| PM2.5 does great harm to human health and atmospheric environmental quality.The traditional dust removal equipment has low removal efficiency for fine particles with particle size less than 2μm.The growth of coal-fired PM2.5 by vapor condensation has broad application prospects,but the high energy consumption brings difficulties to the industrial application of this technology.Therefore,this paper puts forward the technical route of flue gas reflux to promote the growth of PM2.5.The growth characteristics and mechanism of SiO2 and CaSO4 fine particles of typical coal-fired fly ash components under flue gas reflux were experimentally studied.In this paper,the experimental platform of flue gas reflux promoting the growth of fine particles was built.In order to ensure the uniform diffusion of hot water flowing into the growth tube and form a stable supersaturated environment,felt was adhered to the inner wall of the growth tube as a lining,so that the hot water could be evenly distributed around the tube wall.The growth characteristics of two kinds of fine particles without flue gas recirculation and with flue gas recirculation were studied.The results show that when there is no flue gas reflux,the maximum average particle size of SiO2 fine particles after growth is 1.7μm,and that of CaSO4 fine particles after growth is 2.7μm.After introducing flue gas recirculation,the maximum average particle sizes of SiO2 and CaSO4 are 5.2μm and 5.8μm respectively,and the average particle sizes of SiO2 and CaSO4 are increased by 206%and 115%,respectively,indicating that flue gas recirculation can effectively promote the growth of SiO2 and CaSO4 particles.In addition,the effects of supersaturation and flue gas velocity on the growth of fine particles under the action of flue gas reflux were studied.The results show that the growth effects of SiO2 and CaSO4 fine particles become better with the increase of supersaturation,and the reduction of flue gas velocity can enhance the promotion of flue gas reflux on the growth of fine particles.In addition,the optimal flue gas velocity for promoting the growth of fine particles is different under different supersaturation.When the average supersaturation is 1.03 and 1.06,the optimal flue gas velocity for the growth of two particles is 5 L/min,and when the average supersaturation is 1.1 and 1.14,the optimal flue gas velocity for the growth of two particles is 4 L/min.Collision and coalescence growth tube and secondary growth tube were designed,in order to research the influnece law and mechanism of collision and coalescence and secondary growth in the process of flue gas reflux.The results show that the collision can promote the growth of SiO2 and CaSO4 fine particles,increasing by 100%and55.6%,respectively.Under the same experimental conditions,the average particle size increases by 53%and 41%,respectively.The results show that with the increase of supersaturation,the promoting effect of collision and secondary growth on the growth of these two kinds of fine particles is increasing;The effect of collision on the growth of SiO2 fine particles with poor wettability is more obvious than that of secondary growth,and the effect is almost same for CaSO4 fine particles with good wettability under different supersaturation. |
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