A discovery by German researchers underscores the potential of the giant Chinese reed Miscanthus for providing sustainable fuel through agriculture: if the harvested plant material contains shares of native wild plants, significantly less problematic slag residues are produced during combustion, the study shows. In this case, more biodiversity on the field could benefit both nature and the climate-friendly production of an energy source, say the scientists.
It is considered a green beacon of hope in the context of the energy transition: the giant Chinese reed Miscanthus x giganteus, which can be up to three meters high, very quickly forms enormous amounts of biomass and binds carbon dioxide from the atmosphere. In addition, the plant shines with other positive properties in cultivation: It is perennial, requires few nutrients and defies pests and drought. In Germany, miscanthus is already cultivated on an area of around 4500 hectares and researchers are currently further exploring the potential for using this plant.
Adverse combustion residues
It has already been shown that the material is suitable for the production of building materials and for the pulp industry. With regard to the energy crisis, however, the use as a fuel appears to be of particular interest: in the form of pellets or briquettes, Chinese reed could represent a more sustainable alternative to wood materials. So far, however, there has been one shortcoming: Compared to wood, miscanthus material forms slag residues due to the easier melting of the ash, which is problematic for incineration plants.
As part of their study, the researchers led by Moritz von Cossel from the University of Hohenheim have therefore now investigated the extent to which admixtures could improve the ash melting behavior of Miscanthus material. Specifically, they concentrated on substances that could get into the fuel during harvest: wild plants growing between miscanthus. The test included wild teasel, yellow sweet clover, mugwort and yellow-flowering tansy. These species, which are native to us, appeared as doubly promising candidates because of their fairly high biomass yield and the ecologically important range of flowers. "The integration of these plants could also have a positive effect on biodiversity," says Cossel.
Double positive effect
As the researchers report, the study delivered promising results: When mixed with wild plants, the ash melting behavior actually improves significantly compared to pure Miscanthus. It determines at which temperatures in a furnace the ash of a fuel begins to melt and thereby forms the problematic slag. "We were able to show that when 30 percent wild plants were added to the Miscanthus biomass, the ash melting temperature increased significantly by 20 percent from 1000 to 1200 degrees Celsius," says co-author Nicolai David Jablonowski from the Institute of Plant Sciences at Forschungszentrum Jülich. “So the mixture of wild plants and miscanthus improves the combustion quality. This leads to an increase in efficiency and a reduction in costs in the operation of the system," the scientist sums up.
According to the team, the effect of the wild plants is due to an improvement in their biochemical composition. Because compared to miscanthus, they contain higher proportions of calcium and magnesium. These elements form mixed phases with the miscanthus ash components during combustion, which leads to a higher melting temperature than pure miscanthus ash, the scientists explain.
As they emphasize in conclusion, however, further investigations are now necessary in order to further explore the profit potential of the joint cultivation of the giant reed with wild plants. In the sense of a holistically sustainable bioeconomy, the economic advantage is important: According to the scientists, it is now necessary to clarify to what extent the savings in the costs of incineration exceed the loss due to the lower yields of wild plant biomass.
Source: University of Hohenheim, specialist article: Renewable and Sustainable Energy Reviews, doi: 10.1016/j.rser.2022.112814