Absorption and recovery of SO2 in flue gas by wet absorption combined with bipolar membrane electrodialysis

Na2SO3-NaHSO3 wet absorption process can absorb and regenerate SO2 from industrial flue gas. Aiming at the problem of SO2 incomplete regeneration and complicated process, a combined system of Na2SO3 wet absorption bipolar membrane electrodialysis is constructed. The oxidation by-product Na2SO4 in absorption process is applied for electrodialysis to produce acid and alkali, which are used for SO2 regeneration and absorption respectively. The purpose is to absorb and regenerate SO2 in flue gas with high efficiency, and to solve the accumulation problem of Na2SO4. The acid production, alkali production and desalination performance of the bipolar membrane electrodialysis are studied. The concentrations of H+ and OH- reach 0.37 mol/L and 0.31 mol/ L, respectively, and the desalination efficiency is 53.1% in 240 min. The influencing factors such as electrolyte concentration, voltage, flow rate and the initial concentration of Na2SO4 are discussed and optimized. The alkali produced is used for SO2 absorption as the supplementary absorbent, which can make the absorption process sustainable. The acid produced is used for SO2 regeneration. When there is no additional acid, the regeneration efficiency of SO2 is only 3.7% at ambient temperature and atmospheric pressure, while 100% regeneration can be achieved after adding acid. The way of acid addition is studied, and the regenerate efficiency of continuous addition is higher. The efficient absorption and regeneration of SO2 can be realized by simultaneous absorption with adding alkali and regeneration with adding acid. The absorption and regeneration efficiency can reach 100%.