| In China,coal resources account for up to 70% of the primary energy structure.Therefore,the amount of pollutants emitted by coal combustion is extremely high,which has a great impact on the health of the atmospheric environment.The particulate matter produced by coal combustion includes filterable particulate matter(FPM)and condensable particulate matter(CPM),of which condensable particulate matter predominates with particle size less than 1 ?m.The condensable particles contain a large amount of organic pollutants,such as polycyclic aromatic hydrocarbons(PAHs),n-alkanes,etc.,which contribute greatly to organic pollutants in atmospheric particulate matter.At the same time,the condensable particles has small size,so they are hard to settle in the atmosphere,and can travel far away.The particles can enter the human lung through the respiratory system,interfere with the gas exchange in the lungs and damage the respiratory system,thereby leading to asthma,bronchitis,cardiovascular diseases and so on.In summary,the condensable particulate matter emitted during the coal combustion process has caused certain harm to the atmospheric environment and human health.At present,the research on the emission and composition characteristics of condensable particulate matter is still scarce.Therefore,this paper mainly studies the emission and distribution characteristics of organic pollutants in condensable particles emitted from coal combustion.The main research contents and conclusions are as follows:(1)Research on the emission and distribution characteristics of CPM and FPM in coal-fired power plants.The removal efficiency of the low-low temperature electrostatic precipitator(LLT-ESP)for FPM of different particle sizes is greater than 99%.The larger the particle size,the higher the removal efficiency of the particles,and the removal efficiency of CPM is only around 70%.The wet desulfurization device(WFGD)and the wet electrostatic precipitator(WESP)also have a certain removal effect on FPM and CPM,but are far less than LLT-ESP.The concentration of FPM in the flue gas of the ultra-low emission coal-fired unit studied was from 1.20 to 8.62 mg/Nm3,and the concentration of CPM was higher than that of FPM,with the range from 6.66 to 24.80 mg/Nm3.PM2.5 is the main component of FPM discharged from coal-fired power plants,accounting for 64.33 to 85.45%;the organic component is the main component of CPM,accounting for 50.90 to 93.17%.(2)Research on the composition characteristics of CPM.As for the anion in the inorganic fraction,SO42-is the main component,and Ca2+ and NH4+ are the main components in the cation.The composition of the organic fraction is complex,including hundreds of organic substances.Among them the hydrocarbons(including n-alkanes)and esters(including phthalate)qualitatively detected accounts for more than 80%.So they are the main component of the organic fraction.The concentration of n-alkanes and phthalate is quantitatively detected at about 20%.(3)Study on the influencing factors of the emission characteristics of CPM organic components.The organic components in CPM are mainly from the incomplete combustion of coal.The coal combustion efficiency is high under high load conditions,so the emission concentration of the organic fraction is reduced.For the same reason,the concentration of organic fraction of CPM discharged from large-capacity coal-fired units such as ultra-supercritical coal-fired units is lower than that of general coal-fired units.The influencing factors of the emission concentration of n-alkanes and phthalates in CPM is consistent with the organic fraction.At the same time,the low smoke temperature can promote the removal process of organic matter and reduce its emission concentration.(4)The controlled characteristics of n-alkanes and phthalates by different flue gas purification devices.The main removal mechanism of each flue gas purification device for CPM is to condense it and make it adsorbed to FPM and then remove FPM.LLT-ESP removes a large amount of FPM and simultaneously removes n-alkanes and phthalates adsorbed on the surface.WFGD has a good removal effect on water-soluble substances such as esters(including phthalates).WESP has a certain removal effect on hydrocarbons(including n-alkanes),and n-alkanes with higher carbon numbers are more easily adsorbed and removed. |
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