Mechanical shakers use a mechanical rapping device to remove the excess dust cake; however, the airflow through the collector must be temporarily stopped to clean the bags. These shakers involve low maintenance and low operating costs, but they require large amounts of space, have limited design flexibility, and have low air to cloth ratios (2:1). Shaker collectors employ tubular filter bags fastened on the bottom and suspended from a shaker mechanism at the top.
Dust-laden air enters the collector and is deposited on the outside of the tubular bags. Continuous processes use compartmentalized collectors where airflow can be diverted to other compartments during the bag cleaning cycle. Bag materials must be made from woven fabrics such as cotton to withstand shaking. Some shaker collectors have been converted to pulse jet collectors. However, this is an expensive operation and should not be necessary if the collector is properly maintained.
When using mechanical shakers, a number of recommendations should be followed:
- Manometer gauges should be installed on each compartment to monitor differential pressures during the cleaning cycles.
- Differential pressures should be as close as possible to 0.0-inch wg to ensure that the dust cake breaks and is released from the bags. Differential pressures above 1/4-inch wg during the cleaning cycle will dramatically interfere with bag reconditioning, which can lead to reduced airflow, high static pressures, and low bag life.
- Bags should only be shaken when differential pressures across a section of bags have increased by 1/2-inch wg.
- Experiments to determine the optimum time interval between the shaking of bags should be performed so that bags are not shaken excessively. This lessens wear on the bags and the mechanical parts.
Reference
NIOSH Mining Program Report of Investigations, « Dust Control Handbook for Industrial Minerals Mining and Processing», Second Edition
