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Figure 2 Alternatives for natural gas sweetening.
11.4 BATCH PROCESSES
In this case, H 2 S is basically removed and the presence of CO 2 does not
affect the processes. Usually, batch processes are used for low-sulfur-content
feeds.
11.4.1 Iron Sponge
Iron sponge fixed-bed chemical absorption is the most widely used batch
process. This process is applied to sour gases with low H 2 S concentrations
(300 ppm) operating at low to moderate pressures (50–500 psig). Carbon
dioxide is not removed by this treatment. The inlet gas is fed at the top of
the fixed-bed reactor filled with hydrated iron oxide and wood chips. The
basic reaction is the formation of ferric sulfide when H 2 S reacts with ferric
oxide:
2Fe 2 O 3 þ 6H 2 S ! 2Fe 2 S 3 þ 6H 2 O ð1Þ
The reaction requires an alkalinity pH level 8–10 with controlled injection
of water. The bed is regenerated by controlled oxidation as
2Fe 2 S 3 þ 3O 2 ! 2Fe 2 O 3 þ 6S ð2Þ
Some of the sulfur produced might cake in the bed and oxygen should be
introduced slowly to oxide this sulfur, Arnold and Stewart [2]:
S 2 þ 2O 2 ! 2SO 2 ð3Þ
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