Design Modification of Acid Gas Cleaning Units for an Enhanced Performance in Natural Gas Processing

Acid gas cleaning is one of the natural gas processing steps where the acid gases are removed to satisfy the quality of the sweet gas. Conventionally, this is achieved by processing the sour gas through an acid gas removal (AGR) unit to produce the desired sweet gas while concentrating the H₂S gas in the acid gas enrichment unit. Together with achieving the required high heating value of 930 BTU/SCF in the sweet gas, it is also desired from the process that the acid gases must contain 30-55% H₂S content before feeding to the sulfur recovery unit. In addition, the waste gases sent to the thermal oxidizer must not contain more than 2000 ppmv H₂S. However, these requirements put a constraint on the process operational flexibility especially when the feed gas has a high CO₂ content. In this study, a novel acid gas cleaning design has been proposed that can significantly reduce the energy requirement while maintaining all the streams' design specifications. The proposed design recommends first producing acid gas with the required purity and then producing the sweet gas in another AGR unit. The results show that the proposed design requires 22% lower operational energy compared to the base design. The economic analysis reflects a saving of more than $7.25 million in total annual cost compared to the conventional design.