Page 331 - Petroleum and Gas Field Processing

where
¼ water adsorbed/cycle (lbs/cycle)
w 1
¼ heat required/cycle (Btu/cycle)
Q H
M d , C d ¼ mass and specific heat of desiccant
¼ mass and specific heat of tower
M t ,C t
¼ heat of water desorbed (given) (Btu/lb)
H d

¼ maximum outlet temperature ( F)
T m

¼ ambient temperature ( F)
T a
To calculate gas flow rate V H (lbs/cycle) required to desorb water,
you need to raise heating gas to T H from ambient temperature T a to
supply Q H .
Thus,
Q ¼ V ðT T ÞC g
H
H
av
H
where C g is specific heat of gu; or
Q H lbs
V H ¼ ð23Þ
ðT T ÞC cycle
av
g
H
The gas heater load, Q G (Btu/cycle), is
Btu
Q G ¼ V H ðT H T a ÞC g
cycle
If the heating period is H , h for each cycle is then
V H ðT H T a ÞC g Btu
Q G ¼ ð24Þ
H h
where Q G is the gas heater load and H is the heating time per cycle.
Usually, 25% excess load is assumed for losses.
For cooling part cooling requirements, H C (Btu/cycle),
H ¼ m ðT T ÞC þ m ðT T ÞC t ð25Þ
m
a
d
a
t
d
m
C
and the gas flow rate for cooling, V C (lbs/cycle),
H C lbs
V C ¼
ðT av T a ÞC g cycle
or
lbs
H C
V C ¼ ð26Þ
ðT av T a ÞC g C h
where C is the cooling time, (h/cycle)

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