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Using cohesive strength, wall friction, compressibility, internal friction, and permeability test results, and in some cases, DEM (discrete element method) modeling, functional design recommendations including dimensions, angles, materials of construction, and feeder details are provided.
Rotary testers do a poor job of measuring wall friction, and permeability testers are difficult to find. I have drawings and parts lists for wall friction and permeability testers that can be fabricated from readily available, inexpensive components or I can recommend testers that are commercially available.
I have access to Rocky DEM modeling tools to design transfer chutes and other equipment and testers to calibrate DEM inputs.
Biomass is variable and therefore challenging to handle. The key is to avoid convergence and/or include divergence in the bin and to design a feeder that ensures flow everywhere.
Caking problems are challenging because unwanted agglomeration is not always immediately evident. I can find causes and propose remedies. The adjacent photograph shows modifications to a 30-gal drum that reduces the compaction pressure inside.
Gravimetric feeders are often unreliable because during the refill stage when new powder is added, stress is transmitted to the material in the feeder, increasing its bulk density. This causes the the discharge rate to increase. Once the controller returns to gravimetric mode, it recognizes the error and compensates, often overshooting due to outdated tuning parameters. My design ensures that the solids stress in the feeder remains nearly constant during filling and emptying, allowing a constant bulk density and steady discharge rate.
Greg Mehos, Ph.D., P.E., • 4 Crusade Road, Westford, MA 01886 USA • 1-978-799-7311
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