Experimental Study Of The Conversion Of Trona To Increase Its Reactivity With SO₃ From Coal-fired Flue Gas

The coal-fired power plant selective catalytic reduction(SCR)technology resulted in a significant increase of SO3 concentration in flue gas,causing the surface of low temperature corrosion,the rear heating air preheater clogging,smoke opacity high hazard.The flue gas injection of alkaline material can effectively remove SO3 in flue gas,and has become the focus of research at this stage.In this paper,the technical idea of using CO2 in flue gas after desulfurization to modify trona and modify and realize high efficiency removal of SO3 has been put forward.The activity of absorbent and the operation cost will be improved.The natural alkali conditioning,quenching and tempering,product pyrolysis and absorption characteristics of SO3 were studied.The key technological parameters of SO3 removal were obtained,and the mechanism of SO3 removal was revealed.Firstly,the reaction characteristics of CO2 and natural gas in flue gas under typical smoke extraction conditions were studied by an atmospheric pressure fixed bed reactor.The reaction kinetics was simulated by gas-solid reaction model.It is found that the reaction rate is controlled by the chemical reaction process at the initial stage of the reaction.The reaction is controlled by diffusion process as the reaction proceeds.Decreasing the reaction temperature,increasing the moisture content and CO2 concentration in the flue gas both increased the rate of chemical reaction and promoted the reaction.The kinetic simulation shows that the deactivation model can well simulate the carbonation process of trona,and the correlation coefficients are greater than 95%.The deactivation rate constants of active sites are significantly affected by the reaction temperature and moisture content.When the CO2 concentration changes,the carbonation of trona is mainly affected by the diffusion of CO2.Based on the above research,the pyrolysis process of trona and its modulation products was analyzed by thermogravimetric analyzer,and the pyrolysis process was simulated by pyrolysis kinetics model.The Kissinger,Flynn-Wall-Ozawa and Satava-Sestak methods can well fit the weightless process of trona and its modulated products and obtain reliable kinetic parameters.The temperature of the decomposition of trona began to be about 90?,and the weight loss peak appeared between 100?120?.With the increase of heating rate,the weight loss peak shifted to the high temperature region.And products began to decomposition temperature is about 90?,in the vicinity of 100? and 140? two obvious peaks,peaks at about 100? in the trona modulation process,a small amount of condensed water formed in the generated NaHCO3 above the liquid water and water evaporation crystallization NaHCO3,The weight loss peak at 140? is the weight loss peak of NaHCO3 decomposition.The analysis shows that the physical and chemical properties and before and after trona,with Trona Carbonation degree deepening,the structure of pyrolysis products changed significantly,smooth surface into particles by staggered strip and gradually deepened,more porous surface structure,internal voids increase with the increase of natural soda modulation conversion rate,the specific surface area of linear increase of pyrolysis products and compared with the original natural alkali surface area increased by 2.35 times,is favorable to the subsequent removal of SO3.The widespread application of selective catalytic reduction(SCR)technology in coal-fired power plants has led to a significant increase in SO3 concentration.At the initial stage of the reaction,the rate of chemical reaction is the main controlling factor,and the increase of temperature is beneficial to the increase of the rate of chemical reaction.Therefore,with the increase of temperature,the reaction rate increases,but the range of increase is limited.At the late stage of the reaction,with the decrease of the temperature of SO3 conversion to sulfuric acid mist,promote the removal reaction.increase after tempering trona surface area,surface structure is loose,obviously promote the reaction rate and SO3.With the increase of flue gas water content,the reaction rate is accelerated,but the moisture content is greater than 5%,the change is not obvious.With the increase of flue gas water content,the reaction rate is accelerated,but the moisture content is greater than 5%,the change is not obvious.In the absence of oxygen,the SO2 in the flue gas does not react with the trona.When oxygen reacts,a small amount of sodium sulfate is produced,which inhibits the removal of SO3.Simulated by removing reaction of three kinds of gas solid chemical reaction kinetic model of SO3,the research shows that compared with the shrinking core model.The simulation of reaction process Na2CO3 and SO3 active site deactivation model can better simulate the reaction rate,consistent with the experimental values.