How Does Biogas Work Exactly?
Biogas is classified as a biofuel that is produced from the fermentation of plant-based carbohydrates. To understand how biogas works you need to first have an understanding of how the biofuel is created.
Biogas is produced anaerobically, meaning without oxygen. Archaea, the microscopic organisms that break down the pant matter to produce biogas, are some of the oldest living organisms on Earth. Because the organisms can survive without oxygen, archaea existed over three billion years before the Earth’s oxygen-based atmosphere was formed. As the organisms do not need oxygen to survive, archaea are not technically classified as bacteria.
As the planet’s atmosphere became oxygenated, roughly 500 million years ago, archaea only survived in airless places, such as stagnant bodies of water, like swamps, hot springs and deep oceans and in the stomachs of vertebrates. In order to make biogas, the conditions that Archaea thrive in must be recreated.
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Biogas is composed of up to 80 percent methane with trace amounts of other gases. The amount of methane present is dependant on the levels of oxygen present during the fermentation process. As archaea can only function without oxygen, the higher the level of oxygen during the fermentation process the lower the concentration of methane will be.
Plant-based materials are fed into a biogas generator known as a “digester” and the archaea are introduced after the oxygen has been removed from the digester. The archaea then begin to break down and ferment the carbohydrates in the plant matter. Large sophisticated digester are use to generate biogas on a large scale. People in some undeveloped parts of the world, as well as some people who live off grid, use a small-scale homemade biogas generator to satisfy their personal-power needs. On either a commercialised scale or personal-sized operation, the produced biogas is used to generate electricity and heat.
The optimal temperature four the production of biogas is from 32 to 35 degrees Celsius. Temperatures outside the optimal range typically results in reduced amounts of biogas, and this can pose a problem in areas with hotter and cooler climates.
In cooler countries, like the UK, the solution is to somehow insulate the digester to keep the inside of the generator warmer than the outside atmosphere. Insulating the digester is also the solution in warmer climates as well, and burying the digester in the ground will help maintain a cooler temperate during the day and a warm temperature at night.
Biogas also occurs naturally in landfills as archaea break down the rubbish, but here the methane typically passes, uncontrolled, into the atmosphere where many believe it hastens global warming. However, if some sort of collection system can be installed, such as a network of pipes, and the landfill site is covered with plastic the methane can be collected and used.
Biogas Production in the UK
Biogas generators of various sizes are becoming increasingly commonplace in the UK, with the size of the generator being dependant on its intended use. A sustainable means of recycling food waste, biogas production is the lone renewable-energy technology that is able to create electricity and heat as well as fertiliser without solar energy or wind power.
Most biogas is sent to power and heat units consisting of an internal-combustion engine with an alternator to produce electricity. However, a small percentage of the power created is used up in the operation of the generator, with the generator essentially creating the power to run itself. Incentives four the generation of anaerobically-produced energy are provided by the feed in tariff regime and paid against each generated kilowatt hour of electricity.
Biogas can also be cleaned of trace impurities, including carbon dioxide, by a process known as biogas upgrading. Once upgraded, biogas can be injected into the national gas supply or compressed into cylinders to be used as a fuel for automobiles, buses and tractors.
Upgrade biogas four national-grid use requires sophisticated systems, so it is best suited to larger-scale commercial production plants. However, small-scale systems used to produce upgraded fuel are currently in production and should be appearing on the market soon.