Monday, May 21, 2012

30d - A "rocket" stove with adobe blocks

I am convinced that rocket stoves can be of great value to institutions where there is no cooking gas and where large pots are used every day to cook a lot of food for lots of hungry mouths. These large pots can be 40cm to 60cm in diameter and 20cm to 30cm or more in height. They are heavy when full.
In some institutions I have seen kitchens where cooking is done on a three stone fire on the ground.
I have also seen valiant attempts at improving the situation with gas stoves only to see them abandoned (see picture above) either because the supply of gas was not reliable or because these stoves stopped working and there was no one to fix them.
I have also noticed that in some cases an attempt was made to install rocket stoves but these were not being used either. In one case the rocket stove was not properly built and did not work at all filling the kitchen with smoke. In another case, see picture above, these stoves were too high, unstable and difficult to use by the women and children who had to work with the large and heavy pots. 
Compared with the metal frame we see on the ground these solutions did not help at all and were abandoned for very valid reasons.
There are lessons to be learned from these two situations. A rocket stove must be low to the ground for easy access and stable to avoid accidents. It must also be made with easily replaceable materials because these implements do break and need to be fixed.
If we make use of very well tested rocket stove design principles and use the idea Dr. Larry Winiarski experimented with (see attached video), a rocket stove made out of 16 adobe blocks, we come up with the following idea:
Take 16 adobe blocks (not fired) to form a simple and insulated combustion chamber. This insulation is very important to the proper operation of a rocket stove. And a metal frame that will support the weight of the cooking pots. This metal frame is not attached to the adobe blocks.
The whole stove will be less than 40cm in height and looks very much like the metal frame we saw in the first pictures above. It is as if we had taken the original metal frame and inserted the adobe combustion chamber inside. We can do that if the frame is big enough.
The combustion chamber is built with adobe blocks stacked on top of each other as shown:
The first layer is made with 3 blocks and one half block. In the middle we place a thinner block. This central piece will improve the efficiency of the combustion chamber.
The second layer is made with another 3 blocks and one half block just like the previous one. We must leave an open gap in the front. Through this gap we will feed the firewood and air will enter the chamber. We also place a full block on the ground in front of the stack as seen in the picture. This will support the wood pieces to keep them above the bottom of the chamber.
The third layer is made with 4 full blocks. This layer will form part of the combustion chamber as shown in the picture above.
The fourth and last layer is also made with 4 full blocks. This completes the combustion chamber. The rocket stove is ready to be tested. All the adobe blocks will be left loose. No mortar is used. If one breaks we replace it. That is it. Very simple.
Use small pieces of firewood, kindling, paper and/or dried leaves to start a fire inside the combustion chamber. Just like you light any other fire. As the stove heats up, it should not take very long, the flame at the top will start turning blue or even colorless. This indicates that the firewood is burning well and all combustion gases are being burned.

These gases are released when wood burns. In a typical fire they are lost and create pollution. In a rocket stove they burn making a very hot fire.
It is a good idea to install the metal frame over the stack of adobe blocks before starting the fire. Later everything will be too hot to handle.
We can place the cooking pot on the stove now. The pot shown in the picture above is about 20cm in height and the stove is about 35cm high. This is a good height even for short people. There are no high heat shields and so the pots can be handled without a lot of lifting. This makes life easier for those working in the kitchen and minimizes the possibility of spills, a common cause of severe burns.
Heat shields are useful to concentrate the heat that otherwise gets lost all around the cooking pot. The shields devised for this stove are set on the ground. This model has two half-shields, one on one side,
and another heat shield on the other side,
making them easy to install and remove. A couple of handles would be nice too... they can get very hot.
In this final picture we show a larger pot. This one about 55cm in diameter and 30cm in height. Still a good height for whomever is cooking and the pot is still nicely placed to make a very good hot soup.
This type of stove does not use large pieces of firewood. It burns small pieces of firewood. This smaller firewood is cheaper and is much easier to find. Small pieces of wood do not contribute to deforestation since they can be harvested from broken branches.
Children of all ages do help in institutional kitchens. This is often a necessity and a good learning experience for many of them. Small pieces of firewood are easier for them to lift and handle. Less work and less accidents. This is good too. Right?
The attached video is by Dr. Winiarski. It is worth watching.

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