ZHU Kangning，LI Yuan，SHEN Xiaoyou，WU Jingjing，CAI Jie，GU Zhongzhu (School of Energy and Mechanical Engineering，Nanjing Normal University，Nanjing 210023，China)

Abstract

Objective Fine particles are ubiquitous in various settings including industrial production，daily activities，and natural surroundings， 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 diseases，thus necessitating urgent attention to their mitigation. The granular bed filter （GBF）emerges as a promising solution in this regard，employing granular materials like silica sand，gravel，slag，or coke to form an efficient filter layer capable of capturing fine particles 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，the GBF technology has garnered rapid adoption across diverse sectors encompassing energy，chemical processing，metallurgy，and environmental conservation. However，the current comprehension of the dust removal mechanisms and operational dynamics of GBF remains inadequate，necessitating urgent bolstering through intensified research efforts. This paper aims to advance the understanding and refinement of GBF technology，thereby facilitating its continued evolution and application.

Methods This paper presents the establishment of a three-dimensional filtering model for fixed bed Granular Bed Filters（GBF），encompassing both geometric and mathematical aspects. The geometric model，illustrated in Figure 1，portrays the entire structure as a cylindrical tube， divided into three distinct sections：the entrance，the filter layer（composed of stacked granular material），and the exit. The mathematical model adopts a gas-solid unidirectional coupling approach， focusing solely on the influence of airflow on fine particles， disregarding the reverse effect. Gas phase dynamics are simulated using the Reynolds-averaged Navier-Stokes（RAN）method with standard equations serving as the closed model， while the solid phase （fine particles）is analyzed via Lagrange-based force calculations. Validation of model accuracy is conducted through compari⁃ son with experimental verification，as depicted in Figure 2. Subsequently， the paper investigates the filtration efficiency of GBF for fine particles ranging from 1 to 21 µm in diameter， with a density of 2 100 kg/m3 ， under varying electric field intensities （0， 1 000，2 000，3 000 V）. Furthermore， the distribution of fine particles with different sizes （4，11，21 µm） within the stacked granular layer is examined and compared.

Results and Discussion As depicted in Figure 3， the introduction of an applied electric field yields 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， the degree of improvement in filtration efficiency correlates positively with the strength of the applied electric field. Notably， under a 3 000 V applied electric field， the filtration efficiency for 21 µm fine particles reaches 98. 8%， nearing full efficiency. However， while the 1 000 V electric field intensity significantly enhances filtration efficiency，further increases in electric field intensity exhibit diminishing returns. For instance，transitioning from 1 000 V to 2 000 V or 2 000 V to 3 000 V results in a marginal improvement of no more than 5% in the filtration efficiency for fine particles ranging from 1 to 21 µm. Figures 4，5，6，and 7 illustrate that as the size of fine particles increases， their distribution within the stacked granular layer becomes more concentrated in regions with higher gas flow velocities，particularly near the walls of the GBF. This phenomenon is attributed to the porous channels between the GBF walls and the stacked particle spheres，facilitating the passage of larger fine particles. Figure 8 indicates that compared to the scenario without an applied electric field，the presence of a 1 000V applied electric field minimally alters the distribution of 11 µm fine particles within the stacked granular layer at 0. 1s，primarily leading to a reduction in the quantity of fine particles. This reduction reflects the enhanced filtration efficiency due to the applied electric field. However，by 0. 3 s，the applied electric field induces a more diffuse distribution of 11µm fine particles within the GBF， accompanied by mass accumulation near the GBF wall， even in low-velocity areas. Figure 9 reveals that at the same time point （0. 3 s），the applied electric field causes a more pronounced accumulation of 21 µm fine particles near the GBF wall compared to 11 µm fine particles，while 4 µm fine particles do not exhibit significant accumulation.

Conclusion The primary conclusions drawn from this study are as follows：1）The introduction of an applied electric field yields a substantial enhancement in the filtration efficiency of GBF for fine particles. Furthermore，the degree of improvement in filtra⁃ tion efficiency is directly proportional to the strength of the applied electric field. Additionally，the impact of the applied electric field on the filtration efficiency varies depending on the size of the fine particles. 2）Fine particles exhibit a tendency to accumu⁃ late in regions characterized by high gas flow velocities within the stacked granular layer. Moreover，larger fine particles demonstrate a greater propensity to traverse through the channels between the stacked granular layer and the GBF wall. 3）The presence of an applied electric field results in a significant reduction in 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）exhibit a tendency to aggregate near the GBF wall under the influence of the applied electric field.

Keywords：granular bed filter；electric field；fine particle； filtration efficiency；numerical simulation

Get Citation:ZHU K N， LI Y， SHEN X Y， et al. Numerical study on the filtration performance by granular bed filter under applied electric field［J］. China Powder Science and Technology，2024，30（3）：88−99.

Received:2023-12-21.Revised:2024-03-13,Online:2024-04-23。

Funding Project:国家自然科学基金项目，编号:51878356。

First Author:朱康宁(1999—)，男，硕士生，研究方向为颗粒层除尘。E-mail:211902024@njnu. edu. cn

Corresponding Author:蔡杰(1978—)，男，教授，博士，研究方向为多相流。E-mail:caijie@njnu. edu. cn

DOI：10.13732/j.issn.1008-5548.2024.03.008

CLC No:TK284.5 Type Code:A

Serial No:1008-5548（2024）03-00088-12