Page 38 - Elements of Chemical Reaction Engineering 3rd Edition

10 Mole Balances Chap. 1

The difference between equations (El-2.1) and (El-2.3) for the two different types
of reactors is apparent.

1.4 Continuous-Flow Reactors

1.4.1 Continuous-Stirred Tank Reactor

A type of reactor used very commonly in industrial processing is a stirred
tank operated continuously (Figure 1-4). It is referred to as the continuous-stirred
tank reactor (CSTR) or backmix reactor: The CSTR is normally run at steady
state and is usually operated so as to be quite well mixed. As a result of the latter
quality, the CSTR is generally modeled as having no spatial variations in concen-
tration, temperature, or reaction rate throughout the vessel. Since the temperature
and concentration are identical everywhere within the reaction vessel, they are
the same at the exit point as they are elsewhere in the tank. Thus the temperature
and concentration in the exit stream are modeled as being the same as those
inside the reactor. In systems where mixing is highly nonideal, the well-mixed
model is inadequate and we must resort to other modeling techniques, such as
residence-time distributions, to obtain meaningful results. This topic is discussed
in Chapters 13 and 14.

Reactants

Products

Figure 1-4 Continuous-stirred tank reactor.

When the general mole balance equation

is applied to a CSTR operated at steady state (i.e., conditions do not change
with time),

in which there are no spatial variations in the rate of reaction,

rj dV = Vr,