Simulation and optimization of sweetening and dehydration processes in the pretreatment unit of a mini-scale natural gas liquefaction plant

Abstract

This study focuses on the simulation of sweetening and dehydration processes for natural gas feed to achieve the liquefied natural gas specifications. The analysis and optimization of these two units have been carried out to reduce energy consumption. The sweetening and dehydration units lower the amount of carbon dioxide and water in treated gas to less than 50 ppmv and 0.1 ppmv, respectively. In the sweetening unit, due to the high energy consumption (45.63 kW) in the reboiler of the amine regeneration column, sensitivity analysis is used to investigate the variables causing high energy consumption. The optimum values for the main influencing variables were obtained by the response surface method. The optimization results in reboiler duty reduction by 30% compared to the base case simulation. In the dehydration unit, due to the high energy consumption of the furnace (100.7 kW) inlet stream temperature and regeneration temperature are analyzed as the influencing variables. By optimizing the unit, the energy consumption per mole production is reduced by 20% compared to the base case simulation. Through exergy analysis 836.13 kJ/kg CO2 exergy loss is estimated for sweetening plant and 5724.73 kJ/kg H2O exergy destruction for dehydration plant. The regenerator and absorber have a significant share of exergy losses in the sweetening plant and the furnace is the major contributor to exergy destruction in the dehydration plant.