Kiln to Briquettes

To begin where we left off, last weekend we busted out of Leganga and headed to Moshi for a change of scenery. On Saturday morning we caught a daladala on the Moshi-Nairobi Highway, and an hour and half later we were passing by the Coca-Cola sponsored clock tower on the north side of town. Every newspaper we saw was printed with Obama’s face in anticipation of his arrival on Monday. We spent the day walking around and exploring the streets, and stumbled upon a rice processing plant when we veered a bit off the major roads. They were drying out the grains before they were to be hulled:


Sunday we went on a walking tour around Mataruni, a village on the southern slopes of Kilimanjaro. We were able to connect with a young man named Richard who grew up there. He had recently converted a part of his family’s farm into area to bring guests (and tourists) to demonstrate how fresh coffee beans are prepared into a brew. He showed us how a large mortar and pestle is used to remove the husk from the beans before roasting. Quite a bit of work if you wanted to do it every morning. But in the end this trip was invaluable to our larger mission this summer, and the coffee was delicious.

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One of the major ventures of this past week has been the initial experiments of our freshly constructed tanuru (charcoal kiln). The charcoal from this kiln, made from sawdust, rice husk, and corn leaves given the season, will supply a clean burning filler for making briquettes. The kiln is designed to bring a large amount to biomass to a high temperature in the presence of limited oxygen. To perhaps make this a bit simpler, but also a little bit more inaccurate, let’s think of three different reactions:

1)      Gasification of Biomass: Biomass + Heat + Air (primary air) = Ash + Syngas + Heat

2)      Pyrolysis of Biomass: Biomass + Heat = Charcoal + Syngas + Heat

3)      Combustion of Syngas: Syngas + Heat + Air (secondary air) = CO2 + H20 + Heat

A bit funny to have heat on all sides of the equations, but the point to be made is that it takes heat to get started, but once going, the reactions can produce excess heat to run to completion. Syngas, essentially biomass that turned into gas, contains several compounds but has a high percentage of hydrogen gas so we can consider it combustible. Check out a picture of Rachel doing some work on our design:


The kiln is designed with four holes along the base which allow limited air to enter the packed biomass. This is where we begin 4 small fires to get the process going. The air will turn some of the feedstock into ash but it will also create a lot of heat which helps drives pyrolysis (reaction #2 above). So we let in a little bit of primary air into the kiln, sacrifice some of the biomass to ash, but create a lot of heat to make a bunch of charcoal. Because the top of the kiln is sealed shut, all the syngases produced get drawn into the chimney through an opening right below Rachel’s left hand. Rachel’s right hand is working on the secondary air tunnel which allows air to flow under the kiln and get preheated before entering the chimney. There the secondary air meets the syngas and a second round of combustion occurs. Most charcoal production systems in Tanzania simply allow syngas to escape, but our design will produce few emissions and create extra heat which can be fed back into the kiln.

Now we just need to figure out how to pack the kiln. Here’s a picture of the kiln filled with biomass (sawdust and rice husk). We are using some plastic pipes to make sure we can get primary air coming up from the base.


After removing the pipes, we have nice “biomass chimneys” that cut through the feed stock. Also nice to sprinkle some corn leaves on top.


Then take a piece of metal roofing properly cut to size and place it on top of the kiln. This will make sure that the syngas produced will enter the chimney.


Then cover the metal roof with dirt to make a tighter seal which also acts as insulation. Remember the kiln is gonna get hot! Then start some fires in the side holes (where the primary air enters). Here Tucker and Emily are inspecting one side while Naomi and Rachel work on the other. Most of the gas coming out of the chimney at this point was water vapor.


About 5 hours later we had dried out a bunch of wet sawdust and made a little bit of charcoal! We separated out our winnings, and I did a little physical processing to grind it up to dust. Thanks to Richard we had some experience with this before.


Then we mixed up some cassava flour (tapioca) and water, heated it up and made a starch binder which we then added to the charcoal mash. This acted as our briquetting mixture.


And from there we were able to start making briquettes in our new Musket Press. Exciting to see the whole process!

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But we know we can get a better yield from the kiln, so we are setting ourselves up for success. We’ve taken all the feed stock we’re planning on carbonizing and are letting it dry out in the sun. Let’s hear it for surface area to volume ratio.


Another exciting update is that DHE has a new partner in Arusha, Vision for Youth, or V4Y, which offers health education and entrepreneurial training for young adults. Rachel and I first met with Violet, a cofounder of the organization, on Wednesday and heard that they’ve been wanting to start a charcoal briquetting operation for some time. All four of us went back to visit them again on Friday to meet with Veda, the other cofounder, and Happy, Raymond, and Pendo, some of the “youths” (they’re our age…) who are interested in briquetting. A wonderful meeting that left everyone energized! They’ll be coming out to Leganga on Tuesday to see our developing briquetting operation.

Next week will be a busy one. After meeting with Didas and Maricel from EMORG (Educational Model Organization), a growing library/vocational/community center, we promised to help them paint their new building on Monday. On Tuesday morning we have the V4Y group visiting, and then we are going to go meet Julius Sossy and the briquetting group he helped DHE begin last summer in his village of Moivaro. Then on Wednesday we will be visiting Bernard, an inventor who runs an organization to inspire young Tanzanians to solve their own technical challenges who has also helped us design stoves in the past. We want to talk to him a bit kilns and briquettes. I’m sure he’ll have a lot to say. And in between all of those visits and meetings, we’ll keep making charcoal, keep making briquettes, and keep making food. More updates soon, Kwa heri!

Published by

James Kennedy

James is the current head of DHE's Bioenergy project. He began his work in stove design but now is more interested in biofuel production and methods for making renewable resource harvesting sustainable.

5 thoughts on “Kiln to Briquettes”

  1. Wow, James, this “briquette factory” is quite an innovation beyond the activities of last year and looks like an interesting and promising briquette making process. I would be interested in hearing more about your concepts for commercialization or community adoption of the process. I also read the post about Sossy and his village group and felt sad that their briquettes did not work out well for them. I am so glad that the group is back there again though, to talk about that with them and possibly offer new solutions. Keep up the good work DHE!

    1. Great to hear from you Carrie! I agree, I think the process we are laying out this summer is both interesting and promising, and the most exciting thing is it is quite a bit better now than as when I lay it out in the post above. And I agree is unfortunate that Sossy’s group seemed to reach difficulty, but the dedication by the Lulu Vicoba has added more reassurance to our work. Hopefully as we hone this process even further we can offer something to Moivaro that they can really use.

  2. Hi James,

    We are very impressed by your work! You have been in our thoughts and prayers. We know that Ian and your Dad are visiting. Your life is truly an adventure. We are so proud of you and so happy for you. I fondly remember me trip to Rwanda last February. You will definitely experience God in Africa.

    Be safe.


    John and Shaw

    1. My dear uncles! Excuse the delay in my reply, getting a computer for myself is a bit difficult sometimes. Yes, it seems as if everything here awe inspiring. It was wonderful to have Ian and my dad visit. They took more pictures in their two weeks than in my entire time so far, and it will be wonderful to have them reinforce the memories. I hope I can see you both soon, though it seems as if I’m always running around and never set aside the time to give you proper visit. Soon though.

      Much love,

  3. Hi James,
    Thanks for a fascinating article. Great work!

    I was just curious if you guys found some raw materials better than others at carbonizing, and which binding agents do the best job in the area?

    Best wishes,

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