The pulse-jet bag filter dust collector has been designed to achieve maximum operating efficiency whilst reducing maintenance cost and time.
Bag filters are generally used in application requiring high yield recoveries from pneumatic transport systems, or for the removal of hazardous materials from the working environment.
Such systems may incorporate the use of a cyclone as the primary means of recovery followed by a bag filter unit for final separation of particles from the air stream. Alternatively the bag filter may be used as the only means of separation.
The total recovery of conveyed product is the prime objective in each instance and this criteria can only be reached by balanced designed of the total system. Often the costs of installing such a system can be justified from increased yields.
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.
We believe that each application requires further careful evaluation and that the filter unit recommended should be on the basis of product characteristics, product to air loading and air to filter cloth ratios, with consideration of product heat stability and other physical and chemical properties. By selection of the correct filter sock material and consideration of the above factors optimum performance is assured.
ADVANTAGES OF THE PULSE-JET DUST COLLECTOR
- Automated self-cleaning of filter bags
- Continuous operation
- High filter rates
- No internal moving part
- Low maintenance
- Fast top removal of bags – working at the clean air side
- Dependable solid state timer controls
- Weather proof – all welded construction
- Dust pre-separator – baffle plate deflector
HOW THE PULSE-JET DUST COLLECTOR WORK?
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. The remaining lighter dust particles are drawn against the outer surface of the filter bags where they are retained.
Clean air passes through the filter bags and leaves the clean air chamber through an outlet duct.
As dust accumulate on the filter bags, periodic cleaning of the bags are important in order to maintain continuous operation. This periodic cleaning of bags is achieved by introduction of timed, momentary pulse of compress air through a specially designed blow pipe with nozzles mounted above each filter bag. Only a portion of the filter bags are cleaned at one time, allowing the remaining filter bags to continue their filtering action.
Pulse Jet Bag Filter is cleaned by a blast of compressed air or N2. The filter bags are arranged in rows and the number of rows depends on the filter size. A blowpipe is mounted above each row of bags and fed by a compressed air or N2 manifold (or tank) mounted on the outside of the filter. The blowpipe contains nozzles to coincide with the centre line of each bag. When each pipe receives a signal to blow, the appropriate diaphragm valve is opened by means of a solenoid valve allowing compressed air into the blowpipe.
An equal amount of compressed air is blown vertically downwards into each bag. Each row of bags therefore 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. This falls into the hopper below.
Bags are held firmly in place at the top by clasps and usually have an enclosed bottom (the bag is sewn closed 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 (see Figure below). 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 (See Figure below).
PULSE-JET OFF-LINE PULSING SYSTEM
Pulse-jet baghouse 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 are equipped with pulse valves that supplies compressed air that direct pulsing 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 & outlet pneumatic damper then automatically reopens, 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).