Tutorial de Low-tech Lab | Catégories : Alimentation, Énergie
Build an economical and transportable wood cooking system.
Build an economical and transportable wood cooking system.
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One of the major energy and health issues of our time concerns cooking. In many developing countries, the most widely used technology is the three classic stone fireplace. It offers catastrophic yields (10 to 15% thermal efficiency sheltered from the wind, 5% without wind shelter) and releases a lot of toxic fumes into homes. Two concerns arise from this:
Some technologies use the same biomass but with higher yields. Here is one :
The micro gasifier is a low-tech and very economical cooking technology. It offers higher yields than a conventional three-stone fireplace (around 35% thermal efficiency) when well manufactured, and even better in its optimized industrial version (thermal efficiency of around 45%).
It is possible to manufacture very simple but not optimized models, with tin cans. It will be useful for example for heating water, cooking small amounts of food and for demonstration/pedagogy.
More complex models exist, more expensive but allowing to manage the power of the flame with an improved duration.
For drilling, two possibilities:
It is based on the principle of gasification: The wood is heated in a low oxygen atmosphere, which will allow the release of flammable gases called "Syngas", which will then be burned in the upper part of the stove.
The micro gasifier lights up from above. The primary air introduced in the lower part passes through the mass of the fuel and makes it possible to maintain a pyrolysis bed which goes down as the combustible gases are released. The secondary air is injected in the upper part to provide oxygen necessary for the combustion of the gases that are released upwards.
Better results are obtained in forced convection with the use of an integrated fan under the fuel support grid, but this induces a reliable supply of electricity.
The combustion temperature is around 800°C, and the thermal yields range from 30 to 45%, depending on the quality of manufacture of the system and its insulation.
It is light, compact, reliable, uses little fuel and generates, at best, reusable coal for other applications. It is thus a very low-tech system and very powerful compared to the traditional systems used in the world.
For comparison, the graph opposite shows the energy performance of different systems. The micro gasifier is called here "wood gas stove".
1 - En partie haute de la grande boite de conserve (1), marquez l'emplacement d'une dizaine de trou, répartis équitablement tout autour de la boite.
2 - Then drill at the marked locations with a 12mm drill bit (or with hammer and nail). (For a cleaner result it is recommended to pre-drill with the 7 mm drill bit before attacking with the 12 mm drill bit).
Note: For ease and cleanliness, it is possible to clamp the wooden wedge on a vice and use it as a support to make the holes in the box.
3 - Cut the bottom of the large tin can (1). The hole must have a slightly smaller diameter than the small tin can (so that it can be embedded in it).
1 - On the bottom of the box (2), mark the location of about fifteen holes distributed over the entire surface. In the upper part of the box (2), mark the location of about ten holes, evenly distributed around the can.
2 - Then drill at the marked locations with a 7 mm drill bit (or with the hammer and nail).
1 - Mark the location of about ten holes evenly distributed around the small can (3).
2 - Then drill at the marked locations with a 12mm drill bit (or with hammer and nail).
3 - Cut the bottom of the can.
4 - NB: For ease of use, you can cut a large hole on the side of the small box (3): it will easily feed the wood fire!
1 - Insert the box (2) into the large box (1) as shown in the diagram.
2 - Place the box (3) on the other two flush-mounted boxes.
Your pyrolysis stove is ready!
Even though this type of cooker is cleaner than the "three stone" cookers, it still emits smoke. This is why it must be used in a highly ventilated environment.
The stove works with wood pellets or biomass chips. To light the stove, fill the stove and light in the upper part.
To turn off the stove, simply wait until all the wood is consumed and the enclosure has cooled.
ATTENTION: THE COMBUSTION TEMPERATURE OF WOOD AND GASES IS AROUND 1200°C. THE STOVE IS TO BE USED WITH GREAT CARE: DO NOT TRY TO MOVE THE STOVE WHEN IT IS ON
The system presented here is very simplified and therefore does not allow to manage for example the size of the flame.
Due to the materials used, the life of the stove is rather limited.
Des versions améliorés de ce système sont en phase de test/validation dans différents contextes urbains, ceci du aux efforts de Paul Anderson, spécialiste des micro gazéificateur.
Des essais d'implantation ont eu lieu en Inde sans grande réussite: Il est en réalité compliqué de trouver des granulés ou de la biomasse en copeaux dans ces contextes, le prix du micro-gazéificateur optimisé se rapproche du coût de la cuisson au gaz, sans en avoir tous les avantages.
Afin de pouvoir s'adapter à n'importe quel récipient ou conserve disponible utilisé en enceinte extérieure, il est possible de confectionner la chambre de combustion à partir d'une tôle, de préférence en acier inoxydable. Son épaisseur doit être de 1mm maximum pour une découpe à la cisaille à tôle. Il faudra découper des languettes et percer les trous dans la tôle à plat avant de la rouler et de la fermer par agraffe. L'utilisation d'acier inoxydable augmentera la durée de vie du réchaud. Les photos ci-contre montrent la fabrication d'un réchaud à partir d'un pot de peinture et d'une tôle en acier inoxydable de 1mm d'épaisseur. La tôle est usinée à plat avant d'être roulée et agraffée (l'agraffage consiste à replier sur environ 5 mm les deux bords d'une la tôle dans des sens contraires, avant des les marteler l'un dans l'autre pour vérouiller l'ensemble). Porter des gants pour éviter les coupures !
Télécharger le tutoriel ici
Rapport comparatif des différents types de cuiseurs par Planète Bois (en français): http://www.planetebois.org/glossaire/cuiseur-domestique-econome-cde/
Site internet du Docteur Paul Anderson, spécialiste des micro-gasifiers (en anglais): http://www.drtlud.com/
N'hésitez pas à commenter, partager, et agrémenter le tutoriel d'informations utiles à son amélioration.
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