Page 327 - Petroleum and Gas Field Processing

5. Calculate the mass transfer zone height h z (ft) using
0:7895 !
q
h z ¼ 31:25 ð13Þ
0:5506 0:2646
V g RS
where RS is relative saturation.
6. Calculate the bed length h B (ft). The bed weight W B (lb) is
calculated using

Amount of water adsorbed (lbs H OÞ
2
W B ¼
Capacity of desiccant (lbs H O=lb desiccantÞ
2
VY 1 1
W B ¼ X C ð14Þ
3
3
The desiccant density B (lbs/ft ) is used to calculate bed volume
3
V B (ft ) using
W B
V B ¼ ð15Þ
B
The bed length h B (ft) is calculated using
V B
h ¼ 2 ð16Þ
B
d =4
7. The maximum useful desiccant capacity (lbsH 2 O/100 lbs desic-
cant) is calculated from
0
X S ðh B 0:45 h Z Þ
X C ¼ ð17Þ
h B
where X S is the dynamic desiccant capacity at saturation and is
0
a function of temperature as
0
X S ¼ X S ð1:518 0:00673 T B Þ ð18Þ

X S is the dynamic capacity at 77 F and T B ( F) is the bed
temperature and can be calculated using gas relative saturation

(RS) at 77 F:
X S ¼ 7:407 þ 0:09357 RS ð19Þ
The calculated value of X C from Eq. (17) is compared with the
assumed value and is readjusted so that assumed and calculated
values become close.
8. Calculate the breakthrough time b from:

0:01X C B h B
¼ ð20Þ
B
q
The cycle time C should be greater than the breakthrough time:
C > b

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