Dust Deposit Profiles in a High Velocity Pulse-Jet Fabric Filter

Dust deposit profiles in a pilot-scale pulse-jet fabric filter were measured using a beta gauge. Fly ash was collected on polyester needled felt bags, and the dust profiles were measured after the test system was operated to equilibrium at superficial filtration velocities of 50, 75,100,125, and 150 mm/s. The profiles measured show that a large mass of dust is retained on the fabric of a pulse-jet filter when operated at high filtration velocities. This dust mass retention can be caused by two mechanisms: the failure to remove dust from the fabric during a cleaning pulse, and the redeposition of suspended dust onto the fabric after a cleaning pulse. The dust deposit measured at the highest test velocity was found to be much different from the deposits measured at all other velocities. The deposit found at 150 mm/s had almost twice the average areal density and was more evenly distributed than the deposits found at lower velocities.     

Performance of a Pulse-Jet Filter at High Filtration Velocity I. Particle Collection

The fly ash collection characteristics of a pulse-jet fabric filter have been studied. Fly ash penetration was found to decrease as the dust deposit increased from 0 to 60 micrometers in thickness, to increase as face velocity through the bags increased from 5 to 15 cm/s, and to remain relatively constant for particles from 0.3 to 4.0 µm in diameter. Experiments employing chemically tagged fly ash were performed to investigate three dust penetration mechanisms. On resumption of filtering after cleaning, penetration by straight through dust loss declined rapidly from its maximum, reached a minimum, and then increased. Seepage of dust through the fabric was found to be constant throughout the filtration cycle. Dust lost as pinhole plugs increased after cleaning, passed through a maximum, and then declined. The pinholes appeared to open the way for further penetration by the straight through mechanism.     

On the forming mechanism of the cleaning airflow of pulse-jet fabric filters

To reveal the formation mechanism of a pulse-jet airflow’s cleaning effect in a filter bag, a theoretical model is built by using the theory of the gas jet and unitary adiabatic flow according to given specifications and dimensions of the bags and resistance characteristics of the cloth and dust layer. It is about the relationship between cleaning system structure and operating parameters. The model follows the principle that the flow and kinetic energy of jet flow injected into a filter bag should be consistent with the flow of cleaning airflow in the bag and the pressure drop flowing through the filter cloth and dust layer. The purpose of the model is to achieve the peak pressure of cleaning airflow, which dominates the effect of the pulse-jet cleaning process. The cleaning system structure includes air pressure in the nozzle, structure and size of nozzle, exit velocity of nozzle, jet distance, and diameter of jet cross section. Based on the condition of the cleaning system structure and operating parameters established by using the theoretical model, Fluent software is applied to carry out a numerical simulation of the jet airflow field at the nozzle’s outlet, jet airflow field between nozzle and bag top, and cleaning airflow field in the filter bag. Experimental results are used to verify the reliability of the theoretical model. They are obtained in a pilot-scale test filter with a single bag, with length 2 m and in general full-scale dimensions of the cleaning system. The results show that when any rectification measure is not installed at the bag opening, the cross-sectional area covered by the jet gas is hardly sufficient to cover the entire area of the bag opening. A large portion of the gases injected into the filter bag will overflow reversely upward from the edge due to pressure differences between the upper area and lower area inside the bag opening. This led to a serious shortage of the cleaning airflow and ar limited increase in static pressure. When a venturi-type rectifier tube is installed at the bag opening, the jet flow is converted to funnel flow for which the cross-section velocity distribution is more uniform at the throat of the rectifier tube due to the guided effects of the upper tapered pipe. Then it is transited to stressful flow below the bag opening via rectified effects of the lower dilated pipe. The results show that the gap between the static pressure of gas in the bag and the expected value is significantly reduced. The theoretical value of the nozzle diameter is enlarged to compensate for two aspects of adverse effects of cleaning airflow and energy. This is because the flow is not a purely free-form jet from the nozzle to the entrance of the rectifier tube and because the gas suffers from local resistance while flowing through the rectifier tube. The numerical simulation and experiment show that the peak pressure of cleaning airflow in the filter bag is able to reach the expected value. The results confirm that the mechanism of the pulse-jet cleaning airflow and the calculation method of the pulse-jet cleaning system structure and operating parameters offered in this study are correct. The study results provide a scientific basis for designing the system of pulse-jet fabric filters.

Implications: Pulse-jet cleaned fabric filters are commonly used for air pollution control in many industries. Pulse-jet cleaning is widely used for this purpose as it enables frequent cleaning while the filter is operating. However, the theoretical system of the forming mechanism of the pulse-jet cleaning has not formed so far. This indicates the theoretical model plays an important role in designing effective pulse-jet cleaned fabric filters.     

Theory for Penetration in A Pulse-Jet Cleaned Fabric Filter

Presently, there is no effective way to interpret or predict dust penetration through a pulse-jet cleaned fabric filter. This paper presents a model which considers penetration straight through the filter and penetration by seepage. A considerable number of studies have been devoted to penetration by the straight through process; however, a comparison of data from the literature with the present model indicates that seepage and not straight through penetration accounts for virtually all penetrating dust. Although insufficient information is presently available to use the model to predict penetration, the model does show trends that should occur with changes in filter operating variables such as filtration velocity and pulse pressure, and suggests areas in which further research is necessary.     

响应面法优化袋式除尘器脉冲清灰性能

基于计算流体动力学的方法采用三维、可压缩、非稳态流动数学模型对袋式除尘器脉冲清灰过程进行了数值模拟,得到了滤袋内外压差,并与文献实验值进行了比较,验证了仿真模型的可靠性。基于响应面法研究了喷吹压力、喷吹高度、滤袋直径和滤袋长度对脉冲清灰性能的影响,得到这4个影响因子的二次多项式预测模型,并进行优化。结果表明,喷吹压力为0.3 MPa,喷吹高度为0.2 m,滤袋直径为0.16 m,滤袋长度为6 m时,内外压差峰值最优,优化结果与仿真模拟结果相差小于3%。研究结果为袋式除尘器脉冲清灰系统的设计与优化提供了重要参考。     

文丘里对脉冲喷吹过滤系统清灰的影响

在自建的脉冲喷吹实验台上，利用Y—YD-7044型压电式传感器和MYD-8801加速度传感器，测试0120×2000mm覆PTFE膜无纺布滤袋在不同喷吹压力下，加文丘里与不加文丘里时的最大侧壁压力峰值和最大反向加速度，并对比计算了获得同样清灰强度时的脉冲阀一次喷吹耗气量。结果显示，添加文丘里能显著增大滤袋中下部最大侧壁压力峰值和整条滤袋上的最大反向加速度，即提高脉冲喷吹清灰强度；对应同样的喷吹压力，加文丘里时的平均最大侧壁压力峰值和平均最大反向加速度比不加文丘里时分别平均提高大约70％和50％；加文丘里获得同样清灰强度时的脉冲阀一次喷吹耗气量比不加文丘里时节省40％左右。证实对于脉冲喷吹清灰系统，添加文丘里能有效改善清灰效果以及减小能量？肖耗。     

Survey on the Use of Pulse-Jet Fabric Filters

Pulse-jet fabric filters rely on the filtration of dirty flue gas by the outside surface of the bags, which are then cleaned by a shock wave generated by an air pulse entering each bag from the top. As it travels down the length of the bag, the shock wave flexes the fabric and dislodges the dust cake. Enhancement of the pulse may be achieved by using a venturi, and cleaning may be on-line or off-line. This paper summarizes the results of an exhaustive study conducted for the Electric Power Research Institute to provide a convenient and versatile information base about the use of pulse-jet fabric filters on coal-fired boilers. Predominant features of the many pulse-jet installations identified by vendor survey and literature survey are shown in graphical and tabular form.     

Dust Collection Efficiency Analysis in a Two-Dimensional Circulating Granular Bed Filter

Abstract

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 ± 0.24, 21.50 ± 0.11, and 30.51 ± 0.57 g/sec at louver angles of 45°, 30°, and 20°, respectively. Optimal dust collection efficiency peaked with a louver angle of 30°. Average particle sizes of bed material by sieve diameters (μm) of 795 μm had higher dust collection efficiency than the average collector particle size of 1500 μm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

滤料负载粉尘层对气态汞脱除性能的实验研究

通过不同性能纤维滤料负载燃煤飞灰粉尘层,来模拟袋式除尘器滤袋表面粉尘附着层,进而研究袋滤器用不同性能纤维滤料和粉尘附着层对燃煤烟气中Hg0的联合脱除性能。在固定床实验系统上分别进行了不同纤维滤料和燃煤飞灰粉尘层,以及经实验优选得到的华博特滤料负载燃煤飞灰粉尘层脱除燃煤烟气中Hg0的实验研究。结果表明,燃煤飞灰粉尘层和华博特滤料对Hg0分别有一定的脱除作用,脱除效率可达35%和42.5%,它们对Hg0的脱除是物理吸附和化学吸附共同作用的结果;同时,华博特滤料负载燃煤飞灰粉尘层对Hg0的联合脱除效率受到吸附反应温度、入口汞浓度和烟气停留时间等因素的影响,最佳脱汞率可达64.4%;吸附反应温度越高,脱除效率越低;烟气停留时间越大,脱除效率越高;入口汞浓度的提高并不一定提高华博特滤料负载飞灰粉尘层的脱汞效果。     

Prediction of Particulate Loading in Exhaust from Fabric Filter Baghouses with One or More Failed Bags

Abstract

Loss of filtration efficiency in a fabric filter baghouse is typically caused by bag failure, in one form or another. The degree of such failure can be as minor as a pinhole leak or as major as a fully involved baghouse fire. In some cases, local air pollution regulations or federal hazardous waste laws may require estimation of the total quantity of particulate matter released to the environment as a result of such failures. In this paper, a technique is presented for computing the dust loading in the baghouse exhaust when one or more bags have failed. The algorithm developed is shown to be an improvement over a previously published result, which requires empirical knowledge of the variation in baghouse pressure differential with bag failures. An example calculation is presented for a bag-house equipped with 200 bags. The prediction shows that a small percentage of failed bags can cause a relatively large proportion of the gas flow to bypass the active bags, which, in turn, leads to high outlet dust loading and low overall collection efficiency from the baghouse.     

Precipitator Gas Flow Distribution

An electrostatic precipitator, furnished on a 500-Mw tan-gentially-fired steam generator burning coal, was to collect 99.6% of the fly ash being generated in the furnace of this unit. Preliminary measurements indicated that the installation was not meeting its collection guarantee. Precipitator outlet flue dust distribution indicated that poor gas flow distribution might be one of the causes of the low performance. When observation ports were installed in the outlet flue to permit a direct visual evaluation of the problem, it was found that high velocity jets were present in the collecting electrodes, and that hopper sweepage was present. A model study along with velocity distribution measurements of the installation were authorized. Flow analysis indicated that the field and model correlated well. Extensive changes were made in the model, which eliminated or minimized the high velocity jets and hopper sweepage. After these changes were made in the field installation, it was able to achieve the required dust collection efficiency.     

Dust collection efficiency analysis in a two-dimensional circulating granular bed filter

Dust collection efficiency data were analyzed to determine better operating conditions for a two-dimensional circulating granular bed filter (CGBF). The dust collection efficiency in the granular bed was affected by the following operating parameters: the louver angle, the solids mass flow rate, and the particle size of the bed material. Experimental results showed that higher dust collection efficiency occurs when the solids mass flow rates were 20.34 +/- 0.24, 21.50 +/- 0.11, and 30.51 +/- 0.57 g/sec at louver angles of 45 degrees, 30 degrees, and 20 degrees, respectively. Optimal dust collection efficiency peaked with a louver angle of 30 degrees. Average particle sizes of bed material by sieve diameters (microm) of 795 microm had higher dust collection efficiency than the average collector particle size of 1500 microm. Dust collection efficiency is influenced by bed material attrition phenomenon, causing dust collection efficiency to decrease rapidly. The dust collection efficiency analysis not only found the system free of design defects but also assisted in the operation of the two-dimensional CGBF system.     

Adhesive Behavior of Dust in Electrostatic Precipitation

In 2-stage precipitators particles are driven to the collecting plates by electrostatic forces but then the electrostatic force reverses and tends to pull the particles off so that dust is held on the collecting electrodes only by adhesion. In Cottrell or single-stage precipitators the corona current can provide a significant force tending to hold the collected dust to the electrode provided that the resistivity of the dust is 10¹⁰ ohm-cm or more. Adhesion is still essential in the collection of lower resistivity dust and is of vital importance in the transfer of dust from the collecting electrodes to the hopper. As the dust falls from the plates to the hopper it must be held in agglomerations or chunks. There are many peculiarities in the adhesive behavior of electrostatically collected dust. A better understanding of this adhesive behavior is essential if we are to improve the transfer of dust from the collecting electrodes to the hopper.     

Fabric Filter Applications on Coke Oven Pushing Operations

Coke oven pushing emissions containing quantities of tars and dust require new approaches to adapt fabric filter collectors. This paper deals with the Wheelabrator/Taisei precoat filter systems being used on coke oven pushing operations. The Taisei test program and the filter installation at Tokyo Gas are discussed. The variables to be evaluated in the design of a fabric filter emission control system are examined.     

Influence of pleat geometry on filter cleaning in PTFE/glass composite filter

A pleated filter bag is often used to treat exhaust gas in many industrial applications, due to its fairly high dust collection efficiency and relatively low pressure drop. This work deals with the optimum pleating geometries of a pleated filter made with a newly developed PTFE/glass composite filter. It was found that pleating geometries, including pleat height and pleat pitch, directly affect the cleaning efficiency. The design index, α, which stands for the ratio of pleat height to pleat pitch, is 1.48 for optimum operation. When the α value was higher than 1.48, the pressure drop across the pleated filter medium increased, resulting in a decreased cleaning interval due to the difficulty of filter cleaning. Therefore, it is necessary that the optimum pleating geometry should be determined by employing the dimensionless parameter, α, in the design of cartridge filters.

Implications: A pleated filter bag is often used to treat exhaust gas in many industrial applications due to its fairly high dust collection efficiency and relatively low pressure drop. The present paper introduces an optimum design configuration to make a pleated filter with newly developed PTFE/glass composite filter media. A dimensionless parameter that is the ratio of pleat height to pleat pitch should be considered to make the best quality pleated filter.     

Endurance of Fiberglass Filter Fabrics

A study was made to determine the effect of production process variables on fiberglass filter life in an accelerated endurance test at high temperatures. Tests were conducted in a unit designed to provide conditions simulating those encountered in field use. Test variables investigated included filtering temperature, fabric finish, bag tension, and aging at elevated temperatures. The paper discusses the relative effect of these variables with respect to the endurance of four standard, commercially available, filtration fabrics.     

Mineral dust is a sink for chlorine in the marine boundary layer

Dust particles affect the budgets of important traces gases by providing a surface on which heterogeneous reactions can occur. The uptake of soluble species on dust alters the physical, chemical, and optical properties and the overall ability of dust to act as cloud condensation and ice nuclei. It is commonly assumed that all measured chloride in particulate filter samples is associated with sea-salt particles and any chloride in dust occurs as the result of internal mixtures of sea-salt and dust particles, formed by cloud processing. Here we show high temporal resolution data demonstrating the direct uptake of chlorine by dust via heterogeneous reaction with HCl(g). This reaction added significant amounts of chlorine to the dust particles during a major dust storm, representing 4–9% of the individual dust particle mass. Up to 65±4% of the dust particles contained chlorine due to this heterogeneous reaction during the dust front. Ignoring this process leads to an overestimation of sea-salt concentrations from bulk measurements, and an underestimation of the degree of sea-salt aging. The uptake of chloride will change the pH and hygroscopic properties of the dust and thus can influence the budgets of other reactive gases. Including this heterogeneous process in atmospheric measurements and chemical transport models will improve our ability to predict the atmosphere's composition and radiation budget with greater accuracy.     

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.     

Long-range transport of polycyclic aromatic hydrocarbons (PAHs) from the eastern Asian continent to Kanazawa,Japan with Asian dust

Aerosol particles were collected for 1 year, starting in April 2003, in rural areas of Kanazawa, Ishikawa, Japan to understand the role of Asian dust as a long-range transporter of polycyclic aromatic hydrocarbons (PAHs). Three sampling intervals were designated in this study, namely: (1) Dust period 1 (March 11–19, 2003); (2) Dust period 2 (March 28, 2003–April 9, 2003); and (3) Dust period 3 (April 9, 2004–April 25, 2004). The Asian dust particles are predominantly in the coarse particle size range (2.1–11 μm). PAH analyses were performed separately on both the coarse and fine (<1.1 μm) particle ranges. Seasonal trends in PAH concentrations for coarse and fine particles showed that the Asian dust particles in Dust period 3 contained significant amounts of less-volatile PAHs such as benzo[a]pyrene (BaP) and benzo[g,h,i]perylene (BghiP). A kinetic model developed in this study shows that almost none of these PAHs would be accumulated on Asian dust particles in the atmosphere, due to their extremely slow adsorption rates. These PAHs would have to originate from PAH-polluted soil particles around industrialized areas. Back trajectory analyses suggest that the Asian dust in Dust period 3 came from loess regions around industrialized areas. This indicates that geologic materials play a significant role in the atmospheric circulation of PAHs.     

滤袋数目对翼形上进风袋式除尘器内流场影响的数值模拟研究

针对实际运行过程中,袋式除尘器滤袋使用寿命短,压力损失过大的问题,本文以翼形上进风袋式除尘器为研究对象,采用CFD(computational fluid dynamics)技术模拟分析不同滤袋数(分别为92、88、84、80、76和72)时袋式除尘器内气流分布和压力损失规律。主要考察了流量分配系数、最大流量不均幅值、气流迹线、滤袋表面速度分布与压降等指标。结果表明,滤袋数为76个时,气流分布最为均匀,各滤袋负载均衡;相同过滤速度下,装置的压降随滤袋数目的增加而上升,即压降大小顺序为9288847672;与72个滤袋相比,76个滤袋的可用过滤面积更大。综合考虑,袋式除尘器的最优滤袋数目为76个。模拟结果为袋式除尘器的设计和优化提供了依据。