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

Abstract

• A combined system is constructed to absorb and then regerate SO 2 from flue gas. • SO 2 is efficiently regenerated with adding acid produced by electrodialysis. • The absorption by-product Na 2 SO 4 is electrodialysis to prevent accumulation. Na 2 SO 3 -NaHSO 3 wet absorption process can absorb and regenerate SO 2 from industrial flue gas. Aiming at the problem of SO 2 incomplete regeneration and complicated process, a combined system of Na 2 SO 3 wet absorption-bipolar membrane electrodialysis is constructed. The oxidation by-product Na 2 SO 4 in absorption process is applied for electrodialysis to produce acid and alkali, which are used for SO 2 regeneration and absorption respectively. The purpose is to absorb and regenerate SO 2 in flue gas with high efficiency, and to solve the accumulation problem of Na 2 SO 4 . 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 Na 2 SO 4 are discussed and optimized. The alkali produced is used for SO 2 absorption as the supplementary absorbent, which can make the absorption process sustainable. The acid produced is used for SO 2 regeneration. When there is no additional acid, the regeneration efficiency of SO 2 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 SO 2 can be realized by simultaneous absorption with adding alkali and regeneration with adding acid. The absorption and regeneration efficiency can reach 100%.