Study On The Thermal Decomposition Process Of Flue Gas Desulfurization Ash

Semi-dry flue gas desulfurization ash is a solid powder produced by flue gas desulfurization of coal-fired power plants.Because its composition is complex and most of the components are calcium sulfite with extremely unstable properties,comprehensive utilization of desulfurization ash is difficult.Except for a small amount of applications,most of the desulfurization ash is currently used for stacking or landfill disposal,which not only causes secondary pollution to the environment,but also loses sulfur resources.Therefore,the resource recovery and reuse of desulfurized ash has become an urgent demand.In order to solve these problems,this paper uses calcium sulfite to simulate the desulfurized ash,and studies the influence of the remaining components in the desulfurized ash on the decomposition of calcium sulfite.Finally,taking the desulfurization ash of a thermal power plant as the object,its physical and chemical properties and thermal decomposition were analyzed,and the thermodynamics and kinetics of thermal decomposition were studied.The research work mainly includes:?1?Analysis of physical and chemical properties of desulfurized ash.Scanning electron microscopy?SEM?was used to observe the morphology of desulfurized ash,and it was found that its components were agglomerated.X-ray fluorescence analysis?XRF?and X-ray diffraction analysis?XRD?were used to analyze the components and phases of the desulfurized ash,and it was concluded that the main components in the desulfurized ash are calcium sulfite hemihydrate,calcium hydroxide,calcium carbonate and the content of calcium sulfate dihydrate is 41%,22%,10%and 16%respectively.It can be seen from the TG curve that from 700^oC to 1200^oC,the desulfurized ash has a total of four weightlessness stages.Finally,some physical characteristics of the desulfurized ash were analyzed,and it was concluded that the specific surface area of the desulfurized ash was 2.905 m²/g,the bulk density was0.82 g/mL,the water content was 0.35%,the acid insoluble content was 2.01%,and the pH value was 10.21.?2?The experiment of pyrolysis with calcium sulfite simulated desulfurization ash.The effects of temperature,Ca?OH?₂,CaCO₃,Fe₂O₃,fly ash,KOH,NaOH,SiO₂,and reduced carbon powder on the decomposition efficiency of CaSO₃ were studied respectively.According to the experimental results,temperature is an important factor affecting the high-temperature thermal decomposition of CaSO₃.As the temperature continues to rise,the decomposition efficiency of CaSO₃ continues to increase;after adding Ca?OH?₂,the decomposition efficiency increases by 7.97%at 900^oC.The decomposition efficiency of CaSO₃ increased the most at 1000?,being 16.09%.After adding CaCO₃,the decomposition efficiency of CaSO₃ increased by 5.89%at900^oC,and the decomposition efficiency decreased by 13.01%at 1000^oC.Fe₂O₃ did not play a role in the decomposition of calcium sulfite.By adding 5%carbon powder,the decomposition efficiency of CaSO₃ at 1000^oC can reach the decomposition efficiency when no carbon powder is added at 1100^oC.?3?The thermal decomposition study of desulfurized ash shows that the temperature increased from 1000^oC to 1100^oC,the desulfurized ash decomposition efficiency and calcium oxide content increased by 38.88%and 11.72%respectively.When the heating rate is 6^oC/min and the gas flow rate is 100 mL/min,it is most beneficial to the decomposition of desulfurized ash.In addition,the effects of calcium hydroxide,carbon powder,ferrous chloride,and cuprous chloride on the high-temperature decomposition of desulfurized ash were studied through thermal decomposition experiments.Among them,the most significant effect on the desulfurization ash decomposition is carbon powder.After adding 5%carbon powder,the decomposition temperature of the desulfurization ash is reduced from 1100^oC to1000^oC.At 1000^oC,the decomposition efficiency of CaSO₃ in the desulfurization ash increased from 55.56%to 89.48%.At 1100^oC,the content of activated calcium oxide reached 62.27%.?4?The thermodynamics and kinetics of pyrolysis of desulfurized ash are analyzed.According to the thermodynamic data,the disproportionation reaction of calcium sulfite in the desulfurization ash produced calcium sulfide.TGA-DCS was used to conduct the dynamic analysis of the desulfurization ash,and the kinetic parameters were obtained.The activation energy and pre-finger factor ln?A/s-1?calculated by the Kissinger method were 194.70 kJ/mol and 18.09,respectively.And verified by Starink method and Ozawa-Doyle method,the calculated results are basically consistent.Finally,using the?atava-?esták method,22 mechanism functions are substituted into the equation for fitting,the dynamic behavior of the desulfurization ash is analyzed,and the kinetic equation is obtained.