Cuiseur micro gazéificateur/en-gb

Low-tech Lab

https://wiki.lowtechlab.org/wiki/Cuiseur_micro_gaz%C3%A9ificateur/en-gb

Dernière modification le 25/07/2018

Difficulté

Very easy Très facile

Durée

1 hour(s) heure(s)

Coût

0 EUR (€)

Description

How to make an inexpensive portable wood cooking system.

Sommaire

en-gb fr 1

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Introduction

Factors relating to cooking remains one of the biggest challenges in the areas of health and energy. In many developing countries, the classic three-stone cooking fire is the technology that is most commonly used.This is extremely inefficient (with a thermal yield of 10 to 15% if sheltered from the wind and 5% if exposed) and releases toxic smoke into dwellings.There are two concerns with this:

• Energy output is so poor that a huge amount of wood is needed to cook one meal.

This leads to extensive deforestation in certain parts of the world.

• Evidently, this creates certain problems with regards to health: smoke given off causes respiratory problems for people in the community and the reduces their quality of life. A technology that uses the same biomass but has a higher output

is:

The micro gasifier which is a low-tech and very economical way of cooking and, if well-made, has an output higher than a three stone stove (thermal output of approximately 35%). Output is even higher with the enhanced industrial version (which has a thermal output in the order of 45%)

It is possible to make a very basic model out of tin cans, but this will have a limited number of features. However, this can be very useful for instance for heating water, cooking small quantities of food and for doing demonstrations/teaching purposes.

More complex models do exist which, although more costly, tend to last longer and allow control over the power you can get from the flame.

Matériaux

• A large tin can (in terms of height and width) (1): for the external chamber;
• A tin can which is slightly shorter and thinner (2): for the combustion chamber;
• A tin can of the same diameter to the combustion chamber (3): for the stand on which the pan sits.

Outils

• Marker
• Wire cutter

For drilling, there are 2 options:

• A drill and 2 drill bits:11mm and 7mm respectively
• A hammer and a large nail (or a metal punch)
• A wooden block, a part of which can be inserted inside the tin can.

Étape 1 - How it Works

This is based on the concept of gasification: Wood is heated in an environment containing very little oxygen, giving off combustible gases known as “Syngas” which are then burnt in the upper part of the stove.

The micro-gasifier is lit from the top. Primary air, flowing into the lower part, passes through the mass of combustible fuel, maintaining a pyrolysis layer which then drops as the combustible gases are released. Secondary air is forced into the top of the stove, supplying the oxygen that is needed for combustion of gases emitting in an upward direction.

Better results are obtained with forced convection, using an integrated fan under the grid which supports the fuel. However you will need a reliable supply of electricity for this.

The temperature at which combustion takes place is around 800°C and thermal yields are between 30 to 45% depending on how well it is made and the quality of the insulation.

It is light, compact, reliable, uses little fuel and, in the right circumstances, produces reusable charcoal which can be used in other applications. This system is therefore extremely low-tech and very efficient compared to conventional systems used throughout the world.

To compare, the diagram opposite shows the energy performances of various systems. The micro-gasifier here is called “wood gas stove”.

Étape 2 - External Chamber

- Mark the positions of a approximately 10 holes, spread out evenly all around the upper part of tin can (1).

- then drill where marked using a 12mm drill bit (or with a hammer and nail) (For a cleaner finish, we recommend that you make pilot holes with a 7mm drill bit before tackling it with a 12mm drill bit).

Note:To make things cleaner and easier, you can clamp the wooden block onto a vice and use it as a support when making the holes in the tin can.

Cut the bottom out of the large tin can (1). The opening must be of a slightly smaller diameter to that of the small tin can (so that it can go inside)

Étape 3 - Combustion Chamber

- Mark the position of approximately 15 holes spread out over the whole surface on the bottom of the tin can (2). - Mark the positions of a approximately 10 holes, spread out evenly all around the upper part of tin can (2).

- then drill where marked using a 7mm drill bit (or with a hammer and nail)

Étape 4 - Pan Support

- Mark the positions of approximately 10 holes spread out evenly all the way around the small tin can (3).

- then drill where marked using a 12mm drill bit (or a hammer and nail)

- Cut out the bottom of the can.

- NB: For ease of use, you can cut out a large hole on the side of the small can (3): this makes it easier for the fire to catch the wood

Étape 5 - Final Assembly

- Put tin can (2) into the large tin can (1) as shown in the diagram.

- Place tin can (3) on top of the two other tin cans which have been nested one inside the other.

- The pyrolytic stove is now ready for you to use !

Étape 6 - Directions for Use

Despite this type of cooker being more environmentally friendly than the “three stoned” ones, it still gives off smoke. For this reason, it needs to be used in a well-ventilated area.

To light the stove, fill up and light it in the upper part.

To ‘turn off’ the stove, simply wait until all the wood has burnt down and the casing has cooled down,

THE TEMPERATURE OF WOOD AND GASES WHEN BURNT CAN REACH UP TO ALMOST 1200°C. HANDLE THE STOVE WITH EXTREME CARE :

Étape 7 - DO NOT MOVE THE STOVE WHEN LIT.

Le système présenté ici est très simplifié et ne permet donc pas de gérer par exemple la taille de la flamme.

De part les matériaux utilisés, la durée de vie du réchaud est assez limitée.

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.

Étape 8 - Fabrication d'un réchaud de plus grande taille

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 !

Notes et références

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.

L’équipe du Low-Tech Lab vous invite également à consulter sa Biblilowtech.

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