PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE *

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.     

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE*

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.

     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370-450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Filter Press for Electrodewatering of Waterworks Sludge

An electrodewatering filter press was designed and its performance was evaluated for basic operating parameters such as the electric field strength, time of electric field application, and changes in pressure. Dewatering efficiency improves with the increase of the electric field strength, application time, and pressure. Considering the operating costs due to energy consumption and electrode erosion, the optimal conditions were found to be: 70 V/cm of electric field strength, 30 min of application time, and 588 kPa of pressure. The rate of electrodewatering doubled compared with that of mechanical dewatering (MDW) while the water content of the dewatered cake decreased by 25%. When an electric field is applied to the cake, clogging of the filter cloth becomes minimized due to electrophoretic mobility. The discharge of water from the cake porous matrix is facilitated owing to electroosmosis and the thermal effect due to joule heating. As a result, the dewatering capacity of electrodewatering improves compared with the mechanical dewatering. The energy consumption of electrodewatering was about 370–450 kWh/t (dry solid), which accounts for only one tenth of the existing sludge treatment costs.     

Influence of conductivity on the electro-dewatering of sewage sludge under constant voltage

In this work, the influences of sewage sludge conductivity on the electro-dewatering (EOD) effect and energy consumption under constant voltage were evaluated. The results showed that on adding NaCl solution to the sludge, the average water content in 20 min decreased with the increasing electric current. However, the energy consumption increased with increasing conductivity. Decreasing the sludge conductivity by deionized water washing had little impact on the average water content. However, the energy consumption decreased with the reduction of electric current. To sum up, increasing the conductivity can help shorten the EOD time, but decreasing the conductivity can lower the energy consumption of EOD.     

Improvement of sludge electrodewatering by anode flushing

An improvement of the sludge electrodewatering process is proposed: anode flushing by filtrate recirculation. According to this technique, the mixture of filtrates obtained at cathode and anode sides is used for continuous flushing of the anode chamber of the filter press during electrodewatering. Anode flushing aims to eliminate essential problems of electrodewatering: ohmic heating, rise of electric energy consumption, electrode corrosion, and filtrate contamination. This is attained by better control of the filtrate pH, the filter cake temperature, and the dryness at the anode side, where the physicochemical conditions are most aggressive. The efficiency of the proposed technique is evaluated at lab scale on drilling sludge electrodewatering with and without anode flushing. In experiments without anode flushing, increasing electric current density caused strong increase of anode temperature, desiccation of the filter cake at the anode side, rise of voltage, and significant alkaline contamination of filtrate. The application of anode flushing allowed controlling the electric field strength and temperature. Thus, the dewatering of the sludge has been extended at high electric field without damaging the filter equipment by drastic heating. Furthermore, it reduced filtrate contamination by neutralization of the electrolysis products.     

立式压滤机在4A沸石分离工序上的试验

利用立式自动压滤机对4A沸石晶化料浆和合格料浆进行了一系列分离洗涤和风干试验,试验结果表明,该设备的洗涤效果不明显,不能用该设备对4A沸石晶化滤饼进行直接洗涤;但是其滤饼水分可以降到15%以下,故可以用在晶化料浆和合格料浆的分离与风干工序上,能大大降低搅洗工序的洗涤水耗和烘干工序的能耗。     

Analyses of Compressible Suspensions for an Effective Filtration and Deliquoring

Cake filtration is frequently used in the industry to remove the majority of liquid from a suspension before the solids are dried in a thermal dryer. As the amount of liquid removed in the filtration step is an order of magnitude greater than the liquid removed during thermal drying, a slight improvement in the cake dryness from a filter can greatly reduce the duty and energy cost of the dryers. The most challenging issue in cake filtration is when a compressible material is encountered. High cake compressibility will not only slow down the filtration process, but also cause high moisture content in the final cake. Instead of pumping pressure, mechanical expression is the best deliquoring method when dealing with highly compressible cakes. Therefore, it is important for industrial users to recognize the degree of compressibility of the material being treated. In this work, a simple method is developed to estimate the cake compressibility from a single filtration run. This method provides a practical tool for engineers to understand the compressibility nature of the cake and select the right filtration/deliquoring strategy.     

Analyses of Compressible Suspensions for an Effective Filtration and Deliquoring

Cake filtration is frequently used in the industry to remove the majority of liquid from a suspension before the solids are dried in a thermal dryer. As the amount of liquid removed in the filtration step is an order of magnitude greater than the liquid removed during thermal drying, a slight improvement in the cake dryness from a filter can greatly reduce the duty and energy cost of the dryers. The most challenging issue in cake filtration is when a compressible material is encountered. High cake compressibility will not only slow down the filtration process, but also cause high moisture content in the final cake. Instead of pumping pressure, mechanical expression is the best deliquoring method when dealing with highly compressible cakes. Therefore, it is important for industrial users to recognize the degree of compressibility of the material being treated. In this work, a simple method is developed to estimate the cake compressibility from a single filtration run. This method provides a practical tool for engineers to understand the compressibility nature of the cake and select the right filtration/deliquoring strategy.     

The influence of temporal cake moisture content on a discontinuous washing process in the centrifugal field

In solid/liquid separation processes, filter cake washing is an essential step in improving the quality of particulate products by elimination of impurities. During cake washing and dewatering, the cake saturation changes depending on the flow conditions and it cannot always be measured and controlled accurately. This article deals with investigations on the influence of the initial and temporal cake saturation on washing PVC and silica sand particles in the centrifugal field. It was found, that high initial saturation levels and high maximum saturations during the washing process had a positive impact in inducing a high hydrostatic pressure for advective flow and enabling a homogeneous distribution of the wash water inside the cake. This was achieved by increasing the wash water flux and/or decreasing the g‐factor. A good method to obtain low final impurity quantity is the combination of washing at a low g‐factor and dewatering at a high one. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Calcium‐Ion Removal from Peat by a Mechanical Filter Cake Washing Process

This contribution aims to bridge two different fields of science, viz., geoecology and mechanical process engineering. The study reports on the application of mechanical washing processes especially filter cake washing, on calcium‐ion removal from peat, which is a natural material that is used in different fields of application such as agriculture, medicine, cosmetics, etc. The interesting properties of peat such as its porous structure and the sorption behavior influence the distribution of liquid inside the bulk and the liquid flow behavior through the porous structure. Experimental results are obtained from filtration tests using differential gas pressure in a filter nutsche. The washing efficiency is determined for different pressures and specific amounts of applied wash liquor. It is found that the water repellent phenomena that occurs when peat has been dried, affects the washing efficiency in a very negative way. The results obtained are compared to the conventional filter cake washing process.     

Experimental Study on the Loading Characteristics of Needlefelt Filters with Micrometer-Sized Monodisperse Aerosols

In this work, three types of needlefelt filters, made of Polyester (PE), Ryton Sulfar (RS), and Polyaramid (PA), were tested to in- vestigate the aerosol loading characteristics of fabric filters when challenged with micrometer-sized monodisperse potassium sodium tartrate (PST) particles. A fibrous filter with packing density of 9%, thickness of 0.38 mm, and fiber diameter of 5.1 θ m was included for comparison. A vibrating orifice monodisperse aerosol generator was used to produce three different sizes (5, 10, and 20 θ m) of PST particles for aerosol loading experiment. An ultrasonic atomizing nozzle and a TSI constant output nebulizer were used to generate polydisperse PST particles for the aerosol penetration test. The aerosol penetration of submicrometer-sized particles through the filters was measured by using a Scanning Mobility Particle Sizer. An Aerodynamic Particle Sizer was used to measure the penetration fraction of aerosol particles larger than 0.8 θ m. The pressure drop across the filter was monitored by using pressure transducers, which were calibrated against an inclined manometer. Airflows of 5, 10 , 20, and 30 cm/s were used to study the flow dependency. The aerosol penetration results showed that the particles larger than 3 θ m did not penetrate the clean fabric filters tested in the present study. The loading curves (plots of pressure drop against sampling time) displayed three regions: an initial region of fast increase, a transition region, and a final linear region after the dust formation point. After the formation point of the dust cake, both fabric and fibrous filters shared the same slope (of the loading curves). The slope of different regions of the loading curves was determined by many factors, such as size of challenge aerosol, face found to be critical to the performance of the fabric filters. In order lower porosity, which caused an extra rise in pressure drop across velocity, surface treatment, and the compressibility of the dust cake forming on the filter. The method of final surface treatment was to avoid the unnecessary rise in air resistance, the melting clumps formed during final surface treatment should be as thin and narrow as possible, just enough to support the filter bag cleaning. From the standpoint of filter quality and energy consumption, the low filtration velocity has to be adopted whenever possible, because high filtration velocity not only led to lower filter quality (in particular for submicrometer-sized particles) but also created dust cake of lower porosity, which caused an extra rise in pressure drop across thet dust cake.     

阴极滤布对活性污泥电渗透脱水的影响(英文)

The mechanical dewatering of activated sludge is troublesome due to its high compressibility of solids. The dewatering can be enhanced dramatically by the use of electroosmosis,in which an electric field is applied to the sludge cake.In this study,the influence of filter cloth on the cathode on the dewatering of activated sludge was investigated.It was found that thicker filter cloth led to lower water removal from the sludge cake,so a stainless steel cathode net with small pore size instead of filter cloth was applied,which improves the dewatering efficiency and reduces the electric power consumption.Moreover,water absorbent materials were helpful to remove the water from the sludge cake.For the electroosmotic dewatering at 7 kPa and 24 V·cm-1,the water content in the sludge cake decreased to 60%(by mass) with the average 0.075 kW·h·kg-1of water removed by using the cathode net.     

Constant Rate Expressing of Juice from Biological Tissue Enhanced by Pulsed Electric Field

Abstract

Pulsed electric field (PEF) is an innovative technology, which can be successfully combined with solid/liquid expressing of juice from biological materials. The fresh juicy plants contain the juice in closed cells. The application of PEF ensures the electropermeabilization of cellular membranes, which facilitates the expulsion of liquid from the interior of cells. This article describes the influence of PEF on the kinetics of juice extraction from the layer of sugar beet particles expressed at a constant rate. Experimental study was carried out using a laboratory filter-press cell connected to a PEF treatment system. The PEF was applied by two different modes: as a pretreatment operation before pressing and as a treatment during pressing. The application of PEF to nonpressurized cake leads to increase of energy consumption and higher applied voltage. The PEF treatment of excessively pressurized cakes enhances the juice yield; however, the expressing of juice is significantly delayed. The best result is obtained when the sugar beet tissue is treated with PEF at 1.5–5 bars. The influence of PEF parameters on the juice yield was also studied. The intensity of PEF was varied from 0 to 1000 V/cm and the number of pulses was varied between 0 and 1000. It was established that the optimal parameters of PEF after the cake pressurization at 5 bar were in the next range: intensity of PEF E = 500 V/cm and duration of PEF application 0.03–0.05 s.     

Constant Rate Expressing of Juice from Biological Tissue Enhanced by Pulsed Electric Field

Pulsed electric field (PEF) is an innovative technology, which can be successfully combined with solid/liquid expressing of juice from biological materials. The fresh juicy plants contain the juice in closed cells. The application of PEF ensures the electropermeabilization of cellular membranes, which facilitates the expulsion of liquid from the interior of cells. This article describes the influence of PEF on the kinetics of juice extraction from the layer of sugar beet particles expressed at a constant rate. Experimental study was carried out using a laboratory filter-press cell connected to a PEF treatment system. The PEF was applied by two different modes: as a pretreatment operation before pressing and as a treatment during pressing. The application of PEF to nonpressurized cake leads to increase of energy consumption and higher applied voltage. The PEF treatment of excessively pressurized cakes enhances the juice yield; however, the expressing of juice is significantly delayed. The best result is obtained when the sugar beet tissue is treated with PEF at 1.5-5 bars. The influence of PEF parameters on the juice yield was also studied. The intensity of PEF was varied from 0 to 1000 V/cm and the number of pulses was varied between 0 and 1000. It was established that the optimal parameters of PEF after the cake pressurization at 5 bar were in the next range: intensity of PEF E = 500 V/cm and duration of PEF application 0.03-0.05 s.     

Cake filter scale-up, simulation and data acquisition—A new approach

This paper details a unique, automated filtration apparatus and the newly developed Filter Design Software (FDS) which facilitates equipment selection, scale-up and simulation through an integrated experimental and theoretical approach.By way of example, experimental data were obtained with the apparatus over constant, variable and stepped pressure regimes. Inherent suspension properties were maintained throughout by utilising a computer-controlled pressure regulator and cake formation was monitored by micro-pressure transducers capable of providing up to seven independent measures of liquid pressure within 3.3 mm of the filter medium surface. For constant pressure and moderately compressible talc cakes the liquid pressure increased with cake height in a non-linear manner and generally exhibited a concave profile. When a pressure step was applied following a period of constant pressure filtration, the cake structure typically required up to 30 s to reach a new pseudo-equilibrium state. During this time the reciprocal filtrate flow rate vs. filtrate volume plot was non-linear and the liquid pressures in the cake increased rapidly before remaining nearly constant. When the cake was thicker or the pressure step larger, the liquid pressure measured closer to the filter medium remained either constant following the increase in pressure or increased slowly over the 360 s duration of the pressure step which indicates potential difficulties with the stepped pressure test.The filtration data were analysed using FDS to obtain scale-up coefficients and the impact of using incorrect scale-up coefficients on likely filter performance at the process scale is shown. The simulation capabilities of FDS are also highlighted through a case study in which, by way of example, the influence of crystal formation and other operating parameters on the filter cycle for a pharmaceutical product are shown. Simulations quantify how crystal form can detrimentally influence all phases of a cycle and lead to, for instance, slower filtration and wetter filter cakes.     

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.     

Wiederbefeuchtung bei der Pressfiltration

During press filtration, the filter cake experiences a plastic deformation. However, a filter cake expansion may occur once the pressing forces are released, which is confirmed by experiments with an aqueous coal suspension. Rewetting of the cake occurs when a liquid film is present during cake swelling, which deteriorates the cake dryness significantly. However, this can be prevented when the liquid film is successfully removed, and lower pressures suffice for mechanical cake drying.