Raw biogas produced from digestion is roughly 60% methane and 29%
CO2 with trace elements of
H2S, and is not high quality enough to be used as fuel gas for machinery. The corrosive nature of
H2S alone is enough to destroy the internals of a plant. The solution is the use of biogas upgrading or purification processes whereby contaminants in the raw biogas stream are absorbed or scrubbed, leaving more methane per unit volume of gas. There are four main methods of biogas upgrading, these include water washing, pressure swing absorption, selexol absorption, and
amine gas treating.
[18] The most prevalent method is water washing where high pressure gas flows into a column where the carbon dioxide and other trace elements are scrubbed by cascading water running counter-flow to the gas. This arrangement could deliver 98% methane with manufacturers guaranteeing maximum 2% methane loss in the system. It takes roughly between 3-6% of the total energy output in gas to run a biogas upgrading system.
Biogas gas-grid injection
Gas-grid injection is the
injection of biogas into the
methane grid (
natural gas grid). Injections includes biogas:
[19] until the breakthrough of
micro combined heat and power two-thirds of all the energy produced by
biogas power plants was lost (the heat), using the grid to transport the gas to customers, the electricity and the heat can be used for
on-site generation resulting in a reduction of losses in the transportation of energy. Typical energy losses in natural gas transmission systems range from 1–2%. The current energy losses on a large electrical system range from 5–8%.
Biogas in transport
If concentrated and compressed, it can also be used in vehicle transportation. Compressed biogas is becoming widely used in Sweden, Switzerland, and Germany. A biogas-powered train has been in service in Sweden since 2005.
Biogas also powers automobiles and in 1974, a British documentary film entitled
Sweet as a Nut detailed the biogas production process from pig manure, and how the biogas fueled a custom-adapted combustion engine.
In 2007, an estimated 12,000 vehicles were being fueled with upgraded biogas worldwide, mostly in Europe.
Post a Comment