Fghfghf

ch01.qxd

9/11/2002

11:40 AM

Page 9

S E C T I O N

1
Conceptualization and Analysis of Chemical Processes
The first section of this book consists of Chapters 1–4. Chapter 1 covers the important diagrams that are routinely used by chemical engineers to help design and understand chemical processes. The book commences with this section and chapter because nearly all the technicalinformation that is presented in the remainder of the book is, in some way, related to the three principal diagrams that are presented in Chapter 1. These three diagrams are the block flow diagram (BFD), process flow diagram (PFD), and the piping and instrument diagram (P&ID). In addition, the three-dimensional representation of a process is introduced, and some of the basic issues regardingequipment location are addressed. In Chapter 2 the evolutionary process of design is investigated. The inputoutput structure of a process is presented, and the basic building blocks that are common to all processes are introduced. The different recycle structures of processes are illustrated, and the rationale for adding inert material to the feed is also explained. In Chapter 3, methods for tracingchemical species through a process flow diagram are given. By following the paths of feed chemicals and reactants, it is possible to obtain a much clearer picture of what is happening in an existing process. Finally, in Chapter 4, the conditions at which different equipment operate are discussed and explained. The concept of conditions of special concern is explained, and examples of such conditionsare identified and explained in the context of the toluene hydrodealkylation process. Chapter 1: Diagrams for Understanding Chemical Processes The technical diagrams commonly used by chemical engineers are presented. These diagrams include the block flow diagram (BFD), the process flow diagram (PFD), and the process and instrumentation diagram (P&ID). 9

ch01.qxd

9/11/2002

11:40 AM

Page10

10

Section 1

Conceptualization and Analysis of Chemical Processes

A standard method for presenting a PFD is given and illustrated using a process to produce benzene via the catalytic hydrodealkylation of toluene. The 3D topology of chemical processes is introduced, and some basic information on the spacing and elevation of equipment is presented. These concepts are furtherillustrated in the Virtual Plant Tour AVI file on the CD accompanying the textbook. Chapter 2: The Structure and Synthesis of Process Flow Diagrams The evolutionary process of design is investigated. This evolution begins with the process concept diagram that shows the input-output structure of all processes. From this simple starting point, the engineer can estimate the gross profit margins of competingprocesses and of processes that use different chemical synthesis routes to produce the same product. In this chapter, it is shown that all processes have a similar input/output structure whereby raw materials enter a process and are reacted to form products and by-products. These products are separated from unreacted feed, which is usually recycled. The product streams are then purified to yieldproducts that are acceptable to the market place. All equipment in a process can be categorized into one of the six elements of the generic block flow process diagram. The process of process design continues by building preliminary flowsheets from these basic functional elements that are common to all processes. Chapter 3: Tracing Chemicals through the Process Flow Diagram In order to gain a betterunderstanding of a PFD, it is often necessary to follow the flow of key chemical components through the diagram. This chapter presents two different methods to accomplish this. The tracing of chemicals through the process reinforces our understanding of the role that each piece of equipment plays. In most cases, the major chemical species can be followed throughout the flow diagram using simple...