Development of air and GHG emission calculators integrated in UNISIM-based process simulator: Case study of a gas sweetening with effects of process parameters

This paper reports the development of air and GHG emission calculators embedded in UNISIM-based process simulators, which are used as a computational tool to generate estimated values of air and GHG emission integrated with process simulation. A gas sweetening unit is taken as an example for the case study, with the effects of process parameters on the resultant emission being emphasized. Air and GHG calculators are developed based on up-to-date standards and national regulations concerning oil and gas processing facilities. The simulation's base case is designed to produce sweet gas with sales gas specifications using MDEA solvent, which reveals 1,527 tonnes CO2e/day (representing GHG emission) and 0.348 tonnes SO2e/day (representing air emission). Pressure decline in the sour gas stream leads to a slight increase in emission up to 1,554 tonnes CO2e/day and 0.368 tonnes SO2e/day because of the additional compression systems. Using DEA as a solvent does not significantly affect air and GHG emission for the same sweet gas specification. The simulation also revealed that the gas flow rate (capacity) is not directly proportional to the eventual emission. In this case, the driver for air and GHG emission is the reboiler's duty, dependent on the amine flow rate. As there is a critical (minimum) lean amine flow rate regarding the sour gas flow rate, the non-proportional relationship between gas flow rate and emission is expected. To produce sweet gas with LNG specification, the emission rises considerably to 2,652 tonnes CO2e/day and 0.747 tonnes SO2e/day because CO2 loading of rich amine is higher in this case, eventually increasing the reboiler duty significantly.