Page 332 - Petroleum and Gas Field Processing

Example 6
Find the flow rate of a heating gas at 400 F to desorb 2000 lbs of water from

a solid desiccant bed weighing 30,000 lbs and has C d ¼ 0.24 Btu/lb F. The

tower weight is 50,000 lbs and its C t ¼ 0.1 Btu/lb F. The ambient
temperature is 110 F and the maximum outlet temperature is 360 F.

The8-hcycleisoperatedas6 hheating and2 hcooling. Assume
C g ¼ 0.6 Btu/lb F.

Solution
Using Eq. (22), the following results are obtained:
360 þ 110
T m ¼ 360, T a ¼ 110, T av ¼ ¼ 235
2

Q H ¼30,000ð360 110Þð0:24Þþ 50,000ð360 110Þð0:1Þ
þ 2000ð1100Þþ 2000ð235 110Þ
¼5,500,000 Btu=cycle
The flow rate of heating gas V H is obtained from Eq. 23:
5,500,000 lbs
V H ¼ ¼ 55,555
ð400 235Þð0:6Þ cycle
or
lbs
V ¼ 9259
H
h
The gas heater load Q G is obtained from Eq. (24):
55,555ð400 110Þð0:6Þ 6 Btu
Q G ¼ ¼ 1:6 10
6 lb
For cooling, use Eq. (25) to find H C :
H C ¼ 30,000ð360 110Þð0:24Þþ 50,000ð360 110Þð0:1Þ
Btu
6
¼ 3:05 10
cycle
The gas flow rate for cooling is calculated from Eq. (26); for 2 h cooling, the
value of V C is found to be
6
3:05 10 lbs
V ¼ ¼ 20,233
C
ð235 110Þð0:6Þð2Þ h
Additional heat requirements of 25% can be used for each cycle.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.