Biomethanation is a fermentation process similar to that taking place in the rumen of a cow. The materials entering the digester (tank where the fermentation takes place) undergo biological degradation carried out by microorganisms (bacteria and archaea).
This fermentation takes place in the absence of oxygen (anaerobiosis).
Two processes are common, the dry method and the wet method (the most common in Europe), they are explained below.
Biogaz
Biogaz with the batched dry process
Production of bioenergy and biocompost
The digester is in the form of a container, a silo or a garage depending on the size and type of the installation. It is filled with agricultural machinery and is hermetically closed. The materials are left in piles throughout the bacteriological decomposition process and sprayed with fermentation juice.
These "juices" are collected under the pile, pumped, heated and reapplied on decomposing materials to inoculate and keep them moist.
Once the materials are exhausted (that is, no longer producing biogas), the digester is opened and the rather solid digestate (40% solids) is removed from the tank or dumped from the container.
The biogas is stored in a gasometer near the tanks. Most often, several tanks are installed in parallel, which will be filled a few days apart, thus smoothing the production of biogas. When this system is applicable, it is called a batched dry process.
Biogaz with the slurry, continuous process​
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The tank (seen on the left) works on the same bacteriological principle as the stomach (fermentation in suspension).
The rigid tank makes it possible to fix a stirring system that makes it possible to digest substrates with liquid (pumpable) raw material.
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If the tank is mixed continuously / semi-continuously (via the action of an agitator or mixer), we will speak of a slurry digester.
This technology is the most used for medium and large installations in Europe, often in farms that release slurry or manure.
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The biogas that is released is stored either in the upper poach tank.
The gazification,
a solution dedicated to waste with persistant pollutants
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In Europe, gasification began during the 19th century, with the production of "city gas" used for urban lighting from mineral coal.
In 1920, appears the first gasifier to wood developed by the French Georges Imbert. The latter inspired many builders of gas-powered vehicles during the Second World War to alleviate the oil shortage.
The interest for this technology quickly stopped at the end of the second world war in favor of a plentiful and cheap oil.
Gasification is a thermochemical process that converts a solid fuel (coal, wood, straw, etc.) into a gaseous fuel through the injection of a reduced and controlled amount of an oxidizing agent (O2, air, CO2, steam, etc.). 'water...).
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