Dust collection equipment utilizing the principle of wet dust collecting is available in numerous designs utilizing a number of principles and featuring wide variation in effectiveness, initial cost, operating and maintenance expense, space, arrangements and material of construction. Dust collectors are used extensively in industry for a wide range of applications. They require more space than most other types of air cleaning devices, necessiating outdoor installation in most cases. Oleg Systems Co. designs industrial dust collection systems including dry type dust collectors.
One of the most popular and efficient dry type dust collector designs is Pulse-Jet Dust Collector.
In a pulse-jet dust collector, dust is collected on the outer surface of the filter bag. To remove these accumulated dust, a pulse of compressed air is sent down the inside of the bag to flex the bag surface outward, dislodging the dust. Dust falls of the bag for removal from the dust collector. This pulse of air is automatically triggered by a timer or a pressure differential signal monitored accross the filter media, allowing self-cleaning and unattended operation. Dust-laden air enters the dust collector through an inlet and comes into the dusty air plenum that contains filter elements. An inlet baffle deflects some of the larger particles in the airstream downwards for immediate removal, thus reducing filter bag wear by removing the larger abrasive particles before they accumulate on the bag.
The pulse-jet dust collector also has a header commected to the plant compressed air (100 PSI pressure) and acts as a reservoir. At predetermined intervals, a solenoid valve releases a blast of compressed air down the air pipe to the set of filter bags. The pulse of compressed air produces a shock wave along the lenght of the bag. A converging venturi aspirates filtered air into the bag from the clean air plenum to assist in the bags cleaning, thereby minimizing plant air consumption. The timer sequences the cleaning cycle, row-by-row, until all the bags are clean. The cycle is then repeated.
The cleaning cycle is also initiated by monitoring differential pressure across the tube sheet that separates the plenums. As the dust accumulates on the surface of the filter, the differential pressure across the media increases. At a certain value, the solenoid is triggered and cleaning happens. Triggering the cleaning cycle at a predetrmined differential pressure setting eliminates cleaning during periods of light dust load, increases bag life, and reduces the use of compressed air.
Filter material is selected based on the operating temperatures, type and size of duct particles, dust collector capacity. At ambient temperature, majority of pulse-cleaning collectors use 10 to 14-oz polyester felt media. Synthetic materials have better temperature resistance than natural materials. At elevated temperatures up to 500 F, fiberglass bags can be used. Nomex is well suited to the 250 to 400 F range. Surface finish of the bag enhances release of sticky dusts. Applying a silicon finish layer to the bag is commonly used. Special coatings provide a membrane with tiny perforations that achieve very high filtration efficiencies. Pleated filter elements allow for more surface area and are often retrofitted into the system.
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