Inspecting and changing bags takes a long time and are the highest maintenance costs in a baghouse.
Bag failures occur at varying times depending on the operation of the collector. The
longer the time before bag changeout, the lower the maintenance cost to the owner. Typical
bag life is from two to five years. Table 1 lists some common causes and reasons for bag
failures.
Table 1. Common causes of fabric failures
Bag failures can be spotted through daily monitoring and inspection. Stack opacity is a good
indication of bag failure. If the plume is dirty, then some problem exists, either in a single
compartment or throughout the baghouse. In a compartmentalized baghouse it is possible to
monitor the stack while isolating a compartment. Stack emissions would be reduced if the
compartment with broken bags were taken off-line. In a noncompartmentalized baghouse it
may be necessary to check the entire unit for broken bags.
Three ways to search for broken bags are (Reigel and Applewhite 1980):
1. Hunt for the hole.
2. Hunt for the accumulation of dust which can be related to a nearby hole.
3. Use a detecting device.
In shaker and reverse-air baghouses where dust is collected on the inside of the bags, bag failures
occur frequently at the bottom of bags. Accumulation of dust on the cell plate is sometimes visible, making it relatively easy to spot the failure. It may be necessary to inspect the
entire circumference and length of the bag if the hole is higher up on the bag tube. In reverseair
baghouses, other bag failures can also occur near the anti-collapse rings and at the top cuff
where the bags are attached. In shaker baghouses, bags tend to fail at the top where they are
attached to hooks or clamps.
In pulse-jet baghouses it is normally very difficult to locate bags that have failed. However, in
many baghouses dust accumulation on the top tube sheet or in the blow pipe above the failed
bag will be readily noticeable (Reigel and Applewhite 1980).
A technique for locating torn bags is to use fluorescent powder and a black light. Fluorescent
powder is injected in the inlet to the baghouse. An ultraviolet light is used to scan the clean air
inside of the baghouse. Leaks can be detected by the glow of the powder getting through a torn
bag. This technique is useful for spotting broken welds or leaks in the cell plates, tube sheets
or housing.
The importance of detecting broken bags depends on the baghouse design. In reverse-air and
shaker units, leaks in the bags can cause air streams or jets of dust to abrade adjacent bags.
This causes what is known as the "domino effect", where one torn bag creates another torn
bag. In pulse-jet baghouses however, torn bags generally do not cause tears in adjacent bags
since the dust leaves the inside (clean side) of the bags. If opacity limits are exceeded beyond
the permit level, corrective action should be initiated immediately and the bag(s) should be
changed. It may take several broken bags to cause an opacity violation.
In the past, bags were usually replaced as they failed. However, a new bag in the vicinity of
old ones will be forced to take on more dust (air will tend to follow the path of least resistance)
and will become worn-out quicker than the old "seasoned" bags (Reigel and Applewhite
1980). It has become accepted practice in reverse-air and shaker baghouses to simply tie off a
torn bag and stuff it into the cell plate. If the failure is close to the cell plate then the hole
should be plugged by using steel plate plugs with gaskets or sand bags to seal off the hole. In
pulse-jet baghouses with top access, a plug is placed over the tube sheet hole of the failed bag.
The operator should keep track of the bag failure rate of individual bags to correct any conditions
that would cause premature bag failure. In addition, the tracking is helpful to determine
the scheduling of a complete changeout of bags at a convenient time.
Bag failures occur at varying times depending on the operation of the collector. The
longer the time before bag changeout, the lower the maintenance cost to the owner. Typical
bag life is from two to five years. Table 1 lists some common causes and reasons for bag
failures.
Table 1. Common causes of fabric failures
indication of bag failure. If the plume is dirty, then some problem exists, either in a single
compartment or throughout the baghouse. In a compartmentalized baghouse it is possible to
monitor the stack while isolating a compartment. Stack emissions would be reduced if the
compartment with broken bags were taken off-line. In a noncompartmentalized baghouse it
may be necessary to check the entire unit for broken bags.
Three ways to search for broken bags are (Reigel and Applewhite 1980):
1. Hunt for the hole.
2. Hunt for the accumulation of dust which can be related to a nearby hole.
3. Use a detecting device.
In shaker and reverse-air baghouses where dust is collected on the inside of the bags, bag failures
occur frequently at the bottom of bags. Accumulation of dust on the cell plate is sometimes visible, making it relatively easy to spot the failure. It may be necessary to inspect the
entire circumference and length of the bag if the hole is higher up on the bag tube. In reverseair
baghouses, other bag failures can also occur near the anti-collapse rings and at the top cuff
where the bags are attached. In shaker baghouses, bags tend to fail at the top where they are
attached to hooks or clamps.
In pulse-jet baghouses it is normally very difficult to locate bags that have failed. However, in
many baghouses dust accumulation on the top tube sheet or in the blow pipe above the failed
bag will be readily noticeable (Reigel and Applewhite 1980).
A technique for locating torn bags is to use fluorescent powder and a black light. Fluorescent
powder is injected in the inlet to the baghouse. An ultraviolet light is used to scan the clean air
inside of the baghouse. Leaks can be detected by the glow of the powder getting through a torn
bag. This technique is useful for spotting broken welds or leaks in the cell plates, tube sheets
or housing.
The importance of detecting broken bags depends on the baghouse design. In reverse-air and
shaker units, leaks in the bags can cause air streams or jets of dust to abrade adjacent bags.
This causes what is known as the "domino effect", where one torn bag creates another torn
bag. In pulse-jet baghouses however, torn bags generally do not cause tears in adjacent bags
since the dust leaves the inside (clean side) of the bags. If opacity limits are exceeded beyond
the permit level, corrective action should be initiated immediately and the bag(s) should be
changed. It may take several broken bags to cause an opacity violation.
In the past, bags were usually replaced as they failed. However, a new bag in the vicinity of
old ones will be forced to take on more dust (air will tend to follow the path of least resistance)
and will become worn-out quicker than the old "seasoned" bags (Reigel and Applewhite
1980). It has become accepted practice in reverse-air and shaker baghouses to simply tie off a
torn bag and stuff it into the cell plate. If the failure is close to the cell plate then the hole
should be plugged by using steel plate plugs with gaskets or sand bags to seal off the hole. In
pulse-jet baghouses with top access, a plug is placed over the tube sheet hole of the failed bag.
The operator should keep track of the bag failure rate of individual bags to correct any conditions
that would cause premature bag failure. In addition, the tracking is helpful to determine
the scheduling of a complete changeout of bags at a convenient time.
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