Use of recycle for H2S removal by MDEA scrubbing in IGCC systems

This work focuses on the analysis of the H2S removal section of an Acid Gas Removal (AGR) station in an Integrated Gasification Combined Cycle (IGCC) plant. The AGR station is composed of one absorption section for H2S and one absorption section for CO2S. The first section aims at removing most of the hydrogen sulfide from the syngas in order to obtain, in the following unit for the CO2S removal, a CO2S-rich stream containing less than 200 ppmv of H2S on a dry basis. The H2S-rich stream obtained from the regeneration and exiting the H2S removal section is sent for sulfur recovery in a Claus plant, which needs a minimum content of H2S in the feed. The acid gas removal is performed by using an aqueous solution of MethylDiEthanolAmine (MDEA). Although it selectively absorbs hydrogen sulfide, part of carbon dioxide is co-absorbed with H2S, and the minimum content in H2S required for feeding the Claus plant may be not achieved. A recycle of the H2S-rich stream exiting the regeneration to the absorption section is not usually employed in these systems, but it has been considered for increasing the amount of hydrogen sulfide absorbed and therefore present in the H2S-rich stream at the outlet. A sensitivity assessment has been performed in this work to determine the influence of the recycle stream on the overall absorption process and the minimum amount of the flowrate necessary to accomplish the required specifications.