Wet desulphurization technologies include physical absorption, chemical absorption and chemical oxidation. The need of reprocessing hydrogen sulfide of Physical and chemical absorption restrict their applications in actual projects. The widely used method is chemical oxidation, with alkaline solution as the absorbent and oxygen carrier as catalyst. The alkaline chemicals dissolved in water and goes into tower to contact with hydrogen sulfide to make oxidation reaction with elemental sulfur generated. The desulphurization efficiency of mature chemical oxidation method can reach above 99.5%.
For large projects, the desulphurization process is usually the combination of wet and dry types. Wet type is for the primary filtration while dry type for the fine desulphurization.
The wet desulphurization tower is composed of scrubbing tower, H2S sampling and monitoring system, alkaline solution deploying groove, softening water feed device, liquid level control system, supports and connection fittings. Automatic operation would be achieved through the monitoring of outlet hydrogen sulfide content and Ph value.
When system in operation, raw biogas gets through tower in the bottom-up flow, while the Na2CO3 solution(or NaOH solution) sprays into tower from the top down, by this means the complete reaction occurs between H2S and alkaline solution. The liquid is gathered in the bottom groove of tower, with automatic addition by metering pump by means of the monitoring of H2S concentration at outlet.
Main reaction mechanism if take Na2CO3 as alkaline chemicals
1, Absorption: H2S + CO32- = HS- + HCO3-
2, Oxidation Separation of Sulfur: HS- + [Catalyst]·O = OH- + [Catalyst]·H
3, Regeneration: [Catalyst]·H + O2 = [Catalyst]·O
OH- + HCO3- = CO32- + H2O
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