High yield from green mass
It is possible to use not only waste as a substrate for biogas but also specially grown green mass. In the tropics and subtropics, perennial elephant grass (royal, Sudanese, Napier grass) is widespread. The feature of Napier grass is high yield (3 cuts per year). This grass is also a forage crop.
Feasibility and construction features
The best biogas yield is demonstrated by grass with an age of 4-4,5 months and 33% dry matter. This yields a biogas output of 240 m³ per ton. Grass is so cheap in production that the payback for this type of biogas plant is comparable to the payback of biogas plants using waste. The cost of grass is €2-3 per ton. To provide 1 MW electric power (24 000 kWh electric energy per day), 50 tons of Napier grass per day are needed.
The construction of decentralized biogas plants, for generating power on islands or in remote areas of developing tropical countries, is especially feasible.
In the case of grass unlike in the case of maize silage, one doesn’t need to build a silage storage for 1 year. 2 months of storage is sufficient.
Biogas plants for napier grass are not structurally different from the plants for maize silage. The most suitable technology is high-load reactor.
Nexgen Energia implemented the world's largest projects with high-load reactor technology (HLR).10.5 MW at Teofipol-2 and 5 MW at Teofipol-3. These projects use maize silage, amaranth silage. The same technology is suitable for napier grass.
Nexgen Energia Biogas also performed laboratory studies of grass samples at different ages.