H_2S Scrubbing from Noncondensable Gas in After-Condensers

摘要

At Unit 12 in The Geysers, Calpine operates a Burner/Scrubber system to remove H_2S from the noncondensable gas. The operating rate of this unit has been declining over the years, and the noncondensable gas flow rate and H_2S concentration are about 10% or less of the original design. The partitioning of H_2S to the vent gas in the main condenser is low, and the absorbed H_2S in the cooling tower water systems is mostly naturally oxidized without the need for chemical addition. Additionally, the heating value of the noncondensable gas is now much lower than design, resulting in the need to add supplemental fuel to the burner. As a result of the low current H_2S and gas rates, if the Burner/Scrubber system is shut down, only a portion of the H_2S in the gas will have to be removed in order to comply with the permit limit. The after-condenser was considered for use in the bulk removal of H_2S from the gas. A study, based on process simulations and data taken at other Calpine facilities, was conducted to evaluate H_2S removal in the Unit 12 after-condenser i) in its current spray-tower arrangement and also ii) assuming the addition of a packed section. The methods used to predict H_2S removal in the after-condenser with and without the addition of a packed bed are discussed. Ideally only condensate would be used to absorb the H_2S, with the absorbed H_2S being naturally oxidized in the cooling tower loop. Some caustic addition could also be required to enhance H_2S removal, and also to control cooling water pH. The effect of operating conditions and packing characteristics on the performance of the after-condenser as an H2S scrubber are also discussed.