Compressibility Of Filter Cake Research Articles

Analytical and numerical modelling of the effect of filter medium resistance on the mechanical dewatering of wastes and industrial filter cakes

A nonlinear model is proposed to predict the effect of filter medium resistance on the filter cake compression and dewatering at constant pressure. This model is based on the Darcy-Terzaghi-Shirato filtration-compression equations presented in material coordinates and modified to consider the power-law pressure dependence of the specific cake resistance α. Above mentioned model is extended to consider the filter medium resistance Rmintroducing the number of Biot, Bi=αavWRm.Local profiles of compressive pressure and filter cake characteristics, as well as consolidation ratio and cake dryness, are simulated and compared for different moderately and highly compressible filter cakes (silica, activated sludge, Baker’s yeast, and CaCO3) based on the analytical and numerical solutions of the model. It is shown that the behavior of cake compression and dewatering significantly depends on the filter medium resistance Rm, especially at the small numbers of Bi≤1.

Preparation of amphiphilic cationic polyacrylamide (CPAM) with cationic microblock structure to enhance printing and dyeing sludge dewatering and condition performance.

Flocculation is an important pretreatment technology for sludge dewatering, and the flocculant's performance is the key factor to determine the flocculation effect. Cationic polyacrylamide (CPAM) is commonly used in dewatering and conditioning of printing and dyeing sludge (PD sludge), and the research of high-efficiency flocculant is a hot spot in the field of PD sludge dewatering. Hydrophobic butylacrylate (BA) and (2-(Methacryloyloxy)ethyl) trimethylammonium chloride (DMC) were introduced into the copolymer, and amphiphilic (hydrophilic/lipophilic) CPAM, namely TP-ADB, with microblock structure was synthesized by ultrasonic initiated template copolymerization in this study. The functional group composition of TP-ADB was determined by FTIR and 1H NMR. Thermogravimetric analysis (TGA) showed that TP-ADB had good thermal stability. The amphiphilic rheological properties of the copolymer were measured according to the apparent viscosity. In addition, 1H NMR and TGA results confirmed the existence of microblock structure in the copolymer chain. The polymerization mechanism was discussed by association coefficient (KM) measurement. The results showed that the template copolymerization initiated by ultrasonic followed the law of free radical copolymerization. The pre-adsorption of DMC with sodium polyacrylate template (NaPAA) before the reaction confirmed that the template polymerization accorded with ZIP I mechanism. The cationic microblock structure and hydrophobic association of TP-ADB promoted the dewatering performance of PD sludge (FCMC = 72.9%, turbidity removal rate = 98.9%, SRF = 4.2 × 1012m·kg-1). Hydrophobic association enhanced the bridging, sweeping, and net catching effect, and promoted the growth of floc size and fractal dimension. Cationic microblock structure can produce compact floc with higher mechanical strength by enhancing electrical neutralization and electrical patching. As a skeleton, the compressibility of filter cake was reduced and the permeability was enhanced, and the PD sludge dewatering effect was significantly improved.

Particle movements provoke avalanche-like compaction in soft colloid filter cakes

During soft matter filtration, colloids accumulate in a compressible porous cake layer on top of the membrane surface. The void size between the colloids predominantly defines the cake-specific permeation resistance and the corresponding filtration efficiency. While higher fluxes are beneficial for the process efficiency, they compress the cake and increase permeation resistance. However, it is not fully understood how soft particles behave during cake formation and how their compression influences the overall cake properties. This study visualizes the formation and compression process of soft filter cakes in microfluidic model systems. During cake formation, we analyze single-particle movements inside the filter cake voids and how they interact with the whole filter cake morphology. During cake compression, we visualize reversible and irreversible compression and distinguish the two phenomena. Finally, we confirm the compression phenomena by modeling the soft particle filter cake using a CFD-DEM approach. The results underline the importance of considering the compression history when describing the filter cake morphology and its related properties. Thus, this study links single colloid movements and filter cake compression to the overall cake behavior and narrows the gap between single colloid events and the filtration process.

Hydrogel membranes made from crosslinked microgel multilayers with tunable density

Membranes with precisely adjustable properties are needed to master the separation challenges in modern biochemical processes. Composite membranes are composed of a conventional membrane and an adaptive coating. Adaptive polymers like polymer brushes or hydrogels have proven to be excellent candidates for this challenge. In the present work we envision the utilization of temperature responsive microgels as colloidal building blocks, forming an adaptive separation layer on top of a porous support. Until now, microgels are mainly used as a functional gating element, influencing the retention or permeability of conventional membranes. In the present study microgel assemblies should be used as the only selective layer. To overcome the repulsive forces between the microgel particles, we utilize the interparticle crosslinking within a microgel filter cake. We could show that the crosslinking leads to stable and responsive microgel multilayers with a temperature responsive retention performance based on charge repulsion and size exclusion. The developed methodology enables the control of the filter cake compression, which can be adjusted and preserved via crosslinking enabling full control over the thickness and density of the selective layer. While the resistance of the crosslinked microgel multilayer shows the classical temperature responsiveness and collapse into a low resistance state, the retention increases simultaneously, indicating that the crosslinked microgels behave like a macroscopic hydrogel.

Formulation and evaluation of β-cyclodextrin polymer microspheres for improved HTHP filtration control in water-based drilling fluids

β-cyclodextrin polymer (β-CDP) microspheres were investigated as high temperature resistant filtration reducers for water-based drilling fluid in this study. The microspheres were synthesized by crosslinking reaction between β-CD and epichlorohydrin with inverse emulsion polymerization. The structural and morphological characteristics of the prepared microspheres were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), particle size distribution measurement, and thermogravimetry analysis (TGA). The filtration control properties of the microsphere were evaluated via American Petroleum Institute (API) filtration test and high temperature and high pressure (HTHP) filtration test. The results indicated that β-CDP microspheres could effectively reduce the filtration of bentonite suspension both before and after thermal aging at 200 °C without significant influence on drilling fluid's rheology. A substantially enhanced filtration control behavior was observed after thermal aging, which was contrary with conventional filtration reducers. The β-CDP microspheres could absorb a large number of water and became swellable and deformable, which enhanced the compressibility of filter cake. What is more, hydrothermal reaction occurred for part of β-CDP microspheres under high temperature environment, resulting in the formation of numerous carbon spheres ranging from hundreds of nanometers to several micrometers. The β-CDP microspheres, bentonite particles and small carbon spheres in combination contributed to form a dense and compact filter cake with low permeability. β-CDP microspheres were potential candidates as environmental friendly and high temperature filtration reducers in deep well drilling.

Determination of filtration and consolidation properties of protein crystal suspensions using analytical photocentrifuges with low volume samples

Proteins and in particular pharmaceutical proteins like monoclonal antibodies are expensive products. Protein crystallization is an interesting alternative process step to the common purification and formulation of such proteins. The solid-liquid separation of proteins however, is a challenging task because the proteins are sensitive to mechanical stress, which could lead to crystal breakage and often are only available in small amounts for research and development. In this study a newly developed filtration cell for the LUMiSizer® centrifuge is used to analyze the filtration behavior with low volume samples. Isometric and needle shaped lysozyme crystals serve as model protein crystals. The needle shaped crystals showed about twice as high compressibility and much higher cake resistance than the isometric lysozyme crystals. After the filtration at maximum pressure in the centrifuge the mean particle diameter decreased compared to the unstressed median diameter. With the filtration cell the cake height and filter cake compression can be monitored in situ and the filter cake resistance and solids volume fraction can be calculated with one experiment using 200–300 μl sample.

Characterization of membrane fouling via single centrifugal ultrafiltration

The article introduces a novel method for accelerated analysis of membrane fouling during ultrafiltration of colloids: centrifugal ultrafiltration with a stepwise change of centrifugal rotation speed. The method allows simultaneous analysis of membrane fouling for different colloidal samples in a single analytical centrifugation experiment. The analysis for determination of fouled membrane resistance, specific cake resistance and reversibility of the filter cake compression is provided. The method applicability was tested with bovine serum albumin solutions at different protein concentrations. Fouled membrane resistance as well as pressure dependency of specific cake resistance was determined in a wide pressure range of 10…450 kPa. Results obtained with the help of the proposed method were in a good agreement with those obtained using the conventional method of constant pressure dead-end ultrafiltration.

Influence of process operating parameters on dryness level and energy saving during wastewater sludge electro-dewatering

Electrically assisted mechanical dewatering, known as electro-dewatering (EDW), is an alternative emerging technology for energy-efficient liquid/solids separation in the dewatering of wastewater sludge. In this study, the performance of the electro-dewatering (EDW) process for activated wastewater sludge was investigated. The influence of the operating modes; being the timing of voltage (U-EDW) or current (I-EDW) application to either or both the filtration and compression stages, and the influence of the applied pressure (in successive 30 min pressure steps) were studied. The results showed that by delaying the application of the electric field to the filter cake compression stage, there was a potential saving in power consumption of around 10–12% in the case of U-EDW and about 30–46% in the case of I-EDW.The increase of the applied pressure from 0.5 to 12 bar during the filter cake compression stage leads to an increase in electro-dewatering kinetics. The results also reveal that at a low electric field level the increase of the processing pressure has a relatively pronounced effect on the dewatering process. At high levels of the electric field, a minimum processing pressure (4–6 bar) is required to improve the electrical contact between the electrode and the sludge and thus lower the energy consumption.

Modeling cake buildup under TMP-step filtration in a membrane bioreactor: Cake compressibility is significant

Fouling is inevitable in membrane bioreactors (MBRs) due to the complex nature of activated sludge, which contains a broad variety of potential foulants. Filter cakes that build up from sludge particles are traditionally highly compressible due to both the deformation of the individual sludge particles and the rearrangement of these particles in the cake. However, this phenomenon has been little examined in studies of fouling mechanisms in MBR systems. This study examines the properties of the cake layer, modeling the cake buildup and specific cake resistance (α), including compressibility, in terms of pressure-dependent α.The changes in fouling resistance during transmembrane pressure (TMP)-step filtration in an MBR setup were simulated using an empirical pressure dependence of the specific cake resistance and a simple mass balance model. The total change in fouling resistance in each TMP step could be divided into an initial rapid change in specific cake resistance due to filter cake compression followed by simple cake buildup. By including cake compression in this simple model, the model fitted the data with high precision. We demonstrated that compressibility should be considered when describing cake fouling in MBRs.

Simulation and experimental verification of the filtration and filter cake compression model

Modelling of the solid–liquid mixture separation including free suspension filtration and expression of filter cake and thick slurry is presented in the paper. Determination of the filtration parameters and model verification using simple experiments is proposed. The model predictions are verified experimentally using three different suspensions.

Filtration experiments with compressible filter cakes in centrifugal fields with superimposed static pressure

Combined application of centrifugal and static pressure field has shown improved results for filtration rate and dewatering performance in various applications. Especially for compressible filter cakes, hyperbaric centrifugal filtration promises better results than separation in conventional filter centrifuges. In a beaker centrifuge filtration experiments were carried out up to C-values of 3000. A static pressure field with a maximum pressure up to 5 bar was superimposed in the centrifuge (hyperbaric centrifugal filtration). Visualisation techniques allowed the observation of the filter cake compression during the filtration experiment. Under various C-value and static pressure conditions filtration experiments have been carried out using suspension systems with solids of distinct compressibility. The filtrate flow versus time was monitored. Complementary, the mechanical filter cake properties and filter cake structures were analysed under different process conditions. Relationships between filtrate flow rate and filter cake properties (mechanical behaviour, structure) are described.

A model for clay filter cake properties

Clay filter cake properties, such as porosity, compressibility and permeability, have been studied by means of a structural network model. The electric double layer repulsion and Van der Waals attraction forces together with the equilibrium conditions of the network structure are shown to be fundamental in simulating the properties of filter cakes. The factors which affect the properties of filter cakes, such as clay particle size, salt concentration, and surface charge density have also been investigated. Results from the model show that the porosity, compressibility and permeability are predictable functions of compression pressure. The porosity of a filter cake is very sensitive to the degree of aggregation of clay particles. The compressibility of filter cakes is most sensitive to the size of clay particles and to the salt concentration. Salt concentration is also a sensitive factor influencing the permeability of filter cakes and its dependence on applied pressure. The porosity, compressibility and permeability are obtained as a function of compression pressure and can be used in static or dynamic filtration calculations.

Analysis of Fluid-Loss Data

Summary Over the last few years, fluid-loss testing has evolved from static to dynamic testing. Data analysis, however, has not progressed as rapidly as the experimental techniques used to gather the data. In this paper, various techniques of analyzing dynamic fluid-loss data are discussed and a simple, yet effective, method of describing dynamic fluid-loss curves is presented. The analysis of dynamic fluid-loss data is usually based on the traditional square-root-of-time treatment. This type of analysis works well for static fluid-loss test data because the dynamic processes are less complex than those in dynamic situations. During a dynamic fluid-loss test, a number of different events influence the fluid loss and the shape of the fluid-loss curve. Not only filter-cake compression, but also dynamic cake deposition and cake erosion must be taken into account. In most cases, Darcy flow does not occur over the whole time span of the test. Several complex methods of treating the data from dynamic fluid-loss tests have been suggested, but most rely on modifications of the static fluid-loss-data analysis technique. These techniques are based on the data as a function of the square root of time. With dynamic fluid-loss test data, the square-root-of-time relationship does not adequately describe the fluid-loss data. A straightforward technique to analyze dynamic fluid-loss data is discussed in this paper.