Numerical prediction of CO2 capture process by a single droplet in alkaline spray

• CO2 capture by a single droplet is studied numerically.
• Three different initial pH values of 10, 11, and 12 in the droplet are considered.
• The initial pH value has a significant influence on the capture process.
• The carbon capture rate is raised as the initial pH value rises.
• The droplet with the initial pH value of 12 is feasible to perform CO2 capture.

Carbon dioxide captured by single droplets in sprays plays a fundamental role in reducing greenhouse gas emissions. This study focuses on CO2 capture processes in single droplets in alkaline sprays using a numerical method. Three different initial pH values of 10, 11, and 12 in the droplet are considered. The capture behavior in the absence of chemical dissociation is also investigated for comparison. The predictions suggest that the chemical dissociation in the droplet substantially elongates the CO2 capture process and the mass diffusion is the controlling mechanism of CO2 capture process. For the chemical absorption, the final CO2 capture amount by the droplet is mainly determined by HCO3- which is significantly influenced by the initial pH value. An increase in initial pH value raises the carbon capture amount by the droplet. The mean concentration of CO32- is highly related to the variation of mean pH value, but its concentration is by far lower than those of H2O⋅CO2 and HCO3-. Corresponding to the initial pH values of 10, 11, and 12, the times required for turning the basic droplet to the acidic one are in the orders of 10, 100, and 1000 ms. On account of larger carbon capture amount and shorter absorption period at a higher initial pH value, the carbon capture rate is lifted as the initial pH value rises, and CO2 capture by droplets at the initial pH value of 12 is better than those at 10 and 11.