The quantitative evaluation of two-stage pre-combustion CO2 capture processes using the physical solvents with various design parameters

In this study, redesign and modeling of the two-stage pre-combustion CO2 capture process, using three different physical solvents, was conducted. The quantitative design modeling analysis was performed using the computational software ASPEN Plus®. The Selexol process was evaluated as the most efficient pre-combustion CO2 capture process from the points of electric/thermal energy consumption as a result of ASPEN Plus® modeling. The Selexol modeling process resulted in electric energy of about 3.2 MWe to maintain the operating temperature and pressure by using the pump, the compressor and the chiller. The consumption of thermal energy was also evaluated to be 0.85 MWth for regeneration of the solvent in the H2S stripper. Concomitantly, various comparison and performance results were obtained by changing the key design modeling parameters; Water-Gas Shift conversion rate, operating temperature and CO2 capture rate were varied for their individual effects on energy consumption, solvent and hydrogen loss. As Water-Gas Shift conversion rate increased, the Selexol process consumes the least amount of electric energy among the modeled CO2 capture processes using the physical solvents. On the other hand, changing the operating temperature turned out to be advantageous for the Rectisol process over other CO2 capture processes using the physical solvents. The reboiler heat duty and hydrogen loss with total solvent flow rate can also be reduced by dropping the operating temperature. As CO2 capture rate increased, Selexol process was more efficient than other processes using the Methanol and NMP (N-Methyl-2-Pyrrolidone). This modeling result is explained by the decrease in the reboiler heat duty and electrical energy consumption although the solvent flow rate increased.