Filter Cake Layer Research Articles

Removal of Hematite Water-Based Filter Cake Using Hydrochloric Acid

The filter cake layer, which is essential to reduce the fluid invasion to the drilled formation, has been reported to be composed mainly of the weighting materials. The complete removal of this layer is recommended to restore the rock permeability. Hematite is one material that is used to create the filter cake. However, the cleanup of hematite-based filter cake has not been studied thoroughly. The objective of the work presented in this paper is to investigate the removal of hematite water-based filter cake using hydrochloric acid. Numerous solubility tests were conducted to study the different factors affecting the treatment of hematite such as temperature and particle size. Based on these results, the treatment duration and acid concentration were selected. The high-pressure high-temperature filtration cell was used to build the filter cake and to soak it in the treatment solution at 100°C. Even though the solubility is increasing with acid concentration, however, no significant improvement was noticed above 12.5 vol.% of HCl. The particle size distribution has a considerable effect on the treatment, and the solubility was found to be 86 wt.% for particles finer than 25 microns and 47 wt.% for particle sizes above 75 microns, all in 10 vol.% HCl. The temperature has a significant influence as the solubility doubled when the temperature increased from 75°C to 100°C. The solubility rate decreased with time and reached the maximum in 16 hours which has been taken as treatment duration. Using 12.5 vol.%, 91 wt.% of the filter cake was successfully removed. In the literature comprehensive study on the cleanup of hematite-based filter cakes is lacking. This research provides new insights into hematite removal and address the different factors that impact the treatment efficiency.

Simulation analysis of UF membrane filtration process based on magnetic field characteristics

Abstract Membrane fouling will affect the performance of the membrane, resulting in the increase of filtration cost and reduced membrane life. Magnetization technology has the advantages of being green, pollution-free and energy saving, and it has broad potential applications in water treatment. In this study, COMSOL Multiphysics realizes the coupling of magnetic field and flow field by adding the magnetic field force formula in the fluid module. The influence of magnetic field on fluid flow and inorganic pollutant distribution in an ultrafiltration (UF) membrane device were investigated. The simulation results show that the magnetic field improves the water flow velocity in the device to a certain extent, reduces the volume fraction of pollutant particles on the membrane surface, and then reduces the possibility of forming a thicker filter cake layer, which is beneficial to slow down membrane fouling and thus slow down the reduction rate of membrane flux. In addition, the simulation results were verified by the membrane specific flux experiment, and consistent conclusions were obtained.

Prevention of hematite settling using perlite in water-based drilling fluid

The stability of the weighting materials in the high-density water-based drilling fluid was remarked as a serious issue to be controlled. It can cause several problems including formation fracturing, circulation loss, well control issues, etc. The usage of an anti-sagging chemical as a drilling additive is one of the sagging mitigation methods. In this study, amorphous volcanic alumina silicate (perlite) was evaluated as an anti-sag additive for hematite water-based drilling fluid. Several experiments were conducted to assess the perlite efficiency including static and dynamic sag test, mud properties measurements such as filtration behavior, filter cake properties, rheological and viscoelastic behavior. The tests were conducted at elevated temperature (250 °F). Perlite concentration was varied from 0, 1, 2, 3, and 4 lb/bbl. The obtained results showed that the loaded perlite was able to improve the mud stability and eliminate the sagging under static and dynamic issues at an optimum concentration of 4 lb/bbl. In term of filtration properties, there was an obvious improvement that could be observed through the reduction of filtration volume with 50% and filter cake thickness. In addition, the perlite contacting drilling fluid was able to form a thin and dense filter cake layer. The filter cake porosity and permeability were decreased by 24% and 68%, respectively. The rheological and viscoelastic behaviors were improved as well by the addition of perlite.

Diatomite Dynamic Membrane Fouling Behaviour during Dewatering of Chlorella pyrenoidosa in Aquaculture Wastewater.

Combined microalgal and membrane filtration could effectively treat aquaculture wastewater; however, the membrane fouling induced by extracellular organic matter (EOM) during the dewatering process is an issue. This study investigated diatomite dynamic membrane (DDM) fouling behaviour during the dewatering of Chlorella pyrenoidosa under the influence of copper ions. The results indicate that copper ion heavy metals in aquaculture wastewater significantly affected purification and algae dewatering by DDM. Aquaculture wastewater with a high copper concentration (1 and 0.5 mg/L) could induce serious DDM fluxes and cake layer filtration resistance (Rc), whereas fewer filtration fluxes were induced when aquaculture wastewater had a low copper concentration, particularly that of 0.1 mg/L, at which the Rc was lowest and the concentration effect was highest. Macromolecular organics of EOM, such as biopolymers, polysaccharides, and proteins, were responsible for DDM fouling and accumulated mostly in the slime layer, whereas only a small amount of them accumulated in the diatomite layer. The DDM rejected more protein-like organics of EOM in the slime layer when dewatering algae at low copper concentrations (<0.1 mg/L); however, when using the DDM to dewater algae at high copper concentrations, more polysaccharides of EOM were rejected (0.5 < Cu2+ < 5 mg/L). This result has significant ramifications for aquaculture wastewater treatment as well as algae separation and concentration by the DDM.

Reduction of Breakdown Pressure by Filter Cake Removal Using Thermochemical Fluids and Solvents: Experimental and Numerical Studies.

The process of well cleanup involves the removal of an impermeable layer of filter cake from the face of the formation. The inefficient removal of the filter cake imposes difficulty on fracturing operations. Filter cake’s impermeable features increase the required pressure to fracture the formation. In this study, a novel method is introduced to reduce the required breakdown pressure to fracture the formation containing the water-based drilling fluid filter cake. The breakdown pressure was tested for five samples of similar properties using different solutions. A simulated borehole was drilled in the core samples. An impermeable filter cake using barite-weighted drilling fluid was built on the face of the drilled hole of each sample. The breakdown pressure for the virgin sample without damage (filter cake) was 6.9 MPa. The breakdown pressure increased to 26.7 MPa after the formation of an impermeable filter cake. Partial removal of filter cake by chelating agent reduced the breakdown pressure to 17.9 MPa. Complete dissolution of the filter cake with chelating agents resulted in the breakdown pressure approximately equivalent to the virgin rock breakdown pressure, i.e., 6.8 MPa. The combined thermochemical and chelating agent solution removed the filter cake and reduced the breakdown pressure to 3.8 MPa. Post-treatment analysis was carried out using nuclear magnetic resonance (NMR) and scratch test. NMR showed the pore size redistributions with good communication between different pores after the thermochemical removal of filter cake. At the same time, there was no communication between the different pores due to permeability impairment after filter cake formation. The diffusion coupling through NMR scans confirmed the higher interconnectivity between different pores systems after the combined thermochemical and chelating agent treatment. Compressive strength was measured from the scratch test, confirming that filter cake formation caused added strength to the rock that impacts the rock breakdown pressure. The average compressive strength of the original specimen was 44.5 MPa that increased to 73.5 MPa after the formation of filter cake. When the filter cake was partially removed, the strength was reduced to 61.7 MPa. Complete removal with chelating agents removed the extra strength that was added due to the filter cake presence. Thermochemical and chelating agents resulted in a significantly lower compressive strength of 25.3 MPa. A numerical model was created to observe the reduction in breakdown pressure due to the thermochemical treatment of the filter cake. The result presented in this study showed the engineering applications of thermochemical treatment for filter cake removal.

Effect of Different Weighting Agents on Drilling Fluids and Filter Cake Properties in Sandstone Formations.

Weighting agents such as barite, micromax, ilmenite, and hematite are commonly added to drilling fluids to produce high-density fluids that could be used to drill deep oil and gas wells. Increasing the drilling fluid density leads to highly conspicuous fluctuation in the drilling fluid characteristics. In this study, the variation in the drilling fluid’s rheological and filtration properties induced by adding different weighting agents was evaluated. For this purpose, several water-based drilling fluid samples were prepared and weighted up using the same concentration of various weighting materials including barite, micromax, ilmenite, and hematite. The characteristics of the used weighting agents’ (particle size distribution and mineralogy) were measured. Subsequently, the rheological properties of the drilling fluid were obtained using a Fann viscometer at 80 °F. The filtration test was carried out at 200 °F and 300 psi differential pressure to form a filter cake over the sandstone core samples. The properties of the formed filter cake layer such as thickness, porosity, and permeability were determined. Furthermore, the typical properties of core samples including porosity and permeability were assessed before and after the filtration test. The displayed results confirmed that the plastic viscosity (PV), yield point (YP), and filter cake sealing properties were all significantly influenced by the ratio of the large to fine particle size (D90/D10) of the weighting agents irrespective of the weighting material type. Among the examined weighting agents, barite showed novel potency to control both rheological and filter cake properties for 14 ppg drilling fluid. The results showed that D90/D10 is a key factor for the PV and YP properties as increasing the D90/D10 ratio caused PV increase and YP decrease, which indicated that the interaction among the loaded weighting materials in the drilling fluid dominated its viscosity.

Combined alginate-humic acid fouling mechanism and mitigation during microfiltration: Effect of alginate viscosity

In membrane-based water and wastewater treatment processes, understanding the interactive effect of various types of organic components on membrane fouling is crucial in order to identify effective fouling mitigation strategies. In this study, the effect of humic acid on alginate filtration was examined under both dead-end and crossflow constant flux microfiltration conditions using low viscosity and medium viscosity alginate as model foulants. The presence of humic acid (100 mg/L) appeared to accelerate alginate fouling under both dead-end and crossflow filtration conditions, following cake layer filtration mechanism (dead-end) and a combined intermittent pore blocking and cake layer filtration mechanism (crossflow) respectively. Under the crossflow filtration condition, the fouling mechanism of the alginate-humic acid mixture was dependent with the permeate flux and alginate nature, e.g., less pore blocking with more cake layer fouling were present at a higher permeate flux during filtration medium viscosity alginate-humic acid mixture. When intermittent relaxation was employed during crossflow filtration, the presence of humic acid could alleviate medium viscosity alginate fouling. This was attributed by a significant shift of irreversible fouling to reversible cake layer fouling, which was readily removed by shear force during relaxation. A comparison of membrane performance during intermittent filtration with periodical flushing using clean water, NaClO (5%), and persulfate (100 mg/L) at 50 °C indicates that high temperature clean water flushing was effective in maintaining membrane performance during filtrating alginate-humic acid complex, which majorly contributed to a reduction of reversible cake layer fouling.

Effect of PAC on the Behavior of Dynamic Membrane Bioreactor Filtration Layer Based on the Analysis of Mixed Liquid Properties and Model Fitting.

Recently, dynamic membrane bioreactor (DMBR) has gradually gained the interest of researchers for the development of membrane technology. In this paper, we set up parallel experiments to investigate the effect of powder activated carbon (PAC) on organic matter removal, transmembrane pressure, and filter cake layer characterization to make an overall performance assessment of DMBR. The results showed that DMBR has a good removal effect on organic matter removal, and with a chemical oxygen demand removal rate over 85%. Protein was found to be the main membrane fouling substance. Due to the electric double-layer effect, membrane fouling tended to be alleviated when the PN/PS value was low. Using a filtration model under constant current conditions, the filtration process through the cake layer was observed to be consistent with cake-intermediate model.

Anaerobic offsite Fe2+ releasing for electrocoagulation in ABMBR: Membrane fouling mitigation, nutrients removal and anodes protection

To solve the problems of pollutants removal and membrane fouling in membrane bioreactor (MBR) and plate passivation in the process of electrocoagulation (EC), anaerobic baffled membrane bioreactor (ABMBR, 4 cells for anaerobic process and 1 cell for membrane separation) was proposed for anaerobic offsite release of Fe2+ in the process of EC. The iron plates were placed in the anaerobic unit and the membrane module was placed outside the electric field. The results showed that the operation time could be extended from 5 to 8 days to 63 days when 3 V intermittent voltage (5 min on and 5 min off) was adapted. As the result of EC, protein and polysaccharide contents of soluble microbial products (SMP) and extracellular polymeric substances (EPS) from sludge and filter cake layer were decreased obviously. The sludge particle size was increased from 400 nm to 80 μm and zeta potential was decreased from −11 mV to −20 mV. The water quality results showed that almost 100 % of ammonia nitrogen (NH4+-N) and 87 % of total phosphorus (TP) were removed under the action of EC without excess sludge discharge. By placing the iron plate in the anaerobic unit, plate passivation was very slow during 195 days of operation, which solved the problem of plate passivation in EC.

Contribution to head loss by partial penetration and well completion: implications for dewatering and artificial recharge wells

A wide variety of well drilling techniques and well completion methods is used in the installation of dewatering and artificial recharge wells for the purpose of construction dewatering. The selection of the optimal well type is always a trade-off between the overall costs of well completion and development, the optimal well hydraulics of the well itself, the hydraulic impact of the well on its surroundings, and the required operational life span of the well. The present study provides an analytical framework that can be used by dewatering and drilling companies to quantify the contribution to head loss of typical dewatering and artificial-recharge well configurations. The analysis shows that the placement of partially penetrating wells in high-permeability layers could promote the use of quick and cheap installation of naturally developed wells using jetting or straight-flush rotary drilling. In high-permeability layers, such wells can be favorable over wells completed with filter pack, which require extensive well development to remove the fines from the filter cake layer. The amount of total head loss during discharge/recharge at a volumetric rate of 20 m3/h per meter of filter length, into or from a gravely aquifer layer, is reduced by factors of 3–4 while using naturally developed well types instead of well types completed with a filter pack that contains a filter cake layer due to borehole smearing.

Novel metal mesh filter using water-based regeneration for small-scale biomass boilers

Particulate matter emissions are a key issue of modern biomass boilers. A novel gas cleaning method using a metal mesh filter combined with water-based cleaning was developed and tested. The filter was tested batch-wise. Flue gas of a commercial 50-kW boiler was filtered until a pressure drop of 2000 Pa was reached. Afterwards, the filter was regenerated. The initial prototype used ultrasound in order to remove the filter cake from the filter candles. Regeneration was complete and, even after boiler malfunctions producing tar, the filter cake could still be removed. Given the good results, a second cleaning mode, flushing the filter candles with water, was tested. The results were as good as with ultrasonic cleaning. Peak mass collection efficiency was very high with 98 ± 2% (burning wood pellets). However, directly after cleaning, the first layer of filter cake has to be developed. In this initial phase, collection efficiency is low. Service time until maximum pressure drop was reached depended on the gas velocity. Using pellets as fuel, at a gas velocity of 66.6 m/h, 12-h service time was reached and 4.1 g dust was collected per square meter filter surface, while at 33.3 m/h, service time increased to 55 h and collected dust to 13.9 g/m2. Using low-quality wood chips, the raw gas dust loading was much higher but also the maximum loading of the filter was higher with 13.3 to 28.9 g dust separated per square meter. Still, the service time decreased to 3.4 respective 38 h. Peak collection efficiency increased to 99.5 ± 0.8%. The overall collection efficiency including the buildup of the filter cake depends on the gas velocity and fuel. It ranges from 74 ± 4 to 91 ± 1%. The feasibility of the filter concept could be proven, and further development towards a commercial application is in progress. Metal mesh filters with countercurrent cleaning showed a high potential given their simple and robust design, as well as high collection efficiency.

Experimental and statistical investigation of drilling fluid loss in porous media: Part 2 (Fractures)

Drilling fluid loss and mud filtration occur concurrently during overbalanced drilling. Characterization of fluid loss is mostly done via experimental studies with several types of setups and porous media. The first part of this study has been conducted on pore-scale homogenous and heterogenous media. Sequel to the study, this paper presents fracture-scale characterization of drilling fluid loss using experimental and statistical methods. The statistical methods that were used in this study include: experiment design, hypothesis testing, analysis of variance (ANOVA), and multiple linear regression analysis. Dynamic fluid loss experiments were conducted with a setup capable of simulating drillpipe rotation inside thick-walled cylindrical fracture slots that represents natural fractures.The results show that temperature, fracture size and orientation, and type/concentration of lost circulation material (LCM) are the critical factors that influences dynamic fluid loss in fractures. The results from testing the filter cake stability showed that the filter cake layer ruptured on three of the experiments out of the nine that were conducted. For the experimental conditions with the vertical fractures, the regression analysis showed that dynamic fluid loss can be predicted from changes in LCM concentration and fracture width with a considerably high R2 and adjusted R2 values. The R2 value is a parameter that is used to quantify the predictability of an empirical model. The effect of fracture positioning and orientation was also observed and recorded. The originality in this experimental method is the application of thick-walled cylindrical fracture slots (simulating natural fractures) to characterize dynamic drilling fluid loss. Temperature, drillpipe rotation, and pressure conditions were programed to simulate dynamic wellbore conditions under which fluid loss, filter cake evolution, and plastering occur. The methods used in this study can be employed in mud design for wellbore strengthening application and selection of operating conditions.

Reducing Membrane Fouling from Micro-Flocculation in a Humic Acid Ultrafiltration Process

This study investigated the influence of different floc morphologies produced by micro-flocculation process on filtration of a self-constructed polyvinylidene fluoride (PVDF) ultrafiltration membrane. Aluminum sulfate was used as a flocculant and humic acid (HA) and kaolin as raw water. Both the properties of flocs formed during the micro-flocculation process (floc size and distribution, fractal dimension) and the effects of floc formation on membrane flux under different conditions were investigated. The surface morphology of the contaminated membrane was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and adhesion between the PVDF membrane and organic pollutants was measured to analyze the membrane fouling mechanism. Results showed that the main mechanism during a micro-flocculation process using Al3+ as a flocculant is electrical neutralization to remove organic matter. With an increase in flocculant dosage, floc size increased and the fractal dimension of flocs decreased. The attenuation rate of membrane flux was negatively correlated with floc size. The larger the floc, the lower the membrane flux attenuation rate, and the looser the filter cake layer formed during the ultrafiltration process. Comparatively, membrane fouling caused by flocs with smaller fractal dimension was lighter, and the membrane flux recovery rate was also higher. The interaction force between PVDF and organic matter was positively correlated with the corresponding membrane flux attenuation rate during the initial stage of operation. When dosage of Al3+ was 5 mg·L-1 and initial pH was 7, the HA removal rate was 96.7%, the membrane flux attenuation rate was lowest, and the flux recovery rate reached 88%.

Guidelines to define the critical injection flow rate to avoid formation damage during slurry injection into high permeability sandstone

In a slurry injection application, the goal is to inject high solid content fluids (up to 25%). To accomplish this without plugging the near-wellbore pore space, the fracture is created using a pad of clean fluid. Once the fracture is open, the slurry is introduced to the formation. In some cases, where the formation has a high permeability-thickness product (k × H), a high injection flow rate is needed to open up the fracture with clean fluids. Most disposal wells do not have large enough pumps to provide high enough flow rates in these circumstances.A combination of a lack of geomechanical understanding combined with poor injection or facility design leads some operators to create high formation damage around the wellbores in slurry injection applications by injecting slurry at flow rates which are insufficient to open fractures. When solids-laden fluid slurries are injected under a matrix flow regime, suspended solids will plug the near-wellbore pore throats and will form a filter cake layer at the formation face, causing the injection pressure to gradually increase. At the point where the injection pressure exceeds the formation fracture pressure, the formation will finally fracture. However, the near-wellbore filter cake remains a factor in future injection and leakoff characteristics. Moreover, the damage causes injection pressure to build up rapidly, facilitating the creation of short fractures which tend to cause near-wellbore stresses to increase more rapidly for a given amount of solid deposition than is the case with longer fractures.Case studies have been presented in this paper which evaluates such slurry injection wells. Based on the data analyzed in this study, inducing the fracture with solids-laden slurry rather than with clean fluid by causes the injection pressure to continuously increase, ultimately leading to significantly reduced formation capacity. Recommendations are presented as well for how to avoid this condition even if the pumps do not have the capacity to provide the required injection flow rate using clean fluid. One such solution is to add a viscosifier to the clean pad fluid to raise the fluid viscosity which enables the creation of a hydraulic fracture at lower flow rate.

Presence of Fe-Al binary oxide adsorbent cake layer in ceramic membrane filtration and their impact for removal of HA and BSA

To enhance the removal of natural organic matter (NOM) in ceramic (Ce) membrane filtration, an iron-aluminum binary oxide (FAO) was applied to the ceramic membrane surface as the adsorbent cake layer, and it was compared with heated aluminum oxide (HAO) for the evaluation of the control of NOM. Both the HAO and FAO adsorbent cake layers efficiently removed the NOM regardless of NOM's hydrophobic/hydrophilic characteristics, and the dissolved organic carbon (DOC) removal in NOM for FAO was 1–1.12 times greater than that for HAO, which means FAO was more efficient in the removal of DOC in NOM. FAO (0.03 μm), which is smaller in size than HAO (0.4 μm), had greater flux reduction than HAO. The flux reduction increased as the filtration proceeded because most of the organic foulants (colloid/particles and soluble NOM) were captured by the adsorbent cake layer, which caused fouling between the membrane surface and the adsorbent cake layer. However, no chemically irreversible fouling was observed on the Ce membrane at the end of the FAO adsorbent cake layer filtration. This means that a stable adsorbent cake layer by FAO formed on the Ce membrane, and that the reduced pure water flux of the Ce membrane, resulting from the NOM fouling, can easily be recovered through physicochemical cleaning.

Description and Regulation of Drilling Completion Fluid Cake Structure

In the process of oil and gas well drilling and completion, under the action of positive pressure gradient or self-absorption, drilling and completion fluid solid phase particles block the reservoir pore and form the filter cake. The filter cake plays a vital role in reservoir protection, and is closely related to the oil and gas well productivity from cake formation to remove. The filter cake is always expected to be thin, tough, with low permeability and easy to remove. Many scholars made a lot of research from the filter cake layer structure, space truss structure, pore structure and the structure of fractal structure of filter cake. However, the researches on the structure of the filter cake are mainly conducted qualitatively at home and abroad, while the quantitative research progress is slow. At the same time, the research on the relationship between the filter cake structure and its performance is also relatively weak. In recent years, with the wide application of horizontal wells, it has called widespread attention on how to effectively remove filter cake in order to improve the oil and gas well production capacity at home and abroad. The widely-used filter cake removal technology mainly includes natural clear, mechanical removal, chemical removal and biological removal technology currently. Among them, the biological removal technology is developed in recent years as a new type of filter cake removal technology. With the further development of mud cake removal technology and downhole filter cake removing circumstance with increasing complexity, a single filter cake removal technology cannot completely meet the requirements. The filter cake removal technology is developing in the direction of the composite to clear, in order to obtain ideal filter cake removal effect.

Fluorescent natural organic matter responsible for ultrafiltration membrane fouling: Fate, contributions and fouling mechanisms

Membrane fouling has been a main obstacle to the success of ultrafiltration (UF) technology. Recently, fluorescent natural organic matter (FNOM), including humic-like substances (HS) and protein-like substances, has been recognized as substances responsible for membrane fouling. In this study, the matrix of FNOM in natural river water was substantially modified by combined coagulation and powdered activated carbon adsorption to enhance the diversity of the FNOM matrix. Fluorescence excitation emission matrix spectroscopy was employed to characterize FNOM components during the UF process. The correlations between FNOM components of the feedwater and membrane fouling were evaluated for the initial period and long-term operation. Reliable correlations of the maximum fluorescence intensity of HS with initial membrane fouling indicated that HS were major foulants in the initial period. Furthermore, the protein-like component exhibited significant correlation with the concentration effect fouling (R2 = 0.6131) and with irreversible fouling (R2 = 0.8711). We found that the fouling mechanism changed from pore obstruction to a protein concentration polarization layer followed by protein cake layer filtration. Total fouling of the UF membrane over long-term operation was alleviated with powdered activated carbon (PAC) adsorption; however, the mitigation of irreversible fouling was dependent on whether PAC adsorbed protein-like substances.

Study on the structure of filter cake layer of water based drilling fluid

Study on the structure of filter cake layer of water based drilling fluid

The removal of typical pollutants in secondary effluent by the combined process of powdered activated carbon–ultrafiltration

This paper focused on the effects of powdered activated carbon (PAC) dosage on ultrafiltration (UF) membrane flux caused by natural organic matter (NOM). Three model foulants, humic acid (HA), bovine serum albumin (BSA) and sodium alginate (SA), were adopted to represent different NOM fractions in secondary effluent treated by the combined process of PAC-UF. Moreover, the membrane fouling resistance and fouling mechanism were also analyzed. The results indicated that the best PAC dosage for the membrane flux variation was 20 mg/L for HA and SA, and 10 mg/L for BSA. SA caused the most serious membrane fouling, which was mainly reversible fouling. The membrane fouling caused by HA and BSA was mainly irreversible membrane fouling. The membrane fouling caused by organics happened mainly at the initial stage of filtration. Because the filter cake layer formed by a moderate amount of PAC could intercept organics, the membrane fouling, especially the irreversible fouling, could be reduced.

Functional composites based on refractories produced by pressure slip casting

The present study investigates the sequential pressure filtration of two filter cake layers with a maximum grain size of 3mm and 1mm, respectively, using a water soluble additive system consisting of xanthan and guar gum. The pressure slip casting of the resulting composites was optimized with a factorial experimental design. The best combination was a lower filtration pressure for the first filter cake layer and a higher filtration pressure for the second one. Furthermore, a shorter filtration time of the first filter cake layer together with the application of a filter aid of a xanthan/guar gum solution resulted in an easy demolding of crack-free graded composites with an excellent bonding. The results of the full factorial experimental design were verified by X-ray computed tomography. The demonstrated pressure slip casting of graded refractories offers the possibility to produce functional composites with tailored compositions, microstructure and thus functionality.