Dust Collectors

Dry dust collectors, also known as baghouses, cartridge filters or fabric filters, are used to capture and remove particulate matter (dust) from air within an industrial process. They are commonly used in industries such as manufacturing (food, pharmaceutical, metals, aggregates), power generation, chemical processing, and mining to maintain air quality standards and protect the health and safety of workers and the environment.

How do they work?

• Inlet Section: The dirty exhausted air containing particulate matter enters the dust collector through an inlet duct or hood.
• Filter Media: Inside the dust collector, the air passes through a series of fabric filter bags or cartridges. These are made of porous materials like woven or felted fabrics made from natural or synthetic fibres. The fabric acts as a barrier, allowing the air to pass through while trapping the dust particles.
• Dust Collection: As the air flows through the filter media, the particulate matter is captured by the filter bags or cartridges. The dust accumulates on the outside of the filter, forming a layer known as the dust cake.
• Clean Air Outlet: After passing through the filter media, the clean air exits the dust collector through an outlet duct, returning to the atmosphere or via secondary filtration if clean air is to be returned to the workplace.

• Cleaning Mechanism: Over time, the dust cake buildup on the filter media can reduce the air volume of the dust collector due to the increased pressure drop across the system. To maintain optimal performance, the dust collector typically employs a cleaning mechanism to remove the accumulated dust from the filter elements. Common cleaning methods include:

  • Pulse Jet Cleaning: This is the most common method used in dry filter units. It involves periodically releasing a pulse of compressed air into the filter bags or cartridges. The sudden increase in air pressure dislodges the dust cake, which then falls into a hopper located at the bottom of the dust collector for disposal. Pulse cleaning can be used to regenerate individual filter elements or multiple filter elements depending on the system design.
  • Mechanical Shaking: Some dust collectors use mechanical devices to vibrate and shake the filter elements, causing the dust cake to fall off.
  • Reverse Air Cleaning: In this method, the direction of airflow is temporarily reversed by an axial type fan to dislodge the dust cake, and is usually applied to whole sections / rows of filter elements.
• Dust Disposal: The collected dust is typically discharged via a hopper at the bottom of the dust collector into varying disposal methods. Disposal can be with a bag or bin, a drum or via automated discharge devices such as screw conveyors and rotary valves where larger dust loads are being handled or manual handling is not desired. Depending on the application and regulatory requirements, the dust may be disposed of or recycled.

Advantages

Dry dust collectors offer several advantages, including very high efficiency in capturing fine particulate matter, relatively low operating costs, and versatility for handling a wide range of dust types and concentrations. Proper design, operation, and maintenance are essential to ensure optimal performance and compliance with environmental regulations.

A wet filter unit, sometimes known as a wet scrubber, typically separates solid particulate from the air stream by passing it through an atomized liquid whereby particles get encapsulated by droplets and then 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.

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%. They are recommended when machining reactive white metals such as aluminium, titanium and magnesium etc. due to their highly volatile nature and the wet collector’s inherent ability to quench any incoming ignition sources. They are also ideal for handling sticky particulates or dusts extracted with liquid moisture dependent on the contaminant characteristics.

A wet extractor is a highly efficient and reliable solution for eliminating noxious mechanically generated dusts generated within the workplace. Specifically designed to handle flammable metal dusts, wet dust collectors offer an optimal solution for filtering and gathering combustible dust generated by various processes such as grinding, fettling, linishing, deburring, polishing, and trimming metals like Aluminium, Magnesium, Titanium, Zirconium, Lithium, and Tantalum. Dust produced from these activities is deemed highly explosive.

The wet dust settles at the bottom of the water chamber, forming a compact layer of sludge. The collected sludge is agitated and discharged manually or automatically, and water volume is maintained by level control systems that ensure optimal performance at all times. Clean air is then discharged from the top of the unit - either direct to atmosphere or back into the working environment, depending on where the unit is sited and whether secondary filtration can be applied.

Selecting the most suitable dust control equipment is not an easy task. Many manufacturers will encourage businesses to buy equipment that happens to be in their own product portfolio; but is it always the right equipment for the job?

Filtermist manufactures dust control equipment that utilises either media-based filtration or liquid separation under the Dustcheck brand – one of very few UK manufacturers that can offer both solutions. This means we are not restricted by a limited product range and are able to specify the optimal solution for any application.

Choosing the right dust control equipment requires expertise, knowledge and experience due to the multiple design considerations for each individual application and varying characteristics of dusts that need to be captured. Dustcheck has been providing dust control and air filtration equipment for more than 40 years and as such is perfectly positioned to specify the most appropriate solution to the dust control requirements of its clients.

Click here to find out more about Application considerations for dry and wet filter systems.