CO2 Capture in A Bubble-Column Scrubber Using MEA/CaCl2/H2O Solution—Absorption and Precipitation

Abstract

This study used the solvent monoethylamine (MEA)/CaCl2/H2O to investigate CO2 absorption and CaCO3 crystallization in a bubble column scrubber. The variables explored were pH, gas flow rate, gas concentration, the liquid flow rate of the solution to absorb CO2, and CaCO3 crystallization. Under a continuous mode, the solution of CaCl2 was fed continuously, and the pH dropped after CO2 absorption. To maintain the set pH value, there was an automatic input of the MEA solvent into the bubble column. In addition to maintaining the pH, the solution could also absorb CO2 and produce CaCO3 crystals, which served two purposes. The results showed that there were mainly vaterite crystals. At different pH values, the lower the pH, the higher the precipitation rate of vaterite (Fp), and vice versa. However, under different gas flow rates, the Fp decreased as the pH value increased. Additionally, the process variables also affected the absorption rate (RA) and the overall mass-transfer coefficient (KGa) generally increased with increasing pH, gas concentration, and gas flow rate. However, it slowed down under operating conditions at high pH and high gas flow rate. Finally, correlation equations for RA, KGa, and Fp were also obtained and discussed in the study.