Biomass Hopper Design
Charm Industrial
My main design project while at Charm was to design an improved Hopper for our processed biomass. I was very unfamiliar with hopper and screw feeder designs so I dove straight into research. The original hopper was made to replicate other grain and agricultural hoppers used on farms. It had a rectangular opening and outlet but also utilized sloping sides to ensure the sawdust-like material all flowed to the bottom. The feeders at the bottom were shaftless flex augers that rotated and transferred the material 8 feet up to a metered airlock. This airlock removed the air so when it was conveyed in the the pyrolysis reactors, there would be no combustion.
My task initially was to redesign the auger attachment plate and interface between the hopper and the hammer mill (the device above the hopper that beat the material into 2-4 mm pieces for efficient reaction) to prevent leaks that were observed onsite. This grew to a larger project to redesign the hopper to replace the current hopper, including all the design improvements needed to reduce stagnant material. The goal of the new design was to improve efficiency of feeding the material and to prevent biomass build up which could lead to mold and excess moisture.
The Concept Design Review was first held to present my research, calculations, concept designs, trades, costs and lead times, and rough test plans of the new hopper design. The calculations included how we would know the volume of material in the hopper with different bulk densities (wheat straw, corn stover, king grass, etc.) after certain time period of auger operation. This would then give us a set point for testing to be conducted to validate the design. My CDR presentation was received very well and I was given compliments on my diagrams and explanations. I then began to prepare for the Detailed Design Review, also called the Deployment Readiness Review because it included plans of implementation into the system. The review included detailed system model and drawings, full test plan, verification metrics, bill of materials, and other vital steps needed for deployment of the new design.
One issue that a Software Engineer brought up to me was that the level sensors were misleading when reading the level of the biomass in the hopper. He explained that it was due to the tendency for granular material to gather in a pile when poured. I discovered that if we knew the angle of repose of the material, then we could calculate the volume of the cone of material to be added to the volume below to determine the total volume of biomass. Knowing the true volume would give us a more accurate time until the hopper is empty. Because our milling process was unique we needed to test our material, either in-house or at a lab, for the exact angle of repose. To design the most efficient hopper, we also needed accurate tests for key variables such as the wall friction angle, cohesive strength, and flow factor to determine the hopper wall angles and minimum and maximum outlet width. To reduce operator and equipment error and to receive results quicker than in house, I connected with Jenike & Johanson, a lab that specializes in testing flow properties of materials. I conducted virtual meetings where we discussed project scope, evaluated which tests were needed, submitted paperwork, and collected and shipped biomass samples. The lab results were received and were planned to be reviewed later with the team.
Another issue that arose was the collection of excess material that was gathering under the augers at the bottom of the hopper. To ensure the stagnant material was not left there, I designed a ‘W’ curved metal piece to go under the twin augers so there was no volume under the cylindrical screw feeders. A window was also added for cleaning, other maintenance, and visual verification of level sensors. I discussed the drawings with Metalmen, a local sheet metal manufacturer, and they successfully fabricated and partially assembled the hopper. Unfortunately, after the ‘W’ piece was welded into place at our factory, the team lead decided we should find another work around for the current issues and continue this new design for version 2 of the system. However, I successfully completed and validated the detailed test plan with our Test Engineer, which included equipment and cost (load cells, reuse of a previous hopper stand, augers and motors, etc.), data to collect (how to collect, sensors, software needed, etc.), process details, personnel, and test time. I also completed the operational BOM and test plan BOM, which was maintained throughout and included vendors, suppliers, costs, lead times, and equipment alternatives. These reviews, drawing, and plans were documented and saved so the next engineer to pick up the project would have everything they need to complete the version 2 hopper.
