Natural gas processing is facing an increasing challenge with producing more complex sour gas and complying with more stringent regulations in terms of residual emissions to the atmosphere. In these conditions, the definition of the basis of design is key and detailed attention must be dedicated to all sulfur species: H2S, but also the mercaptans and the carbonyl sulfide (COS). Surprisingly, if the routing of RSH is well understood, the way of COS remains today uncertain.
Recent projects dealing with sour gas containing mercaptans and COS have to select specific configurations to ensure product sweetening and compliance with local environmental regulations, with additional OPEX and CAPEX. The selection was mainly driven by the COS routing through the different steps, for example within the AGRU, with impact for the design of the overall plant including NGL extraction and sweetening units, sulfur recovery units with or without CO2 reinjection. However, laboratory test results and feedback from operating units indicate that the COS routing seems definitively not clearly understood.
This paper presents a review of the COS chemistry, in particular its behaviour in amine solvents. Pilot data and plant data will be used to describe the COS reactivity in the amine process. Then impact on the plant design will be discussed.
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