6.2. Town gas

Town gas is a mixture of methane and other gases, [55] mainly the highly toxic CO₂, which can be used in a similar way to natural gas and can be produced by treating coal chemically. This is a historic technology, still used as best solution in some local circumstances, although coal gasification is not usually economical at current gas prices. However, depending upon infrastructure considerations, it remains a future possibility. Most town gashouses located in the eastern United States in the late 19th and early 20th century, were simple by-product coke ovens which heated bituminous coal in air-tight chambers. The gas driven off from the coal was collected and distributed through town-wide networks of pipes to residences and other buildings where it was used for cooking and lighting purposes. The coal tar that collected in the bottoms of the gashouse ovens was often used for roofing and other water-proofing purposes, and also, when mixed with sand and gravel, was used for creating bitumen for the surfacing of local streets.

6.3. Biogas

Biogas typically refers to a gas produced by the anaerobic digestion or fermentation of biodegradable materials (biomass). Biogas is manly composed of 60–70% methane, 30–40% CO₂ and low amount of other gases. Sources of biogas include swamps, marshes, and landfills as well as sewage sludge and manure by way of anaerobic digester, in addition to enteric fermentation particularly in cattle. Methanogenic archea are responsible for all biological sources of methane, some in symbiotic relationships with other life forms, including termites, ruminants, and cultivated crops.

The future sources of methane, the principal component of natural gas are landfill gas (LFG) [56],[57] and [58], biogas [59], and methane hydrate. Biogas and LFG are already used in some areas but their use could be greatly expanded.

LFG is a type of biogas which is produced from the decomposition of waste in landfills. If the gas is not removed, the pressure may get so high that it works its way to the surface, causing damage to the landfill structure, unpleasant odor, vegetation die-off and an explosion hazard. Once water vapors are removed, about half of landfill gas is methane and rest of the gas is carbon dioxide. In addition to CO₂ and methane the small amounts of nitrogen, oxygen, hydrogen and H₂S also exists in LFG, but their concentration varies widely. Landfill gas cannot be distributed through natural gas pipelines unless it is cleaned up to the same quality. It is usually more economical to combust the gas on site or within a short distance of the landfill using a dedicated pipeline. Water vapor is often removed, even if the gas is combusted on site. Biogas [59] is usually produced using agricultural waste materials, such as unusable parts of plants and manure.

Biogas can also be produced from domestic waste that otherwise goes to landfills. In general, the waste materials do not generate any income, even they require money to get rid of it. However, the utilization of the waste materials can contribute to the economy and sustainable energy balances.

Anaerobic lagoons produce biogas from manure, while biogas reactors can be used for manure or plant parts. Once biogas is upgraded to the required level of purity, it can be used as an alternative vehicle fuel in the same form as conventionally derived natural gas (CNG & LNG).