Biogas is gas obtained from biomass as a result of anaerobic fermentation, during which organic matter is broken down by bacteria into simple compounds. The process involves four stages:
Biogas is a mixture of gases, above all methane (50-75%) and carbon dioxide (25-45%), as well as small amounts of other gases, e.g. hydrogen sulphide, nitrogen, oxygen and hydrogen. Its composition depends on the type of charge and process, and its calorific value is between 18 and 24 MJ/m3.
High-energy biogas is produced from renewable raw materials that most often include:
The most basic parent substance that is most frequently used for the production of biogas is corn, as it has high capacity as regards the amount of the generated biogas.
Corn has relatively low soil requirements, however, it requires good fertilisation. Varieties with a high ratio of vegetative parts - stems and leaves - are used for the production of biogas. The corn maturity class is determined on the basis of its FAO number. Corn of a variety whose FAO number exceeds 300 is recommended for the production of biogas.
The content of dry matter in silage should be between 28-35%.
Silage is used by itself of combined with slurry.
Cogeneration is a process during which energy contained in a fuel is converted into electric energy and heat as a result of a single process. Its main advantage is the fact that the overall efficiency of energy conversion in a cogeneration process is much higher than with separated production of electric energy and heat.
A gas combustion engine, a power generator, a system of heat exchangers and a system of automatic regulation and control are the main components of the unit. The rating of the generator is chosen depending on the amount of the generated biogas and the capacity of electric energy and heat consumption. Generators of rating between 40 kW and up to 3 MW are available on the market.
In Poland, generators of between 400 kW and 1 MW are used most often. In case of a more than 1 MW biogas plant, two or three parallel generators are selected whose total rating corresponds to the designed rating of the biogas plant. In view of operation, such a solution is much more favourable, as it facilitates maintenance and ensures continuity of electric energy and heat generation.
Biogas plants enable the diversification of energy sources and a continuous percentage increase on the renewable energy market - the market of environmentally friendly energy. This is connected with multiple factors: