Page 354 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

Section 3

Synthesis and Optimization of Chemical

Processes

In this section, the problems of how to create, simulate, and optimize a process and how to develop a
process flow diagram (PFD) are addressed. In order to create a PFD, a considerable amount of
information needs to be gathered. This includes reaction kinetics, thermodynamic property data, required
purity for products and by-products, types of separations to be used in the process, reactor type, range of
conditions for the reaction, and many others. Once this information has been gathered, it must be
synthesized into a working process. In order to accommodate the synthesis of information, the chemical
engineer relies on solving material balances, energy balances, and equilibrium relationships using a
process simulator. The basic data required to perform a simulation of a process are covered, and other
aspects of using a process simulator are discussed. Once the PFD has been simulated, the optimization of

the process can proceed. In general, process optimization involves both parametric and topological
changes, and both these aspects are discussed.

This material is treated in the following chapters.

Chapter 11: Utilizing Experience-Based Principles to Confirm the Suitability of a Process
Design
When designing a process, the experienced engineer will often have a good idea as to how large a
given piece of equipment needs to be or how many stages a given separation will require. Such
information is invaluable in the early stages of design to check the reasonableness of the results of
rigorous calculations. To assist the inexperienced engineer, a series of heuristics or guidelines for
different equipment is presented in the form of tables.
Chapter 12: Synthesis of the PFD from the Generic BFD
The information required to obtain a base-case process flow diagram is discussed and categorized
into the six basic elements of the generic block flow process diagram. The need to obtain reaction
kinetics, thermodynamic data, and alternative separation methods is discussed in the context of
building a base-case process. Special emphasis is placed on alternative distillation schemes and the
sequencing of columns needed for such separations.
Chapter 13: Synthesis of a Process Using a Simulator and Simulator Troubleshooting
The structure of a typical process simulator and the basic process information required to simulate a
process are discussed. The various types of equipment that can be simulated, and the differences

between alternative modules used to simulate similar process equipment, are reviewed. The
importance of choosing the correct thermodynamic package for physical property estimation is
emphasized, and strategies to eliminate errors and solve simulation problems are presented.
Chapter 14: Process Optimization
Basic definitions used to describe optimization problems are presented. The need to look at both
topological changes in the flowsheet (rearrangement of equipment) and parametric changes (varying
temperature, pressure, etc.) is emphasized. Strategies for both types of optimization are included. A
new section on batch systems, including batch scheduling and optimal batch cycle times, has been
included.