Oxidation Characteristics Of Calcium Sulfite As An Intermediate Product In Wet Desulfurization

In order to complacement increasingly stringent emission standards,SO₂ removal technology need be studied on coal-fired power plants.Wet desulfurization technology is applied widely,but there are still some problems.If CaSO₃ oxidation insufficient,there have not enough seed to rapid growth.Gypsum dewatering difficulties cause the equipment scaled.So it is necessary to select the appropriate additive to promote oxidation.The experiments were carried out on a bubbling reaction device with volume of 2.4 L.The research focused on oxidizing calcium sulfite oxidizing and the oxidation rate of calcium sulfite during the SO₂ removal process.The oxidation experiment of calcium sulfite was carried out under the condition of no additives and catalyst or inhibitor respectively.SO₂ removal process in oxidation of calcium sulfite is simulated limestone-gypsum desulfurization process to study the intermediate product-the oxidation rate of calcium sulfite and other issues.In the oxidation experiment of calcium sulfite,the macroscopic reaction characteristic of calcium sulfite was explored.And it was found that the oxidation rate of sulfite was affected obviously by the oxygen concentration,which showed the response of 0.76 level.The lower the initial pH value,the faster the reaction rate.Addition of the appropriate catalyst can significantly accelerate the reaction process,manganese salt,ferric salts,magnesium salts,copper chloride and power plant ash can accelerate the oxidation rate of calcium sulfite.The oxidation rate of divalent manganese salt is the best,and the oxidation rate can be increased to about two times under proper concentration.The effect of ferric salts on the oxidation process is obvious,but the effect of ferrous salts on the oxidation process is not obvious.Different power plant ash has promoting effect on the oxidation process.And the mechanism of ash is also needed to be further analyzed.In inhibitors,the effect of sodium stearate < humic acid sodium <sodium thiosulfate,to achieve the same inhibitory effect,the sodium stearate to be added about six times the mass concentration of humic acid sodium.Sodium thiosulfate has a good inhibitory effect.When the concentration of 0.3g,the oxidation rate reduced to about 3% of the original.In the simulated limestone-gypsum desulfurization experiment,the effect of O₂ concentration,manganese chloride and sodium thiosulfate on the oxidizing ratio of calcium sulfite was investigated.When the O₂ concentration is more than 5%,the oxidized calcium sulfite can be completely oxidized.When the concentration of O₂ is 3%,the oxidation rate is about 84.9% at the first 100 min.The addition of MnCl₂ can increase rate of CaSO₄ in the desulfurization product.With the addition of more than 0.06g/L,all of calcium sulfite can be Oxidation.And the oxidation rate of calcium sulfite decreases with the addition of manganese chloride,but it is still higher than that without additive.When the concentration of sodium thiosulfate was 0.05g/L,the oxidation rate of calcium sulfite was about 44.2%.When the concentration was 0.15g/L,the sulfurous acid formed at first 100 min Calcium oxidation rate decreased to 11.2%.That means limestone slurry absorption of SO₂ in nearly 90% are in the form of calcium sulfite.