Dust Extractor Cleaning Systems Reverse Pulse Jet Mechanical Shake
There are a number of different cleaning methods which have been developed; mechanical shake, reverse air and compressed air reverse pulse jet.
Mechanical Shaker Cleaning Systems
This is the basic cleaning system and requires the dust extractor to be shut-down at regular intervals, nominally every 2-3 hours. Once the extractor fan has stopped a mechanical or rotary ‘shaking’ system dislodges the dust from the surface of the bag or cartridge filter, into the process or a collection bin. The cleaning operation generally runs between 30s – 2 mins depending upon collector / process dust etc. The filter pressure will rise during the extractor operation, which will then drop after cleaning has taken place.
Reverse Pulse Jet Cleaning System Design.
Reverse Pulse Dust Collectors incorporate a fully balanced and designed continuous cleaning system for the removal of dust from process air streams. The technique is relatively simple; a jet of high-pressure air is injected into the filter element against the direction of process airflow. This allows particulate which has built up on the surface of the filter media to be dislodged, allowing it to fall back into the process (or in the case of a dust collector into a collection bin). This enables continuous process / dust collector operation and operates as follows:
- The Dust Collector is divided by a filter cell plate (filter plate) that separates the clean air side of the collector from the dirty air side.
- Filters are retained in the cell plate by a number of methods: clamping, bayonet or screw type systems, bolted flanges etc. All have a sealing, ’O’ ring arrangement that facilitates removal from either the clean or dirty product side.
- The dirty gas stream passes through the filters leaving an agglomeration of dust particles on the filter surface. This agglomeration is a permeable cake, the permeability of which varies depending on the characteristics of the dust involved.
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- The Reverse pulsejet system is a fully automatic cleaning system where a pulse of compressed air is accelerated to sonic speed (>340m/sec) via venturi nozzles installed in the pulse tubes which are located in the lid assembly directly above each rows of filters.
- As the dust cake builds up on the filters the differential pressure across the filters increases causing a reduction in the airflow.
- To control this increase in differential pressure an electronic controller monitors the pressure and periodically energises normally closed solenoid coils, which in turn activate diaphragm valves. The diaphragm valve then opens for a short duration of around 150-200 milliseconds.
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- These valves release compressed air (pulse) from the air receiver into the pulse tubes, then through the nozzles and into the centre of the filter elements.
- The shock wave generated by the nozzle travels down the inside of each filter and loosens the dust cake from the outside of the filter. The pulse of compressed air together with the induced air from the clean air side of the cell plate inflates the filters and causes the dust to be released form the surface of the filters. (Tests have shown that this combination of shaking (created by the sonic shock wave) and blowing of air in the reverse direction of dust entrainment (momentarily created by the compressed air pulse) most effectively cleans with minimal degradation of the fiber matrix of the filter fabric.
- Filters should be cleaned as gently and as least as possible to limit fabric degradation. It is the fabric degradation which leads to migration of dust into the fabric and hence; increased differential pressure, greater cleaning requirements, passing of dust and eventually filter failure.)
- The filters pulsed are only a small percentage of the total filtration area, in the dust collector, and are only off line for approximately 0.2 seconds. This enables the collector to run continuously.
- The rows of filters are pulsed out of sequence to prevent re-entrainment of dust from one row onto the adjacent row due to the higher cleaned permeability.