Page 391 - Chemical process engineering design and economics

Reactor Design 371

The factors that influence the selection of a heat exchanger are:

1. heat-transfer coefficients
2. jacket pressure
3. reactor pressure
4. jacket pressure drop
5. cleanliness
6. cost

Figure 7.3 compares calculated overall heat-transfer coefficients for several
reactor heat exchangers, using water for both the jacket and reactor fluid. The
figure shows that the highest heat-transfer coefficient is obtained with internal
coils and the lowest with the simple jacket (called the conventional jacket in Fig-
ure 7.3) without a spiral baffle or agitation. It is assumed that the flow rate for the
internal coil is the coil flow rate and not the jacket flow rate, as plotted in Figure
7.3. Heat-transfer coefficients for the half-pipe coil, agitated, and baffled jackets
are comparable.
The jacket pressure and reactor pressure also influences jacket selection. If
the jacket pressure is large the reactor wall thickness becomes large, reducing

1,200

1,000

600 • Internal Coil
• Half-Pipe Jacket
• Agitated Conventional
• Baffled Conventional
400 A Dimple Jacket
A Conventional

Z 200

SO 100 150 200 250 300
Jacket Fluid-Water—Reactor Fluid-Water

Figure 7.3 Comparison of STR heat exchangers. From Ref. 20 with
permission.

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