Agricultural companies usually think about growing maize for silage, when thinking about building a biogas plant. With this approach, land can be used either to produce grain or silage. However, with new straw preparation technology, there is an alternative to silage. An enterprise can double the benefits from their land: both grain and biogas from straw.
Substrates suitable for biogas processing are wheat straw, sunflower straw, rapeseed straw, and corn stover.
Of course, straw can be processed into pellets. But in pellet production energy is consumed. With biogas production, this is not the case. In addition, there are regions where it is logistically unprofitable to produce pellets.
The new technology that allows straw to be processed into biogas is steam explosion. This technology came to the biogas industry from the paper industry where it has been used for over 100 years. In the biogas industry, this technology appeared as recently as 4 years ago.
There are two ways to process straw into biogas: direct and through ethanol.
The direct method is steam explosion and then, fermentation in biogas reactors. The best choice with the direct method is high-load biogas reactors.
In straw processing though ethanol, straw is treated by steam explosion first and then biogas is produced out of distillery wastewater. Upflow Anaerobic Sludge Blanket (UASB) or CSTR vertical reactors with central mixers are the optimal technology choices in this case. A by-product of processing through ethanol is lignin.
1 ton of straw yields 425-460 m³ of biogas or 1000 kW-hour of electric energy. The cost of straw is €30-60 per ton. When selling electric energy, 1 ton of straw is equivalent to €143. The advantage of straw versa silage is the absence of silage storage.
NGE Biogas is implementing a project for straw steam explosion and processing the substrate in high-load reactors in Teofipol-4.
The straw productivity is 150 tons per day. The electric power of the biogas plant is 6 MW.