陶瓷过滤管表面粉尘层清除过程的图像分析

Based on the analysis of high-speed video images, the detachment behavior of dust cake from the ceramic candle filter surface during pulse cleaning process is investigated. The influences of the dust cake loading,the reservoir pressure, and the filtration velocity on the cleaning effectiveness are analyzed. Experimental results show that there exists an optimum dust cake thickness for pulse-cleaning process. For thin dust cake, the patchy cleaning exists and the cleaning efficiency is low; if the dust cake is too thick, the pressure drop across the dust cake becomes higher and a higher reservoir pressure may be needed. At the same time there also exists an optimum reservoir pressure for a given filtration condition.     

Distributions of age, thickness and gas velocity in the cake of jet pulsed filters—application and validation of a generations filter model

Different imperfections are observed with jet pulsed filters. They manifest themselves most obviously in the curve of the pressure drop versus time. A convex pressure drop curve indicates cake compaction. But jet pulsed filters frequently show a concave rise of the pressure drop curve. This phenomenon is due to a strongly nonuniform cake area load on the filter and it is generally attributed to incomplete cake removal. Incomplete cake removal takes place when only a fraction of the total filter area is cleaned at the end of a filter cycle or when patchy cleaning prevails. Patchy cleaning means that a jet pulse removes the entire filter cake of only a fraction of the exposed filter area except for a thin adhesive dust layer.In this paper a filter model is proposed in which the different classes of cake thickness are understood to result from different cake generations. A cake becomes one generation older when it survives the jet pulse cleaning at the end of a filtration cycle, although the area that is occupied by the cake on the filter medium is diminished by the jet pulse.This generations filter model can be used to find the distributions of age, thickness and gas velocities in the cake from steady-state operational data. The steady-state, periodic model provides a complete basis for the simulation of heterogeneous gas/solid reactions in the cake of jet pulsed filters.In the model intermediate cake build up during the cleaning procedure is considered. There redeposition of removed filter cake also takes place, and its extent is estimated. The model can also serve to determine from macroscopic process data, if the cleaning system of a filter installation operates in the undesirable mode of patchy cleaning.Experiments from a pilot plant for dry flue gas cleaning are presented and the generations filter model is validated with the experimental data.     

An approximate theory for stresses in dust cake of ceramic candle filters

A simplified theory is developed that yields the approximate stresses within a dust cake on the outer surface of ceramic candle filter and gives the critical factors which ensure complete detachment of cake. The radial and tangential stresses in cake during filtration have been derived by consideration of active state of stress in the dust cake. Back pulses of cleaning gas expand dust cake on the condition, that their power is just adequate to properties of cake, such as angle of internal friction and cohesion. Expansion of the dust cake induces tension cracks and disintegration of the cake. Back pulses of higher values hamper expansion of cake and cause “patchy” cleaning.     

On the Stability of Pulse‐Jet Regenerated‐Bag Filter Operation

Problems with the pulse‐jet bag filter operation have a direct influence on process plant operation and may result in loss of production time. Therefore, long‐term stable operation of the plant is desirable for both the manufacturers and operators. The effects of operating parameters are studied experimentally on filter operation with regeneration between the upper and lower pressure drop limits. Many combinations were identified when the filter operation derailed from stable to unstable operation on changing one of the operating parameters. Filtration velocity, pulse pressure, and the upper limit of pressure drop had the potential of creating instability. A threshold detachment overpressure existed below which the operation led to unstable conditions at a certain filtration velocity and which increased with increasing velocity.     

颗粒沉积量对细颗粒层清灰力和清灰效率的影响

采用中径3.31 mm的细颗粒在PPS普通滤料和涤纶覆膜滤料表面形成不同沉积量的颗粒层,用缓慢增加反吹气流和低压脉冲清灰的方法进行清灰测试. 随着颗粒层沉积量增加,颗粒层低压脉冲清灰的效率均提高,缓慢反吹的清灰力也呈减小趋势. 涤纶覆膜滤料表面颗粒层沉积量从200 g/m2增长到401 g/m2时,平均清灰应力从350 N/m2降到100 N/m2,比PPS滤料低90 N/m2以上. PPS滤料上低压脉冲清灰效率随颗粒层沉积量的增加线性增加,涤纶覆膜滤料上颗粒层沉积量超过200 g/m2时非线性快速增加,缓慢反吹产生的颗粒层碎片均随着颗粒层沉积量增加而增大.     

烛状陶瓷过滤器的清灰分析

研究了脉冲清灰效率对过滤过程的影响。假定粉尘结构在过滤和清灰中不变的条件下,对清灰效率的影响进行了分析。发现,在一定的启动压降下,有一个最佳的清灰效率,在90%～95%之间。由于在运行的前几个循环中,粉尘压降、残留粉尘压降以及粉尘厚度、残留粉尘厚度存在较大的变化,因而在开始的几个循环中,不宜采用相同的清灰时间间隔。     

Experimental study of cake formation on heat treated and membrane coated needle felts in a pilot scale pulse jet bag filter using optical in-situ cake height measurement

Pulse-jet bag filters are frequently employed for particle removal from off gases. Separated solids form a layer on the permeable filter media called filter cake. The cake is responsible for increasing pressure drop. Therefore, the cake has to be detached at a predefined upper pressure drop limit or at predefined time intervals. Thus the process is intrinsically semi-continuous. The cake formation and cake detachment are interdependent and may influence the performance of the filter. Therefore, understanding formation and detachment of filter cake is important. In this regard, the filter media is the key component in the system. Needle felts are the most commonly used media in bag filters. Cake formation studies with heat treated and membrane coated needle felts in pilot scale pulse jet bag filter were carried out. The data is processed according to the procedures that were published already [Powder Technology, Volume 173, Issue 2, 19 April 2007, Pages 93-106]. Pressure drop evolution, cake height distribution evolution, cake patches area distribution and their characterization using fractal analysis on different needle felts are presented here. It is observed that concavity of pressure drop curve for membrane coated needle felt is principally caused by presence of inhomogeneous cake area load whereas it is inherent for heat treated media. Presence of residual cake enhances the concavity of pressure drop at the start of filtration cycle. Patchy cleaning is observed only when jet pulse pressure is too low and unable to provide the necessary force to detach the cake. The border line is very sharp. Based on experiments with limestone dust and three types of needle felts, for the jet pulse pressure above 4 bar and filtration velocity below 50 mm/s, cake is detached completely except a thin residual layer (100-200 μm). Uniformity and smoothness of residual cake depends on the surface characteristics of the filter media. Cake height distribution of residual cake and newly formed cake during filtration prevails. The patch size analysis and fractal analysis reveal that residual cake grow in size (latterly) following regeneration initially on the base with edges smearing out, however, the cake heights are not leveled off. Fractal dimension of cake patches boundary falls in the range of 1-1.4 and depends on vertical position as well as time of filtration. Cake height measurements with Polyimide (PI) needle felts were hampered on account of its photosensitive nature.     

清灰效率对炷状陶瓷过滤器的影响

研究了脉冲清灰效率对过滤过程的影响。假定粉尘结构在过滤和清灰中不变的条件下 ,对清灰效率的影响进行了分析。发现在一定的启动压降下 ,存在着一个最佳的清灰效率 ,即在 90 %～ 95 %之间。由于在运行的前几个循环中 ,粉尘压降、残留粉尘压降以及粉尘厚度、残留粉尘厚度存在较大的变化 ,因而在开始的几个循环中 ,不宜采用相同的清灰时间间隔     

圆盘真空过滤机的改造与实践

针对原有圆盘真空过滤机存在的诸多问题,从滤扇结构、主轴传动装置、卸料方式的改进和新型过滤布选用入手,对武钢矿业公司大冶铁矿的圆盘真空过滤系统进行了改造,并在现场取得了成功应用。与改造前相比,过滤效率提高了25-30%,滤饼水分也有所下降。     

高温气体过滤除尘脉冲反吹再生过程的研究进展

叙述近年来高温气体过滤除尘技术的实验和理论研究进展,指出脉冲反吹再生过程是高温气体过滤除尘过程持续操作的关键。操作参数以及结构设计(包括喷嘴直径、喷嘴与文氏嘴之间的距离、喷嘴出口速度以及文氏嘴结构等)对除尘工艺过程和再生效果具有很大影响。分析了脉冲反吹过程中所涉及的传递现象数值模拟,以期更为深入地了解反吹再生过程的气流流动与能量传递规律,以指导和优化过滤装置的操作参数和结构设计。     

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.     

湿法磷酸净化中液固分离过程的实验研究

针对湿法磷酸净化过程中存在的液固分离问题,采用离心过滤的方法,探讨了磷酸预处理脱色液的过滤特性,研究了分离因素、滤饼厚度、过滤介质等因素对过滤的影响。实验结果表明,当分离因素约为252,滤饼厚度约为20 mm,采用涤纶加密型滤布时,过滤效果最佳。     

Semicontinuous Discharge of Non‐Newtonian Filter Cakes in Electrofiltration

A novel mode of operation for electrofiltration is presented. The newly developed operation procedure allows for cake removal without disassembling the chamber. Highly viscous filter cakes are discharged from the filtration chamber by inserting air which permits a rapid restart of the process. The cleaning time could be reduced from about 10 min to a few seconds. The semicontinuous operation is liable to full automation and allows for cake discharge and filtration in a short period of time. In successive cycles was proved that the process efficiency is maintained using the same membrane. A fully continuous system can be accomplished by assembling several units in parallel in a single filtration press.     

Pressure Slip Casting of Graded Coarse Grained Oxide Ceramics for Refractory Applications

In the present study the fabrication of graded coarse grained ceramic bodies for refractory applications was investigated using a pressure filtration cell,which uses pressurized air as the pressure medium. The pressure filtration cell was used to examine the influence of different ceramic raw materials,two dispersants,and of the particle size distribution on the filtration behavior and on the filter cake surface quality. Pressure slip casting of spinel based slips resulted in crack-free filter cakes,while alumina based slips resulted in filter cakes,which always stuck on the used PMMA filter medium. Furthermore,citric acid as an electrostatic dispersant resulted in a much lower filtration cake resistance and hence shorter filtration times than an electrosteric dispersant. A broader particle size distribution with a higher addition of the finest particle fraction caused an increase in the filter cake resistance but also yielded much better surface qualities. Finally,graded filter cakes with three layers of alumina rich magnesium aluminate spinel with a maximum grain size of 3 mm,1 mm,and 0. 5 mm,respectively,were fabricated. The computed X-ray analyzes indicated a perfect bonding between the three layers,which is a significant improvement to previous studies. However,the graded filter cakes exhibited frequently cracks at the bottom,which was probably caused by tensile stresses from the friction of the filter cakes with the pressure filtration cell. This will be further investigated in subsequent studies. The achieved results demonstrate thefeasibility to produce coarse grained oxide ceramics for refractory applications by pressure slip casting,which eventually allows the production of composites with tailored compositions,microstructure and functionality.     

Process micro filter combines backwashing and ultrasonic technology to extend operating life

The Type 25 micro filter system from Faudi combines backflush pulses and ultrasonic cleaning technology to ensure a thorough cleaning of the integrated depth filter after each use, dispensing with the need for one-way filter cartridges and continuous production stoppages for filter change-outs. The result, according to the manufacturers, is longer lasting filters, leading to reduced operating costs, personnel costs and environmental waste.This is a short news story only. Visit www.filtsep.com for the latest filtration industry news.     

Clarification of liquids using filter aids Part III. Cake Resistance in surface filtration

The specific cake resistance of mixed cakes was studied in filter-aid filtration using pre-coat and body feed. The influence of the relative amounts (weight ratio c/a) and the properties of the filter aid and the impurity on the specific cake resistance (r) was determined. An exponential relationship between r and c/a was derived, based on the blocking behaviour of a filter cloth. This relationship was confirmed in the filtration of protein flocs from turbid beer, and yeast, iron hydroxide flocs and monosize polystyrene particles from water. Based on this law, an optimum body-feed dosage can be predicted in order to obtain a minimum cake resistance. In beer filtration special attention has been paid to the compressibility of the mixed cakes.     

聚乙烯醇微球抗污染动态膜的制备及性能

采用静电自组装和过滤预涂技术将表面富含羟基、具有强亲水性和电负性的聚乙烯醇微球(polyvinyl alcohol micro-sphere, PVA-MS)与工业滤布基膜相结合,分别制备无滤饼标准型和完全堵塞型PVA-MS动态膜。对膜的表征和性能的对比研究表明, PVA-MS组成的动态膜结构能明显改善基膜的亲水性、负电性。自组装PVA-MS动态膜的有效过滤孔径为2.1 μm, 清水阻力为1.02×10¹⁰ m^-1, 对基膜的截留性能基本没有提高, 预涂PVA-MS动态膜的有效过滤孔径为0.4 μm, 清水阻力为1.07×10¹¹ m^-1, 对浊度为21.34 NTU和TOC为18.3 mg•L^-1的上清液过滤出水为0.23 NTU和9.4 mg•L^-1, 分别提高基膜截留效果20%和30%。动态膜不可逆污染的去除性能研究表明, 自组装PVA-MS动态膜在化学清洗后能保持大部分PVA-MS的存在,预涂PVA-MS动态膜利用物理反冲洗可完全去除不可逆膜污染,再预涂后即再生。     

恒压过滤介质阻力分析

A mathematical model for constant pressure filtration is established. The distribution of hydraulic pressure within the cake and the medium resistance are measured. The medium resistance Rm is calculated from the suppositional filtration time Ore. It is demonstrated that Rm is nearly a constant for a given filter cloth.     

Compression,Permeation and Flow Behavior of Wet Nanoparticle Cakes,in situ Tested with a Press‐Shear Cell

A new test apparatus for in situ simulation of the expression operation and rheological testing of compressed cake was developed to combine the compression‐permeability cell with a high‐performance ring shear tester. The yield loci for water‐saturated titania (d_S = 200 nm) are measured. These flow parameters can be used to determine in situ the shear strength and compressive strength of a consolidated cake after the pressure filtration steps. The permeability of the compressed cake is characterized by the conventional filter cake resistance versus particle pressure and, for comparison, by an averaged pore size.     

一种基于膜污染指数的超滤膜污染评价方法

利用浸没式中空纤维膜小试系统,基于膜污染指数（FI）建立超滤膜污染的评价和试验方法。通过试验考察超滤膜污染变化规律,以及运行周期对膜污染指数计算的影响,并确定计算膜污染指数的运行周期;并对膜污染指数评价方法的可重复性进行检验：对化学清洗前后膜污染指数进行比较。试验表明,在过滤初期,滤饼污染和吸附污染并存,所以初期水力不可逆膜污染指数（HIFI）增长较快;中期超滤膜的吸附能力不断减弱,膜污染主要是滤饼污染,所以膜污染较为稳定：后期跨膜压力过大,压缩滤饼层,减小滤饼孔隙率,增加滤饼阻力,所以HIFI有所增加。同时短期的膜污染试验可以用来反映长期的膜污染情况,该超滤膜污染的评价方法重复性好,污染后的超滤膜经过化学清洗后。可以重复利用。