Study On PM Formation Mechanism And Mitigation Method During The Combustion Of Densified Biomass In Fixed Bed Reactor

As a renewable carbonaceous solid fuel,biomass has the advantages of carbon neutrality,large reserves and wide distribution.It is the only carbonaceous solid fuel that can replace coal in most applications.The densified biomass fuel has been widely used due to its high energy density,uniform particle size and strong hydrophobicity,which effectively solves the problems of storage,transportation and supply.However,the high content of volatile inorganic components such as alkali metals,alkali earth metals and chlorine in densified biomass is likely to cause serious particulate matter(PM)emission,which limits its large-scale utilization.Therefore,it is of great significance to study the formation and mitigation mechanism of PM in the combustion process of densified biomass for promoting its application in coal-fired power plant and heating system.Based on this,this paper selected two common crop processing residues(rice straw and rice husk)and two typical woody biomass(spruce and eucalyptus)in south of China to study the PM formation mechanism and mitigation method.The main research contents are as follows:(1)The influence of densification on the combustion characteristics of biomass fuel was studied.The densified biomass fuels were produced according to the national standard,and were compared with the powdery biomass fuel samples in combustion characteristics.The densified and powdery fuel samples were analyzed by thermogravimetric analysis(TGA),respectively.The ignition temperature,burnout temperature,combustible characteristic index,comprehensive combustion characteristic index of apparent combustion performance of biomass fuels of various types and forms were calculated.The kinetic triplets of fuel sample were calculated.The influence of densification on the combustion characteristics of biomass fuel was quantitatively revealed by comparing the characteristic values of combustion performance and kinetic features.(2)The influence of the initial occurrence and precipitation characteristics of biomass inorganic components on PM formation was studied.The initial forms of ash forming components of biomass fuel were determined by chemical fractionation experiments to reveal the influence of biomass initial components on PM generation during combustion.A tubular furnace device was used to quantitatively reveal the precipitation rules of volatile elements in the combustion process of biomass.Additionally,the precipitation forms of main PM components in different temperature ranges were summarized.The thermodynamic equilibrium states of the main inorganic components in biomass during combustion were calculated by the thermodynamic equilibrium calculation software HSC,and the evolution and transformation routes of the inorganic components in biomass fuel during combustion were simulated.(3)The generation characteristics of biomass PM during combustion were studied.A PM detection platform based on a fixed bed was established.The generation characteristics of PM under different temperatures,in various fuel types and shapes were investigated by experiments.The microscopic morphologies of PM at different particle sizes were observed by an environmental scanning electron microscopy(ESEM).An energy spectrum analyzer(EDX)was used to determine the compositions and contents of PM in different particle sizes.The formation road map and mechanism of PM in different particle sizes of biomass fuels were revealed.(4)PM mitigation methods with ingredient regulation in biomass combustion were developed.According to the retention effects of some inorganic substances on the main forming elements of PM,a research on the realization of PM mitigation method with inorganic additives was carried out to summarize the law of PM mitigation in biomass combustion process.In view of the paths and mechanisms of PM formation of various biomass in the combustion process were different,a research on PM mitigation method of biomass blended-fuel combustion was carried out to summarize the law of mixed combustion with different biomass types and proportions.(5)A real-time detection technology of biomass feed was developed for maintaining the stable quality of biomass feedstock before combustion.A laser induced breakdown spectroscopy(LIBS)method combined with the mixed classification algorithem was proposed to realize the identification of biomass blended fuel instantaneously and accurately.Furthermore,a biomass fuel rapid detection platform was developed based on the research finding above.This study revealed the rule of PM formation in the combustion process of densified biomass fuels,amd discussed the formation mechanism of PM with various diameters for proposing effective PM mitigation technology.The research results of this paper can provide a theoretical basis for the clean and efficient use of biomass densified fuel,which is conducive to promoting the application of biomass fuel significantly.