[目的]研究外加电场和细颗粒物粒径对固定床颗粒层除尘器(granular bed filter,GBF)过滤性能的影响.[方法]建立GBF的三维过滤模型和电场力模型并验证其准确性;研究有、无外加电场及不同电场强度情况下GBF对粒径为1～21 μm的细颗粒物的过滤情况,并分析不同粒径的细颗粒物在GBF内部的分布规律.[结果]外加电场的存在能显著提高GBF对粒径为3～21 μm的细颗粒物的过滤效率,且外加电场强度越大,细颗粒物粒径越大,GBF过滤效率提升越明显;随着粒径的增大,细颗粒物在堆积颗粒层内部的分布更加集中在高气流速度区域,且更容易通过堆积颗粒层与GBF壁面之间形成的通道;外加电场的存在使得堆积颗粒层内部的细颗粒物数量减少,分布散乱,且大粒径细颗粒物在GBF壁面附近区域发生较大规模聚集.[结论]外加电场和细颗粒物粒径的增大与GBF内部细颗粒物的分布规律密切联系,且对GBF过滤性能的提升发挥积极作用.
Numerical study on filtration performance of granular bed filter under applied electric field
Objective Fine particles are ubiquitous in various settings including industrial production,daily activities,and natural environ-ments,exerting a profound influence on atmospheric conditions,industrial operations,and human health.Notably,PM2.5,in particular,poses significant health risks,such as cardiopulmonary dysfunction,respiratory ailments,and cardiovascular dis-eases,thus necessitating urgent attention to their mitigation.The granular bed filter(GBF)emerges as a promising solution by employing granular materials like silica sand,gravel,slag,or coke to form an efficient filter layer capable of capturing fine par-ticles from polluted air streams.Owing to its adeptness in dust removal,along with its resilience to elevated temperatures and pressures,corrosion,and abrasion,as well as its cost-effectiveness and simplistic design,GBF technology has garnered rapid adoption across diverse sectors encompassing energy,chemical processing,metallurgy,and environmental conservation.How-ever,current comprehension of the dust removal mechanisms and operational dynamics of GBF remains inadequate,necessitat-ing further research.This paper aims to advance our understanding of GBF technology,thereby facilitating its progress and application.Methods This paper established a three-dimensional filtering model for fixed bed granular bed filters(GBF),incorporationg both geometric and mathematical aspects.The geometric model,illustrated in Fig.1,portrayed the entire structure as a cylin-drical tube with three distinct sections:entrance,filter layer(composed of stacked granular material),and exit.The mathemati-cal model adopted a gas-solid unidirectional coupling approach,focusing solely on the influence of airflow on fine particles,while disregarding the reverse effect.Gas phase dynamics were simulated using the Reynolds-averaged Navier-Stokes(RAN)method with standard equations serving as the closed model,while the solid phase(fine particles)was analyzed via Lagrange-based force calculations.The model's accuracy was verified experimentally,as depicted in Fig.2.Subsequently,the paper investigated the filtration efficiency of GBF for fine particles ranging from 1 to 21 μm in diameter,with a density of 2 100 kg/m3 and under varying electric field intensities(0,1 000,2 000,3 000 V).Furthermore,the distribution of fine particles with dif-ferent sizes(4,11,21 μm)within the stacked granular layer was examined and compared.Results and Discussion As depicted in Fig.3,the introduction of an applied electric field yielded a notable enhancement in the filtration efficiency of the filter layer,particularly for fine particles ranging from 1 to 21 μm,with a more pronounced effect observed for particles larger than 3 μm.Moreover,applied electric field correlated positively with greater efficiency.Notably,at 3 000 V,the filtration efficiency for 21 μm fine particles reached 98.8％,nearing full efficiency.However,while 1 000 V significantly enhanced filtration efficiency,further increases in electric field intensities exhibited diminishing returns.For instance,transitioning from 1 000 V to 2 000 V or 2 000 V to 3 000 V only resulted in a marginal improvement of no more than 5％in filtration efficiency for fine particles ranging from 1 to 21 μm.Fig.4,5,6,and 7 illustrated that as the size of fine par-ticles increased,their distribution within the stacked granular layer became more concentrated in regions with higher gas flow velocities,particularly near the GBF walls.This phenomenon was attributed to the porous channels between the GBF walls and the stacked particle spheres,which facilitated the passage of larger fine particles.Fig.8 indicated that,compared to scenarios without an applied electric field,an electric field of 1 000 V minimally altered the distribution of 11 μm fine particles within the stacked granular layer at 0.1 s,primarily leading to a reduction in the quantity of fine particles.This reduction reflected an enhanced filtration efficiency due to the applied electric field.However,at 0.3 s,the applied electric field induced a more dis-persed distribution of 11 μm fine particles within the GBF walls,accompanied by a mass accumulation near the GBF walls,even in low-velocity regions.Fig.9 revealed that at the same time point(0.3 s),the applied electric field caused a more pro-nounced accumulation of 21 μm fine particles near the GBF walls compared to those of 11 μm fine particles,while 4 μm fine particles did not exhibit significant accumulation.Conclusion The primary conclusions drawn from this study are as follows:l)The applied electric field substantially enhance the filtration efficiency of GBF for fine particles.Furthermore,the improvement in filtration efficiency is directly proportional to field intensity.Additionally,its impact varies depending on fine particles sizes.2)Fine particles exhibit a tendency to accumu-late in high-velocity regions within the stacked granular layer.Moreover,larger fine particles demonstrate a greater propensity to traverse channels between the stacked granular layer and the GBF walls.3)The applied electric field significantly reduces the quantity of fine particles within the stacked granular layer,leading to a more dispersed distribution.Notably,fine particles with larger particle sizes(11 µm and 21 μm)tend to aggregate near the GBF walls under the influence of the applied electric field.
granular bed filterelectric fieldfine particlefiltration efficiencynumerical simulation
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