Valorisation of rice husks and bean straws through fuel pellets production: an experimental and modelling approach

Worldwide, some agricultural wastes represent an environmental problem due to their high volumes, slow degradation, and inadequate disposal. Due to this, the valorization of agricultural wastes has been reported in the literature, being the production of biofuels a promising option. In a previous study, rice husks were proposed to produce fuel pellets, but they did not fulfill the ISO 17225-6 standard due to its elevated ash content; thus, it remains as an opportunity area its mix with other wastes available in the same region. In Mexican states where rice is produced also bean is cultivated, whose residues are not used and have an elevated content of volatile solids. Therefore, the objective of this research is to produce fuel pellets from mixtures of rice husks and bean straws, with the objective of satisfying ISO 17225-6 standard. For this, the densification was carried out using three levels of moisture content and mixing ratios of the biomasses. Based on the experimental data, optimal densification conditions were found through a response surface analysis. Results show that fuel pellets produced from bean straw (90%) and rice husk (10%) with 15.0% of moisture content fulfill ISO 17225-6 standard. At these conditions, fuel pellets have calorific power of 3,645.78 kcal/kg, 6.98 ash, 9.76% final moisture, 610.78 kg/m(3) bulk density, and 99.51% durability.