Technology

The process, the concept, the future.

How An Anaerobic Digestion Plant Works

Regardless of where a biogas plant is operated, the basic principle is relatively simple. An anaerobic digestion (AD) plant is essentially a power station whose fuel is biological material such as energy crops or even food waste. Anaerobic digestion or AD plants use the natural process of fermentation on a large scale to produce a biogas which can be converted into electricity or a natural gas quality gas which can be exported into the national grid.
 
A constant feedstock of organic material such as maize silage, grass, sunflowers, sugar beet or food waste is fed into the digester and because these input materials all primarily consist of water, they liquefy during the biogas production process. After the input material has been completely broken down, an odourless liquid remains – the digestate: which is a high quality fertiliser. This creates an additional revenue stream for the operator as fertiliser is one of the biggest expenses for any farmer.
 
The biogas produced through this process can then be converted in two different ways. The first is to run it through a CHP (Combined Heat and Power) unit which turns the biogas into electricity and heat (in the form of steam). A proportion of this electricity and steam is then fed back to the digester system to power the plant components and keep the digester at the correct temperature to ensure optimum biogas production. The second option is to run the biogas through a gasification system, this device upgrades the gas to a natural gas quality bio-methane. This bio-methane can then be injected into the national gas grid network.