Research On The Formation And Growth Of Aerosol Particle In Coal-fired Flue Gas

With the rapid development of economy and the sustained growth of energy demand in China,the problem of particulate matter emission from coal-fired power plants has become increasingly prominent.The particulate matter in coal-fired flue gas can be divided into filterable particulate matter?primary solid particulate matter such as fly ash?and condensable particulate matter?secondary particulate matter formed by condensation of gas components such as H2SO4,NOX,NH3,VOCs?.At present,most of the existing technologies for controlling particulate matter in coal-fired flue gas are directed at filterable particulate matter,and the research on condensable particulate matter is less.The condensable particulate matter will be generated in the wet desulfurization tower and the high humidity flue gas in the future,which is difficult to be effectively removed by the traditional particulate matter control technology.In order to solve this problem,this paper focuses on the formation and growth of particles in coal-fired flue gas.The formation and growth of flue gas particles at various scales from molecule to particle under the influence of temperature,humidity and charge were studied by means of quantum chemistry and dynamics calculation.The nucleation rate?the amount of new particles in flue gas aerosol per unit volume of time?and the growth rate?per unit time?of particles in high humidity flue gas atmosphere were obtained.Increase in particle size.On this basis,the inhibition of particle growth on particle formation in flue gas aerosols was studied.The conclusions of this paper can be used to guide the secondary particle control technology of flue gas in coal-fired power plants.Firstly,the formation and growth of aerosol particles in flue gas were studied.It is found that sulfuric acid molecules can form aerosol particles with more than critical radius through condensation of water molecules around them and grow spontaneously in high humidity flue gas atmosphere.Environmental temperature and water vapor supersaturation are the main factors affecting the formation and growth of aerosol particles.For the nucleation rate of aerosols,when the water vapor supersaturation is1.05 and the ambient temperature increases from 50 to 100 C,the nucleation rate of aerosols increases by 5.7 times.The nucleation rate of aerosols increased by 1.2 times when the ambient temperature was 50 C and the water vapor supersaturation increased from 1.00 to 1.04.For the growth rate of particles in aerosols,the supersaturation of water vapor increases from 1.001 to 1.003 when the particle size is 0.5 micron and the temperature is 50 C,and the growth rate of particles increases by two times.When the supersaturation of water vapor is 1.005,the growth rate of particles increases by 2.7times when the temperature is raised from 50 to 70.Secondly,by comparing the charged HSO₄^--H2O system with the neutral H₂SO₄-H2O system,the effects of charges on the formation and growth of aerosol particles were studied.The results show that under the same conditions,HSO₄^-is easier to bind water molecules than H₂SO₄,which makes the critical number of charged molecular clusters smaller,so the nucleation rate of charged sol is higher.The nucleation rate of electrically charged aerosols is 3.2 times of that of neutral aerosols at ambient temperature of 50 C and water vapor supersaturation of 1.05.The effect of charge on the growth rate of particles is not obvious with the increase of particle size.Thirdly,the inhibition of particle growth on particle formation in flue gas aerosols was studied.On the one hand,particle growth reduces the overall level of water vapor supersaturation and inhibits aerosol nucleation by absorbing water molecules in the environment.Under the condition of constant cooling rate,the nucleation law of aerosol under the influence of particle growth was studied.It was found that after the same time,the larger the cooling rate,the more aerosol particles accumulated.But when the flue gas is cooled to the same temperature,the faster the cooling rate is,the shorter the cooling time is,and the less aerosol particles accumulated.On the other hand,the water vapor distribution in space is changed by the absorption of water molecules around the particles,and the supersaturation of water vapor decreases gradually from infinite distance to the surface of the particles.Therefore,the closer to the particle area,the more difficult it is to form new particles.The region with small enough nucleation rate near the particles is defined as the region that inhibits nucleation.The larger the radius of the region,the more favorable it is to inhibit the formation of secondary particles.The influence of single parameter on the radius of the region was studied under the initial conditions of ambient temperature of 50 C,water vapor supersaturation of 1.1and particle size of 5 nm.It is found that the radius of the region increases 2.6 times when the ambient temperature decreases from 95 to 50.When the ambient water vapor supersaturation decreases from 1.19 to 1.1,the radius of the region increases by 4.6times.When the particle size of aerosol particles increases from 5 to 15 nm,the radius of the region increases by 1.12 times.