The document outlines the stages of process plant design, including inception, economic evaluations, engineering design, and procurement. It discusses types of designs such as preliminary and detailed-estimate designs and emphasizes the importance of feasibility surveys in assessing technical and economic viability. A case study on the development of a non-biodegradable detergent manufacturing process illustrates practical applications of these design principles.

1. Process Plant Design
(Concepts and Case Studies)
Dr. Suraj Kumar Tripathy

2. A plant-design project moves to completion through a series of stages:
1. Inception
2. Preliminary evaluation of economics and market
3. Development of data necessary for final design
4. Final economic evaluation
5. Detailed engineering design
6. Procurement
7. Erection
8. Startup and trial runs
9. Production

3. Process Design Development
The development of a design project always starts with an initial idea or plan. This initial
idea must be stated as clearly and concisely as possible in order to define the scope of
the project. General specifications and pertinent laboratory or chemical engineering
data should be presented along with the initial idea.
Types of Designs
1. Preliminary or quick-estimate designs
2. Detailed-estimate designs
3. Firm process designs or detailed designs
Preliminary designs are ordinarily used as a basis for determining whether further
work should be done on the proposed process. The design is based on approximate
process methods, and rough cost estimates are prepared. Few details are included,
and the time spent on calculations is kept at a minimum.
If the results of the preliminary design show that further work is justified, a
detailed-estimate design may be developed. In this type of design, the cost and
profit potential of an established process is determined by detailed analyses and
calculations. However, exact specifications are not given for the equipment, and
drafting-room work is minimized.
Before the final step before developing construction plans for the plant is the
preparation of a firm process design. Complete specifications are presented for all
components of the plant, and accurate costs based on quoted prices are obtained.
Detailed-estimate design indicates that the proposed
project should be a commercial success

4. Feasibility Survey
 Before any detailed work is done on the design, the technical
and economic factors of the proposed process should be
examined.
 The various reactions and physical processes involved must be
considered, along with the existing and potential market
conditions for the particular product.
 A preliminary survey of this type gives an indication of the
probable success of the project and also shows what additional
information is necessary to make a complete evaluation.

5. 1. Raw materials (availability, quantity, quality, cost)
2. Thermodynamics and kinetics of chemical reactions involved
(equilibrium, yields, rates, optimum conditions)
3. Facilities and equipment available at present
4. Facilities and equipment which must be purchased
5. Estimation of production costs and total investment
6. Profits (probable and optimum, per pound of product and per
year, return on investment)
7. Materials of construction
8. Safety considerations
Feasibility Survey…………

6. 9. Markets (present and future supply and demand, present
uses, new uses, present buying habits, price range for
products and by-products, character, location, and number of
possible customers)
10. Competition (overall production statistics, comparison of
various manufacturing processes, product specifications of
competitors)
11. Properties of products (chemical and physical properties,
specifications, impurities, effects of storage)
12. Sales and sales service (method of selling and distributing,
advertising required, technical services required)
13. Shipping restrictions and containers
14. Plant location
15. Patent situation and legal restrictions

7. Process Flow Diagram
The chemical engineer uses flow diagrams to show the sequence
of equipment and unit operations in the overall process, to
simplify visualization of the manufacturing procedures, and to
indicate the quantities of materials and energy transfer.
These diagrams may be divided into three general types:
(1) Qualitative
(2) Quantitative, and
(3) Combined-detail

8. Case Study-1 Petrochemical company
Problem Statement
 A conservative petroleum company has recently been reorganized and the
new management has decided that the company must diversify its
operations into the petrochemical field if it wishes to remain competitive.
 The R & D division of the company has suggested that a very promising
area in the petrochemical field would be in the development and
manufacture of biodegradable synthetic detergents using some of the
hydrocarbon intermediates presently available in the refinery.
 A survey by the market division has indicated that the company could
hope to attain 2.5 percent of the detergent market if a plant with an
annual production of 15 million pounds were to be built.
 To provide management with an investment comparison, the design
group has been instructed to proceed first with a preliminary design and
an updated cost estimate for a non-biodegradable detergent producing
facility similar to ones supplanted by recent biodegradable facilities.

9. Literature Survey
A survey of the literature reveals that the majority of the nonbiodegradable detergents
are alkylbenzene sulfonates (ABS). Theoretically, there are over 80,000 isomeric
alkylbenzenes in the range of C,, to C,, for the alkyl side chain.
Costs, however, generally favor the use of dodecene (propylene tetramer) as the starting
material for ABS.
There are many different schemes in the manufacture of ABS. A brief description of the
process is as follows:
Process involves
(1) reaction of dodecene with benzene in the presence of aluminum chloride catalyst
(2) fractionation of the resulting crude mixture to recover the desired boiling range of
dodecylbenzene
(3) sulfonation of the dodecylbenzene and subsequent neutralization of the sulfonic acid
with caustic soda
(4) blending the resulting slurry with chemical “builders”; and
(5) drying

10.  Dodecene is charged into a reaction vessel containing benzene and aluminum
chloride. The reaction mixture is agitated and cooled to maintain the reaction
temperature of about 115°F maximum. An excess of benzene is used to suppress
the formation of by-products. Aluminum chloride requirement is 5 to 10 wt% of
dodecene.
 After removal of aluminum chloride sludge, the reaction mixture is fractionated to
recover excess benzene (which is recycled to the reaction vessel), a light alkylaryl
hydrocarbon, dodecylbenzene, and a heavy alkylaryl hydrocarbon.
 Sulfonation of the dodecylbenzene may be carried out continuously or batch-wise
under a variety of operating conditions using sulfuric acid (100 %), oleum (usually
20 % SO,), or anhydrous sulfur trioxide.
 The optimum sulfonation temperature is usually in the range of 100 to 140°F
depending on the strength of acid employed, mechanical design of the equipment,
etc. Removal of the spent sulfuric acid from the sulfonic acid is facilitated by adding
water to reduce the sulfuric acid strength to about 78 %.
 This dilution prior to neutralization results in a final neutralized slurry having
approximately 85 percent active agent based on the solids. The inert material in the
final product is essentially Na2SO4.
 The sulfonic acid is neutralized with 20 to 50 % caustic soda solution to a pH of 8 at
a temperature of about 125°F. Chemical “builders” such as trisodium phosphate,
tetrasodium pyrophosphate, sodium silitate, sodium chloride, sodium sulfate,
carbovethyl cellulose, etc., are added to enhance the detersive, wetting, or other
desired properties in the finished product. A flaked, dried product is obtained by
drum drying or a bead product is obtained by spray drying.

11. A literature search indicates that yields of 85 to 95 % have been obtained in the
alkylation step, while yields for the sulfonation process are substantially 100 %, and
yields for the neutralization step are always 95 % or greater. All three steps are
exothermic and require some form of jacketed cooling around the stirred reactor to
maintain isothermal reaction temperatures.
Laboratory data for the sulfonation of dodecylbenzene, described in the literature,
provide additional information useful for a rapid material balance.

12.  Sulfonation is essentially complete if the ratio of 20 % oleum to dodecylbenzene is
maintained at 1.25.
 Spent sulfuric acid removal is optimized with the addition of 0.244 lb of water to
the settler for each 1.25 lb of 20 % oleum added in the sulfonation step.
 A 25 percent excess of 20 % NaOH is suggested for the neutralization step.

13. Material and Energy Balance
The process selected for the manufacture of the nonbiodegradable detergent is
essentially continuous even though the alkylation, sulfonation, and neutralization steps
are semicontinuous steps. Provisions for possible shutdowns for repairs and maintenance
are incorporated into the design of the process by specifying plant operation for 300
calendar days per year. Assuming 90 percent yield in the alkylator and a sodium
dodecylbenzene sulfonate product to be 85 percent active with 15 percent sodium sulfate
as inert, the overall material balance is as follows:
Equipment Design and Selection
Equipment design for this preliminary process evaluation involves determining the size of
the equipment in terms of the volume, flow per unit time, or surface area. Some of the
calculations associated with the alkylation unit are presented in the following to indicate
the extent of the calculationsware sometimes adequate for a preliminary design.

14. A Hierarchical Approach to
Conceptual Process Design
1. Decide whether the process will be batch or
continuous
2. Identify the input-output structure of the
process
3. Identify and define the recycle structure of the
process
4. Identify and design the general structure of the
separation system
5. Identify and design the heat exchanger network
or process energy recovery system

15. Input Information
• Reactions and reaction conditions
• Desired production rate
• Desired product purity or some information
about price versus purity
• Raw materials and/or some information
about price versus purity
• Information of the rate of reaction
• Information of the rate of catalyst
deactivation

16. Input Information
• Any process constrains
• Other plant and site data
• Physical properties of all component
• Information concerning the safety, toxicity,
and environmental impact of the materials
involved in the process
• Cost data for by-products, equipment and
utilities

17. Reaction Information
• Stoichiometry of the participating reactions
- main reaction
- side reaction
• Thermal and other physical properties
• Heats of reaction and equilibrium data
• Rate of reaction relating it to composition,
temperature, pressures, catalysts, and so on
• Activity of the catalyst as a function of time
• Phase(s) of the reaction system

18. Reaction Information
• Catalyst deactivation and regeneration
• Some information on the product distribution
versus conversion
• Stability and controllability of the process
• Special considerations of heat and mass
transfer
• Corrosion and safety hazards

19. Bioethanol producion plant

20. Specific Design Data
• Required products: their compositions,
amount, purities, toxicities, temperatures,
pressures, monetary values.
• Maximum yield: numerous processes have
been designed to operate at the conditions of
maximum yield, but this operation often does
not correspond to the optimum economic
conversion

21. Specific Design Data
• Reaction: A B C where B is desired
product
B
A
C

22. Specific Design Data
• Selectivity:
and we refer to the conversion of A to C as a selectivity
loss

23. Specific Design Data
• Selectivity:
and we refer to the conversion of A to C as a selectivity
loss

24. Specific Design Data
• Raw materials costs and selectivity losses are the
dominant factors in the design of a process
•The optimum economic conversion is less than the
conversion corresponding to the maximum yield

25. Specific Design Data
• Production rate
- is fixed by the maximum size of one or more
pieces of equipment and marketing
considerations
• Product purity
- is normally is also fixed by marketing
considerations

26. Specific Design Data
• Raw materials: their compositions, amounts,
impurities, toxicities, temperatures, pressures,
monetary values, and all physical properties.
• Constraints: safety, material decomposition,
corrosive materials, etc.
• Any available existing plant data of similar
process.
• Local restrictions on means of disposal of
wastes.

27. Physical Property Data
• molecular weights, boiling points, vapor
pressures, heats of vaporization, heats of
reactions, liquid densities, and fugacity
coefficients (or equation of state).

28. Basic Engineering Data
• Characteristics and values of gaseous and
liquid fuels that to be used.
• Characteristics of raw makeup and
cooling tower waters, temperatures,
maximum allowable temperature, flow
rates available, and unit costs.

29. Basic Engineering Data
• Steam and condensate: mean pressures
and temperatures and their fluctuations
at each level, amount available, extent of
recovery of condensate, and unit costs.

30. Basic Engineering Data
• Electrical power: Voltages allowed for
instruments, lighting and various driver
sizes, transformer capacities, need for
emergency generator, unit costs.
• Compressed air: capacities and pressures
of plant and instrument air, instrument
air dryer.

31. Basic Engineering Data
• Plant site elevation.
• Soil bearing value, frost depth, ground
water depth, piling requirements,
available soil test data.

32. Basic Engineering Data
• Climate data: Winter and summer
temperature extreme, cooling tower
drybulb temperature, air cooler design
temperature, strength and direction of
prevailing winds rain and snowfall
maxima in 1 hr and in 2 hr, earthquake
provision.

33. Basic Engineering Data
• Blowdown and flare: What may or may
not be vented to the atmosphere or to
ponds or to nature waters, nature of
required liquid, and vapor relief systems.
• Drainage and sewers: rainwater, oil,
sanitary.

34. Basic Engineering Data
• Building: process, pump, control
instruments, special equipment.
• Paving types required in different areas.
• Pipe racks: elevations, grouping, coding.
• Battery limit pressures and temperatures
of individual feed stocks and products.

35. Basic Engineering Data
• Codes: those governing pressure vessels,
other equipment, buildings, electrical,
safety, sanitation, and others.
• Miscellaneous: includes heater stacks,
winterizing, insulation, steam or
electrical tracing of lines, heat exchanger
tubing size standardization, instrument
locations.

36. A Hierarchical Approach to
Conceptual Process Design
1. Decide whether the process will be batch or
continuous
2. Identify the input-output structure of the
process
3. Identify and define the recycle structure of the
process
4. Identify and design the general structure of the
separation system
5. Identify and design the heat exchanger network
or process energy recovery system

37. Input-Output Structure
of the Flowsheet

38. Flowsheet Alternatives
Process
Process
Product
By-product
Product
By-product
Feed
streams
Feed
streams
Purge

39. Structure Consideration
• Should we purify the feed streams before
they enter the process?
• Should we remove or recycle a reversible by-
product?
• Should we use a gas recycle and purge
stream?
• Should we not bother to recover and recycle
some reactants?

40. Structure Consideration
• How many product streams will there be?
• What are the design variables for the input-
output structure, and what economic trade-offs
are associated with these variables?

41. Purification of Feed
• If a feed impurity is not inert, remove it.
• If an impurity is present in a gas feed stream,
as a first guess process the impurity.
• If an impurity in a liquid feed stream is a
product or by-product, usually feed the process
through the separation system.
• If an impurity is present in large amounts,
remove it.

42. Purification of Feed
• If an impurity is present as an azeotrope with a
reactant, process the impurity.
• If a feed impurity is an inert, but is easier to
separate from the product and by-product than
from the feed, it is better to process the impurity.
• If a feed impurity is a catalyst poison, remove it.
If we not certain that our decision is correct, we
list the opposite decision as a process
alternative.

43. Recover or Recycle Reversible
By-products
• Should we recycle the reversible by-products
or should we remove it?
• Example
Toluene + H2 Benzene + CH4
2Benzene Diphenyl + H2

44. Gas Recycle and Purge
• If we have a “light” reactant and either a
“light” feed impurity or a “light” by-product
produced by a reaction, it used to be common
practice to use a gas recycle and a purge stream
for the first design.
• We define a light component as one which
boils lower than propylene (-55 F, -48 C).

45. Do Not Recover and Recycle Some
Reactants
• For example, water and air are much less
valuable than organic ones, we normally do not
bother to recover and recycle unconverted
amounts of these components.
• Often we feed them as an excess to try to
force some more valuable reactant to complete
conversion.

46. Destination Codes and Component
Classifications
Vent Gaseous by-products and
feed impurities
Recycle and purge Gaseous reactants plus inert
gases and/or gaseous by-product
Recycle Reactants, reaction intermediates
Azeotropes with reactants (sometimes)
Reversible by-product (sometimes)
None Reactants-if complete conversion or
unstable reaction intermediates
Excess-vent Gaseous reactant not recovered and
recycled

47. Destination Codes and Component
Classifications
Excess-waste Liquid reactant not recovered and
recycled
Primary product Primary product
Valuable by-product Separate destination for different
by- products
Fuel By-products to fuel
Waste Byproduct to waste treatment

48. Number of Product Streams
• List all the components that are expected to
leave the reactor.
• Classify each component in the list and assign
destination code to each.
• Order the components by their normal boiling
points.
• Group neighboring components with the
same destination.

49. Number of Product Streams
• Example 1

50. Number of Product Streams
• Example 2: Hydroalkylation (HDA) of toluene
to produce benzene
Process
Benzene
Diphenyl
H2, CH4
Purge: H2, CH4
Toluene

51. Evaluation of Flowsheet
• Be certain that all by-products and impurities
leave the process!

52. Process Alternative
• If we are not certain that our decision is
correct, we list the opposite decision as a
process alternative.

53. Overall Material Balances
• Start with specified production rate.
•From the stoichiometry find the by-product
flows and the reaction requirements.
• Calculate the impurity inlet and outlet flows
for the feed streams where the reactants are
completely recovered and recycled.

54. Overall Material Balances
• Calculate the outlet flows of reactants in
terms of a specified amount of excess for
streams where the reactants are not recovered
and recycled.
• Calculate the inlet and outlet flows for the
impurities entering with the reactant stream in
step 4.

55. Overall Material Balances
• Example: See the accompanied sheet for HDA
process

56. Stream
Table
• Example: Stream table

57. Economic Potential (EP)
• EP = Product Value + By-Product Value
- Raw Material Cost
• Economic potential is a cost per year basis
(annual cost)
• EP for HDA example would be
EP = Bezene Value + Fuel Value of Diphenyl
+ Fuel Value of Purge – Toluene Cost
- Makeup Gas Cost

58. Economic Potential (EP)
• Example: HDA process

59. Economic Potential (EP)
• Example: HDA process

60. Process Synthesis: 5Ms CONCEPT

65. HEALTH AND SAFETY HAZARDS
Layers of Protection in Process Plant
ALARMS
SIS
RELIEF
CONTAINMENT
EMERGENCY RESPONSE
BPCS
Strength in Reserve
• BPCS - Basic process control
• Alarms - draw attention
• SIS - Safety interlock system to
stop/start equipment
• Relief - Prevent excessive
pressure
• Containment - Prevent
materials from reaching,
workers, community or
environment
• Emergency Response -
evacuation, fire fighting,
health care, etc.
A
U
T
O
M
A
T
I
O
N

66. SAFETY STRENGTH IN DEPTH !
PROCESS
RELIEF SYSTEM
SAFETY INTERLOCK
SYSTEM
ALARM SYSTEM
BASIC PROCESS
CONTROL SYSTEM
Closed-loop control to maintain process
within acceptable operating region
Bring unusual situation to attention
of a person in the plant
Stop the operation of part of process
Divert material safely
Seriousness of
event
Four
independent
protection
layers (IPL)
In automation
Key Concept in process Safety: REDUNDANCY

67. 1. Safety
2. Environmental Protection
3. Equipment Protection
4. Smooth Operation &
Production Rate
5. Product Quality
6. Profit
7. Monitoring & Diagnosis
Important
Objectives of Process Control

68. • First line of defense
• Process control maintains variables at set points, which are fixed at
some desired values
• Technology - Multiple PIDs, cascade, feedforward, etc.
• Guidelines
• Always control unstable variables (Examples in flash?)
• Always control “quick” safety related variables
Stable variables that tend to change quickly (Examples?)
• Monitor variables that change very slowly
Corrosion, erosion, build up of materials
• Provide safe response to critical instrumentation failures
- But, we use instrumentation in the BPCS?
Basic Process Control System (BPCS)

69. F1
Where could we use BPCS in the flash process?

70. The level is unstable;
it must be controlled.
The pressure will change
quickly and affect safety;
it must be controlled.
F1

71. • Alarm has an anunciator and visual indication
- No action is automated!
- require analysis by a person - A plant operator must
decide.
• Digital computer stores a record of recent alarms
• Alarms should catch sensor failures
- But, sensors are used to measure variables for alarm
checking?
Alarm System

72. • Common error is to design too many alarms
- Easy to include; simple (perhaps, incorrect) fix to prevent repeat of
safety incident
- One plant had 17 alarms/h - operator acted on only 8%
• Establish and observe clear priority ranking
- HIGH = Hazard to people or equip., action required
- MEDIUM = Loss of RM, close monitoring required
- LOW = investigate when time available
Alarm System

73. 73
F1
Where could we use alarm in the Flash Process ?

74. 74
A low level could
damage the pump; a
high level could allow
liquid in the vapor
line.
The pressure affects
safety, add a high alarm
F1
PAH
LAH
LAL
Too much light key could
result in a large
economic loss
AAH