Study On Emission Of SO₂ And Its Mechanism Analysis In The Process Of Thermal Utilization Of Dry And Sim-dry Desulphurization Residues

Dry and semi-dry flue gas desulfurization (FGD) is a desulfurization technology with advantages of low investment, simple process and no sewage discharge. Comparing to the desulphurization byproduct of wet FGD technology,the desulphurization byproduct of dry and semi-dry FGD technology has more complex composition. The desulphurization byproduct consists of calcium carbonate, calcium sulfite, calcium sulfate, calcium hydroxide, silica and mullite, etc, but these composition limit the application range of the desulphurization byproduct greatly. Calcium sulfite, calcium carbonate and calcium hydroxide could converted to calcium sulfate and calcium oxide, they are flux that are needed in the thermal decomposition of potash feldspar, so the desulphurization byproduct and potash feldspar could make up of the reaction system of potassium feldspar-gypsum-calcium carbonate in order to manufacture soil amendment which contains K,Si,Ca and S that all the elements are needed by crops.The desulphurization byproduct in the desulphurization byproduct is not stable and if the use is unreasonable, the sulfur dioxide production will be yielded along with secondary pollutions. So it is necessary to do the research in the filed of sulfur dioxide emission in the process of thermal utilization of dry and sim-dry desulphurization residues. The results showed that: calcium sulfite could be oxidized into calcium sulfate rapidly in air atmosphere at 450～700℃. When calcination temperature is in the range of 700℃to 850℃,sulfur dioxide escaped quantity will reduce with the calcination temperature increase, and increase with calcination temperature increase in temperature range 850℃to 1050℃. Calcination time and ventilation volume has little influence on sulfur dioxide escaped quantity. Oxygen ratio has direct effect on escaped quantity of sulfur dioxide. The maximal emission concentration of sulfur dioxide is about 94mg/m3 which is much lower than that in national standard when oxygen ratio is 4%. The effect of calcination temperature, oxygen ratio, calcination time and ventilation volume on sulfur dioxide escaped quantity in the roasting process of mixture of the desulphurization byproduct and potash feldspar is basically identical to that in the roasting process of the desulphurization byproduct. Coal dust content has obvious influence on sulfur dioxide escaped quantity. When coal dust content increase from 6% to 8%, sulfur dioxide escaped quantity will increase about 10%. In the process of manufacturing soil amendment, n(K-feldspar):n(CaSO₄):n(CaCO₃)=1:1:14, so the desulphurization byproduct content in mixture is small, and the content of calcium sulfite in mixture is much lower than that in the desulphurization byproduct, therefore the emission concentration of sulfur dioxide should be lower than 94mg/m³.The thermodynamic analysis results show that: sodium sulfite can be oxidized when the temperature is 700K. But it can not be decomposed when the temperature is 1000K, so sodium sulfite is oxygenized easily in the air. XRD spectrum prove the emission of SO₂.