Page 248 - Modeling of Chemical Kinetics and Reactor Design

218 Modeling of Chemical Kinetics and Reactor Design

CHAPTER FOUR

Industrial and

Laboratory Reactors

INTRODUCTION

Chemical reactors are the most important features of a chemical
process. A reactor is a piece of equipment in which the feedstock is
converted to the desired product. Various factors are considered in
selecting chemical reactors for specific tasks. In addition to economic
costs, the chemical engineer is required to choose the right reactor that
will give the highest yields and purity, minimize pollution, and maximize
profit. Generally, reactors are chosen that will meet the requirements
imposed by the reaction mechanisms, rate expressions, and the required
production capacity. Other pertinent parameters that must be deter-
mined to choose the correct type of reactor are reaction heat, reaction
rate constant, heat transfer coefficient, and reactor size. Reaction
conditions must also be determined including temperature of the heat
transfer medium, temperature of the inlet reaction mixture, inlet
composition, and instantaneous temperature of the reaction mixture.
An important factor in reactor operation is the outlet degree of
conversion. Operating conditions such as temperature, pressure, and
degree of agitation, are related for the most economic operation. The
optimum reactor that will best meet the process requirements requires
a review of whether the process is continuous or batch, and whether
a combination of reactor types or multiple reactors in series or parallel
would be most adequate. It is also important to determine whether the
mode of operation involves either an isothermal (i.e., constant tem-
perature) or an adiabatic (i.e., heat does not exchange with the sur-
roundings) condition, whether a single pass operation is best, or
whether recycling is needed to achieve the desired degree of con-
version of the raw feedstock. The degree of conversion affects the

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