Page 405 - Chemical process engineering design and economics

Reactor Design 385

SIZING BATCH REACTORS

The equipment for batch reactors is identical to that of CSTRs. Table 7.8 lists
the equations for sizing batch reactors, and Table 7.9 outlines the calculation
procedure. First, calculate the reaction volume, V, by using Equations 7.8.3 to
r
7.8.6. This calculation requires an estimate of the batch time, defined by Equa-
tion 7.8.5, which is the sum of the times for charging, heating, reacting, dis-
charging, cooling, emptying, and cleaning. These times are given in Table 7.8
for a polymerization reaction. No other time data seems to be available. Next,
find the reactor volume, V, using Equation 7.8.7. The reactor volume is greater
R
than the reaction volume because of an allowance for headspace.
After calculating the reactor volume, the next step is to calculate the heat-
transfer area. The reactant concentration, and therefore the heat-transfer rate
decreases as the reaction proceeds. We have to calculate the heat-transfer area
when the heat-transfer rate is a maximum, which is at initial conditions. First,
calculate the initial rate of reaction, r, from Equation 7.8.4, and then calculate
Ao
the heat transferred using Equations 7.8.1, 7.8.2 and 7.8.18 to 7.8.21. Next,
determine the heat-exchanger type using Equations 7.8.11 and 7.8.15.

Table 7.8 Summary of Equations for Sizing Batch Reactors_______

Energy Equation

Q R = r Ao V R Ah R (7.8.1)

Ah R = Ah! + AH° R + Ah 2 (7.8.2)
Rate Equations

t R = f(k',x/) (7.8.3)

r Ao = f(k',c Ao') (7.8.4)

t B = t F' + t H' + t R + V + t E' (7.8.5)

V r = mi 't B /p' (7.8.6)

V R = f(V r) — Table 7.3 (7.8.7)

Qj = Uj Aj (Tj -T R') (7.8.8)

T, = (T, 1' + T, 2 ')/2 (7.8.9)

Copyright © 2003 by Taylor & Francis Group LLC