What is plant design?
Chemical engineering design of new chemical plants and
the expansion or revision of existing ones require the
use of engineering principles and theories combined
with a practical realization of the limits imposed by
industrial conditions. A successful chemical engineer
needs more than a knowledge and understanding of the
fundamental sciences and the related engineering
subjects such as thermodynamics, reaction kinetics, and
computer technology. The engineer must also have the
ability to apply this knowledge to practical situations for
the purpose of accomplishing something that will be
beneficial to society. The course title includes three
definitions namely:
Definition of design
1. Design: design is a creative activity and is defined
as the synthesis, the putting together of ideas to
achieve a desired purpose. Also it can be defined as
the creation of manufacturing process to fulfill a
particular need. The need may be public need or
commercial opportunity.
2. Process Design: Process design establishes the
sequence of chemical and physical
• operations; operating conditions; the duties, major
specifications, and materials of construction (where
critical) of all process equipment (as distinguished
from utilities and building auxiliaries); the general
arrangement of equipment needed to ensure
proper functioning of the plant; line sizes; and
principal instrumentation. The process design is
summarized by a process flowsheet.
Process Design Steps
1. Flowsheet development.
2. Process material and heat balances.
3. Auxiliary services material and heat balances
(utilities requirements).
4. Chemical engineering performance design for
specific items of equipments required for a
flowsheet.
5. Instrumentation as related to process performance.
6. Preparation of specifications (specification sheets) in
proper form for use by the project team as well as
for the purchasing function.
7. Evaluation of bids and recommendation of qualified
vendor.
3. Plant Design: includes items related directly to
the complete plant, such as plant layout, general
service facilities, and plant location.
Design Development Stages
Figure (2.1), The design process
The Design Objectives (The Need)
Chemical engineering projects can be divided into three
types:
A. New process development.
B. New production capacity to meet growing sales.
C. Modification and addition to existing plant.
In the design of a chemical process the need is the public
need for the product, the commercial opportunity as
foreseen by the sales and marketing organization.
Setting the Design Basis (Data Collection)
The most important step in starting a process design is
translating the customer need into a design basis. The design
basis is a more precise statement of the problem that is to be
solved. It will normally include the production rate and
purity specifications of the main product, together with
information on constraints that will influence the design,
such as:
1. Information on possible processes and the system
of units to be used.
2. The national, local or company design codes that
must be followed.
3. Details of raw materials that are available.
4. Information on potential sites where the plant
might be located, including climate data, seismic
conditions, and infrastructure availability.
5. Information on the conditions, availability, and
price of utility services such as fuel (gas), steam,
cooling water, process air, process water, and
electricity, that will be needed to run the process.
Generation of Possible Design Concepts (Solutions)
It is the creative part of the design process. This part
is concerned with the generation of possible
solutions for analysis, evaluation, and selection
(ways of meeting objective problems).
Source of solutions:
a- Past experiences.
b- Tried and tested methods.
Build Performance Model and Fitness Testi
When design alternatives are suggested, they must be
tested for fitness of purpose. In other words, the
design engineer must determine how well each
design concept meets the identified need. In the
field of chemical engineering, it is usually
prohibitively expensive to build several designs to
find out which one works best (a practice known as
“prototyping” which is common in other
engineering disciplines). Instead, the design
engineer builds a mathematical model of the
process, usually in the form of computer simulations
of the process, reactors, and other key equipment.
In some cases, the performance model may include
a pilot plant or other facility for predicting plant
performance and collecting the necessary design
data.
The design engineer must assemble all of the information
needed to model the process so as to predict its
performance against the identified objectives. For process
design this will include information on possible processes,
equipment performance, and physical property data.
If the necessary design data or models do not exist, then
research and development work is needed to collect the
data and build new models. Once the data has been
collected and a working model of the process has been
established, then the design engineer can begin to
determine equipment sizes and costs. At this stage it will
become obvious that some designs are uneconomical and
they can be rejected without further analysis. From this
step a few candidate designs that meet the customer
objective are identified.
Economic Evaluation, Optimization, and Selection
Once the designer has identified a few candidate
designs that meet the customer objective, then the
process of design selection can begin. The primary
criterion for design selection is usually economic
performance, although factors such as safety and
environmental impact may also play a strong role.
The economic evaluation usually entails analyzing
the capital and operating costs of the process to
determine the return on investment.
The economic analysis of the product or process
can also be used to optimize the design. Every
design will have several possible variants that make
economic sense under certain conditions. For
example, the extent of process heat recovery is a
tradeoff between the cost of energy and the cost
of heat exchangers (usually expressed as a cost of
heat exchange area). In regions where energy costs
are high, designs that use a lot of heat exchange
surface to maximize recovery of waste heat for
reuse in the process will be attractive. In regions
where energy costs are low, it may be more
economical to burn more fuel and reduce the
capital cost of the plant.
When all of the candidate designs have been
optimized, the best design can be selected. Very
often, the design engineer will find that several
designs have very close economic performance, in
which case the safest design or that which has the
best commercial track record will be chosen. At the
selection stage an experienced engineer will also
look carefully at the candidate designs to make
sure that they are safe, operable, and reliable, and
to ensure that no significant costs have been
overlooked.
Detailed Design and Equipment Selection
Here the detailed specifications of equipment such as
vessels, exchangers, pumps, and instruments are
determined. During the detailed design stage there
may still be some changes to the design, and there
will certainly be ongoing optimization as a better idea
of the project cost structure is developed. The
detailed design decisions tend to focus mainly on
equipment selection though, rather than on changes
to the flowsheet. For example, the design engineer
may need to decide whether to use a Utube or a
floating-head exchanger, or whether to use trays or
packing for a distillation column.
Procurement, Construction, and Operation
When the details of the design have been finalized, the
equipment can be purchased and the plant can be built.
Procurement and construction are usually carried out by an
EPC firm (Engineering, Procurement, and Construction)
unless the project is very small. Because they work on many
different projects each year, the EPC firms are able to place
bulk orders for items such as piping, wire, valves, etc., and
can use their purchasing power to get discounts on most
equipment. The EPC companies also have a great deal of
experience in field construction, inspection, testing, and
equipment installation. They can therefore normally
contract to build a plant for a client cheaper (and usually
also quicker) than the client could build it on its own. Finally,
once the plant is built and readied for startup, it can begin
operation. The design engineer will often then be called
upon to help resolve any startup issues and teething
problems with the new plant.
Flowsheeting (special language conveying
information)
Process design normally starts with a process
scheme (flowsheet). The flowsheet is the key
document or road map in process design. It's
a diagrammatic model of the process
describe the process steps in a proper
sequence using symbols to represent the
various components (equipment, lines, and
control instrumentation) that make up the
unit.
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The Flowsheet Importance
Shows the arrangement of the equipment
selected to carry out the process.
Shows the streams concentrations, flow rates &
compositions.
Shows the operating conditions.
During plant start up and subsequent
operation, the flow sheet from a basis for
comparison of operating performance with
design. It's also used by operating personnel for
the preparation of operating manual and
operator training.
Flowsheet Presentation
1- Block diagram
• Represent the process in a simplified form.
• No details involved.
• Don’t describe how a given step will be
achieved.
• When is it used?
• In survey studies.
• Process proposal for packaged steps.
• Talk out a processing idea.
Figure (2.2), Block diagram
2- Pictorial Flow Sheet
The equipments are normally drawn in a stylized
pictorial form. For tender documents or company
brochures actual scale drawing of the equipment are
sometimes used.
Types of pictorial flowsheets
a) Process Flow Diagram (PFD)
A PFD is a simplified flow diagram of a single process
unit, a utility unit, a complete process module. The
purpose of a PFD is to provide a preliminary
understanding of the process system indicating only
the main items of equipment, the main pipelines and
the essential instruments, switches and control valves.
A PFD also indicates operating variables, such as mass
flow, temperatures and pressures, which are tabulated
at various points in the system.
The PFD is a document containing information on:
•Process conditions and physical data of the main
process streams.
•Main process equipment with design data.
•Main Process lines.
•Mass (material) balance.
•Heat balance (if applicable).
NOTE: If the PFD doesn’t contain any data about the
flow rates, it is called a qualitative flowsheet, while if
the flow rates are involved the PFD is called a
combined flowsheet in which qualitative information
and quantitative data are combined on the basis of
one flowsheet.
b) Piping and Instrumentation Diagram (P & ID)
(mechanical flow diagram)
A P&ID diagram shows the arrangement of the process
equipment, piping, pumps, instruments, valves and
other fittings. It should include:
• All process equipment identified by an equipment
number.
• All pipes identified by a line size, material code and
line number.
• All valves with an identified size and number.
• Fittings.
• All pumps identified by a suitable code number.
• All control loops and instruments.
c) Utility Flowsheet (Process Engineering Utility
Flow Diagram (PEUFD))
Used to summarize and detail the interrelationship of
utilities such as air, water (various types), steam
(various types), heat transfer mediums, process vents
and purges, safety relief blow-down, etc., to the basic
process. The amount of detail is often too great to
combine on other sheets, so separate sheets are
prepared.
The PEUFD is a document containing information on:
Main distribution or arrangement of each individual
utility system, expect electrical systems.
PEUFD Function:
The PEUFD shall state characteristics and
consumption figures of the particular utility
concerned, cooling water, fire water, drinking
water, steam, plant air, instrument air, fuel oil/gas,
inert gas and similar utilities.
d) Process Safeguarding Flow Diagram (PSFD)
The PSFD is a document highlighting information
on:
Types and levels of protection offered by the
devices installed and their inter relation to
demonstrate the plant’s safety.
The P&ID contains all information required
for a PSFD; however, the PSFD highlights
protection in case of extreme conditions and
measures to be taken to safeguard personnel
and environment.
Note: In general these schemes will only be
made for complex installations like offshore
process platforms. For simple applications
the information shown on the P&ID is usually
sufficient to highlight safety devices and
aspects.
• What is meant by the following
identifications? PFD, P&ID, PEUFD and
• PSFD State the information you can get from
the following schemes: PFD, P&ID, PEUFD and
PSFD?
Figure (2.3), PFD [Qualitative flow diagram for the manufacture of nitric acid by the
ammonia-oxidation process]
Figure (2.4), PFD [Combined flow diagram for the manufacture of nitric acid by the
ammonia-oxidation process]
Figure (2.5), Process and Instrument Diagram (P&ID)
Figure (2.6), Typical utility flow diagram
Figure (2.7), Engineering P&I flowsheet of the reaction section of plant for dealkylation of
benzene
Flowsheet Symbols
To reduce detailed written descriptions on flowsheets, it
is usual practice to develop or adopt a set of symbols
and codes which suit the purpose. Many symbols are
pictorial which is helpful in representing process as well
as control and mechanical operations. See Fig. (2.8).
Line Symbols and Designation
The two types of lines on a flowsheet are (1) those
representing outlines and details of equipment,
instruments, etc., and (2) those representing pipe
carrying process or utility liquids, solids, or vapors and
electrical or instrument connections. The latter must be
distinguished among themselves as suggested by Fig.
(2.9).
The usual complete line designation contains the
following: (1) line size (nominal); (2) material cod; (3)
sequence number; and (4) materials of construction.
Examples: 2"-CL6-CS40 3"-CL6a-CS40
Equipment Designation
Equipment code designations can be developed to
suit the particular process, or as is customary a
master coding can be established and followed for all
projects. A suggested designation list (not all
inclusive for all processes) for the usual process plant
equipment is given in Table (2.1). The various items
are usually numbered by type and in process flow
order as set forth on the flowsheets. For example:
Item code
• S-1
• S-2
• C-1
Designation
First separator in a processs
Second separator in a process
First compressor in a process
Figure (2.8.a), Flowsheet symbols.
Figure (2.9), Line symbols.
Types of Designs
The methods for carrying out a design project
may be divided into the following classifications,
depending on the accuracy and detail required:
Preliminary or quick-estimate designs
Used as a basis for determining whether further
work should be done on the proposed process.
This type of 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.
Detailed-estimate designs
In this type of design, the cost and profit potential
of an established process is determined by
detailed analysis and calculations. However, exact
specifications are not given for the equipment,
and drafting-room work is minimized. The
following factors should be established within
narrow limits before a detailed-estimate design is
developed:
• Manufacturing process
• Material and energy balances
• Temperature and pressure ranges
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Raw-material and product specifications
Yields, reaction rates, and time cycles
Materials of construction
Utilities requirements
Plant site
i.e. the above factors should be determined
after a preliminary design.
Before proceeding any further with the
development of a process design and its
associated economics, it will be desirable to
consider an overall view of the various functions
involved in a complete plant design. Particular
emphasis in this discussion will be placed on
important health, safety, loss prevention, and
environmental considerations. Other items that
will be noted briefly include plant location, plant
layout, plant operation and control, utilities,
structural design, storage, materials handling,
patents, and legal restrictions.
I. Plant Location
The geographical location of the final plant can
have strong influence on the success of an
industrial venture. Considerable care must be
exercised in selecting the plant site, and many
different factors must be considered. Primarily,
the plant should be located where the minimum
cost of production and distribution can be
obtained, but other factors, such as room for
expansion and safe living conditions for plant
operation as well as the surrounding community,
are also important.
A general consensus as to the plant location
should be obtained before a design project
reaches the detailed estimate stage, and a firm
location should be established upon completion
of the detailed-estimate design. The choice of the
final site should first be based on a complete
survey of the advantages and disadvantages of
various geographical areas and, ultimately, on the
advantages and disadvantages of available real
estate. The following factors should be considered
in selecting a plant site:
1. Raw materials availability
2. Markets
3. Energy availability
4. Climate
5. Transportation facilities
6. Water supply
7. Waste disposal
8. Labor supply
9. Taxation and legal restrictions
10. Site characteristics
11. Flood and fire protection
12. Community factors
The factors that must be evaluated in a plant-location study
indicate the need for a vast amount of information, both
quantitative (statistical) and qualitative. Fortunately, a large
number of agencies, public and private, publish useful
information of this type greatly reducing the actual original
gathering of the data.
Raw materials availability: The source of raw materials is
one of the most important factors influencing the selection
of a plant site. This is particularly true if large volumes of
raw materials are consumed, because location near the raw
materials source permits considerable reduction in
transportation and storage charges. Attention should be
given to the purchased price of the raw materials, distance
from the source of supply, freight or transportation
expenses, availability and reliability of supply, purity of the
raw materials, and storage requirements.
Markets: The location of markets or intermediate distribution
centers affects the cost of product distribution and the time
required for shipping. Proximity to the major markets is an
important consideration in the selection of a plant site, because
the buyer usually finds it advantageous to purchase from nearby
sources. It should be noted that markets are needed for byproducts as well as for major final products.
Energy availability: Power and steam requirements are high in
most industrial plants, and fuel is ordinarily required to supply
these utilities. Consequently, power and fuel can be combined as
one major factor in the choice of a plant site.
Electrolytic processes require a cheap source of electricity, and
plants using electrolytic processes are often located near large
hydroelectric installations. If the plant requires large quantities of
coal or oil, location near a source of fuel supply may be essential
for economic operation. The local cost of power can help
determine whether power should be purchased or selfgenerated.
Climate: If the plant is located in a cold climate,
costs may be increased by the necessity for
construction of protective shelters around the
process equipment, and special cooling towers or
air-conditioning equipment may be required if
the prevailing temperatures are high. Excessive
humidity or extremes of hot or cold weather can
have a serious effect on the economic operation
of a plant, and these factors should be examined
when selecting a plant site.
Transportation facilities: Water, railroads, and highways
are the common means of transportation used by major
industrial concerns. The kind and amount of products and
raw materials determine the most suitable type of
transportation facilities. In any case, careful attention should
be given to local freight rates and existing railroad lines. The
proximity to railroad centers and the possibility of canal,
river, lake, or ocean transport must be considered: Motor
trucking facilities are widely used and can serve as a useful
supplement to rail and water facilities. If possible, the plant
site should have access to all three types of transportation,
and, certainly, at least two types should be available. There
is usually need for convenient air and rail transportation
facilities between the plant and the main company
headquarters, and effective transportation facilities for the
plant personnel are necessary.
Water supply: The process industries use large quantities
of water for cooling, washing, steam generation, and as a
raw material. The plant, therefore, must be located where a
dependable supply of water is available. A large river or lake
is preferable, although deep wells or artesian wells may be
satisfactory if the amount of water required is not too great.
The level of the existing water table can be checked by
consulting the state geological survey, and information on
the constancy of the water table and the year-round
capacity of local rivers or lakes should be obtained. If the
water supply shows seasonal fluctuations, it may be
desirable to construct a reservoir or to drill several standby
wells. The temperature, mineral content, silt or sand
content, bacteriological content, and cost for supply and
purification treatment must also be considered when
choosing a water supply.
Waste disposal: In recent years, many legal
restrictions have been placed on the methods for
disposing of waste materials from the process
industries. The site selected for a plant should
have adequate capacity and facilities for correct
waste disposal. Even though a given area has
minimal restrictions on pollution, it should not be
assumed that this condition will continue to exist.
In choosing a plant site, the permissible tolerance
levels for various methods of waste disposal
should be considered carefully, and attention
should be given to potential requirements for
additional waste-treatment facilities.
Labor supply: The type and supply of
labor available in the vicinity of a
proposed plant site must be examined.
Consideration should be given to
prevailing pay scales, restrictions on
number of hours worked per week,
competing industries that can cause
dissatisfaction or high turnover rates
among the workers, and variations in
the skill and productivity of the workers.
Taxation and legal restrictions: State and local tax
rates on property income, unemployment
insurance and similar items vary from one location
to another. Similarly, local regulations on zoning,
building
codes,
nuisance
aspects,
and
transportation facilities can have a major influence
on the final choice of a plant site.
In fact, zoning difficulties and obtaining the many
required permits can often be much more
important in terms of cost and time delays than
many of the factors discussed in the preceding
sections.
Site characteristics: The characteristics of the
land at a proposed plant site should be
examined carefully. The topography of the tract
of land and' the soil structure must be
considered, since either or both may have a
pronounced effect on construction costs. The
cost of the land is important, as well as local
building costs and living conditions. Future
changes may make it desirable or necessary to
expand the plant facilities. Therefore, even
though no immediate expansion is planned, a
new plant should be constructed at a location
where additional space is available.
Flood and fire protection: Many industrial plants
are located along rivers or near large bodies of
water, and there are risks of flood or hurricane
damage. Before selecting a plant site, the regional
history of natural events of this type should be
examined and the consequences of such
occurrences considered. Protection from losses by
fire is another important factor in selecting a plant
location. In case of a major fire, assistance from
outside fire departments should be available. Fire
hazards in the immediate area surrounding the plant
site must not be overlooked.
Community factors: The character and facilities of a
community can have quite an effect on the location
of the plant. If a certain minimum number of facilities
for satisfactory living of plant personnel do not exist,
it often becomes a burden for the plant to subsidize
such facilities. Cultural facilities of the community are
important to sound growth. Churches, libraries,
schools, civic theaters, concert associations, and
other similar groups, if active and dynamic, do much
to make a community progressive. The problem of
recreation deserves special consideration. The
efficiency, character, and history of both state and
local government should be evaluated. The existence
of low taxes is not in itself a favorable situation unless
the community is already well developed and
relatively free of debt.
Selection of the Plant Site
The major factors in the selection of most plant
sites are (1) raw materials, (2) markets, (3) energy
supply, (4) climate, (5) transportation facilities, and
(6) water supply. For a preliminary survey, the first
four factors should be considered. Thus, on the
basis of raw materials, markets, energy supply, and
climate, acceptable locations can usually be
reduced to one or two general geographical
regions. For example, a preliminary survey might
indicate that the best location for a particular plant
would be in the south-central or south-eastern
part of the United States.
In the next step, the effects of transportation facilities and
water supply are taken into account. This permits reduction
of the possible plant location to several general target areas.
These areas can then be reduced further by considering all
the factors that have an influence on plant location.
As a final step, a detailed analysis of the remaining sites can
be made. Exact data on items such as freight rates, labor
conditions, tax rates, price of land, and general local
conditions can be obtained. The various sites can be
inspected and appraised on the basis of all the factors
influencing the final decision. Many times, the advantages of
locating a new plant on land or near other facilities already
owned by the concern that is building the new plant
outweigh the disadvantages of the particular location. In any
case, however, the final decision on selecting the plant site
should take into consideration all the factors that can affect
the ultimate success of the overall operation.
II. Plant Layout
After the process flow diagrams are completed and
before detailed piping, structural, and electrical design
can begin, the layout of process units in a plant and
the equipment within these process units must be
planned. This layout can play an important part in
determining construction and manufacturing costs,
and thus must be planned carefully with attention
being given to future problems that may arise. Since
each plant differs in many ways and no two plant sites
are exactly alike, there is no one ideal plant layout.
However, proper layout in each case will include
arrangement of processing areas, storage areas, and
handling areas in efficient coordination and with
regard to such factors as:
• 1. New site development or addition to previously
developed site
• 2. Type and quantity of products to be produced
• 3. Type of process and product control
• 4. Operational convenience and accessibility
• 5. Economic distribution of utilities and services
• 6. Type of buildings and building-code requirements
• 7. Health and safety considerations
• 8. Waste-disposal requirements
• 9. Auxiliary equipment
• 10. Space available and space required
• 11. Roads and railroads
• 12. Possible future expansion
Preparation of the Layout
• Scale drawings, complete with elevation
indications can be used for determining the
best location for equipment and facilities.
Elementary layouts are developed first. These
show the fundamental relationships between
storage space and operating equipment. The
next step requires consideration of the safe
operational sequence and gives a primary
layout based on the flow of materials, unit
operations, storage, and future expansion.
By analyzing all the factors that are involved in
plant layout, a detailed recommendation can be
presented, and drawings and elevations,
including isometric drawings of the piping
systems, can be prepared.
Templates, or small cutouts constructed to a
selected scale, are useful for making rapid and
accurate layouts, and three-dimensional models
are often made. The use of such models for
making certain a proposed plant layout is correct
has found increasing favor in recent years.
III. Storage
Adequate storage facilities for raw materials,
intermediate products, final products, recycle
materials, off-grade materials, and fuels are essential
to the operation of a process plant. A supply of raw
materials permits operation of the process plant
regardless of temporary procurement or delivery
difficulties. Storage of intermediate products may be
necessary during plant shutdown for emergency
repairs while storage of final products makes it
possible to supply the customer even during a plant
difficulty or unforeseen shutdown. An additional
need for adequate storage is often encountered
when it is necessary to meet seasonal demands from
steady production.
Bulk storage of liquids is generally handled by closed
spherical or cylindrical tanks to prevent the escape of
volatiles and minimize contamination. Since safety is
an important consideration in storage-tank design,
the American Petroleum Institute? and the National
Fire Protection Association publish rules for safe
design and operation. Floating roof tanks are used to
conserve valuable products with vapor pressures
which are below atmospheric pressure at the storage
temperature. Liquids with vapor pressures above
atmospheric must be stored in vapor-tight tanks
capable of withstanding internal pressure. If
flammable liquids are stored in vented tanks, flame
arresters must be installed in all openings except
connections made below the liquid level.
Gases are stored at atmospheric pressure in wetor dry-seal gas holders. The wet-gas holder
maintains a liquid seal of water or oil between the
top movable inside tank and the stationary
outside tank. In the dry-seal holder the seal
between the two tanks is made by means of a
flexible rubber or plastic curtain. Recent
developments in bulk natural gas or gas-product
storage show that pumping the gas into
underground strata is the cheapest method
available.
High-pressure gas is stored in spherical or
horizontal cylindrical pressure vessels.
Solid products and raw materials are either stored
in weather-tight tanks with sloping floors or in
outdoor bins and mounds. Solid products are
often packed directly in bags, sacks, or drums.
IV. Materials Handling
Materials-handling equipment is logically divided into
continuous and batch types, and into classes for the handling of
liquids, solids, and gases. Liquids and gases are handled by
means of pumps and blowers; in pipes, flumes, and ducts; and
in containers such as drums, cylinders, and tank cars. Solids may
be handled by conveyors, bucket elevators, chutes, lift trucks,
and pneumatic systems. The selection of materials-handling
equipment depends upon the cost and the work to be done.
Factors that must be considered in selecting such equipment
include:
1. Chemical and physical nature of material being handled
2. Type and distance of movement of material
3. Quantity of material moved per unit time
4. Nature of feed and discharge from materials-handling
equipment
5. Continuous or intermittent nature of materials handling
The major movement of liquid and gaseous raw
materials and products within a plant to and from
the point of shipment is done by pipeline. Many
petroleum plants also transport raw materials and
products by pipeline. When this is done, local and
federal regulations must be strictly followed in the
design and specification of the pipeline.
Movement of raw materials and products outside of
the plant is usually handled either by rail, ship, truck,
or air transportation. Some type of receiving or
shipping facilities, depending on the nature of the
raw materials and products, must be provided in the
design of the plant. Information for the preparation
of such specifications can usually be obtained from
the transportation companies serving thearea.
In general, the materials-handling problems in
the chemical engineering industries do not differ
widely from those in other industries except that
the existence of special hazards, including
corrosion, fire, heat damage, explosion,
pollution, and toxicity, together with special
service requirements, will frequently influence
the design. Themost difficult of these hazards
often is corrosion. This is generally overcome by
the use of a high-first-cost, corrosion-resistant
material in the best type of handling equipment
or by the use of containers which adequately
protect the equipment.
Firm process designs or detailed designs
• When the detailed-estimate design indicates that
the proposed project should be a commercial
success, the final step before developing
construction plans for the plant is the preparation
of a firm process design. In this type complete
specifications are presented for all components of
the plant, without any change in the process
flowsheet and accurate costs based on quoted
prices are obtained. The firm process design
includes blueprints and sufficient information to
permit immediate development of the final plans
for constructing the plant.
Design Information (literature survey)
General information and specific data required to the
development of a design project can be obtained from
many different sources such as:
A. Textbooks
A large number of textbooks covering the various
aspects of chemical engineering principles and design
are available. In addition, many handbooks have been
published giving physical properties and other basic
data which are very useful to the design engineer. A
primary source of information on all aspects of
chemical engineering principles, design, costs, and
applications is “The Chemical Engineers’ Handbook”
published by McGraw-Hill Book Company with R. H.
Perry and D. W. Green as editors and Encyclopedia of
Chemical Technology by Kirk Othmer.
B. Technical journals
Regular features on design-related
aspects of equipment, costs, materials of
construction, and unit processes are
published in Chemical Engineering. In
addition to this publication, there are
many other periodicals that publish
articles of direct interest to the design
engineer. The following periodicals are
suggested as valuable sources of
information for the chemical engineer
who wishes to keep abreast of the latest
developments in the field:
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American Institute of Chemical Engineers journal (AICHE)
Chemical Engineering Progress
Chemical and Engineering News
Chemical Engineering Science
Industrial and Engineering Chemistry Fundamentals
Industrial and Engineering Chemistry Process Design and
Development
Journal of the American Chemical Society, Journal of
Physical Chemisty
Journal of the American Chemical Society
Hydrocarbon Processing
Oil and Gas Journal
Engineering News-Record
Canadian Journal of Chemical Engineering
C. Trade bulletins
Trade bulletins are published regularly by most
manufacturing concerns, and these bulletins give much
information of direct interest to the chemical engineer
preparing a design. Some of the trade-bulletin information is
condensed in an excellent reference book on chemical
engineering equipment, products, and manufacturers.
This book is known as the “Chemical Engineering Catalog”,
and contains a large amount of valuable descriptive material.
New information is constantly becoming available through
publication in periodicals, books, trade bulletins, government
reports, university bulletins, and many other sources. Many
of the publications are devoted to shortcut methods for
estimating physical properties or making design calculations,
while others present compilations of essential data in the
form of nomographs or tables. The effective design engineer
must make every attempt to keep an up-to-date knowledge
of the advances in the field.
D. Patents
A patent is essentially a contract between an inventor
and the public. In consideration of full disclosure of
the invention to the public, the patentee is given
exclusive rights to control the use and practice of
the invention. A patent gives the holder the power
to prevent others from using or practicing the
invention for a period of 17 years from the date of
granting. In contrast, trade secrets and certain types
of confidential disclosures can receive protection
under common-law rights only as long as the secret
information is not public knowledge. A new design
should be examined to make certain no patent
infringements are involved. If the investigation can
uncover even one legally expired patent covering
the details of the proposed process, the method can
be used with no fear of patent difficulties.
The Preliminary Design
In order to amplify the remarks made earlier
concerning the design-project procedure, it is
appropriate at this time to look more closely at a
specific preliminary design.
Only a brief presentation of the design will be
attempted at this point. However, sufficient detail
will be given to outline the important steps which
are necessary to prepare such a preliminary design.
The problem presented is a practical one of a type
frequently encountered in the chemical industry; it
involves both process design and economic
considerations.
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
research 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.
Literature Survey
A survey of the literature reveals that the majority of
the non biodegradable detergents are alkyl benzene
sulfonates (ABS). Theoretically, there are over 80,000
isomeric alkyl benzenes in the range of C10 to C15
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. Most of the schemes are
variations of the one shown in Fig. (11) for the
production of sodium dodecylbenzene sulfonate. A
brief description of the process is as follows:
This process involves:
i. Reaction of dodecene with benzene in the
presence of aluminum chloride catalyst
(alkylation)
ii. Fractionation of the resulting crude mixture to
recover the desired boiling range of
dodecylbenzene.
iii. Sulfonation of the dodecylbenzene.
iv. Neutralization of the sulfonic acid with caustic
soda.
v. Blending the resulting slurry with chemical
“builders”; and drying.
Process Description
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
percent), oleum (usually 20 percent SO3), 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 percent. 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
percent caustic soda solution to a pH of 8 at a
temperature of about 125°F. Chemical “builders”
such as trisodium phosphate, tetrasodium
pyrophosphate, sodium silicate, sodium chloride,
sodium sulfate, carboxymethyl 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.
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Chemical Process Simulators
This is a list of software used to simulate the material and energy balances of
chemical processing plants.
APMonitor Modeling Language
ASCEND
Aspen Plus, Aspen HYSYS, Aspen Custom Modeler by Aspen Technology
ASSETT, D-SPICE and K-Spice by Kongsberg Oil & Gas Technologies AS
CADSIM Plus by Aurel Systems Inc.
CHEMASIM, inhouse thermodynamical simulation program at BASF
CHEMCAD by Chemstations
COCO simulator
COMSOL Multiphysics
Design II for Windows by WinSim Inc.
Distillation Expert Trainer [1]
DWSIM (open-source)
EcosimPro
EMSO, the Environment for Modelling, Simulation and Optimisation from the ALSOC
Project
Dymola
FlowManager™ by FMC Technologies
GIBBSim
gPROMS by PSE Ltd
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INDISS by RSI
ICAS: Integrated Computer Aided System developed by CAPEC
IDEAS by Andritz Automation
ISE Simulator by VRTech
Jacobian (Numerica Technology)
LIBPF, the C++ LIBrary for Process Flowsheeting
Mobatec Modeller by Mobatec
OLGA by SPT Group (Scandpower)
Omegaland by Yokogawa
OpenModelica
PIPE-FLO Professional by Engineered Software, Inc.
PottersWheel Matlab toolbox to calibrate parameters in chemical reaction networks (free for
edu/academic usage)
Prode Sim, Properties
ProSimulator by Sim Infosystems
ProSimPlus by ProSim
Petro-SIM
PETROX
ProMax, TSWEET, and PROSIM by Bryan Research and Engineering
PRO/II,DYNSIM and ROMeo[1]ROMeo_(process_optimizer)
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RecoVR by VRTech
Sim42 by Raul Cota and others
SimCreate by TSC Simulation
Simulis by ProSim
SPEEDUP by Roger W.H. Sargent and students
SolidSim - flowsheet simulation of solids processes by
SolidSim Engineering GmbH
SuperPro Designer by Intelligen
SysCAD
System7 by Epcon International
UniSim Design & Shadow Plant by Honeywell
Usim Pac by Caspeo
VMGSim by Virtual Materials Group
Main principle
• Process flow diagram of a typical amine treating process
used in industrial plants
• Process simulation is a model-based representation of
chemical, physical, biological, and other technical processes
and unit operations in software. Basic prerequisites are a
thorough knowledge of chemical and physical properties[1]
of pure components and mixtures, of reactions, and of
mathematical models which, in combination, allow the
calculation of a process in computers.
• Process simulation software describes processes in flow
diagrams where unit operations are positioned and
connected by product or educt streams. The software has to
solve the mass and energy balance to find a stable operating
point. The goal of a process simulation is to find optimal
conditions for an examined process. This is essentially an
optimization problem which has to be solved in an iterative
process.
• Process simulation always use models which
introduce approximations and assumptions but
allow the description of a property over a wide
range of temperatures and pressures which
might not be covered by real data. Models also
allow interpolation and extrapolation - within
certain limits - and enable the search for
conditions outside the range of known
properties.
Modelling
• The development of models[2] for a better
representation of real processes is the core of the
further development of the simulation software.
Model development is done on the chemical
engineering side but also in control engineering
and for the improvement of mathematical
simulation techniques. Process simulation is
therefore one of the few fields where scientists
from chemistry, physics, computer science,
mathematics, and several engineering fields work
together.
• VLE of the mixture of Chloroform and Methanol
plus NRTL fit and extrapolation to different
pressures
• A lot of efforts are made to develop new and improved
models for the calculation of properties. This includes for
example the description of thermophysical properties like
vapor pressures, viscosities, caloric data, etc. of pure
components and mixtures properties of different
apparatuses like reactors, distillation columns, pumps, etc.
chemical reactions and kinetics environmental and safetyrelated data
• Two main different types of models can be distinguished:
• Rather simple equations and correlations where
parameters are fitted to experimental data.
• Predictive methods where properties are estimated.
• The equations and correlations are normally preferred
because they describe the property (almost) exactly. To
obtain reliable parameters it is necessary to have
experimental data which are usually obtained from factual
data banks[3][4] or, if no data are publicly available, from
measurements.
• Using predictive methods is much cheaper than
experimental work and also than data from data
banks. Despite this big advantage predicted
properties are normally only used in early steps of
the process development to find first approximate
solutions and to exclude wrong pathways because
these estimation methods normally introduce
higher errors than correlations obtained from real
data.
• Process simulation also encouraged the further
development of mathematical models in the fields
of numerics and the solving of complex problems
History
• The history of process simulation is strongly
related to the development of the computer
science and of computer hardware and
programming languages. First working simple
implementations of partial aspects of chemical
processes have been made in the 1970 where, for
the first time, suitable hardware and software
(here mainly the programming languages
FORTRAN and C) have been available. The
modelling of chemical properties has been started
already much earlier, notably the cubic equation
of states and the Antoine equation are
developments of the 19th century.
Steady state and dynamic process simulation
• Initially process simulation was used to simulate steady
state processes. Steady-state models perform a mass
and energy balance of a stationary process (a process in
an equilibrium state) but any changes over time had to
be ignored.
• Dynamic simulation is an extension of steady-state
process simulation whereby time-dependence is built
into the models via derivative terms i.e. accumulation of
mass and energy. The advent of dynamic simulation
means that the time-dependent description, prediction
and control of real processes in real time has become
possible. This includes the description of starting up and
shutting down a plant, changes of conditions during a
reaction, holdups, thermal changes and more.
• Dynamic simulations require increased calculation
time and are mathematically more complex than a
steady state simulation. It can be seen as a multiply
repeated steady state simulation (based on a fixed
time step) with constantly changing parameters.
• Dynamic simulation can be used in both an online
and offline fashion. The online case being model
predictive control, where the real-time simulation
results are used to predict the changes that would
occur for a control input change, and the control
parameters are optimised based on the results.
Offline process simulation can be used in the design,
troubleshooting and optimisation of process plant as
well as the conduction of case studies to assess the
impacts of process modifications.