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Study On The Formation Model Of Particles Coupled With The Mechanism Of Mineral Coalescence And Char Fragmentation

Posted on:2022-03-30Degree:MasterType:Thesis
Country:ChinaCandidate:T P ZhangFull Text:PDF
GTID:2491306572477344Subject:New Energy Science and Engineering
Abstract/Summary:PDF Full Text Request
The combustion of coal and biomass is still the main energy utilization mode in China.A large amount of particulate matter produced in the combustion process not only affects the safe operation of the boiler,but also has great harm to the environment and the human body.Therefore,it is of great significance to study the formation of particulate matter for controlling its emission and improving environmental quality.The process of producing particulate matter by char combustion involves various combustion reactions,char fragmentation and mineral coalescence.The change of atmosphere affects the combustion of char,and the included minerals also play a major role in the formation of particles.Therefore,the key to establish the particle generation model is to describe the process of mineral coalescence and char fragmentation in different atmospheres during combustion.Based on the percolation theoretical model of char combustion,this study first introduces the included mineral species and particle size distribution as input parameters by using CCSEM.In the char model,the included minerals of different kinds and particle size are constructed.At the same time,by simulating the process of mineral coalescence and char fragmentation to form particulate matter fragmentation model coupled with included mineral properties,the accuracy is verified.Compared with the original model,the improved model can predict the experimental results of various samples more accurately.The results show that in the combustion process of char,there will be two obvious fragmentation peaks.And there is a violent char fragmentation in the later stage of the reaction.For biomass char,the fragmentation process shows certain regularity.At the same time,the included mineral coalescence rate decreases obviously in the stage of char fragmentation,which indicates that fragmentation will inhibit the coalescence process.Based on the char data of four kinds of included mineral content,mineral particle size distribution and porosity,it is found that its properties are closely related to the mass particle size distribution of particulate matter.It is found that the peak value of Shenhua coal with large particle size mineral distribution is obviously backward,and the model results show that the mineral properties have obvious influence on the particle size distribution.Further,the effect of char combustion reaction on the formation of particulate matter in different combustion environments is considered.Firstly,that is studied by using the double film model and intrinsic kinetic equation in O2/N2and O2/CO2atmosphere.The reaction between carbon and O2,CO2,H2O and the oxidation of CO and H2in boundary layer are considered.The sub-model considering the relationship between combustion atmosphere,particle size of char and combustion temperature on the surface is established.At the same time,thermodynamic model software is used to analyze and calculate the melting characteristics of representative minerals at different temperatures to form a sub-model of mineral melting and temperature.Finally,a fine particle generation model can be constructed for coupling mineral coalescence and char fragmentation mechanism at different temperatures and atmospheres.The model can well predict the combustion temperature of char particles at different atmospheres.When the concentration of H2O increases,it causes the proportion of carbon consumption in the reaction between carbon and H2O increases,and the reaction between carbon and CO2decreases.The particle size distribution curve of different atmosphere will show significant difference.Along with the increase of CO2concentration,O2concentration decreases,carbon and CO2reaction increase,the combustion temperature of char surface decreased,the peak value of particle size distribution curve moves forward and PM2.5production increased.In O2/CO2atmosphere,the increase of water vapor concentration in atmosphere increases the amount of particulate matter size,which can effectively control the formation of fine particles.
Keywords/Search Tags:char combustion, percolation theory, particulate formation, included minerals, combustion atmosphere, char surface temperature
PDF Full Text Request
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