Experimental And Simulative Studies For Evaluating Desorption Performance With Blended Amine Solvents In Post-Combustion CO2: Capture Systems

Abstract

Desorption is a very important process to liberate CO2 from CO2 saturated rich solution by adding thermal energy provided by a reboiler. This process should be studied very seriously for improving economic efficiency because fresh solvent for every cycle of capture is very expensive and also up to 70% high energy consumption is required for solvent regeneration procedure. The objective of this research was to evaluate the desorption performance using reactive aqueous MDEA/PZ blends and aqueous MEA/MDEA/PZ experimentally in a bench-scale packed column and compared with the benchmark aqueous 5M MEA solution in terms of cyclic capacity, rate of desorption, desorption efficiency, liquid-side mass transfer coefficient and regeneration energy. The ProMax simulation results were validated with the experimental results. Results showed that the desorption performance was ranked as 3M MDEA+2M PZ>2M MDEA+3M PZ>1M MEA+2M MDEA+2M PZ>5M MEA and it highly depended on the amine type and concentration. It was observed that higher MDEA concentration in the blends can produce more bicarbonate ions which helped to accelerate desorption process with lower regeneration energy consumption. On the contrary, the higher percentages of MEA could cause more regeneration energy due to the high thermally stable carbamate formation. Although PZ could improve the absorption performance significantly, it was not beneficial for the desorption process like MEA. The parametric sensitivity analysis was conducted by the full absorption- desorption process with Promax simulation by changing operating conditions including CO2 concentration in the flue gas, amine flow rate, flue gas flow rate and reboiler temperature. Results demonstrated that cyclic capacity, rate of desorption, desorption efficiency and liquid-side mass transfer coefficient were strongly impacted by the flow rate of flue gas, concentration of CO2 in the flue gas and flow rate of amine. The regeneration energy not only was dependent upon the molar ratio of each amine in the blends, but also highly influenced by amine flow rate and reboiler temperature. The initial cost assessment was simulated later for calculating CO2 capture cost by computing amine cost, pump electrical energy cost and regeneration energy cost with the target of 90% CO2 removal efficiency. Results revealed that the best choice of removing CO2 is 3M MDEA+2M PZ because it only costed $93.88/kg CO2 and it could save approximately 34.59% cost than 5M MEA with the lowest regeneration energy. It was also observed that regeneration energy cost was the most contributor in the operating cost.