H2S Lean Loading, the Balance Between Specifications, Corrosion and Actual Performance

Saudi Aramco guideline is to maintain a minimum H2S in lean amine as part of the Corrosion Monitoring Program, however, the minimum of 300 ppmw is not always achievable. Gas Operations Technical Support initiated a study to identify the reason for deviations between the guideline and field measurements, finding feed gas H2S/CO2 ratio, Gas Treat unit design, design basis, analytical procedures, and amine type were factors. The findings will be discussed along with examples when low residual H2S is beneficial or detrimental. The importance of residual H2S in lean amine is that the H2S in the sweet gas or partial pressure is related to the residual H2S in lean amine, with the H2S in sweet gas increasing with increasing lean amine temperatures or residual H2S in lean amine. Lower residual H2S allows operating at higher lean amine temperatures or lower pressures, but can negatively impact corrosion. Typical control parameters are the lean amine temperature, lean amine flow, regenerator overhead temperature or steam flowrate/gpm amine. Lean amine temperature is significantly impacted by the ambient temperature in Saudi Arabia that reaches 49°C (120°F) during summer, especially for gas treatment units operating with ambient cooling. Regenerator overhead temperatures or steam flow were reduced in a number of plants, to increase the residual H2S in lean amine without significant increases, before causing H2S breakthrough to the sweet gas.