In the past two weeks, we have made a lot of progress towards our winter quarter goal of having an apparatus that produces biochar. Reflecting on what priorities are most practical for our first year of experimentation, we decided on prototyping a simple dual-chamber TLUD using recycled food cans (a 32 oz can (ex: quart-sized paint can), a 19 oz can (ex: Progresso soup can), and a 5 oz can (ex: tuna can)) that will use pyrolysis to convert the cacao husks into biochar. Pyrolysis is the thermal decomposition of biomass at high temperatures in the absence of oxygen, producing biochar. This simple design was inspired by Brian Zaro and was in line with our current most pressing project requirements that we’ve identified through research, including using cacao husks to make biochar and limiting particulate emissions of toxic syngas.
The TLUD is constructed with two concentric cylindrical containers and a riser (see figure from Week 6 blog post). The inner cylinder acts as the fuel chamber which has holes in the base and the bottom on the sides. These holes act as the primary air inlet to allow air to go inside the inner fuel chamber to initiate pyrolysis. There are also holes on the neck which serve as an inlet for secondary air to mix with syngas for complete combustion; this will limit the emissions of toxic syngas. The outer cylinder has holes near the bottom on the sides that act as the secondary air inlet. During combustion, air enters these holes via a natural air draft. The upward flow of heated gases causes a negative pressure (partial vacuum/suction) that draws new cooler air into the combustion zones to sustain the chemical reactions causing the burning. The riser acts to accomplish sufficient natural draft by concentrating the flames from syngas to increase the upward draft. We started out our Week 6 weekends by dumpster diving around campus. We were able to collect cans of various sizes for future prototypes. Afterwards, we divided up into two groups to finish the construction of the apparatus. Adam and Wenxi configured three cans to be assembled easily for the apparatus. D’Arcy, Jessica, and Pauline learned how to use the drill press in the PRL to drill the appropriate holes into the three cans. Currently, we are working on obtaining a thermocouple and appropriate lighting material as well as screening the cacao husks to prepare for our burn in Week 9! Beyond our design, we were able to connect with Brad, the chief chocolate maker at TCHO, for our second partner call. During our call, we shared our slide deck with him (derived from our midpoint presentation). Brad is currently traveling to Ghana and is excited to share our slide deck with his contacts at CRIG so that we can begin a partnership with CRIG. Considering ethical community involvement, we are hopeful that after Brad’s trip, we will be able to establish connections with CRIG and receive input from the groups of people we hope to potentially benefit with our biochar apparatus. Being mindful of these considerations, our group had a lot of discussions with our hesitations about moving forward with this project without having had much conversation with potential stakeholders that we have not yet established connections with. Finally, towards the end of Week 8, our group worked on outlining an O&M manual to enumerate system description, routine operation and maintenance procedures, emergency response plan, laws and regulation, commissioning and testing results, training, and relevant resources. We hope that by having an O&M manual, our future community partners will have the tools to be able to sustainably operate and maintain the relevant infrastructure.
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May 2020
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