Page 513 - Elements of Chemical Reaction Engineering Ebook

Sec. Q 5 Nonadiabatic Reactor Operation: Oxidation of Sulfur Dioxide Example 483

temperature to the reactor will be adjusted so as to give the maximum conver-
sion. 'Two constraints are present here. The reaction rate over V,O, catalyst is
negligible below -750"F, and the reactor temperature should not exceed
-1125°F at any point.I8 A series of inlet temperatures should be tested, and the
one above 760°F giving the maximum conversion, yet having no reactor tem-
perature exceeding 1120"F, should be used.
'The cooling substance should operate at a high temperature so as to
improve thermal efficiency by reuse of heat. The most suitable substance
appears to be Dowtherm A, with a normal operating limit of -750°F but which
on occasion has been used as the coolant in this preliminary design.lg

Exmnple 8-10 Oxidation of SO,

The feed to an SO, converter is 7900 lb mol/h and consists of 1 1 % SO,, IO% O;, and
79% inerts (principally N2). The converter consists of 4631 tubes packed with cata-
lyst, each 20 ft long. The tubes are 3 in. 0.d. and 2 782 in. i.d. The tubes wdl be
cooled by a boiling liquid at 805"F, so the coolant temperature is constant over this
value. The entering pressure is 2 atm.
For inlet temperatures of 740 and 940°F, plot the conversion, temperature, equi-
librium conversion, and reaction rate profile down the reactor.

Additional information:
9 = 0.45 U = 10 Btu/h.ft2.R
po = 0.054 lb/ft3 A, = 0.0422ft2
Po = 2 atm To = 1400"R (also To = 1200 R)
D, = 0.015 ft g, = 4.17 X IO8 Ib;ft/lbf~h2
p = 0.090 lb/ft. h at 1400 R pb = 33.8 lb/ft3 (bulk density)
Using recent JANAFZ0 values of K, at 700 and 900 K, the equilibrium constant at
any temperature Tis
1
42,3 1 1
11.24 (K, in atm-1/2, Tin R) (E8-X0.1)

at 1600"R,

K, = 7.8 atm-",

18J. R. Donovan and J. M, Salamone, in Kirk-Othmer Encyclopedia of Chemical Tech-
nology, 3rd ed. (New York: Wiley, 1984).
lgThe vapor pressure of Dowtherm A at 805°F is very high, and this pressure would
have to be maintained in the shell side of the reactor for boiling Dowthenn A to be
used as a coolant at this temperature. This aspect will be included in the discussion of
the problem results.
R.
20D. Stull and H. Prophet, Project Directors, JANAF Thermochemical Tables, 2nd
ed., NSPDS-NBS 37 (Washington, D.C.: US. Government Printing Office, 1971).