Operational and Asset Integrity Implications on Sour Gas Processing Facilities of Higher than Design H2S Carryover in Sweet Gas Leaving the Acid Gas Removal Unit Amine Absorber

摘要

This paper presents the findings of a study into the consequences of H2S slip into sweet gas from an Acid Gas Removal (AGR) unit amine absorder. Whilst the study was initiated to investigate consequences to downstream consumers with respect to sales gas product specification, during this assessment the implications from a plant operational and metallurgical perspective were also investigated and found to be of critical significance and defined the maximum permissible H2S concentration in the sweet gas leaving the amine absorber. The study assessed the maximum H2S concentration permissible in the sweet gas leaving the AGR amine absorber when considering stress corrosion cracking regions for the downstream plant materials of construction to determine maximum allowable H2S content in sales gas from a metallurgical perspective. The paper also investigated a multitude of operational implications regarding higher than design H2S in the plant sweet gas, including high H2S in the plant fuel gas network. The study found that while the normal operating concentration of 3ppm(mol) H2S in the sweet gas is normally respected, the maximum allowable H2S concentration limit must not exceed 15ppm(mol) due to the risk of stress corrosion cracking in the downstream processing facility. This maximum limit from a metallurgical perspective also avoids all of the operational concerns identified. In the event of an AGR amine absorber operational upset (e.g. loss of lean amine feed), after a relatively short duration, the concentration of H2S in the sweet gas leaving the AGR amine absorber rises rapidly beyond the normal operational concentration and will significantly exceed the 15ppm(mol) minimum limit. As such, plant modifications have been implemented to trip the AGR unit whenever process operating conditions exceed the normal operating envelope due to the potential of the sweet gas to go off spec. This paper will be of interest to sour gas plant operators who remove H2S from their raw gas to meet a gas product specification using amine absorption processes. This paper presents findings of as study in to the operational and metallurgical consequences of exceeding H2S specification in Sweet Gas for a sour gas processing facility.