This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
How many people can you fit in a dala-dala?
Answer: One more. Plus a chicken.
Dala-dala is the main mode of public transportation in Tanzania. All the dala-dalas seem to operate more or less individually with very little group organization. A dala-dala is, in essence, a retrofitted van. Start with a 15 passenger van. Now rip out the huge cushy seats and replace them with four rows of small, plastic-cushioned chairs. In front of the first row, throw in an extra bench for people to sit facing backwards. Then raise the ceiling by a foot and you've got a dala-dala.
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Every dala-dala has one driver and one conductor. The conductor handles the payment and advertising by respectively shaking a stack of coins in your face and by beckoning out the window and sometimes forcible pulling you toward the vehicle to encourage you to ride his dala-dala. Then there are the passengers. Fill up the seats. Fill the bench. Squeeze two or three passengers next to the driver. All this extra aisle space? What a waste. Push 'em in, fill it up. Passengers pile in and stand, bracing themselves on seat-backs, leaning precariously over seated passengers. Babies get passed around depending on whether the mother managed to snag a seat. Bring you chickens along, why not.
And just when the van is stuffed to overflowing and the conductor has left the sliding door open so that he can hang on to the outside, right when the mass of people on board could not possible compress anymore, the dala-dala stops and one more passenger pushes on board. It is a thrilling way to travel.
The record so far: 30 people at one time. Plus a large spider on the roof.
The days are far too quickly turning to weeks for our stay in Arusha, filled with many kiln burns, hundreds of briquettes, and perhaps most exciting, meetings with several groups interested in learning about briquetting and charcoal production. One of the major ventures of this summer has been our experiments with our freshly constructed tanuru (charcoal kiln) which have been becoming steadily more successful, with a greater charcoal yield, on each successive run. 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.
The kiln is designed with four holes along the base which allow limited primary 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 in the kiln body. Along the floor of the kiln, we have the secondary air tunnel which allows air to flow under the kiln and get preheated before entering the chimney. In the chimney, 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 fewer emissions and create extra heat which can be fed back into the kiln.
After letting the kiln burn with primary air for some time, we plug up the bottom holes so no air enters the kiln body. About 24 to 48 hours later, we unseal the kiln and, volia! We have a pile of black charcoal particles. Then, we pound away at the charcoal to make a finer dust for a few hours (the same physical processing for making ground coffee and about the same color. I doubt the caffeine content is quite as high though.). On the side, we mix up some binder, either a cassava flour porridge (cassava flour is also used to make ugali which is a staple dish in Tanzania which is a white paste usually served with mboga, vegetables, and meat.
It is interesting to consider that the same glue that we’re using to make charcoal fuel we are also consuming. I wonder what it does in our digestive tract. This also brings up another important point which is that we are using a resource to make fuel that is also a food. For some, the convenience and inexpensive cost are worth it but for others, another binder such as newspaper is more desirable.) or soggy newspaper which we then added to the charcoal mash. This is our briquetting mixture. And from there we were able to start making briquettes in our new Musket Press. From there, we leave our fuel briquettes in the sun to dry for a few days and finally, we burn them.
Besides the technical work, we’ve also been interacting with groups eager to give briquetting a shot. One of the groups is Vision for Youth, or V4Y, which offers health education and entrepreneurial training for young adults. James and I first met with Violet, a cofounder of the organization, 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 to meet with Veda, the other cofounder, and four other “youths” (they’re our age…) who are interested in briquetting. A wonderful meeting that left everyone energized!
For our third meeting, the V4Y group came over to learn about our briquetting operation. We walked them through the process of making briquettes from collecting and drying the biomass, to using our kiln to turning it into charcoal, to making a sticky mixture of charcoal dust and cassava flour, to pressing the mixture into briquettes and letting them dry. Judging by the laughs, the questions, and the ideas on how they would improve various aspects of the presses, I’d say they really enjoyed the session and learned a lot from it. Success! We are going to continue to work with them and help them to set up their own operation on some land they have in Arusha. Very exciting.
And tomorrow another day awaits us, full of charcoal, Swahili, ugali, and the ever thrilling dala-dala rides. One last note on the dala-dalas. They might sound insanely dangerous but I fully believe that if the dala-dala were to come to an abrupt stop or hang a sharp left turn, all passengers would remain secure and in place as there's no physical way for anyone to move in any direction, we're wedged so tightly in. Never a dull moment on a dala-dala.
Previously in this series: