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Gaseous fuels can be distinguished into gas generated from a fossil fuel source, such as Liquefied Petroleum Gas (LPG) and natural gas, and gas generated from a renewable energy source, such as biogas and wood-gas, which are obtained from biomass. Fossil gas is traded on markets and households need to possess money to purchase the fuel. In comparison, gas from biomass can be generated by the household itself providing the investment into the generating equipment and the availability of biomass and water in the case of biogas. Biomass gas contains more unburnable substances e.g. water, carbon-dioxide, as fossil gases and has a lower heating value. Biogas as well as wood-gas are difficult to bottle for transport, so they are best used near the location of production.
In case households are used to solid fuels, the introduction of gaseous fuels for cooking require a change of cooking habits. This is influenced by a new handling of the fuel itself, the new cooking equipment and the different cooking process, e.g. due to different flame temperature.
Biogas and wood-gas can be obtained from biomass via two different processes:
- Methanization: Wet biomass can be transformed by microbes in the absence of oxygen into biogas, which mostly consists of methane. The remaining solid part is slurry with a high value as an agricultural fertilizer. The precondition to generate biogas in a controlled manner is a digester and the regular supply of water as well as sufficient organic feedstock, e.g. dung and residues from agriculture or food.
- Pyrolysis: Any dry biomass can be transformed by heating of wood or other substances in the absence of oxygen into a combustible gas usually called 'wood-gas' while solid char remains. A gasifier is a device in which the pyrolytic gas-generation can be controlled.
Biogas and wood-gas offer very convenient cooking properties. They cause to cook faster, safer and cleaner compared to fuelwood stoves. They offer a “modern way of cooking” based on renewable resources especially for remote areas. Their by-product (slurry or biochar respectively) can be a valuable input in the agricultural production as they are excellent fertilizers. Biogas is produced at low temperatures and can be stored in a deposit, from where it can be piped to the point of use. In contrast, wood-gas is hot upon creation (above 350 °Celsius) and best combusted 'close-coupled' to the location of the gas-generator to avoid condensing tars and costly cleansing of the gases.
Further articles within the Cooking Energy Compendium: