Granular-bed filtration assisted by filter-cake formation 5. Treating a liquid in a panel bed with pulseback renewal of liquid-entry granular-bed faces

A “panel bed” of granular solid, held in place by louvers, can serve to filter “dirt” from a liquid (the filtration assisted by filter-cake formation) or to place the liquid in countercurrent contact with the solid. A sharp “reverse” pulse of liquid, at sufficient intensity and not too long duration, produces a body movement of the solid capable of causing it to spill in a substantially uniform amount from each liquid-entry face of the granular solid. The paper reports experiments elucidating the physical behavior of the granular solid during “pulseback” and casting light, as well, upon the behavior of a “sand” during puffback of a panel bed gas filter. In both puffback and pulseback, the quantity of spilled solid is a function of “active time” (time during which a reverse pressure gradient across the panel bed exceeds a value just capable of producing a spill). Puffback quickly achieves a maximum attainable spill rate (a function of louver geometry); accordingly, spill quantity is linear in active time. In pulseback, however, spill rate increases gradually, achieving at last a maximum attainable spill rate (whereupon spill quantity becomes linear in active time).     

Granular-bed filtration assisted by filter-cake formation: 2. The panel bed gas filter with puffback renewal of gas-entry surfaces

Laboratory studies, confirmed by field studies at both large and small scales, elucidated behavior of a granular panel bed for gas filtration with accumulation of filter cakes on gas-entry surfaces (filtering occurring by a sieving mechanism). Filtration is cyclic: intermittently, flow of dusty gas is interrupted, and the panel is subjected to a sharp “reverse” puff of gas (a “puffback”), producing a body movement of sand toward gas-entry faces, dumping both dust cake and a relatively small quantity of sand from each face.     

Granular-bed filtration assisted by filter-cake formation: 1. Exploiting a new mode of soil failure for renewal of filtration surfaces in a panel bed

A new mode of soil failure can renew filtration surfaces in a bed of granular solid held in place by louvers mounted to provide a tall, narrow “panel bed” filter. A sharp “reverse” puff of gas (or pulse of a liquid), at sufficient intensity and not too long duration, produces a body movement of the solid capable of causing it to spill in a substantially uniform amount from each fluid-entry surface of the bed's face. The new phenomenon places the panel bed in contention to filter dirt from a gas (or from a liquid) wherein an accumulated filter cake becomes the primary locus for dust capture, by a sieving mechanism.     

Investigation of the particle flowpattern and segregation in tapered fluidized bed granulators

The particle flowpattern and granule segregation in tapered fluidized beds have been studied using two techniques. The first technique is to fluidize beds of varying total mass and granule fractions, then defluidize them suddenly to “freeze” the composition, section the bed in layers, and determine the composition of each layer by sieving. The second technique is to track a radioactive particle mimicking a granule as it moves in the bed. The results show that the segregation behaviour of granules is complex, their behaviour changing from flotsam at low granule concentrations to slightly jetsam at higher concentrations. The flow in the tapered bed is very different from what is expected based on relations derived for cylindrical beds. In the tapered bed a central region of high bubble activity and upward flow was a dominant feature. This “gulf streaming” became more pronounced as the total bed mass, and therefore the bed height, was increased, resulting in a bed turn-over time almost independent of the total bed mass. Quantitative data are given for upward and downward particle velocities and flows, bed turnover times, and axial granule concentration profiles.     

Effect of coagluant dosage and grain size on the performance of direct filtration

The performance of flocculation in direct depth-filtration was assessed in relation to the shear rate and the floc size in the filter pore. Quantitative measurements of the pressure drop of bed, as well as the turbidity and the floc size in the filtrate, and estimation of the shear rate in the filter during filtration were made to investigate the effects of chemical doses and grain sizes on the performance of direct filtration. Furthermore, a method was suggested to determine the porosity in the deposited layer. In this study, the product was estimated to be two to three times that in the initially clean bed after a 6 h operation of the filter using 50–100 ppm of alum. It was also found that the porosity of the deposited layer is very high up to a range of 0.93–0.99. The porosity decreased with the filtering time and filtration rate, and increased with the alum dosage. However, it was only slightly affected by the grain size used in the study.     

Flow of filter granules in moving granular beds with louvers and sublouvers

It is important to develop the technology of high-temperature gas cleanup for some advanced power generation systems based on the gasification or combustion of coal or biomass. The moving granular bed filter has great potential to be developed for the hot gas cleanup. However the existence of stagnant zones in granular moving bed systems with louvered walls cause major technical problems, especially in filtration and adsorption processes. With the existence of stagnant zones, the dust particulates and fly ash coming with flue gas may plug the system and the filtration efficiency decreases remarkably.We propose a new design by placing sublouvers into the convergent channel between louvers to diminish the stagnant zones. This paper presents the results of a study of the flow patterns in a quasi two-dimensional cross-flow moving granular bed with systems of louvers and sublouvers. Silica sands were used as filter granules which were discharged from an upper hopper and circulated to the bed. An image processing system was used to record the granular flow for the investigations in flow patterns of filter granules. The velocity field and velocity distributions of filter granules are also evaluated and discussed. In this study, the design of sublouver-system moving bed has been optimized to almost completely eliminate the stagnant zones.     

滤料表面电位对滤床过滤效果的影响

滤床过滤工艺广泛应用于水处理领域，滤料表面电位对水中悬浮颗粒的过滤去除有很大的影响。石英砂滤料表面带较高的负电位，一些情况下不利于悬浮颗粒的去除。对石英砂、氧化铁改性滤料、复合改性滤料的表面电位和过滤效果的对比表明，复合改性滤料表面电位接近于中性，对水中的悬浮颗粒有稳定良好的去除效果。     

热压过滤完善选煤工艺

论述了热压过滤干燥脱水机具有过滤与干燥的双重作用、脱水效率高等特点;分析了干燥压滤机内脱水峰面的形成和移动过程,以及物料中液体饱和度与时间的关系;介绍了热压过滤干燥工艺系统与装备,并通过应用实例说明其完善选煤工艺的意义。     

Effect of membrane morphology on rising properties of filtration resistance in microfiltration of dilute colloids

The effect of membrane morphology on the flux decline behaviors in dead‐end unstirred microfiltration of very dilute colloids of polystyrene latex was examined using mixed cellulose ester and cellulose acetate membranes with interconnected tortuous pores and track‐etched polycarbonate membranes with uniform straight cylindrical pores. The plots of reciprocal filtration rate against the filtrate volume per unit membrane area for the former two membranes exhibit concave downward curves in the initial period when the membrane pore blocking is significant, whereas the plot for the latter shows a concave upward curve in that period. The former results were described by a serial resistance model consisting of the initial membrane pore blocking followed by filter cake growth, and the latter was represented by a parallel resistance model in which the pore blocking and cake growth develop simultaneously from the beginning of filtration. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3511–3522, 2017     

Onset of pulsing in gas-liquid trickle bed filtration

When liquid suspensions containing low concentration of fine solids are treated in catalytic packed bed gas-liquid-solid reactors, which are operated in trickle flow or near the transition between trickle and pulse flow, plugging develops and increases the resistance to two-phase flow. Also due to obstruction, such accumulation of fines in the catalyst bed shifts progressively the flow pattern from trickling to pulsing flow. The progressive onset of pulsing flow along the packed bed was estimated using a sequential approach based on combining a “large time-scale” unsteady-state filtration solution of two-phase flow with a “short time-scale” solution of a linear stability analysis of two-phase flow. Space-time evolution and two-phase flow of the deposition of fines in trickle bed reactors under trickle flow regime was described using a one-dimensional two-fluid model based on the volume-average mass and momentum balance equations and volume-average species balance equation for the fines. The model hypothesized that plugging occurred via deep-bed filtration and incorporated physical effects of porosity and effective specific surface area changes due to the capture of fines, inertial effects of phases, and coupling effects between the fines filter rate equation and the interfacial momentum exchange force terms. The transition between trickle flow and pulse flow regimes was described from a stability analysis of the solution of the transient two-fluid model around an equilibrium state of trickle flow under pseudo steady state conditions. The impact of liquid superficial velocity, viscosity and surface tension, gas superficial velocity and density, feed fines concentration, and fines diameter on the transition between trickle and pulse flows in the presence of fines deposition was analyzed.     

高效节能过滤技术与强化过滤过程的途径

叙述了国内外过滤与分离技术的发展和趋势。介绍了在节能型压榨过滤、陶瓷过滤、纳米过滤等3种节能型过滤技术的研究进展与结果;并针对难过滤物料及高精度过滤与分离的要求,分析了难过滤物料的特点,针对酶解液过滤的应用实例,提出了改善物料性质和强化过滤的有效途径,即添加助滤剂进行掺浆过滤,降低比阻,控制滤饼厚度,降低滤饼阻力的薄层滤饼过滤,这2种强化过滤技术的集成应用于某个难过滤物料分离的应用实例。     

Single wall diesel particulate filter (DPF) filtration efficiency studies using laboratory generated particles

Diesel engines offer higher fuel efficiency, but produce more exhaust particulate than conventional gasoline engines. Diesel particulate filters are presently the most efficient means to reduce these emissions. These filters typically trap particles in two basic modes: at the beginning of the exposure cycle the particles are captured in the filter holes, and at longer times the particles form a “cake” on which particles are trapped. Eventually the “cake” is removed by oxidation and the cycle is repeated. We have investigated the properties and behavior of two commonly used filters: silicon carbide (SiC) and cordierite (DuraTrap^® RC) by exposing them to nearly-spherical ammonium sulfate particles. We show that the transition from deep bed filtration to “cake” filtration can easily be identified by recording the change in pressure across the filters as a function of exposure. We investigated the performance of these filters as a function of flow rate and particle size and found that the filters have the highest filtration efficiencies for particles smaller than ∼80 nm and larger than ∼200 nm. A comparison between the experimental data and a simulation using incompressible lattice-Boltzmann model shows good qualitative agreement, but the model over-predicts the filter's trapping efficiency.     

Network simulation for deep bed filtration of Brownian particles

The effect of different interaction energy curves of DLVO theory on the permeability reduction in a filter bed is investigated by using the Brownian dynamics simulation method and the modified square network model to track the individual particles movement through the filter bed. When energy barrier exists and both particle and pore size distributions are of the Raleigh type, it is found that particles with Brownian motion behavior are easier to get straining at small pores, and cause higher permeability reduction than those without considering the Brownian motion behavior. But, this result was not observed for the constant particle and pore sizes case. The permeability reduction for the Raleigh size distribution is higher than that of the constant size. Similar results are also obtained for the “barrierless” type interaction energy curve for the case of Raleigh type size distribution, with the exception that the decreasing rate of permeability reduction of Brownian particles is smaller than that without considering the Brownian motion behavior. When comparing with the permeability reduction experimental data, it is found that the present model shows fair agreement between the theory and the experimental results when the direct deposition mechanism is dominant.     

Use of edta to clean up filtration materials in clean-up works

Conclusions The fundamental possibility of using an EDTA solution to remove chemical contaminants on the filter bed of a quartz sand filter has been demonstrated.Translated from Khimicheskie Volokna, No. 2, pp. 54–55, March–April, 1987.     

Slow sand filtration of UASB reactor effluent: A promising post treatment technique

The study was carried out to evaluate the feasibility of slow sand filtration as a promising post treatment method for the up-flow anaerobic sludge blanket (UASB) reactor effluent. Laboratory scale filter column of 10 cm diameter and 0.54 m sand media depth was used to study the process performance. It was found out that slow sand filtration with 0.43 mm effective sand size is the most effective at a filtration rate of 0.14 m/h. It is capable of removing 91.6% of turbidity, 89.1% of suspended solids (SS), 77% of chemical oxygen demand (COD) and 85% of bio-chemical oxygen demand (BOD), 99.95% of total and fecal coliforms (TC and FC) and 99.99% of fecal streptococci (FS). Slow sand filters efficiently reduce the mass of suspended material and extend the filter run for more time (7 days) at a hydraulic load of 0.14 m/h as compared to the hydraulic load of 0.19 m/h and 0.26 m/h. Therefore, due to excellent effluent quality, it can be said that slow sand filtration would be a promising technology for the post treatment of small-scale UASB reactor effluent in developing countries, where treated effluent can be reused for various recreational purposes i.e. gardening and irrigation, as well as for safe discharge.     

微絮凝连续砂滤技术在矿区生活污水回用中的应用

采用微絮凝连续过滤技术深度处理矿区生活污水,当滤料粒径采用0．8～1．0mm,滤床厚度1．2m,滤速6～8m／h,砂循环速率在4mm／min,PAC投加量20mg／L,PAM投加量0.3mg／L时,出水SS小于5mg／L,去除率达到94．7％以上,其它各项指标达到并优于建设部《生活杂用水水质标准》（CJ25．1—89）要求,可以实现中水回用。     

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.     

The performance of pumice as a filter bed material under rapid filtration conditions

Deep bed sand filters are used extensively in drinking water and wastewater treatment. In this study, sand and pumice were used as a filtration media under rapid filtration conditions and performance results for both were compared. Turbidity removal performance and head losses were investigated as functions of filtration rate, bed depth and particle size. Under the same experimental conditions such as 750 mm bed depth, 7.64m³/m².h flow rate and, 0.5−1.0 mm grain size, turbidity removal rates for sand and pumice were found to be 85-90% and 98-99%, respectively. Furthermore, the head loss for sand and pumice were found to be 460 mm and 215 mm, respectively. The results obtained have shown that pumice has a high potential for use as a filter bed material.     

Moving granular filter bed of quartz sand with louvered-walls and flow-corrective inserts

This study investigated the effect of a simple flow-corrective element, a vertical plate, on the flow patterns and wall stresses in a two-dimensional louvered-wall moving granular filter bed of quartz sand. The static wall stress distributions produced by the granular solids were measured, and compared with the theoretical prediction, using the differential slice and Runge-Kutta (order four) methods. The variations in the dynamic wall stresses over time were obtained using a two-directional pressure gauge. The results show that a vertical plate placed in each stage of the granular filter bed effectively diminished the quasi-stagnant zone adjacent to the louvered-wall, and reduced the wall pressure pulsation. For example, the ratio of the stagnant zone area in the second stage to the area of quartz sand in the second stage decreased from 50.66% (without an insert) to 27.86% (with a vertical plate). The maximum dynamic normal wall stress on the convergent section of third-stage louvered-wall (louver angle: 40°) declined remarkably from 9.95 kPa (without an insert) to 5.9 kPa (with a vertical plate), and then the reduction of the maximum dynamic normal wall stress was up to 40.7%. Furthermore, a vertical plate installed at an appropriate location satisfies the following requirements: (1) it shrinks the stagnant zone and reduces the wall stresses on the louvered wall of a moving granular filter bed; and (2) it solves the potential problem of a roof-type insert, on which the stagnant zone may sit.     

倾斜角对液体燃料润湿条件下砂床表面火蔓延的影响

利用纹影系统、CCD相机以及K型热电偶对正丁醇润湿条件下不同角度的砂床表面火蔓延特性进行了研究,分析了不同砂床表面倾角对火蔓延的影响机理。研究结果表明:正丁醇润湿条件下变角度砂床表面火焰是稳定匀速蔓延的,向上蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而增大;向下蔓延时,火焰的高度、黄色发光区以及蔓延速度随着倾角的增加而减小;蔓延火焰前方存在预热区,且预热区随表面倾角的增大而增大:砂层内部存在热边界层,且砂床热边界层厚度随表面倾角的增加而减小。得到的火蔓延特性及燃烧机理为此类液体燃料的储存、使用以及环境保护提供了一定的科学依据。