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Pressure filtration provides an opportunity for dewatering coal refuse sufficiently to reduce or possibly eliminate the need for a slurry impoundment. In this study, pressure filtration was performed in a lab-scale unit to evaluate the dewatering nature of coal refuse slurry, which was obtained from a coal preparation facility. Evaluation of the process was performed using a fractional factorial design with cake moisture as the response and pressure, pH, and solids concentration as the variables of interest. Results indicated a decrease in cake moisture with increase in solids concentration and pressure, and an increase in cake moisture with pH. With pH playing a significant role in dewatering coal refuse slurry, zeta potential measurements were performed at different pH values to confirm the likeliness of agglomeration at lower pH. Filtrate flux values from the current test matrix were compared with the flux values of a bench-scale pressure filter, and a logarithmic relationship between the filtrate fluxes of the two units was developed. Results also indicated that for lower values of filtrate flux, the flux per discharge port remained constant during the scale-up from bench-scale to lab-scale units. [ABSTRACT FROM AUTHOR]

Water removal in colloidal processing is a tough and crucial problem because deformation and cracking of the wet body easily happen during the drying process. Inspired by conventional pressure filtration (PF), we combined spontaneous coagulation casting (SCC) with PF to partially remove water from the gelled sample before drying for the purpose of lessening the risk of cracking and shortening the drying period. The effect of pressure, holding time, and solid loading on the particle packing ratio of wet samples, the drying process, and the bulk density and homogeneity of green and sintered bodies was surveyed systemically. The PF process of 0.4 MPa for 2 h was optimized based on dewatering ratio from ceramic slurries. The particle packing ratio of the pressure-filtrated samples increased with the solid loading of ceramic slurries, and 61 vol% was obtained for the slurry with 56 vol% solid loading. The drying time of the pressure-filtrated samples was shortened by as much as 42%–53% compared with that of the gelled samples, and the linear shrinkage for the pressure-filtrated samples during drying was only approximately 0.5%, much smaller than that of the gelled samples (2.4%–4.6%). Furthermore, the bulk density of the pressure-filtrated green bodies was more than 2% higher than that of the gelled green bodies, and more homogeneous green bodies were obtained by PF than by SCC. The alumina ceramic with 98.8% relative density and a homogenous density distribution was obtained after being sintered at 1550 °C for 2 h. [ABSTRACT FROM AUTHOR]

Laboratory testing was conducted to evaluate the performance of a plate-and-frame filter press and solid-bowl centrifuge for dewatering a bituminous coal refuse slurry. Filter press testing was conducted using a pilot-scale Technicas Hidraulicas (TH) filter press, which contains a single set of plates. The unit is also equipped with an air-blow system to remove additional moisture from the filter cake voids. Testing was conducted to evaluate the effects of filter time on filtrate flow and solids content, cake moisture, solids recovery, and unit capacity. Product moistures ranged from 27.3% to 29.6%. Filtrate solids contents were less than 0.6% with solids recoveries over 98%. The unit capacities ranged from 73 kg/hr/m2 to 131 kg/hr/m2, with the lower values corresponding to the lower cake moistures. Centrifuge testing was conducted using a Sharples P660 solid-bowl centrifuge. Testing was conducted at several slurry feed rates at one dam setting with another test at a second dam setting. Product moistures ranged from 24.2% to 36.4%. Centrate solids ranged from 0.5% to 11.0% with solids recoveries from 65.2% to 98.4%. The solids feed rates ranged from 89 kg/hr to 338 kg/hr. Lower product moistures were associated with higher solids feed rates but at lower solids recoveries. [ABSTRACT FROM AUTHOR]

Abstract: A number of interesting and potentially useful regularities have been observed in high pressure batch filtration of fine and colloidal suspensions carried out to equilibrium under a wide variety of physical and chemical process conditions. Two such regularities are described here. The first regular behavior, demonstrated by a large number of colloidal suspensions, can be represented by the Pareto profile, which relates filtration rate with solid content of filter cake at equilibrium. The profile is found to be a strong function of material fineness but is seemingly independent of physical and chemical process conditions. Since it can be treated as a constrained performance benchmark for the filtration of a suspension, it is germane for evaluating the filtration process in terms of two of its more important process measures, namely, kinetics and maximum extent of dewatering that is achievable. The Pareto regularity reflects the fact that in general it is not feasible to improve both measures simultaneously in a batch filtration which is driven to equilibrium, and any process modification may improve one measure but invariably at the expense of the other. The second regular behavior, namely, self-similarity in pressure filtration is demonstrated for filtration of wide variety of varying materials and process conditions. Simple transformation and scaling of slurry filtration data with critical solid volume fraction and critical time at the transition from cake formation stage to cake consolidation stage translate the filtration curves into a form which are remarkably self-similar. This self-preserving behavior is demonstrated for a wide variety of experimental data under varying physical and chemical process conditions for different colloidal systems. Some implications of the regularities are discussed. [Copyright &y& Elsevier]

Solid inclusions in liquid metal have been a main concern for metallurgical industries. Pressure filtration or preconcentration techniques have been the main methods of measuring solid inclusion contents. The concentrations, however, are usually reported in terms of inclusion area in the filter cake per unit filtrate weight. This unit (mm2 kg-1) is not helpful because the 'real' inclusion concentrations are still not known. To date, therefore, no effective scientific method has been used to calculate solid inclusion concentrations. Through the derivations of general equations, inclusion concentrations in liquid metal can be calculated now from volume (area) fraction of the solid inclusions in filter cakes. In addition, the concentrations expressed in inclusion area in filter cakes per unit filtrate weight (mm2 kg-1) can also be converted to volume concentrations or other forms. Typical examples to calculate or to convert solid inclusion concentrations are demonstrated in the work. [ABSTRACT FROM AUTHOR]

This paper reports on progress towards the first continuous application of electrical impedance tomography to a production scale industrial process. It includes the design and implementation of the worlds first certified intrinsically safe electrical tomography system. Zener barrier (ZB) modules and intrinsically safe relays provide electrical isolation and the instrument is certified for operation in a Zone 0 environment. Two systems have been operating successfully on production pressure filters for two years. A sensor architecture has been implemented that is compliant with the process such that it is not detrimental to efficiency or the integrity of the associated vessel structure. The MATLAB-based EIDORS three-dimensional software toolkit has been employed to yield images from simulated data. To overcome problems that arise due to dramatic changes in the conductivity of materials in the vessel during the process, a new approach is introduced that proposes the use of dynamic sensitivity maps that evolve during the batch based on the predicted mean conductivity at each stage. Real data present challenges due to a number of factors, notably the ZB modules that are integral to the intrinsically safe instrumentation. However, a simple approach to data processing has yielded process relevant information using real tomographic data. [ABSTRACT FROM PUBLISHER]

Sludge dewatering is a key element in sludge's processing and management. Solid-phase separation, sludge volume reduction and the separation of a high-quality supernatant are the main tasks of the dewatering devices. The effectiveness of this task, in turn, results from the selection of the dewatering method and conditioning of the sludge before dewatering. The aim of the research was to determine the influence of conditioning substances (polyelectrolyte, fly ash and zeolite) on the efficiency of dewatering at variable filtration pressure. The use of polyelectrolyte in sludge conditioning was a solution that increased the efficiency of the filtration process. On the contrary, the use of structure-forming substances (fly ash and zeolite) slows the process but reduces the hydration of the filter cake. The same trends were obtained in dual conditioning combining dosing of polyelectrolyte and ash or zeolite. It was also shown that the dewatering efficiency of conditioned sludge with these two different substances (ash and zeolite) was the same. The use of zeolite in independent or dual conditioning was important for the quality of the supernatant. [ABSTRACT FROM AUTHOR]

In this study, batch electrocoagulation (EC) experiments were performed with synthetic mining water in various conditions in a laboratory-scale 1L reactor. The process was scaled up and the selected results were verified with both synthetic and real mining water in a 70 L reactor. The generated solids were characterized by XRD, SEM, and a laser diffraction particle size analyzer. After preconcentration by settling and decantation, the EC solids were separated by constant pressure filtration at 2–6 bar. In order to improve the separation, various filter aids were used in body-feed and precoat modes. The results show that the overall removal efficiency was the highest with consumable electrode pairs such as Fe/Fe, Al/Al and Fe/Al, and the highest treatment efficiency was achieved with Fe/Al electrodes where 100/100% of the nitrate and 96/87% of the sulfate were removed in small/large-scale experiments. Depending on the dissolved electrode material, different solid species were formed: crystalline primary particles with a minor degree of agglomeration were observed in Fe/Fe slurry, whereas aluminium-containing solids (Al/Al and Fe/Al) were mainly amorphous agglomerates. High values of average specific cake resistances (α av = 2·1012 - 4·1013), average porosities (>90%) and moisture contents (>68 wt%) of filter cakes were obtained for all filtered samples. The highest values of the above-mentioned cake characteristics were observed for aluminium-based solids, which might be explained by its highly amorphous structure. The application of filter aids improved the filterability of the sludges by reducing the average specific cake resistance by as much as 95–96% in the body-feed mode and by 84% in the precoat mode. Image 1 • The highest overall removal efficiencies were obtained with the Fe/Al electrodes. • Removal in 70 L & 1 L reactors: 96 & 100% (NO 3 −) and 87 & 100% (SO 4 2−). • The type of produced solids, crystalline or amorphous, depended on the electrodes. • Filter cakes had high specific resistances (α av), porosities and moisture contents. • The use of filter aids reduced α av by up to 95% (precoat) and 84% (body feed). [ABSTRACT FROM AUTHOR]