Experimental Investigation of Pelletization after Torrefaction for producing pellets from rapeseed straw, Walnut shells and meadow hay

• Experimental research of pelletization after torrefaction (PAT) and determining the difficulties of this process. • Research of the influence of organic binders (lignosulfonate, potato starch) on the physical-mechanical and chemical-thermal properties of the pellets from non-wood biomass. • Use of waste biomass - rapeseed straw, walnut shells and meadow hay. • Determination of the characteristic ash melting temperature and the effect of PAT on this temperature. Given the growing demand for energy, rising fossil fuel prices and worsening environmental impacts, with increasing greenhouse gas emissions, especially CO₂, the search for alternative and renewable energy sources is essential. One effective way is to use biomass and treat it using modern technological processes. This study focused on the PAT process (pelletization after torrefaction), with the aim of improving the quality of biomass fuel and at the same time increasing its energy efficiency. The pellets were made from rapeseed straw, meadow hay and walnut shells. Pelletization reduces the volume of the material and increases its density, which facilitates transportation and storage. Torrefaction increases the amount of carbon and reduces moisture. As a result of these properties, the calorific value of the biomass increases. After torrefaction, the material is hydrophobic, which allows for better storage. The research included testing various binders to increase the mechanical resistance of the pellets. The effectiveness of lignosulfonate and potato starch was compared. The results showed that lignosulfonate achieved better results, with pellets being harder, more resistant to abrasion and having a higher ash melting point. These properties improved further with increasing amounts of binder. The highest lower calorific value (energy content) was found in pellets made from walnut shells and rapeseed straw. These materials therefore appear to be very promising for sustainable biofuel production and as a promising alternative to classic fossil fuels.