Migration And Transformation Of Trace Elements In Particulate Matter With Different Particle Sizes In Coal Flue Gas

The atmospheric environment is a problem worth paying close attention to in today’s era.China’s power industry cannot do without the use of coal.As people pay more attention to environmental pollution,ultra-low emission technology has been applied in coal-fired power plants.However,some particles with small particle sizes,especially condensable particles,are still discharged into the atmosphere.Trace elements such as Cr,As,Se,Pb and Hg in these particles have the most serious impact on the environment and the human body.This paper takes total particulate matter(PM)and condensable particulate matter(CPM)as the main research objects.Although some researchers have analyzed the total amount of trace elements in condensable particulate matter,they have not analyzed and explored the distribution of trace elements in particle size.According to particle size,PM and CPM smaller than 10μm can be divided into ultrafine particles(0-0.1 μm),submicron particles(0.1-1 μm)and ultrafine rice particles(1-10μm).For the morphology characterization of condensable particles,no one has analyzed and discussed them under different particle sizes.In this paper,the dropper furnace in the laboratory was used as the experimental platform to study the migration and transformation law of trace elements under different particle sizes in the sampling system of total particulate matter and condensable particulate matter.A low voltage charged impactor(ELPI+)was used to collect PM and CPM with different particle sizes,and the change law of their mass and quantity concentrations with different particle sizes was studied.The distribution of particle shape and size under different particle sizes was observed by SEM technology.To investigate the distribution of trace elements in particulate matter with different particle sizes.In the dropper furnace experiment,PM was collected by the ELPI+combined with the dilution method,and CPM was collected by the ELPI+combined with the OTM28 method.In the PM and CPM sampling system under the dropper furnace experiment platform,the concentration migration sequence of trace elements is Cr>Pb>As>Se>Hg,which is consistent with the concentration sequence of trace elements in raw coal.Among the solid particles with the mass balance rate of Cr in each sampling system,it is the highest,reaching more than 97%.As a highly volatile element,Hg is only collected in less than 20%of solid particles.Among the particles collected at different locations(ash hopper,cyclone separator,PM 10 cyclone separator,FPM filter membrane,ELPI+),the concentration of trace elements in the particles collected in ELPI+is the highest.The mass concentration of PM10 and CPM10 increased with the increase of particle size,and the quantity concentration increased with the decrease of particle size.In addition,the mass concentration of PM10 collected by ELPI+in real time is about 100 times that of CPM10,and the quantity concentration is also dozens of times.In the morphology of PM10 and CPM10,there are regular and irregular spherical particles in each particle size range,and the proportion of spherical particles to irregular particles increases with the decrease of particle size from 10μm to 0.1μm.For PM10 and CPM10 with different particle sizes,trace elements generally present a state of small particle size enrichment.The enrichment index of mercury,selenium,arsenic and lead in CPM10 is 3-10 times of that in PM10.The enrichment variation is greatest in the submicron size range.According to the conclusion of this study,it is very important for the removal of particles,especially those with small particle size.