Baghouses are industrial dust collectors that remove particulates, dust, and pollution created in manufacturing processes from the workplace air. The baghouse dust collectors use fabric or felt filters to extract dust from the air. A fan pulls dirty air into the dust collection housing through an inlet, where it passes through the filters inside. Dust particles collect on the outside of the bag filters, the dust is deposited into a waste hopper, and the cleaned air exits through an outlet. Baghouse units are a very common type of dust collector used in a wide variety of industrial facilities.
Industries That Use Baghouse Dust Collectors
Baghouse dust collectors are used in many different types of applications, including:
- Bin Ventilation
- Building Materials
- Cement and Asphalt
- Corn Processing
- Food processing
- Iron & Steel
- Mineral Wool
- Mixing Oil, Gas & Petroleum
- Pulp & Paper
Baghouse dust collectors can filter many types of particulates, including stringy or irregular shaped dust.
Advantages of Baghouse Dust Collection
Economical. A baghouse dust collector requires periodic bag changes. Maintenance on a baghouse is less intensive than on other types of dust collectors. Cartridge filter dust collectors remove air pollution and particulate that is more fine, but these require more frequent filter changes than a baghouse.
Easy to Change Filters. Top-entry baghouses give you access to snap-band filter bags. Change the bags by securing them to the baghouse filter cages. Bottom-access or side-access baghouses require a worker to go into the enclosure and change the bags.
Versatile. You can use baghouse dust collection systems in many different applications. Baghouses are a good solution where dust particles have a range of sizes. If there are mostly dust particles larger than 50 microns, baghouses are a solid choice for dust collection.
Durable. Baghouse filters can withstand more heavy use than cartridge filters. The baghouse filters have a longer service life than cartridges and are built for harsher conditions.
Heat-Resistant. A typical baghouse can filter dust from air that is up to 550 degrees Fahrenheit. With filters made from specialty fibers, a baghouse can remove dust from air that is as hot as 750F.
Components of Baghouses
The fabric filter bag and supporting frame is the filter media. The bag filter itself may be made of woven or nonwoven materials. Baghouse filters are usually long cylindrical tubes, supported by a filter cage, that draws air through the filter. A “cake” of dust and particulate accumulates on the outside or inside of the bag, depending on how the baghouse collector is set up.
Dusty air is pulled through the baghouse by an industrial fan through an air inlet. In larger baghouses, the dirty air may hit a baffle plate, knocking some of the dust into the hopper. The remaining dusty air passes through a series of baghouse filter cages and filters.
A cylindrical frame that supports the filter bag, keeping it open, so dusty air can flow through the filter.
The collected dust and contaminants are encrusted on the outside of the baghouse filter in a “cake”. This encrusted dust must be cleaned from the filter into a hopper. Baghouse dust collectors are generally classified by the method of bag cleaning they use. These types are mechanical shakers, reverse air, pulse jet, and sonic cleaning.
The collection hopper is where the dust from the bag is collected after being cleaned off the filter. Sometimes, there is a vibration plate that moves the collected dust towards a discharge unit.
In small baghouse units, this may be a drawer that the operator empties out. In larger baghouse units, this is usually an automatic discharge, which can take the form of rotary airlock valves or double dump devices.
How Does a Baghouse Dust Collector Work?
A baghouse compartment contains many baghouse filter cages, each wrapped with a bag filter of woven or nonwoven material. For cleaning gas streams of less than 250F, the filter material may be pleated instead of a regular bag. The number of baghouse filter surfaces may vary by type but can be anywhere from a half dozen to several hundred.
Dirty air enters through an inlet on its way to the baghouse filters. In larger units, this dusty air may pass through a baffle first, to knock out larger dust particles into the collection hopper.
The polluted air passes through the baghouse filter media surfaces. Depending on the cleaning method of the baghouse collector, the dust may “cake” on the inside or the outside of the filters. When there is no longer air pressure to draw the dirty air through the filters, a sensor is activated, and the cleaning cycle initiates.
In some baghouse units, this will mean the section goes offline for cleaning. This is known as intermittent cleaning. In other units, like pulse jet baghouse units, the filter surface is cleaned with bursts of compressed air, and the different sections of the baghouse never shut down. This is known as continuous cleaning.
As the cleaning cycle goes forward, the caked dust falls from the bag filters, and is deposited into a collection hopper. This dust is moved to a discharge unit for final disposal.
The cleaned air exits the baghouse unit through a clean air outlet.
Types of Baghouses
Baghouse collectors are referred to by /the cleaning method they use. The three basic types of baghouse dust collectors are mechanical shakers, reverse air, and pulse jet.
In this type of baghouse, cylindrical filter bags are attached to a plate on the floor, where dirty air is passed through the inside of the filters. Dust collects on the inside of the filters. The top of the filter cages are attached to beams at the top of the housing. When the cleaning cycle initiates, the beams shake to dislodge the dust cakes and the dust falls into the hopper.
Shaker style baghouses can be intermittent cleaning or continuous cleaning. Smaller shaker baghouses usually cease operation when pressure drops, and the cleaning cycle starts. In larger shaker baghouses, there are compartmentalized areas that shut down for cleaning one area at a time, so these are usually continuous cleaning.
Mechanical shaker baghouse collectors require s lot of room because the air-to cloth ratio is low.
In a reverse air baghouse, tubular filter frames are attached to a plate at the bottom of the unit. The top of the baghouse filter cages are attached to an adjustable frame near the top of the unit. Dirty air enters the through the bottom via an air intake, passes through the inside of the filters, and dust collects on the outside of the bag filters.
During the cleaning cycle, a reverse current of air enters through the top, causing the air pressure to drop, and the bag filters to partially collapse. This causes the dust cakes on the outside of the bag to crack, and the dust particles fall into a collection hoper at the bottom of the unit. Rigid rings are built into the reverse air baghouse filters at regular intervals to keep the filters from collapsing completely during the cleaning cycle.
Reverse air baghouses have compartmentalized sections, which allows them to be continuous cleaning. One section stops for cleaning, while the other sections continue filtering the workspace air.
The space requirements for a reverse air baghouse are similar to those of a mechanical shaker baghouse, however the maintenance requirements are slightly higher.
Pulse jet baghouses are similar to reverse air baghouses, with a few key differences. In a pulse jet baghouse, the filter cages are hung from a tube sheet near the top of the unit. Dirty air enters through the bottom of the unit, and dust accumulates on the outside of the bag filters . During the cleaning cycle, a short burst of compressed air travels down the length of the bag, dislodging the caked dust, where it falls into the collection hopper.
One advantage of pulse jet dust collectors is they have a high air-to-cloth ratio, meaning they require less space to operate. Pulse jet baghouses are usually continuous cleaning collectors, because the pulses of compressed air are very short, about 0.1 second in length. This means less downtime.
The disadvantages to pulse jet baghouses are increased operating costs. These associated costs are having compressed air for the bag cleaning, and increased wear and tear on the bag filters (vs reverse air baghouses).
Note: Some baghouse dust collectors also use sonic horns to help dislodge dust cakes. These horns emit low frequency, high intensity sound waves to help break the bonds between the dust particles on the surface of the filter media.
Considerations for Baghouse Design
Air-to-cloth ratio is the ratio of flow volume to filter area. The lower the air-to-cloth ratio, the more filter area is required. The higher the air-to-cloth ratio, the less filter area is necessary.
Pressure Drop is the resistance to air flow across the unit, expressed by the symbol (ΔP). This is calculated by measure the pressure between two points in the baghouse, most often the inlet and outlet valves. A high pressure drop means a high resistance to air flow. A low pressure drop means low resistance to air flow.
Filter drag is the resistance between the filter fabric and dust that cakes on the filter surface.
Types of Filter Media
Baghouse filters are usually round, cylindrical, or oval bag filters that are supported by filter bag cages that allow air to flow through the filter material. The type of material used for the filters may vary depending on the application, the type of gas being filtered, the temperature of the gas, the size of the particles being filtered, etc. Common filter materials include cotton, nylon, fiberglass, polyester, and polypropylene.
Nonwoven fabrics are commonly used for baghouse filters. The nonwoven part of the filter may be either felted or a membrane. These are usually attached to a woven backing, known as a scrim. Nonwoven filters are necessary for certain types of baghouses, such as pulse jets.
Woven filters a defined by a repeating pattern, and are commonly used for mechanical shaker or reverse air baghouses. The smaller the gaps between the fiber patterns, the tighter the weave, the smaller the particles the filter can process. Some woven bag filters may have a thin PTFE membrane to prevent dust particulate from being embedded in the fibers of the filter.
Considerations for Baghouse Filters
Filters are designed to operate within a certain temperature range. If the gas being filtered is outside of the normal filter range, it will shorten the life and effectiveness of the filters. Pressure drop and the air flow rate (by volume) are two additional factors in choosing the right filters for your baghouse unit. If you are unsure which filters to use for your unit, contact us for a consultation. We can make a recommendation based on your facility conditions and requirements.
Maintaining Efficiency in Baghouse Dust Collectors
Routine maintenance and upkeep help keep your baghouse running efficiently. Here are some things to look at periodically.
Inspecting ductwork on a regular basis will alert you to any structural issues that need to be addressed. Look at the joints, welds, and seals every so often to make sure the integrity of the dust collection system is intact.
Differential pressure over time is something to keep an eye on. New filters have low air flow resistance, since they are not clogged with dust particulate. As time goes on, they fill with dust, and the pressure drop may increase. A large pressure drop may indicate it is time to inspect the filters for a possible change. This may also indicate it’s time to inspect the cleaning system.
The cleaning system should be examined on a regular schedule to ensure it is operating at peak efficiency. If there is an issue with the cleaning system, dirty air may be recirculated to the workspace, or dust may accumulate in the crevices and joints of the ductwork. It may also cause the filters to require premature changing.
Lastly, the hopper discharge should be checked to make sure it is operating correctly from time to time. The hopper is not meant to be the final storage place for accumulated dust. If the discharge is malfunctioning, dust can return to the air in the collector, or the final disposal of the dust can be jammed up.
Every facility and manufacturing plant have different dust collection needs. If you have questions about your baghouse unit, or if you need a consultation, reach out to us using our contact form, or give us a call at (888) 501-3163.