| The fine particles have the characteristics of light weight,small particles,good following performance,strong adsorption and difficult to remove.These characteristics are important factors to cause serious problems such as reduced atmospheric visibility,haze weather and the pollution.The problem caused by them have become a prominent atmospheric environmental problem in China.Most of the existing coal-fired power plants use electrostatic precipitator(ESP)to removal dust,The dust removal efficiency of ESP is up to more than 99%for particle size more than 10?m,But the removal efficiency of fine particles(particle size less than 10?m)is not ideal.Simultaneous effects of electric field,thermophoresis and water film can effectively improve the removal efficiency of fine particles in electrostatic precipitator.However,the current experimental study is limited to the macro removal efficiency analysis,The concentration distribution,particle size distribution and motion state of fine particles in electrostatic precipitator in the synergy effect of electric field,thermophoresis and water film have not been studied further.In this paper,The concentration distribution along the path,particle size distribution,concentration reduction rate along the path,particle trajectory and deposition efficiencyare described in detail by means of ELPI online test method in the effect of multi field synergy.The internal physical process of the particle movement in the electrostatic precipitator is deeply studied,which provides a theoretical basis for improving the efficiency of the removal of fine particles.The type,size,and direction of the forces particles subjected in electrostatic precipitator were summarized,and these forces were classified in different regions(polar region,mainstream region,near wall region),and under different operating conditions(original state,dry state,wet state,heat exchange state and synergy state),then based on the known parameters,the magnitude of these forces was analyzed.The mechanical behavior of particles was modeled according to the analysis of force type,size,direction and magnitude of particles in electrostatic precipitator,the kinematic model of the fine particles moving towards the wall and the adhesion model between the fine particles and the dust collecting plates were established respectively.Then,the electrostatic precipitation test bench for multi-field synergistic removal of fine particles was constructed,the distribution of temperature and humidity in the electrostatic precipitator was tested by the temperature and humidity instrument.Expect to analyze the motion characteristics of fine particles in electrostatic precipitator further on these basisthe online test and analysis was carried out by ELPI,and the distribution and movement characteristics of fine particles were studied,The concentration distribution law of the cross section,the variation law of the particle concentration along the path and the reduction rate of the concentration of the fine particles in different conditions were compared,the following conclusions are obtained:1)in the dry state,the highest concentration of particles in the cross section parallel to the polar line;When the heat transfer occurred at the wall,the high concentration area moved in the direction of the wall with the development of airflow,and the mixing phenomenon slowed down;When the water film was evenly distributed on the wall,in the near wall region,there was a low concentration area,and with the development of air flow,the area increased gradually,and the phenomenon of back mixing disappeared;In synergistic state,the field synergy effect was better than the above field superposition effect,the concentration gradient of the near wall region was higher than that of the wet state,and the low concentration area in the near wall region was more obvious.2)in the dry state,The dust collection effect of particles in the range of 0.04 to 0.6?m was not good,and the phenomenon of back mixing occurred;When the heat transfer occurred at the wall,The back mixing phenomenon of particles in the range of 0.4 to 0.6?m disappeared and the particle concentration in the near wall region increased significantly;When the water film was evenly distributed on the wall,the concentration of the particles in the range of 0.1 to ?m was greatly reduced and the near wall area was reduced by about 30%;In synergistic state,the particle number concentration curves were similar with that of wet state,but the concentration of particles in the whole particle size range had decreased,and the particles in the range from 0.1 to 1?m decreased by about 50%.3)in the dry state,the increase of the voltage had a significant effect on the removal of particles having a size greater than or less than 0.3?m,and the decrease rate of the concentration along the path was increased by 20%?50%;When the heat transfer occurred at the wall,The increase magnitude of the reduction of particles with size of 0.01?m was increased by a factor of 30%,while the rate of reduction of the particle size in the other particle size range was slightly lower,about 10%;When the water film was evenly distributed on the wall,the effect of liquid bridge force caused the decrease of the number of small particles and the increase of the number of particles with larger particle size.In synergistic state,the synergistic effect of multi-field could increase the concentration reduction rate of particles in the whole particle size range,compared with wet state,the concentration reduction of particles of size greater than 1?m was more obvious than that of 10%,The synergistic effect of the particles in the range of 0.1 to 1 m was the most obvious,and reduced by about 15%.Considering the flow field model,the corona electric field model,the particle motion model,the particle charge model,the wall heat transfer model and the water film evaporation diffusion model,the distribution and movement characteristics of fine particles under different conditions was studied by numerical simulation using COMSOL software.The distribution of electric field,temperature and humidity,particle trajectory,concentration the distribution and distribution efficiency along the path were analyzed in detail.According to the test results,and the numerical model for the distribution and motion characteristics of fine particles was established,the following conclusions were obtained:The electric field intensity and particle saturation charge exhibit an axisymmetric distribution and the lance line was taken as the axis of symmetry.The electric field intensity and the particle saturation charge were the strongest in the polar region.When the the voltage increased,the electric field intensity of the spike tip and the saturation charge of the particles increased gradually.The trend of temperature and humidity,the concentration distribution and the distribution of deposition efficiency along the path obtained by simulation were consistent with the experimental results in different states.Beacase the relative error was within the acceptable range,the model could accurately described the temperature,humidity,concentration distribution.There was a trend of offset to the dust collecting plate of fine particles in the electric field in dry condition.With the increase of voltage,the offset degree of particles became stronger and the deposition position of the particle moved forward gradually and the deposition amount increased gradually.Compared with dry state,the deposition position of the particle moved forward gradually and the deposition amount increased gradually under the condition of heat exchange and heat exchange.According to the results of the above experiments,simulation and theoretical analysis,the force changes and the mechanical behavior of fine particles in different states were summarized.The stress model of fine particles and mechanical behavior in the flow field,particle field,electric field,temperature field,humidity field,concentration field and their coupling were revealed.The types and changes of the force of the electrostatic precipitator caused by the electric field/heat/water film/synergy effect were analyzed,and the stress model of fine particles was established and the magnitude of the fine particles were determined under different conditions.According to the results,the basic motion of the particles in the electrostatic precipitator in different state were drawn. |
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