Page 23 - The engineering of chemical reactions

Industrial Processes 7

An engineer is typically asked to solve some problem as quickly as possible and
move on to other problems. Learning about the process for its own sake is frequently
regarded as unnecessary or even harmful because it distracts the engineer from solving
other more important problems. However, we regard it as an essential task to show the
student how to construct models of the process. We need simple analytical tools to estimate
with numbers how and why the reactor is performing as it is so that we can estimate how
it might be modified quickly and cheaply. Thus modeling and simulation will be constant
themes throughout this text.
The student must be able to do back-of-the-envelope computations very quickly and
confidently, as well as know how to make complete simulations of the process when that
need arises. Sufficient computational capabilities are now available that an engineer should
be able to program the relevant equations and solve them numerically to solve problems
that happen not to have analytical solutions.
Analysis of chemical reactors incorporates essentially all the material in the chemical
engineering curriculum. A “flow sheet” of these relationships is indicated in the diagram.
thermodynamics Ifluidlmathematicsl (designl -1

4 -1 J 4 4
pzzq+Ichemical reactor -+ chemical process + m

heat
transfer
r---++--+-Jmaterials &
transfer
mass
In this course we will need to use material from thermodynamics, heat transfer, mass transfer,
fluid mechanics, and especially chemical kinetics. We assume that the student has had some
exposure to these topics, but we will attempt to define concepts when needed so that those
unfamiliar with particular topics can still use them here.
We regard the subject of chemical reactors as the final topic in the fundamental
chemical engineering curriculum. This course is also an introduction to process design
where we consider the principles of the design of a chemical reactor. Chemical reaction
engineering precedes process control, where the operation and control of existing reactors is
a major topic, and the process design course, where economic considerations and integration
of components in a chemical plant are considered.

INDUSTRIAL PROCESSES

In parallel with an analytical and mathematical description of chemical reactors, we will
attempt to survey the petroleum and chemical industries and related industries in which
chemical processing is important. We can divide the major processes into petroleum refining,
commodity chemicals, fine chemicals, food processing, materials, and pharmaceuticals.
Their plant capacities and retail prices are summarized in Table l-l.
The quantities in Table l-l have only qualitative significance. Capacity means the
approximate production of that product in a single, large, modern, competitive plant that
would be operated by a major oil, chemical, food, or pharmaceutical company. However,
the table indicates the wide spread between prices and costs of different chemicals, from
gasoline to insulin, that chemical engineers are responsible for making. There is a tradeoff