Biogas

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Biogas

Biogas, typically refers to gas produced by the anaerobic digestion or fermentation of organic matter including manure, sewage sludge, municipal solid waste, or any other biodegradable feedstock, under anaerobic conditions. Biogas is comprised primarily of methane and carbon dioxide.

Biogas is also called:

swamp gas
marsh gas
landfill gas
digester gas

This generally depends on where it is produced. Each variant typically has different levels of methane and carbon dioxide with other minor gases.

Biogas can be used as a fuel on which vehicles can be run.

Biogas and Anaerobic Digestion

Production of biogas by anaerobic digestion is popular for treating many types of organic waste because it provides a convenient way of turning biodegradable waste into renewable electricity, decreasing the amount of waste to be disposed of, and of destroying disease-causing pathogens which can exist in the waste stream. The use of biogas is encouraged in waste management because it does not increase the amount of carbon dioxide in the atmosphere, which is responsible for much of the greenhouse effect, if the biomass it is fueled on is regrown. Also, the methane in the biogas burns relatively cleanly compared to coal.

Recently, developed countries have been making increasing use of biogas generated from both wastewater and landfill sites or produced by mechanical biological treatment systems for municipal waste. High energy pricess and increases in subsidies for electricity generated from renewable energy (such as renewables obligation certificates) and drivers such as the EU Landfill Directive have led to much higher utilisation of biogas sources.

Landfill Gas

Landfill gas is produced from organic waste disposed of in landfill. The waste is covered and compressed mechanically and by the pressure of higher levels. As conditions become anaerobic the organic waste is broken down and landfill gas is produced. This gas builds up and is slowly released into the atmosphere. This is hazardous for three key reasons:

Risk of explosion
Global warming through methane as a greenhouse gas
Volatile organic compounds (VOCs) as precursor to photochemical smog

US Legislation

In the US because landfill gas contains these VOCs the United States Clean Air Act, and Part 40 of the Federal Code of Regulations, requires landfill owners to estimate the quantity of VOCs emitted. If the estimated VOC emissions exceeds 50 metric tons, then the landfill owner is required to collect the landfill gas, and treat it to remove the entrained VOCs. Usually, treatment is by combustion of the landfill gas. Because of the remoteness of landfill sites, it is sometimes not economically feasible to produce electricity from the gas.

Siloxanes and Gas Engines

In some cases, landfill gas contains siloxanes. Burning converts them to silica particles, which are abbrasive and clog conventional combustion engines. Stirling engines are more resistant against them.

Biogas to Natural Gas

If biogas is cleaned up sufficiently, biogas has the same characteristics as natural gas. In this instance the producer of the biogas can utilise the local gas distribution networks. The gas must be very clean to reach pipeline quality. Water (H_{2_{O), hydrogen sulfide (H_{2_{S) and particulates are removed if present at high levels or if the gas is to be completely cleaned. Carbon dioxide is less frequently removed, but it must also be separated to achieve pipeline quality gas. If the gas is to be used without extensively cleaning, it is sometimes cofired with natural gas to improve combustion. Biogas cleaned up to pipeline quality is called renewable natural gas}}}}

Applications of Renewable Natural Gas

In this form the gas can be now used in any application that natural gas is used for. Such applications include distribution via the natural gas grid, electricity production, space heating, water heating and process heating. If compressed, it can replace compressed natural gas for use in vehicles, where it can fuel an internal combustion engine or fuel cells.

External links

References

"Friendly fuel trains". (Oct. 30, 2005). New Straits Times, p. F17.

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