Patent ID: 8435325

Claim:
A method for removing CO 2 and H 2 S from a feed gas including at least CO 2 and H 2 S, comprising: a step of introducing the feed gas into a first absorber, and removing CO 2 and H 2 S from the feed gas by contacting the feed gas with a lean solution in the first absorber; and a step of subsequently introducing the feed gas into a second absorber, and further removing CO 2 and H 2 S remaining in the feed gas by contacting the feed gas with a semi-lean solution in the second absorber; wherein a rich solution composed of the lean solution and the semi-lean solution that have absorbed CO 2 and H 2 S in the first absorber and in the second absorber respectively is introduced into a flash drum in which an internal pressure is kept lower than that in the first absorber and in the second absorber; after a part of CO 2 and H 2 S is released from the rich solution and a semi-lean solution is obtained in the flash drum, a part of the semi-lean solution in the flash drum is cooled and introduced into the second absorber to contact again with the feed gas in the second absorber; a remaining part of the semi-lean solution in the flash drum is introduced into a stripper and heated to release remaining CO 2 and H 2 S from the semi-lean solution and a lean solution is obtained in the stripper; a part of the lean solution in the stripper is cooled and introduced into the first absorber to contact again with the feed gas in the first absorber; and after a remaining part of the lean solution in the stripper is cooled, the remaining part of the lean solution is introduced into the second absorber at a level above a level where the semi-lean solution from which a part of CO 2 and H 2 S has been released in the flash drum is introduced, and again is contacted with the feed gas in the second absorber, and thereby obtaining treated gas, and wherein CO 2 concentration and H 2 S concentration in the treated gas are measured; and if the measured CO 2 concentration or H 2 S concentration in the treated gas exceeds a predetermined concentration, an amount of the semi-lean solution to be introduced from the flash drum into the stripper is increased and at the same time an amount of steam to be introduced into a reboiler in the stripper is increased to thereby increase a rate of regeneration of the rich solution.