseeable future … we will continue to manage the risks.
• E.g., Air travel
ChE 4172 Lecture: Process Safety, Green Engineering, and Inherently Safer DesignH.J. ToupsSpring 2004
32
Based on: Inherently Safer DesignDennis C. Hendershot
Rohm and Haas Company
63/63
02468
1012
1973 1983 1993 2003Tota
l Rec
orda
ble
Inju
ry/Il
lnes
s Ra
te
Is It Worth the Effort?
Number of US workplace injuries/illnessesper 100 employees continues to drop …
… due to comprehensive safety strategies,including Inherently Safer Design
64/63
END OFPRESENTATION