Understanding the Impact of Hydrocarbon Co-absorption Losses on Revenues from Your Gas Plants: The Reality Through Life-Cycle Costs Analysis

Abstract

Gas development projects face growing challenges from increasingly sour resources with relatively high levels of CO2, H2S, Mercaptans and COS, and tighter sales specifications and stricter environmental emission standards. The removal of trace components such as COS and RSH can have detrimental effect on project value as considerable CAPEX and OPEX investments have to be made. Predominantly mercaptans are either removed in Acid Gas Removal Unit (AGRU) with the use of hybrid solvents such as Shell's Sulfinol solvent, or slipped to downstream dehydration/mercaptan removal adsorption unit using molsieves. While the former line-up involves a single process unit to remove all sulphur compounds (H2S, RSH and COS) and CO2, the latter process line-up involves multiple process steps including an AGRU absorber with aqueous amines to remove H2S and CO2, and a molecular sieve downstream unit to dehydrate and remove mercaptans in combination with a dedicated physical or hybrid solvent for removal of mercaptans from molsieve regeneration gas. There is the perception that the use of hybrid solvents reduces revenue through hydrocarbon absorption losses. Simple hydrocarbon-loss percentages around AGRU absorber provide some insight, but this data must be used cautiously, as this data alone will not tell the full story. Previous work has shown that, in most cases, higher hydrocarbon losses through co-absorption with hybrid solvents compared with using aqueous amines such as methyl diethanolamine (MDEA) are offset by savings in reboiler energy consumption. This paper goes a step further by modelling the full life-cycle costs of the two conventionally used process line-ups so that informed solvent-selection and capital investment decisions can be made. This paper also discussed capital- and additional operating-cost savings associated with hybrid solvents, which further tip the economic balance in favour of hybrid solvent systems.

Decision support methods and applications in the upstream oil and gas sector

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