Lignin content and briquette quality of different fibre hemp plant types and energy sunflower

Fibre hemp and energy sunflower are potential energy crops for production of solid biomass as renewable energy. The current study estimated (i) the lignin content of fibre hemp and energy sunflower plants grown on different nitrogen treatments and (ii) the quality of the briquettes made from different plant types of fibre hemp (i.e. monoecious and dioecious), energy sunflower and the combination of fibre hemp and energy sunflower. The monoecious and dioecious fibre hemp cultivars (Chameleon, Finola and Santhica-27, USO-31, respectively) and the energy sunflower cultivar Wielkopolski were grown in the experimental field in 2008–2010 on Stagnic Luvisol soil. The plants were grown on N treatments of N0, mineral nitrogen (100 kg N ha−1), cattle slurry (100 kg N ha−1), sewage sludge (100 kg N ha−1) and vetch (100 kg N ha−1). Calorific values (16.6–17.4 MJ kg−1) of briquettes pressed from different materials did not differ significantly and had relatively low sulphur (<0.05%) and chlorine content (0.03–0.37%). Briquettes with higher compactness were made from the sunflower and the dioecious hemp. Dioecious hemp had significantly higher lignin content. The dioecious hemp needs lower GDD values for maturating, its stems lignin content was higher than of monoecious hemp by harvest time and therefore this plant type is more suitable for briquetting in Nordic climatic conditions. Comparison of the different N treatments indicated that application of sewage sludge decreased the emergence and density of the fibre hemp plants and the lignin content per kg of DM.

• The lignin content of hemp was significantly influenced by nitrogen treatment and plant type. • Dioecious hemp matured at lower Growing Degree Days value, had higher lignin content and is more suitable briquetting material in Nordic conditions than monoecious hemp. • The application of waste-water sludge decreased the emergence and density of the fibre hemp plants. • Briquettes without major fractures and with high compactness were made from the sunflower and the dioecious hemp.