Air Cleaning with Fabric Type Dust Collectors

By: Oleg Chetchel


Oleg Systems Co. produces various types of industrial dust collection systems. Dust collecting equipment 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.

One of the most widely used type of dust collector is Fabric Dust Collector.

Fabric arresters are high efficiency, medium cost collectors. The effectiveness of passing air or gas through a fabric at low velocity has been recofnized and used for many years in air cleaning devices. Fabric is arranged in envelope or tubular (stocking) shapes. While removal appears to take place by a staining action of the media, in reality dust collection is obtained by building up a mat of the material on the dirty side of the media. This mat provides the actual filtering or straining bed. By means of this bed a high degree of removal is obtained even on sub-micron size particles.

The 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.

Some spesific types of Fabric Dust Collectors engineered by Oleg Systems Co. are:

INTERMITTENT DUTY FABRIC DUST COLLECTORS

These types may use either envelope or stocking arrangement of the fabric but will generally employ shaking or vibrating as a means of reconditioning. Periodically Uusually at 4 to 6 hour intervals the air flow must be stopped to effect reconditioning - thus the classification "intermittent".

Rate of flow through the media seldom exceeds 4 fpm and often as low as 2 fpm. Ratings are usually selected so pressure drop will be in the 2" - 5" WG range between the beginning and the end of a cycle.

As dust accumulates on the media. resistance to flow increases and air flow decreases until the fan is stopped and the media reconditioned. Variation in air flow due to changing pressure losses is sometimes a disadvantage and when coupled with requirement to periodically stop flow may preclude use of intermittent dust collectors.

MULTIPLE-SECTION, CONTINUOUS DUTY, AUTOMATIC FABRIC DUST COLLECTORS

The disadvanteges of stopping the air flow to permit vibration and variations in the airflow can be overcomed by using of sectional arresters allowing continuous operation of the exhaust system as automatic dampers periodically take one section out of service for reconditioning the fabric while the remaining sections take the entire gas volume. The large the number of sections, the nearer the pressure loss will remain constant. The use of reverse air flow to increase effectiveness of removing adhering material is sometimes incorporated in such designs. Reverse-flow collapse type and occasionally reverse-jet type dust collectors utilize the multiple-section principle.

When employing shakers as a means of reconditioning, rate of flow through the media (air to cloth ratio) will range from 2 to 4 fpm as with intermittent type dust collector. Generally this air to cloth ratio is based on net cloth area available when one compartment is out of service for reconditioning.

REVERSE-JET, CONTINUOUS-DUTY, FABRIC COLLECTORS

The reverse-jet type differs from the conventional arrEsters in its use of high pressure air to clean the fabric. One type uses high pressure air (30" - 40" WG) from a travelling "blow ring" to dislodge the collected cake from inside the fabric tube. Since dust laden air enters the top of the fabric tube, air flow within the stocking is downward to the hopper allowing the fabric to be cleaned without stopping air flow. Multiple sections or comartmentation is not required for continuous duty. The"blow ring" is normally operated continuously.

Another type uses high pressure compressed air (100 PSI) to break the dust cake from the exterior of the fabric tube or envelope by the intermittent application of reverse-jet compressed air. In some dust collectors of this type multiple sections are utilized. Other dust collectors apply the compressed air on only one or very few tubes or envelopes at a time prventing air flow in adjacent tubes or envelopes and decreasign the possibility of re-entrimane and redeposition.

Cleaning or reconditioning by the reverse-jet method is more complete than that obtained by vibrating or shaking. Higher air flows are possible due to short reconditioning cycle. Air flow rates of 6 to 12 fpm are usual. Pressure loss will be more nearly uniform (generally 4" to 6" WG if properly rated) and exhaust air volume will be more nearly constant. Fabric dust collectors of this type might be more expensive and require added maintenance for the cleaning mechanism.

REVERSE-FLOW COLLAPSE, CONTINUOUS DUTY DUST COLLECTORS

Reverse-flow collapse cleaning is generally used with glass media which is fragile and requires a gentle cleaning technique. Reversing the glass flow provides a gentle collapse of the fabric usually in a "four point star" braking the dust cake which falls by gravity into the hopper.

For additional information please refer to http://www.olegsystems.com/fan/Index.html.

Oleg Chetchel
Industrial Process Designer
Oleg Systems Co.
http://olegsystems.com/blowerimpeller/Index.html
http://olegsystems.com/blowerrepair/Index.html

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Oleg Chetchel Industrial Process Designer Oleg Systems Co. www.olegsystems.com/blowerimpeller/Index.html www.olegsystems.com/blowerrepair/Index.html

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