Page 550 - Elements of Chemical Reaction Engineering Ebook

520 Steady-State Nonisothermal Reactor Design Chap. 8

(b) Plot the reactor temperature as a function of the feed temperature.
(c) To what inlet temperature must the fluid be preheated for the reactor to
operate at a high conversion? What are the corresponding temperature
and conversion of the fluid in the CSTR at this inlet temperature?
(d) Suppose that the fluid is now heated 5°C above the temperature in part
(c) and then cooled 20°C, where it remains. What will be the conversion?
(e) What is the inlet extinction temperature for this reaction system? (Ans.:
To = 87°C.)

Additional information:
Heat capacity of the inert: 30 cal/g mol. "C
Heat capacity of A and B: 20 cal/g mol."C
UA: 8000 cal/min."C
Ambient temperature, T, : 300 K
z = 100 min
AHRx = -7500 cal/mol
k = 6.6 X lod3 min-l at 350 K
E = 40,000 cal/mol.K
P8-18* Radial flow reactors are used to help eliminate hot spots in highly exothermic
reactions. The velocity is highest at the inlet and then decreases as l/r as the
fluid moves away from the inlet. The overall heat-transfer coefficient varies
with the square root of the radial velocity:

velocity at r,
u = U(r= ro)
velocity at r
and at the inlet U = U(r = r,) = 100 Btu/h.ft2."F.

Figure PS-18 Radial flow reactor.

(a) Rework Problem P8-6 for a radial reactor.
(b) Rework Problem P8-12 for a radial reactor.
(e) Consider the flow conditions to one of the tubes for the SO, oxidation
described in Example 8-10. Replace the tube with a radial flow reactor 1
cm in height with an inlet diameter of 0.5 cm. The reactor is immerse3 in
the same boiling liquid as in Example 8-10. Plot the temperature and con-
version as a function of radius and catalyst weight for three different inlet
temperatures. Study the behavior of this reactor by varying a number of
parameters, such as flow rate and gas composition.