Page 250 - Modeling of Chemical Kinetics and Reactor Design

220 Modeling of Chemical Kinetics and Reactor Design

mass and heat transfer or at equilibrium with the surroundings. Reactors
that are free of the effect of macrokinetic properties are classified as:

• Batch isothermal perfectly stirred reactor (the reaction mixture is
at equilibrium with the heat transfer medium).
• Batch adiabatic perfectly stirred reactor.
• Semi-batch perfectly stirred reactor.
• Continuous isothermal perfectly stirred flow reactor (the reaction
mixture is at equilibrium with the heat transfer medium).
• Continuous adiabatic perfectly stirred flow reactor.
• Continuous isothermal plug flow reactor (the reactor mixture is
at thermal equilibrium with the surroundings).
• Continuous adiabatic plug flow reactor.

Knowledge of these types of reactors is important because some
industrial reactors approach the idealized types or may be simulated
by a number of ideal reactors. In this chapter, we will review the above
reactors and their applications in the chemical process industries.
Additionally, multiphase reactors such as the fixed and fluidized beds
are reviewed. In Chapter 5, the numerical method of analysis will be
used to model the concentration-time profiles of various reactions in
a batch reactor, and provide sizing of the batch, semi-batch, continuous
flow stirred tank, and plug flow reactors for both isothermal and
adiabatic conditions.

BATCH ISOTHERMAL PERFECTLY
STIRRED REACTOR

The concept of a batch reactor assumes that the reaction is instan-
taneously charged (i.e., filled) and perfectly homogenized in the
reactor. Also, its temperature is immediately adjusted to that of the
heat transfer medium. Therefore, the chemical reaction takes place at
the temperature of the heat transfer medium under perfect mixing. The
process is stopped as soon as the degree of conversion is achieved.
Figure 4-1 shows two nozzles at the top of a batch reactor where
charging of the reactants occurs. Batch reactors are used extensively
in a final scale-up of an industrial plant. The choice of a batch reaction
over a continuous system is often a result of special considerations.
The size of batch reactors range from 5 gal (19 l) in small industrial
pilot plants to 10,000–20,000 gal (38,000–76,000 l) in large plants.