Common Operating Problems

When a baghouse begins to have problems that cannot be readily identified, the operator
should contact the vendor to identify and correct the problem. Problems and/or failure of components
within a baghouse can occur for a number of reasons. Some problems may be unique
to a particular type of baghouse design while others are generic to all fabric filters. The following
is a summary of some of these problems (EPA 1984).

Dust Discharge Failures

Hopper pluggage can cause serious problems in a fabric filter. Many dusts flow less easily
when they are cold. Thus, insulation, hopper heaters, air tight seals, and continuous dust
removal may be necessary to minimize the hopper pluggage problems. Regardless of the
reason (cooling of the dust, inleakage, failure of the discharge system operation, or simply
using the hoppers for storage), failure to remove the dust from the hopper usually results in having to open up the hoppers to clean them out. The fugitive emissions generated by a
single cleaning out of the hoppers may be greater than the emissions emanating from the
fabric filter outlet for an entire year. Therefore, the occurrences of hopper pluggage should
be minimized. Air inleakage is most common through the dust discharge valves and hopper
access doors.

Shaker Cleaning System Failures

Several problems are characteristic of shaker type baghouses

1. Failure of the shaker motor may lead to excessive dust cake buildup on the bags and an increase in pressure drop. In some applications, when the gas flow is stopped by closing the dampers, the dust will slide off the bag. In most applications, however, the shaker system is needed for adequate removal of the dust and maintenance of a reasonable pressure drop.
2. Shaker linkages must be maintained in a manner that allows the energy provided by the shaker motor to be distributed through the shaking system to the bags. Because these systems are mechanical, periodic lubrication, checking for wear or loose parts, and replacement of broken parts are required to maintain their cleaning effectiveness. The only way to evaluate this system is to watch it in operation to ascertain that all the bags are being cleaned at approximately the same intensity.
3. Bag tension changes with the age of the bag and with the amount of material collected on the dust layer. Bags that are too tight may not transfer the shaker energy effectively and may be damaged during shaking. Bags that are too loose may sag on the tube sheet, and bag abrasion may result from the bag being placed in the gas stream or being contacted by the thimble or other bags. Loose bags also may not use the cleaning energy effectively and may block the flow of dust out of the bags if they sag, fold, or close off above the tube sheet.

Reverse-Air Cleaning Systems

Common problems associated with reverse-air cleaning baghouses include isolation

dampers, bag tensioning, and corrosion. The reverse-air system is a low-energy system

and no gas flow can be present in the module or compartment being cleaned. The damper

systems for fabric filters with this cleaning mechanism tend to be complex because a

reverse flow of gas is used to collapse the bag, to break and release the dust cake, and to

allow it to be collected and removed from the fabric filter. This requires a positive seal on

the reverse-air isolating damper (a poppet damper is often used). Without proper sealing,

the bags may not collapse properly and the cleaning action may be ineffective. Unlike the

other cleaning systems, relatively little energy is available to clean the fabric, as the

reverse flow of gas through the bags is usually small compared with normal, on-line gas

flow.

Failure of the isolation dampers is usually easily detected, as the actuators are generally

pneumatically or hydraulically operated and the movement of the piston is visible. Too little

movement of the piston usually indicates that the damper is not sealing properly. In

some situations, the failure of the damper system can be detected by a missing spike and

subsequent decrease in pressure drop after the affected module comes off-line for cleaning.

Moisture and oil in the compressed-air supply lines can cause blockage during freezing weather and result in the failure of these pneumatically operated systems. Damper

operation failures, however, usually result from failures of the controlling timers or pressure

drop sensors that are used to activate the cleaning cycle at certain intervals or at certain

pressure-drop thresholds.

Buildup of materials around the dampers or deformation of the dampers or their seals can

cause problems with proper isolation of a compartment for cleaning. Confirmation of poor

damper sealing is only possible by internal examination of the equipment. Even internal

inspection of the damper system may be inconclusive because the system must be cooled

sufficiently for safe entry. An internal inspection, however, may indicate the presence of

light leaks, warped dampers and seals, or buildup or wear of the dampers caused by material

passing through the fabric filter. The damper operation and seal should be checked

periodically as part of a preventive maintenance program.

As with shaker baghouses, proper bag tension is essential to provide effective bag cleaning.

Bags that are too tight may not collapse enough to allow effective flexing of the dust

cake. Too much tension can also damage the fabric. On the other hand, insufficient bag

tension may cause the bags to collapse to the point where they are closed down during the

reverse-air cleaning cycle (even when anticollapse rings are used). Loose bags also may

suffer abrasion from being sucked down into the thimble. Thimbles should be rounded and

free of sharp edges to prevent tears, if this should occur.

Proper bag tension is a function of attention to detail during the initial installation. Bags

must be hung properly, without damage, to achieve the proper bag life expectancy. Bag

tension will vary with the age of the bag and also within any given cleaning cycle as material

builds up on the bags. Poor bag tension can increase bag wear, cause high pressure

drop, and shorten bag life.

Proper bag tension is a function of attention to detail during the initial installation. Bags

must be hung properly, without damage, to achieve the proper bag life expectancy. Bag

tension will vary with the age of the bag and also within any given cleaning cycle as material

builds up on the bags. Poor bag tension can increase bag wear, cause high pressure

drop, and shorten bag life.

Pulse-Jet Cleaning Systems

Common operating problems associated with pulse-jet cleaning systems include bag abrasion,

bag misalignment, and failure of the pulsing system. Pulse-jet fabric filters are

widely used because of their smaller size and their higher available cleaning energy which

allows for higher A/C ratios. The higher A/C ratios on this fabric filter type increase the

potential for fabric abrasion.

Typically, the bags in a pulse-jet fabric filter are suspended from a tube sheet and supported

by a cage. This single-point method of attachment allows the bag to move around

during normal operation. One source of bag abrasion is bag-to-bag contact due to

improper installation, poor alignment of the bag/cage assemblies with the tube sheet, or

bent/warped cages. The rubbing together of the bags (usually at the bottom) can wear a

hole in one or more of the bags.

The misalignment of bag/cage assemblies can also cause other problems. In some designs,

the misalignment of the cage will prevent proper sealing of the bag with the tube sheet. 

This may allow some of the dust to bypass the filter area, which decreases performance

but probably causes little or no change in pressure drop. Particularly abrasive dust has

been known to wear the bags and the tube sheet so severely at the point of the leak that

achieving an adequate seal may be impossible without replacing the tube sheet.

Another abrasion-related problem concerns poor distribution of inlet gas flow such that

the larger particles strike the bottom of the bags opposite the inlet. Some designs are

equipped with a blast or diffuser plate, which is designed to bring the gas flow below the

bottom of the bags. When failure of the bags occurs within about 18 inches of the bottom

on the side opposite the inlet, the presence and/or integrity of the blast plate or diffuser

plate should be checked.

The pressure supplied by the compressed-air system must be high enough to clean the

entire length of the bag during the pulse, but not so high that it damages the upper portion

of the bag. Insufficient cleaning of the bag may gradually increase pressure drop and

reduce the useful bag life. Too low compressed-air pressure, which is usually more common

than excessive pressure, may be caused by wear of the compressor rings, leakage of

diaphragms, or excessive draining of the reserve of the compressors by other equipment

tied to a common supply line.

The leakage around a diaphragm, which can usually be detected by a continuous audible

leak, affects the cleaning effectiveness for all the bags. Although it may take several hours

or several days, the pressure drop usually will increase eventually if the leak is severe

enough.

Failure of the solenoid(s) or the timer circuit may cause one or more rows not to be

cleaned. Effects on fabric filter performance may range from indiscernible to complete

cutoff of gas flow, depending upon the percentage area of the bags affected and the dust

characteristics. Both mechanical and electronic timers are still in use, and both have certain

advantages and disadvantages. Both types must be kept in a dust-free, dry environment

and relatively free from the shocks and jolts that can accompany normal operations.

Solenoid failures affect the row that has experienced the failure whereas timer failures

tend to affect most, if not all, of the fabric filter system.

Several problems may result from improper operation of the pulse pipe cleaning system.

First, the pulse pipe may not be properly aligned to provide effective cleaning to that row.

Second, the alignment may be such that the nozzles are aimed directly at the bags and can

blow holes in them. Lastly, a loose pipe may damage the tube sheet or even the fabric filter

enclosure, which would necessitate additional repairs.

Although all of these problems are relatively common in most pulse-jet systems and may

produce bag abrasion or shorten bag life, the one problem that seems to occur with greatest

frequency is the presence of water and/or oil in the pulse-jet compressed-air supply.

Water and oil that are blown into the bags during cleaning tend to absorb through the bag

and cause bag blinding as the dust cake becomes wet. The result is an increase in pressure

drop and ultimate replacement of the blinded bags. The oil usually comes from leakage of

the compressor rings and seals and the moisture from the atmosphere. Compressed-airsystems can be equipped with small water and oil traps that work well if the system is

maintained and the humidity is not excessive.

A typical troubleshooting guide is listed in Table and should be used only as a general

guide. When a baghouse begins to have problems that cannot be readily identified, the

operator should contact the vendor to assist in correcting the problem.

                                                 Troubleshooting guide