Baghouse / Fabric Filter
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This page describes how baghouses work, along with an overview of industry standards for cost-effective fabric filter operation and maintenance. PDF documents on the right, courtesy Environmental Protection Agency, explain baghouse/fabric filter operations in more detail. A glossary of terms is also provided. Visit our Technical Tips page for articles about baghouse maintenance and troubleshooting.
About Baghouses | How Baghouses Work | Types of Baghouses (Reverse Air - Pulse Jet - Shaker)
Cleaning Sequences | Misconceptions | Troubleshooting (Principles - Upstream Influences)
A baghouse (B/H), aka fabric filter, is a particular air pollution control device, used in similar applications as electrostatic precipitators. In the 1970s, introduction of fabrics capable of withstanding high temperatures (> 350 degrees Fahrenheit) made baghouses practical for use in electrical generation and industrial processes. Baghouses are highly efficient particulate collection devices, regardless of the incoming dust loading or particle size. Baghouses also offer adaptability as dry collection devices using absorbents for removing gases and heavy metals.
How Baghouses Work
Dust enters the baghouse compartment through inlet on the hoppers. Larger particles drop out while smaller dust particles collect on filter bags. When the dust layer thickness reaches a level where flow through the system is sufficiently restricted (called pressure drop or delta P), bag cleaning is initiated. Cleaning can be done while the baghouse is still online (filtering) or in isolation (offline). Once cleaned, the compartment is placed back in service and the filtering process starts over.
Types of Baghouses [Save as PDF]
Baghouses are classified by cleaning method. Three types of baghouses predominate in the U.S.: reverse air (gas cleaning), pulse jet (compressed air cleaning) and shaker.
Reverse Air (R/A)
R/A baghouses are compartmentalized so bags can be cleaned off-line by stopping the dirty gas flow and backwashing the compartment with low pressure air from a separate fan. Cleaning action is very gentle, which lengthens bag life. Dust collects on the inside of the bags. The bags are held taut by tension springs at the top, and have anti-collapse rings sewn into them to prevent pancaking during cleaning.
Components of a reverse air baghouse:
- Isolation dampers
- Filter bag tensioning system
- Anti-collapse rings on bags
- Reverse air fan
Pulse Jet (P/J)
In this type of baghouse, a high pressure jet of air is used to remove dust from bags supported by rings or metal cages. Bags in a P/J baghouse can be cleaned on-line. Dust collects on the outside of the bags.Torit baghouses (round with an automated, rotating arm to distribute compressed air row-by-row) are a type of P/J fabric filter.
Components of a pulse jet baghouse:
- Compressed air source
- Compressed air storage header
- Solenoid valve
- Diaphragm valve
Cleaning shaker baghouses takes considerably more energy and more time than other designs, so they’re used less often than R/A or P/J. Like R/A, the compartments of a shaker baghouse must be cleaned off-line.
Components of a shaker baghouse:
- Attachments for top and bottom of each bag
- Movable frame from which bags are hung
- Shaft and rod attached to external motor
Cleaning Sequences for Baghouses
Baghouses are cleaned using one of the following sequences, depending on type.
This cleaning sequence is used for single compartment baghouses, usually shaker types. The fan/process must be stopped while the bags are cleaned.
This cleaning sequence is used with multiple-compartment reverse air or pulse jet baghouses. Each compartment is taken offline in turn to clean; the overall process is not shut down during cleaning.
This fully automated cleaning sequence is typically used for pulse jet baghoses. The process flow continues during cleaning.
Baghouse Misconceptions [Save as PDF]
Several key misconceptions about baghouses tend to crop up. These are debunked in the image below. Click the image to download a printable PDF with this and other information about baghouses.
Principles for Fabric Filter Troubleshooting
Effectively troubleshooting baghouse issues is a matter of understanding and applying fundamental principles of fabric filter operation. The image below shows some possibilities to explore. Click the image to download a printable PDF with this and other information about baghouses.
Influences on Baghouse Operation
As with any type of particular collection device, upstream influences such as process conditions and gas flow distribution impact the efficiency of and costs associated with operating a baghouse. The image below shows some factors to consider when troubleshooting baghouse issues. This is part of a complete set of checklists for various plant systems, from the coal pile to the stack. (Click the image to download a PDF copy.)