Research On Chemical Agglomeration Enhanced Dust Removal Mechanism Of Fine Particulate Matter In Flue Gas During Coal Combustion

Fly ash fine particles caused by coal combustion had given rise to the air pollution,which had great impact on human health and living environment.China is now under intense pressure to control the emission of particulate matter,especially the fine particle PM_2.5.Aiming at solving the above-mentioned issue,a new approach,namely,chemical agglomeration technique,has been studied in depth.Before the dust removal,fine particles agglomerated into larger particles as chemical agglomeration solutions were sprayed.The capture of fine particles was enhanced and the removal efficiency of dust removal was increased.First,the fly ash samples collected from 12 different typical coal-fired power plants were chosen.Influence of fly ash element content on resistivity and zeta potential was studied,as well as the accumulation regulation of heavy metal elements.Results showed that content of Si and Al had a positive correlation with fly ash resistivity and a negative correlation with zeta potential of the suspension,whereas content of Ca and S had a negative correlation with resistivity and a positive correlation with zeta potential.The contents of various heavy metal elements varied in fly ash particles with different sizes.The contents of heavy metal elements increased significantly with the decrease of particle sizes.Then,the experiments of chemical agglomeration enhanced dust removal of fine particle were conducted.The results showed that the removal efficiency was as high as47.1%after chemical agglomeration solution KC was sprayed.As in the same concentration,a mixture of KC and KGM within the same mass attained a removal efficiency of 59.3%.After the chemical agglomeration solution KC was sprayed,the efficiency,which reached peak of 57.6%,as the solution K⁺concentration increased.Cationic surfactant CTAB and non-ionic surfactant TX100 enlarged the removal efficiency by 9.0%and 3.7%,respectively,whereas anionic surfactant SDS lessened average removal efficiency by 5.6%.As the solution concentration of KC increased from 0.01%to2%,the removal efficiency rose by 28.1%,while the flue gas temperature increased from105?C to 140?C,the average fine particle removal efficiency rose by 11.4%.Research on zeta potential of fly ash particle suspension helped us have a better understanding of mechanism of agglomeration.The experimental results of zeta potential indicated that the zeta potential value of the solution decreased as the pH increased.At the isoelectric point?IEP?,namely,pH of 4.3,the highest fine particle removal efficiency of25.9%was achieved.As the concentration of Al³⁺increased from 0.1%to 1%,zeta potential increased from-32.1 mV to-11.2 mV.After 1%of Al³⁺was added into the solution,the highest fine particle removal efficiency of 9.2%was achieved.Zeta potential increased to-6.4 mV and-14.4 mV,respectively,after 1%of CTAB and TX100 were added,whereas it decreased to-60.4 mV after SDS was added.In the meantime,the fine particle removal efficiency increased by 22.5%and 15.6%,respectively after CTAB and TX100 were added,respectively,whereas it decreased by 19.8%after SDS was added.The highest fine particle removal efficiency of 41.8%was acquired after 0.5%of KC was added.The lowest absolute value of zeta potential was achieved when 1%of chemical agglomeration solution KC/CTAB was add,which was 1.3 mV.The highest fine particle removal efficiency was achieved at the same time,which was 38.9%.It can be inferred that the zeta potential of the solution can be used as an indicator of the fine particle removal efficiency.The numerical simulation results of the process of agglomeration between the fine particles and chemical agglomeration solution droplets showed that velocity,mass,diameter,and number of the particles after agglomeration was affected by the physicochemical characteristic of the chemical agglomeration solutions.Variation trend of the characteristic quantity of the particles increased as the density and viscosity of chemical agglomeration solution increased.The solutions with larger flux and larger droplet diameter had higher probability of collision with the particles.Therefore,the effect of agglomeration was better.As the particles got agglomerated,their mass and diameter became larger,and velocity became lower.As a result,the probability of collision with the particles became lower and finally values of all the characteristic quantity kept stable.Based on the experimental and theoretical research,the industrial application of chemical agglomeration in a power plant with 2?340 Mega Watt coal-fired boilers in Jiangxi province was studied in this chapter.In 4#boiler,after continuous-spraying the chemical agglomeration solutions for about 180 minutes,the average particle concentration after electrostatic precipitator?ESP?decreased from 60 mg?m^-3 to 23 mg?m^-3,which was decreased by 61.7%.The particle concentration after wet desulphurization?WFGD?also decreased about 50%to as low as 8.4 mg?m^-3.The whole year data of Continuous Emission Monitoring System?CEMS?in 4#boiler revealed that after the solutions were sprayed,the average particle concentration after ESP decreased by 51.6%,which was from 34.3 mg?m^-3 to 16.6 mg?m^-3,and concentration of SO₂ decreased by14.7%,which was decreased from 2217 mg?m^-3 to 1890 mg?m^-3.The average temperature of flue gas was decreased by 8.2?C.The initial investment for chemical agglomeration technique was less than half of the cost for the wet electrostatic precipitation.Besides,the following cost for annual operation of was also same as that of the wet electrostatic precipitation.Considering all the experiment results and its economical efficiency,chemical agglomeration technology was suitable for industrial application.