Dust collectors using reverse pulse compressed air cleaning are often a problem in industrial plants. These dust collectors are usually located on the top of bins that collect dust and debris from industrial processes. A fan blows the contaminated air through a set of filters, in the form of bags or cartridges.
The flow of air through the filters causes the elements to collect the dust, which will form a layer on the filter media. If left to collect, the filter may prematurely plug from excess contaminants, so some filter design uses a reverse blast of compressed air to knock the cake off the elements.
The blast of air is typically supplied at regulated 60 to 80 psi from the compressed air system. A set of blast valves, one per row of filters, is designed to fire at a set timed frequency for a duration of 100 to 300 milliseconds. These blast valves are usually quite large, consuming hundreds of cubic feet per minute, but only for a short time period.
However, problems can happen with the blast valves, which are usually diaphragm style in design. The internal diaphragms can age and crack, control circuits fail, air circuits freeze up, or the worst of all, the valves may fail open, consuming hundreds of cubic feet per minute constantly. When this happens, the plant pressure can fall to very low levels — and the problem can be difficult to find.
The accompanying photograph shows a dust collector with a control circuit connection that has broken off, this unit left unrepaired is consuming a significant amount of compressed air. Some maintenance is required to correct this problem.
If your plant has reverse pulse dust collectors, you should ensure they are working correctly and you design the feed lines so failure of the blast valves cannot upset your plant pressure. This usually requires designing in a restriction to flow and adding a storage receiver to help the cleaning pulse.
Tips on dust collectors:
- If your dust collector is pulsing excessively or for a duration longer than 300 milliseconds, consult the original specifications — there could be a problem.
- Carefully maintain dust collectors so failed valves don’t cause problems with system pressure or the cost of compressed air.
- Use differential control to save compressed air, most dust collectors have the capability of turning off the pulses if the filter differential is lower than a set amount.
- Turn off the dust collector when the filter is not in use.
- For outdoor dust collectors in cold climates ensure the air has an adequate dew point or freeze-up may occur.
- Add extra storage to the dust collector manifold to increase cleaning force, this often allows the pulse duration and frequency to be reduced.