Study On Formation And Transporting Mechanism Of Ultrafine Particles From Coal Combustion

Particulate matter (PM) is the dominant air pollutant in most Chinese cities,and has brought serious impacts on human health and the ecological environment. Inthis paper, the author has designed and set up a modeling experimental chamber tomeasure the ultrafine particle size distribution, number concentration and particlediameter of coal combustion particles, by using fast mobility particle sizerTMspectrometer (FMPS). The particulate characteristics have been analyzed, and thedynamic variations of coal combustion particles in the formation and growth processare studied based on the measuring data.Different combustion particles have been measured and analyzed. It has foundthat both the mosquito coils particles and tobacco smoke particles are logarithmicunimodal distribution. The number concentration and the surface concentration ofcoal combustion particles are logarithmic bimodal distribution, and its volume andmass concentration are logarithmic unimodal distribution. Alcohol combustionparticle shows an unstable and irregular multimodal distribution. We also find thatdifferent combustion modes have a certain impact on particle sizes. The combustionmodes of mosquito coils and tobacco smoke particles are spark-free smolder, whichmakes particle diameter larger, of which geometry mean diameter (GMD) are about45nm and130nm respectively. The alcohol and coal particles belong to fire burning,and the particulate matter is formed through gasification and condensationmechanism. As a result, GMD of alcohol and coal particles are smaller, as much as10nm and20nm respectively.The combustion experiment of different weight pulverized coal has been carriedout. The dynamic variation of ultrafine particles size distribution, numberconcentration and particle diameter have been studied in the formation and growthprocess of coal combustion particles. The results show that size distribution of thecoal combustion particles growth rapidly in the formation stage, and its number concentration increases exponentially with time. In the growth stage, the particle sizedistribution of coal combustion particles decrease slowly and its numberconcentration decays exponentially or linear with time. Greater the amount of coal,particle number concentration and particle dynamics are more obvious. Great weightof pulverized coal makes dynamic changing more obviously.The particle formation rate and growth rate are also calculated based on themeasuring data. It shows that the formation rate and growth rate of coal combustionemissions are much greater than the atmospheric condition. The result shows that theaverage number emission of nucleation mode, Aitken mode, accumulation mode andtotal particles are1.61×1010,1.31×1010,0.22×1010and3.14×1010units·mg-1respectively. The growth rate of GMD is7.5nm·h-l·mg-l.