Experimental Study On The Promoting Effect Of Charge On Particles Heterogeneous Coagulation

Due to the rapid urbanization and economic development,air pollution in China is more prominent,especially in eastern and central China,which is often affected by large-scale and long-term haze weather in winter.PM_2.5（fine particles）produced by industrial emissions is one of the main pollutants.However,conventional industrial dust removal technology is difficult to effectively remove fine particles emitted from industrial production.At present,one of the main technical means to reduce the emission of fine particles is to use coagulation technology to promote the agglomeration and growth of fine particles.Among them,heterogeneous coagulation technology can be applied to extreme flue gas conditions such as high temperature and humidity,and it can be realized in a simple water vapor environment,with low price,simple operation and maintenance,and has a broad application prospect.In order to meet the increasingly stringent environmental quality standards,it is necessary to continue to optimize and develop heterogeneous coagulation technology to achieve the purpose of efficient removal of fine particles.The study shows that charging can promote condensation of water vapor on the surface of particles and improve the efficiency of collision and agglomeration,which provides a new idea for improving the growth effect of fine particles in a water vapor environment.In order to grasp the promoting mechanism of charging on heterogeneous coagulation,combined with the particle size distribution in the pipeline,the process and law of heterogeneous coagulation and growth of particles under different charging conditions were studied in this paper.The research is expected to be able to reveal the influence mechanism of different charging conditions on the heterogeneous coagulation process,and provide a theoretical basis for the combination of heterogeneous coagulation and charging technology.In this paper,an experimental research platform for charge-heterogeneous coagulation and growth of particulate matter was built,and the coagulation growth effects of particles under three conditions of particle charging,droplet charging and particle and droplet agglomeration were studied.Firstly,the effects of different water vapor saturation on the heterogeneous coagulation and growth of particles were investigated.Then,under the optimal water vapor saturation,the particle size distribution under three charging conditions was measured,and the effects of different charging conditions on the heterogeneous coagulation and growth of particles were explored by combining with the analysis of scanning electron microscope（SEM）.Finally,compared with the uncharged condition,the variation of particles along the pipeline under three charged conditions was studied to study the effect of charging on the heterogeneous coagulation and growth process of particles.The results show that:（1）In a certain range,with the increase of water vapor saturation,the agglomeration and coagulation of particles increases,but with the further increase of water vapor saturation,the agglomeration effect decreases.（2）Particle charge,droplet charge and particle and droplet condensation charge can further increase the particle size and promote the heterogeneous coagulation and growth of particles.In the range of charged voltage,the median size and the effect of coagulation and growth of particles increase with the increase of charging voltage.The influence mechanism is compared with the uncharged particles,the critical free energy of heterogeneous nucleation is smaller when the particles are charged,which leads to the activation and heterogeneous condensation growth of more small particles,which shows that the median particle size is larger than that of the uncharged particles;after the droplet is charged,the surface tension is weakened and the energy barrier of heterogeneous nucleation is reduced,so the median particle size is larger than that before droplet charging;when the particles are charged with the droplets,the charge not only reduces the free energy needed for the nucleation of the particles,but also activates more small particles,resulting in nucleation and growth,and can also improve the cohesion between the particles,so as to increase the particle size.（3）Under the same water vapor saturation and charging voltage,the effect of charging on particle growth is the most obvious when the particles are reunited with the droplets,followed by the droplets,and the effect of charging on particle growth is not as good as the former two.（4）Under the same inlet water vapor saturation,the median particle size and the growth rate of particle size in the pipeline are larger than those in the pipeline when the particles are charged,the droplets are charged and the particles agglomerate with the droplets.