Plant Design and Economics

Lecture One
General design considerations
❖ This course assists chemical engineering students
in making the shift from solving well-posed
problems of a specific subject to integrating all the
subject/knowledge acquired in their undergraduate
education for solving open-ended process
problems.
❖ Plant design is an integration or assembly of all
knowledge you gained from your undergraduate
education as a chemical engineer.
❖ Plant design generally includes all engineering
aspects involved in the development of a new,
modified, or expanded industrial plant.
Introduction
Aim of chemical engineering design
✓ Construction of a new chemical plant
✓ Expansion of the existing plant to increase productivity
✓ Modification of the existing plant to change the production or the
way of the production process
▪ Chemical Engineering design of a new and the expansion or
modification of the existing chemical processes requires the
use of engineering principles and theories combined with a
practical realization of the limits imposed by environmental,
safety, and health concerns.
▪ A successful chemical engineer needs a full understanding
of the fundamental sciences and related engineering
subjects: material and energy balances, thermodynamics,
reaction kinetics, heat and mass transfer, and computer
technology.
▪ The engineer must also apply this knowledge to practical
situations for solving the problem of society.
▪ Plant design project involves different skills: research,
market analysis, equipment design, cost estimation,
computer programming, and plant location surveys.
▪ A plant design project is accomplished by passing through a
series of stages as shown below:
1. Inception: launching/ introducing
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: identifying location
7. Erection: plant construction
8. Startup and trial runs: sample production
9. Production: main production
Design
Design is a creative activity, it is a synthesis or collecting of ideas
together to achieve the desired purpose.
➢ It can be also defined as “the creation of a manufacturing process
to fulfill a particular need”. The need may be a public or a
commercial opportunity.
❖ Design is generally a construction of a system or an object
according to a plan or specifications.
❖ Process Design: refers to the real design of the equipment and
facilities necessary for providing the desired products and
services.
➢ Process design includes paper prepared before implementation:
flow sheets, material & energy balance, major specifications
sheets, materials of construction of all necessary process
equipment, and the general arrangement of the required
equipment, etc.
➢ The process design is the base for plant design.
❖ Plant Design: includes items related directly to the complete
plant, such as plant layout, general service facilities, and plant
location.
➢ Process design is intended to include: steps
1. Creating idea and flowsheet development.
2. Process material and heat balances.
3. Auxiliary services or utility requirements.
4. Chemical Engineering performance design for specific items of
equipment required for a flow sheet.
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 a qualified vendor.
General design considerations
❑ The development of the overall design involves many different design
considerations. Factors that should be considered are:
✓ Environmental protection and the safety and health of living things and
the community.
✓ Other factors that affect the profitability of a plant design include plant
location, plant layout, plant operation & control, utility requirements,
structural design, storage and buildings, materials handling, and patent
considerations.
➢ Failure of these considerations in the design may, in many
instances, harshly affect the entire economic situation, and make
the project unprofitable.
a. Environmental protection
▪ Because of the greater concern for the continued degradation of the
environment, the Environmental Protection Agency has systematically
been rewriting and tightening many policies and regulations.
▪ The agency designed to protect the environment focused on the
removal of pollutants from gas, liquid, and solid waste streams.
▪ It is very clear that chemical engineers must be familiar in the latest
federal and state regulations involving environmental protection,
worker safety, and health.
▪ This requirement is especially great for engineers in design-related
functions, such as capital cost estimating, process and equipment
design, and plant layout.
b. Safety and health hazards
▪ The potential health hazard of a material used in any chemical
process to an individual is depend on the toxicity nature of the
material and the frequency and duration of exposure.
▪ There are short-term and long-term effects of the material.
▪ A highly toxic material that causes immediate injury is classified as
a safety hazard while a material whose effect is apparent only after
long exposure is considered as an industrial health and hygiene
hazard.
▪ Both the acceptable limits and the protections to be taken to ensure
that such limits will not be exceeded are quite different for these two
classes of toxic materials.
c. Loss prevention
▪ “Loss prevention” in the chemical industry is an insurance and
“Loss” generally represents the financial loss associated with an
accident. This loss signifies:
✓ the cost of repairing or replacing the damaged facility
✓ taking care of all damage claims
✓ the loss of earnings from lost production during the repair
period and any associated lost sales opportunities.
▪ The process designer must be aware of these hazards and ensure
that the risks involved with these hazards are reduced to acceptable
levels through the application of engineering principles and proven
engineering practices.
▪ Loss prevention in process design can be summarized
under the following broad headings:
1. Identification and assessment of the major hazards.
2. Control of the hazards by the most appropriate means, for
example, inhibition, substitution, improved maintenance, etc.
3. Control of the process, i.e., prevention of hazardous
conditions in a process operating variables by utilizing
automatic control, interlocks, alarms, etc.
4. Limitation of the loss when an incident occurs.
d. Plant location
▪ The geographic location of a final plant can have a strong
influence on the success of an industrial project.
▪ Considerable care must be taken in selecting the plant site.
❑ A Plant should be located where:
➢ Transportation cost (RM & distribution cost of the product) and
production cost is minimum.
➢ Area for expansion and plant operation is safe for the
environment, the surrounding community and other living
things.
The following factors should be considered in selecting a plant site:
1. Raw materials: transportation cost
2. Energy availability: Power and steam requirements
3. Markets: to reduce the cost and time of product distribution
4. Climate: cooling towers/air conditioner for hot areas
5. Transportation facilities: Water, railroads, and highways
6. Water supply: as a raw material & for other purposes
7. Waste disposal
8. Labor supply: skilled and ethical workers
9. Taxation and legal restrictions
10. Site characteristics: topography & soil structure of the land
11. Flood and fire protection
12. Community factors
e. Plant layout
▪ After the process flow diagram are completed and before detailed
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 to
mitigate 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.
▪ Proper layout includes arrangement of processing areas, storage
areas, and handling areas in efficient coordination regarding the
following factors:
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. Economic distribution of utilities and services
5. Type of buildings required and building code requirements
6. Health and safety considerations
7. Waste disposal requirements
8. Auxiliary/ supporting equipment
9. Space available and space required
10. Roads and railroads
11. Possible future expansions
f. Plant operation and control
▪ In the design of an industrial plant, the methods which will be
used for plant operation and control helps to determine many of
the design variables. For example, the extent of instrumentation
can be a factor in choosing the type of process and setting the
labor requirements.
▪ NB: maintenance work will be necessary to keep the installed
equipment and facilities in good operating condition.
▪ The engineer must recognize the importance of such factors
which are directly related to plant operation and control and must
take them into proper account during the development of a
design.
g. Utilities
1) Electricity
▪ In the chemical industries, power is supplied primarily in the form of
electrical energy.
▪ Agitators, pumps, hoists, blowers, compressors, and similar equipment
are usually operated by electric motors,
▪ When a designer setting up the specifications for a new plant, must
decide whether to use purchased power or own power unit.
▪ E.g., It may be possible to obtain steam from the self-generation of
electricity for processing and heating purposes.
▪ Power can be transmitted in various forms: mechanical energy,
electrical energy, heat energy, and pressure energy.
▪ The engineer should recognize different methods for transmitting
power and must choose the best suited for a particular process.
2) Water
▪ Water used for industrial purposes can be obtained either from
plant's own source or from public supply.
▪ The plant is more economical if it uses its own water source.
▪ Such a source may be obtained from drilled wells, rivers, lakes,
dammed streams, or other impounded supplies.
▪ Before a company agrees to go ahead with any new project, it
must ensure a sufficient supply of water for all industrial, sanitary,
and safety demands, both present and future.
h. Structural Design
▪ A correct structural/foundation design of process industries with
allowances is necessary for heavy equipment and vibrating
machineries.
▪ The purpose of the foundation is to distribute the load so that
excessive or damaging settling will not occur.
▪ The type of foundation depends on the load involved and the
material on which the foundation acts.
▪ It is necessary to know the characteristics of the soil at a given
plant site before the structural design can be started.
▪ Corrosive effects of the process, cost of construction, and climatic
effects must be considered when choosing structural materials.
i. Storage
▪ Adequate storage facilities for raw materials, intermediate products,
final products, recycle materials, and fuels are essential to the
operation of a process plant. Adequate storage is necessary for:
▪ For temporary storage of the raw material
▪ For storage of intermediate products during plant shutdown or
emergency repairs
▪ For storage of final products to supply the customer even during a
plant difficulty or unexpected shutdown.
▪ To meet seasonal demands from steady production.
j. Materials Handling
▪ Materials-handling equipment is divided into continuous and batch
types, used for the handling of liquids, solids, and gases.
▪ Liquids and gases are handled by pumps and blowers in pipes,
waterfalls, and vessels; and in containers such as cylinders, and
tanks.
▪ However, Solids may be handled by conveyors, bucket elevators,
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 alternating nature of materials handling

▪ In general, the materials-handling equipment should be a

resistant material from any physical and chemical
damages like corrosion. The most difficult of these
hazards often is corrosion.
k. Patent considerations
▪ A patent is essentially a contract between an inventor and the
public. In consideration of full expose of the invention to the
public, the patentee is given exclusive rights to control the use
and practice of the invention.
▪ Although most large corporations have patent lawyers to
handle investigations of this type, the design engineer can be of
considerable assistance in determining if violations are
involved.
▪ An engineer, therefore, should have a working knowledge of
the basic practices and principles of patent law.