Study On The Modified Process Of Sintering Flue Gas Desulfurazation Ash By Circulating Fluidized Bed

The SO₂ of sintering flue gas which is discharged from iron and steel industry accounts for 50%～70%,it will cause serious environmental pollution and waste of resources if discharged directly.The method of circulating fluidized bed flue gas desulfurization(CFB-FGD) technology is widely used for existing businesses due to its many advantages,such as small footprint,simple operation,no waste water generation,no produce secondary pollution,et al.However,the by-products of CFB semi-dry flue gas desulfurization is ash.Because of a large amount of CaSO₃,the by-products can not be used into the cement production directly.Based on the analysis of the physical and chemical properties,the phase structure and the thermal stability circulating of the fluidized bed sintering flue gas desulfurization ash,the mathematical-regression model was eatablished about the dependent variable(conversation rate of desulfurization ash) and independent variables(temperature,time and gas/solid ratio),and came to the modification process of the best optimization conditions,set up the desulfurization ash oxidation kinetics equation.The modified desulfurization ash can be used in the production of cementitious materials,retarder,et al.Thus it expands the new utilization ways of the desulfurization ash.Method for chemical analysis of cement,methods for chemical analysis of gypsum and iodometric method,Scanning electron microscope(SEM) and X-ray diffraction(XRD) were employed to identify the samples in order to investigate the physical and chemical characteristics and the thermal stability of the ash.The result shows that:desulfurization ash is stable,and the physical and chemical characteristics of the ash have no significant change in the dry environment at room temperature.The contents of asia calcium sulfate and sulfur trioxide in the desulfurization ash from sinter gas are higher than that from power plant.The desulfurization ash has smooth surface,loose structure and contain many small holes.It is consist of asia calcium sulfate,calcium sulfate,calcium carbonate, corundum and mullite,et al.Scanning electron microscope(SEM) and X-ray diffraction (XRD) were employed to identify the thermal stability of the ash,calcium sulfite has been oxidized before decomposed either in the air or in the nitrogen.It only lose crystal water below 450℃,and it is much easier oxidated in humid state than in dry state.At high temperature conditions,the higher the concentration of oxygen in the atmosphere,the more easier the CaSO₃ oxidized to CaSO₄.CaO has an inhibition role on oxidative desulfurization ash,while Fe₂O₃ has a catalytic role on oxidative desulfurization ash. On the basis of sigle-factor tests,the modified process of semi-dry sintering flue gas desulfurization ash was studied.The conversion rate of desulfurization ash does not exceed 3%with MnO₂,Fe₂O₃ and V₂O₅ as catalysts,and the catalytic effect is MnO₂＞Fe₂O₃＞desulfurization ash＞V₂O₅.The conversion rate slowly increased with the rise of temperature between 100℃and 400℃,and sharply increased between 400℃and 550℃.When t＜30 min,the conversion rate increased with time increases,and the conversion rate is 81.3%at 30 min,when t＞30 min,the conversion rate did not change significantly with time increased;the conversion rate increased with a positive correlation when gas-solid ratio is between 0.01m³Â·h^-1·g^-1 and 0.06m³Â·h^-1·g^-1,and when the gas solid ratio continue to increase,the conversion rate actually dropped.The modified process of semi-dry sintering flue gas desulfurization ash was studied through Box-Benhnken design and response surface methodology(RSM).The mathematical-regression model was eatablished about the dependent variable (conversation rate of desulfurization ash) and independent variables(temperature,time and gas/solid ratio).The results show that:temperature has the most significant influence on the efficiency of the conversion rate.The interactions of temperature and time and the ones of temperature and gas/solid ratio play the same roles in the conversion rate.The improved response surface model is helpful to decribe the conversion rate of the desulfurization ash.According to this improved prediction model, Y=0.841+0.195X₁+0.0748X₃-0.113X₁²,which is X₁ and X₃ represent the coding of the reaction temperature and the gas-solid level,and the best modifided process is 453℃,30 min and 0.04m³Â·h^-1·g^-1According to the experimental results and the time-conversion rate which was set up by Szekely,the reaction kinetics was discussed.When t＜30 min,the diffusion process at this stage control the process;when t＞30 min,the time-conversion rate relationship show that oxygen still maintains a certain rate of diffusion and mass transfer,chemical reaction rate decreased.Thus,the chemical reaction process control the entire transformation reaction in the latter steps.Conversion reaction is not elementary reaction,the oxidation rate is 0.7 order in calcium sulfate and 2.0 order in oxygen.