Reverse-air cleaning baghouses are compartmentalized to permit a section to be off-line for cleaning. In a reverse-air baghouse, the flow of dirty gas into the compartment is stopped and the compartment is backwashed with a low pressure flow of air. Dust is removed by merely allowing the bags to collapse, thus causing the dust cake to break and fall into the hopper. Cleaning air is supplied by a separate fan which is normally much smaller than the main system fan, since only one compartment is cleaned at a time (see Figure 1). The cleaning action is very gentle, allowing the use of less abrasion resistant fabrics such as fiberglass.
In reverse-air baghouses, dust is collected on the inside of the bag. The bag is open at the bottom and sealed by a metal cap at the top (see Figure 2). Bags are connected to a tension spring that is attached to the frame located above to hold them in place. The tension spring allows the bags to move slightly during the cleaning process. The tension spring can be adjusted to make sure the bags do not sag too much, thus preventing the bags from creasing and eventually wearing out. The bottom of the bag fits over a thimble and the bag is attached snugly to the thimble by a clasp or clamp (see Figure 3).
The bag contains rings to keep it from completely collapsing during the cleaning cycle. Complete collapse of the bag would prevent the dust from falling into the hopper. Bags are supported by small steel rings sewn to the inside of the bag (see Figure 3). Rings are usually made of 3/16 inch carbon steel. Depending on flue gas conditions, they can also be composed of cadmium-plated galvanized, or stainless steel. The rings are placed every 2 to 4 feet apart throughout the bag length depending on the length and diameter of the bag. Usually, the spacing between anti-collapse rings is larger at the top of the bag and is smaller near the bottom of the bag. Reverse-air baghouses use very large bags (as compared to shaker or pulse-jet baghouses) ranging from 8 to 18 inches in diameter and from 20 to 40 feet in length.
Reverse-air cleaning is generally used for cleaning woven fabrics. Cleaning frequency varies from 30 minutes to several hours, depending on the inlet dust concentration and the pressure drop of the baghouse. The cleaning duration is approximately 10 to 30 seconds; the total time is 1 to 2 minutes including time for valve opening and closing, and dust settling. Typical design parameters for reverse-air cleaning are given in Table
Reverse-air cleaning parameters
Fig.1 Typical reverse-air baghouse
During the filtering mode, the compartment’s outlet gas damper and inlet gas damper are both open. When bag cleaning begins, the outlet damper is closed to block the flow of gas. The bags are allowed to relax for a short time and the reverse air damper located at the top of the compartment is opened to bring reverse air for bag cleaning into the compartment. The reverse air flow usually lasts from about 30 seconds to as long as several minutes. During this time, dust falls into the hopper. Reverse-air baghouses also have by-pass dampers that allow the dirty gas to by-pass the compartments during malfunctions and start up periods.In reverse-air baghouses, dust is collected on the inside of the bag. The bag is open at the bottom and sealed by a metal cap at the top (see Figure 2). Bags are connected to a tension spring that is attached to the frame located above to hold them in place. The tension spring allows the bags to move slightly during the cleaning process. The tension spring can be adjusted to make sure the bags do not sag too much, thus preventing the bags from creasing and eventually wearing out. The bottom of the bag fits over a thimble and the bag is attached snugly to the thimble by a clasp or clamp (see Figure 3).
Fig. 2. Bag attachment for reverse-air baghouses
The bag contains rings to keep it from completely collapsing during the cleaning cycle. Complete collapse of the bag would prevent the dust from falling into the hopper. Bags are supported by small steel rings sewn to the inside of the bag (see Figure 3). Rings are usually made of 3/16 inch carbon steel. Depending on flue gas conditions, they can also be composed of cadmium-plated galvanized, or stainless steel. The rings are placed every 2 to 4 feet apart throughout the bag length depending on the length and diameter of the bag. Usually, the spacing between anti-collapse rings is larger at the top of the bag and is smaller near the bottom of the bag. Reverse-air baghouses use very large bags (as compared to shaker or pulse-jet baghouses) ranging from 8 to 18 inches in diameter and from 20 to 40 feet in length.
Fig 3. Bag construction for a reverse-air baghouses
Reverse-air cleaning is generally used for cleaning woven fabrics. Cleaning frequency varies from 30 minutes to several hours, depending on the inlet dust concentration and the pressure drop of the baghouse. The cleaning duration is approximately 10 to 30 seconds; the total time is 1 to 2 minutes including time for valve opening and closing, and dust settling. Typical design parameters for reverse-air cleaning are given in Table
Reverse-air cleaning parameters
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