The Dust Collector; Fabric, Baghouse, Cartridge and Jet Dust Collector

by Gary Berwick, P. Eng.
Quality Air Management
Waterloo, Ontario, Canada

Excerpts from an article published in various media.
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History

The first pulse jet dust collector was developed ... early 1960’s... The pulse valves selected were diaphragm valves ...They decided to use several valves in a baghouse dust collector and pulse them with an electronic timer ... It became apparent that the frequency of cleaning was a function of the load to the fabric dust collector. ... for loadings of 300 grains the collectors would operate at a filtering velocity of between 7 and 9 feet per minute. At material handling facilities such as a quarry would operate at a filtering velocity of 14 to16 feet per minute. The typical pressure drop in these baghouse dust collector designs were about 2 to 3.5 inches water gage pressure ... Determining the filter velocity (then referred to as filter ratio) became a rather complicated procedure. The ratio presumably was determined by dust load, fineness of the dust, temperature of process gas stream, and other factors. The hopper inlet was a carry over design from both the blow ring fabric dust collectors and the previous mechanical shaker dust collectors.

By 1969, there were over 10,000 collectors in operation. Almost all of them were installed on process equipment or in Foundries.... units had nominally eight foot long bags. Bag life was usually 4 to 7 years.

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Engineering Disaster 1971

...The market changed radically because Air Pollution Control Regulations became effective. Many new suppliers entered the market. In order to compete ... They went from 6 foot to 10 foot bags. They increased their pulse pipe holes by the same ratio. The whole industry followed and copied the new design... At the time ... kept the same venturi sizes. This increased the jet velocity of the cleaning jet by 66 per cent.

...With the new designs pressure drop increased to 4 ½ - 6 ½ inches w.c.. Compressed air consumption increased by over 50% for similar applications. Bag life was reduced by over 50%.

In reaction to these problems the filter ratios were reduced to between 4-6 on almost all applications.

Reasons for Disaster ... obvious truth, that the velocity with which the dust is ejected from the bag during cleaning is proportional to the velocity of the cleaning jet. At the new velocities, dust is driven toward adjacent rows of bags in the filter mode. Depending on the dust density, the dust will be driven through the adjoining cake into the clean side of the bags... Even after the equilibrium the dust still penetrates and bag wear is high...

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Reverse Air Fan induced pulsed air collectors

...compressed air as it left the pulse pipes was subject to refrigeration cycle as the compressed air expanded. The first approach was to apply reverse air blowers to the cleaning system ... The downside of these collectors was that the fan on top of the roof of the collectors were difficult to service ...

Air Pump Pulse Jet collectors with 8-10 psi operation

...They used the technique of a cylindrical housing and a rotating pulsing arm but reduced the effects of the refrigerant cycle and loss of energy ... Also in the advanced technology concepts, they reduced the velocity and the effect of the air leaving the bags propelled to adjoining bags during cleaning.... The collectors usually had the effect of a high inlet as the air entered the bags mostly through the hollow cylinder in the middle of the cylindrical housing...

Today’s Conditions

The disastrous design, mentioned above, continues to be employed by most of the pulse jet collector suppliers in the world... equipment is built by the lowest cost suppliers.

New Technology

Some 25 years ago ... developed a new pulse jet collector that basically changed the cleaning system design. The key to this design was that he changed the jet velocity to a fraction of the existing designs. This eliminated the penetration of dusts from the row of cleaning bags to the adjoining rows in a filtering mode.

Baghouse dust collectors now being manufactured in Canada click here for more information

This allowed pulse jet collectors to operate at lower pressure drops (2-3 inches w.c.), lower air consumption (50-75% less), 3 to 4 times more bag life and filter ratios of over 12 : 1 on any application while decreasing dust penetration by up to 90%.

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There are many different considerations of using this new technology more effectively... This technology is an on going process. We have seen radical changes in periods of less than six months as new components and new manufacturing procedures are developed.

This technology allows the client to adapt to different field conditions... These collectors have been applied to incinerators which operate under the most difficult conditions... There are techniques to design nozzles to install on pulse pipes which will increase the velocity to around 1690 feet per second and lower air consumption by 30%.

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Click here for more information on baghouse dust collectors