Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from raw materials such as agricultural waste, manure, municipal waste, plant material, sewage, green waste or food waste by anaerobic digestion with anaerobic bacteria, which digest material inside a closed system, or fermentation of biodegradable materials.
Biogas is primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulfide (H2S), moisture and siloxanes. The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel; it can be used for any heating purpose, such as cooking. It can also be used in a gas engine to convert the energy in the gas into electricity and heat.
The main part of a biogas system is a large tank, or digester. Inside this tank, bacteria convert organic waste into methane gas through the process of anaerobic digestion. Each day, the operator of a biogas system feeds the the digester with household by-products such as market waste, kitchen waste, and manure from livestock. The methane gas produced inside biogas system is transported to power plants whereas waste that has been fully digested exits the biogas system in the form of organic fertiliser.
With a combined heat and power (CHP) system, electricity and thermal energy are efficiently produced onsite for local consumption. CHP eliminates the wasteful process of purchasing electricity while separately burning fuel in an onsite boiler to produce heat. The system is further enhanced by avoiding the electricity losses that occur in the transport, transmission and distribution processes from the point of power generation to facility.
- generate an economical energy supply
- improve waste management
- reduce global climate change
- simple and low cost technology that encourages a circular economy
Biogas as a fuel
Biogas can also be used as a replacement for natural gas in vehicle fuel.
Energy that can be stored and used at the drop of a hat
Biogas can be stored without difficulty, meaning that it can be used at any time in any location irrespective of where it is produced. Hybrid power plants, for example, are able to take advantage of these qualities. They combine different renewable energy sources to complement one another, such that the amount of energy required is always at hand. Owing to its aptitude for storage, biogas is particularly valuable here, as it is able to compensate for fluctuations in other renewable sources such as wind and solar energy.
Heat and power from one energy source
Biogas production also has an indirect impact on climate protection. This is because the controlled fermentation of liquid manure and compostable waste prevents the release of harmful gases such as methane, which has a far more influence on the greenhouse effect than CO2.
Micro gas grids: from biogas plant to combined heat and power plant
If purchasers of heat are located at too great a distance from the biogas plant, transporting this heat is extremely complex and costly. In these cases, the CHP plant can be constructed where the heat is needed. Here, the biogas is simply transported via dedicated pipes to satellite CHP plants in the town, or directly to heat consumers, and then converted into heat and power on site. The waste heat can then be cheaply distributed where it is required.
Biomethane in the natural gas grid
After processing, biogas can also be injected directly into the existing natural gas grid. In this scenario, it exploits the infrastructure available and finds application as a natural gas equivalent (known as biomethane).