Page 277 - Petroleum and Gas Field Processing

and the tower is put back to service. The spent bed is left to react slowly
with oxygen in the air, as shown in reactions (2) and (3), which can be
done by a contracting company.
Design of Iron Sponge Bed

It is noted from Figure 1 that such a bed (batch process) can handle an acid
gas feed of up to 200 ppm and bring it down to 1 ppm in the exit sweet gas
stream.
The design of the iron sponge bed requires the following data:
Q g (MMSCFD) ¼ Gas flow rate
P(psig) ¼ Operating pressure
T( F) ¼ Operating temperature

X AG (ppm) ¼ H 2 S inlet concentration
Z ¼ Compressibility factor from charts
SG ¼ Specific gravity of the gas (assume 0.7 if not
given)

Calculation Procedure
1. Calculate column diameter. First the minimum diameter is
calculated as
Q g TZ
2
2
d m ðin: Þ¼ 360
P
Then, the maximum diameter to prevent channeling is
Q g TZ
2 2
d max ðin: Þ¼ 1800
P
The selected diameter should be between these two values.
3
2. Calculate daily consumption of iron sponge (R,ft /day):
R¼ 0:0133Q g ðX AG Þ
3. Select bed height between 10 and 20 ft. The bed volume (V) becomes
3 2
VðftÞ ¼ 0:7854 D L
where D and L are in feet. The bed is replaced after V/R days.

Example 1
Natural gas flowing at 2 MMSCFD has a specific gravity of 0.7 and acid gas
6
concentration of 25 ppm (MMSCFD ¼ 10 standard cubic feet per day).

The operating pressure and temperature are 1000 psig and 120 F,
respectively. Design an iron sponge unit.

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