CHE414. chemical engineering plant design PDF

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introduction to the basic principles of chem engineering plant design ranging from economic and engineering point of view...

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UNIVERSITY OF ABUJA, ABUJA FACULTY OF ENGINEERING DEPARTMENT OF CHEMICAL ENGINEERING COURSE CODE: CHE 414 (C) (2 CREDITS) COURSE TITLE: PRINCIPLES OF CHEMICAL ENGINEERING PLANT DESIGN COURSE SYNOPSIS: Presentation and discussion of real process design problems; Sources of design data; process and engineering flow diagram; process outline charts incorporating method; study and critical examination; mechanical design of process vessels and piping; Environmental considerations: site considerations; process services. Costing of Design Process; Formulation of feasibility report evaluation; Economics and safety consideration must be stressed.

NAMES, OFFICE AND CONTACT DETAILS OF COURSE LECTURER: Name: Engr. Prof. Abdulfatai Jimoh Office: Chemical Engineering Dept. PS, UniAbuja. Contact Time: Tuesday, 12:00-2:00pm E-mail: [email protected] ; Tel: +2348139682944 Lecture Venue: Chemical Engineering Lab.

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LECTURES: Most of the lecture notes and teaching material are in electronic soft copy form. To make it easier to understand the lectures, you are recommended to print out (or photocopy) and read the lecture notes before attending the classes. OBJECTIVE OF THIS COURSE: The objective of this course is to introduce undergraduate students of chemical engineering to the fundamentals of process and plant design when it comes to the design of new chemical plants, the expansion or revision of existing ones. LEARNING OUTCOMES: On successful completion of this course students will be able to: 1. Explain the fundamentals of process plant design; Identify and explain the series of stages involves in a process plant design 2. Understand and demonstrate how to do a preliminary evaluation of economics and market of proposed plant 3. Understand and demonstrate basic engineering principles in a plant design. 4. Develop and analyze flowsheet, material and energy balance of a proposed plant. 5. Evaluate design constraints 6. Develop and evaluate data necessary for final design 7. Explain final cost and economic evaluation of a proposed plant 8. Identify and understand factors that affects location or siting of a plant 9. Do detailed engineering design and procurement analysis of a proposed plant. 10. Develop a preliminary environmental impact assessment of a proposed plant 11. Develop a comprehensive basic engineering design and design report of a proposed plant

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REFERENCE BOOKS: 1. Chemical Engineering Design: Principles, Practice and Economics of Plant and Process Design 2008, by Gavin Towler and Ray Sinnott . 2. Chemical Engineering – Volume 6: Chemical Engineering Design, ButterworthHeinemann, 1993, by Sinnott, R. K., Coulson & Richardson’s. 3. Plant Design and Economics for Chemical Engineers, 5th Edition, McGraw Hill International Editions, by Peters, M.S. and Timmerhaus, K.D. 4. Conceptual

Design

of

Chemical

Processes, McGraw-Hill International

Editions, Chemical Engineering Series, 1988 by Douglas, J.M., 5. Chemical and Process Design Handbook, McGraw-Hill Series, 2002 by James G. Speight. 6. Analysis, Synthesis, and Design of Chemical Processes, 2nd Edition, Prentice Hall by Turton R., C.B. Bailie, B.W.Whiting and J.A. Shaeiwtz, 7. The Chemical Engineers’ Handbook” published by McGraw-Hill Book Company by R. H. Perry and D. W. Green

ASSESSMENT: 1. Attendance: Mandatory (Class attendance and active participation in all activities) 2. Continuous Assessment (Assignment, Quiz and Test):

30%

3. Final Examination (Defense):

70%

4. Total:

100%

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INTRODUCTION In this modern age of industrial competition, 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. However, in making these applications, the chemical engineer must recognize the economic implications which are involved and proceed accordingly. 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. Development of a new plant or process from concept evaluation to profitable reality is often an enormously complex problem. A plant-design project moves to completion through a series of stages such as: 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. Page 4 of 39

The stages list suggests that plant-design project involves a wide variety of skills. Among these are research, market analysis, design of individual pieces of equipment, cost estimation, computer programming, and plant-location surveys. It should be noted that the services of a chemical engineer are needed in each step of the outline, either in a central creative role, or as a key advisor. There are three parameters that must be carefully defined and explained for good understanding of this course, namely: Design, Process design and plant design.

CHEMICAL ENGINEERING PLANT DESIGN DEFINITION OF DESIGN DESIGN: Design is a creative process or creative activity whereby an innovative solution for a problem is conceived. It 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. A fashion designer creates clothes that will enhance the appeal of an individual. An automobile designer creates a car model that will provide transportation and a certain appeal to the consumer. The car’s appeal may be because of its power, beauty, convenience, economy, size, operability, low maintenance, uniqueness, or gimmicks. A process engineer designs a plant to produce a given chemical. In each of these instances a new thing is created or an old thing is created in a new way.

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Design occurs when a possible answer for a present or projected need or desire by people or industry has been found. If a product were not expected to meet a need or desire, there would be no reason to produce it and hence no reason for design. A company or person is not going to manufacture something that cannot be sold at a profit. Design is a creative activity, and as such can be one of the most rewarding and satisfying activities undertaken by an engineer. The design does not exist at the start of the project. The designer begins with a specific objective or customer need in mind and, by developing and evaluating possible designs, arrives at the best way of achieving that objective—be it a better chair, a new bridge, or for the chemical engineer, a new chemical product or production process. 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 is intended to include: 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 equipment required for a Flowsheet. Page 6 of 39

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. WHAT IS PLANT DESIGN?

In the context of this course, the term plant design includes all engineering aspects involved in the development of either a new, modified, or expanded industrial plant. Similarly, the meaning of plant design is limited by some engineers to items related directly to the complete plant, such as plant layout, general service facilities, and plant location In this development, the chemical engineer will be making economic evaluations of new processes, designing individual pieces of equipment for the proposed new venture, or developing a plant layout for coordination of the overall operation. Because of these many design duties, the chemical engineer is many times referred to here as a design engineer. On the other hand, a chemical engineer specializing in the economic aspects of the design is often referred to as a cost engineer. In many instances, the term process engineering is used in connection with economic evaluation and general economic analyses of industrial processes, while process design refers to the actual design of the equipment and facilities necessary for carrying out the process.

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DESIGN DEVELOPMENT STAGES: The stages in the development of a design, from the initial identification of the objectives to the final design are shown in Figure 1. Each stage is briefly discussed as follows:

Figure 1: The design process.

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I. THE DESIGN OBJECTIVES (THE NEED): 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. II.

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: a. Information on possible processes and the system of units to be used. b. The national, local or company design codes that must be followed. c. Details of raw materials that are available. d. Information on potential sites where the plant might be located, including climate data, seismic conditions, and infrastructure availability. e. 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.

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III. 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.

IV.

BUILD PERFORMANCE MODEL AND FITNESS TESTING:

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 Page 10 of 39

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. V. 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 (R.O.I). 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 4 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 Page 11 of 39

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. VI.

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. VII. 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

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engineer will often then be called upon to help resolve any startup issues and teething problems with the new plant. DESIGN CONSTRAINTS: When considering possible ways of achieving the objective, the designer will be constrained by many factors (which are called the design constraints), which will narrow down the number of possible designs. There will rarely be just one possible solution to the problem, just one design. Several alternative ways of meeting the objective will normally be possible, even several best designs, depending on the nature of the constraints. Design constraints are divided into two types (see Figure 2): a. Internal constraints: over which the designer has some control. b. External constraints: fixed, invariable. These constraints on the possible solutions to a problem in design arise in many ways. Some constraints will be fixed and invariable, such as those that arise from physical laws, government regulations, and standards. Others will be less rigid and can be relaxed by the designer as part of the general strategy for seeking the best design. 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 2. 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, such as choice of process, choice of process conditions, materials, and equipment. Economic considerations are obviously a major constraint on any engineering design: plants must make a profit. Time will also be a constraint. The time

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available for completion of a design will usually limit the number of alternative designs that can be considered.

Figure 2: Design constraints. Assignment/Home work 1: a. What is meant by design constraints? b. What are the different types? Give examples? c. What are the main items that should be included in the process design? d. Draw a block diagram showing the main steps involved in the development of a design process? Page 14 of 39

FLOW-SHEETING: Process design normally start with a process scheme (Flowsheet). A flowsheet is the key document or road map in process design. It shows the arrangement of the equipment selected to carry out the process; the stream connections; stream flowrates and compositions; and the operating conditions. •It is a diagrammatic model of the process. The flow-sheet will be used by the specialist design groups as the basis for their designs. This will include piping, instrumentation, equipment design and plant layout preparation of operating manuals and operator training. During plant start-up and subsequent operation, the flow-sheet forms a basis for comparison of operating performance with design THE FLOW-SHEET IMPORTANCE a. Shows the arrangement of the equipment selected to carry out the process. b. Shows the streams concentrations, flow rates & compositions. c. Shows the operating conditions. d. During plant startup 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 The presentation of Flowsheet must be clear, comprehensive, accurate and complete. Flowsheet presentation can be in the following categories 1. Block Diagram 2. Process Flow Diagram (PFD)

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3. Process and Instrumentation Diagram (P&ID) INFORMATION TO BE INCLUDED ON A FLOWSHEET The amount of information shown on a flow-sheet will depend on the custom and practice of the particular design office. The list given below has therefore been divided into essential items and optional items. The essential items must always be shown, the optional items add to the usefulness of the flow-sheet but are not ...