Long-term solutions are: 1) reduce the speed with a belt-driven pulley; 2) replace the high shear mixer with a pump and static mixer or in-line mixer; 3) consider a viscosity-modifier to reduce the viscosity of the batch; 4) make some electrical changes; 5) replace the mixer with a better design. Replacing the current motor with a belt-drive pulley would reduce the power draw but it also would increase the mixing time. The existing pump might be okay in recirculation-mode using a static mixer. A more expensive option would be an in-line mixer but the results would be better than a static mixer. Mixing time would definitely be increased with either a static mixer or inline mixer. Talk to motor manufacturer about whether increasing the motor voltage with a transformer might be an alternative to consider. (Motor wiring etc. has safety factor built in which might allow increased voltage.) In the same vein as reducing the speed, consider buying an off-the-shelf motor with a lower rpm if a reduction in mixing efficiency can be accepted.
Dan Breeding, retired engineer
Lone Jack, Mo.
A vibrating screen separates pulverized lumps of coal from dust. The screen is fed from a lock-hopper above. The fine particles must be separated because they could become carry-over for a gasifier (entrained-flow); a pelletizer scheme is being tested to re-use this material. The lumps are then fed to a screw conveyor to the gasifier. On a vibrating screen, solid is supposed to be spread evenly across a mesh screen (Figure 2). The rocking motion and the slight slope cause the solid to flow towards the discharge and into either the pneumatic conveyor pick-up pipe or the hopper for the screw conveyor. This isn’t happening. Instead, coal is building up on the screen and blocking flow from the lock-hopper above. The screw conveyor hopper is plugged and the pick-up pipe is plugged. Adjustments to the slope and the rocking motion have been increased to no avail. Any suggestions?
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