Baghouse Filters or Cyclones for Dust Collection
Before dust can be controlled, it must be contained first. Most often, this means making sure equipment is “tight” and gasketed properly. Equipment that emits dust should have suction vent connections and/or suction hoods attached. These connect to a manifold, which then connects to a separator (cyclone and/or baghouse dust filter).
Some dust problems are solved best by cyclones, others best by filters. The trick is to use each type for the jobs they do best.
Baghouse Filter Operation
Filters require more space and come with a higher cost than cyclones for a given air volume. As installed, most filters have more resistance than cyclones, resulting in less suction, or more fan power cost. They can handle heavy dust loads and materials that may be slightly sticky or agglomerate.
The biggest advantage and argument for filters is their efficiency. They can be very efficient, up to and above 99.9%, even with low micron dust. If the bags are the right type of filter media, the bags are kept in good repair, and the bag cleaning system is working right, air leaving the filter can be cleaner than the air outside most mills.
Filter bags and “dust cake” on the surface of media act to separate particles from the incoming dirty airstream, resulting in clean air exiting baghouse to the atmosphere. If the filter is sized and designed correctly, the maintenance required is moderate for the consumer.
For maximum operating efficiency, dust must be allowed to fall out of the negative airstream that is going through the filter to discharge out of the system. If bags are spaced too closely together or if the housing size is too small, excessive “can velocity” causes dust to be held in suspension. Suspended dust then chokes the system regardless of cleaning mechanism or air-to-cloth ratio. Kice filters are conservatively designed to provide proper bag spacing to eliminate this potential problem.
Cyclone advantages include simplicity and comparatively low cost. They are compact in proportion to the volume of air they handle, so they are easy to install in most any locations, indoors or outdoors. They are particularly effective at removing large and/or abrasive material and large amounts of material before the final filtration of the air by a baghouse or cartridge filter.
Their main disadvantage is the inability to retain the extremely fine particulate. Although most well-designed and well-fabricated cyclones are better than 90% efficient with particulate above 30 microns, their efficiency drops off rapidly below that size.
Another positive is that Cyclones require very little maintenance. The bad news is that since they need so little maintenance, they get practically none. About the only attention most cyclones receive is when a machine below plugs and backs up stock, filling them up. The cyclone keeps going – unfortunately going and blowing – blowing dust very visibly.
Cyclone efficiencies can vary tremendously based on the following parameters:
- Particle size distribution
- Particle density
- Air and material volume entering the cyclone
- Cyclone design and dimensions
- Quality of fabrication
- Quality of installation
Designed to handle air volumes from 500 CFM to 45,000 CFM, Kice cyclones are engineered to be highly efficient at separating particles from air streams. The geometry of Kice cyclones provides a balance between efficiency of separation and resistance to air flow.
Filters and cyclones often supplement each other. In many situations, several different process streams may each be directed to its cyclone for primary separation – with their exhausts vented to a large central filter for the final separation to remove the hazardous fines, permitting the filtered air to be returned to the plant. Most pneumatic lifts are vented this way, and there are many other applications where filters and cyclones work together providing results that neither could do alone.