| It is difficult to change China's coal-dominated energy consumption structure in the short term,and the problem of atmospheric environmental pollution is still serious.Therefore,it is very urgent to control coal soot emissions.Dry electrostatic precipitator(ESP),as one of the mainstream devices of control coal soot emissions,has relatively high dust collection efficiency which can reach more than 99.5%,but the collection efficiency of the fine particles is lower,mainly due to the low ion concentration generated in the electric field of the traditional ESP and the low probability of the fine particles being charged and coagulated,resulting in the problem of poor dust collection effect.Vortex electric precipitation technology is an effective way to capture fine particles.It adopts staggered vortex dust collecting plate that are laid against gas flow direction,places discharge wire in the outlet end of the same row dust collecting plate gap,makes flue gas flow form vortex in dust collecting plate surface,then the considerable increase of the ion concentration in the discharge electric field,and the charging,collision,coagulation and inertia separation of fine particles is promoted.So the collecting efficiency of fine particles is improved effectively.Because vortex electrostatic precipitator(VEP)involves very complex charging,coagulation and dust collection process,there is no more accurate and practical calculation model of electrocoagulation precipitation efficiency.Based on the principles of turbulent flow mass transfer,the two-dimensional transport equation,the electric coagulation equation and the theory calculation model of electrocoagulation precipitation efficiency of the charged particles were established.The internal flow field characteristics and movement characteristics of fine particles inside the VEP were analyzed by solving the model.Besides,the regularity of coagulation and the dust collecting of charged particles was revealed.On the basis of theoretical research,the external voltage and other physical parameters were regulated,and the collection experiment of fine particles were conducted so as to provide the best design parameters for the practical application of the VEP.The main research contents and conclusions of this paper are as follows:1.Considering the influencing factors of turbulence diffusion,dispersion,electric wind and field intensity distribution inequality,the two-dimensional transport equation and electric coagulation equation of homo-polar charged dust particles were established.By combining with the boundary conditions,the transport equation was solved with the separation variable method,and the precipitation efficiency formula was obtained.Based on coupling electrocoagulation efficiency formula,the calculation model of electrocoagulation precipitation efficiency of different fine particle sizes was obtained.2.The VEP calculation model of electrocoagulation precipitation efficiency was solved through MATLAB.In addition,the influence law of the fine particle size(di)on charge quantity(C),the particle migration velocity(?),and the electrocoagulation precipitation efficiency(?0)was revealed.When the fine particle size increased,the charge quantity,the particle migration velocity,and the electrocoagulation precipitation efficiency increased unceasingly.The calculation values of electrocoagulation precipitation efficiency were slightly larger than the experiment value of dust collecting efficiency,and both increased with the increase of particle size;the maximum difference and the minimum difference between them were 3.7%,0.2% respectively;the calculation values of Deustch precipitation efficiency considerably differed from the experiment value of dust collecting efficiency,with the maximum difference and the minimum difference between them being 17.2% and 4.5% respectively.Visibly,the calculated value of electrocoagulation precipitation efficiency formula was more close to actual value.3.The internal flow field of VEP was simulated with FLUENT software;the section system was used to analyze thee influence of physical parameters such as dust collecting plate side width(B),row spacing(L),field average velocity(V)on flow field characteristics;the evolution law of the vortex structure was revealed;the state of the flow field of dust catcher was the most favorable when B was 15 mm,L was 120 mm,and V was 3.4 m/s,and there were around four stable symmetrical vortexes between the gap of dust collecting plate,and near the discharge wire was high gas velocity turbulent area,and near dust collecting plate was low gas velocity laminar flow area.Furthermore,by means of DPM model,further analysis was conducted on the influence of fine particle size(di),field average velocity(V),and charged state of fine particles on the trajectory and the capture efficiency of fine particles(??);the evolvement trajectory of fine particles was illustrated,and the capture efficiency of fine particles at various levels was concluded.When the external voltage was 18 k V,and di was 1 ?m,2.5 ?m,4 ?m,10 ?m and 15 ?m respectively,?? was 67.4%,70.9%,75.7%,87.8% and 94.8% respectively.4.The external voltage(U),field average velocity(V),collecting electrode spacing(D)and other physical parameters were controlled so as to conduct single factor and multiple factor ion concentration experiments,study the ion transport properties,and determine the quantitative law of between physical parameters and ion concentration(ne).Under the condition of the optimal operation parameters,the ion concentration in discharge electric field of the VEP exceeded 9 37.0 ?10 /cm,being far greater than the ion density generated in traditional ESP electric field.5.Single factor experiment and multiple factors experiment were conducted through the regulation of the external voltage(U),gas residence time(T),row spacing(L),effective collecting area(S)and other physical parameters.The influence law of these physical parameters on VEP precipitation efficiency(?)and grade precipitation efficiency(??)was studied from the macroscopic angle so as to seek the best design parameters.When U was18 k V,T was 0.59 s,L was 100 mm,and S was 1.13 m2,? was 90.4%;for particle size of 0-1 ?m,1-2.5 ?m,2.5-4 ?m,4-10 ?m,and 10-15 ?m,?? were 82.5%,84.4%,86.5%,90.6% and 95.3% respectively.6.The internal flow field features of the VEP was explored through particle image velocimetry(PIV)from the microscopic view,and the evolution law of the vortex structure was revealed.Results show that the obvious vortex region and laminar flow region are distinctly formed within the VEP,was conducive to improve the charged effect,condensation,coagulation chances and capture efficiency of the fine particles under certain gas velocity range.As gas velocity increased,the ion transport rate increased,and the vortex region increased,which could improve the ion concentration,and the charging and coagulating rates of fine particles,so as to improve the collecting efficiency of fine particles.However,due to the thinning of the laminar flow,it is not conducive to capture the dust particles,trapped particles would return to the flue gas stream again,which prone to secondary flying.Therefore,the gas velocity must be controlled within a certain range.7.In order to further improve the coagulation effect of fine particles,the experiment system of double discharge wire VEP was designed.Single factor experiment and multiple factors experiment were conducted through the regulation of the external voltage(U),gas residence time(T),collecting electrode spacing(D)and other physical parameters.The influence law of these physical parameters on precipitation efficiency was studied so as to seek the optimal design parameters.Under the condition of the optimal operation parameters,the precipitation efficiency of double discharge electrode VEP for PM10,PM15 were 92.5% and 93.1% respectively.In conclusion,compared with the traditional ESP,VEP can efficiently capture fine particles with high efficiency,and considerably reduces the volume,reduce energy consumption,and shows obvious technical and economic advantages.Thus,it is a new type of electrostatic precipitator with great potential for application. |
PDF Full Text Request