Chemical Engineering Apparatus Design introduction

1. Chapter One
Introduction
By:
-Mohammed S.-
Chemical Engineering Apparatus
Design, ChEg4191
School of
Chemical Engineering
Jimma University
Jimma Institute of Technology

2. Introduction
 What is Chemical Process?
 Chemical Process is basically a method or a route through which we can convert raw
material to the desired product.
 What is Chemical Equipment?
 Chemical equipment is a place or a unit where the conversion process is carried out.
 What is Design?
 Design is a creative activity undertaken by an engineer.
 It is the synthesis, the putting together, of ideas to achieve a desired purpose.
 What is Equipment Design?
 Determination of the dimension of the equipment like internal structure and mechanical
parts, operating condition, etc. of that equipment is what we call equipment design.

3. Introduction …
 Process Design
 Establishes the sequence of chemical and physical operations; operating conditions;
the duties, major specifications, and materials of construction of all process equipment;
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 flow sheet, a material and energy
balance, and a set of individual equipment specifications.
 Stages for the Design of chemical process are:
 Conception and Definition (Design Objectives)
o Collection of data, physical properties
• Generation of possible Design
• Selection and evaluation (Optimization)
• Final design

4. NATURE OF DESIGN
 The design does not exist at the commencement of the project. The designer starts
with a specific objective in mind, a need, and by developing and evaluating
possible designs, arrives at what he considers the best way of achieving that
objective.
 When considering possible ways of achieving the objective the designer will be
constrained by many factors, which will narrow down the number of possible
designs.
 The constraints that are outside the designer's influence can be termed the external
constraints. These set the outer boundary of possible designs; as shown in Figure.
Within this boundary there will be a number of plausible designs bounded by the
other constraints, the internal constraints, over which the designer has some
control.

5. NATURE OF DESIGN…
 Economic considerations are
obviously a major constraint on any
engineering design: plants must make
a profit.
 Time will also be a constraint. The
time available for completion of a
design will usually limit the number
of alternative designs that can be
considered.

6. Design Objectives (the need)
 All design starts with a perceived need. In the design of a chemical process, the
need is the public need for the product, creating a commercial opportunity, as
foreseen by the sales and marketing organization.
 Within this overall objective, the designer will recognize sub-objectives, the
requirements of the various units that make up the overall process.
 Before starting work, the designer should obtain as complete, and as
unambiguous, a statement of the requirements as possible. It is important to
distinguish between the needs that are ‘‘must haves’’ and those that are ‘‘should
haves.’’

7. Setting the Design Basis and Data collection
 The most important step in starting a process design is translating the customer need in to
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.
 To proceed with a design, the designer must first assemble all the relevant facts and data
required. For process design this will include information on possible processes,
equipment performance, and physical property data.
 Many design organizations will prepare a basic data manual, containing all the process
"know-how" on which the design is to be based.

8. Generation of Possible Design Concepts
 The creative part of the design process is the generation of possible solutions to the
problem for analysis, evaluation, and selection. In this activity, most designers largely rely
on previous experience—their own and that of others. It is doubtful if any design is
entirely novel.
 Experienced engineers usually prefer the tried-and-tested methods, rather than possibly
more exciting but untried novel designs.
 Projects in chemical engineering, which requires designing is divided in to three types:
 Modifications, and additions, to existing plant; usually carried out by the plant design group.
 Increasing capacity or New production capacity to meet growing sales demand and the sale of
established processes by contractors; Repetition of existing designs, with only minor design
changes
 New processes, developed from laboratory research, through pilot plant, to a commercial
process. Even here, most of the unit operations and process equipment will use established
designs.

9. Selection and Evaluation (Optimization)
 The designer starts with the set of all possible solutions bounded by the external
constraints, and by a process of progressive evaluation and selection, narrows
down the range of candidates to find the "best" design for the purpose.
 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 selection process can be considered to go through the following stages:
 Possible designs (credible) - within the external constraints.
 Plausible designs (feasible) - within the internal constraints.
 Probable designs - likely candidates.
 Best design (optimum) -judged the best solution to the problem.

10. THE ANATOMY OF A CHEMICAL MANUFACTURING PROCESS
 The basic components of a typical chemical process are shown in Figure, in
which each block represents a stage in the overall process for producing a
product from the raw materials.
 Chemical engineering design is concerned with the selection and arrangement
of the stages and the selection, specification, and design of the equipment
required to perform the function of each stage.
Anatomy of a chemical process

11. The anatomy …
Ancillary Processes
 In addition to the main process stages shown in the figure, provision must
be made for the supply of the services (utilities) needed, such as process
water, cooling water, compressed air, and steam. Facilities are also needed
for maintenance, firefighting, offices and other accommodation, and
laboratories.

12. Chemical Equipment Design
 Although the maximum capacity or the size of the equipment is specified, it is
necessary to ensure a satisfactory performance even under certain amount of
overload. The overall satisfactory performance and reliability of the equipment are
dependent on the following factors:
 Optimum process condition
 Appropriate material of construction
 Strength and rigidity of components
 Satisfactory performance of mechanism and an adequate operating range
 Reliable methods of fabrication
 Ease of maintenance and repair
 Ease of operation and control
 Safety requirement

13. Concepts of Chemical Industry
 The process design hierarchy can be represented
by “onion diagram” as
Onion
diagram

14. Equipment to be designed

15. Meaning of Design for CHE equipment

16. Design Information and Data
Sources of information
 Information on manufacturing processes, equipment parameters, materials of
construction, costs, and the physical properties of process materials are needed at all
stages of design, from the initial screening of possible processes to the plant startup and
production.
 When a project is largely a repeat of a previous project, the data and information
required for the design will be available in the company’s process files, if proper detailed
records are kept. For a new project or process, the design data must be obtained from the
literature, or by experiment (research laboratory and pilot plant), or purchased from
other companies.
 The information on manufacturing processes available in the general literature can be of
use in the initial stages of process design, for screening potential processes, but is
usually mainly descriptive and too superficial to be of much use for detailed design and
evaluation.

17. SOURCES OF INFORMATION ON MANUFACTURING PROCESSES
 The chemical process industries are competitive, and the information that is published
on commercial processes is restricted. The articles on particular processes published in
the technical literature and in textbooks invariably give only a superficial account of the
chemistry and unit operations used. They lack the detailed information on reaction
kinetics, process conditions, equipment parameters, and physical properties that is
needed for process design.
 The information that can be found in the general literature is, however, useful in the
early stages of a project, when searching for possible process routes. It is often sufficient
for a flow sheet of the process to be drawn up and a rough estimate of the capital and
production costs made.

18. SOURCES OF …
 The most comprehensive collection of information on manufacturing processes
is probably:
 The Encyclopedia of Chemical Technology edited by Kirk (2003), and Kirk and
Othmer (2001), which covers the whole range of chemical and associated products.
The extensive German reference work on industrial processes, Ullman’s
Encyclopedia of Industrial Technology, an English translation (Ullman, 2002).
 Patents: Patents can be useful sources of information, but some care is needed in
extracting information from them.
 The Internet: It is worthwhile searching online for information on processes,
equipment, products, and physical properties. Many manufacturers and government
departments maintain websites. In particular, up-to-date information can be obtained
on the health and environmental effects of products.

19. GENERAL SOURCES OF PHYSICAL PROPERTIES
 Tables and graphs of physical properties are given in many handbooks and text books in
Chemical Engineering and related subjects.
 Many of the data given are duplicated from book to book, but the various handbook do
provide quick, easy access to data on the more commonly used substances.
 International Critical Tables (1933) is still probably the most comprehensive compilation
of physical properties and is available in most reference libraries.
 A quick search of the literature for data can be made by using the abstracting journals,
such as Chemical Abstracts (American Chemical Society) and Engineering Index
(Engineering Index Inc., New York).
 Engineering Index is now called Engineering Information (Ei) and is a web-based
reference source owned by Elsevier Information (www.ei.org).

20. GENERAL SOURCES …
 On the other hand, Computerized physical property data banks have been set
up by various organizations to provide a service to the design engineer.
 They can be incorporated into computer-aided design programs and are
increasingly being used to provide reliable, authenticated design data.
 Examples of such programs are the PPDS (Physical Property Data Service)
available from National Engineering Laboratory (NEL).

21. Accuracy Requirement of Engineering data
 The accuracy needed depends on the use to which the data will be put. Before
spending time and money for searching of the most accurate value, or arranging
for special measurements to be made, the designer must decide what accuracy is
required; this will depends on several factors:
 The level of design: Rough Scouting calculation or Detail Design.
 The reliability of designing method.
 The sensitivity to the particular property: how much will a small error affects
design calculation.

22. PREDICTION OF PHYSICAL PROPERTIES
 Whenever possible, experimentally determined values of physical properties
should be used. If reliable values cannot be found in the literature and if time or
facilities are not available for their determination, then to proceed with the
design, the designer must resort to estimation. Techniques are available for the
prediction of most physical properties with sufficient accuracy for use in
process and equipment design.
Refer Coulson & Richardson's Chemical Engineering Chapter 8 for
more

23. Codes and Standards
 A large body of rules has been developed over the years to ensure the safe and economical
design, fabrication and testing of equipment, structures, and materials.
 Codification of these rules has been done by associations organized for just such purposes,
by professional societies, trade groups, insurance underwriting companies, and
government agencies.
 Engineering contractors and large manufacturing companies usually maintain individual
sets of standards so as to maintain continuity of design and to simplify maintenance of
plant.

24. Codes and Standards …
 All of the developed countries, and many of the developing countries, have national
standards organizations, responsible for the issue and maintenance of standards for the
manufacturing industries, and for the protection of consumers.
 For instance, In the United Kingdom the British Standards Institution (BSI)is responsible
for national standards, whereas in United States the National Bureau of Standards is
responsible for coordinating information on standards. The principal ones of interest to
chemical engineers are the American National Standards Institute (ANSI), the American
Petroleum Institute (API), the American Society for Testing Materials (ASTM), and the
American Society of Mechanical Engineers (ASME).

25. Safety Factors
 Design is an inexact art; errors and uncertainties will arise from uncertainties in the design
data available and in the approximations necessary in design calculations.
 To ensure that the design specification is met, factors are included to give a margin of safety
in the design; safety in the sense that the equipment will not fail to perform satisfactorily,
and that it will operate safely: will not cause a hazard. "Design factor" is a better term to
use, as it does not confuse safety and performance factors.
 Where design factors are introduced to give some contingency in a process design, they
should be agreed within the project organization, and clearly stated in the project documents
(drawings, calculation sheets and manuals). If this is not done, there is a danger that each of
the specialist design groups will add its own "factor of safety"; resulting in gross, and
unnecessary, over-design.

26. Safety Factors …
 When selecting the design factor to use a balance has to be made between the desire to
make sure the design is adequate and the need to design to tight margins to remain
competitive. The greater the uncertainty in the design methods and data, the bigger the
design factor that must be used.

27. End of chapter One
Thanks for your attention
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