Outlet Mass Flux from a Pulse-Jet Cleaned Fabric Filter: Testing a Theoretical Model

Mass penetration through a pulse-jet cleaned fabric filter was evaluated as a function of particle size. The fabric bags were conditioned by 150 cleaning cycles before data were collected. Particle penetration data were collected over 24 different operating conditions for a three-bag, pilot-scale filter using polyester felt bags with either a rough, untreated surface or a smooth, polytetrafluoroethylene-laminated surface. Each bag filtered limestone dust or fly-ash for 30, 120, or 480 seconds and was then cleaned either on-line or off-line. The applicability to these data of the Leith and Ellen becker (1980) model for outlet mass flux through a filter was analyzed for a geometric progression of 13 particle diameters from 0.10 to 6.7 μm. Model parameters were found to be strongly dependent on particle size and on fabric surface treatment but were not affected by fabric cleaning mode or cleaning cycle time. Dust type may have affected filter performance but the effect was not significant statistically. After the model had been calibrated using the present data set, it was used to predict results for an independent data set and performed reasonably well. Model parameters may be sensitive to the degree to which bags are conditioned with dust.     

Origin and mechanisms of dust emission from pulse-jet cleaned filter media

The respective contributions of direct particle penetration vs. particle reentrainment to emissions of pulse-jet cleaned filter media were measured for needle felts of different construction, in combination with two particle materials, one free-flowing and one agglomerating. Different media conditioning protocols (including accelerated aging up to 20,000 pulses) were applied as well, in order to simulate longer-term use of the filters.With about 96-99% of emissions per cycle, direct particle penetration was by far the dominant mechanism under all circumstances. The size distribution of emitted particles was centred narrowly around the MPPS between 0.5 and 1 µm, and tended to shift toward finer particles with progressive media aging, much like in a depth filter. The total reentrained dust mass per cycle was on the order of 10^− 5 of the mass stored inside the medium. Cross-sectional analysis of a few media by electron microprobe indicates that the support scrim may act as an effective barrier to particle seepage more than to direct penetration.The well known increase in emission level with cleaning pulse intensity can be attributed to a slowing-down or prevention of the clogging process, rather than enhanced reentrainment of stored dust. Earlier reports of increased emissions at higher filter face velocities are probably due to the redeposition of dust from the filter cake immediately after a cleaning pulse.     

Experimental study of pleated fabric cartridges in a pulse-jet cleaned dust collector

Six pleated filter cartridges with different base media and geometrical dimensions were tested in a full-size dust collector periodically cleaned by a short burst of pulse-jet. The evaluation was performed under two different cleaning modes called clean-on-demand (to clean the filter once the pressure drop reaches a preset value) and clean-on-time (to clean the filter at a fixed time interval). The filter performance was evaluated by the effective residual pressure drop and downstream particle concentration. The results showed that the pleat ratio, defined as the ratio of pleat height to pleat pitch, had a great influence on the preferred operating mode for cleaning the filter. Clean-on-time mode demonstrated better performance for filters with a high pleat ratio (> 4.0), while clean-on-demand mode performed better for filters with a low pleat ratio (< 4.0). The test results also showed the tank pressure was critical for cleaning the pleated filter cartridges, whereas the pulse duration only had a small effect on the cleaning efficiency. With the same base media, cartridges with surface treatment such as fine fiber were superior to those without surface treatment. Pulse-jet cleaning could also promote particle penetration through filter media. The downstream particle concentration during cleaning was at least twice of that during filtration process for all pleated filter cartridges tested. Further, the downstream particle concentration was independent of the applied cleaning mode and the cleaning intensity in this study.     

Collection of fine adhesive and cohesive dusts with pluse-jet fabric filers

The collection of reactive and therefore extremely adhesive and cohesive fine particles (< 1 μm) by means of bag filters with pulse-jet cleaning may present problems. The electron-beam dry scrubbing (EBDS) process, used to remove SO₂ and No_x in a power plant of the Badenwerk AG, Karlsruhe, serves as an example. To solve the occurring problems and achieve a satisfactory filter performance, extensive know-how of process engineering is necessary. This contribution deal with the following aspects: construction of the cleaning system, selection of filter medium, precoating, and dosage of an auxiliary dust during filtration.     

Effects of a Shroud Tube on Flow Field and Particle Behavior Inside a Bag-Filter Vessel

A shroud tube was used to decrease the amount of particles toward the bag filters from whole particles entering a filter vessel. The effects of the shroud tube on the flow field and particle behavior inside the vessel were studied. The air mixed with dust particles enters the vessel through a tangential inlet duct. Some of the particles are deposited on the inside wall of the vessel and the surface of the shroud tube. The other ones are collected on the filter surface or passed through it. The particles deposited on the wall surfaces fall into a hopper by gravity, and those collected on filters are removed by back pulse-jet flow. Computational simulation was performed to know the prereduction rate of particles by deposition on the wall surfaces for the different shroud tubes. The experiment was accomplished with some shroud tubes suggested by the results of computational simulation, and the experimental results were compared qualitatively with the computational results. The shroud tube blocked the direct transport of particles toward the bag filters and reduced the particle loading onto the filters. The particle loading was reduced when the upper region of the vessel was not blocked by the shroud tube more than when the vessel was blocked wholly with the filters from the upper end wall. However, the re-entrainment of the particles removed from the filters by the back pulse cleaning increased when the upper region of the vessel was not blocked by the shroud tube more than when the vessel was blocked wholly with the filters from the upper end wall.     

下进风袋式除尘器内部气固两相流动数值模拟

为了研究袋式除尘器滤袋失效机理 ,进一步指导除尘器的设计、运行和改进 ,通过简化滤袋结构和应用结构化 /非结构化混合网格技术 ,对DMC180型下进风袋式除尘器实际运行条件下的内部气固两相流动进行了数值模拟。计算结果表明 ,袋室内形成了旋涡回流和不均匀压力场 ,袋室后端滤袋组过滤速度和滤袋间隙速度大大超过最大允许值 ,是后端滤袋易于磨损失效的主要原因。通过计算还得到了不同处理风量和过滤介质表观渗透率条件下 ,各滤袋组过滤速度和颗粒沉积量分布规律。指出了该型袋室结构设计缺陷和改进方向     

A study on the characteristics of improvement in filtration performance by dust precharging

A hybrid dust-collector combining electrostatic charging with fabric filtration was developed and its performance characteristics were evaluated. Charged particles build porous dendritic structure on the filter surface by electrostatic attraction, increasing the collection efficiency of dust particles and reducing the pressure drop through the deposited dust layer and filter media. The cleaning performance of the dust layer is improved because the dendritic structured dust layer may be removed more easily by pulse jet cleaning flow. The results of the experiment showed a reduction of fine particle emission by 37% and 13% energy saving by precharging dust particles before filtration.     

袋式除尘器在复混肥装置上的应用

介绍我国复混肥装置尾气处理的现状 ,以及在项目设计中选用袋式除尘器的经验 :要考虑尘粒的吸湿性、粘结性、尘粒工况的不稳定性 ;在袋式除尘器设计中 ,应设置热风循环系统 ;为防止糊袋应选用表面滑爽易清灰的滤布 ,并进行涂布厌水厌油处理 ,膜滤布应具有更优良的耐湿和易清灰性能 ;宜采用圆形滤袋。 2 0 0 2年在营口 15万 t/ a复混肥项目上使用袋式除尘器 ,尾气粉尘浓度小于 30 mg/ m3,远低于现行国家标准 12 0 m g/ m3。袋式除尘器应用在复混肥装置上 ,不仅可以降低尾气的排放浓度 ,还可以解决目前复混肥装置上洗涤液无法处理的问题     

改进布袋除尘器在燃煤电站锅炉除尘中的应用

介绍了改进布袋除尘器在燃煤电站锅炉除尘中的应用,阐述了该布袋除尘器的主要特点,总结了其存在的主要应用问题。针对灰斗堵灰的问题提出采用加入灰斗预热程序和选用安全可靠、封闭性能较好的锁气器来解决;针对反吹清灰系统的故障提出从温度角度来考虑改善;对于反吹清灰的控制模式问题,提出应根据除尘器上下室的压差尽量多设定几种反吹清灰模式。     

磷复肥企业除尘设备的选择

通过对袋式除尘器与旋风除尘器的设计及实际运行情况的比较，提出在磷复肥企业中应根据产品粉尘易吸潮的特点，以旋风除尘器替代袋式除尘器。     

Numerical study of pleated fabric cartridges during pulse-jet cleaning

We established a numerical model and used computational fluid dynamics (CFD) analysis to observe transient flow behavior across pleated filter cartridges in a dust collector during pulse-jet cleaning. The numerical results were in good agreement with the filter-testing data during important periods including during pressure ramp-up and valve opening. Larger errors for predicting overpressure occurred during the pressure ramp-down period likely due to the uniformity of the filters' permeability. This confirmed that the numerical model demonstrated the cleaning efficiency and the local cleaning quality of three different filter cartridges with different filter dimensions and pleat ratios. Data calculated from the average static pressure on the filters' surfaces were more closely correlated to cleaning efficiency than overpressure. The surface static pressure distribution along all filter cartridges showed that the top area of the filter cartridge is difficult to clean because of the lower surface pressure generated by the pulse jet. Filter cartridges with higher pleat ratios were found to have greater instances of incomplete cleaning due to the large variation of static pressure distribution along the filter cartridges. Our results showed that although information such as average pressure and pressure distribution on the filter surface is difficult to obtain by physical measurement, this data is tractable using CFD analysis and is useful for filter design and system optimization.     

袋除尘器滤袋失效分析

袋除尘器具有很多的优点而被广泛采用,但一旦滤袋失效,将造成粉尘超标排放,且滤袋更换费用巨大.详细总结了水泥工业领域现场经常出现的袋除尘器滤袋失效问题,包括机械磨损失效、气流磨损、温度高低造成的失效等,并针对这些问题,提出了避免和预防措施.只要选材合理,制作安装质量保证加上维护操作得当,袋除尘器完全可以满足国家越来越严格的粉尘排放标准要求.     

我厂以旋风除尘器替代袋式除尘器的运行情况

对贵溪化肥厂除尘设备中袋式除尘器与旋风除尘器的设计及运行情况进行比较 ,提出磷复肥企业根据生产粉尘易吸潮的特点 ,应以旋风除尘器替代袋式除尘器     

化工除尘器的选用

作者通过比较旋风除尘器,袋式除尘器在湛化股份有限公司的运用情况,建议在磷复肥企业以旋风除尘器取代袋式除尘器。     

A Rotary Fine Filter for High-Efficient Dry Dust Collecting in the Production of Refractories

A fine filter for treatment of dust-laden gases in the production of refractories is developed. Its testing in a pilot filtering unit using a model quartz dust has shown a high-efficient on-line recovery of 75 – 85%. The aerodynamics of the filter equipped with rotary impellers is discussed. The engineering solution proposed expands the application of fine filters and allows the treatment of dust-laden gases to be carried out without preliminary separation of large-sized particles using other facilities.     

脉冲袋式除尘设计制造检验

袋式除尘器是重要的环保设备,而脉冲袋式除尘器是目前袋式除尘器中效果最好、最常用的除尘器,除尘效率可达到99%。由于它的高效、经济环保,而被广泛应用。文章主要介绍脉冲袋式除尘器的选型设计、制造及检验等。     

A simplified model to predict the total efficiency of gravity settlers and cyclones

The total efficiency of gravity settlers and cyclones is usually calculated by summing the product of the grade efficiency and the weight fraction of particles over a series of particle size intervals. The accuracy of this method strongly depends on the number of the particle size intervals and the width of the individual intervals. Moreover, the design of these devices is based on specifying a required efficiency for a given size of particles. However, since these collectors are usually used for precleaning the dust-laden gas so as to reduce the dust loading before the gas enters a subsequent high-efficiency collector, one needs to know what total efficiency must be achieved. Therefore, the present paper uses a simplified model to predict the total efficiency of these devices based on the assumption of a normal size distribution. It is further shown that the equations developed assuming a normal size distribution can be extended for other particle size distributions.     

The influence of granular flow rate on the performance of a moving bed granular filter

The goal of this study is to evaluate the effect of granular flow rate on the performance of a moving bed granular filter designed for hot gas filtration of fine char particles (dust) produced during fast pyrolysis of biomass. The filter employs a counter-current configuration, in which down-flowing granular material spreads out at the bottom of the filtration vessel to form an interfacial area where the dusty gas enters the granular bed and much of the gas cleaning is hypothesized to occur. This study uses a real-time particle counter to measure the instantaneous filtration efficiency during cold flow tests of the filter. Differential pressure measurements at various locations within the granular bed are used to assess the level of char dust hold-up over time. These experiments reveal a critical granular residence time below which the filter must be operated to achieve filtration efficiencies exceeding 99%. Operating above the critical value causes the filter to “clog” and decrease in efficiency. The clogging is characterized by a critical dust volume fraction as determined through a fixed bed filtration test. The filter is found to accumulate most of the dust at the interfacial region. Also the interfacial region is more efficient than the downcomer section of the granular bed in removing dust. Decreasing residence time of granular material in the filter reduces the hold-up of char dust in the filter, which is expected to mitigate coking reactions of organic vapors when the filter is used to remove char from fast pyrolysis gas streams.     

滤袋安装过程中易出现的问题及解决方法

介绍了滤袋安装前期工作不到位、设备损耗、袋笼质量未达标和对滤袋保护不到位的问题,针对这些问题总结出前期须做好的准备工作,严格按要求安装,安装完毕后要进行荧光粉检漏和预涂灰操作等,这些工作为袋收尘器正常投运起到一定指导作用。