The fan (the engine)
The fan is the engine that supplies energy to the dust collector system. An improperly sized fan can hinder the performance of the other components (hood, ductwork, dust collector). The fan must be sized to handle a calculated volume of air at a calculated system pressure. If the fan is undersized, it cannot move the desired air volume. If the fan is moving more air volume than needed, it puts unnecessary stress on the whole system, which leads to numerous maintenance problems.
If the fan is not sized for the correct system pressure, it will not move the desired air volume. This usually occurs when existing fans are used on a new application with only the air volume capacity taken into consideration. Just speeding up a fan will not always result in more air volume. System pressure must be calculated and matched to a fan curve.
Dust handling equipment
At this point in the dust collector system, the dust has been captured (hood), transported (ductwork), filtered and collected (dust collector). Now the collected dust in the hopper must be conveyed away from the dust collector. To do this properly conveyors and air locks must be sized correctly to evacuate the hopper(s). Once the dust has been collected in the hopper, it should be taken completely away from the dust collector. If hoppers are allowed to stay full of dust, the air steam coming into the hopper lifts the dust and it is collected back on the filters. This creates a circulating dust load in the dust collector and causes the filters to be cleaned at an increased pace, raising differential pressure and shortening filter life.
Air locks must be on the bottom of each hopper before the conveying equipment.
If there is no air lock there will be a flow of air up through the hopper against the flow of material you are trying to discharge from the hopper. This will create another re-entrainment of dust that has been already collected. Once again this requires the filter bags to clean more and most likely raise differential pressure. Airlocks must be installed and used as they are intended. In practical terms, do not take rotors out of rotary air locks and do not wire double flap valves open.
When experiencing airflow or dusting problems with your dust collector system, check all of the system’s components first. Do not settle for a quick fix in one area. Usually a quick fix just moves the problem to another area of the system. Understanding and using sound guidelines on all system components, and properly fixing the real problem areas, is the best way to create and maintain a reliable dust collection system and reduce maintenance cost.
This is part three of a three-part article written for World Cement’s August issue and abridged for the website. Subscribers can read the full August issue by signing in, and can also catch up on-the-go via our new app for Apple and Android. Non-subscribers can access a preview of the August 2016 issue here.
Read the article online at: https://www.worldcement.com/special-reports/04082016/common-sense-dust-collector-system-maintenance-and-troubleshooting-part-three-40/