Impact of Reactor Design on the Chemical Absorption of Carbon Dioxide

Abstract

Chemical absorption of carbon dioxide from point sources remains one of the most promising technologies to offset greenhouse gas discharges from heavy industries. A recent study highlighted the promise of using screen-type static mixers in intensifying CO2 capture using alkaline solutions and new insights into their flow dynamics led to the development of a novel variant. These new mixers utilize carefully designed, and strategically placed, inserts downstream of a woven mesh to further improve their mixing action. Therefore, the current study attempts to compare the performance of these different mixers for the intensification of CO2 absorption into a sodium hydroxide solution under various operating conditions and design configurations. Using the same reactor, seven equidistant screen mixers were employed while only three novel mixers were used. Two different screen geometries were utilized in each case and the gas and liquid flow rates were changed to maintain a total flow velocity ranging between 0.67 and 1.7 m/s. Pressure drop, removal efficiency, and specific energy consumption of each design were compared at the various gas and liquid flow rates with the gas phase volume fraction ranging between 0.09 and 0.38. The pressure drop per element of the novel design was on average 25.3 % higher than the screen mixers. However, the total pressure drop across the reactor equipped with the novel mixer was approximately 46.3 % lower than the case of screen mixers because of the lower number of elements. The removal efficiency enhanced with an increase in the liquid and gas flow rates, with the liquid flow rate having a more pronounced effect. The mixer geometry also impacted the CO2 removal efficiency where using the novel mixers yielded higher efficiencies than screen-type static mixing elements with the enhancement being a function of a smaller screen open area. Removal efficiencies as high as 95% were reached within 361 milli-seconds of contact time between the phases. In addition, the novel mixer geometries were found to require 40 to 300% less energy to achieve CO2 removal rates similar to those obtained using screen-type static mixers.