Engineered solid biofuel from herbaceous biomass mixed with inorganic additives

This study focuses on verifying the influence of some additives in the ash melting process of herbaceous biomass, developing a pelletized biofuel from the mixture of herbaceous biomass and various inorganic substances through a series of experimental tests. Therefore, different materials were sampled, chemically characterized and combined in mixtures of low-melting biomass materials. Tests were performed with various inorganics products added directly on the relative ashes to verify the interaction between the two systems. Subsequently, herbaceous biomass pellets containing growing amounts of additive were produced, verifying their effectiveness by analyzing the ash melting temperatures and adopting the PASSA test, that investigates the size of the ashes after incinerating the biomass in a muffle. The same method was then used to evaluate the ashes of an industrial boiler. Results show that the addition of inorganic additives in the extent of 3–5% by weight determines an increase in deformation temperatures over 547 °C for several biomass materials and additives. Tests carried out on forage pellets made with alfalfa and CaO as additive brought instead to an increase in deformation temperature between 43 and 107 °C. This work could be of interest in the evaluation of the energy reuse of herbaceous materials that would otherwise be considered as waste, and also it suggests the possibility of using egg shells as inorganic additives in accordance to the circular economy approach. Furthermore, the additivation level of these pelletized biofuel is perfectly in line with the provisions of ISO 17225-6 for non-woody pellets (≤5% weight).