Experimental Research On The Removal Of Chlorine-containing Acid Gas From Municipal Solid Waste Thermal Treatment By Calcium Oxide At High Temperature

The increase of municipal solid waste（MSW）has brought tremendous pressure on environment,resources in China.In recent years,MSW incineration technology with features of reduction,harmlessness,and resource utilization,has been rapidly developed in our country.However,MSW in our country has a complex composition and high chlorine content.Acid gases such as HCl generated during incineration will cause problems such as high-temperature corrosion and secondary pollution,which will restrict its advantages in economy and environmental protection,and restrict its further development.Although the flue gas treatment system in the tail of plant can make the flue gas emissions meet increasingly strict standards to a certain extent,it cannot avoid the high-temperature corrosion and dioxin formation caused by HCl.Therefore,the simultaneous removal of HCl and other acid gases in the furnace at high temperature can provide the possibility for a more efficient and clean solution to the problem of MSW.However,the mechanism and mutual influence of calcium-based absorbents for the simultaneous removal of different acid gases are relatively complicated,and the research in this area is relatively insufficient.Therefore,further research and exploration in this area have certain engineering significance and economic potential.Firstly,this paper uses the thermodynamic simulation software Fact Sage to preliminarily explore the regular pattern of temperature,composition,reaction ratio and other aspects of the calcium oxide react with flue gas from the heat treatment process of MSW.The results show that the response ability of several acid gases with Ca O can be summarized as SO₂>HCl>CO₂,and the stability of their products is basically the same,but the competition between HCl and CO₂at600℃～800℃has been reversed.In the pyrolysis gasification atmosphere,the decomposition temperature of Ca Cl₂,the corresponding product of HCl,increased from about 800°C in the incineration atmosphere to 950°C,indicating that under the conditions of pyrolysis gasification,Ca O has a better absorption and fixation effect on HCl.Secondly,thermodynamic calculations and kinetic analysis are carried out on the gas-solid reaction mechanism of calcium oxide and hydrogen chloride,and the shrinking unreacted nucleus model is sorted out.The experiment of absorbing HCl by Ca O alone was carried out.When the reaction temperature increased from 650℃to 850℃,the absorption of HCl decreased from312.2mg/g-Ca O to 217.8mg/g-Ca O,which accorded with the result of thermodynamic simulation.However,the absorption rate at the initial stage of the reaction is basically the same,all around3.0 mg/g-Ca O·min.A critical Ca/Cl molar ratio Ca:Cl=6.76:1 is defined according to experimental data.When the Ca/Cl molar ratio is greater than this ratio,continue to increase the Ca/Cl ratio will not affect the initial reaction rate.Combining the experimental data to fit the model,it is determined that chemical reaction control and product layer diffusion control are the key mechanisms of the initial and final stages of the reaction process,and then some relevant kinetic parameters are calculated.As the temperature rises from 650°C to 850°C,theθ²,which characterizes the degree of product layer diffusion resistance and chemical reaction resistance,decreases from 7.42 to 4.19,indicating that as the temperature rises,the effect of chemical reaction control has a certain increase,but the influence of product layer diffusion is still dominant.Finally,a coordinated absorption experiment of different acid gases was carried out in a fixed bed reaction system.It was found that only when HCl-SO₂ or HCl-CO₂ react with calcium oxide,SO₂and CO₂ both showed a certain inhibitory effect on the absorption of HCl in the high temperature.And the absorption effect at 850℃is better than 750℃.However,when the simulated flue gas is used,HCl,SO₂,CO₂,etc.react with Ca O at the same time,the absorption conversion rate of Ca O to HCl is close to the level when Ca O absorbs HCl alone.Through SEM,BET and other detection and analysis of the products of these experiment,the growth and changes of the morphological structure of the product layer are clearly determined.Combining literature analysis,it is clear that CO₂ promotes the active sites of pores when removing chlorine-containing acid gas at high temperature under incineration atmosphere,and the sulfated products and their eutectic have encapsulation and protection effect on chlorinated products,which promote the further absorption of HCl,and show the potential and advantages of high temperature dechlorination.By fitting this set of experimental data with the kinetic model,it is also found that the diffusion control effect of the product layer is enhanced.Experiments on the influence of other parameters on the removal of chlorine-containing flue gas at high temperature were carried out at 850℃,and the key factors for the removal of chlorine-containing acid gas at high temperature by calcium-based absorbents were pointed out,which provided reference for subsequent research.