Cake Permeability Research Articles

The Effect of the Dust Cake Resistance on Fluid Flow Passing through the Filter Media

A filter box was used to obtain the experimental data of filtration operation with different air velocities as 5, 10 and 15 cm/s. The experimental data were compared to the simulated ones using CFD technique. For all range of air velocity and dust cake porosity and permeability employed, data of pressure drop in filter box could be satisfactorily predicted by simulations in CFD. Furthermore, the CFD simulations showed that undesirable patchy cleaning might be overcome using air velocities lower than 15cm/s.

Evaluation of Constitutive Equation for Stress in Solids in Porous Media Composed of Bridging Agents Used in Drilling Fluids

During oil well drilling processes in reservoir-rocks, the drilling fluid invades the formation, forming a layer of particles called filter cake. The formation of a thin filter cake and low permeability helps to control the drilling operation, ensuring the stability of the well and reducing the fluid loss of the liquid phase in the interior of the rocks. The empirical determination of the constitutive equation for the stress in solids is essential to evaluate the filtration and filter cake formation in drilling operations, enabling the operation simulation. In this context, this study aims to evaluate the relationship between the porosity and stress in solids of porous media composed of bridging agents used in drilling fluids. The concentration distribution in sediments was determined using a non-destructive technique based on the measure of attenuated gamma rays. The procedure employed in this study avoids the use of compression-permeability cell for the sediment characterization.

Experiments on Cake Development in Crossflow Filtration for High Level Waste

Crossflow filtration is a key process step in many operating and planned waste treatment facilities to separate undissolved solids from supernatant slurries. This separation technology generally has the advantage of self-cleaning through the action of wall shear stress created by the flow of waste slurry through the filter tubes. However, the ability of filter wall self-cleaning depends on the slurry being filtered. Many of the alkaline radioactive wastes are extremely challenging to filtration, e.g., those containing compounds of aluminum and iron having particles whose particle size and morphology reduce cake permeability. Low filter flux can be a bottleneck in waste processing facilities such as the Salt Waste Processing Facility at the Savannah River Site and the Waste Treatment Plant at the Hanford Site. To date, increased rates are generally realized by either increasing the crossflow filter axial flow rate, limited by pump capacity, or by increasing filter surface area limited by space and increasing the required pump load. The Savannah River National Laboratory (SRNL) set up both dead-end and crossflow filter tests to better understand filter performance based on filter media structure, flow conditions, and filter cleaning. Using nonradioactive simulated wastes, both chemically and physically similar to the actual radioactive wastes, the authors performed several tests to demonstrate increases in filter performance. With the proper use of filter flow conditions, filter flow rates can be increased over rates currently realized today. This paper describes the selection of a challenging simulated waste and crossflow filter tests to demonstrate how performance can be improved by varied filter operation methods. Those methods were a slow startup to better develop the filter cake and scouring the filter wall. The results showed that for salt waste and metal oxide hydroxide sludges, the process of backpulsing is not necessary to maintain a good filter flux, and the process of periodically scouring the filter improves filter performance. The results also imply that initial filter operation is important to develop a filter cake that minimized pressure drop, the presence of a filter cake can lead to improved solids separation, and a well-developed cake with periodic scouring may allow a good filter flux to be maintained for long periods of time.

Mathematical Model Incorporated Fractal Geometry and Permeability of Compressed Peanut and Sesame for Oil Extraction

Considering the fractal characteristic of oilseed cake, the relationship between the permeability and the pore fractal dimension of peanut and sesame cake has been investigated. The microstructures of peanut and sesame cake under five applied pressures are measured by using stereo light microscope and Image-pro image analyzer. Using the box-counting method, the fractal dimensions of pore size distributions are measured. A mathematical model incorporated fractal dimension and permeability has been developed to predicate the permeability of compressed peanut and sesame under cold condition based upon combining Hagen-Poiseulle equation with Darcy’s law for flow of fluid through porous media. There is a prediction of permeability of peanut and sesame cake. Thus, a measurement is carried out for validation. The values of mean relative errors are 19.4% and 11.4 respectively. A fairly good agreement is obtained in the case of high applied pressure. And there exists a tendency that the value of the difference between the theoretical calculation and the permeability measurement decrease significantly with the increase of applied pressure.

Characterization of Filter Cake Generated by Water-Based Drilling Fluids Using CT Scan

Summary Filter-cake characterization is very important in drilling and completion operations. The homogeneity of the filter cake affects the properties of the filtration process such as the volume of filtrate, the thickness of the filter cake, and the best method to remove it. Various models were used to determine the thickness and permeability of the filter cake. Most of these models assumed that the filter cake was homogeneous. The present study shows that the filter cake is not homogeneous, and consists of two layers of different properties. The objective of this study is to measure the filter-cake thickness and permeability of water-based drilling fluids by a new approach and compare the results with previous models. A high-pressure/high-temperature (HP/HT) filter press was used to perform the filtration process under static conditions (225°F and 300 psi). A computed-tomography (CT) scan was used to measure the thickness and porosity of the filter cake. Scanning electron microscopy (SEM) was used to provide the morphology of the filter cake. The results obtained from the CT scan showed that the filter cake was heterogeneous and contained two layers with different properties under static and dynamic conditions. Under static conditions, the layer close to the rock surface had a 0.06-in. thickness, 10- to 20-vol% porosity, and 0.087-pd permeability, while under dynamic conditions, this layer had a 0.04-in. thickness, 15-vol% porosity, and 0.068-pd permeability. The layer close to the drilling fluid had a 0.1-in. and 0.07-in. thickness under static and dynamic conditions, respectively, and it had zero porosity and permeability after 30 minutes under static and dynamic conditions. SEM results showed that the two layers contained large and small particles, but there was extremely poor sorting in the layer, that was close to the drilling fluid, which led to zero porosity in this layer. Previous models underestimated the thickness of the filter cake by almost 50%. A new method was developed to measure the thickness of the filter cake, and various models were screened to identify the best model that can predict our permeability measurements.

Pore blockage of organic fouling layer with highly heterogeneous structure in membrane filtration: Role of minor organic foulants

Abstract Foulants with low concentration in effluent are generally considered minor for determining resistance to membrane filtration. This study probed spatial distribution of proteins, nucleic acids and α- and β- d -glucopyranose polysaccharides in fouling layer using multiple staining technique and confocal laser scanning microscope (CLSM) imaging and clarify their individual contributions to the overall permeate flow resistance. In the present case, the β- d -glucopyranose polysaccharides occupied over 80% of the volume of the fouling layer and were the major foulant. The other three components (proteins, nucleic acids and α- d -glucopyranose polysaccharides) were minor foulants. The computational fluid dynamics calculations revealed that the β- d -glucopyranose polysaccharides contributed much greater to cake resistance than did the other three foulants; however, its contribution could only count 12–15% of the overall resistance of filter cake. Marked reduction in cake permeability is yielded by blockage of large pore in fouling layer by minor pollutants.

A multiscale theoretical model for fluid flow in cellular biological media

An integrated methodology is developed for the theoretical analysis of momentum transfer in cellular biological media, such as biofilms and tissues. First, the method of local spatial averaging via a weight function is used to establish the equations that describe momentum transfer at the cellular biological medium scale, starting with a continuum-based formulation of the process at finer spatial scales. The constitutive behavior of each constituent phase is postulated at the polymer- or cell-scale and, through the averaging procedure, appropriate constitutive relations are developed for the upscaled stress tensors and the fluid–structure interaction forces. Further, closure problems are developed for the theoretical calculation of the effective material properties that appear in the constitutive relations. The developed closure problem for the static hydraulic permeability tensor is solved using a finite element method in the context of a periodic spherocylinder-in-cell model, which accounts for salient geometric features of microbial aggregates and biofilms at the cell-scale. The degree of structural anisotropy resulting from the shape, orientation, and spatial arrangement of biological cells (from stack formation to nematic alignment), is examined and shown to affect strongly the permeability tensor. Very good agreement is observed with results from previous theoretical studies for sphere packings and experimental data for the hydraulic permeability of mycelial cakes.

Mechanistic study on carboxymethyl hydroxyethyl cellulose as fluid loss control additive in oil well cement

AbstractThe working mechanism of carboxymethyl hydroxyethyl cellulose (CMHEC, Mw 2.6 × 105 g/mol) as fluid loss control additive (FLA) for oil well cement was investigated. First, characteristic properties of CMHEC such as anionic charge amount, intrinsic viscosity in cement pore solution, and static filtration properties of cement slurries containing CMHEC were determined at 27°C and 70 bar. Effectiveness of the FLA was found to rely on reduction of cement filter cake permeability. Consequently, the working mechanism is ascribed to constriction of cement filter cake pores. Zeta potential measurements confirm that at low CMHEC dosages (0–0.3% by weight of cement, bwoc), adsorption of the polymer onto the surface of hydrating cement occurs. However, at dosages of 0.4% bwoc and higher, an associated polymer network is formed. This was evidenced by a strong increase in hydrodynamic diameter of solved CMHEC molecules, an exponential increase in viscosity and a noticeable reduction of surface tension. Thus, the working mechanism of CMHEC changes with dosage. At low dosages, adsorption presents the predominant mode of action, whereas above a threshold concentration of ∼ 10 g/L (the “overlapping concentration”), formation of associated polymer networks is responsible for effectiveness of CMHEC. Addition of anionic polyelectrolytes (e.g., sulfonated melamine formaldehyde polycondensate, Mw 2.0 × 105 g/mol) to cement slurries containing CMHEC greatly improves fluid loss control. Apparently, the presence of such polyelectrolytes causes the formation of colloidal associates from CMHEC to occur at lower dosages. Through this mechanism, effectiveness of CMHEC as cement fluid loss additive is enhanced. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The Effects of Filter-Cake Buildup and Time-Dependent Properties on the Stability of Inclined Wellbores

Summary The effects of filter-cake buildup and/or filter-cake-property variation with time on wellbore stability have been plaguing the industry. The increasing use of lost-circulation materials (LCMs) in recent years for wellbore strengthening in weak and/or depleted formations necessitates models that can predict these effects. However, the complexities of effective-stress and pore-pressure evolution around the borehole while drilling, coupled with the transient variation of mud-filtration properties, have delayed such modeling efforts. In this paper, the analytical solutions for the time-dependent effects of mudcake buildup and mudcake properties on the wellbore stresses and formation pore pressure, and thus the safe-drilling-mud-weight window, are derived. The transient effects of mudcake buildup and mudcake buildup coupled with its permeability reduction during filtration on the safe-drilling-mudweight window are illustrated through numerical examples. The results showed that the safe-mudweight windows were greatly affected by the buildup of filter cake and its permeability variation. For example, the analysis for filter-cake buildup with cake permeability of 10–2 md showed that the safe-mudweight window was widened by 0.5 g/cc after 2.5 hours post-excavation when compared to the case of a wellbore without mudcake. On the other hand, a lower mudcake permeability of 10–3 md widened the mudweight window by as much as 1 g/cc. Last but not least, the analyses revealed that even for mudcake permeability as low as 10–3 md, neglecting the permeable nature of the mudcake can result in overestimation of the safe-drilling-mudweight window.

Processing of concentrated aqueous fluorapatite suspensions by slip casting

In order to produce stable aqueous fluorapatite (FA) suspensions, its surface reactivity in an aqueous solution having two initial pH values with a concentration of ammonium polyacrylate (NH4PA) was investigated as a function of time. The rheological behaviour of concentrated aqueous FA slips stabilized with NH4PA was studied; besides, the effect of poly(vinyl)alcohol (PVA) addition on the relative viscosity of the suspensions was investigated. The influence of the slip rheology on the microstructure of the resultant green slip cast compacts and their sintering behaviour were determined. Upon the FA introduction in the aqueous solutions, an initial release of F anions located at the surface was found, which was not dependent on the pH and the presence of dispersant. The increase in the initial pH of the solution above 7 and/or the addition of NH4PA markedly reduced the Ca++/H+ exchange reaction rate. As a result, well-stabilized concentrated aqueous suspensions could be obtained at pH close to 9. The minimum viscosity of 40 vol.% slips at pH 8.9 occurred at 0.6 wt% of NH4PA added. The addition of 0.5 wt% PVA to a well-stabilized FA slip caused aggregation of particles by a depletion flocculation mechanism, thereby increasing the slip viscosity. The greater permeability of cakes produced from slips with high viscosity values (0.5 wt% PVA) increased the casting rate. The highest sintered densities were obtained for the compacts prepared from the slips without PVA, due to the denser particle packing achieved in the green bodies.

Modeling instantaneous pressure drop of pleated thin filter media during dust loading

In this paper, we present a modeling methodology for studying the effects of dust loading on the pressure drop across pleated filters. Our simulations demonstrate that there exists an optimum pleat count for clean filters at which pressure drop reaches a minimum regardless of the in-plane or through-plane orientation of the fibers. With the particle deposition included in the analysis, our results indicated that the rate of increase in pressure drop decreases with increase in the pleat count. We demonstrated that a higher pleat count results in a higher flow velocity inside the pleat channels causing more non-uniformity in the dust deposition across the pleat. Especially when particles are sufficiently large, the dust cake tends to form deeper inside the pleated channel when the pleat count is high. This effect is observed to be less pronounced when the pleats have a triangular shape. We also showed that if the dust cake permeability is higher than that of the filters fibrous media, the rate of increase in pressure drop does not always decrease with increase in the pleat count. Finally, by comparing filters having 15 pleats per inch, we observed that rectangular pleats are preferred over the triangular pleats when the particles are highly inertial, i.e., filtering high-speed large particles. When particle's inertia is small, our results indicate that triangular pleats cause less pressure drop, and so are recommended.

Analytical Model for Fracture Grouting in Sand

A conceptual, analytical model has been developed to describe the fracture grouting process in sand. The objective of the model is to improve understanding about this process in sand and to model propagation of the fractures. The results can be used to assess the parameters that control the fracture process. It is assumed that the complicated shape of a fracture in sand can be simplified to a geometrical shape (such as a tube or a plane) as a first approximation. Filtration of the grout appears to have a significant influence on the fracture shape when grout is injected into permeable subsoil such as sand. By assuming a pressure at which a fracture starts and a minimum pressure for propagation, it appeared possible to calculate the width-to-length ratio of the fracture independent of other soil properties. Quantification of the flow inside a fracture and the filtration processes resulted in a model that has been used to study differences in fracturing behavior in model tests and field tests on fracture grouting in sand. It was concluded that the width-to-length ratio of the fractures in a permeable soil decreases if the injection pressure of the grout or the permeability of the grout cake is decreased.

Dewatering of coal plant tailings: Flocculation followed by filtration

A sustainable alternative to tailings dam disposal of coal refuse is mechanical dewatering of tailings, which provides fast production of dry solids and water reuse. In this study, flocculation followed by filtration of coal plant tailings, a new concept in tailings dewatering is investigated in detail. This paper focuses on the effect of preconditioning tailings with varying flocculants and dosages on filtration kinetics and the resultant moisture content of the filter cake. The results show that the cationic flocculant, MAGNAFLOC LT 425, requires a high dosage to produce a low moisture content filter cake and clear filtrate. Optimal sized flocs were produced with the anionic flocculant, MAGNAFLOC 5250, even though the particles are negatively charged. The kinetics of the filtration was dependent on the composition of process water as indicated by supporting sedimentation tests. The concentration of divalent alkali earth metals such as Ca 2+ and Mg 2+ allow for large floc growth by a bridging mechanism, which involves binding of the polymer and the negativity charged particle. Filtration and settling curves at this dosage were also supported by filter cake analysis using Darcy plots. It was found that the large floc size significantly increases the permeability of the filter cake. Floc size measurements and fractal dimension showed that while the large flocs were produced with anionic flocculant, the flocs produced with the cationic flocculant were small and weak. The results indicate that the optimum dosage and flocculant type for effective and efficient filtration of coal plant tailings is approximately 350 g/t of anionic flocculant at a 35% solids content and 40 kPa filtration pressure.

The Porosity, Permeability and Restructuring of Heterogeneous Filter Cakes

AbstractThe constant pressure filtration characteristics of cellulose fibers, titania (rutile) and mixtures of the two were studied using an automated filtration apparatus. With filtrations at 450 kPa, the average permeability (kav) for pure fiber and rutile were approximately 3.2 × 10–17 and 1.3 × 10–16 m2, respectively, with the variation of kav with fiber fraction showing a maximum. Similar trends were observed at filtration pressures of 150 and 600 kPa. The porosities (ϵav) of filter cakes formed from pure fiber and rutile suspensions were approximately 0.75 and 0.6, respectively. Interparticle penetration and additive porosity models were applied to the porosity data, and the additive porosity model appeared to better represent the experimental data. Also, the results obtained suggest that abrupt transitions in cake structure occur part way through some filtrations, resulting in anomalous filtration behavior.

Agglomeration and filtration of colloidal suspensions with DVLO interactions in simulation and experiment

Cake filtration is a widely used solid–liquid separation process. However, the high flow resistance of the nanoporous filter cake lowers the efficiency of the process significantly. The structure and thus the permeability of the filter cakes depend on the compressive load acting on the particles, the particles size, and the agglomeration of the particles. The latter is determined by the particle charge and the ionic strength of the suspension, as described by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. In this paper, we propose a combined stochastic rotation dynamics (SRD) and molecular dynamics (MD) methodology to simulate the cake formation. The simulations give further insight into the dependency of the filter cakes’ structure on the agglomeration of the particles, which cannot be accessed experimentally. The permeability, as investigated with lattice Boltzmann (LB) simulations of flow through the discretized cake, depends on the particle size and porosity, and thus on the agglomeration of the particles. Our results agree qualitatively with experimental data obtained from colloidal boehmite suspensions.

A power-law model of electrostatic interactions of colloidal particles in cake layer on membrane surface

The permeability of cake on membrane surface is a crucial factor affecting the efficiency of low pressure membrane process. In this study, a power-law model was suggested for better understanding of the effect of solution chemistry on cake permeability. The model equation was derived from the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and the dimensional analysis of parameters affecting the chemical interactions of colloidal particles. Experimental results from unstirred filtration of submicron latex particles at various ionic strengths were used for model application. The permeate flux as well as specific cake resistance and cake porosity was sensitive to ionic strengths. Different behaviors of cake permeability were observed for non-aggregated and aggregated particles. The proposed model aids to interpret complicated relations of cake permeability in terms of the characteristic ratio, which is defined as the ratio of electrostatic repulsion to van der Waals attraction.

Parameters that influence the pressure filtration characteristics of bentonite grouts

The pressure filtration of grout, pressurised against fine sand, has been investigated in a laboratory set-up. The grout mixtures that were tested consisted of water and bentonite, together with cement, fly ash, silica flour and/or retarder. Samples were subjected to a pressure of 100–400 kPa. The permeability of the grout cake formed during pressure filtration was calculated from the results. It appears that the permeability of the grout can differ by more than three orders of magnitude, depending on the grout sample tested. Adding cement increases the permeability. The grain size of the material in the mixture had minimal influence. Mechanisms are discussed.

Experimental Study and Modeling of Freeze-Drying in Syringe Configuration. Part I: Freezing Step

This article concerns the experimental study and the modeling of the freezing step during freeze-drying of a model lyoprotectant formulation in syringe configuration. First, ice crystal morphology observations were carried out in a cold chamber equipped with stereomicroscopy to determine the ice crystal size distribution. We observed that the ice crystal morphology was homogeneous as a function of the radial position and that, contrary to our previous observations in glass vial configuration, no significant ice morphology differences existed between the bottom and the top of syringes. Thus, it seems that the gas cooling by free convection at the walls of the syringe during the freezing step led to higher homogeneity in the ice crystal morphology. These data allowed calculation of the mean ice crystal diameter (which was supposed to represent the mean porous diameter) and then the permeability of the freeze-dried cake. Moreover, a two-dimensional axisymmetric (2D) mathematical model in cylindrical geometry of the freezing step for aqueous sucrose solution was elaborated. It has been proved that this model was able to simulate quite precisely the whole temperature profiles during the freezing step, except the exothermic peak of nucleation. In the last part of this work on syringe geometry, the impact of annealing treatments on the freeze-dried matrix morphology was investigated. Some heterogeneity of sublimation rates was observed, with significant variation of residual humidity. Additionally, the water vapor mass transfer resistance values decreased if a convenient annealing treatment (shelf temperature at −10°C) was applied.

Lignite aided dewatering of digested sewage sludge

Mechanical dewatering is commonly used to increase the solids content of municipal sludge prior to its disposal. However, if the rate of filtration is slow, mechanical dewatering can be expensive. In this study, the use of lignite to improve the sludge dewatering is investigated. The effectiveness of lignite conditioning of polyelectrolyte-flocculated sludge is examined using mechanical compression tests. Results show that lignite conditioning in conjunction with polyelectrolyte flocculation gives much better dewatering than the polyelectrolyte flocculation alone. Using Darcy's filtration theory, the specific cake resistance and permeability of the compressed cakes are obtained. Both of these parameters are significantly improved after lignite conditioning. Mercury porosimetry tests on compressed cakes show that the porosity of the lignite-conditioned sludge cake is much higher than that of the polyelectrolyte-flocculated sludge and it increases with increasing doses of lignite. The mercury porosimetry results show that the lignite pore volume of pores greater than 0.5 μm are reduced with increasing sludge ratio indicating that sludge is trapped within these pores, whereas smaller pores are unaffected. The yield stress curves for sludge, lignite and sludge-lignite mixtures show that the sludge filter cake is very compressible, but the lignite-conditioned cake has a range of compressibility which although more than lignite indicate that the cake is relatively incompressible at low pressures. Thus, lignite conditioning acts to maintain the permeability of the filter cake during compression dewatering by resisting cake compression. This leads to a trade-off between the rate of dewatering and the solids content of the compressed cake. With lignite conditioning, the dewatering rate can be increased by a factor of five for the same degree of water removal.

Modelling the Effect of Particle Size in Microfiltration

Particle deposition at the filter surface in microfiltration is studied to better understand the effect of particle size on cake morphology and permeability reduction. Numerical simulations are carried out on a Hele Shaw cell which consists of a representative unit element of a two dimensional spatially periodic flat plate with pores. The particle concentration in the fluid is assumed to be low so that particles enter one by one into the computation domain. Particles follow the flow streamlines under creeping flow conditions from a random initial location until they are subjected to physico‐chemical interactions near the filter surface or a particle already deposited. The computational domain consists of two regions: a fluid region and a porous medium region, i.e. the particle cake. The flow over the two regions of the Hele Shaw cell is computed using the Darcy model, including the variations of the permeability field due to the cake formation. Results show that both the permeability and the filtration efficiency are affected significantly by particle size.