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     

多管陶瓷过滤器内耦合效应数值模拟

The Reynolds stress transport model and the Eulerian two-fluid model provided by the FLUENT code were applied to evaluate the gas-particle two-phase flow in the ceramic filter vessel. The ceramic filter vessel contains six candle filters, which are arranged in the form of equilateral hexagon. The variation of the areal density of the filter cake during the filtration and the back-pulse process were analyzed. The coupling effect between filters, gas and solid, filtration and pulse cleaning process were investigated, respectively. The numerical results show a good approach to predict the particle distribution in the vessel and the particle deposition on the filter element. This study provides the base for the intensive study on the analysis of the gas-particle flow in the filter vessel.     

金属丝网过滤器性能影响因素研究

对金属丝网过滤器性能的影响因素进行了综合分析,为过滤器的良好运行提供建议。在分析过滤机理的基础上,从过滤效率、压降、残余压降三个方面,分析了过滤器性能的影响因素,包括丝网结构、循环次数、过滤速度、流体浓度及温度、颗粒粒径、滤饼的可压缩性、最大允许压降、反吹压力等。结果表明,各因素之间互相影响,实际过滤过程中须综合考虑,以达到过滤器的预期性能。     

Cleaning of coal-derived oils by filtration

With the development of coal liquefaction processes a major task is the removal of solid particles (mineral components, residual insoluble coal and catalyst) from the hydrogenation products. Depending on the characteristics of these products various cleaning methods are under investigation. Thermal methods (distillation, solvent deashing) are preferred for those hydrogenation processes yielding predominantly distillable oils. The separation of solids from the recently developed SRC I processes presents more problems because the percentage of oils is much too low for distillation to be used exclusively for recovering the recycling oil. Therefore, deashing of the SRC I products using solvents within the critical range as well as filtration processes are under development. The Paper describes the different processes under development at the moment and introduces a newly developed candle filter for SRC I filtration. Besides the design of the filter unit, results of filtration tests, handling of the filter cake and production of a filter aid and coke from the residue are described also.     

Modeling of Particle Fouling and Membrane Blocking in Submerged Membrane Filtration

Abstract

The models of particle fouling and membrane blocking in a submerged membrane filtration are developed in this study. The effects of operating conditions, such as aeration intensity (air flow rate) and filtration pressure, on the filtration flux, membrane blocking, and cake formation are discussed thoroughly. The experimental results show that the filtration resistances due to cake formation and membrane blocking play significant roles in determining the overall filtration resistance, but the latter one is more dominant. An increase in aeration intensity leads the filtration flux to increase due to the reduction of cake formation on the membrane surface. However, a higher filtration pressure causes more severe membrane internal blocking and then to lower filtration flux. The cake properties and the filtration resistance due to membrane blocking are analyzed and can be regressed to empirical functions of filtration pressure. A force balance model for particle deposition on the membrane surface is also derived. In order to estimate the shear stress acting on the membrane surface, the diameter, shape, and rising velocity of air bubbles are analyzed based on hydrodynamics. Once the model coefficients are obtained, the pseudo‐steady filtration flux under various conditions can be estimated by the proposed model and the basic filtration equation. The calculated results agree fairly well with the available experimental data.     

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.     

以颗粒煤为助滤剂对城市污泥进行二段过滤脱水的研究

以颗粒煤为助滤剂,采用二段过滤方式来强化城市污泥的脱水,并对滤饼进行热值分析,探讨城市污泥资源化利用前景.在研究中,具体分析探讨了煤的类型、煤的添加比、煤的粒径、搅拌强度、过滤压力以及煤的添加方式对过滤过程中相关参数的影响.得到以下结论:在污泥和煤的添加比为1:2,颗粒煤粒度为0.15～0.18 mm,低强度搅拌,常温...     

The Effect of Particle Sedimentation on Gravity Filtration

ABSTRACT

Simulation of cake formation of mono-sized and dual-sized particles under gravitational sedimentation and filtration is presented. The dynamic analysis proposed by Lu and Hwang in 1993 is applied to examine the local cake properties formed under a falling head by considering the hindered settling effect of particles in the slurry and the variation of the pressure drop across the filter septum. Results of this study show that, at a given position in a cake, the solid compressive pressure reaches a maximum value and then decreases for a gravity filtration due to the decrease in the driving head. A cake constructed with dual-sized particles has a more compact structure than does one with mono-sized particles, and larger particles will form looser packing than will smaller ones for mono-sized particles. A dual-dispersed suspension with a lower fraction of large particles will result in the lowest cake porosity and the highest specific filtration resistance of cake. Comparison of the porosity distribution in filter cake formed by means of gravity filtration and constant head filtration shows that the porosity near the filter septum of gravity filtration has a convex behavior while that of constant head filtration has a tendency toward concavity. This discrepancy is mainly due to the change in the driving head during the filtration process. Both theoretical and experimental results show that the uniformity of particle size distributions in the filter cake will be much better when the relative settling velocity between large and fine particles is reduced.     

Analysis of Steady-State Filtration and Backpulse Process in a Hot-Gas Filter Vessel

The need to develop a technology for clean and efficient electric power generation has led to the development of advanced pressurized fluidized bed combustors (PFBC) and integrated gasification combined cycles (IGCC). The effective filtration of hot gases for removal of ash and sulfur sorbent, however, is the key to the success of these advanced coal energy systems. Recently, attention has been given to the use of ceramic candle filters for hot-gas cleaning. The ash cake formation on these filters needs to be removed by the backpusle for their successful operation. In this paper, steady-state filtration as well as the transient gas flow during the backpulse process in the integrated gasification and cleanup facility (IGCF) (located at the National Energy Technology Laboratory, NETL) is studied. The steady-state filtration condition is first evaluated, using a compressible heat-conducting flow analysis. Particle transport patterns are studied, and the deposition patterns of 1-30 w m particles on the ceramic filters and the vessel surfaces are analyzed. To simulate the backpulse process, the pressure at the filter exit is increased sharply in a period of about 0.01 s pressure. The stress transport model of the FLUENT code is used to evaluate the time evolution of the transient gas flow velocity, pressure and thermal fields, as well as turbulence intensities and stresses inside the candle filter and in the IGCF filter vessel. Contour plots of the hot-gas flow conditions from the start of the pressure buildup to its saturation level are presented. The results show the rapidly changing flow conditions during the initial stages of the backpulse. The pressure wave propagates along the length of the filter until a monotonic increase of pressure with time is achieved; that is, the pressure field inside the filter at the initial stages of the backpulse is strongly nonuniform. Therefore the potential for incomplete filter cake removal exists. Motions of particles that enter the vessel and/or are ejected from the candle filter during the backpulse process are also studied, and illustrative particle trajectories are presented.     

Nanocolloid cake properties determined from step‐up pressure filtration with single‐stage reduction in filtration area

A sophisticated method was developed for evaluating simultaneously and accurately both the average specific resistance and average porosity of the filter cake formed in unstirred dead‐end ultrafiltration of nanocolloids such as protein solution and nanosilica sol. In the method, a step‐up pressure filtration test was conducted by using a filter with a single‐stage reduction in the effective filtration area. The influence of the pressure drop across the cake on not only the average specific cake resistance but also on the average cake porosity of highly compressible filter cake was evaluated using only flux decline data in one dead‐end filtration test, taking advantage of the decrease in the cake thickness caused by the pressure increase. As a result, the cake properties were easily determined for a variety of nanocolloids. Constant pressure dead‐end ultrafiltration data obtained under various pressures and concentrations were well evaluated based on the method proposed. © 2015 American Institute of Chemical Engineers AIChE J, 61: 4426–4436, 2015     

Law of substance separation on cross-flow filtration in turbulent flow

Cross-flow filtration is a filtration process for separation of a disperse phase from liquids. Suspension flows tangentially to a membrane and the filtrate is drawn off perpendicular to the direction of flow. Formation of a filter cake on the membrane is thus prevented, reduced, or its composition, modified. The principle of the separation is based on tow opposing effects: on the one hand, the particles are transported by the filtration flux to the membrane where they cause and increase in concentration; on the other hand, concentration differences are again reduced by the turbulence of the cross-flow and by Brownian motion of the particles. The two mechanisms compete with each other and depend upon particle size in different ways. An energetic comparison of the two effects yields the separation law of cross-flow filtration as a steady state solution of the Fokker-Planck equation. The separation law has an exponential form and assigns each particle size a separation probability with which it reaches the membrane. Once on the membrane the particles may form a filter cake, flow through the pores or return to the bulk flow. If the particles remain on the membrane the ranges of layer-free and cake-forming filtration can be calculated from the hydro-dynamic and geometric conditions of the cross-flow filter. Conventional cake filtration is regarded as limiting case. In continuous cross-flow filtration process a low separation probability through the filtration pressure on selection of the filter medium resistance.     

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。     

Factors affecting cake resistance in non-Newtonian filtration

A methodology for evaluation of surface effects including polymer adsorption-gel formation or slip within the pores of a filter cake has been developed and applied to constant pressure filtration of calcium carbonate in aqueous hydroxyethyl cellulose (Natrosol 250G, Hercules Powder Company) slurries. The fundamental framework of non-Newtonian filtration is generalized to include the Blake, Kozeny-Ergun and Kozeny-Carman cake models and the cake resistances γ_K and α_R, in conjunction with the correction terms J_RN and J_gen, within a unified framework. Relationships are developed between the latter quantities and the effect of the bed model on the evaluations of the filtration characteristics is delineated. Significant polymer adsorption-gel formation was found to take place in the constant pressure filtration of calcium carbonate in aqueous Natrosol 250G slurries. The resultant cake porosities were larger and the effective cake porosities lower than comparable porosities for cakes deposited from water slurries. The wide variation of J_RN with the characteristic index N is attributed to the small size of the slurry particles. Polymer adsorption is shown to extend, and slip on the particle surface to reduce the variation of J_RN with N.     

液力过滤与液力压密脱水的理论(一)

将滤室固定不变的板框或箱式压滤机的操作过程分成滤饼过滤阶段和液力压密脱水阶段两个过程来研究。在滤饼过滤阶段 ,应用表面过滤机理 ,采用传统的鲁思过滤基本方程和平均过滤比阻的理论进行研究。在液力压密脱水阶段 ,应用达西定律建立了液力压密基本微分方程 ,根据研究得出滤饼渗透系数与孔隙率在压密脱水阶段的线性取代关系的结论 ;滤室固定的限制条件和物料平衡条件 ,推导出液力压密的脱水方程式。分析了影响液力压密脱水的时间因素和液力压密速率的各操作参数。建立了完整的液力过滤和压密脱水理论 ,为自动压滤机的设计提供了理论指导     

Avoiding filter cake cracking: Influence of consolidation on desaturation characteristics

In cake filtration processes with an air-blowing step, cracking is an undesirable phenomenon as it leads to deterioration of the filtration process by highly increasing gas throughput. This leads to higher residual moisture if the pressure difference cannot be maintained and an increase in overall cost. Crack formation can be avoided by compacting the filter cake before desaturation. While this action will make the separation process applicable by highly reducing gas consumption, there are also potential negative effects. Compaction increases filter cake resistance and might therefore slow down desaturation kinetics. Therefore, the authors investigated how the filter cake characteristics governing desaturation change from the nonconsolidated to the consolidated state of the filter cake and compared these findings to the actual dewatering kinetics. The results showed that for the case where cracking could be oppressed, dewatering kinetics of the consolidated cake are actually faster than for the nonconsolidated cake, despite higher resistance of the consolidated cake. Thus, compaction is an appropriate action when dealing with filter cake cracking.     

Effect of Phospholipids on Crude Linseed Oil Filtration

Abstract

Lecithin addition (0 to 10%) in crude linseed oil was used to investigate the effect of phospholipids on oil filtration at 20°C. The addition of lecithin (more than 2%) results in a decrease in the filtration rate, an increase in the cake resistance, and a modification of the filtration mechanism from cake resistance to intermediate blocking. At 20°C the lecithin precipitated on the particles and caused sedimentation of a deposit impermeable to oil that slows down the oil flow through the cake. The magnetic stirring is not an efficient way of filtration improvement on the contrary of filtration at 50°C.     

Cake filtration of suspensions in viscoelastic fluids

The fundamental framework for cake filtration of suspensions in viscoelastic media is extended to include the effects of polymer retention, including adsorption in the filter cake, polymer retention and elongational flow in the filter medium, which also undergoes compaction, and evaluation of polymer degradation in the filter cake and medium. Experimental data obtained in constant pressure filtration of starch suspensions in dilute aqueous polyacrylamide solutions confirmed the prediction of an enhanced apparent medium resistance R_ma and a reduced cake resistance α_R. Evaluations are presented of the contributions to the pressure drop due to enhanced normal stresses in elongational flow and to polymer retention (adsorption), and of the ratio of the particle size with and without adsorbed polymer in the cake. The analysis of the data points to high levels of polymer degradation during the flow of the polymer solution through the filter cake and medium.     

Clarification of liquids using filter aids Part I. Mechanisms of filtration

Filter aids were characterized by an effective particle diameter and a pore diameter in the filter aid cake, calculated from the specific cake resistance using the Kozeny equation. The results agreed well with those from mercury porosimetry. The transition from surface filtration to depth filtration by filter-aid cakes was studied with uniform polystyrene particles as a model impurity. The critical ratio between pore diameter and impurity diameter was between 2 and 3. At conditions of non-surface filtration, an important concentration of impurity exists in the liquid flowing through the cake causing a danger of blocking. When pre-coat and body feed were used with polystyrene particles as an impurity, the blocking appeared to occur rather easily on top of the original pre-coat and on the filter medium. The type of pre-coat and the way in which it was formed were very important. In beer filtration, which is mainly a surface filtration, a small concentration of passing impurity was able to block the pre-coat layer, when the filter aid of the body feed was coarser than that of the pre-coat.     

Performance of fibrous filters during nanoparticle cake formation

Fibrous filters are highly efficient in removing micrometer particles, but their performance in the nanometer particle range is still little known. The aim of this study was to evaluate pressure drop and collection efficiency during nanoparticles cake formation using commercial fibrous filters. The filter media used were High Efficiency Particulate Air (HEPA) and polyester filters. The aerosols were generated by a commercial inhaler using a 5 g/L solution of NaCl and the particles produced were in the size range from 6 to 800 nm, with a peak at around 40 nm. A superficial velocity (v_s) of 0.06 m/s was employed. During the filtration, the maximum pressure drop established was ?P ₌ ?P_f +980Pa, where ?P_f is the initial pressure drop of the filter. The collection efficiency was determined for a clean filter and for intermediate pressure drops. The filtration curves obtained showed that the HEPA filter provided greater surface filtration, compared to the polyester filter. Comparison of the collection efficiencies for clean filters revealed that the HEPA filter was highly efficient, even in the absence of cake, while the polyester filter showed initial collection efficiencies of between 20 and 40% for particles in the size range from 100 nm to 1000 nm. However, after formation of the filter cake, the collection efficiencies of both filters were almost 100% during the final stage of filtration. This shows that the fibrous filter can be applied in several industrial processes with highly efficient nanoparticle separation, after the formation of a thin layer cake filtration.     

Relating quality,capacity and energy consumption of oil filters

In the theoretical part of the paper a simple theory is presented relating filtrate clarity, filter capacity and energy consumption. The particle size distribution is subdivided in coarse, intermediate and fine particles. The key role play the intermediate particles who can enter and clog the filter medium. This combined with a layered cake model selects complete blocking as the filtration mechanism for the intermediate particles. In the experimental part results are given on the Multipass flat cell filtration of SAE 5–80 test dust in oil, monitoring upstream and downstream pressure and particle concentration as a function of time. For the chosen filter media and within the experimental range of flow and concentration the simple theory can be applied successfully to these SAE oil filtration experiments.