Study On The Catalytic Conversion Of The NaHSO₃to Elemental Sulfur In The Desulfurized Liquid From Low Concertration Sulfur Dioxide Flue Gas Desulfurization

:Traditional flue gas desulfurization (FGD) process remains problems of secondary pollution and high cost. Focus on these problems, we develop a new process to recovery element sulfur, e.g. SO2alkali absorption and Se-catalyzed desulfurized liquid to prepare sulfur and sodium bisulfate at low temperature. This process includes SO2adsorption, catalyzed disproportionation of desulfurized liquid containing NaHSO3, destabilization of sulfur colloids, and crystallization of sodium hydrogen sulfate. The advantages of this process include high desulphurization efficiency, high recovery rate of sulfur resource, good economy, and no secondary pollution.In this study, some process parameters were studied and optimized, and the catalytic mechanism was explored. The following results were gained:(1) The absorbing process is influenced by the constituent of absorption liquid and flue gas. The adsorption capacity of SO2decreases by5.98%when using Na2CO3as alkali liquid instead of NaOH. During the absorption process, SO2cannot be absorbed when the pH of the absorption liquid decreases to5. However, the SO2can be absorbed completely through the two-stage absorption. O2in fuel gas reduces the conversion of sulfur. The effect of O2can be inhibited by adding Na2S (2%) in alkali liquid. Moreover, the increase of CO2content in fuel gas can inhibit the separation of CO2from liquid, and then hinder the adsorption of SO2.(2) We first found that selenium could catalyze the disproportionation reaction of NaHSO3and made the reaction temperature decrease from180℃to70℃. Se-catalyzed NaHSO3disproportionation reaction is a solid-liquid-solid phase transformation process. The catalytic efficiency is high and the catalyst Se can be separated easily. Besides, catalyst Se has stable catalytic efficiency when it is reused.(3) The influence of process parameters on the conversion efficiency of Se-catalyzed disproportionation is not significant. Conversion efficiencies are all higher than97%. However, catalysis rate is affected significantly. With the increase of adsorption liquid concentration, the catalysis rate increases. The increase of reaction temperature increases the reaction rate exponentially. When catalyst dosage is4.70g/L and0.64g/L, the reaction rate is enhanced by28%with the increase of stirring rate. When catalyst dosage is greater than18.40g/L, the effect of stirring on the reaction rate is insignificant.(4) The colloid sulfur is derived from the acidolysis of Na2S2O3. Destabilization efficiency of colloid sulfur increases with the increase of time, colloid concentration, heating temperature, and stirring strength. The product sulfur has high purity, large size and high degree of crystallinity. The main functional group on S surface is hydroxyl. The nucleation mechanism of S is heterogeneous nucleation. The growth mechanism is in accord with Ostwald ripening theory.