In the bioeconomy, Miscanthus is an important perennial plant, growing repeatedly for up to 20 years. The tall grass can grow up to a height of 3 metres and is hence also known as ‘elephant grass’. The harvested biomass can be used for bioenergy (in the form of pellets or briquettes), but also for building and insulation materials and in the pulp industry.
About 4,500 hectares of Miscanthus are currently cultivated in Germany, mainly for energy production. Integrating native flowering plants such as tansy, mugwort, wild cardoon and yellow sweet clover into the cropping system can have a positive impact on biodiversity and the resilience of sustainable farming systems. However, these four plants also have a positive effect on burning properties and ash-melting behaviour, a team of researchers from the University of Hohenheim, Jülich Research Centre and Hunan Agricultural University in China discovered. The first results were published in a study in the renowned journal Renewable and Sustainable Energy Reviews.
Higher efficience, lower costs
The calorific value of Miscanthus remained roughly the same after wild plant admixture: 16.3-17.5 megajoules per kilogram (MJ/kg). In comparison, wood pellets have a value of about 18 MJ/kg. However, the ash-melting temperature improved significantly: from 1,000 for pure Miscanthus to 1,200 degrees Celsius when mixed with 30 per cent wild plants. This means the temperature at which ash melts in the stove is 20 per cent higher, reducing the likelihood of slag accumulation and reducing stove efficiency. This leads to higher efficiency and lower costs in operating the plant.
The better melting behaviour of the ash is explained by the different biochemical composition of Miscanthus and the wild plants, which contain higher percentages of calcium and magnesium. These substances react with the Miscanthus ash components, which increases the melting temperature.
In a next step, long-term studies could show whether joint cultivation of miscanthus and wild plants on a larger scale also makes pure economic sense in terms of a holistically sustainable bioeconomy.
For more information, visit the University of Hohenheim website or see the publication in Renewable and Sustainable Energy Reviews.
Image: flowering wild cardoon, Janson George/Shutterstock