Mass transfer characteristics of a continuously operated hollow-fiber membrane contactor and stripper unit for CO2 capture

Mass transfer performance of a polypropylene hollow-fiber membrane contactor as part of a continuously operated CO2 capture unit with amino acid salt (potassium glycinate) absorbent and vacuum solvent regeneration was studied. The effects of key operating parameters on the absorption mass transfer characteristics were explored. Without vacuum stripping, absorption rate was found to be limited by low CO2 desorption efficiency from the loaded absorbent solution in the stripping unit, resulting in high solvent CO2 loadings and limited chemical absorption rates. Introduction of vacuum stripping greatly improved desorption performance, resulting in improved steady-state absorption performance. The overall mass transfer coefficient increased at higher stripping temperatures and lower vacuum pressures in the range of 60-80 degrees C and 300-800 mbar (abs). The overall mass transfer coefficient increased with increasing liquid flow rate, and the highest value reached was 1.8.10(-4) m s(-1). The individual mass transfer coefficients in absorption were calculated based on mass transfer correlations and experimental data, including estimation of the enhancement factor for chemical absorption. The overall mass transfer resistance was found to be dominated by the liquid-side resistance, at almost 90 % of the total resistance. The estimated membrane mass transfer coefficient was low compared to a theoretical value assuming non-wetted operation, suggesting potential partial wetting of the membrane. Stable performance of the unit and the membrane contactor was demonstrated during a stability test with over 30 h of operation.