Work

Impact of Operational Parameters on the CO2 Absorption Rate in Ca(OH)2 Aqueous Carbonation─Implications for Process Efficiency

Year: 2024

Type: article

Abstract: The impact of operational parameters on the CO 2 absorption rate (η( t )) during Ca(OH) 2 aqueous carbonation has been investigated, including the reagent concentration, CO 2 volumetric flow rate, temperature, Na- and K-salt impurity concentration, ionic strength, and mixing system. The carbonation mechanisms were numerically investigated with the modeling tool Phreeqc. Positive correlations were predicted and confirmed between η( t ) and Ca(OH) 2 initial concentrations, reduced volumetric flow rate, elevated temperature, and less obvious parameters like salt impurities and increased ionic strength. The present results indicate a modest impact (a few percent increase) on the absorption rate when varying Ca(OH) 2 concentration from 1 to 10 wt %. Increasing the temperature from 283 to 363 K enhances the η( t ) of about 37%. The average seawater NaCl concentration (3.5 wt %) enhances η( t ) values by as much as 75%. Na 2 SO 4 and K 2 SO 4 in place of NaCl and KCl, respectively, suggest that sulfate ions promote the dissolution of CO 2 in aqueous solutions more efficiently than chloride ions. We demonstrate that the CO 2 –water interfacial surface area plays a crucial role, causing a cascade of kinetic acceleration of dissolution. Utilizing a static mixer (sparger and porous stone diffusor) significantly accelerates dissolution–precipitation, leading to enhanced absorption rates and reducing energy consumption associated with mixing. This approach, coupled with 3.5 wt % NaCl concentration, achieves a CO 2 absorption rate of up to 90% for a 2 L/min CO 2 flow. The proven enhancements pave the way for more efficient reactor design tailored for ex situ carbon capture both “at the smokestack” and potentially for direct air capture.

Source: Energy & Fuels

DOI: 10.1021/acs.energyfuels.4c02455