Bipolar membrane electrodialysis combined with ozone oxidation wet scrubbing to remove SO2 and NOx from flue gas and achieve CO2 mineralization

Abstract

This study proposed a new process based on bipolar membrane electrodialysis (BMED) for the one-stop simultaneous removal of SO2 and NOx and mineralization of CO2 from flue gas. The process could be divided into two simultaneous aspects: the mineralization of CO2 into calcium carbonate using calcium ions in seawater; meanwhile, and the removal of SO2 and NOx by wet scrubbing. During this process, the OH– generated by the bipolar membrane was used as an absorbent, and ozone (O3) was used as an oxidizer for NO in the flue gas. It was found that at higher current density, the absorption rate of CO2 could be enhanced, but the calcium and magnesium were precipitated in the form of carbonate at the same time, and the product was no longer pure calcium carbonate product, thus reducing the purity and added value of the product. Enhancing the liquid flow rate could reduce the membrane surface resistance, thus effectively decreasing the energy consumption of the system. The increase of SO2 concentration and n (O3/NO) could significantly improve the NOx removal efficiency, however, higher SO2 concentration would consume more OH– and inhibit CO2 absorption. Under the optimal conditions, the average CO2 absorption rate, decalcification rate, and denitrification rate were 53. 57%, 92.56%, and 87. 61%, respectively, and the desulfurization rate was close to 100%. Given the high energy consumption in the decalcification process and the problem that the by-product was calcium carbonate with mixed crystal form, the experiment was optimized. The electrodialysis process could produce aragonite-type calcium carbonate, which was utilized as crystal seed to ensure the purity of subsequent by-products. Especially, the energy consumption was effectively reduced by utilizing the accumulation of carbonate and bicarbonate in the mother fluid of the electrodialysis process through the self-crystallization process of calcium carbonate induced by crystal seed to shorten the time of the electrodialysis process.