Page 278 - Petroleum and Gas Field Processing

Solution
The feed acid concentration is 25 ppm, which is below 200 ppm, so a batch
process such as iron sponge unit can be used.

d 2 min ¼ 360ð2Þð580Þð0:86Þ ¼ 353:43 and d min ¼ 18:8 inch
1014:7
2 1800ð2Þð580Þð0:86Þ
d max ¼ ¼ 1769:7 and d max ¼ 42 inch
1014:7
A diameter between 18.8 and 42 in. can be used. Select a diameter of 24 in.
(2 ft). Daily iron consumption R is
3
R ¼ 0:0133ð2Þð25Þ¼ 0:665 ft =day
Select a bed height of 10 ft. The bed volume becomes
2
V ¼ 0:7854ð2Þ ð10Þ¼ 31:416 ft 3
31:416
Bed life ¼ ¼ 47 days
0:665
Thus, the bed should be replaced in 6 weeks.

11.4.2 Zinc Oxide

Zinc oxide can be used instead of iron oxide for the removal of H 2 S, COS,
CS 2 , and mercaptans. However, this material is a better sorbent and
the exit H 2 S concentration can be as low as 1 ppm at a temperature of
about 300 C. The zinc oxide reacts with H 2 S to form water and zinc

sulfide:
ZnO þ H 2 S ! ZnS þ H 2 O
A major drawback of zinc oxide is that it is not possible to regenerate it to
zinc oxide on site, because active surface diminishes appreciably by
sintering. Much of the mechanical strength of the solid bed is lost due to
fines formation, resulting in a high-pressure-drop operation.
The process has been decreasing in use due to the above
problems and the difficulty of disposing of zinc sulfide; Zn is considered a
heavy metal.

11.4.3 Molecular Sieves
Molecular sieves (MSs) are crystalline sodium alumino silicates and have
very large surface areas and a very narrow range of pore sizes. They possess
highly localized polar charges on their surface that act as adsorption sites for

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