Developments in air & gas filtration technology

A special sampling unit enables representative aerosol sampling downstream without disturbing the pulse jet cleaning effect and can be added for online particle size and particle concentration determination using the light scattering spectrometer Promo. The unit can also test filter media with different dust standards from real-life practical applications..

As the range of filtration and separation technologies increases and develops alongside the numerous air and gas filtration applications, there is a growing need for development and production of reliable and effective filter test systems to enable effective monitoring of regulatory compliance. Factors driving this need include primarily regulatory compliance, the need to reduce total lifecycle costs by optimizing process efficiency, and the focus on mitigating health concerns by purifying air and controlling the potential effects of air pollution.

Reliable and effective filter test systems have been developed and manufactured by companies such as Palas®. Investing in the development of safe standards in particle and filter technology, this company is represented on several committees including ISO (International Standardization Organisation), DIN (Deutsches Institut für Normung/German Institute for Standardization) and VDI, the Association of German Engineers. These regulatory standards apply to filter test systems, counting aerosol measuring devices and calibrating aerosol measuring devices.

Filtration and separation technology applications in air and gas filtration are diverse as demonstrated by the various markets companies such as Amazon Filters. Blücher, Freudenberg Filtration Technologies, and Macrotek are involved with. A primary focus for such companies is on reducing the total lifecycle cost of manufactured equipment to meet industrial requirements by investing in research and development activities.

Industry sectors include automotive, pharmaceutical, food and beverage, chemicals, coatings, water treatment, oil and gas, gas turbines and compressors, nuclear and other contaminated wastes, mining and, incineration and building services. All these applications require filtration of air and other gases, such as biogas from liquid waste recycling using membrane bioreactor technology and waste ‘off-gases’ from a range of other process technologies.

Membrane and depth microfiltration cartridges and associated industrial, hygienic and sanitary housings for clarification, stabilization and sterilization filtration applications are provided by Amazon Filters. Freudenberg Filtration Technologies design and manufacture Viledon air filtration technology for industrial and consumer applications.

Blücher, for example, specializes in mitigating health concerns by providing internal air filtration technology for use inside aircraft and vehicles that can operate in environments that are hazardous to health, whilst also concentrating on odor adsorption in a range of consumer appliances such as vacuum cleaners, refrigerators and kitchen hoods. Macrotek specializes in providing custom designed industrial air pollution control systems utilizing wet and dry technologies including quench systems, scrubbers, absorbers, and particulate collectors.

Regulatory compliance

Two main standards specify the testing regime for cleanable filter media in air and gas filtration applications. VDI 3926 (2004) specifies testing and evaluation procedures for filter media which are used in dry-operating cleanable filters. ISO 11057 (2011) specifies a standard reference test method for comparative characterization of pulse-jet cleanable filter media. The test evaluates filter elements such as bag filters and cartridge filters, and it is applied in dry gas cleaning applications under standardized test conditions. The main purpose of the testing process is to gain information about both the operational performance and the particle emission levels of cleanable filter media.

Filter testing technology

Because of the expanding requirement for reliable and effective filter test systems to enable accurate monitoring of regulatory compliance, a filter test rig (the MMTC) for cleanable filter media has been developed by Palas. The unit tests media in accordance with and in excess of the VDI 3926 (2004) and ISO 11057 (2011) standards.

The MMTC technology is a precise, reproducible testing system for the development and quality control of cleanable filter media. As an addition to the well-established MMTC 2000 system, Palas has introduced the MMTC 11057 design (Figure 1), which covers the ISO 11057 reference test for filter channel design. Features include the duct design, a vertical upstream duct with separate air flow control, and a very stable BEG 1000 dust feeding unit.

Figure 1. Filtration media testing system. Courtesy of Palas® GmbH

A special sampling unit enables representative aerosol sampling downstream without disturbing the pulse jet cleaning effect and can be added for online particle size and particle concentration determination using the light scattering spectrometer Promo. The unit can also test filter media with different dust standards from real-life practical applications.

The MMTC 2000 EHF version can operate at temperatures up to 250°C with an adjustable relative humidity up to 80%. It was installed in 2016 at the Institute of Energy and Environmental Technology (IUTA e.V.) in Duisburg, Germany and was utilized in research into the influence of humidity and temperature on filtration characteristics.

Sampling probes enable in-situ measurements in the filter housing. With the aid of specially shaped filter holders, the so-called ‘garland effect’ on a filter hose during cleaning can be simulated.

In addition, the Promo aerosol spectrometer can enable high frequency particle concentration and particle size distribution determination. Test specimens can, therefore, be accurately analyzed during the cleaning pressure burst, allowing the cleaning parameters to be optimized to the medium.

Optimizing process efficiency

Reducing the total lifecycle costs of air filtration and separation systems can be achieved by optimizing the process efficiency of technologies to meet site specific requirements in the various industry sectors. Reducing energy consumption and associated economic costs is a focus for a number of companies operating in the sector. Here we consider examples of new technologies now available from Freudenberg Filtration Technologies and Amazon Filters, in bag filtration, cartridge filtration and online filtration monitoring applications.

The latest range of Viledon NEXX filter bags are designed for dust removal applications where dust levels are especially high (Figure 2). Based on the Evolon filtration medium, developed by Freudenberg, the filter bags are made from a patented microfiber material. The bags are up to 50% lighter than conventional needle felt variants. The manufacturing process also consumes fewer raw materials. Spun from endless filaments, the fine microfiber surface has been designed to ensure that valuable recovered products remain free from contamination.

Figure 2. Bag filtration for dust removal. Courtesy of Freudenberg Filtration Technologies SE & Co. KG

The filter bags are aimed to be effective in applications involving the recovery of powdery products and silo dusts in the food and pharmaceutical industries. For example, flour in mills can be easily recovered from the gas flow and reused.

The filter bags are also used for capturing inorganic colour-pigment dust. Their ultra-fine pores and fibers enable pigments to be produced with small particle diameters, down to the nanometer range. The filtration medium is also free from silicone, making the filters suitable for recovering the color pigments used in the automotive industry.

Nanofiber coatings

Viledon sinTexx Plus filter cartridges are another development from Freudenberg. The technology is intended for applications such as separation of smoke and fine dust. The filtration cartridges are made from corrugated polyester nonwovens with a nanofiber coating, which makes them capable of separating very fine dust and smoke. The cartridges can be manufactured with an antistatic option for separating potentially explosive dusts.

In common with NEXX filter bags, the filtration media used in sinTexx Plus filter cartridges can be fitted into all cartridge geometries, offering customers design and application flexibility. According to Freudenberg, high initial efficiency can be guaranteed because, unlike conventional filters, these filters do not need pre-coating with dust. The corrugated filter medium ensures constant low resistance, reducing power and compressed air consumption, potentially extending the product lifetime. Nanofiber coated filter cartridges are straightforward to handle and require minimal maintenance.

Online monitoring for corrosivity measurements

Corrosion caused by harmful gases in switching and control rooms can cause systems to shut down and damage production processes. Combined with the Viledon ChemControl filter system technology, that provides electronic components with protection against corrosion, Freudenberg's Viledon ChemWatch online monitoring system can provide reassurance that no harmful corrosive gases will affect sensitive electrical and electronic devices.

The monitoring system features corrosion sensors stretched right across its surface by means of two sensor boards: one made of copper and one of silver. As corrosion changes electrical resistance, values are periodically measured on the boards and compared with a reference value. To ensure continuous all-round analysis, the technology also detects room temperature, relative humidity and room pressure.

The unit features an operator interface screen that displays a color curve diagram, showing whether the concentration of harmful gases is in the ‘green zone’ and how it has altered over time. All information is incorporated in real time, stored and kept available for tracing and analysis for at least an eighteen-month period. The system is installed to meet specific industrial site requirements. For example, users can choose to retrieve data via WLAN or define individual alarm signals with alerts sent by email. This flexibility can enable users to recognize and remedy problems as they arise.

Commonly used to remove contaminants from air and gases, pleated media cartridge filters are typically used on venting applications on tanks and vessels and filtration of compressed air and gases.

“Our microfiltration cartridge technology,” Keith Wickert, at Amazon Filters explained, “can be used to control particulate contamination in critical applications, such as in the biopharmaceutical, pharmaceutical and beverage industries.” The technology is primarily used for the removal of microorganisms and viruses.

Such types of filter often utilize hydrophobic filter media to ensure that high flow rates and low pressure drops are achieved under a range of conditions. Many major multinational pharmaceutical companies have biotech manufacturing operations, typically producing high value products. This sector is a significant one for filtration and separation technology specialists such as Amazon Filters.

“At one particular site,” Wickert explained, “the biopharmaceutical material is produced by genetically modified microorganisms which are cultured in fermenters to provide high microorganism numbers and high product yields.”

The microorganisms require a constant stream of air to enable them to live, grow and manufacture the required product. The air is sterile filtered before it is bubbled through the culture liquid that the microorganisms are grown in, and also the air is filtered as it exits the fermenter, a large sanitary stainless steel vessel.

Cartridge filtration of fermenter off-gas

The air is sterile filtered to prevent contamination of the fermenter with external microorganisms and to prevent any carry-over of contamination into the surrounding environment. This particular pharmaceutical manufacturer uses large-scale filtration systems which are required to operate for long periods continuously to ensure the operation is economically viable, whilst maintaining the sterility of the operation. The systems are large as there is a need for high air flows. The application is demanding and the filters are required to provide sterile air, withstand multiple steam cycles and maintain low pressure drops.

SupaPore TPB microfiltration filter cartridges are used. These are manufactured using a naturally hydrophobic polytetrafluoroethylene (PTFE) membrane, providing a reliable solution for critical applications

“Use of the SupaPore technology in the in biopharmaceutical manufacturing is a solution for companies operating fermentation plants as the technology meets the demands for large volumes of sterile air supplied over a long period of time,” Wickert concluded.

Amazon Filters also offer SupaPore FP H0P and PPG pleated filters for air filtration. FP H0P filters are manufactured using a hydrophobic borosilicate based media and according to the manufacturer does offer effective microbiological contamination control. PPG filters utilize a polypropylene media and are used in a range of applications where particulate control is required.

Purification and pollution

Having firstly considered regulatory compliance, followed by the need to reduce total lifecycle cost by optimizing process efficiencies, we now focus in this section on controlling the potential effects of air pollution.

Blücher specializes in this field by providing internal air filtration technology inside buildings and also in aircraft and vehicles that are used in hazardous environments. Macrotek specializes in providing bespoke system design solutions for industrial air pollution control applications.

Over the last few years there has been a steadily increasing demand for improved air quality, particularly indoors, whether in private, public or industrial areas. Emissions may come from a variety of sources, such as gases from interior materials, particles which enter a room via the external air supply or processes running within the room. Further complicating factors may be the small size of a room, too many people in the room and the restricted availability of fresh air.

Any sustainable improvement of air quality must include the elimination of unpleasant but harmless odors, but more importantly the elimination of hazardous substances is required. These can include components such as volatile organic compounds (VOCs), polychlorinated biphenyl (PCB), insecticides, and other forms of airborne molecular contamination (AMC), solid particles and aerosols.

These concerns, as identified by Blücher, can arise in storage rooms in museums where vapors from lindan on stored items can be so strong that people are not permitted to enter the rooms due to the existing hazard to their health. But even non-contaminated items, brought in for storage at a later stage, can begin to attract contaminants over time.

The SARATECH indoor air purifier with its integrated filter media and spherical absorbers claims to ensure the elimination of unpleasant odors and also the separation of hazardous substances. Combined with particulate filters the purifier removes solid particles such as dust, pollen and spores.

Any gaseous impurities are permanently bonded within the adsorptive micropore system, and relatively high humidity has no major impact on filtration performance. The absorbers have a defined internal surface of up to 2,100 m2/g, a multimodal distribution of pores and thus a high level of adsorption capacity and kinetics. Particle size, pore system and level of activation can be individually adjusted to suit varying requirements.

The adsorptive filter stage can be adjusted to suit the contaminant matrix that needs to be filtered. The units are designed to filter a maximum air flow of 450 m³ per hour, and they include coarse dust filters and particulate air (HEPA) filters.

To operate effectively and efficiently, it is essential that indoor air purification technology is positioned in the correct location. If the design is poor or if the device is noisy, then the air purifier may not always be positioned in the optimum location, so that it fails to capture and clean the air within the entire space.

The Sartech filter media that form part of one of its purifiers is designed to reduce the level of air pollution in a contaminated environment, resulting in an improvement of air quality in small and poorly ventilated rooms. Locations where access is not recommended or even prohibited under regulatory requirements can potentially be made accessible again.

Hydrogen sulfide removal

Macrotek's SULFCAT process (Figure 3) is a new scrubbing technology targeted at the removal of contaminants from various gas streams. Hydrogen sulfide (H2S), commonly found in oil and gas reservoirs, is an extremely toxic gas produced naturally in anaerobic digestion processes and many industrial processes.

Figure 3. Hydrogen sulfide scrubbing system. Courtesy of Macrotek Inc.

“Our process is based on a regenerative technique that scrubs hydrogen sulfide from industrial gas streams by using a regenerative reagent which eliminates the sulfate-containing wastewater stream produced by traditional technologies. The result is a reduced rate of scrubbing reagent consumption,” explained Chris Ristevski at Macrotek.

The company has developed a technique which utilizes a catalytic reagent that converts H2S to solid sulfur. After the reaction, this reagent is regenerated by forced oxidation. It is then recycled back into the system. This process eliminates the sulfate-laden wastewater stream and hence reduces reagent consumption.

A mixture of Sulfcat aqueous solution (a blend of stabilized metal oxide particles) facilitates a set of reactions with the absorbed H2S and converts it to innocuous elemental sulfur, a potentially marketable product. The simple addition of air regenerates the reaction solution.

The process is delivered installed alongside one of Macrotek's novel process gas scrubbing systems (Figure 4). Firstly, H2S is absorbed in the absorber tower before the oxidation vessel regenerates the SULFCAT reagent and releases the elemental sulfur. This is then filtered or centrifuged and removed from the solution. A number of reaction pathways occur in the process but all reactions in the system can be summarized by the following overall reaction:

2H2S + O2 → 2S(solid) + 2H2O

Figure 4. Hydrogen sulfide removal process flow diagram. Courtesy of Macrotek Inc.

According to the manufacturer there are several benefits to the process compared to traditional technologies. Reagent is not consumed by the reaction and is continually regenerated. Also, the technology's design eliminates the sulphate wastewater stream, drastically reducing reagent consumption. The technology can also reduce blowdown volumes in scrubber systems and minimize water consumption, thereby reducing costs and minimizing environmental impact.

“Operating costs can be reduced by as much as 70% compared to traditional scrubber technologies,” claims Ristevski, “along with high H2S removal efficiency.”


This article has investigated a number of new filtration and separation developments for the filtration of air and gases. The theme of reducing energy consumption continues to be a major focus for manufacturers and process design engineers. It is clear that this requirement is being driven by regulatory compliance, the need to optimize process efficiency and meet specific customer requirements, and the need to focus on mitigating health concerns by purifying air and controlling the potential effects of air pollution.