To Build a Tanuru
Time to get our hands (and some pants) dirty. During our meeting with Naomie on Tuesday, she pointed out a space in the EARD-CI yard where we could construct our tanuru, our kiln for making charcoal. With EARD-CI generously providing the space for our kiln, we had only to gather the materials and our engineering minds to build it.
As mentioned in the previous post, the idea behind the kiln is to produce charcoal out of biomass which can then be press into briquettes. By first pyrolyzing biomass (heating up the biomass in the absence of oxygen) and turning it into charcoal, the remaining carbon structure of the material will burn cleaner when burned in a cook stove. But what about the detrimental effect of the emissions released from the kiln during pyrolysis? Does it matter that the biomass is being pre-burned and converted into charcoal before being used as fuel in a cook stove? There are two main reasons for making charcoal in this manner for the briquettes (besides the fact that consumers prefer charcoal briquettes). First, we have designed our kiln to allow the syngas (gasses including hydrogen, oxides, and others) produced by the burning biomass to undergo complete combustion before leaving the kiln. In other words, when making the charcoal we burn away the harmful emissions. If the biomass were burned straight in a cookstove, it could release that carbon monoxide and other gasses in the syngas into the space where the cook is breathing. Secondly, biomass in the form of charcoal is much more energy dense than un-carbonized biomass making it a more appealing form for cooks who want to spend less time tending their fire.
The science is great in theory but our goal is to make it great in practice. Wednesday was the day to begin hunting and gathering our materials to construct our tanuru and as luck would have it (and good planning by us) Wednesday was also market day in Tengeru. We wandered through entire streets over crowded with tables and blankets filled with shoes, rows of mboga (vegetables) and dried beans, and interspersed throughout everything were tables overflowing with various buckets and cooking supplies. While Emily and I ventured to purchase vegetables using our limited knowledge of Kiswahili to varying degrees of success, Tucker and James searched for supplies for the technical side of cooking. Back at the house, the girls got to work cooking our first home cooked dinner of the summer including all manner of fresh veggies. As the food was just about done, James and Tucker returned from their visit to a brick maker with Naomie where they picked out a load of bricks to be purchased the following day.
Back at EARD-CI on Thursday, Naomie directed us to a hardware shop just down the road which supplied us with all the fun toys with which to build our kiln: tiles, a shovel, and one of those triangular spreader tools (now that was a tricky tool to explain through the language barrier). Then, with a delivery of 300 bricks, we were itching to get building.
Thursday afternoon was beautifully sunny and perfect for mixing mortar (also called mud) with our fingers, smearing that mud over bricks and our clothing, and building our kiln up, up, up. Five hours, many pictures, and several wheel barrows of dirt later we had a kiln. We’re very proud of it.
The kiln is designed with three main areas: the kiln body, the chimney, and the combustion tunnel. Biomass will be pyrolized in the kiln body and any gasses which are released during pyrolysis will be drawn into the combustion tunnel and up through the chimney. Secondary air from the front of the combustion tunnel will mix with the released syngas and ideally undergo complete combustion (or as close to as possible) in the chimney. Basically fire and biomass will go in and charcoal (hopefully) will come out. Or alternatively, as Naomie pointed out, fire and dough could go in and homemade bread could come out. Another very tempting option we should look into.
Again, this is the scientific theory, and we have these next few weeks to attempt to make it reality. With a newly constructed kiln, several bags of biomass composting in the yard, a hammer press in commission, reports being written, new friends to play football and Frisbee with, and an entire house to call our home for the next two months, I will say that this has been a productive and satisfying first week in Arusha. Baadaye! Until later!