Page 512 - Elements of Chemical Reaction Engineering Ebook

482 Steady-State Nonisothermal Reabtor Design Chap. 8

It is desirable to have a low mass velocity through the bed to minimize
blower energy requirements, so the 75 ft3/min ft2 value will be used. Normal
conversions in adiabatic converters are 70% in the first stage and an additional
18% in the second.’5 Using Eklund’s Reymersholm catalyst, solution of the adi-
abatic reactor problem at the end of the chapter shows that these conversions
require 1550 ft3 (23 in. deep) in the first stage and 2360 ft3 (35 in. deep) in the
second. As a result, in our cooled tubular reactor, we shall use a total catalyst
volume of 3910 ft’.

8.5.3 Reactor Configuration

The catalyst is packed in tubes, and the tubes are put in heat exchangers
where they will be cooled by a boiling liquid. The outside diameter of the tubes
will be 3 in. Severe radial temperature gradients have been observed in SO, oxi-
dation systems,Ih although these systems had platinum catalysts and greatly dif-
ferent operating conditions than those being considered here, The 3-in. diameter
is chosen as a compromise between minimizing temperature gradients and keep-
ing the number of tubes low. For this service, 1Zgauge thickness is specified,
which means a thickness of 0.109 in. and an inside diameter of 2.782 in. A 20-ft
length will be used, as a compromise between decreasing blower energy
Optimizing capital requirements (shorter tube length) and lowering capital casts (fewer tubes from
and operating Costs a longer tube length). For 3910 ft3 of catalyst, the number of tubes that wilI be
required is
volume of catalyst - 3910
N, = - = 4631 tubes
volume per tube (20)(~)(2.782/ 12),/4
The total cross-sectional area of the tubes is

The overall heat-transfer coefficient between the reacting gaseous mixture and
the boiling coolant is assumed to be 10 Btu/ h ft2 OF. This coefficient is toward
the upper end of the range of heat-transfer coefficients for such situations as
reported by Colburn and Berge1in.I’

8.5.4 Operating Conditions

Sulfur dioxide converters operate at pressures only slightly higher than
atmospheric. An absolute pressure of 2 atm will be used in our designs. The inlet

lSJ. R. Donovan and J. M. Salamone, in Kirk-Othtner Encyclopediu of Ckeniicd Tecli-
ndogy, 3rd ed., Vol. 22 (New York: Wiley-Intencience, 1978), p. 190.
I6For example, R. W. Olson, R. W. Schuler, and J. M. Smith, Chenr Eng. Pmg., 46, 614
(1950); and R. W. Schuler, V. P. Stallinps, and J. M. Smith, Cheni. Eng. Prog. Syrnp.
Sex 48(4), 19 (1952).
i7Colburn and Bergelin, in Chernictrl Eoghzeen’ Hmdhod : 3rd ed. (New Yorh:
McGraw-Hill, 1950).