SOLAR BRIQUETTE DRYER
check out this video feature on my team in Uganda!
THE BIG PICTURE
Approximately half of the world's population uses solid fuels like wood as their primary source of cooking fuel. The fumes produced by burning these fuels indoors contribute to the premature deaths of over 4 million people every year, the majority affected being women and children.
THE PROBLEM
Charcoal briquettes produce substantially less smoke than wood and other traditional fuels. However, they take many days to dry in the sun, and the drying process is halted entirely by rain.
THE APPROACH
In 2018, a team of three classmates and I partnered with Appropriate Energy Saving Technologies (AEST), a cleaner-burning fuel producer in rural Uganda, to help scale up their charcoal briquette production.
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From our initial conversations with the AEST team, as well as observations made during a preliminary trip to Uganda, we identified the briquette drying process as the bottleneck in production. Production machines were being run just three days a week, while the open-air drying racks were full nearly every day.
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Our initial approach was to speed up the drying process using covered solar dryers. Testing in the US with sponges as briquette stand-ins, we measured humidity, temperature, and airflow in several dryer prototypes.
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We found a design that dried the sponges substantially faster than open air, and returned to Uganda excited to share our design.
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To our surprise, the design didn't perform nearly as well in the real world as we'd expected. In fact, the dryer had little to no effect on the drying rate.
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We quickly realized it was going to be difficult to out-perform the hot Ugandan sun with our dryer. To remove the drying bottleneck, we had to view the problem through a different lens.
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THE SOLUTION
Our team realized that the drying wasn't simply a bottleneck due to the drying rate in the hot sun - the rain also majorly impacted the effective drying rate. When wet weather was forecasted, AEST covered all of their open-air dryers with tarps, effectively halting the drying process.
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Since even a few drops of rain could ruin the briquettes, the dryers were covered much more often than they needed to be. We estimated the briquettes were covered almost 20% of the time they were on the racks.
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To address this bottleneck, we worked closely with the AEST production team to design permanently covered dryers that allowed easy access to the briquettes, took advantage of the sun and natural airflow, and most importantly, allowed the briquettes to dry even in the rain.
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After constructing prototypes of the new design, we tested the drying rate during the rain and compared it to the existing solution.
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THE EFFECT
Our new dryers increased the wet-weather drying rate from 5% of the sunny weather rate to almost 90%.
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Implementing these dryers would increase annual profits by approximately 10%.
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