Pulsejet Bagfilter
General Overview
The PULSEMATIC bag filter is a self-cleaning modular dust collector designed to remove dust particles from flue gas streams.
Fabric bags within the "PULSEMATIC" module filter dust from the flue gas. Dust laden gas enters the "PULSEMATIC" module side inlet chamber and is partially separated in a low velocity baffled area. The air then moves upwards over the baffle. This creates a downward flow over the bags which helps to direct the dust downwards into the hopper as the bags are cleaned. Figure PM-2 shows this arrangement.
PM-2 Flow Diagram
To keep pressure losses at an acceptable level, the filter bags are periodically cleaned of the collected material. The
PULSEMATIC bag filter cleans the bags using a short pulse of compressed air (600-700 kPa) directed into the clean interior of the bags from their top open ends. The compressed air pulse, opposite to the direction of gas flow, draws in additional air from the clean air plenum, expands the bag and releases the dust cake collected on the outside of the bag to fall into the hopper below.
PULSEMATIC controls sequence the bag filter through alternate modes of filtering and cleaning. Figure PM-1 illustrates the arrangement of a typical single
PULSEMATIC filter module.
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The casing /hopper assembly is fabricated from carbon steel plate, fully sealed by welded construction and suitably stiffened to accommodate the design negative pressure. The tube sheet assembly is fabricated from carbon steel plate with laser cut holes welded to stiffener sections and houses the blowpipes. The hopper is provided with a 55° valley angle and has a special lower section to avoid material hang up or bridging.
Access to the outlet plenum section for maintenance purposes is gained through hatch cover doors on top of clean air plenum i.e. bags are accessed from clean area. Bags are easily replaced – refer attached figure BF-BCA-WT.
Access to the body section is gained from the hopper, however this is not necessary for normal maintenance purposes.
The integral pilot/diaphragm valves are readily accessed from top of the module.
Filter
Bag / Cage Assembly
(Wire Top Cage)
BF-BCA-WT
Bag Cleaning System
The filter features reverse pulse air cleaning by compressed air controlled by a solid state timer unit. The bag cleaning system is the fast peaking pulse/shock wave air injection technique and is a fully automatic continuous operation system. Quick response pilot solenoid valves are used to provide optimum performance.
The cleaning system includes air manifold, quick response integral solenoid and diaphragm valves, internal piping, and other appurtenances required for a complete system.
The air distribution (blow) pipes are of quick disconnect design for ease of removal during maintenance. Sequencing of cleaning controls and a dedicated distribution pipe per row provides that only one row of bags are cleaned per each compressed air pulse.
Timing Sequence Control
Control philosophy of the PULSEMATIC is that "demand" type cleaning be utilised, i.e. a pressure switch is installed across the system and when the differential pressure rises to the pre-set value on the switch the cleaning cycle is initiated. The system reduces the amount of wear on the bags as cleaning is only done when required. If a straight time only sequence is used the bags are cleaned unnecessarily in time of light load thus shortening bag life and wasting compressed air.
The filter contains integral pilot/diaphragm valves which are located along the air header at the top access level of the filter. These valves are operated in sequence to achieve the cleaning function.
A solid state timer and Photohelic gauge complete with pressure switch control the cleaning function of the filter.
The differential pressure switch of the Photohelic gauge is connected across the tube sheet supporting the bags and is linked to the timer. Two adjustable pre set pressure levels may be set on the Photohelic dial.
Lower setting is utilised for cleaning initiation and the higher setting for "alarm" only. Alarm to be provided by Purchaser.
A "manual" switch is provided so that the "clean" sequence can be initiated at any time for equipment check etc. The timer, Photohelic gauge and switch are mounted in a metal enclosure complete with terminals for wiring termination.
The cleaning program has two options available (selected on timer card) after initiation of the clean signal:
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All bag rows of the module are cleaned in sequence.
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Only the required number of bag rows are cleaned until the differential pressure falls below the set point. This option provides a reasonably constant pressure drop for the system.