Dust extraction works by drawing contaminated air through ducting into a dust collector which filters the air and captures the dust particles. Local Exhaust Ventilation (LEV) is generally considered to be the most effective type of dust extraction as it captures contaminated air at source before it has a chance to escape into the atmosphere.
Dust extraction LEV systems include:
End-users looking for the ‘top industrial dust extraction system’ will need to be clear about what type of system they need – different dust extraction systems are designed to handle different types of dust with different properties. Kst values, free flow characteristics, volume of dust, particle size, and the proposed location of the dust extraction system are just some of the factors which should be considered when looking for the ‘top industrial dust extraction system’.
Filtermist’s dust extraction experts advise on all aspects of dust extraction system specifications to ensure our customers get the best system for their specific requirements.
The term ‘efficient’ in the context of dust collection units can mean different things to different people. Efficiency can refer to energy consumption, running costs, filtration performance, operator input needed, maintenance requirements, forecast uptime – all factors which contribute to efficient dust collection units.
Our dust team ensures a clear understanding of what matters most to each individual customer before suggesting the most efficient dust collector for their needs.
The Health and Safety Executive (HSE) requires all employers to comply with regulations which are part of the Health and Safety at Work etc. Act 1974. These include COSHH (Control of Substances Hazardous to Health) Regulations 2002 and DSEAR 2002.
For dust extraction, the HSE requires that people are adequately protected from exposure to dust particles. The hierarchy of controls should be used when evaluating how to minimise risk. If the risk cannot be eliminated or substituted, engineering controls should be employed to reduce the risk to ‘as low as reasonably practicable’ (ALARP), or for substances that have a specific WEL (Workplace Exposure Limit), the risk must be reduced to below the WEL (see EH40 for guidance on WELs).
The difference between dust extraction, dust collection and dust filtration is:
LEV dust extraction units and dust collectors effectively do the same job, and that includes all of the above. They extract air from a specified pick-up point or multiple pick-up points, they filter it to separate particulate from the airflow, and they collect dust to be disposed of or reused.
Yes! Dust can be a problem even when it’s not visible. Particles may be so small that they are difficult to see with the naked eye, and dust can gather in out of reach places making it difficult to see. This includes ceiling mounted lighting, beams, ducting and other places with limited accessibility.
Using a dust lamp, also known as a Tyndall beam, is one way of seeing airborne particulate. Contamination can also be measured with an aerosol particle counter. Filtermist engineers use dust lamps and particle counters to assess air quality in their initial site assessments before recommending suitable dust controls.
Fundamentals of dry dust filter unit separation
These types of dust extractors typically utilise elements made from permeable filter media in various degrees of efficiency and finish to separate solid particulates from a gas stream utilising the four main components of membrane filtration mechanics; impaction, interception, diffusion and electrostatic attraction. Usually, dry dust filter units used in industrial applications utilise some method of automatic cleaning to dislodge filtered particulate from the media (dynamic filters) however this is not always the case, some dust filters are designed to be simple dust barriers without the need for media re-generation (static filters).
As particulates accumulate on the filter elements there is an increase in differential pressure (the static pressure measured each side of the filter media) and depending on the type of application this will either need to be periodically cleaned (usually high dust load applications with automatic cleaning systems) or the filter element(s) changed completely (low dust load applications without a cleaning system such as secondary HEPA filters).
Membrane type filtration offers very high levels of efficiency which can be over 99.99% at 0.3 microns (E10 rated) with primary automatically cleaned media, and up to and even past H14 efficiency on static dust filters. Dry filter extraction systems are suited to a myriad of different applications in multiple industries and offer a reliable, low maintenance and high efficiency solution.
Limitations of dry dust filter units
Dry filter units that utilise membrane type medias usually contain filter elements in one of the following formats; pleated cartridges, pleated cassettes, tubular bags or flat bags.
Common constraints across all of these formats are that they are all essentially using a permeable media which requires filtration to occur on the surface and through the depth of the material in some cases. As such these types of dust filters are challenged if there are high moisture levels (in liquid form) in the extracted air which can saturate the filter media or the particulates being filtered are very adhesive in nature and difficult to remove with an automatic cleaning system.
High moisture levels that exist in a gaseous state i.e., the relative humidity of the air passing through the dust filter, is not necessarily an issue as long as any temperature differences between the extract air and the extraction filter unit are considered in terms of not letting the air cool to ‘dew point’ which is where condensation into a liquid will occur. This is usually addressed by the addition of trace heating and/or lagging to minimise dew point issues.
Other considerations for the application of dry dust filters are where potential ignition sources are introduced into the system by the process itself e.g., metal grinding producing sparks, and limitations of protection when handling highly explosive and volatile dusts.
Most dry dust filter medias are flammable and introduction of ignition sources can pose a risk of fire unless some means of protection is implemented such as spark extinguishing or similar. If the dust being extracted is explosive then the risks are even greater if ignition sources are known to be present as there is a potential mix of fuel and an ignition source co-existing. Even with adequate explosion protection in line with ATEX Regulations, this type of application may pose a high enough risk to move away from a dry dust filter solution.
A limiting factor with dry dust filters is also the maximum level of explosion protection available. In terms of explosibility the vast majority of particulates handled in industry are well within the capabilities of a dry dust extraction system. However, care should be taken when handling ST3 rated dusts with a KST value >300 bar m/s (as per BS EN 14034 - Determination of explosion characteristics of dust clouds). These high explosibility levels are usually found when handling reactive white metals such as aluminium, magnesium etc. and can reach levels of 1,000 bar m/s or more. In this instance it is unlikely that a dry dust filter unit could be made strong enough and with enough explosion vent area to handle the application. The customer is also likely to deem the potential risk and significant repercussions of such a violent explosion, should it occur, too great and to seek an alternative.
Fundamentals of wet dust filter unit separation
A wet filter unit typically separates solid particulate from a gas stream by passing it through an atomized liquid whereby particles get encapsulated by droplets and subsequently submerged into a tank where sedimentation occurs. As the method of separation is provided by a liquid which is recovered and re-used within the unit, there is no requirement for replaceable filter elements such as those in a dry unit.
Scrubbing Stages
Wet dust collectors, or wet dust scrubbers, are mass separators. The efficiency of wet dust collection is determined by the mass of the dust particle present in the extracted dust cloud relative to the size of the water droplets generated.
Wet collectors are more suited to particles with heavier mass and they function by generating very fine droplets or aerosols in the 'spray generation zone'. These droplets will impinge on, and encapsulate dust particles of similar momentum.
Wet units usually require dusts of relatively high specific gravity (>2500kg/m3) and with particle sizes >10 microns to achieve acceptable filtration efficiencies of >99%. Wet collectors are recommended when machining reactive white metals such as aluminium, titanium and magnesium etc. due to their highly volatile nature and are also ideal for handling sticky particulates or dusts extracted with liquid moisture.
Limitations of wet dust filter units
Unlike a dry dust extraction system where filtered dust is discharged from the unit, then collected and disposed of, wet dust extraction systems effectively create a liquid waste stream as the means of filtration and is also the medium in which the particulate accumulates. This requires regular manual cleaning and therefore some limitation of operation during maintenance down-time.
Treatment is also required to be added to the water in a wet unit to minimise corrosion, and this requires regular checks to maintain correct levels. In addition, the scrubbing liquor will collect water soluble salts, liquids and gases and will therefore require periodic drainage. Hydrophobic (water repellent) dust particulate will not be contacted by the droplets and therefore not filtered out in the unit.
A proportion of water is consumed and given off as a vapour and a visible discharge plume from the unit so a permanent water supply is required to be connected to it to allow operating levels to be maintained. Consideration must be given to the dust extractor discharge position because of the vapour plume and it is also worth noting that the plume can sometimes be misinterpreted as excessive carry-over and require validation by the supplier to the end user.
Due to the mechanics of atomized liquid filtration, the efficiency of wet units is linked to the specific gravity of the extracted dust as well as dust particle size distribution. A SG of 2,500kg/m3 and typical particle sizes >10 micron are usually required to achieve acceptable efficiencies as stated above, and this can rule out wet collector application in some industries.
Filtration efficiency based solely on particle size is limited when compared to dry dust units. Typically, the mean particle sizes in a wet dust extractor need to be >25 microns to achieve the same levels of efficiency as dry dust extractors handling dusts at 5 microns and less. Therefore careful consideration of required filtration efficiency and dust particle size distribution should be applied before selecting a wet dust extractor. The main applications for wet filtration are based around mechanically generated dusts such as polishing, linishing, grinding, crushing and fettling - typically in the metals and stone masonry sectors as the particle sizes and specific gravity of dusts generated from these processes generally fall within the capabilities of the equipment.
Yes, according to HSE, The Health and Safety at Work etc. Act 1974 places general duties on employers to ensure that people are not exposed to unnecessary risks to their health or safety arising from the employer's work activities. Dust in the workplace requires general principles of protection from dust.
In addition, the Control of Substances Hazardous to Health (COSHH) 2002 Regulations were established to protect workers from exposure to hazardous materials. (Asbestos and lead are not covered by COSHH as they have their own separate regulations). COSHH helps employers control risks by providing a framework underpinned by a risk assessment.
Other legal requirements include alignment with the Atex Regulations if handling explosive dusts or gasses and the Environmental Protection Act which deals with limits on how much contaminant is allowed to be discharged to atmosphere from various industrial processes.
Dry dust collectors from different manufacturers can include different types of filter elements.
Cartridge filters are cylindrical in shape and made up of filtration media, often housed in a metal or plastic casing. They often contain synthetic media or pleated paper of varying depths (deep pleat or shallow pleat). The pleating structure enables a very large amount of filter media to be housed in a relatively small space. For example, AD dust extraction units can include individual filter cartridges containing 25m² of filter media.
Cartridge filters are best for fine, dry, free-flowing dust.
Bag filters, or ‘filter socks’, are made from fabric and suspended inside the dust collector in a baghouse system. They are mainly used for abrasive, heavy, fibrous and coarse dusts with larger particle sizes.
Dustcheck dry dust collectors can be supplied with a choice of filter cartridges (deep pleat or shallow pleat) or bag filters depending on the application.
Filter cassettes are used in oil mist and oil smoke extraction units – Absolent filter units contain filter cassettes. The cassettes are boxes containing pleated filter media made of different materials depending on the nature of the application. As with filter cartridges, the pleating enables a large amount of filter media to be used, giving a large overall filtration surface.
The cost of dust collectors can vary enormously depending on the nature of the application, the air volume needed, the type of filter media used, whether it needs to be suitable for use in ATEX zones, and additional functionality including performance monitoring and IoT connectivity.
It will also depend on whether the dust collector is being bought as a stand-alone item or as part of an LEV system that includes ducting and any other components.
Dustcheck dust collectors and the AD range from Absolent can all be configured to meet specific customer requirements. Contact our team to get a quote based on your needs.
There are many factors to take into consideration when purchasing a dust collector, including:
Our dust extraction experts take all of these factors and more into account when specifying dust collectors – contact them now to discuss your dust collector requirements.
Filtermist provides oil mist collectors in over 60 countries worldwide