Dust collection systems are essential for a safe working environment, protecting your equipment, protecting your facility, and complying with government regulations.
A dust collection system also ensures public safety by eliminating or reducing the amount of particulate matter or dust that flows from your facility into the atmosphere.
Baghouse filters are ideal for their efficiency and cost effectiveness. We can often refurbish and reuse your baghouse filter bags, saving you money and keeping them out of your local landfill.
What Are Baghouse Filters?
Also called ‘socks’, baghouse filters are cost-effective and highly efficient air pollution control bags used in manufacturing plants to filter out particulate matter and dust from an incoming airstream.
A baghouse uses a fabric filtration system consisting of bags with special filter media to capture, collect, and separate dust and different-sized particles from the air. Depending on the manufacturer and the type, a baghouse dust collection system may have anywhere from six, to hundreds of baghouse filter bags.
Components of a Baghouse Dust Collector
Not all baghouse dust collector systems will have the same structure and components. It will often depend on the baghouse filter design and the manufacturer.
Generally, a baghouse dust collector consists of the following parts.
Fan
The industrial fan in a baghouse pulls air into the system through an air inlet.
Air Inlet and Air Outlet
The air inlet brings dirty air into the baghouse filter bag, while the air outlet expels clean air from the system into the atmosphere or back into the facility.
Filter Media
The media used in the construction of baghouse filters bags depends on the particulates and dust that is being collected. Filters eventually fill with dust and are often thrown away by manufacturers. Robinson’s Filter Solutions specializes in helping manufacturers save money by cleaning their baghouse filters multiple times before replacing them.
Filter Cage
The filter cage is the cylindrical support frame that holds the baghouse filter bags in place to keep them open for the airstream to pass through.
Collection Hopper
The collection hopper, or simply the hopper, is where the dust and contaminants collect before emptying through the discharge unit. Some baghouses have a vibration plate for moving dirt from the hopper to the discharge unit.
Discharge Unit
The discharge unit, or discharge valve, empties the hopper of the dust and particles collected by the filter. The nature of the discharge unit depends on the size of the baghouse dust collection system. A small unit may have a simple drawer where the system disposes of the particles. A large baghouse may feed the dust and particles through rotary airlock valves or a double dump device.
Not all baghouse filter discharge units have the same cleaning methods, as we’ll see later.
Types of Baghouse Filters
There are three main types of baghouse filters.
Shaker Fabric Filter Collectors
Also called shakers or mechanical baghouse filters, these are the simplest types of fabric filters. However, they require a lot of maintenance, which can be costly. Shaker baghouse filters also have a lower air-to-fabric ratio, requiring a lot of space.
The cylindrical baghouse filter bags attach to a plate at the base. From there polluted air passes through the filter media inside to allow thecontaminants to collect on the inner surfaces of the filters.
At the top, the filter cages are held in position by beams, which shake during the cleaning phase to dislodge the contaminants and cause them to fall into the collection hopper.
Continuous and intermittent baghouse filter cleaning are both possible for mechanical shaker baghouse filters. However, if the shaker baghouse is small, normal operations will stop when there is a pressure drop, causing the cleaning phase to begin.
If the shaker is large, a compartmentalized area is shut down for cleaning while the rest of the compartments are still in operation.
Reverse Air Fabric Filter Collectors
A reverse air baghouse requires as much space as a mechanical shaker baghouse. It also requires high levels of maintenance.
The tubular filter frames in a reverse air baghouse attach to a plate at the base, while the top filter cages attach to an adjustable frame close to the top.
When polluted air enters the system through the air intake at the base, it passes through the inner surface of the filters, but theparticles deposit on the outside surfaces of the filter media.
A reverse air current is streamed into the system from the top to clean the filter bags. The current drops the air pressure, partially causing the filter bags to collapse. The collected matter on the exterior filter surfaces cracks and falls into the hopper.
Continuous baghouse filter bag cleaning is also possible in reverse air fabric filter collectors since the other compartmentalized sections continue filtering air while cleaning one of the compartments.
Pulse Jet / Reverse Pulse Fabric Filter Collectors
Also called compressed air baghouse filters, pulse jet or reverse pulse fabric filter collectors are quick and highly efficient systems, but they come at a higher operating cost. Using compressed air is costly in itself, as is the wear and tear on the bags.
A reverse pulse baghouse filter has filter frames hung from a tube sheet close to the system’s top. When contaminated air enters from the base, thecontaminants collect on the outside surfaces of the filters.
Pulse jet filters use a short compressed air stream along the length of the filter bags to dislodge the contaminants and drop them into the hopper.
Continuous cleaning of filters is possible in pulse jet baghouses because compressed air pulses are pretty short.
Unlike shakers and reverse air cleaning collectors, pulse jet baghouses require less operating space because their air-to-cloth ratio is high.
Types of Baghouse Filter Media
Discussing standard filter media used to achieve optimum baghouse air pollution control is essential.
Baghouse filter systems use different filter materials based on factors like the air it is filtering, the size of particles in the air, and the types of materials the system is designed to filter out.
Woven
Woven filters are standard in reverse air and mechanical shaker baghouses. The filters have a tightly woven fibre pattern with tiny gaps between the fibres. The smaller the openings, the smaller the particles processed by the filter.
Nonwoven
Nonwoven filter media is best suited for removing extremely fine contaminants, aerosols, and dust. The filters are bonded together by a mechanical or chemical process.
Pleated Filter Bags
Pleated filter bags are highly efficient because they have a bigger surface requiring a lower air-to-fabric ratio. They have lots of space for retaining dust in the deep pockets of the woven fabric.
Felted Filter Bags
Felted filters trap particles through impact (they act as the target for particles) and intercept them. They are arranged irregularly with each other to provide more target space for capturing any form of matter that tries to pass through them.
Other Types of Baghouse Filter Media Worth the Mention
The filter types discussed below are all synthetic fibres ideal for replacingnatural fibres such as wool and cotton.
Polyester filters
Made from polyester, these filters are highly resistant to abrasion, dry heat, and chemicals. You can’t use polyester filters in damp heat because it degrades them.
Nylon filters
Nylon filters are resistant to abrasion and the effects of alkali compounds but aren’t conducive in applications with high temperatures and mineral oxides.
Teflon filters
Teflon filters are ideal for high-temperature environments since they highly resist abrasion and chemicals.
PTFE Tetratex filters
Baghouses with a high concentration of alkalis and acids and high-temperature facilities require filter bags with PTFE Tetratex membrane.
Fibreglass filters
Facilities with high acid concentration levels can use fibreglass filters. However, they aren’t ideal for industries with cyanides, hydrofluoric acid, bromides, and chlorides.
How Do Baghouse Filters Work?
Now that we know what a baghouse filter is, the baghouse types available, and the different types of filter media, let’s look at how baghouse filters work.
When polluted air enters the baghouse through the inlet at the bottom, it flows through the filters. Depending on the cleaning system, the dust collects on the outer or inner surfaces of the baghouse filters.
The dust collected on the filters is called the “cake.” As the cake grows thicker on the surface of the filters, the pressure drop increases across the filters.
The cleaning cycle starts when there is no more air pressure to bring in the polluted air. Regular cleaning ensures the pressure drops won’t be excessive.
However, cleaning the caked dust too often isn’t a good idea. The initial caked dust acts as a “magnet” to trap other incoming particles in the airstream, and removing the caked dust reduces the ability of the fabric to capture the particles.
Depending on the type of baghouse filter, the cleaning cycle may be continuous or intermittent. Periodic cleaning means that the system shuts down first. Constant cleaning implies the cleaning of one section while other sections continue working.
The cleaning process causes the caked dust to fall from the baghouse filters onto the hopper and then to the discharge unit, ready for appropriate disposal.
The now cleaned air leaves through the clean air outlet. It then flows into the atmosphere or back into the facility.
What Materials Are Filtered by Baghouse Filters?
Baghouse systems filter materials such as:
- Grain dust
- Wood fibres
- Asphalt
- Cement factory dust
- Silica dust
Where Are Baghouse Filters Used?
Baghouse filters are typical in industries or manufacturing plants such as:
- Aggregate (sand and gravel) processing plants
- Sawing, sanding, and woodworking
- Food processing and grain production houses
- Moulded Pulp, paper, plastics, and packaging
- Steel, aluminum, copper, and iron mills
- Ceramics, brick, and building materials
- Power plants, including coal for electricity production
- Pharmaceuticals
- Chemical production (such as fertilizers and acids)
Factors that Affect Baghouse Performance
Below are some factors that affect how well or poorly a baghouse performs.
Materials the Fabric Is Filtering
As we mentioned earlier when discussing types of filter media, when exposed to dry heat, damp heat, high temperatures, acids and alkalis, fabrics behave differently. For example, you can’t use a polyester filter in humid heat conditions.
Frequency of Cleaning
While regular cleaning ensures the optimum permeability of baghouse filter media, too much of it removes the dust cake. It causes the filters to fail to trap as many particles as possible. You’ll want to leave some cake for later.
Installing a baghouse filter in an industrial establishment helps you take care of the environment and prioritize your employees’ health while adhering to government regulations.
Robinson’s Filter Solutions can help you choose, install, and maintain the right baghouse for your facility. Schedule an on-site visit to your premises today.