Optimal design of multi-stage porous plate collection system

The main objective of this study was to investigate the optimal design parameters of a multi-stage porous plate system, numerically and experimentally. Characteristics of pressure drop and collection efficiency are analyzed with the operation parameters such as the stage number, plate interval, hole diameter and system inlet velocity, etc. In the results, pressure drops of a 5 stage system [2, 2, 3, 2, 2mm] at v_s,in=1.0, 1.2 m/s are shown as 296, 428 mmH₂O by the numerical simulation and 259, 399 mmH₂O in the experiment. For 5 stage [2, 2, 3, 2, 2 mm] and v_s,in=1.0 m/s, the overall collection efficiencies with the plate interval 4, 10, 15 mm are estimated as 99.5, 96.0, 92.8% computationally and 97.9, 89.2, 85.3%, showing slightly lower efficiency compared to the numerical results due to the particle rescattering effect, experimentally.     

Performance characteristics of air intake pleated panel filters for internal combustion engines in a two-stage configuration

Previous numerical studies that have used computational fluid dynamics (CFD) and experimental software to address the effects of the geometric parameters of pleats on the pressure drop and air flow rate through a fibrous filter are analyzed. The analysis establishes that using a test dust with gradually smaller particle sizes (10, 5, and 1?μm) results in a more intense increase in the filter pressure drop, thus decreasing the service life of the filter. The benefits of using a multicyclone as the first stage of air filtration are discussed. Selecting the air filter by determining the active surface of the filter medium A_c based on the allowable filtration rate is not sufficient; to select the filter medium of a motor vehicle air filter, the dust mass retained per unit of filtration area (mass loading of dust k_m) must be known for a specific allowable pressure drop Δp_fdop. New methods and conditions for determining the mass loading of dust k_m for filter paper and non-woven fabric in single-stage and two-stage filtration systems are presented. The characteristics of the separation efficiency and filtration performance as well as the pressure drop of a filter set comprising a single cyclone and a filter element with a specific filter medium surface are determined. The effects of the particle size distribution of the dust in the air downstream of the cyclone on the mass loading of dust k_m of the filter paper and non-woven fabric in a two-stage filtration system are presented. The mileage of a truck fitted with a single-stage or two-stage filtration system in a “multicyclone–panel filter” configuration is estimated based on the calculated mass loading of dust k_m of the filter paper and non-woven fabric.

© 2018 American Association for Aerosol Research     

Assessment of surface and depth filters by filter quality

This paper reviews the concept of filter quality (q_F) for dust filtration media composed of different structures: metal fiber beds (MFB), fabric filters (BF), and fly ash filters (FAF). Filter quality is a useful index of the filtration performance, which incorporates both pressure drop and filtration efficiency. Major parameters affecting the filter quality are filtration velocity in the range of 0.06-0.19 m/s, dust loading, porosity of the medium in the range of 75-93%, and internal structure of the medium. The experimental observation showed that filter quality decreased with increasing filtration velocity or dust concentration. A unique increase in filter quality during the initial stage of filtration appeared with the FAF as a result of the predominately surface filtration with less pore clogging. Nevertheless, the filter quality cannot be taken as an absolute indicator of filter performance, but rather it should be used just as a reference parameter depending on operating conditions. The results of this work show that fly ash filters are capable of providing more stable performance, particularly during the initial stage of filtration, and thereafter of a certain time filter quality initiates to decline as other filters.     

Granular-bed filtration assisted by filter cake formation 3. Penetration of filter cakes by a monodisperse aerosol

For several types of granular solids (sands, silicon carbide and copper shot), penetrations have been measured for a monodisperse aerosol (1.1 μm Dow microspheres) passing through fly ash deposited upon horizontal surfaces of the solids. Fractional penetrations can run as low as 10⁻⁵. Pressure drop data for dust cake/granular medium combinations are also given. The data illustrate significance of dust autohesivitiy and dust/granular solid adhesivity for granular-bed filtration assisted by dust cake formation.     

气固并流式轴向移动床过滤器的压降特性

通过冷模实验,改变移动床表观气速、颗粒循环速率、入口气体含尘浓度等操作参数,研究了轴向移动床过滤器的压降特性和合适的操作条件,结合移动床内气固两相运动特点,修正了Ergun公式,在加尘条件下分析了床内滤饼对压降稳定性的影响。结果表明,在无尘负荷条件下(“纯”移动床操作),颗粒的循环速率由0增至2.26 kg/(m2?s)时,设备的压降减小0.03 kPa。表观气速为0.126 m/s、入口气体含尘浓度为89.10 g/m3时,移动床内滤饼形成和破损呈动态平衡,过滤500 s后,压降可稳定在0.88 kPa,此时设备具有较高的除尘性能,粉尘捕集效率可达96%以上。     

The reduction of pressure drop due to dust loading in a conventional cyclone

Experiments have been conducted to examine the effect of dust loading on pressure drop in a conventional cyclone. The presence of dust in the air stream reduced the cyclone pressure drop by as much as 30%, even at extremely low concentrations, such as 0.2 g/m³. In the range of 1.5–50 g/m³, the pressure drop ratio (the ratio of the pressure drop of dusty air to that of pure air with the same inlet velocity) was independent of dust concentration, and kept nearly constant; but it decreased as the concentration increased above 50g/m³. It was observed that the presence of dust reduced the tangential velocity. However the radii of a cross section of the cyclone, where the pressures are equal to those of the entrance and the exit, did not change noticeably. Calculating the pressure drop by integrating the term due to centrifugal force is also examined.     

A study on the characteristics of improvement in filtration performance by dust precharging

A hybrid dust-collector combining electrostatic charging with fabric filtration was developed and its performance characteristics were evaluated. Charged particles build porous dendritic structure on the filter surface by electrostatic attraction, increasing the collection efficiency of dust particles and reducing the pressure drop through the deposited dust layer and filter media. The cleaning performance of the dust layer is improved because the dendritic structured dust layer may be removed more easily by pulse jet cleaning flow. The results of the experiment showed a reduction of fine particle emission by 37% and 13% energy saving by precharging dust particles before filtration.     

A lab-scale study on the humidity conditioning of flue gas for improving fabric filter performance

A centrifugal separator was constructed to examine the effect of flue gas humidity on the adhesional force between fabric and collected dust. A lab-scale fabric filter sampling system (FFSS) was also manufactured by using a piece of flat fabric as a sample of bag material. In addition, an automatic control system for gas humidity was devised and installed in the FFSS, and, then, the following effects were studied: (i) the influence of gas humidity on the adhesional force between fabric and dust particles; (ii) the influence of gas humidity on the performance of fabric filter in terms of pressure drop, ΔP, dust removal efficiency, η, and specific cake resistance, K′₂; (iii) the variations in the composite-performance indices with gas humidity; and (iv) the influence of gas humidity on cleaning of dust-cake in terms of effective residual pressure drop. The main objectives were to determine the minimum and maximum values for the gas humidity range and to find the appropriate conditions for dust cleaning in terms of the critical value of effective residual pressure drop.     

Novel low pressure drop and easy regeneration ceramic whisker membrane for submicron particulate matter filtration

Aiming to efficiently remove submicron particulate matter (PM), a low pressure drop ceramic whisker membrane was prepared via precursor solution dip coating followed by high temperature firing. Aluminum nitrate 9-Hydrate and boric acid were used as the precursors for the formation of aluminum borate. A highly porous film comprising interconnected single phase 9Al₂O₃·2B₂O₃ whiskers of high aspect ratio, was successfully formed on an alumina support. Flue gas filtration tests indicated that as-fabricated ceramic whisker membrane exhibited outstanding filtration performance. More than 95 % PM in 0.3–1 µm was removed by using the as-prepared ceramic whisker membrane, and the pressure drop after three rounds of back blow regeneration remained stably at approximate only 1.3 times of the air pressure drop. This work provided a feasible approach to the preparation of a novel ceramic membrane with low pressure drop, and a novel strategy for high efficiency removal of submicron PM.     

Compression,Permeation and Flow Behavior of Wet Nanoparticle Cakes,in situ Tested with a Press‐Shear Cell

A new test apparatus for in situ simulation of the expression operation and rheological testing of compressed cake was developed to combine the compression‐permeability cell with a high‐performance ring shear tester. The yield loci for water‐saturated titania (d_S = 200 nm) are measured. These flow parameters can be used to determine in situ the shear strength and compressive strength of a consolidated cake after the pressure filtration steps. The permeability of the compressed cake is characterized by the conventional filter cake resistance versus particle pressure and, for comparison, by an averaged pore size.     

Particle size effect on the filtration drag of fly ash from a coal power plant

In order to investigate the filtration properties of fly ash from a conventional coal power plant, the filtration drag across the dust cake over an absolute fiberglass filter element was measured. A fluidized bed column was utilized to obtain a well characterized particle stream. The cake resistance coefficient was analyzed by the equation proposed by Endo et al. [1998] in order to observe the effect of particle size and polydispersity. The filtration drag was measured for three kinds of particle stream having the geometric mean particle size of 3.15, 6.07, and 7.83 μm and the geometric standard deviation less than 1.44 in the practical operation conditions for the field applications of face velocity of 0.03–0.06 m/s and area dust load up to 0.2 kg/m². A dust cake of smaller particle size showed larger pressure drop even though the porosity was higher and presented high compressibility according to the face velocity. The particle polydispersity was also a dominant factor affecting the compressibility of the dust cake.     

Filtration and regeneration behavior of polytetrafluoroethylene membrane for dusty gas treatment

With micron talcum particles and nano-CaCO₃ powder as test dust, a series of experiments have been carried out to systematically study the gas filtration and regeneration behavior of polytetrafluoroethylene membrane, and some comparisons were made with common filter media. The experimental results showed that the PTFE membrane had a filtration efficiency of above 99.99% for micron particles, and excellent regeneration behavior was obtained, though a much higher initial pressure drop existed. Based on the results, it was concluded that the PTFE membrane is an excellent surface-filtration media for micron particles. Effects of operation parameters, including airflow velocity, particle concentration and particle characteristics were also investigated. To better understand the evolution of pressure drop during the filtration process, a mathematical model with operation parameters and characteristics of particles was derived from the gas-solid two-phase flow theories. A novel method on the determination of regeneration period of the filter media was put forward based on the analysis of the pressure drop according to this model.     

清灰效率对炷状陶瓷过滤器的影响

研究了脉冲清灰效率对过滤过程的影响。假定粉尘结构在过滤和清灰中不变的条件下 ,对清灰效率的影响进行了分析。发现在一定的启动压降下 ,存在着一个最佳的清灰效率 ,即在 90 %～ 95 %之间。由于在运行的前几个循环中 ,粉尘压降、残留粉尘压降以及粉尘厚度、残留粉尘厚度存在较大的变化 ,因而在开始的几个循环中 ,不宜采用相同的清灰时间间隔     

Design and Optimization of Fibrous Filter Media Using Lifetime Multipass Simulations

The goal of this study was to optimize fibrous filter media by increasing the dust holding capacity (DHC) while maintaining the β ratio and initial pressure drop of the filter media. The key was the use of microstructure models to optimize the filter media. The microstructure of three different variations of a filter media for oil filtration was modeled by using the FiberGeo module of the GeoDict® software package. It was found that by optimizing the fiber volume distribution over the height of the filter media, higher DHC values could be achieved while keeping the pressure drop considerably low. This confirms the hypothesis that the macroscopic properties of the filter element can be improved by modifying the microstructure of the filter media.     

The effect of particle shape on the pressure drop across the dust cake

In order to observe the effect of particle shape of poly-dispersed dusts on filter performance, the pressure drop across the dust cakes of fly ashes from a conventional power plant (PC), fluidized bed combustion (FBC), and paint incinerator (FI) was measured over a metal filter element in the accurate conditions. A fluidized bed column was used to prepare the dust feed stream of uniform particle distribution. The fine particles of FI ash have a tendency to be agglomerated at low transport velocity. The aggregates were broken at high velocity of more than 21 cm/sec. FBC ash composed of jagged type particles and containing high concentration of unburned-carbon showed higher pressure drop than that of PC ash composed mostly of spherical particles. FI ash composed of aggregates of very fine carbon particles presented the highest pressure drop among the fly ashes tested. The shape factors of PC, FBC, and FI ash were estimated as 0.91, 0.76, and 0.65, respectively, by the Ergun equation. The results implied that the irregular particle tends to form a higher pressure drop and to be more compressible than spherical one. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Highly porous fibrous mullite ceramic membrane with interconnected pores for high performance dust removal

Porous fibrous mullite ceramic membranes with different content of fibers were successfully fabricated by molding method for dust removal. The properties of the samples, such as microstructure, porosity, bulk density and mechanical behavior were analyzed. Owing to the highly porous three-dimensional structure of ceramic membranes, all the samples exhibited low density (lower than 0.64?g/cm³), high porosity (higher than 73%), low linear shrinkage (lower than 1.0%) and low thermal conductivity (lower than 0.165?W/mK). Significantly, the as-prepared porous ceramic membrane possessed of enhanced dust removal efficiency with almost 100% for 3–10?µm, 97% for 1.0?µm, 87% for 0.5?µm and 82% for 0.3?µm dust particles in diameter from dust-laden air passed through the test module. Moreover, the pressure drop was lower than 80?Pa when the airflow linear velocity reached 1.25?m?min^?1. The results indicated that the ceramic membranes prepared in this work were promising high efficiency dedusting materials for the application in gas filtration field.     

Modelling pressure drop evolution on high temperature filters

A high temperature high pressure filtration facility is available at the ETSI-University of Seville, which allows testing different elements and cleaning reverse-flow pulse strategies using real coal ash under diverse operating conditions. The facility is capable of processing 850 Nm³/h gas flow rate at maximum temperature and pressure of 550 °C and 7.5 barg respectively. An extensive testing campaigns have been carried out with the aim of evaluating alternatives for hot gas filtration technologies and optimising the performance of commercial filtering elements.In this framework, this paper focuses on a semi-empirical model developed for predicting the rise of the pressure drop with time. The model is based on theoretical considerations and the application of the experimental data generated using four filtering elements (PTFE and 3MFB700 bag filters, DSN1020 and CS1150 rigid filters). Nonlinear regression has been used to estimate and validate the coefficient of the model (specific dust cake coefficient) with arbitraries relations between independent and dependent parameters, by using iterative estimation algorithms. This is a valuable tool to select the best filtration options and optimum cleaning strategies in high temperature applications. Investigations about the factors affecting the specific dust cake resistance coefficient (filtration velocity, temperature, filter medium) are also presented.     

Effects of Vehicle Cabin Filter Efficiency on Ultrafine Particle Concentration Ratios Measured In-Cabin and On-Roadway

Understanding the in-cabin microenvironment of vehicles is important for assessing human exposure to ultrafine particles (UFPs) of vehicular origin. Filtration through the cabin filter is one of the processes that determine the ratio of in-cabin to on-roadway (I/O) UFP concentrations. In this study, two filter test systems were used to measure the particle filtration efficiencies of fine, ultrafine, and coarse particles. Two types of particles (diesel exhaust UFPs and Arizona test particles) were used to represent the particle types expected in the on-roadway environment. The most penetrating particle size was around 300 nm with filtration efficiency lower than 20%. As the filter face velocity increased from 0.1 to 0.5 m s^?1, the filtration efficiency decreased by 10–20%. For vehicles that were frequently driven under heavy traffic conditions (65,000–72,000 vehicles day^?1) the pressure drop across the cabin filter increased up to 45 Pa within 10 months. It took 20 months to achieve the same pressure drop under moderate traffic conditions (10,000–24,000 vehicles day^?1) and 30 months under light conditions (700–2,000 vehicles day^?1). When the vehicle ventilation fan was on and the recirculation was off, it took approximately 10 months under heavy traffic conditions for UFP I/O ratios to increase by 40%. Explicit relationships between UFP I/O ratios and filter usage under various conditions were derived to facilitate cabin filter change decisions based on individual preferences.     

Treatment of Air Filters Using the Antimicrobial Natural Products Propolis and Grapefruit Seed Extract for Deactivation of Bioaerosols

Two natural products; i.e., grapefruit seed extract (GSE) and propolis, were investigated for use in antimicrobial air filters. Staphylococcus aureus was investigated as a test bioaerosol, and was deposited on the antimicrobial filters, which were treated by spraying with various areal densities of GSE and propolis. The pressure drop and particle penetration were investigated to assess the filtration performance of the bioaerosol, and the bacterial-inactivation performance of the filters was evaluated by quantifying S. aureus. There was little change in the pressure drop as a function of the areal density of GSE up to 185.9 μg/cm²; however, a significant change in the pressure drop was found for the air filter coated with propolis at an areal density of 98.4 μg/cm². The penetration levels of bioaerosols in both filters were uniform and in the range 1.4–2.0% (based on particle number), regardless of the areal density of the deposited GSE or propolis. The inactivation rates of the filters with identical deposition masses of GSE and propolis were similar in the ranges of 92.1–100%, 75.2–89.1%, and 54.4–75.5% at the control filters with colony numbers of 10³, 10⁴, and 10⁵ CFU/mL, respectively. The bacterial inactivation rate could be described by an exponential function of the areal density of GSE/propolis per number of colonies.

Copyright 2015 American Association for Aerosol Research     

Simulation of operational behaviour of patchily regenerated, rigid gas cleaning filter media

Particle removal from hot process gases is frequently accomplished with regenerable ceramic filters. When regenerating such media periodically, the dust cake may be detached from parts of the filter surface while other regions remain intact (‘patchy cleaning’). The filtration process depends on how these patterns of incomplete regeneration evolve over a number of cycles, how they change the build-up of the new cake, and how they affect the pressure drop. A two-dimensional quasi stationary flow model is used to predict pressure drops as a function of regeneration efficiencies and regeneration patterns, taking into account the finite thickness and flow resistance of the medium itself. The effect of non-uniform cake build-up on the pressure rise during a filter cycle is also modelled for a partially regenerated filter. The calculations prove that the pressure drop rises faster for lower regeneration efficiencies and that also cycle times become briefer with lower regeneration efficiency. It can also be shown, that the regeneration pattern only influences the pressure drop curve at the very beginning of the filtration cycle but does not influence the filtration cycle times.