Research On Generation And Emission Characteristics Of PM_2.5 From The Coal-fired Boiler

With the rapid progress of industrialization and urbanization,China has been in the stage of economic development with the most serious pollution,which can be called as Heavy Chemical Industry Era.At present,in China,the problems of atmospheric environmental pollution are very serious,especially of the ash haze caused by PM_2.5 and the photochemical smog caused by ozone,which are restricting the harmonious development of economy and social of our country seriously.The coal-fired boiler is a significant source of PM_2.5 in the environmental atmosphere.The research on PM_2.5 generation and emission characteristics of the coal-fired boiler is of great significance for the development of the control countermeasures and the development of the control technique of PM_2.5 emission from the coal-combustion sources,meanwhile,the research is the base of researching the formation mechanism of PM_2.5 emitted from coal-combustion sources,analyzing the toxicity of the coal-fired PM_2.5 to human health and researching the influence of PM_2.5 emission of coal-combustion sources on the natural environment.In this thesis,the influences of the combustion method,the dust-collecting process and wet desulfurization process of forty-nine coal-fired boilers on concentration characteristics,morphology,elementary composition and the contents of organic carbon（OC）and elemental carbon（EC）of PM_2.5 are researched systematically.Besides,in this thesis,the emission factors and the hazards of PM_2.5 from the different types of the coal-fired boilers are researched,the PM_2.5 total emission amounts of the coal-fired boiler of China and the various regions of China and the PM_2.5 emission amounts per unit area of the coal-fired boiler of the various regions of China are researched.In this thesis,a dilution sampling system is established based on an electrical low-pressure impactor（ELPI）,with which the samples of PM_2.5 are taken in situ.The concentrations and the particle size distributions of PM_2.5 are analyzed by ELPI,morphological characteristics of PM_2.5 are analyzed by scanning electron microcopy（SEM）,the elemental compositions of PM_2.5 are analyzed by X-ray fluorescence（XRF）and inductively coupled plasma optical emission spectrometer（ICP-OES）,and the contents of OC and EC in PM_2.5 are analyzed by carbon analyzer（CA）.Based on the concentrations of PM_2.5 generated and emitted from the coal-fired boiler,the uncontrolled and controlled emission factors of PM_2.5 are calculated.A hazard comprehensive assessment modal is established to research the hazards of PM_2.5 generated and emitted from the different types of the coal-fired boilers.A key technical method of calculating PM_2.5 total emission amount of the coal-fired boiler is proposed,by which the PM_2.5 total emission amounts of the coal-fired boiler of China and the various regions of China in 2014 are calculated,and the PM_2.5 emission amounts per unit area of the coal-fired boiler of the various regions of China in 2014 are calculated.The research results of the influence of the combustion method on concentration characteristics,morphology,elementary composition and the contents of organic carbon（OC）and elemental carbon（EC）of PM_2.5 show that the particle size distributions of PM_2.5 generated from the different types of the coal-fired boilers are obviously different.PM_2.5 generated by utility pulverized coal boilers is mainly spherical.PM_2.5 generated from utility CFB boilers is mainly irregular in shape.PM_2.5 generated from grate-fired boilers is dominated by the flocculent fine particles in number.PM_2.5 generated from industrial fluidized bed boilers is mainly irregular in shape and spherical.The contents of Si and Al in PM_2.5 generated from the different types of the boilers are higher than those of the other elements.The contents of Si and Al in PM_2.5 generated from the industrial grate-fired boiler are lower than those from the other types of the coal-fired boilers,meanwhile,the contents of Na,S,organic carbon and elemental carbon are higher.The research results of the influence of the dust-collecting process on concentration characteristics,morphology,elementary composition and the contents of organic carbon（OC）and elemental carbon（EC）of PM_2.5 show that the curve characteristics of the particle size distributions of PM_2.5 from different types of the boilers change in various extents after the dust-collector.The pulse back blowing of the fabric filter（FF）can make the fractional removal efficiencies of PM_2.5 decrease,and the fractional removal efficiencies of the ultrafine particles in PM_2.5 through the FFs tend to decrease with the particle sizes decreasing.The dust-collecting process has obvious effects on the morphological characteristics of PM_2.5 generated from the utility pulverized coal boiler,but has few effects on the morphological characteristics of PM_2.5 generated from the other types of the boilers.The contents of Si and Al in PM_2.5 generated from all types of the boilers after the dust-collectors are lower than those before the dust-collectors,but the contents of As and Se in PM_2.5 after the dust-collectors are higher than those before the dust-collectors.The contents of OC and EC in PM_2.5 after the electrostatic precipitator（ESP）are higher than those before the ESP,but the other types of dust-collectors has few effects on the contents of organic carbon and elemental carbon in PM_2.5.The research results of the influence of the wet desulfurization process on concentration characteristics,morphology,elementary composition and the contents of organic carbon（OC）and elemental carbon（EC）of PM_2.5 show that the concentrations of the finer particles in PM_2.5 get higher and the concentrations of the coarser particles in PM_2.5 get lower after the WFGD.After the WFGD,there can appear nubbly,stratiform and flocculent microstructures on the surfaces of some particles in PM_2.5,and there appear fine crystalline pillars on the surfaces of several particles in PM_2.5.The contents of Si,Al,OC and EC in PM_2.5 after the WFGD are lower than those before the WFGD,but the contents of Ca and S in PM_2.5 after the WFGD are higher than those before the WFGD.The research results of the emission factors of PM_2.5 from the different types of the coal-fired boilers show that the uncontrolled and controlled number-based emission factors of PM_2.5 from the grate-fired boiler are both larger than those from the other types of the boilers.The calculation results of the hazard comprehensive assessment model of PM_2.5 from the coal-fired boilers show that the hazards of the uncontrolled and controlled PM_2.5 from the grate-fired boiler are higher than those from the other types of the coal-fired boilers.The research results of PM_2.5 total emission amount of the coal-fired boiler and PM_2.5 emission amounts per unit area of the coal-fired boiler of the various regions of China in 2014 show that the total emission amount of PM_2.5 emitted from the coal-fired boiler in China is 47.31×104 tons in 2014.PM_2.5 emission amounts per unit area of the coal-fired boiler of Shanghai,Tianjin,Jiangsu,Beijing,Zhejiang,Shandong,Guangdong and Liaoning in 2014 are higher than those of the other regions in China,which belong to the first-level-polluted regions of PM_2.5 emitted from the coal-fired boiler.