CHE-494
Chemical Process Design
What is Chemical Engineering?
Chemical engineering involves the design,
development, operation, and management of
facilities to transform natural and artificial
raw materials into more useful and more
valuable products through physical, chemical,
and biological changes in an economical and
environmentally acceptable manner .
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What is Chemical Process Design?
Process and Plant Design is the creative
activity, whereby one tries to generate new
ideas and translate them into processes and
equipment for processing raw materials, or
upgrading the value of existing materials in
a profitable
and environmentally
acceptable manner.
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Manufacture of Chemical Products
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Chemical Process Design - Driving Forces
 The Purpose of engineering is to
create/enhance/increase material wealth
for the benefit of mankind and to meet
societal needs Produce Higher Value Product
 Reduce manufacturing cost through process
improvement, increased efficiency
 Retrofit to solve Environmental & Safety
problems
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Chemical Process Design - Initiators
New process/product designs develop - To satisfy customer needs (Textile, plastics, etc.)
 Because of availability of new sources of cheap raw
materials
 Because of availability of new markets
 By accident (e.g., Teflon )
 By engineering gut feeling
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Chemical Process Design - Examples
Generate new Designs to:
 To produce a purchased raw Material
 Find a new way of producing an existing product (i.e.,
new Catalyst)
 Create a completely new product materials (i.e.,
synthetic fibers, food substitute)
 To convert a waste product into a salable commodity
 Exploit a new technology
 Exploit new materials of construction (i.e., High T &P,
specialty chemicals)
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Chemical Process Design – Various Industries
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petrochemicals
petroleum products
polymers
industrial gases
coatings
bio-chemicals
pharmaceuticals
foods
electronic materials
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Figure 4.8
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Curriculum
Feed
Preparation
Reactions
Product
Separation
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CHE Areas of Application
 Data Needed
 Physical / Chemical Properties
 Thermodynamic Properties
 Transport Properties
 Physical Changes
 Phase Equilibria, T and P changes, Unit Operations
 Mass, Heat, and Momentum transfer
 Chemical Changes
 Reaction Kinetics & Reactor Design
 Control
 Process Control
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CHE Areas of Application
 Data Needed
 Physical / Chemical Properties (CHEM 343, CHEM 344)
 Thermodynamic Properties (CHE 351, CHE 451)
 Transport Properties (CHE 301)
 Physical Changes
 Phase Equilibria, T and P changes, Unit Operations (CHE 302)
 Mass, Heat, and Momentum transfer (CHE 406)
 Chemical Changes
 Reaction Kinetics & Reactor Design (CHE 433, CHE423)
 Control
 Process Control (CHE 435)
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Commercialization Path
 Laboratory Scale
 Bench Scale
 Pilot Scale
 Demonstration Scale
 Commercial Scale
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Success Rates
 Laboratory Scale
 Bench Scale
 Pilot Scale
 Demonstration Scale
 Commercial Scale
1-2%
10-20%
40-60%
90-100%
???
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Design Problems are Underdefined!!
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You define as you go
Therefore it is a synthetic activity
Consists of several stages
There may by millions of ways to do it
It is Open-Ended
 Consequently, evaluation is a very significant component of any
design methodology. Efficient procedures are needed to screen out
unacceptable ones ($$, technical, etc.), and to modify and generate
alternatives.
 As a project advances toward commercialization, through various
stages, different kinds of design &evaluation procedures are
needed.
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Process Design vs. Painting
Painting
Process Design
Pencil Sketch
Preliminary design
(assess primitive problem)
Evaluation, Modification
(using only gross outline)
Evaluation, generation of
process alternative that might
lead to improvement
Rigorous design and costing
procedure for most expensive
equipment, improve accuracy
of M&E balances, add details
Continue until diminishing
return
Color, Shading, details
+ major modification (if
needed)
Never Completed
No single solution
No single solution
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Design Factors
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Technical Viability
Cost
Safety
Environment
Startup
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Steps in Design Synthesis
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Initial Assessment
Literature Survey
Process Synthesis
Develop Base Case Design (Petro-SIM, HYSYS)
Detailed Process Synthesis (algorithmic )
Detailed Equipment Design
Capital Cost Estimation
Profitability Analysis
Other Issues
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Other Issues
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Optimization
Controllability
Reliability
Safety
Environmental Issues
Engineering Ethics
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Ethical Issues
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Safety (Employees, Public)
Health (Employees, Public)
Environment
Welfare (Employer, Client, Public)
Honesty
Fairness
Confidentiality
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PROFESSIONAL ETHICS
AIChE Code of Ethics
Members of the American Institute of Chemical
Engineers shall uphold and advance the integrity, honor,
and dignity of the engineering profession by: being honest
and impartial and serving with fidelity their employers,
their clients, and the public; striving to increase the
competence and prestige of the engineering profession;
and using their knowledge and skill for the enhancement
of human welfare.
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AIChE Code of Ethics, cont’d
To achieve these goals, members shall:
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Hold paramount the safety, health, and welfare of the
public in performance of their professional duties.
Formally advise their employers or clients (and
consider further disclosure, if warranted) if they
perceive that a consequence of their duties will
adversely affect the present or future health or safety
of their colleagues or the public.
Accept responsibility for their actions and recognize
the contributions of others; seek critical review of their
work and offer objective criticism of the work of
others.
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AIChE Code of Ethics, cont’d
 Issue statements or present information only in an objective
and truthful manner.
 Act in professional matters for each employer or client as
faithful agents or trustees, and avoid conflicts of interest.
 Treat fairly all colleagues and co-workers, recognizing their
unique contributions and capabilities.
 Perform professional services only in areas of their
competence.
 Build their professional reputations on the merits of their
services.
 Continue their professional development throughout their
careers, and provide opportunities for the professional
development of those under their supervision.
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NSPE Code of Ethics for Engineers
Engineering is an important and learned profession. As
members of this profession, engineers are expected to
exhibit the highest standards of honesty and integrity.
Engineering has a direct and vital impact on the quality of
life for all people. Accordingly, the services provided by
engineers require honesty, impartiality, fairness and
equity, and must be dedicated to the protection of the
public health, safety, and welfare. Engineers must
perform under a standard of professional behavior that
requires adherence to the highest principles of ethical
conduct.
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NSPE Code of Ethics cont’d
Fundamental Canons
Engineers, in the fulfillment of their professional duties,
shall:
1. Hold paramount the safety, health and welfare of the public.
2. Perform services only in areas of their competence.
3. Issue public statements only in an objective and truthful
manner.
4. Act for each employer or client as faithful agents or trustees.
5. Avoid deceptive acts.
6. Conduct themselves honorably, responsibly, ethically, and
lawfully so as to enhance the honor, reputation, and
usefulness of the profession.
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NSPE Code of Ethics cont’d
Rules of Practice
1. Engineers shall hold paramount the safety, health, and
welfare of the public.
a. If engineers' judgment is overruled under circumstances that endanger life or
property, they shall notify their employer or client and such other authority as
may be appropriate.
b. Engineers shall approve only those engineering documents that are in conformity
with applicable standards.
c. Engineers shall not reveal facts, data or information without the prior consent of
the client or employer except as authorized or required by law or this Code.
d. Engineers shall not permit the use of their name or associate in business ventures
with any person or firm that they believe are engaged in fraudulent or dishonest
enterprise.
e. Engineers having knowledge of any alleged violation of this Code shall report
thereon to appropriate professional bodies and, when relevant, also to public
authorities, and cooperate with the proper authorities in furnishing such
information or assistance as may be required.
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Safety
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Flammability
Pressure
Toxic Materials
Exothermic Reactions
Over-Design
Redundancies
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Resources
 IIT
 Center for the Study of Ethics in the Profession
(CSEP).
 http://ethics.iit.edu
 Case Western Reserve University
 http://www.onlineethics.org/
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Environmental Issues in Design
 Handling of toxic wastes
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97% of hazardous waste generation by the chemicals and nuclear
industry is wastewater (1988 data).
In process design, it is essential that facilities be included to remove
pollutants from waste-water streams.
 Reaction pathways to reduce by-product toxicity
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As the reaction operations are determined, the toxicity of all of the
chemicals, especially those recovered as byproducts, needs to be
evaluated.
Pathways involving large quantities of toxic chemicals should be
replaced by alternatives, except under unusual circumstances.
 Reducing and reusing wastes
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Environmental concerns place even greater emphasis on recycling, not
only for unreacted chemicals, but for product and by-product
chemicals, as well. (i.e., production of segregated wastes - e.g.,
production of composite materials and polymers).
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Environmental Issues in Design (Cont’d)
 Avoiding non-routine events
 Reduce the likelihood of accidents and spills through the
reduction of transient phenomena, relying on operation at the
nominal steady-state, with reliable controllers and faultdetection systems.
 Design objectives, constraints and optimization
 Environmental goals often not well defined because economic
objective functions involve profitability measures, whereas the
value of reduced pollution is often not easily quantified
economically.
 Solutions: mixed objective function (“price of reduced
pollution”), or express environmental goal as “soft” or “hard”
constraints.
 Environmental regulations = constraints
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Safety Considerations
 Example Disaster 1 – Flixborough: 1st June 1974
Flixborough (Nypro UK) Explosion 1st June 1974 (hse.gov.uk)
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50 tons of cyclohexane were released from Nypro’s KA plant (oxidation of
cyclohexane) leading to release of vapor cloud and its detonation. Total loss of
plant and death of 28 plant personnel.
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Highly reactive system - conversions low, with large inventory in plant.
Process involved six, 20 ton stirred-tank reactors.
 Discharge caused by failure of
temporary pipe installed to
replace cracked reactor.
 The so-called “dog-leg” was not
able to contain the operating
conditions of the process (10 bar,
150 oC)
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 Flixborough - What can we learn?
 Develop processes with low inventory, especially of
flashing fluids (“what you don’t have, can’t leak”)
 Before modifying process, carry out a systematic
search for possible cause of problem.
 Carry out HAZOP analysis
 Construct modifications to same standard as original
plant.
 Use blast-resistant control rooms and buildings
T. Kletz, “Learning from Accidents”, 2nd Ed. (1994)
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Safety Considerations (Cont’d)
 Example Disaster 2 – Bhopal: 3rd December 1984
http://www.bhopal.com/chrono.htm
 Water leakage into MIC (Methyl isocyanate) storage tank leading to
boiling and release of 25 tons of toxic MIC vapor, killing more than
3,800 civilians, and injuring tens of thousands more.
 MIC vapor released because the refrigeration system intended to cool
the storage tank holding 100 tons of MIC had been shut down, the
scrubber was not immediately available, and the flare was not in
operation.
 Bhopal - What can we learn?
 Avoid use of hazardous materials. Minimize stocks of hazardous
materials (“what you don’t have, can’t leak”).
 Carry out HAZOP analysis.
 Train operators not to ignore unusual readings.
 Keep protective equipment in working order.
 Control building near major hazards.
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Safety Considerations (Cont’d)
 Example Disaster 3 – Challenger: 28th January 1986
http://www.onlineethics.com/moral/boisjoly/RB-intro.html
 An O-ring seal in one of the solid booster rockets failed. A highpressure flame plume was deflected onto the external fuel tank,
leading to a massive explosion at 73 sec from lift-off, claiming the
Challenger with its crew.
 The O-ring problem was known several months before the disaster,
but down-played by management, who over-rode concerns by
engineers.
 Challenger - What can we learn?
 Design for safety.
 Prevent ‘management’ over-ride
of ‘engineering’ safety
concerns.
 Carry out HAZOP analysis.
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Safety Issues: Fires and Explosions
Flammability Limits of Liquids and Gases
LFL and UFL (vol %) in Air at 25 oC and 1 Atm
Compound
LFL (%) UFL (%)
Acetylene
2.5
100
Cyclohexane
1.3
8
Methan
5
15
Gasoline
1.4
7.6
Hydrogen
4.0
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These limits can be extended for mixtures, and for elevated
temperatures and pressures (see Seider et al, 2003).
With this kind of information, the process designer makes sure that
flammable mixtures do not exist in the process during startup, steadystate operation, or shut-down.
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