Health and safety regulations in the construction work are becoming more and more important. This trend is visible in new regulations for the occupational limit values of, for example, silicate dust systems in the last years (Occupational Safety and Health Standards 1910.1053; 2016).

State of the art filter materials for critical dust systems (HEPA and IFA H (EN60335) filter elements) are micro glass fibre based materials. The big disadvantage of this type of materials is the filter mechanism itself – depth filtration. Due to this, the lifetime of such elements is extremely low, especially if high dust loading rates prevail, like in construction work applications. A regeneration/ back cleaning of such materials is from the technical point of view not possible.

The low lifetime of this type of materials is one reason for the OSHA 126.1153 regulation, which requires for a lot of construction applications a filter element that has to be cleanable and should reach an efficiency of >99% or a HEPA efficiency of 99,97% @0,3µm (monodisperse).

The company Hengst SE as leading supplier of air filter elements for professional vacuum cleaners, which are used in such construction work applications, set oneself the target to develop a cleanable filter element with the filtration classes US HEPA, EN1822 HEPA and IFH class H (EN60335).

During this development many influencing parameters are identified, like the filter material composition and structure, the pleat pack construction and the interface of the filter element to the vacuum cleaner...

Eurovent energy rating RS4/C/001-2019 has been updated beginning of 2019. It is not based anymore on efficiency measured according EN779, it is linked to efficiency measured according ISO 16890.

Lydall Performance Materials developed a range of fiber glass media with improved pressure drop. The complete range of grades (from efficiency ePM2,5 50% to ISO ePM1 80%) has been tested flat sheet. In parallel V bank filters have been produced with the complete range of HD products. Efficiencies according ISO 16890 of the filters have been tested and compared to the efficiencies of media flat sheet.

Filters have been tested according Eurovent RS4/C/001-2019 for their energy rating.

The LydAir® MG fiberglass media in our portfolio (HD range) will allow the filter manufacturer to obtain the desired ePM_x efficiency on the complete filter element at the lowest pressure drop. This low initial pressure drop and the optimized increase of pressure drop during the dust loading with ISO fine dust is consequently giving performant energy rating of the filters when measured according Eurovent RS4/C/001-2019...

Polyacrylonitrile (PAN) has been used as fiber for improves particulate matter collection efficiency, be good stability and mechanical properties. Polar solvents is commonly used to solubilize PAN and dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) are frequently used as solvents.

The aim of this work was to evaluate fiber diameter, pore area, superficial porosity and filtration performance of filter medias covered with fibers produced by Forcespinning (centrifugal spinning method) from PAN dissolved in DMF and DMSO...

Heating and cooling of the cabin air drains energy especially for electric vehicles. This energy comes from the battery, and, as a consequence, cannot be used for car propulsion. In addition, requirements are more and more important concerning the cabin air quality. The objective is to protect the passengers from ultrafine particles or harmful gases by using advanced filtration technologies (HEPA filter, adsorption). Compared to houses or buildings, car passengers are confined in only a few cubic meters volume. Cabin air quality depends on fresh and recirculated air flows. As a consequence, filtration solutions are developed and implemented in the HVAC (Heating, Ventilation and Air Conditioning) system.

From the outside to the cabin, the system studied in this paper is composed of three individually adjustable elements: ambient filter, HEPA filter and cabin filter. These different stages are activated depending on the air pollution level of the environment and driving conditions (traffic jam, tunnel, city, outback…) with possibility to minimize the energy consumption for heating or cooling. In addition, different sensors (particles, gases, temperature…) monitoring the indoor and outdoor air quality can be used in order to optimize the filtration system regulation. In reality, for typical driving conditions, ambient air enters by infiltration (depending on the vehicle speed), allowing particles, NO_x, SO_x, and NH_x to enter into the cabin but not through the HVAC system (and as consequence not through the filters). The infiltration level depends on the cabin pressure and the vehicle speed.

In this article, a compromise was found between fresh air and recirculation mode for every driving condition, number of passengers, history, outside air pollution level, energy consumption level and cabin thermal management system...

Cabin filters are used for comfort purposes but also as safety equipment. Especially the use of gas filters in protection cabins requires knowledge about the cleaning efficiency at the expected ambient air conditions. With a series of experimentally determined test results the ILK Dresden shows the influence of air temperature, humidity, air velocity and test gas concentration on the gas separation.

By upgrading a test rig designed according to ISO 11155 it became possible to test filters and adsorptive materials also at low flowrates, high humidity and with toxic gases like SO₂, NH₃ and H₂S. The ILK proposes a test routine to qualify cabin filters, which should be tested in a comparable way to standards for mask filters of personal protection equipment. Essential parts of actual standards are included or adapted in the new test routine. So a basis was made to create a new official test standard...

Vehicle thermal management and air conditioning systems play an important role in protecting the driver and passengers from pollution ingress into the vehicle, and from the build-up of carbon dioxide in the cabin. With air pollution in excess of legal limits and World Health Organisation guidelines in many areas across Europe, drivers may be particularly susceptible.

Emissions Analytics has worked in collaboration with National Air Quality Testing Services (NAQTS) and the University of California Riverside to develop a new in-cabin air quality test programme that measures the rate of particle number (down to 15nm in size) ingress into the cabin under different air conditioning and air recirculation modes. In those same scenarios, it also measures the build-up of carbon dioxide and compares it to levels associated with cognitive impairment. Finally, it considers the air replacement rates and therefore the speed with which the air conditioning system can clean up pollutant concentrations in the cabin.

Through this testing, Emissions Analytics will make comparative EQUA Index ratings in order assess the effectiveness of the filtration design components on the vehicle and to compare between vehicles. In this way, it will incentivise the development of the most effective systems and allow optimal choices to be made on the trade-off between pollution ingress and cabin stuffiness.

Furthermore, data from a new EQUA Index programme on in-cabin air quality will be presented, covering the rate of particle infiltration from a range of modern cars, and the propensity of carbon dioxide concentrations to rise when the air recirculation mode is activated.

In biomass combustion plants (P_th < 5 MW), hot, dust-laden flue gases are generated, which frequently also include gaseous pollutants such as, SO₂, NO_X and HCl. The steady updating of the pollutant limit values requires the development of a more efficient flue gas cleaning technology. Methods available on the market for the flue gas purification of all components to be considered are not yet economically viable for biomass combustion plants < 5 MW_th. Within the research project “SCRCOAT”, which is financially supported by the Federal Ministry of Economics and Technology (BMWi), new ways of designing gas purification systems for biomass combustion plants with a thermal output of < 5 MW have been developed.

For this reason, an existing test rig at the Paderborn University was extended. A catalytically coated fabric material (filter blank diameter = 100 mm) enables the combination of dust filtration with fabric filters and selective catalytic reduction (SCR) of NO_X. The dust is deposited on the outer surface of the filter element and then the nitrogen oxide reduction on the catalytically coated inside. First, the deposition of noxious gases was investigated. This means that the pellet boiler (P_th = 15 kW) remained off and thus the fine dust was not considered. The aim was to investigate the dependence of the deposition of noxious gases (NO_X, HCl, SO₂) on the precise dosage of these gases and on the precoat material used in the laboratory test rig. Due to the defined addition of the abovementioned noxious gases, various operating states could be simulated...

It is considered to be a valid method for using the waste water of an industrial plant to control the air pollution of the exhaust gas, which is one of the main sources of atmospheric particulate matter. A GLCA (Gas-Liquid Cross-flow Array) wet scrubber system, already described in detail by Zhu J. et al ^[1], is proposed to be a dust separator to remove particles in the exhaust gas. A continuous and regular liquid column array is formed under the force of gravity with a holed distributor, by which the particles will be captured when the dusty gas flows through the column array.

Tests were executed on a lab scale test rig for different operation and apparatus parameters and the fractional separation efficiency and the pressure drop were measured. Using a simplified PM2.5 definition ^[2], a method will be presented how the minimum number of water column unit rows in series n could be found, with the aim to reach a certain PM2.5 limit value. Further a quality factor is used to optimize other parameters, e.g. the gas through-put velocity...

The progress of pressure loss during the filtration phase as well as the residual pressure loss after regeneration are characteristics of the performance of surface filters for dust separation. These characteristics are significantly influenced by both the specific cake resistance and the adhesive forces of dust particle contacts. The specific cake resistance decreases, besides other factors, with increasing pore sizes. The mechanical strength of the dust cake in turn depends on the adhesive forces of particle contacts in the dust cake. For the removal of the dust cake from the filter medium an increased mechanical strength is desirable, since the amount of energy needed for regeneration can be reduced. In terms of process technology, these characteristics can be influenced by raw gas conditioning, for example by changing the particle characteristics in the dust cake.

The metered addition of a fraction of hygroscopic salt particles provides a possibility for influencing the performance of surface filters for dust separation. By temporary modification of the gas humidity deliquescence and efflorescence of the added salt particles will be induced to subsequently change the adhesive forces of particle contacts as well as the structure of the dust cake formed on the filter medium. This changes the performance of the filter.

The present contribution presents investigations into the influence of the change in the performance of test filters by inducing deliquescence and efflorescence of a fraction of salt particles in a dust cake. These investigations were carried out on an adapted filter test apparatus according to VDI 3926-1. The conditioning concept as well as the operating behavior of test filters, such as the pressure loss curves and the regeneration results are presented.

Coalescence filters are commonly used to separate oil droplets from air streams and nonwoven glass fiber filter media are used for applications where high efficiencies are required, for instance for compressed air preparation. The relevant mechanisms in oil mist filtration and their impact on operational behavior of the filters have received increasing attention in research over the last few years and are qualitatively well understood by now. However, the relationship between structural properties of the filter media and the operating performance of the filters is relatively unknown and therefore filter media are commonly chosen based on empirical values depending on the application. In this work filtration relevant media properties were identified and their qualitative impact on operating performance was tested.

To find correlations between media properties and operating performance of the filters, various custom made nonwoven glass fiber filter media were characterized using several methods, such as x-ray microtomography and scanning electron microscopy. These methods were evaluated regarding their suitability in identifying structural and surface properties. Based on theoretical approaches the qualitative impact of these properties on oil deposition and transport mechanisms in the media and therefore on the operation performance was estimated. Filtration tests were carried out to evaluate these approaches by measuring filter efficiencies and differential pressure and their respective changes during filtration.

Recent data obtained in the experiments will be presented, evaluated and discussed...

Coalescence filtration is a widely used technique in industry to remove oil from compressed air and to achieve suitable air qualities for production processes in order to protect devices and the workforce. Typical filters are constructed of nonwoven fibers and represent a heterogeneous media with complex permeability and capillary properties, which are defined by the fiber sizes and media density, surface tensions, oil viscosity, and droplet dimensions. One of the important parameters among the filter efficiency parameters is the saturation of the filter medium. The resulting pressure drop increases significantly the energy costs of the process. According to the channel-jump model the formation of an oil film in the filter media has a major influence on the pressure drop. In case of an oleophilic filter medium, the oil film is formed on the downstream side of the filter and is directly coupled to the drainage efficiency. The presented work aims at reducing the pressure drop and directing the oil drainage by introducing...

The dilution of large droplets is particularly important when measuring highly concentrated droplet aerosols. Since large droplets are difficult to dilute, standard systems only work up to a size of 1 - 2 μm

Problem of existing dilution systems:

• Large droplets (above 3-5 µm) are destroyed
• Change of the dilution ration in regards to the particle size

According to this Problem it is very difficult to get a good correlation between the optical measured mass and the gravimetrical evaluated mass with a droplet aerosol, e.g. in the crankcase ventilation filter testing.

The target for the development of the new dilution system LDD was to dilute large droplets with practically no losses to get a better correlation between the optical measurement and the gravimetrical result. To prevents condensation, the model variant LDD 100 H can be heated up to 120 °C.

The newly developed dilution system LDD 100 H (dilution factor 100) is the first system to dilute almost loss-free large droplets up to 10 μm. The good dilution ratio was proven with monodisperse DEHS oil droplets of different sizes. The results of 5 µm & 7 µm are...

Dust emissions caused by industrial processes are regulated at almost any place on earth by local statutory rules. In almost all cases the emission limits are still defined on a gravimetric basis in mass per volume units, e.g. mg/Nm³.

Obviously, these gravimetric limits are focussing more on coarser or bigger sized particles than on fine dust particulate matter, as the mass of the particle corresponds to the diameter in a dimension of around 10³. On the other hand, exposition of living individuals to the fine dust fraction (PM 2.5, PM 1) is considered very critical under aspects of health and environment. Fine dust is evident as a cause of illness, intoxication and premature death. For this reason, a significant reduction of the fine dust particulate matter should be accomplished, and this is possible by use of sophisticated cleanable filter media in particle filtration processes.

The lecture will demonstrate that the use of an optimized cleanable filter media results in an emission rate that cannot be detected by standard gravimetric methods. By means of a scattered light measurement device only few particles can be detected on the clean gas side of the filter equipment during the filtration process, that will not result in an amount of dust that can be determined by standard gravimetric means.

Filter media achieving that low emissions are newly developed...

Metallurgical processes such as thermal spraying, metal cutting and arc welding emit high concentrations of metallic nanoparticles. These particles pose a real threat to workers in work places and to the environment due to their toxicity. Dust collectors, namely fibrous media, used for the filtration of such particles are currently challenged with a rapid increase of the pressure drop and an inefficient cleaning. Because of their size, the metallic ultrafine particles tend to form a filter cake that is extremely adherent and difficult to detach. This means that filters need to be replaced more frequently, inducing higher operational costs. Industrial feedbacks have also reported that aged deposits can sometimes be more problematic, as the filter cake undergoes some transformation that impedes its removal. Facing all these problems, it is of outmost importance to optimize the industrial filtration systems subjected to metallic nanoparticles.

This study aims to identify the parameters that affect the cleaning efficiency of a filter cake composed of metallic nanoparticles, in order to improve the regeneration of filters...

Based on the revision of the BREF- guidelines in European community and the redesign of the TA Luft in Germany, there will be a further reduction in the emission limit values for industrial plants. According to the current draft of TA Luft 2019, the emission concentrations of air pollution sources with mass flows above 0.40 kg / h are limited to 10 mg/ m³. That is a halving of the current level.

Other legislative changes also in work in case of emission limits in relation to particulate and ultrafine dust concentrations. This also requires an improvement in filter technology and, above all, the creation of test methods that can be used to produce reliable forecast values for emissions. As part of a research project, a measuring method has been developed which takes into account the influence of the filter cake thickness on the degree of separation efficiency. In addition, the degree of separation for an ultrafine aerosol as well as the determination of the total degree of separation for test dust as the basis for the assessment of the separation efficiency was established. The special feature of the new test method is the determination of the separation performance compared to nano-scale aerosols and the determination of the fine dust concentration in the clean gas...

Soluble particles are present in the surrounding air and can often uncontrollably find their way into filtration processes. In dry processes, this does not lead to issues or unforeseen filtration outcomes, but upon contact with high humidity or fine liquid droplets, the effect of the mobilized soluble particles on the filtration process remains unpredictable and unexplained. The exposure of soluble particles in filtration processes to fully formed liquid droplets especially leaves many unanswered questions.

The aim of this research is to understand the behavior of soluble particles upon contact with liquid droplets during filtration processes and its impact on the processes’ operational performance.

The movement and rearranging of soluble particles upon contact with liquid droplets are being investigated. As this topic is still fairly new and first results will determine the further direction the research in the field will take, it is crucial to choose a suitable material system, which will show effects in a clear fashion, and is relevant to engineering applications. Multiple material systems, including different salts e.g. NaCl and K₂SO₄, and filter media were compared in this work and the material system in the focus of further research will be presented. This research is based on a comprehensive literature review and experimental results. The experiments were...

High Efficiency Particulate Air (HEPA) filtration is a key point for the safety of workers and environment especially for activities dealing with hazardous materials such as nuclear matter. For industrial risks likely to lead to an important release of particles, consequences of such an event need to be quantified. For the specific case of fire event, particles emitted during combustion are mainly formed by aggregates of spherical carbonaceous nanoparticles. For such situation, recent works lead to a phenomenological model of clogging in which one of the most sensitive parameters is the cake porosity. Up to now, existing models use the porosity as an input data, generally experimentally determined or deduced according to empirical relation. Nevertheless it is essential to describe in a rigorous way this parameter since porosity strongly depends on filtration conditions and particles properties and may evolve during the process. The prediction of this porosity is fundamentals to make filter efficiency and clogging models fully predictive. Many authors have experimentally (Choi et al. 2004, Kim et al. 2009, Elmoe et al. 2011, Liu et al. 2013, Thomas et al. 2014…) or numerically (Mädler et al. 2006, Lindquist et al. 2014) investigated the evolution of a deposit of spherical and fractal nanoparticles according to the transport of the aerosol characterized by the Peclet numbers (Pe). The present work aims to describe experimentally and theoretically, the evolution of deposit porosity, according to analytical experiments with controlled particle production and covering a wider range of Peclet numbers...

This work focuses on the pressure drop evolution of HFMs during particle loading. We tested two types of polypropylene HFMs varying in inner fiber diameter with three different types of dust/aerosol. We used an ASHRAE A2 test dust, a submicron TiO₂ powder dispersed using pressure air, and an ammonium sulfate aerosol generated from a solution to simulate a particle laden environment. Data was recorded including pressure drop, permeate velocity, accumulated mass of particles and fan power input until reaching the final pressure drop. After each experiment, the dust cake was weighed, thus obtaining dust-holding capacity. Theoretical models for dust cake pressure drop and energy consumption were compared with the experiment results. The results showed...

Air pollution concerning Fine Dust in- and outdoors are currently one of the most discussed topics in public. The new ISO 16890 provides new filter classes ISO ePM1, ISO ePM 2.5 and ISO ePM 10 to forward the operator an idea how far a certain product may reduce the amount of fine dust in his application.

These efficiency values are based on the fractional efficiency test data, long time known from Standards as EN 779 and ASHRAE 52.2. To evaluate the efficiency by particle size, particle counters (ISO 21501-4) or Aerosol spectrometers according to ISO 21501-1 working with the scattered light principle are used. Afterwards the measured efficiency is transferred into ISO ePMx values based on typical ambient air distributions as given by ISO 16890-1.

Usually, according to ISO 16890, the ISO ePM values are tested at the complete filter element. The efficiency of the complete filter element is resulting from the design of the element as well as the characteristics of the filter material used. The difficulty is now to estimate which filter class results if a certain material is used without manufacturing a completely new element.

Therefor Palas® has designed a new filter material test system, which can perform the whole test procedure according to ISO 16890 at the flat sheet media. An automatic software procedure to evaluate the data measured and automatically converting efficiencies into the ePM values is available.

As the main air flow for such a test is, depending on the size of the sample, up to 120 times lower than for the complete element....

The aim of the new standard ISO 16890 for performance evaluation of air filters for general ventilation was to harmonize existing local standards such as the ASHRAE 52.2 which is common in the United States and EN 779 which was developed in Europe. Since July 2018 the EN 779 is finally withdrawn.

The new standard intends to achieve more realistic laboratory filter evaluation, which has the result, that the test procedure becomes more complex. The more realistic laboratory filter evaluations are realized by rating particle fractions, now the particle sizes from 0,3 µm to 10 µm are considered. Furthermore an additional aerosol KCl is used, the whole filter is discharged with IPA. ISO A2 fine dust is used for optional loading tests. Also the previously known filter classes F,M and G, are replaced by the filter classes ISO ePM₁, ISO ePM_2,5 and ISO ePM₁₀. To classify the filters, the minimum efficiency values ePM_1,min and ePM_2,5,min have to be used in addition to the efficiency values ePM₁, ePM_2,5 and ePM10,

This paper will present a latest state of the art testing methodology which fulfils all the new requirements of ISO16890. The focus of this paper will be the description of the setup of a fully automatic filter test system with two optical particle counters. Furthermore all important key components including the discharging according to ISO 16890-4 will be presented, which are necessary for the determination of the filter performance parameters. As well as the evaluation of the obtained measurement data and the creation of a summary report according to the ISO 16890 standard in which all parameters are determined and recorded for a direct interpretation of the test results as well as the filter classification...

Test standard ISO 16890:2016 (Air Filters for General Ventilation) is now used in the filtration industry to classify the performance of air filter elements in terms of their particulate removal efficiency (ePMx), initial arrestance and test dust capacity. This applies to filter elements used in heating, ventilation and air conditioning systems (HVAC).

Eurovent is the European industry association for HVAC filters. Their sub-unit, known as Eurovent Certita Certification, has a certified performance scheme for participating filter manufacturers. The performance data is collected by approved independent test laboratories and is used to verify the claims made by the filter manufacturers. This helps those who need to specify air filters for certain applications to select with confidence the most appropriate type of air filter.

The measurement of air flow resistance of a filter element is very important because this data is used to determine the energy rating of the filter. The 3^rd edition of Eurovent document 4/21 (2018) describes the test method and calculations. It is based on the dust loading test specified in ISO 16890:2016 part 3, except that it requires a minimum of eight separate dust loading stages, including the initial dust loading of 30 grams (or the quantity of dust required to produce a 10 Pa rise in differential pressure) and the final target pressure drop, which is dependent upon the filter type. The average pressure drop across the filter is determined and then used to calculate the annual energy consumption (kWh/year). Eurovent’s rating standard RS 4/C/001-2019 specifies the energy rating classes based on the annual energy consumption and the ePMx rating of the filter.

The rate at which the differential pressure increases across a filter with respect to the quantity of dust fed to the filter depends upon the physical properties of the test dust. One aspect of interest in this work is the significance of electro-static charges within the aerated dust on the measurement of differential pressure. The results from tests using Particle Technology’s accredited ISO 16890 test rig, with industry standard equipment will be discussed...

In terms of particle removal from gases with surface filters, the periodic building and detachment of particle layers decisively determine the operating behaviour and the performance of the filter. The surface structure of textile filter media including the near-surface, porous transition area between the dust cake and the filter medium is of fundamental importance in view of dust cake formation and detachment. In practice, various surface finishes like singeing, calendering, etc. are used on empirical basis to improve the operating behaviour of textile filter media by modifying the surface texture. For targeted development and implementation of new filter media there is a need for a systematic investigation into the correlation between the surface structure of textile filter media and their operating behaviour on a quantitative basis.

In the current study, the structure of generated dust cake on model fabric filters is investigated by simulation for cake forming dust filtration via calculation of particle trajectories. The changes in the dust cake structure and in the operating behaviour of the filters are evaluated and analysed by systematic variation of the filter surface structure. For comparison, results of corresponding experimental investigations with differently structured needle felts are presented and discussed together with the simulation calculations...

Wall flow filters are used for exhaust aftertreatment in passenger cars and commercial vehicles in order to comply with the legal requirements regarding the emitted particulate mass. The particles to be separated are primarily carbon-based components that are formed in the engine compartment due to incomplete combustion. With increasing operating time, the backpressure behaviour of the diesel particulate filter (DPF) increases due to the high mass of separated particles. For optimum operating performance, the filter must be regularly regenerated actively and/or passively. As a result of the regeneration process diesel ash remains in the filter as a cumulative regeneration residue. This has a particular influence on the separation and backpressure behaviour of the DPF due to different deposition pattern.

The focus of this research project is to describe the storage and rearrangement of the diesel ash within the individual DPF channels and to develop an understanding of the processes inside the filter...

Fibrous depth filters are frequently used in various civil and industrial applications. The loading behavior of fibrous filters determines the evolution of pressure drop and filtration efficiency during their service time. The pressure drop limits the service time and determines the energy costs of the filtration system. For a sustainable and efficient filtration process, knowledge about the loading behavior inside the material is evident. It is well known that the structure of the filter media highly determines the loading behavior and offers the potential for optimizations.

In this work, a calculation method for the filtration kinetics of fibrous depth filters based on tomographic structural data is presented...

Depth filters are used in air-conditioning and cleanroom technology for removal of particles from gases. In those applications the particles deposit and accumulate inside the fibrous filter media causing an increasing separation efficiency, pressure drop and hence more energy consumption. Currently filter systems consist of a static filter structure that is not able to adapt oneself to the changing process conditions. A new elastic fibre could be an opportunity to introduce a new kind of filter systems. Those filters could adapt its mutable fibre diameter and porosity to operation conditions, like particle load, particle diameter and flow velocity, in order to attain necessary collection efficiency with minimal pressure loss and less energy consumption.

Investigations on the single fibre collection efficiency of particles and the deposited particle structure on the fibre are done with a new constructed single fibre-stretching set-up during and after a controlled stretching process. The size, number and morphology of detached particles structures are characterised by an optical particle counter with two consecutively detectors, measuring volumes and a laser band technique for bigger agglomerates. These measuring systems and the single fibre are arranged perpendicular to the direction of aerosol flow. The stretching itself is done by a fibre-mounting with piezo-actuators for controlled movement. The fibre movement is varied in stretching velocity and the number of stretching cycles. Further investigations on stacked fibres should be done in the same way. At the end, the results of the single fibre experiments should be exemplary for all the fibres within a depth filter.

Preliminary tests with an elastic single fibre and glass particles at a test stand showed that...

Depth filters are used in air-conditioning, cleanroom technology and exhaust gas treatment. Particles are separated inside a porous structure where they form particulate structures. High flow velocities are needed to detach particles adhering to the filter media, for example velocities greater than 1 m/s are needed for detaching particles of 10 µm in diameter. Velocities in filtration processes are lower because particle bounce occurs at [endif]--> 1 m/s, reducing separation efficiency. For this reason, detachment of separated particles does not happen in most filtration processes. New findings show that reactive components in deposited particle structures can cause deformation and detachment even at low flow velocities. Understanding of these phenomena is necessary to improve soot particle filtration in fibrous filters. In the scope of this project first experimental results regarding deformation and detachment of soot agglomerates on/from a single steel fiber exposed to hot air flow are presented...

Since 1 July 2018 the standard for testing air filters for general ventilation is ISO 16890. Along with the introduction of new filter classes there are also new requirements for the test. One example is the electrical discharging of the filter: it is now performed with vaporized isopropyl alcohol (IPA) in a conditioning chamber. The previous method in Europe was the dipping of filter media into liquid IPA (EN 779). The reason for change was the observation that efficiencies of electret filter media treated with saturated IPA vapor resulted in significant lower efficiencies compared to measurements of filter media treated with liquid IPA (Cai 2010). Other changes include the use of DEHS (0,3 µm to 1,0 µm) and KCl (1,0 µm to 10,0 µm) aerosols to measure the filtration efficiency and the elimination of a dust-loading test (except for filters with ePM₁₀ values below 50 % in which case a gravimetric efficiency has to be determined). To specify the reproducibility and to evaluate the test method according to ISO 16890 a round robin test was performed.

Eleven laboratories participated in the round robin test. One of them provided the filters which were equally manufactured and consisted of polypropylene fibers. Each laboratory was free to use their equipment with the exception that it had to fulfill the specifications laid out in ISO 16890. This resulted in the use of different optical particle counters (OPC), different atomizers, different conditioning chambers and so on – a perfect situation to evaluate a test method.

The measurements of the pressure differences and the filtration efficiency before and after IPA treatment showed...

Particle filters, e.g. diesel or gasoline particle filters (DPF/GPF), are applied to reduce emissions of combustion engines and have become a standard component in exhaust aftertreatment systems. The emission standards regarding particulate matter (PM) and particulate number (PN) concentrations are getting stricter hence a better understanding is essential for the optimisation of the exhaust treatment. Due to particle deposition and the resulting layer formation in the filters, the pressure drop and energy consumption increase during operation. In order to reduce these influences on the operating conditions, various process parameters and their effects on the filtration process of reactive-inert aerosols have to be identified.

To investigate the operational behaviour of cross-flow-filters, test aerosols are used to characterise the formation of particle layers and to determine structural layer changes due to break-up and rearrangement of deposited particulate matter. Due to the variety of reactive/inert aerosols, various particle size distributions (PSD) and morphologies are identified and have to be replicated. For the separation of reactive and inert particles, two different generation methods are used to produce different compositions of aerosols. The inert particles (ash) are generated with an oil-mist and a subsequent incineration in an oven. Due to the introduced oxygen, the hydrocarbons are fully oxidised to carbon dioxide and water vapour. The process parameters, oven temperature, oxygen concentration and residence time, are varied. The method for the generation of reactive particles (soot) is based on a soot generator where soot is formed with propane and a subsequent diffusion flame pyrolysis. In this process, stable operating points for the reactive particles were detected.

As expected, the inert aerosol properties, e.g. particle size and concentration, are...

Handling with bulk materials, such as sand, gravel, coal or granules, dust is produced as a function of material-specific properties. From the perspective of process engineering the challenge here is to reduce the emission of the fine dust originating from diffuse sources, in particular PM_2.5. Therefore, water dispersing systems are often used at conveyor belts, crushers or on stockpiles where water spray is generated by two-fluid nozzles. Dust particles are wetted depending on the droplet size distribution and the amount of water used. The binding between droplet and dust particle increases the particle mass and results in a faster sedimentation. However, due to the low inertia of dust particles (PM_2.5), a large amount of water is necessary in order to achieve a sufficient separation efficiency.

For resource and energy efficiency, a new water dispersion system is developed. The goal is to increase the probability of precipitation while reducing water consumption...

Dust emissions can be understood as the release of the particles from bulk solids in consequence of handling. These emissions can cause an explosive atmosphere, lead to long-term sickness or environmental pollution. In order to reduce all this kind of possible hazards reliable prediction methods of dust emissions during the handling of bulk solids have to be developed. For this reason, common experimental methods, representing different handling scenarios, are modified and used for investigations.

The paper deals with the experimental methods, their modifications and the first results gained...

One of the ways to modernization of the existing equipment of dust filtration is to use in the filter houses the filter bags with increased by surface of filtration. The other way is concluded in use in bag filter houses the filter bags with increased by surface of filtration at development and design of new compact equipment of dust filtration.... DESA Co.Ltd. brings on the market the new technology 3D Economic System of Aspiration using in the filter houses the filter bags "3DESA filtrpatron" are made from nonwoven filtering materials Patent EP1459796 (golden medal salon INVENTIONS GENEVA 2013), patent RU 2283683.....

New residential units are typically equipped with controlled room ventilation systems with heat recovery to ensure a reliable and controlled air exchange. With dust deposited within pipes, outlets, bends, reductions and filters, the rise in power demand causes higher operating costs. Furthermore, deposed dust layers can be a breeding ground for germs, fungi or other pollutants. Therefore, such systems require regular maintenance, best of all by professionals who carry out special hygiene inspections and cleanings. To minimize dust deposition within the ductwork, operation costs and additional hygienic problems, for example simulation tools and practical guidelines are absolutely essential.

Predictive models for dust deposits in pipes and fittings for room ventilation systems still are insufficient for complex dusts consisting of fibers and particulate materials. The aim of this project is therefore to assess residential ventilation systems regarding the dust deposits of various pipe fittings under controlled conditions....

Air filtration is a „Green Market“. But, this time filtration materials will be classified more by functional aspects than sustainable. Actual tendencies leading to small filter housings and lower use of energy. That’s why filter materials are more and more made by synthetic fibers. Technical features better can be adjusted with polymer chemistry. But this is not “Green”.

Therefore a research project was carried out to push possibilities of natural fibers – paper.

The project aim was to control the porosity of paper by reorienting its fibres through hydro-entanglement in the paper machine. The wet-laid nonwovens will be converted to novel and functionalized paper filter media that can be used to make deep filtration air filters from renewable raw materials and with performance characteristics and performance data comparable to synthetic- / glass-fibre-based filter media. The novel air filter media should offer high filtration efficiency and dust holding capacity as well as comparatively low pressure losses at high layer thickness. The results of the project showed that...

Indoor air quality has received tremendous attention these days because people generally spend more than 80 % of their time in indoors. This indicates that people are placed in more risky situation form inhalation of pollutants due to the level of pollutants in indoor environment is higher than in outdoor environment. The ventilation is known as the most convenient and effective solution to hedge the risk but it’s not in metropolis such as Seoul because the ventilation could migrate particulate matters from vehicular exhaust or industries. Therefore, air cleaning by air purifier is considered as the most feasible option to improve indoor air quality so air purifier market size has been skyrocketing.

At the current stage, photocatalytic decomposition has shown to be a promising and effective technology for pollution control. Unlike traditional method such as adsorption by activated carbon which merely relocates pollutants from indoor environment to deodorizing filter, photocatalysts actually disintegrate pollutants to CO₂ and H₂O. However, photocatalysts are still immature to replace activated carbon because the decomposition rate of pollutants by photocatalysts is quite slower than the adsorption rate of activated carbon. In addition, photocatalytic efficiency is decreased with decreasing pollutant concentration which represents indoor environment. Therefore, we believed that adsorbents and photocatalysts must be combinated to maximize the efficiency of indoor air quality improvement by air purifier...

Air pollution is a serious environmental and public health problem that can be associated with cardiovascular and respiratory diseases, as reported by recent studies. Filter media is commonly used to control and removal particles from the air. Recently, the use of nanofibers applied to air filtration is increasing.

In this context, the aim of this study was evaluate the filtration performance of filters with nanofibers and HEPA. The results showed that collection efficiency and pressured drop of HEPA filter were...

A simple, cheaper and alternative pretreatment for increasing the collection efficiency of fine particulates in nonwoven filter media is precoating, which consists of coating the inside and the surface of the nonwoven filter media with a particulate material forming a layer of initial powder. This layer prevents the particles from penetrating the filter medium and causes clogging. It is also responsible for the clogging which is the initial formation of the pie, acting as a new filtering element ensuring surface filtration. Thus, the purpose of precoating is to assist in the separation of the micrometric and nanometric particles, as well as to ensure that the gas flows freely through the filter medium, improve the performance of the filter sleeves, increase filter media life and facilitate cleaning, promoting better detachment of the pie from the filter media. The choice of the powder to be used in precoating must be judicious because it has a direct influence on the filtration efficiency as well as obtaining the clogging point and the pressure loss at which this point is reached. Thus, the objective of this work was to determine the precoating powder and the precoating limit pressure drop, which ensures the clogging of the filter medium to obtain the best collection efficiency in fine particle filtration from the secondary dusting of the steel plant of a steel industry...

One factor that must be taken into account when selecting the filtration bag is the quality of the seam, which can be a point of powder leakage and increase the concentration of particulate matter released into the atmosphere. The objective of this work was to characterize a bag made of aromatic polyimide (PI) fibers, after 3 years of use in the sintering unit of a steel mill, in order to evaluate the particle collection efficiency after this time, especially in the part that has the seam.

Filtration cycles were performed on the equipment based on VDI 3926, which simulates the industrial operation of a bag filter, in order to verify if the seam of the bag interferes in the collection efficiency of the submicron particulate matter. For comparison, the tests were performed on a bag with 3 years of use, both in the seamed part and in the seamless part. The powder from the primary sintering was used as the particulate mater, which was collected in the silo that is downstream of the bag filter. The following characteristics were obtained...

PPS non-woven fabric is one of the most cost-effective filter media used in processing the flue gas of waste incinerator facilities and coal-fired power plants at high temperatures (e.g., 140 – 200 °C) under presence of acid gases, owing to its excellent chemical, thermal, and mechanical properties. In general, though the service life of a PPS filter can reach several years, the degradation and deterioration of its mechanical and chemical properties progresses gradually throughout the lifetime of the filter. Oxidation and acid-base corrosion is thought to be the main factors causing the degradation of PPS filters.

Therefore, in this study, the durability of the PPS fabric filter media toward NO₂ gas was examined in detail with a continuous-flow type exposure method which is specified in ISO16891:2016.

Moreover, we also suggest an empirical model to estimate the change in the degradation conversion of PPS by NO₂ gas and the tensile strength of PPS filter media...

Nonwovens and felts from synthetic fibers (polyester, polypropylene) or from glass fibers are the mostly used filter media in air filtration. These mterials offer high efficiency, long service life and a good price-performance ratio. However the modern growing trend to replacem petroleum-based fibers with bio-based and bio-degradable polymers dictates a new challenge for researchers, filter developers and manufatures. The research aims presented here at exploring PLA fibers as an alternative material for applications in air filtration. Particular focus is made on the characterisation of the mechanical properties of PLA under aging conditions, which are relevant for the applications as filter media. On the testing the filtration characteristics of the PLA nonwovens depend on the textile parameters as well as on the quantification of the biodegrabiity of the PLA-based materials...

In order to meet process requirements or environmental requirements, dust particles in various process gases and flue gases discharged into the atmosphere usually need to be separated directly under high temperature conditions.

High-temperature ceramic fiber filter element can meet the corresponding filtration performance requirements, and has good thermal stability, chemical stability, thermal shock resistance, fracture toughness and light weight. Therefore, it is one of the ideal hot gas filter media.

The work presents a study on the preparation of ceramic fiber filter element, aiming to improve the overall performance of the filter element, so that it can be better applied in the high-temperature gas-solid separation field...

Filtration process using fibrous filter media is widely used for the removal of particulate material from a stream of air because these have simplicity of use, low cost and can achieve high collection efficiency, however, the study is scarce when referring to filtration of nanoparticles. Moreover, the emergence of new materials with excellent chemical properties further favored the development of filtration technology, combined with the progress of the field of materials science and technology. New filter media producing technologies have emerged to achieve high particles collection efficiencies with low pressure drop as filters with nanofibers. The electrospinning process is the most used for the production of nanofibers and is distinguished from the other production processes by the versatility of processing different polymers, ability to control diameter, morphology, orientation and fiber structure. This method use electrostatic force to obtain fibers with high contact surface compared with those produced by other methods. One of the challenges to produce these filter media is the adjustment and control of several parameters which has influence on nanofiber production such as: polymer concentration, solvent ratio, collection time, tip to collector distance and the applied voltage. The polymer used was polyethylene terephthalate from post-consumer PET bottles in different solvent systems and concentrations. Such polymer has been outstanding owing to its mechanical properties favorable to the filtration tests since it guarantees adequate resistance for use in diverse applications, for both micro and nanofiltration. After the production of fibrous filter media, they were physically characterized (permeability, porosity, fiber diameter distribution), and the collection efficiencies..

Operating efficiency assessments of high-pressure natural gas filters are significant for the protection of pipelines and equipment. The conventional particulate measurement method setting a new isoaxial sampling nozzle in high-pressure natural gas pipelines will bring a safety challenge due to pipeline stress change. The work presents a study on the performance of powder sampling using pressure port for differential pressure gauges in an effort to provide a safe and convenient solution for the efficiency assessment of high-pressure natural gas filter.

The performance of powder sampling efficiency of the pressure port at various gas velocities and sampling velocities was characterized in...

An indoor air quality (IAQ) monitoring has been increasing area of interest, because there are many reports of the harmful volatile organic compounds (VOCs) occurred in the house and building. So, development of air purifiers and filters for removing them is required.

In this study, filter structure was developed to adsorb and remove harmful indoor VOCs using metal organic framework embedded nickel foam fabricated by electrophoretic deposition. To confirm the adsorption, removal performance of VOCs, a filter chamber module including a UV module was developed and through the PID sensor, the excellent performance of adsorption and removal of the fabricated filter structure was confirmed...

Today, liquid aerosols are produced in many industrial processes like machining, manufacturing of catalysts or in pneumatic compressors. While the harmfulness of fine dust aerosols is well known the equally dangerous liquid aerosols (mist) receive less attention. In order to be prepared for future legal regulations we develop efficient mist filters with less energy consumption.

In our research, we couple micro-scale simulations of two-phase flow in a fibrous porous medium with macro-scale simulations to develop efficient filters for a stationary (oil mist separator) and a mobile (pneumatic truck compressor system) application. Because the computational effort to simulate mist deposition in a whole filter on the micro-scale would be much too high, on the macro-scale, the information of the micro-scale is adopted and the whole filter is considered as porous continuum. In other words, the output of the micro-scale becomes the input of the macro-scale. Specifically, parameters like porosity, intrinsic permeability as well as relative permeability - and capillary pressure – saturation relationship determined from micro-scale simulations are used as input to the macro-scale to simulate the filtration process on the domain of the whole filter. Furthermore, a source term of the liquid (oil) phase is derived from micro-scale simulations which may depend on parameters such as velocity and initial saturation. Thanks to this multi-scale coupling, it is possible to predict the pressure drop and the separation efficiency of a filter and figure out the factors to optimize these two properties.

Furthermore, different parameterizations of the capillary pressure – and the relative permeability - saturationships (e.g. Brooks & Corey and Van Genuchten) are compared. We also present the validation of our simulations by comparing both pressure drop and separation efficiency to measurement results....

Today aerosols are produced in many industrial processes like machining, manufacturing of catalysts or in pneumatic compressors. While the harmfulness of fine dust aerosols is well known the equally dangerous liquid aerosols (mist) receive less attention. In order to be prepared for future legal regulations we develop efficient mist filters with less energy consumption.

We present first results of micro-scale simulations of mist deposition on fibrous structures. In our framework, the fibrous structure is obtained from µCT scans. Micro-scale simulations provide information on fractional efficiency as well as parameters and constitutive relationships for macro-scale simulation used to investigate pressure drop. Therefore, the micro-scale simulation is closely linked to the macro-scale simulation.

The aim is to develop fibrous mist filters with less energy consumption (reduced pressure drop) and increased fractional efficiency compared to existing filters...

The usage of cleanable filter media with pulse-jet regeneration is widely used in industry. Dust becomes separated at the surface of the filter medium and by the forming dust cake. When a maximum pressure drop is reached a pulse-jet regeneration is triggered and the dust cake is detached from the filter medium surface. The remaining dust at the filter surface or within the filter medium leads to an increase of the filter medium air resistance.

The regeneration efficiency of the dust loaded filter medium will influence the following filtration cycle. Remaining dust leads to a faster rise of the pressure drop, respectively the filtration cycle duration becomes lower. Depending on various mechanisms of filter clogging the residual pressure drop will nearly never be constant, even after hundreds or thousands of filtration and regeneration cycles. Therefore, the life time of a filter media is either determined by reaching a maximum residual pressure drop or a minimum cycle duration time limit.

Still there is a need of quantification of stable, respectively unstable, filter operations. Therefore, in this work a detailed investigation of the fluctuations of residual pressure drop and cycle duration is done. Thereby, the frequency and intensity of arising fluctuations is used for the stability assessment. Lab-scale filter tests with various filter media (e.g. membranes, needle felts) under different constant operation conditions and cleaning intensities are tested using a VDI 3926 filter test rig with alumina-oxide test dust (Pural NF, Sasol) are done to obtain data on the evaluation of residual pressure drop and cycle duration. Frequency and intensity of deviation ratios of these parameters are calculated and investigated in order to clarify clogging and regeneration of the dust cake.

HEPA (High Efficiency Particulate Air filter) and ULPA (Ultra Low Penetration Air filter) are typically used to clean up the ventilation air for clean room applications like electronic industry, hospitals and also protection of the environment. For such challenging application which could influence health of people and quality of goods, 100 % control of produced HEPA/ULPA filters has to be carried out to verify/confirm the absence of leaks according to the standard EN1822/ISO29463.

Leak testing each filter leaving the production demands an automated and rapidly measuring solution.

Topas GmbH developed a highly automated filter scanning system which combines flexibility and speed in a suitable way. The system itself adjusts the correct dilution and the aerosol amount as well as the correct aerosol material, according to the filter type properties and runs the highly automated test routine. A unique solution for each customer guarantees continuous development starting with the project and includes practically feedback.

The technical implementation of both, standard requirements and customer requirements, will be described in detail as state of the art in the paper...

Allergenic bioaerosols, such as particles originating from animals, mites, fungal spores or plant pollen are ubiquitous in the air. The removal of allergenic bioaerosols from indoor air by air filtration is of high relevance for allergy sufferers. Currently, air filters are mostly tested with well-defined mineral particles or plasticizer aerosols such as ISO 12103-1 A2 fine dust or DEHS. These standardized test dusts represent the particle size of bioaerosols, but not their shape and physicochemical properties, which play an important role in the separation of small, respirable particles (<10 µm).

As biological particles have a different behaviour compared to non-biological particles it is important for filter design and testing to investigate the interactions between biological dusts and (biofunctional) filters also in terms of optimization. The aim was to develop a standardized method for testing filter media and modules with defined test dust containing fungal spores via a special designed filter test rig. The focus lay on comparison of biological separation efficiency with the separation efficiency of common non-biological test dusts as it is important to know about the biological risk of the particles exposed to the filter and to humans and not only number and size...

Fibrous filters are often employed to remove dispersed aerosol particles from a gas stream due to low cost, high capture efficiency and low pressure drop. The performance of such a filter medium is judged based on its capture efficiency and its pressure drop characteristics. Estimating these parameters without setting up experimental investigations of each filter medium is beneficial for choosing and developing optimal filters.

In the present study, numerical simulations using ANSYS CFX are used to predict the pressure drop caused due to an air flow through a randomly oriented fibrous filter medium...

Nanofibers are attractive to use in air filtration, due to the high surface-to-volume ratio, low flow resistance and enhanced filtration performance. However, the cost of nanofibers and slowing down in production process when using them leads to the desire to use as few nanofibers as possible. We treat such optimization issues by simulating filter media and filtration processes resolving the smallest scale.

The low pressure drop for nanofiber filters is explained with the slip flow effect, which states that in nano regime, the velocity of air at a surface does not vanish in the tangential direction. Since in our modeling, we convert a 3D fiber structure into voxels, applying a wall shear stress on such a staircase shape of the fiber surface is quite a challenge.

Previously, the slip-flow boundary condition could not be implemented directly into voxel-based flow solvers in a satisfactory fashion. In our previous work [1-5] we used two methods, the equivalent shrunk fiber and the equivalent permeable fiber, as workarounds. In the equivalent shrunk fiber method, the fiber is shrunk to make a flow possible in the fiber surface voxels. In the equivalent permeable fiber method, the nanofiber is permeable to make flow pass through it. However, there are limitations and disadvantages to both methods. They require either very high resolution of the structure or a lot of computational efforts to find the appropriate hypothetical permeabilities.

In this new approach, the expression of the slip velocity, which assumes the slip velocity proportional to the shear stress at the surface [6], is now reformulated for a locally quadratic velocity profile instead of the standard linear profile, and reimplemented in our flow solver. The direct simulation of the slip flow is then possible. The validations with analytic solutions are presented.

The influence of slip flow in nanofiber structures then is investigated and the results of flow and filtration simulations are compared with measurements...

Electret filter media are commonly used in aerosol filtration to remove particles from gases. They provide a high initial particle removal efficiency combined with a low pressure drop as the fibers of the electret filter media are electrostatically charged. In addition to the mechanical deposition mechanisms (diffusion, impaction and interception), charged particles are deposited by the Coulomb effect and any (charged or uncharged) particles by dielectrophoresis. However, the particle deposition is reduced with increasing exposure time, since already deposited particles can either neutralize or shield the electrostatic charge of the microfibers and thus weaken the above-mentioned electrostatic effects.

In this work the experimental investigations of the loading-dependent particle deposition are performed exposing electret filter media to...

In the field of immission measurement, cheap and compact low-cost PM-sensors have been established for monitoring particle concentration with high temporal and spatial resolution. The accuracy of these sensors is subject to many environmental influences, such as varying aerosol properties, particle concentration or relative humidity.

Another possible application for low-cost PM-sensors could be the emission measurement for industrial dust separation, like pulse-jet cleaned filter bags. Several filter bags could be equipped with low-cost sensors to investigate the contribution of individual filter bags to the total emission. The suitability of the sensors is still subject of research. The behavior during the filtration process in a VDI test rig for filter media has been investigated for the two low cost sensors OPC-N2 from the supplier Alphasense and PMS7003 from the supplier Plantower. A Welas 2100 sensor from the supplier Palas serves as a reference for the experiements.

The sensors are able to...

Cleanable filter media for pulse­jet cleaned filters are tested for operational performance and for particulate emission, where the focus shifts more and more towards particles smaller 2.5 µm. The measured data include generally the total dust concentration in the clean gas as an average over a defined number of filtration cycles and also, as an option, the determination of PM2.5 emission.

For high performance filter media which show very little particle emission, the gravimetric determination of the PM2.5 values becomes very time consuming and results in measurements of six or more hours, when using an impactor or cyclone.

Optical Aerosol Spectrometers are increasingly used in environmental PM2.5 measurements and are also certified by authorities. These instruments offer a viable and very fast method to also determine total dust concentration and PM2.5­values in the laboratory using a specified test dust under defined conditions. A further advantage besides the time saving potential is the very good time resolution and fast measurements of particle size distributions at every stage of the testing.

In this presentation a fast and easy method is introduced to determine PM2.5 emission optically instead of gravimetrically, using an Aerosol Spectrometer Promo LED with a measuring range from 150 nm to 10 µm. Test results gained on an ISO11057 reference filter test rig show...

Every mechanical braking action creates particles through friction on the brake disc and brake pads. These particles contribute to the PM10 emissions of vehicles. Some get collected on the rims seen as grey dust, others are emitted to the ambient air. Thus there is a need for a brake dust particle filter. But first, measuring size and concentration of such brake dust is a quite challenging task. The particle generation happens in the short event of braking and depends on brake load and preconditioning of the brake (disc and pads), e.g. temperature, braking history, to name some. However, a defined way of testing brake dust particle emissions is the pre-requisite for later investigation of filtration performance.

For release of an automotive brake system specific standards are available regarding braking events. Furthermore a braking sequences can be based on standards like WLTP driving cycle. For particle measurement various techniques could be selected, e.g. DMA, impactor, particle counter. For reliable data, the integration of such equipment in the air flow through the brake testing chamber is crucial.

We are going to briefly review published activities regarding measuring brake dust particles. We will then focus on our own measurements and ongoing research. We will describe the challenges and discuss results. Thereby we will focus on the effect of specific braking events on particle emissions.

At this time, because of their very high-efficiency, the fibrous filters are the most commonly dedusting systems used for individual and collective protection. High efficiency particulate air (HEPA) filters are used in many applications: containment in medical, pharmaceutical or nuclear facilities, cabin air treatment in automobiles and aircrafts, vacuum and so on. In addition to their high efficiency, these filters, usually non regenerable, may have an important lifetime (i.e. high dust retention capacity) to avoid too frequent replacements.

In the specific case of nanoparticle filtration, the morphology and the size of these particles induce, for the same area density of collected particles, a faster increase of the pressure drop during the filter clogging than for submicronic and micronic particles. This further reduces the lifetime of the fibrous filter and makes even more important the optimization of its retention capacity.

To further improve the filter performances, a possible solution is to fabricate fibres with diameter lower than 0.5 µm. As the collection efficiency is a decreasing function of the collector size, nanofiber filters could generally achieve a high collection efficiency. Overall, the solution consisting of adding a thin layer of nanofibers allows increasing the collection efficiency but not countering the pressure drop increase during particle loading and consequently the energy consumption. A possible solution to reduce the pressure drop increase is a better distribution of particles collected within the fibrous filter.

In this study, our approach consists in a series association of microfiber filters with various properties...

The construction and building sector requires a constant increasing need for pocket filters to respect and achieve satisfying air conditioning requirements. These pocket filters are consumables produced in various sizes and quantities according to the market needs. In spite of a standardized emerging size representing the big volume, there is a lot of room for non standard sized pocket filter production.

The aim of this paper is to present a modular, sustainable and efficient pocket filter production solution based on riveting, stitching, clinching and stitch-folding as joining techniques. This solution is coupled to a decision making tool allowing the implementation of best practices in lean management...

The filter medium is the most important part of any filter element. It is possible to distinguish filter media into two major classes.

Surface filter media separate the dispersed phase mainly on the first layer of its embodiment. Particles which are bigger than the pore size of the first media layer start to build a filter cake on top of the material. The interaction between the filter medium and the separated particles are very week.

Depth filter media are the second material class. These separate the particles, depending on their size either on top of the media or in the depth of the material. This enable depth filter media to store a high volume of particles or humidity with a comparable low influence on its pressure drop.

Surface filter media are very suitable for pulse cleaning applications due to the point of particle deposition. But they react very sensitive on challenging atmospheric conditions like sticky dust or high humidity in combination with fine dust or salt. These conditions can lead to irreversible blockage of the surface filter media which requires a complete change of the used filter stage in the final application. Especially in air intake systems for gas turbines or turbo compressors this will lead to a loss of production capacity and thus very high cost for the plant owner.

Based on this knowledge it was the aim to design a filter media which merges the advantages of a depth filter with the high efficiency and cleanability of a surface filter media. To achieve this contrary aims the design of the filter media is crucial...

Besides the know-how and experience existing in HAVER & BOECKER OHG, the GeoDict software from Math2Market GmbH is intensively used to determine which wire cloth configuration suits the best for the specific field of application. By simulating different cases, it is possible to optimize existing wire cloth specifications and develop new ones.

Geometrical characteristics such as type of weave, wire diameter and mesh counts have an enormous impact on the specific flow and filtration properties of a wire cloth. Using specific cloth parameters resulting from the type of weave, aperture width, pitch and wire diameter, HAVER & BOECKER can depict the structure of single-layer and multiple-layer cloths as a real 3D model (Fig. 1) using GeoDict. Geometric parameters such as the pore size distribution and bubble point are then determined with the PoroDict module of GeoDict. The behaviour of the respective cloth or cloth laminate in various fluids such as air, water and fuel as a function of flow rate or differential pressure is predicted by the FlowDict module.

The simulation of the calibration process is demonstrated here by digitally compressing the media. The wire diameter, pore sizes and the permeability of the structure are changed by calibration. The simulations predict the difference of these properties before and after the calibration process.

Moreover, filtration experiments are carried out at the IUTA in Duisburg using the single-pass filtration test rig MFP 1000 from Palas GmbH. The tests use ISO A2 fine test dust particles. For finding the pressure drop of the clean media, the samples are measured only under air flow, i.e. without injection of dust particles. Afterwards, the particles are injected with the air flow. For defining the standard deviation, the particle size distribution in the air was measured four times in the upstream flow and three times in the downstream flow of the filter media. In other words, three samples for each kind of filter media were used in the experiments to ensure the confidence in the accuracy of the results. The filtration tests are conducted for roughly 75 seconds. The accuracy of this filtration time may vary due to the time the user needs to adjust the sample and later to take the sample out of the apparatus.

The filtration of solid particles from the fluid is also simulated. Filter life-time simulations were carried out using single-pass filtration parameters, i.e. with a constant contaminant concentration. The simulated quantities are the pressure drop, filter efficiency and count/mass of the deposited solid particles as a function of time. Furthermore, the deposited volume of particles and the pressure drop are animated as a function of time. In these simulations, the solid particles are spherical. Simulations are done by HAVER & BOECKER and in consultation with Math2Market. One of the challenges is to find out a precise distribution for the restitution coefficient of different particle sizes when impacting the surface. As restitution coefficient is a function of material properties, impact velocity and angle, particle size and shape, it can have a considerable effect on the filtration results when considering it in the collision models.

The results, namely the filter efficiency and pressure drop, obtained from the simulations are compared and validated with the experimental data. Using the proposed modeling and simulation technique, it is possible to predict the flow and filtration behavior of woven media and to optimize the micro-structure which suits the best for the specific applications...

Filtration is an essential step in biomass gasification processes. In synthesis gas applications, where full removal of gas contaminants is required, the filter unit is typically placed upstream the catalytic reformer in the purpose of shielding the reformer from dust deposits and preventing plugging of the catalytic layer. In state-of-the-art biomass gasification concepts, the raw product gas is cooled down to ca. 500 °C prior to filtration. This results in increased oxygen consumption in the reformer as the gas must be reheated after filtration to reach the targeted reforming temperatures of 850-950 °C. To improve the biomass-to-fuel conversion efficiency of biomass gasification-synthesis plants, the latest R&D efforts in this field have been targeted at operating the filter unit at gasifier outlet temperature (750-850 °C), which would eliminate the intermediate cooling and reheating steps. According to VTT’s estimate, the overall efficiency from biomass to Fischer-Tropsch liquids could increase from 53% to 58 %, if the filter temperature was raised from the conventional 550 °C level to 850 °C.

Filter elements that are currently available for hot gas filtration at temperatures up to 1000 °C are manufactured from metal alloys, high temperature insulation wool or fine ceramic granules. However, these state-of-the-art filter elements have certain restrictions, such as low ductility, high pressure drop or deficient corrosion resistance. With the aim to generate a metal-based filter material withstanding mechanical loads and corrosive conditions, GKN has developed innovative filter elements out of a modified Iron-Chromium-Aluminium powder (material No. 1.4767 mod.). The focus of this work was on evaluating the performance and corrosion resistance of these novel filters in biomass gasification conditions at temperatures up to 750 °C...

Most of the industrial activities dealing with hazardous matter, such as nuclear industry use glass fibres HEPA filter to prevent the release of any airborne pollution in the environment. This technology, used for many decades is well known and its limitations in terms of particle holding capacity / mechanical resistance is either balanced by the use of pre-filtration systems such as inertial devices (cyclones, impactors …) or less efficient fibrous filters (Charvet et al. 2018). In the specific context of the nuclear energy production cycle, purification of the exhaust air needs to be ensured even in incidental context with vapour release. In this context, fibrous filters exposed to liquid aerosol present a quick an important pressure drop increase (Charvet et al. 2010) leading, in certain cases, to a break of the filters and the release of contaminants. If the purification process could be affected or inefficient, a static confinement of the contaminated areas should be applied. This needs to be done without any use of mechanic/electronic device in order to ensure the reliability of the system.

In this context, the important pressure drop increase of a metallic filter could be used to break the ventilation and to prevent contamination release. In this context, the maximal pressure drop depends on the efficiency/structure of the filter media. In this work, 4 different metallic filter medium, with different filtration efficiencies, and fibrous structure (fibre diameters, packing density layered structure) previously loaded with a solid aerosol simulating a contaminant (fluorescein soda) have been exposed to a water aerosol. The pressure drop

Especially the PM2.5 oil content of these oil-water emulsion droplet fraction (including the oil vapour), which are transported into the human respiratory tract, cannot be measured easily. A measurement device using a short-cut cyclone together with a flame ionisation detector (FID) can detect the oil quantity of the PM2.5 droplets. Together with the use of an optical particle counter also the oil/water ratio of these droplets can be determined, which is usually different compared to the initial working fluid concentration (Wlaschitz, 2007).

This measurement device can be also used for a standard test rig (ÖNORM Z1263), which can evaluate the PM2.5 oil separation efficiency of different filter media. For this purpose an oil-water droplet aerosol generator must be used, which should be rather compact and which can produce high droplet concentrations to ensure sufficient oil masses up- and downstream the tested the filter.

For a droplet disperser using a rotation tool, which imitates a moulding cutter, several parameters influence the droplet emission besides the rotation speed. Especially, the diameter of the rotation tool and the roughness (linked with the number of cutting edges on the rotating surface) are relevant for the generated droplet amount. Using a standard cutter rotating device, with small diameter produces insufficient droplet concentrations. Therefore a new compact aerosol generator (Cooling Fluid Generator - CFG 3000, Palas) was build using a steel brush with many steel needles with comparable small diameter, which can produce very high amounts of droplets.

In this work this new measurement method of the PM2.5 oil concentration with the use of this new generator is shown and the increased number particle numbers of the generator for different operation parameters are investigated.

This presentation will explore the pros and cons of using a single photometer architecture for filter test equipment, and the impact the selected architecture has on equipment performance, reliability and total cost of ownership.

The photometer is a critical component to the operation of an automated filter tester and is used to determine the amount of aerosol that is penetrating the media during testing. The ratio of the aerosol that is challenging the media combined with the amount that is measured penetrating the media is determined to be the filter efficiency in percentile measurement.

There are two schools of thought when it comes to the number of photometers and the placement of the photometer(s) within an automated filter tester. One architecture is to incorporate two photometers; one on the upstream media under test and one on the downstream. Both photometers could be either in-line with the aerosol source or they could be partially sampling the aerosol. An alternative architecture would place a single photometer downstream of the measurement, in-line with the aerosol source. Test results have demonstrated...

Inorganic fertilizer producers usually employ prilling towers to get nutrients bound together in even size particles. As consequence of prilling, fine particulate matter (PM) is emitted being its concentration typically sampled manually applying gravimetric methods. This work evaluates the operational performance of two distinct online PM analyzers, electrodynamic analyzer (EDA) and optical scatter analyzer (OSA) in an fertilizer industrial prilling tower against manual sampling. The results show an artificial high emission reading on the EDA every 15 min, what was found to be injection of cleaning steam in the tower, affecting the response, besides manufacturer states the analyzer can deal with changes on relative humidity. The contamination on the sensors affects the reading on both analyzers at some extent but only the OSA indicates the need for cleaning (span test less than 80%) while the self-check responses on EDA is always at 100%. This false response could be probably due to not optimal flow of purge air injected in the probe of EDA rod to keep it clean. It is also observed that...

To assess reliably the energy impact of air filters it is essential to ascertain changes of their airflow resistance during their whole service life and not just when they are clean. This is true in the case of current filters on the market and for future filter designs too.

An air filter’s ageing behavior is strongly dependent on the characteristics of the challenging aerosol during its service life and on the characteristics of the particles collected on the fibers. The relevant aerosol characteristics include its particle size distribution, the shape of the particles, and whether the particles are solid or liquid. The size (diameter) of aerosol particles is especially important in determining the kinetics of the air filter loading and clogging process. In general, the airflow resistance increases more significantly as the size of the loading aerosol decreases.

Current laboratory standards simulate the ageing of air filters by dispersion and loading of synthetic dusts with particle size distribution completely different from a typical urban atmospheric one. This is considered acceptable for rating filters and comparing their performance against each other, but it will not result in accurate prediction of the airflow resistance increase, likely to occur in a real environment. Therefore, the energy-use assessment cannot be reliably estimated by means of current laboratory test dusts.

We can better predict the impact on air filter resistance of their service time if we perform an accelerated ageing procedure by using synthetic aerosols with a thoughtful size distribution like, for example, a reasonable simulation of typical urban atmospheric aerosols. Knowing how a pressure drop realistically changes in time will allow to estimate optimal air filter changes and to establish a meaningful energy labeling system. ISO 16890-1:2016 defines...

...We describe various methods for generating nanoparticles having approximately the same particle size distribution of a typical urban aerosol, but at higher mass concentrations. The purpose is to allow accelerated ageing in a similar way to what happens in actual service conditions. The paper describes the thermal aerosol generator chosen to produce the desired particle size distribution of the synthetic aerosol in an existing test rig according to ISO 16890:2016 specifications. This generator produces a high amount of nanoparticles by burning a salt stick (e.g. made with KCl) with an oxy-propane flame. The salt vapor condenses in the air stream to form a cloud of ultrafine particles...

Electret filters find many applications since they offer a high initial filtration efficiency combined with a low pressure drop. They carry electric charges on the fibers, which interact either directly with charged particles by Coulomb attraction (electrophoresis), or by interaction with induced dipoles in both charged and uncharged particles (dielectrophoresis). A well-known disadvantage of electret filters is that the charge stored on the fibers can drastically degrade with time under exposure to particles, gases or humidity. In order to assess this effect, the testing of particle filters for general ventilation according to EN 779 required the immersion of the filter media in liquid isopropyl alcohol (IPA). In contrast, ISO 16890 which recently replaced EN 779 requires discharging of the filters in IPA vapor saturated air. So far, there is only little knowledge about the comparability of the two methods.

In order to gain new insights, various filter types were immersed in liquid IPA and discharged with IPA saturated air. Before and after discharging, the fractional filtration efficiencies were determined with a sodium chloride (NaCl) aerosol. For several of the filter types, it turned out that...

The efficiency of virus filtration in gases is an area where the generation of accurate and representative data is difficult to replicate. Process filters to remove viruses and bacteria from gas streams are generally in the range of 0.2µm; an order of magnitude larger than many viruses. The adsorption and Brownian motion mechanisms of filtration allow a high retention of small particles in gases, and thus most viruses can be retained by current process filters. The Parenteral Drug Association¹recommends that sterile gas filtration is carried out with filters that have been validated to remove bacteria in liquids; such PTFE membrane filters are also known to effectively remove coliphage viruses of 25nm in size and even particles of 3nm. Depth filters incorporating glassfibre media are also able to retain viruses in gases, albeit with a risk of breakthrough if the filter becomes wet. In recent years, research has focussed on ascertaining the virus retention efficiency of HEPA filters manufactured with polymeric nanofibre media.

Current methods to assess virus retention using surrogates are based on the retention of oil droplets and sodium particles; neither resembles the surface characteristics of viruses, which are critical to the efficiency of separation.

The use of protein nanoparticles as a surrogate is a practical and reproducible tool that challenges filters with particles that closely replicate the properties of viruses. Braas et. al., 2000² have shown, how such particles show a similar behaviour to adenovirus in aqueous phase, liquid-liquid separations and ion-exchange chromatography; this is indicative of similar surface properties and thereby adsorption characteristics to filter media. The aim of the current project is to explore the application of suitable surrogates based on protein nanoparticles to test the retention of viruses, with the surface properties of the chosen challenge particles taken into account...

The Aerodynamic Aerosol Classifier (AAC) is a novel instrument that classifies particles based on their aerodynamic diameter. This is accomplished by passing the aerosol between spinning concentric cylinders with a coaxial sheath flow. Particles that have aerodynamic diameters larger than the AAC setpoint are dominated by the centrifugal force and impact the outer cylinder surface, while smaller particles remain entrained in the sheath flow; only particles with a narrow range of aerodynamic diameters pass through the AAC classifier. Particle sizes between 25 nm and 6.7 microns can be selected independent of the aerosol charge state, with a high transmission efficiency limited only by diffusion and impaction losses.

This technique can be used to measure an aerosol’s aerodynamic size distribution by stepping the AAC setpoint while recording the classified particle number concentration (Johnson et al., 2018). However, similar to the Differential Mobility Particle Sizer (DMPS) this stepping procedure requires long measurement times to achieve reasonable spectral resolutions. To overcome this limitation, Johnson et al. (In Preparation) recently developed the scanning AAC inversion. Following a similar methodology as the Scanning Mobility Particle Sizer (SMPS) inversion (Wang & Flagan, 1990), this new approach allows the aerodynamic size distribution to be continuously measured by varying the classifier speed while measuring the classified particle concentration. By continuously varying the classifier speed following an exponential function, the change in the centrifugal force a particle experiences during its classifier residence time is independent of its inlet time. Furthermore, when the scan time is sufficiently longer than the scan speed ramping constant, the scanning AAC transfer function converges to the same shape as the steady state transfer function.

This study uses a scanning AAC to collect accelerated measurements of the ambient air particle size distributions in a room before and after the operation of a commercial room air purifier. A filter sample was taken from the air purifier and measurements of the size-dependent filtration efficiency were made, using the AAC to select monodisperse test particles by aerodynamic diameter. The aim was to assess the air purifier performance by comparing size-dependent penetration measurements with the full real-world ambient spectra...

A challenge and decision in the clean room design process is how to determine the required supply air volume to achieve the target cleanliness classification in a given application. Historically, these decisions are made based on experience and following practices and guidelines that have evolved from multiple sources which we can today say have been conservative at best.

Following these practices will supply enough clean air to meet the classification requirements, however at the expense of overdesigning the system with higher capital costs and by default, higher operating costs than necessary. Also, if the experience based approach leads to underestimating the supply air rate, the result could be contamination levels that are too high and costly work to fix the problem. AAF Flanders has developed a scientific approach to this problem for predicting the contamination in a clean room based on sources of particle generation, air filter efficiency and air change rate.

VisionAir Clean is a web based application that allows the user to see factors that impact indoor air quality and energy consumption related to the air filtration system. Starting from the PM 2.5 levels in the outdoor environment, this program displays the particle count in a room as a function of the air change rate and compares it to the selected cleanliness standard requirements. VisionAir Clean also accounts for particle generation within the clean spaces, such as people in various garment types and process related contamination, and shows the changes in contamination as inputs are modified. Filter test data are loaded into the program to estimate filter life and optimize the change-out cycle based on balancing the costs associated with the filter (purchase price, labor, disposal, etc…) and the energy consumption as the filter resistance increases with dust load. The energy cost impact due to resistance across housing components, such as dampers and diffusers, are also taken into account.

The output of this analysis is an optimized solution for air filtration applications, specifications, drawings and models of products, reports indicating total cost of ownership and air quality, a 3D visualization of the products and a technical library of relevant industry information...

Many areas of our daily lives lead us to encounter the term “smart”. Smart phones, smart watches, smart illumination systems, smart vehicle and smart facility management cross our paths almost everywhere.
Once you understand the term smart as a digital and demand specific control system, it appears only a question of time until this terminology reaches the world of air filtration. Already today highly efficient air treatment systems are closely controlled and adjusted according to the actual ventilation requirements in the building. Measuring CO₂ concentrations, for instance, makes it possible to adjust the amount of fresh air in the system, as much as dynamically controlling necessary heating and cooling loads. Contemporary air treatment systems are continuously checking and adjusting their operational configuration.
The mere measurement of CO₂ concentrations does not automatically make any system smart, by any means. Just as important as determining the CO₂ concentrations are the fine dust contaminations, VOCs, nitrogen oxides, ozone, carbon monoxide, relative humidity, etc. in occupied space. Each of these factors may also influence one another, which has to be respected. A comprehensive and continuous data analysis already makes it possible now to accustom the filtration performance to the current requirement of the air treatment system. Filter units can individually be activated for ventilating a building or they are selectively taken out of the main air stream.
This still does not make a filter smart. The intelligent feature in this set up is the air treatment system, that guides use, or non-use of the filter unit. Filtration only becomes truly smart, once the filter actively provides information about its current status into the air treatment control system. The future will introduce microchips in filter elements that provide precise information about the current pressure loss, humidity, and possible microbiological growth.
Sensors in the filter frames will make date of filter commissioning as well as the exact position of filter available to the operator of the facility. Hereby the filter can actively suggest and optimal change interval to the local facility management and can also forecast expected increase in pressure loss, the expected additional operational costs, the replenishing costs and calculate a break-even point. The data needed for replenishing are naturally web-based, making it easy to re-order in a B2B e-commerce channel, as to ensure next day filter delivery and filter commissioning. ... brave new filter world.
The leap from a smart filter unit to a fully digitalized filter order process is less than a stone throw. A strong development of digitalized markets - also known as e-commerce is to be observed in a vast number of industrial sectors. A continuous increase of online transactions will eventually change the access to the filter market mid-term and fundamentally transform the market for air filters...