离心脉冲静电除尘器内颗粒浓度场测试分析

在离心脉冲静电除尘器研究的基础上 ,进行了离心脉冲静电除尘器内的浓度场的测试分析 ,并得出了在一定入口风速、工作电压、入口粉尘浓度下其颗粒浓度场分布规律及实测回归方程。     

离心脉冲静电除尘器内颗粒浓度场测试分析

在离心脉冲静电除尘器研究的基础上，进行了离心脉冲静电除尘器内的浓度场的测试分析，并得出了在一定入口风速、工作电压、入口粉尘浓度下其颗粒浓度场分布规律及实测回归方程。     

高风速复合式电收尘器的试验研究

应用"高风速"理论,将流体力学、电动力学、静电学有机结合设计出的高风速复合式电收尘器(HWSCESP)系统.试验以收尘效率作为收尘指标,以粉尘初始浓度、有效收尘面积、工作电压和系统风速为影响因素进行试验分析.结果表明,当粉尘初始浓度在45 g/m3,工作电压在47 kV,有效收尘面积为14.5 m2,系统风速为3.8 m/s时,收尘效率可达99.92%.从实验结果表明,HWSCESP是高效率、低成本的新型电收尘器.     

ESP粉尘收集性能的影响因素

为了进一步提高电除尘器的收尘效率,尤其是对高比电阻粉尘的收尘效率,依据非稳态静电收集理论,对影响电除尘器粉尘收集性能各项因素的作用程度及机理进行了进一步研究。实验研究了粉尘收尘效率与不同比电阻粉尘的最优极间距、最优工作电压、粉尘层厚度和比电阻之间的相互关系。研究结果表明,随着极间距的增加,对应比收尘极面积,对于不同比电阻粉尘的收尘效率的增加幅度是不同的,其中高比电阻粉尘的收尘效率增加的趋势更加显著;粉尘比电阻越高,所对应的最优极间距越大,宽间距电除尘器对捕集高比电阻粉尘具有一定优越性;在最优极间距条件下,粉尘比电阻越高,其所对应的最优工作电压越小;相对于正常比电阻粉尘,随极板沉积粉尘层厚度的增加,高比电阻粉尘的最佳收尘效率所对应的最优工作电压升高幅度较大,而且最优工作电压所对应的收尘效率下降显著。随粉尘比电阻的增大,电除尘器收尘效率逐渐降低,特别是当粉尘比电阻大于1011Ω.cm后,粉尘收尘效率显著下降。研究结果与非稳态静电收尘理论提出的观点相吻合,有助于透彻理解电场结构和运行参数与粉尘收集性能的关系,特别是对于今后研发提高高比电阻粉尘收集性能的针对性技术措施具有指导作用。     

侧流电除尘增效机理与检验

针对现有许多电除尘器难以满足日益严苛的颗粒物排放要求而面临提效改造的现状,根据经典电除尘理论,降低电场风速是电除尘器提效的一个有效途径,进而提出一种通过改变烟气流向成倍降低电场风速的侧流电除尘器。首先,为阐明侧流电除尘器的增效机理,基于已有的关于紊流情况下流速对颗粒悬浮作用的研究结果,通过受力分析给出了在有悬浮升力影响下带电颗粒的电除尘效率理论表达式,证明了降低电场风速的增效作用比增加电场长度更有效。然后,在极配结构和处理流量相同、平均入口含尘浓度约1 400 mg·m~(-3)和场强在2.5~4.5 kV·cm~(-1)的情况下,采用中位径为3.5μm的硅微粉进行了侧流电除尘器和常规电除尘器的减排效果对比实验研究。结果表明,侧流电除尘器的平均排放浓度比常规电除尘器降低45%,减排作用突出。     

高交通密度道路周边乔灌草型绿地对大气颗粒物的影响

在杭州临安一高交通密度道路周边的乔灌草型绿地中监测了PM1浓度、PM2.5浓度、PM10浓度、温度、湿度、风速、气压、CO2浓度,研究了颗粒物的日变化规律、乔灌草群落对其的消减影响及与气象因子的关系。结果表明:(1)不同粒径的大气颗粒物PM1、PM2.5、PM10的日变化特征一致,表现为"早晚高、中午低"的现象,3者与同一气象因子的决定系数基本相同;(2)道路两边的绿地宽度并不一定越宽越好,还应考虑植物种类的配置结构、植被密集程度及经济性;(3)大气颗粒物浓度与温度、风速成负相关关系,与湿度、气压成正相关关系,其中风速是影响颗粒物浓度的最关键气象因子。     

电袋复合除尘器阻力特性研究

利用电袋复合除尘器试验平台,探讨了清洁滤料过滤阻力特性、电场与过滤风速对过滤阻力的影响及本体阻力与测试风量的关系。结果表明:清洁滤料过滤阻力与过滤风速成线性关系,滤料阻力系数为5.39×10~7 m~(-1);无电场作用下,过滤阻力增长率为2.31Pa/min;而65kV电场作用下,过滤阻力增长率仅为0.63Pa/min,主要因为在电场作用下,颗粒层渗透率增大,且荷电粉尘在滤料表面排列疏松,空隙较多,过滤阻力增加慢,可以有效延长喷吹时间,减少喷吹过程对滤袋的冲刷;过滤阻力增长率随过滤风速的增加而增加,过滤风速由0.65m/min增加到0.97m/min,过滤阻力增长率由0.13Pa/min增加到0.63Pa/min;电袋复合除尘器本体阻力(ΔP,Pa)和测试风量(Q,m~3/s)的拟合方程为ΔP=72.15Q~2+25.07Q。     

北京空气重污染红色预警期间污染物与气象因子特征

揭示空气重污染红色预警期间污染物与气象因子的变化特征对空气质量预报和污染减排措施评估具有重要参考价值。利用大气污染和气象观测资料,研究了北京2015年11—12月空气重污染红色预警时期污染物浓度、气候特征及气象因子对空气质量影响。结果表明,PM_(2.5)在大气颗粒物中占有较大比重,为首要空气污染物;在重污染峰值时段,城郊PM_(2.5)与PM10比值(R)相差不大,可达0.9以上,空气呈均匀混合的高PM_(2.5)浓度特征,而空气质量较好时城区R值明显高于郊区;研究时段气候特征与历史同期相比有明显差异,其中平均风速偏小19%,平均气温偏高0.23℃,气温日较差减小,而多次小型降水增加了空气湿度,导致相对湿度值偏高40%,垂直方向上的逆温层或等温层则加剧了空气重污染的形成和发展,重污染过程中的红色预警措施明显降低了颗粒物浓度;风速与污染物浓度呈指数相关,城郊风速分别低于2.0和2.5 m·s~(-1)时,空气质量较差、污染物浓度随风速升高快速下降,而当城郊风速大于2.0和2.5 m·s~(-1)时变化特征则相反;相对湿度与污染物浓度呈幂相关,相对湿度在65%左右为空气质量特征发生变化的转折点;由于气温日较差存在季节变化,其与空气质量相关关系不太显著。     

原煤暗道通风除尘特征参数的数值模拟及优化

为了掌握输煤过程中原煤暗道粉尘运移扩散规律,确定最优排尘风速,进行通风除尘系统优化改造研究.以中煤平朔木瓜界选煤厂133暗道为研究背景,根据气固两相流理论,利用离散相模型对原煤暗道空间粉尘浓度进行了数值模拟,并与现场实际分布情况进行对比分析,模拟结果与实测数据基本一致.研究结果表明,暗道空间内皮带机尾及导料槽出口处粉尘浓度较大,并以给料机及机尾为中心径向逐步降低;最优排尘风速为2 m/s时,粉尘浓度下降幅度能达到97.2％,降尘效果显著,暗道空间内粉尘浓度保持在4 mg/m3以内.     

室内有害气体的通风净化效应

室内装修材料和家具释放的有害气体严重恶化了室内空气品质,其中甲醛对人体危害尤为突出,而室内通风是清除甲醛行之有效的办法。测试了室内甲醛释放源的释放强度规律,并建立了新装修室内甲醛通风净化的空气动力学模型,数值计算分析了通风情况下室内甲醛的浓度分布特征。结果表明:(1)室内地板和家具的甲醛释放强度均随测试时间呈指数减小;(2)同一通风风速下,装修后第30天时的甲醛浓度较大区域明显减少;(3)在室内人坐姿和站姿呼吸高度(约1.2、1.7m)处,无论风速大小,装修后通风一段时间后室内甲醛浓度均减小,且较低位置(1.2m)甲醛浓度减小更明显;(4)在同种气流组织形式下,较小和较大的通风风速对室内甲醛通风净化效果均不理想,对本研究模型而言,以通风风速2m/s左右时对室内甲醛净化效果较好。     

Performance of a Pulse-Jet Filter at High Filtration Velocity III. Penetration by Fault Processes

Performance data for fabric filters using either woven or felt bags can be better understood when fault processes such as pinhole bypass and seepage are considered. Penetration straight through the dust cake and fabric may not be important by comparison. Observed trends of increased penetration with increased filtration velocity, constant or slightly increased penetration with increasing particle diameter, and constant penetration with additional dust loading can be explained by fault processes. The pulse-jet experimental work described here, done over many filtration and cleaning cycles, shows that penetration increases substantially with increasing filtration velocity and that this increase is due entirely to seepage.     

Experimental analysis of particle concentration heterogeneity in a ventilated scale chamber

The mixing processes of the aerosol particles from an outdoor environment in a ventilated scale chamber were experimentally studied. The particles were classified into five groups by size: 0.3–0.5 μm, 0.5–1.0 μm, 1.0–3.0 μm, 3.0–5.0 μm and 5.0–10.0 μm. The developing process for the concentration of each particle group was measured in different kinds of flow fields.The results show that the flow field configuration can effectively influence the dispersion time rate of the particles at certain positions. The increase in particle diameter can decrease the dispersion time rate. When the gas flow velocity is high, the particle dispersion time rate is independent of particle size; but when the gas flow velocity is low, particle size can significantly affect the particle dispersion time rate because the turbulent diffusion becomes important in the air and particle transport. The uniformity of the particle concentration for certain positions in steady state tends to be controlled by the inflow velocity, flow field configuration and the particle diameters.     

Fine particle removal performance of a two-stage wet electrostatic precipitator using a nonmetallic pre-charger

A novel two-stage wet electrostatic precipitator (ESP) has been developed using a carbon brush pre-charger and collection plates with a thin water film. The electrical and particle collection performance was evaluated for submicrometer particles smaller than 0.01- 0.5 micrometer in diameter by varying the voltages applied to the pre-charger and collection plates as well as the polarity of the voltage. The collection efficiency was compared with that calculated by the theoretical models. The long-term performances of the ESP with and without water films were also compared in tests using Japanese Industrial Standards dust. The experimental results show that the carbon brush pre-charger of the two-stage wet ESP had approximately 10% particle capture, while producing ozone concentrations of less than 30 ppb. The produced amounts of ozone are significantly lower than the current limits set by international agencies. The ESP also achieved a high collection rate performance, averaging 90% for ultrafine particles, as based on the particle number concentration at an average velocity of 1 m/sec corresponding to a residence time of 0.17 sec. Higher particle collection efficiency for the ESP can be achieved by increasing the voltages applied to the pre-charger and the collection plates. The decreased collection efficiency that occurred during dust loading without water films was completely avoided by forming a thin water film on the collection plates at a water flow rate of 6.5 L/min/m(2).     

固定床中粒状脱硫剂除尘效率的研究

建立了非稳态过滤下的固定床颗粒层除尘效率模型.该模型尽可能地包含了影响固定床颗粒层除尘的参数,反映了沉积粉尘对除尘效率的影响;研究了以粒状脱硫剂为滤料的固定床在不同颗粒层厚度、空床气速、粒径下的除尘效率.结果表明,在颗粒层厚度为400～800 cm、空床气速≤0.4 m/s的条件下,颗粒层的除尘效率可达90％以上.     

Study on dust–gas coupling pollution law and selection of optimal purification distance of air duct during tunneling process

During the excavation of high gas mine, gas and dust often exist at the same time. In order to ensure that the gas concentration remains within a safe range and minimize the risk of workers’ pneumoconiosis, we simulated the interaction mechanism of airflow, gas, and dust, explored the pollution law of gas and dust, and obtained the optimal purification distance (L_p) by the CFD method. The reliability of the numerical simulation was verified by field measurements. Firstly, the properties of the gas and dust affected the structure of the airflow field. At the same time, the change in the airflow field affected the concentration distributions of the gas and dust. During the diffusion process, some high-risk regions in which the gas or dust concentrations exceeded 0.80% or 200 mg/m³, respectively, were discovered. Moreover, we have found that the airflow velocity in the top region of the tunnel and at the intersection corner between the cutting face and tunnel wall was the main factor affecting the purification effects. When L_p = 5–8 m, the gas concentration remained below 0.50%. When L_p = 6 m, the dust concentration reached a minimum of 287.5 mg/m³. Therefore, the optimal purification distance was determined to be 6 m; in which case, the gas and dust concentrations decreased by 32.84% and 47.02%, respectively.

     

HCI Sorption by Dry NaHCO3 for Incinerator Emissions Control

The sorption of hydrochloric acid (HCI) by thermally decomposed sodium bicarbonate (NaHCO₃) was investigated using a fixed-bed reactor containing sorbent particles dispersed in a bed of spherical glass beads. The gas flow rate (68° F and 760 mm Hg) was 0.039 cfm (1.1 liter/min) and the bed had a cross-sectional area of 0.0055 sq. ft. (5.1 sq. cm). The influence of particle diameter (10, 45 and 163 μm), temperature (225, 275, 375, 455, and 550° F), superficial gas velocity (11 and 21 fpm at reactor conditions, 375° F), and Inlet HCI gas concentration (415 ppm and 760 ppm in N₂, 275 and 455° F) were studied. Results showed that HCI sorption increased strongly with increasing temperature but was only weakly dependent on particle diameter, superficial gas velocity, and HCI gas concentration.     

Purification characteristics of fine particulate matter treated by a self-flushing wet electrostatic precipitator equipped with a flexible electrode

A self-flushing wet electrostatic precipitator was developed to investigate the removal performance for fine particles. Flexible material (polypropylene, 840A) and carbon steel in the form of a spiked band were adopted as the collection plate and discharge electrode, respectively. The particle concentration, morphology, and trace-element content were measured by electric low-pressure impactor, scanning electron microscope, and energy-dispersive x-ray spectroscopy, respectively, before and after the electrostatic precipitator. With increasing gas velocity, the collection efficiency of fine particles (up to 0.8 μm in diameter) increased, while it decreased for particles with diameters larger than 0.8 μm. Increasing the dust inlet concentration increased the collection efficiency up to a point, from which it then declined gradually with further increases in the inlet concentration. The particulate matter after the wet electrostatic precipitator showed different degrees of agglomeration. The collection efficiency of trace elements within PM₁₀ was less than that of the PM₁₀ itself. Notably, the water consumption in the current setup was significantly lower than for other treatment processes of comparable collection efficiencies.

Implications: Wet electrostatic precipitators, as fine filtration equipment, were generally applicable to coal-fired plants to reduce PM_2.5 emissions in China. However, high energy consumption and unstable operation, such as water usage and spray washing directly in the electric field, seriously restricted the further development. The utilization of self-flushing wet electrostatic precipitator can solve these problems to some extent.     

Determination of the Sodium Carbonate-Sulfur Dioxide Reaction Rate Coefficient at 450°F

Abstract

Gas-phase dispersion in granular biofilter materials with a wide range of particle sizes was investigated using atmospheric air and nitrogen as tracer gases. Two types of materials were used: (1) light extended clay aggregates (LECA), consisting of highly porous particles, and (2) gravel, consisting of solid particles. LECA is a commercial material that is used for insulation, as a soil conditioner, and as a carrier material in biofilters for air cleaning. These two materials were selected to have approximately the same particle shape. Column gas transport experiments were conducted for both materials using different mean particle diameters, different particle size ranges, and different gas flow velocities. Measured breakthrough curves were modeled using the advection-dispersion equation modified for mass transfer between mobile and immobile gas phases. The results showed that gas dispersivity increased with increasing mean particle diameter for LECA but was independent of mean particle diameter for gravel. Gas dispersivity also increased with increasing particle size range for both media. Dispersivities in LECA were generally higher than for gravel. The mobile gas content in both materials increased with increasing gas flow velocity but it did not show any strong dependency on mean particle diameter or particle size range. The relative fraction of mobile gas compared with total porosity was highest for gravel and lowest for LECA likely because of its high internal porosity.