What is a Dust Collector/Baghouse, and how does it work?
A dust collector is a type of pollution control equipment designed to collect and store dust, particulate, and particles from industrial exhaust streams. This equipment is widely used to recover valuable granular pollutants from gaseous exhaust streams in many different industries including woodworking, steel, and packaging. A pulse-jet bag filter dust collector is designed to achieve maximum operating efficiency while reducing maintenance cost and time.
Bag filters are generally used in applications requiring high yield recoveries from pneumatic transport systems or for the removal of hazardous materials from the working environment.
The pulse-jet bag filter dust collector is constructed from a series of modular components which allows for standardization yet retains the ability to be completely flexible with selection, sizing, materials of construction, filter media, and equipment arrangement. As the dust laden air enters the dust collector housing through the inlet duct, the baffle plate located inside of the inlet act as a pre-filter and prevents re-entrainment by guiding the gas stream downward uniformly. The baffle plate deflector directs the heavier dust particles into the hopper for collection. The remaining lighter dust particles are drawn against the outer surface of the filter bags, where they are retained and stored. Clean air then passes through the filter bags and leaves the clean air chamber through an outlet duct.
As dust accumulates on the filter bags, periodic cleaning of the bags is important in order to maintain continuous operation. This periodic cleaning of bags is achieved by introducing a timed, momentary pulse of compressed air through a specially designed blow pipe, with nozzles mounted above each filter bag. An equal amount of compressed air is blown vertically downwards into each bag. Each row of bags receives a short pulse of compressed air of approximately 100 ~ 200m sec duration. The high pressure compressed air creates a shockwave down each bag causing it to release the majority of dust formed around the outside. The removed dust is then collected in the hopper. Only a portion of the filter bags are cleaned at one time, allowing the remaining filter bags to continue their filtering action. This means equipment does not need to be shut down, in order to clean the bags.
Bags are held firmly in place at the top by clasps and are usually sewn shut at the bottom. In another design, a snap ring is sewn into the top of the bag which fits into the tube sheet opening. The cage slides inside the bag and the top of the cage sits on the tube sheet. Dust-laden gas is filtered through the bag depositing dust on the outside surface of the bag. Pulse-jet cleaning is used for cleaning bags in an exterior filtration system as well.
Pulse-Jet Off-Line Pulsing System
Pulse-jet baghouses can also be compartmentalized. In this case, pneumatic controlled dampers located both at the dust laden inlet and clean air outlet are used to stop the flow of dirty air into the compartment. Each compartment is equipped with pulse valves that supply compressed air into the blowpipes above the bag rows in the compartment. During the cleaning cycle, the inlet and outlet pneumatic damper closes stopping the air flow through the compartment. The pulse valve opens for about 0.1 second, supplying a burst of air into the bags for cleaning. The compartment remains off-line for approximately 30 seconds although this time period can be longer or shorter if desired. The inlet and outlet pneumatic damper then automatically re-opens bringing the compartment back on stream (or known as “on-line”).
Alternate compartments are cleaned successively until all the bags in the baghouse have been cleaned. The cleaning cycle in each compartment lasts about 40 to 120 seconds. This cleaning is called off-line cleaning. It is frequently used on fabric filters installed on coal-fired boilers and municipal waste incinerators allowing very thorough bag cleaning while the baghouse continuously achieves very low emission levels (less than 50 mg/m3).
Dust Collector/Baghouse Advantages
- Automated self-cleaning of filter bags
- Designed to handle streams with granular particulates
- Hoppers collect granules which can be valuable in some applications
- Continuous operation possible
- High filter rates
- No internal moving part
- High ROI due to collected product
- Low maintenance requirements
- Fast top removal of bags – working at the clean air side
- Dependable solid-state timer controls
- Weather proof – all welded construction
- Custom built, turnkey systems
- Cyclone recovery option available
- Dust pre-separator – baffle plate
- Integration with other pollution control systems
- Multiple filter stock materials
- Off-line or continuous alternative bag cleaning
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