Maintenance and Inspections

This is usually caused by poorly designed hood and/or insufficient airflow in the system. Excessive cross-draft may also reduce the efficiency of a canopy-style hooding.

For a good capture efficiency, the hood shall be designed to achieve the appropriate capture velocity. The capture velocity (ranges from 50 to 2,000 ft/min) is determined based on the type of contaminant and how it is released into the surrounding air. If the contaminant is released at high initial velocity, for example grinding and shake-out, a high capture velocity would be needed to maintain control of the contaminant until it reaches the hood.

Additionally, the design of canopy hooding for hot processes, for example metal pouring and melting furnace, shall take into consideration the effects of thermal draft. This usually means oversizing the hood to account for the increasing air column diameter as it rises from the hot source.

Insufficient airflow in the ductwork may be caused by poor system air balance, excessive static pressure drop in the system, inapt exhaust fans, or issues with the dust collection filter cleaning system.

Such conditions usually contribute to the diminishing efficiency of the air cleaning device, and they shall be addressed immediately as required by the operating air permit at the plant.

In a dry collector such as a baghouse, visible particulate emissions at the exhaust stack are typically caused by bag or cartridge failure due to (not in any particular order):

• Normal wear (the end of bag life)
• Filter material and/or installation defects
• Other rapid failure modes are caused by excessive cleaning frequency or high entry velocity at the collector inlet (known as “can velocity”). Such rapid failure modes can be prevented by implementing “clean-on-demand” and a better inlet distribution baffle.

In the case of cyclones and wet scrubbers, the condition can be contributed to (not in any particular order):

• decreasing filtering performance as a result of abrasion-induced internal mechanical wear
• Various abnormal operating conditions, such as a higher than normal dust loading in the incoming gas stream
• The air cleaning device does not match its intended application.

Although the effect of short filter bag life can be readily noticeable from the rapid rise in the pressure drop across the collector, the cause of such a condition can be difficult to diagnose and remedy.

The life of a filter varies quite significantly depending on:

• Material (e.g., fiberglass, polyester, Nomex)
• Construction (e.g., dual density, spun/spun)
• Additional fabric treatments (e.g., Teflon)
• Field application factors (e.g., grain loading, particulate abrasiveness, temperature, humidity, etc.)
• The effectiveness of the filter cleaning mechanism

A systematic troubleshooting approach needs to first ensure that the filter cleaning mechanism is operating as intended. This includes checking for proper timing, leaky or plugged blow pipes, and correct reversed air volume and pressure, as applicable.

Condensation in an air pollution control system most often occurs during the cold winter months. It takes place when the warmer gas stream from the process is cooled past its dew point temperature upon contact with the colder duct and equipment surfaces.

In a dry collector, condensation can cause severe blinding and premature bag failure, in addition to bridging in the hopper. Provisions such as insulation and operating at an elevated temperature must be incorporated when there is a potential for condensation in the system.

Undetected condensation and moisture caused by compressed air will cause filter media and pulse valve failure. Learn more about how to solve this common problem.

All fans generate some noise and vibration. It is only when they reach certain amplitude that we consider them “bad” or excessive. Although it is difficult to find the source, the solution to the noise and vibration problems is often obvious.

Some of the more common sources of abnormal noise are (not in any particular order):

• Fan wheel unbalance
• Failing, misaligned, or contaminated bearings
• Rotating components rubbing on stationary parts
• Belt slipping
• Operation in surge or stall

Some of the more common sources of excessive vibration are (not in any particular order):

• Misaligned sheaves
• V-belt drive deterioration
• Bearing deterioration
• Loosening of hardware on the fan and support structure
• Fan wheel imbalance
• Material buildup on the fan blade