Introduction to Chemical Engineering Computing

Bruce A. Finlayson

• Publisher: Wiley
• Year: 2014
• Print ISBN: 9781118888315
• eBook ISBN: 9781118888377
• Edition: 2
• Topic: Technology & Engineering
• Subtopic: Chemical & Biochemical Engineering
• Index: Technology & Engineering

Step-by-step instructions enable chemical engineers to master key software programs and solve complex problems

Today, both students and professionals in chemical engineering must solve increasingly complex problems dealing with refineries, fuel cells, microreactors, and pharmaceutical plants, to name a few. With this book as their guide, readers learn to solve these problems using their computers and Excel, MATLAB, Aspen Plus, and COMSOL Multiphysics. Moreover, they learn how to check their solutions and validate their results to make sure they have solved the problems correctly.

Now in its Second Edition, Introduction to Chemical Engineering Computing is based on the author's firsthand teaching experience. As a result, the emphasis is on problem solving. Simple introductions help readers become conversant with each program and then tackle a broad range of problems in chemical engineering, including:

• Equations of state
• Chemical reaction equilibria
• Mass balances with recycle streams
• Thermodynamics and simulation of mass transfer equipment
• Process simulation
• Fluid flow in two and three dimensions

All the chapters contain clear instructions, figures, and examples to guide readers through all the programs and types of chemical engineering problems. Problems at the end of each chapter, ranging from simple to difficult, allow readers to gradually build their skills, whether they solve the problems themselves or in teams. In addition, the book's accompanying website lists the core principles learned from each problem, both from a chemical engineering and a computational perspective.

Covering a broad range of disciplines and problems within chemical engineering, Introduction to Chemical Engineering Computing is recommended for both undergraduate and graduate students as well as practicing engineers who want to know how to choose the right computer software program and tackle almost any chemical engineering problem.

1
INTRODUCTION

Computers have revolutionized the way chemical engineers design and analyze processes, whether designing large units to make polyethylene or small microreactors used to detect biological agents. In fact, the engineering problems that many of you will study as undergraduates are similar in complexity to problems PhD students solved 30 or 40 years ago. Computer programs can now solve difficult problems in a fraction of the time it used to take. Nowadays, you no longer have to write your own software programs to use computers effectively. Computer programs can do the numerical calculations for you, but you will still need to understand how to apply these programs to specific engineering challenges.

The goal of this book is to help you practice better chemical engineering. Computers are valuable tools that enable progressive, far-reaching chemical engineering. Unfortunately, computers are not as basic as DVD players, where you insert a DVD, push a button, and get the same result every time. Sometimes computer programs do not work properly for the parameters you have given them. Thus, you must be careful to use them wisely.

This book will also

1. Illustrate the problems that you as chemical engineers may need to solve.
2. Compare the types of computer programs you can use and illustrate which ones are best for certain applications.
3. Describe how to check your work to ensure you have solved the problems correctly.

This book demonstrates four computer programs: Excel®, MATLAB®, Aspen Plus®, and Comsol Multiphysics®. You may have access to other programs created by other companies. While the exact details will not be the same, the steps you take will be similar.

TABLE 1.1 Computer Programs Used in Different Chapters

Computer skills are invaluable, but as an engineer, you also need to understand the physical phenomena. Each chemical engineering application chapter starts with a description of the physical problem in general terms. Then those general terms are put into a mathematical context so the computer can represent them. Next, the chapter gives several examples in which such problems are solved, providing step-by-step instructions so you can follow along on your own computer. Sometimes, the same problem is solved using different programs so you can see the advantages of each program. Finally, the chapters give more complicated problems your instructor may use as homework problems.

Examples throughout this book demonstrate how to check your work and how to learn from the answers the computer gives you. When using computers, it is always important to know if the computer obtained the correct answer. If you follow this strategy you will have no trouble convincing your instructor—or your boss—that you have a solution every bit as reliable as an analytical solution for a problem that cannot be solved analytically:

1. Solve the problem
2. Validate your work
3. Understand how you reached that answer

ORGANIZATION

The book is organized into eleven chapters followed by five appendices as listed in Table 1.1. Each chapter treats a type of chemical engineering phenomenon, such as process simulation or convective diffusion. Four of the appendices give additional details about each computer program. The fifth appendix provides the nitty-gritty details of many of the numerical methods. An appendix on parameter estimation that was in the 1st edition is available on the book website.

As a modern chemical engineering student, many of you are computer-savvy. This book assumes that you are not a complete beginner, but have some experience with spreadsheet programs such as Excel. The chapters provide examples and step-by-step instructions for using the computer programs to solve chemical engineering problems. If needed, you can find more detailed information about the individual programs in the appendices.

Algebraic Equations

Chapters 2–5 deal with chemical engineering problems that are expressed as algebraic equations—usually sets of nonlinear equations, perhaps thousands of them to be solved together. In Chapter 2, you can study equations of state that are more complicated than the perfect gas law. This is especially important because the equation of state provides the thermodynamic basis for not only volume but also fugacity (phase equilibrium) and enthalpy (departure from ideal gas enthalpy). Chapter 3 covers vapor–liquid equilibrium, and Chapter 4 covers chemical reaction equilibrium. All these topics are combined in simple process simulation in Chapter 5. This means that you must solve many equations together. These four chapters make extensive use of programming languages in Excel and MATLAB as well as Aspen Plus.

Process Simulation

Chapter 6 provides an extensive discussion of the possible (and reasonable) choices of thermodynamic models, and how you check your choice. It then introduces mass transfer problems such as distillation and absorption and single units. Chapter 7 gives a more detailed look at process simulation, where the power of process simulators like Aspen Plus really is evident. These chapters make use of commercial codes that are run by inserting data into their custom-designed interface.

Differential Equations

Chapters 8–11 treat problems that are governed by differential equations. Chapter 8 gives methods to model chemical reactors. These are usually initial value problems, which are illustrated in Eq. (1.1):

(1.1)

Note that the dependent variable, c, is a function of only one independent variable, z, and that the initial value is specified. For reactors, you start at the inlet and integrate down the reactor using either Excel, MATLAB, Aspen Plus, or Comsol Multiphysics.

Chapter 9 then solves transport problems in one space dimension (1D) using Comsol Multiphysics. If you consider heat transfer through a slab, one side of the slab is kept at one temperature, T₀, and the other side of the slab is maintained at another temperature, T_L. The governing equation is

(1.2)

with boundary conditions

(1.3)

The differential equation, (1.2), is an ordinary differential equation because there is only one independent variable, x. In this case, equations in one space dimension are boundary value problems, because the conditions are provided at two different locations. While it is also possible to solve this problem using Excel, it is much simpler to use Comsol Multiphysics or MATLAB since the numerical analysis will have been done for you. Transient heat transfer in one space dimension is governed by

(1.4)

and this problem can be solved using Comsol Multiphysics or MATLAB, too.

Chapters 10 and 11 use Comsol Multiphysics to solve fluid flow, heat transfer, and mass transfer problems in 2D and 3D. Here, again the power of the software program shows through. You get to solve real problems that go beyond the simple 1D cases in your textbook. Those 1D problems are good for...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Dedication
• Contents
• Preface
• 1 Introduction
• 2 Equations of State
• 3 Vapor–Liquid Equilibria
• 4 Chemical Reaction Equilibria
• 5 Mass Balances with Recycle Streams
• 6 Thermodynamics and Simulation of Mass Transfer Equipment
• 7 Process Simulation
• 8 Chemical Reactors
• 9 Transport Processes in One Dimension
• 10 Fluid Flow in Two and Three Dimensions
• 11 Heat and Mass Transfer in Two and Three Dimensions
• Appendix A Hints When Using Excel®
• Appendix B Hints When Using MATLAB®
• Appendix C Hints When Using Aspen Plus®
• Appendix D Hints When Using Comsol Multiphysics®
• Appendix E Mathematical Methods
• References
• Index