Fuel briquettes produced via the co-treatment of wood sawdust, miscanthus and wheat straw: Physicochemical properties

Beneficiating biomass wastes and energy crops to produce densified fuels represents an interesting alternative to the use of conventional fossil-based energy carriers. Identifying the best-suited operating parameters and biomass resources, which translate into high quality fuels, is far from trivial, however, especially when it comes to co-processing different biomass types in order to combine their respective strengths. To promote the development of innovative, efficient and eco-friendly biomass-based densified fuels, this paper examines the physicochemical properties of briquettes obtained via the co-treatment of wood sawdust (S), miscanthus (M), and wheat straw (WS), using a hydraulic press machine. It aims firstly to elucidate the impact of the feedstock properties and compaction force (CF) on the main features of the fuels obtained. A design of experiments was built considering two CF (225 and 450 kN), two biomass particle sizes (PS) (less than 1.25 mm and between 1.25 and 2.5 mm), and 5 mixing ratios. The latter comprised proportions of each biomass ranging from 0 % to 100 % in S/M, S/WS, and M/WS blends. Tests were then carried out to produce multilayer briquettes with interesting physical and combustion characteristics. The results obtained revealed that all the operating factors influence the density as well as the impact and water resistance indexes (IRI and WRI) of the briquettes. It was found that the higher the CF, the finer the particles, and that the higher the proportion of S, the higher the density, whose values were found to range between 512 and 1121 kg·m⁻³. Moreover, higher M and WS contents were associated with lower IRI and WRI. In line with expectations, the type of feedstock mixtures was found to impact the briquette ash and volatile matter contents (AC and VMC). Raising the S proportion decreases the AC and increases the VMC, hence increasing the net calorific values up to 19.12 MJ·kg⁻¹. As for the ignition time (IT), the higher the CF and the lower the S content, the higher the IT. Alternatively, increasing the WS content increases the IT and the burning time. Finally, the multilayer briquettes produced using S in the outer sheets and high M contents in the central layer were found to exhibit better performances in terms of density, IRI, IT, and combustion time as compared to their conventional single-layer counterparts. While the multilayer briquette production method shows considerable promise, its long-term adoption will require addressing technical challenges, such as those related to the consistent preparation and effective mixing of raw materials.