Clean Filter Research Articles

Polymer-based filter cleans water and recovers oil

In the USA, an engineering professor at the University of Pittsburgh has developed a technique for separating oil from water.

Measurement and prediction of filtration efficiency evolution of soot loaded diesel particulate filters

We here present laboratory based experimental and theoretical methods to characterize the filtration efficiency (FE) behavior of diesel particulate filters (DPFs) exposed to soot laden gas streams. Sensitivity of the FE behavior on filter microstructure and geometry properties have been studied, along with the impact of the hydrodynamic and aerosol flow conditions (flow rate, temperature, aerosol characteristics). Evolution of FE with soot load is reported from clean filter FE to maximum efficiency (100%), as the deposited soot in the filter wall itself acts as the filtering medium. The theoretical model considers different mechanisms (Brownian diffusion, particle interception and inertia) of soot capture and their impact on number based and mass based FE. The predictions from the theoretical model are in good agreement with experimental observations over a broad range of filter microstructure. Sensitivity of FE evolution on bare and coated filters has been reported, along with the impact of ash loading of the filters. Methods presented here are useful in determining the performance of DPFs under well-defined laboratory conditions and their extension to dynamic field conditions. These are also useful in determining filter properties for obtaining high FE and low pressure drop.

Catalytic Activity in Naphthalene Reforming of Two Types of Catalytic Filters for Hot Gas Cleaning of Biomass-Derived Syngas

The catalytic activity in the reforming of naphthalene of two different types of catalytic filter candles for biomass-derived syngas cleaning are presented and compared at superficial velocities of 72 and 90 m/h, respectively. The tests were performed in a laboratory setup on a fixed catalyst bed and small sections of full size candles. In a 50 h long-term test of the first candle type of fixed bed design, complete naphthalene conversion was found at 800 °C, 100 ppmv H2S, and an average superficial velocity of 135 m/h for the integrated Ni catalyst. Doubling the naphthalene concentration from 5 to 10 g/Nm3 has also led to complete conversion in a short-term test at a superficial velocity of 90 m/h. Because of easier manufacturing of the second candle type, several candles of a catalytic layer design were prepared by using different MgO-containing support materials and adjusting NiO loadings between 35 and 194 wt %. As compared to previous work, a conversion increase from 58 to 74% was achieved at 800 °C, ...

Evaluation of gas-liquid separation performance of natural gas filters

Fibrous filters are often used to remove contaminants including both dusts and liquid droplets from natural gas. This paper aims to evaluate the gas-liquid separation performance of three types of cartridge filters used in the West-East natural gas transmission project. The comparison of the original pressure drop of clean filters and the evolution of pressure drop as liquid droplets deposited in the filter media are described. The original pressure drops of these filters were similar but the pressure drops at a steady state were different. Fractional efficiency was used to study the separation performance of cartridge filters. Droplets at the outlet of the filters had small diameters, no more than 3 µm, but were very numerous. The effect of filtration velocity on gas-liquid separation performance was analyzed. Higher filtration velocity indicated better gas-liquid separation performance. Finally the quality factor related to pressure drop and filtration efficiency was applied to evaluate the gas-liquid separation performance.

Ultrasound assisted cleaning of ceramic capillary filter

Research in the fields of filtration and dewatering connected with the use of ultrasound (US) has been carried out mainly with small laboratory-scale batch or continuously operating devices. So far the only large scale industrial cake filtration applications have been developed and manufactured by Larox Oyj for mining industry. These applications apply ultrasound for cleaning of ceramic capillary action elements having at maximum total filtration area of approximately 150 m 2. Several hundreds of filter units have been delivered worldwide during the past two decades.

Clogging modeling in pleated filters for gas filtration

A model of clogging of a pleated filter in gas filtration is presented. The model is obtained by combining a semi-analytical model of the flow in a pleated filter and an empirical model of clogging of the planar filter medium applied locally along the pleated filter channels. The model takes into account the formation of a filtration cake of variable thickness at the porous wall of the pleated filter entrance channels and the resulting evolution of the entrance channels aperture distribution during the filtration/clogging process. Based on the numerical predictions, two main clogging scenarios are identified and analyzed. The optimum pleat density, defined as the pleat density maximizing the filter capacity, is determined and shown to be greater than the pleat density minimizing the pressure drop for a clean filter. Predictions of the evolution of overall pressure drop across the pleated filter due to clogging are compared with experimental data.

Research on fine coal classified flotation process and key technology

In an attempt to resolve the problem of poor clean coal quality and low ash content of tailing in the mixed flotation technology, factors affecting flotation performance were studied by orthogonal experiments, sieve analysis, progressive release flotation test and statistical methods. The classification flotation technology based on 0.125mm as the classification size was introduced, in which the key technology was the application of classification cyclone to separate the flotation feed. The 0.125-0mm fine coal slime was processed by innovative cyclone micro-bubble flotation column and clean coal filter press, while the 0.5–0.125mm coarse coal slimes were dealt with flotation machines and disc vacuum filters. The research results show that a decrease of 1.12% in the ash content of flotation clean coal and an increase of 9.51% in the ash content of flotation tailing coincide with the application of the classification flotation technology. Meanwhile, the corresponding clean coal recovery increases by 2.61%.

Removal of CaCO 3 scales on a filter membrane using plasma discharge in water

In modern wastewater treatment, filters are routinely used for removing unwanted particles from water. The present study investigated if a pulsed spark discharge in water can be used to remove deposits from the filter membrane for its potential application in drinking and industrial water treatment. The test setup included a circulating water loop and a pulsed power system. The present experiments used artificially hardened water with hardness of 1000 mg/L of CaCO 3 made from a mixture of calcium chloride (CaCl 2) and sodium carbonate (Na 2CO 3) in order to produce calcium carbonate deposits on the filter membrane. Spark discharge in water was found to produce strong shockwaves in water, and the efficiency of the spark discharge in cleaning filter surface was evaluated by measuring the pressure drop across the filter over time. Results showed that the pressure drop could be reduced to the value corresponding to the initial clean state and after that the filter could be maintained at the initial state almost indefinitely, confirming the validity of the present concept of pulsed spark discharge in water to clean dirty filter.

Performance enhancement with powdered activated carbon (PAC) addition in a membrane bioreactor (MBR) treating distillery effluent

This work investigated the effect of powdered activated carbon (PAC) addition on the operation of a membrane bioreactor (MBR) treating sugarcane molasses based distillery wastewater (spentwash). The 8 L reactor was equipped with a submerged 30 μm nylon mesh filter with 0.05 m 2 filtration area. Detailed characterization of the commercial wood charcoal based PAC was performed before using it in the MBR. The MBR was operated over 200 days at organic loading rates (OLRs) varying from 4.2 to 6.9 kg m −3 d −1. PAC addition controlled the reactor foaming during start up and enhanced the critical flux by around 23%; it also prolonged the duration between filter cleaning. Operation at higher loading rates was possible and for a given OLR, the chemical oxygen demand (COD) removal was higher with PAC addition. However, biodegradation in the reactor was limited and the high molecular weight compounds were not affected by PAC supplementation. The functional groups on PAC appear to interact with the polysaccharide portion of the sludge, which may reduce its propensity to interact with the nylon mesh.

On-Line Monitoring of Nitrate and Nitrite by UV Spectrophotometry in a SBR Process Used for the Treatment of Industrial Wastewaters

The objective is the adaptation of an existing UV spectrophotometer for the on-line monitoring of nitrate, nitrite and soluble COD during cycles of SBRs. An on-line filtering system was also developed in order to provide particle-free fluids to the sensor. The modified UV-spectrophotometer sensor (called "STAC") was implemented into a pilot-scale bioreactor at INRA-Narbonne, treating a semi-synthetic dairy wastewater. After a calibration and validation steps, results obtained during five months have shown that the on-line spectrophotometer sensor was able to efficiently monitor on-line nitrate, nitrite in SBR content. Ranges of detection were between 0 to 40 mg/L for nitrate and 0 to 18 mg/L for nitrite, with an accuracy of about 10 %. The on-line estimation of soluble COD was less efficient. The major drawback was the time-consumption for the cleaning of the homemade on-line filter.

Adaptive Neuro-Fuzzy Modeling of Head Loss in Iron Removal with Rapid Sand Filtration

Breakthrough and terminal head loss are the main parameters that determine the performance of rapid sand filters. Carman-Kozeny and Ergun equations can be applied to estimate head loss, but can only be applied to clean filter beds. Elaborated models are needed to predict head loss in dirty filters. In this study, a neuro-fuzzy modeling approach was proposed to estimate head loss in dirty filters. Hydraulic loading rate, influent iron concentration, bed porosity, and operating time were selected as input variables. Various types of membership functions were tried. Two rule-base generation methods--subtractive clustering and grid partition--were used for a first-order, Sugeno-type inference system. Using 11 rules and the grid-partition method, an optimum rule base set was developed and the lowest root mean squared error (RMSE) was obtained. Tap and deionized waters were used to obtain testing RMSE values of 1.094 and 0.926, respectively. The fit between experimental results and model outputs was excellent, with the multiple correlation coefficient (R2) greater than 0.99. Based on these findings, the authors conclude that neuro-fuzzy modeling may successfully be used to predict filter head loss.

Modelling gas flow pressure gradients in gelcast ceramic foam diesel particulate filters

New mathematical models are proposed that predict fluid flow pressure gradients in gelcast ceramic foam diesel exhaust particulate filters by considering the foam structure conceptually as serially connected orifices. The resulting multiple orifice mathematical (MOM) model is based on the sum of a viscous term derived from an extended Ergun model and the kinetic energy loss derived from the Bernoulli and conservation of mass equations. The MOM model was calibrated using experimental data obtained from measuring the air flowrate and pressure drop across a physical large-scale three-dimensional model of a cellular foam structure produced using rapid manufacturing techniques. The calibrated model was then validated using fluid flow data obtained from gelcast ceramic foam filters of various cell sizes and was found to require no empirical recalibration for each gelcast ceramic foam sample. The MOM model for clean filters was extended to predict pressure gradients of filters loaded with particulate matter (PM). The prediction of pressure gradients through gelcast ceramic filters using the MOM model for clean and PM-loaded cases was shown to be in reasonable agreement with experimental data. The models were finally applied to design a filter for a turbocharged, charge-cooled, 2.0l, four-stroke, common rail, direct injection passenger car diesel engine.

Investigation on pressure drop evolution of fibrous filter operating in aerodynamic slip regime under continuous loading of sub-micron aerosols

The aim of this study is to experimentally investigate pressure drop and filtration efficiency of fibrous filters operating in aerodynamic slip regime under continuous loading of sub-micron aerosols. Test aerosol is sodium chloride (NaCl) particulates with electrical mobility diameter (EMD) ranging from 41 to 514 nm generated from atomization. Two types of non-woven filters composed of fibers with diameter 1.8 μm (micro-fibrous) and 300 nm (nano-fibrous) are tested. Most penetrating particle size (MPPS) of clean micro- and nano-fibrous filters are 203 and 103 nm EMD, respectively. Both of them have clean filter filtration efficiencies closely agree with Payet's model. Under continuous aerosol loading, MPPS of both types of filters shift to smaller size. A semi-empirical model is developed to describe pressure drop across a fibrous filter operating in aerodynamic slip regime under continuous loading of sub-micron aerosols. Experimental results of filters with thickness ranging from 1 × 10 −5 to 1 × 10 −4 m generally agree with this model. It shows the potential of extending the model to describe pressure drop across aerosol-loaded filter of increased thickness with non-uniform particle deposition across filter depth being taken into account. Although clean micro- and nano-fibrous filters have comparable pressure drop while nano- offers higher filtration efficiency against sub-micron aerosols, which may suggest it as an “absolutely better” filter, experimental results show that the mass holding capacity of nano-fibrous filter is lower than its micro-fibrous counterpart. Hence, it is essential to analyze loading behavior through quantitative model during filter design stage.

Modeling particle fate in ventilation system—Part I: Model development

Aerosol particles are regarded as one of the most significant pollutants in the indoor environment. These particles can travel through ventilation systems, thus impacting indoor air pollution. Accurate modeling and prediction of aerosol particle transport in ventilation systems is therefore a key component of indoor particle pollution. Since recycled air takes particles into the ventilation system again, it can be challenging to calculate the particle concentration in each part of the system. This study theoretically and experimentally proves that the entire ventilation system, including filters, ventilation ducts and ventilation rooms, can be regarded as a serial of filters in steady-state cases. We call this the particle filter group model. Equations are presented to calculate the particle concentration in each component of normal kinds of mechanical ventilation systems. With this model, the particle concentration and deposited particle quantity in each part of the ventilation system can be easily calculated. This model may help to control indoor particle pollution and guide the cleaning of ventilation ducts and filters.

Optimization of Nozzle Design for Pulse Cleaning of Ceramic Filter

The experimental study was carried out to optimize the nozzle shape and dimension for the pulse cleaning of a ceramic filter candle. A bench scale unit of ceramic filter consisting of four commercial filter elements was used to measure the traces of the transient pressure around the nozzle and the overpressure in the filter cavity during the pulse-jet injection of pulse gas. Overpressure in the filter cavity is related to the pulse cleaning force. Nozzle design is concerned to increase the overpressure at the open end of filter element of pulse cleaning inlet, as well as to minimize the consumption of pulse gas. Convergent nozzle induces more secondary flow and generates higher pulse cleaning effect than straight nozzle. Nozzles of different convergent ratio (ratio of outlet to inlet diameter of nozzle) by changing the convergent angle and height were tested. The outlet diameter of convergent nozzle seriously influences the cleaning effect. The optimum convergent ratio increases with the increase of pulse gas pressure. The nozzle position (distance of nozzle tip from the open end of filter inlet) is also important to decide the nozzle dimension. Nozzle of large outlet diameter accepts high pressure of pulse gas to provide large overpressure in the filter cavity of top position by applying long distance.

Catching the sludge with a centrifugal Filterpump

Have you ever wondered where the ideas for specific technologies come from? Inspiration can be found in surprising places. Jim Hosford of Rotorflush Filters provides the inside story of how a big problem on his dairy farm – a clogged centrifugal pump – led him to design a self cleaning filter unit for a range of submersible pumps.

Concepts of Filter Cleaning Mechanism from the position of the demonstration of short-and long-range contaminant capture forces

The work examines mechanism of filtration process extended on basis of forces classification under filtration as short-range and long-range. The article shows, that the well-known sedimentation-loss conception which corresponds to the field of short-range forces is limited. Basic positions of a new accumulation-disconnection conception correspond to the field of long-range forces, for example magnetic forces.

Modeling of Sediment Transport through Stormwater Gravel Filters over Their Lifespan

Gravel filter media are widely used for attenuation and treatment of runoff in a range of stormwater management systems, including infiltration trenches/basins, porous pavements, and soakaways. These systems essentially reduce the effective impervious area of a catchment and also provide stormwater detention and infiltration into the surrounding soils, thus helping to restore predevelopment hydrology. Although it is well-known that these systems eventually clog and their treatment performance diminishes with time, no model developed has so far been developed to predict this behavior. The aim of this study was to develop a mathematical model of the transport of sediment through stormwater gravel filters over their lifespan. A detailed laboratory study of sediment transport was undertaken for different stormwater inflow regimes until the system became clogged. These data were used to test two models, the k-C* model (the first-order decay model) and the Yao model (a physically based model). Although these models were able to predict sediment behavior in clean filters (i.e., at the start of their life), both failed to accurately simulate observed behavior once the filter accumulated sediment. The main variables that impact the sediment process in dirty filters were quantified, and modifications to the Yao model were proposed. The modified model, with three calibration parameters, was calibrated for concentrations of total suspended solids. This model could be used in practice to asses the maintenance requirements of a gravel filter. Although developed for stormwater management, the model could be applied to a number of other disciplines, such as water treatment and groundwater recharge.

Distribution and efficacy of pyrethrin aerosol to control Tribolium confusum (Coleoptera: Tenebrionidae) in food storage facilities

A field test was conducted whereby adult Tribolium confusum (du Val), the confused flour beetle, were exposed in Petri dishes lined with filter paper and containing 0–2000 mg of flour, to a pyrethrin–CO 2 aerosol inside an empty warehouse. Applications were made according to label directions, and beetles were exposed to the aerosol for 2 h. After exposure, knockdown was assessed, and beetles were held for 2 weeks either in the same Petri dishes in which they were exposed or transferred with the flour to new Petri dishes lined with clean filter paper. Resident insect populations inside the test warehouse and outside were assessed through the use of pheromone traps. Virtually all beetles were knocked down at the time of removal from the exposure environment. Recovery from knockdown, or survival, increased with the presence of flour, and varied depending on the position of the exposure dishes inside the warehouse. Survival was also greater for beetles transferred along with the exposed flour to new Petri dishes lined with unexposed filter paper, compared to beetles that were held with the flour and the Petri dish that was exposed to the aerosol. Inside the warehouse, Plodia interpunctella (Hübner), the Indian meal moth, and Trogoderma variabile Ballion, the warehouse beetle, were the major species collected in pheromone traps. Large numbers of T. variabile were captured outside the warehouse, but their numbers declined during the study, while captures of P. interpunctella outside remained relatively constant. The intermittent aerosol treatments did not seem to affect these resident populations.

Fabrication of glassy ceramic membrane filters for filtration of spring water with clogging phenomena

Ceramic membrane filters consisting of a filtration layer of varying thickness coated on a tubular porous support made of quartz-based materials and with a pore size of about 10 μm were fabricated. The filtration performance for spring water clarity was examined. The coatings were prepared by a filtration process with a dilute particle suspension of quartz-natural zeolite–lead borosilicate glass mixture. The filter matrix was of quartz type and the additives (frit glass and zeolite) made the filters with glassy pore walls as the sintering temperature applied was above their fusion temperature. The pores of the filtration layer have a relatively coarse size distribution and thus lead to clogging phenomena within the glassy pores during filtration operation. The pore clogging is a benefit for producing clear filtrate and the glassy pore walls favour the filter cleaning and recovery. It was observed that a sufficiently thick coating (>62 μm) was required for good enough filtrate clarity (0.2 NTU turbidity) and cleaning of the filter was possible by filtrate backflushing and air blowing.