Influence of pulse-jet cleaning pressure on performance of compact dust collector with pleated filter operated in clean-on-time mode

To operate a bag filter continuously, pulse-jet cleaning of dust particles from the filter medium is commonly required, and the pulse-jet pressure significantly affects the filter performance. In this study, the accumulation structure of residual dust particles inside and on the surface of a filter medium at different pulse-jet pressures was investigated by constructing a simple model, and the influence of the dust structure on the filter performance was clarified. Using a simple model, we determined the effective ratio of filtration area β, which represents the ratio of the filterable area to the total filtration area, the true resistance coefficient due to the primary dust layer ζ_p’ thinly deposited on the filter surface, and the true resistance coefficient inside the filter media itself ζ_f’_. The effective ratio of filtration area β decreased with operation time for all pulse-jet pressures; however, it maintained a high value when the pulse-jet pressure was high. The validity of β analyzed by the model was verified using two different methods, and the results showed good agreement, indicating that the model is effective in identifying real conditions. The true resistance coefficient due to the primary dust layer ζ_p’ decreased as the pulse-jet pressure increased; however, the true resistance coefficient inside the filter media itself ζ_f’ was the highest at 0.5 MPa. In addition, the dust collection efficiency was different at each pulse-jet pressure, which was considered to be caused by the difference in the dust particle accumulation structure.     

粉尘对空气滤清器原始过滤效率测试结果的影响

为了比较国内外不同试验粉尘对空气滤清器原始过滤效率测试结果的影响,说明试验粉尘对于过滤效率测试的重要性,对国内外标准所规定的试验粉尘的粒径分布和形貌特征进行测试分析。结果表明:在相同实验条件下,以石英砂作为试验粉尘测得的原始过滤效率为99.35%,以A2细灰作为试验粉尘测得结果为99.10%;从粉尘粒径分布和形貌特征两方面讨论造成原始过滤效率测试结果不一致的原因。     

Granular bed filtration of high temperature biomass gasification gas

High temperature cleaning of producer gas from biomass gasification has been investigated with a granular filter. Field tests were performed for several hours on a single filter element at about 550 °C. The results show cake filtration on the granular material and indicate good filtration of the biomass gasification producer gas. The relatively low pressure drop over the filter during filtration is comparable to those of bag filters. The granular filter can operate with high filtration velocities compared to bag filters and maintain high efficiency and a low residual pressure.     

Effect of filtration velocity and dust concentration on cake formation and filter operation in a pilot scale jet pulsed bag filter

Bag filters are used for the removal of fine solid particles from process gases. Thus, understanding the filter cake build up and its properties is a subject of interest. The filter cakes properties may depend on many factors like, for example, filtration velocity and dust concentration. The effect of dust concentration and filtration velocity on filtration time, specific cake resistance and mean cake density is investigated in a pilot scale jet pulsed bag filter. An in situ optical system is used to measure cake thickness distributions on the filter surface. Additionally, the operation is simulated using a one-dimensional model and results are compared with experiments. The experimental results indicate that cake density and specific resistance increase with increasing velocity at constant dust concentration. The effect of dust concentration on filter cake density and specific resistance is small.     

EXPERIMENTAL STUDY OF DUST FILTRATION IN SURFACE-TYPE NONWOVENS

Surface type nonwovens are widely used in industrial dust control. Recently, they have been utilized in some engine air filtration applications as automotive filters, heavy-duty engine self-cleaning filters or safety filters. Because of their mechanical strength and regenerative ability they are a perfect material for applications where filter replacement is a problem. On the other hand, the random distribution of fibers and needle punching may result in pinhole formation during dust loading, especially at high aerosol velocities. As a result, the seepage mechanism is common in applications involving fine solid aerosols.

In the inertia dominated region, the collection efficiency of particles depends on the adhesion probability. When particle momentum increases, the efficiency decreases. In general, there is no agreement between filtration theory and experiment when the Stokes number is greater than one.

Filter efficiency increases with dust loading when the filter medium is a good dust cake supporter. In this case, dust reentrainment, causing seepage, may occur at high aerosol velocities and pressure drops. In contrast, reentrainment in nonwovens can take place even at lower aerosol velocities and dust loadings. It is difficult to predict conditions favorable for dust reentrainment and pinhole formation. This process depends on media geometry, dust particle size distribution, and aerosol flow parameters.

This paper discusses filter performance of surface-type nonwovens exposed to polydisperse dusts. Filter efficiency and pressure drop are discussed as functions of aerosol velocity, dust loading, and dust particle size distribution.     

EXPERIMENTAL STUDY OF DUST FILTRATION IN SURFACE-TYPE NONWOVENS

ABSTRACT

Surface type nonwovens are widely used in industrial dust control. Recently, they have been utilized in some engine air filtration applications as automotive filters, heavy-duty engine self-cleaning filters or safety filters. Because of their mechanical strength and regenerative ability they are a perfect material for applications where filter replacement is a problem. On the other hand, the random distribution of fibers and needle punching may result in pinhole formation during dust loading, especially at high aerosol velocities. As a result, the seepage mechanism is common in applications involving fine solid aerosols.

In the inertia dominated region, the collection efficiency of particles depends on the adhesion probability. When particle momentum increases, the efficiency decreases. In general, there is no agreement between filtration theory and experiment when the Stokes number is greater than one.

Filter efficiency increases with dust loading when the filter medium is a good dust cake supporter. In this case, dust reentrainment, causing seepage, may occur at high aerosol velocities and pressure drops. In contrast, reentrainment in nonwovens can take place even at lower aerosol velocities and dust loadings. It is difficult to predict conditions favorable for dust reentrainment and pinhole formation. This process depends on media geometry, dust particle size distribution, and aerosol flow parameters.

This paper discusses filter performance of surface-type nonwovens exposed to polydisperse dusts. Filter efficiency and pressure drop are discussed as functions of aerosol velocity, dust loading, and dust particle size distribution.     

Influence of leaks in surface filters on particulate emissions

Compliance with severe limit values of dust emissions is a main characteristic of surface filters. This characteristic is due to the high particle collection efficiency of surface filters. Beside regular operation it is necessary to consider phenomena such as a "pinhole" bypass through leaks in surface filters to ensure the above mentioned compliance with the limit values at all times. Experimental research has been carried out to observe and understand the "pinhole" bypass through leaks and the behaviour of pinholes over filtration time. To work out the influence of different filtration conditions the parameters pinhole diameter, filter face velocity and dust cake thickness were varied. The results can be explained by formulas usually used to calculate volumetric flow rates of orifice gauges. The experiments and the calculations lead to the conclusions that bigger pinholes decrease the collection efficiency and higher filter face velocities increase the collection efficiency of pinholed filter media.     

Structure optimization of granular bed filter for industrial flue gas filtration containing coagulative particles: An experimental and numerical study

A numerical model for the flow and filtration characteristics of industrial flue gas in granular bed filter (GBF) was established and the local filtration efficiency for different granule layers was investigated. Numerical validation results show that the GBF structure with large size granules at the inlet region and small size granules at the outlet region can effectively improve the filtration performance of GBF and the underlying mechanism was revealed. Then an experimental system was built to validate the suitability of the optimized GBF structure for the filtration of industrial flue gas with coagulative particles. The experimental results show that the optimized GBF structure is also suitable and its superiority is more significant with the increase of filtration time. The results show that the pressure drop and filtration efficiency of the experimental system increase with the increase of dust particles concentration. The existing of coagulative particles is conducive to the growth of smaller size dust particles, the pressure drop and filtration efficiency increase significantly. In addition, the pressure drop and filtration efficiency decrease with the increase of cooling rate. The results of this study are expected to be useful for the design and optimization of industrial flue gas purification and waste heat recovery.     

Optimal design and performance evaluation of a metal fiber filter for capturing radioactive aerosols

ABSTRACT

Conventional high-efficiency particulate air (HEPA) filters made of glass fiber media are prone to recycling problem and restrictions in extreme environmental condition such as high flow rate, high temperature, and fire. Therefore, metal fiber filters with minimal maintenance can replace conventional HEPA filters. The objective of the study is to evaluate the theoretical and experimental characteristics of a SUS316L metal fiber filter made from the fiber diameter of 8 µm. Theoretical modeling for predicting the collection efficiency of the radioactive aerosol is performed on the metal fiber as a function of particle size, filter thickness, and flow rate. Comparison between the experimental and theoretical results demonstrates that they are in good agreement. Consequently, the model is later utilized for performance optimization of the metal fiber filter. Also the metal filter for collecting the radioactive aerosol is optimized at the particle collection efficiency of 99.97% in most penetrating particle size (MPPS) of region 0.3 µm which complies with the standards established for conventional glass fiber HEPA filters.     

Effects of cleaning mode on the performances of pulse-jet cartridge filter under varying particle sizes

In order to solve the problem of pollution induced by particulate matters, bag filters and pleated cartridge filters have been widely applied to industries. However, the effects of cleaning mode on the performances of filters under varying particle sizes are rarely studied. In this paper, the influence of cleaning mode on the pressure drop and dust emission concentration under varying particle sizes were studied through experiments. The results show that the smaller the particle size is, the faster the pressure drop increases, and the higher the dust emission concentration becomes. In the cleaning process, the smaller the particle size, the greater the residual pressure drop, and the worse the cleaning effect. The cleaning frequency rises with the decrease of particle size under the clean-on-demand (C-D) mode, while the maximum pressure drop grows with the decrease of particle size under the clean-on-time (C-T) mode. For the medium and fine particulate matters, the average dust emission concentration and the average pressure drop under the C-D mode are both slightly larger than those under C-T mode. By comparing the quality indexes under different cleaning modes, it can be found that for medium and fine particulate matters, the use of the C-D mode can ensure more excellent filtration and cleaning performances, while for large particulate matters, the choice between the two modes has very limited influence on the filtration and cleaning performances of pulse-jet cartridge filters.     

The impact of evaporator fouling and filtration on the performance of packaged air conditioners

The goal of the study presented in this paper was to evaluate the impact of different filter types on the performance of three typical packaged air conditioners under both clean and fouled conditions. In a companion paper, combinations of six different levels of filtration and four different coils were tested under clean and fouled conditions. From the tests, it was found that fouling has a relatively small impact on air-side effective heat transfer coefficient, but can have a large impact on coil pressure drop. Data from the experimental study were used in developing simulation models for the three packaged air conditioners. Simulations show that the equipment cooling capacity is reduced with fouling primarily because of a decrease in air flow due to the increased pressure drop. In most cases, EER (energy efficiency ratio) was reduced with fouling primarily due to increased fan power. However, the changes in EER were relatively small, in the range of 1–10%. Equipment having low efficiency filters had higher EER after fouling than equipment with high efficiency filters, because high efficiency filters result in significantly higher pressure drops than low efficiency filters. The impact of the evaporator side fan efficiency was found to be significant. The energy penalty associated with high efficiency filters was reduced greatly when fan efficiency increased. Although high efficiency filters cause higher energy penalties they provide considerably better air quality. The quantity of dust passing through the coil with an MERV14 filter was approximately 30 times less than the dust passing the coil with an MERV4 filter. This difference was doubled when the MERV14 filter was compared to a case with no filter in place.     

高温烟尘陶瓷纤维过滤技术特性及其应用评述

在综述国外用于高温烟尘净化的几种主要陶瓷纤维滤料和高温陶瓷过滤器结构性能及其发展现状基础上,提出了比表面积大、净化效率高、过滤阻力低、初始投资低和运行较可靠的蜂窝覆膜陶瓷过滤器的选型择优建议;通过对陶瓷过滤器的应用评述,并结合我国对节能减排的客观需要,说明了在我国尽快发展用于高温烟尘净化的陶瓷纤维过滤技术的必要性。     

过滤速度对200 MW机组电袋复合除尘器流场分布影响的数值对比

电袋复合除尘器电场内部气流分布是影响电袋复合除尘器效率最主要的因素之一,采用标准k-ε紊流模型,模拟了0.8、1.2、1.6、2和2.4 m/min 5种过滤风速电袋复合除尘器的流场分布情况。结果表明：电袋复合除尘器内部气流速度出现了明显的分区,在与电除尘相邻的袋除尘区下部空间出现了明显的高速区,过滤速度为1.6 m/min时的高速区面积最小,且随着速度的增加在袋除尘区靠近出口的后墙上部滤袋处出现了狭长的气流聚集区,这将增大滤袋负荷的不均匀度。在袋除尘下部区域、袋除尘区域及净气室区域选取有代表的截面进行流场均匀性检验,得出速度为0.8 m/min时的不均匀性波动最小,且在袋除尘区随着速度增大流场不均匀性也增大,但同时随着高度的增高整体都呈现下降的趋势。     

Design of filter bag media with high collection efficiency

The various filter bag media were prepared by a nonwoven pilot plant coupled with the needle punching and thermal bonding combination processes. The prepared filter media were evaluated by the reliability assessment standard for the filter bag media of the environmental cleaning dust collector (RS K 0001). A new filter bag medium was thermal bonded with polyester felt and polyamide nano-sized web. The air permeability of the filter bag media with nano-sized web was largely reduced as compared with the control media. In the evaluation of filtration test, the filter medium with nano-sized web showed more stable filtration behavior and more higher collection efficiency than the others.     

Modeling of Cross-Flow Across an Electrostatically Charged Monolith Filter

The flow field and filtration efficiency of electrostatically charged micro-channel filters under cross-flow conditions were modeled. In our simulations, the fluid flows tangentially to the filter face (cross-flow). Particles with diameters larger than 2 μm were considered in this study, hence, the effects of Brownian motion were not included in the simulations. The influence of particle size, pressure drop, and electrostatic charge on the filtration efficiency was investigated. Measurements from performing electrostatic force microscopy (EFM) on the monolith sample confirmed the presence of charge and gave a qualitative measurement of the charge distribution. Results from the flow simulations indicate that the electrostatic forces increased the particle capture efficiency only at lower pressure drop. At higher pressure drops, electrostatic forces did not significantly increase the capture efficiency of the particles. Also, the capture efficiency of relatively small particles is found to be more dependent on the pressure drop across the filter than that of larger particles.     

几种陶瓷过滤材料的过滤机理研究

由多孔陶瓷材料制备的过滤元件在分离、净化领域得到日益广泛的应用,陶瓷过滤器的过滤机理和过滤效率的研究、表征日益受到重视.综述了泡沫陶瓷、普通多孔陶瓷管、陶瓷过滤膜过滤机理的研究进展.泡沫陶瓷主要通过滤饼机制、表面效应、整流效应来达到净化金属液的效果.     

COMPARISONS OF MECHANICAL MELT-BLOWN FILTERS AND ELECTROSTATICALLY ENHANCED SPLIT-FIBER FILTERS FOR CABIN AIR FILTRATION APPLICATIONS

In this paper, compared are filtration characteristics of two different filters made from uncharged melt-blown media and electrostatically charged split-fiber media. The split-fiber filters have stronger electrostatic charges in the media than the melt-blown filter, which in turn enhances the initial fractional efficiency. The compared parameters are fractional efficiencies, dust holding capacities, incremental fractional efficiencies, and pressure drop. The advantages and disadvantages of these filters for cabin air filtration applications are discussed based on the experimental results obtained using SAE-fine dust and sodium chloride test aerosol. The optimization process of the filter selection is also discussed.     

Analysis of the performance of a sintered stainless steel wire mesh filter for cryogenic liquid purification

As a traditional and mature solid-liquid separating technique, filtration has been adopted in cryogenic liquid purification system owing to its low energy cost, simplified system, long lifetime and high purifying efficiency. Whereas, few data or result of filtration performance at low temperature is put forward in literatures, most of which are related to room and high temperatures applications. Furthermore, as an excellent cryogenic material, stainless steel medium is suitable for cryogenic liquid filtration, which is also seldom reported. In this paper, we propose a filtration system for purifying CO₂ particles from liquid nitrogen using a sintered stainless steel wire mesh filter with a nominal filtration degree of 0.5 μm, and characterize the separation behavior of this kind of filter medium at cryogenic temperature. Experimental results show that the whole filtration process can be divided into three stages with sufficient particle concentration in the feed slurry according to the evolution of pressure drop. Differences between surface filtration and depth filtration are demonstrated, and the influence of growth of filter cake is characterized. Pressure drop increases with increasing feed slurry flow and CO₂ concentration, and evolution tendency of filtration efficiency is affected by its calculation method. By comparison with the filtration at room and high temperatures, the effects of temperature on the fluid and media are emphasized.     

电气石颗粒/聚苯硫醚针刺毡复合过滤材料的过滤性能

为提高工业用过滤材料对细颗粒物的捕集效率,以袋式除尘用聚苯硫醚（PPS）针刺毡为基材,聚氨酯热熔胶膜为黏合层,通过溶液沉淀法将具有自发极化特性的电气石（TM）颗粒覆于基材表面,经热压处理制备了含不同纯度、不同含量、不同颗粒粒度的TM颗粒/PPS针刺毡复合过滤材料;利用SEM研究了TM对微细粒子的吸附情况,利用滤料性能测试装置研究了TM颗粒/PPS针刺毡的过滤性能,结果表明：附着TM颗粒后,TM颗粒/PPS针刺毡对亚微米粉尘过滤效率明显提高,TM纯度越高效果越好,纯度为87.16%时,滤料对0.3~1 μm粒子过滤效率提高幅度≥13.35%;最优附着浓度为5 mg·cm^-2时,用于综合评价滤料过滤效率与阻力的滤料品质因数Q_F值最高;TM颗粒粒径越小,过滤效率提升效果越明显,TM颗粒粒径18~38 μm时,对0.3~1 μm粒子过滤效率提高幅度≥7.25%。TM颗粒/PPS针刺毡复合滤料较传统针刺毡滤料过滤性能明显增强。     

液氮净化系统仿真设计与性能测试实验研究

针对低温液体净化特点,设计褶皱型316L不锈钢烧结丝网过滤器。建立液氮净化系统动力学模型,仿真结果与实验结果对比表明过滤单元水平布置情况下的颗粒沉积并不影响过滤性能,优于垂直布置。基于过滤单元的水平布置搭建过滤实验台,将液氮与二氧化碳气体混合形成滤浆,测定恒速与恒压工况下的过滤性能并研究滤浆流量、干冰体积含量的影响。结果表明过滤效率均能达到99.99%以上,且滤饼的形成与堆积是影响过滤性能的最关键因素。