People discuss a lot about the sizing and filter efficiency of the dust collector while they discuss the least about requirement of allowing collected materials to freely flow from the hopper to the final bind, drum or sack. Removal of hopper bridging in the dust collectors ensures eradication of possible headache related to maintenance. Often, cartridge collectors and baghouse collectors use hoppers for directing accumulate dust to dust transport system or storage container. Dust collector hoppers are not meant for storing collected products. So, if hopper dust discharge is not occurring properly, it may end up compromising with the performance of the dust collector along with bearing with the maintenance headache.
There are a number of variables that directly lead to bridging in dust collector hopper that results in accumulation of dust while blocking discharge pathways. Bridging, then, traps dust in hopper to raise pressure drop in the collector to a terrific level as the dust doesn’t leave the collector as desired. And, the variables may include,
- Hopper design
- Characteristics of the dust
- Maintenance and size of Rotary airlock valve
- Moisture or condensation
Let’s check out possible ways to avoid negative effects of these variables.
Hopper design and characteristics of the dust – Actually these two variables go hand in hand. Even the finest and driest dust may become difficult to handle within confines of the hopper. Some have higher friction on hopper sides while others just agglomerate. And, as a result they may keep the dust from smoothly flowing down to discharge aperture. Until the dust collector gets installed and starts operating, it may be difficult to gauge its behaviour. But if you can have review of the characteristics of the dust beforehand, you may make changes to design selection reducing the chances of bridging. You may look for hopper design features that lower the risks of bridging. You can, for example, enlarge discharge opening, replace sharp corners of the hopper with corners with larger radius for proper hopper dust discharge. You may also use steeper or taller hoppers for dust retention reduction.
Maintenance and size of rotary airlock valve – The key function of the valve is to provide air seal at the discharge aperture of the hopper. It is installed between the hopper discharge and the discharge bin or conveyor. Though it doesn’t seem to be important initially, the size of the valve can really matter, down the lane. Also, it may affect the functioning of the hopper if not maintained properly. To avoid any negative output, it will be good to check the valve body as well as the rotor blades on the valve for possible wear and tear, regularly. You may also need to replace it if suggested by the technician. Also, it should be sized properly so it can manage higher dust discharge rates.
Moisture or condensation – Some types of dust tend to absorb and retain moisture. If the hopper is moist or moisture enters the hopper discharge aperture somehow, it may condense on the inner side of the hopper letting it shut down for some time. To avoid absorption of moisture and thus condensation, exhaust fans must circulate the air through collector to keep the dust collector housing as well as the hopper warm prior to dust is being drawn into the collection. The fan should also run for a short span of time after the dust stops entering the collector to ensure keeping the surface of the collector warm until the dust is being evacuated.