Development of torrefied and pelletised hybrid solid fuels from corncob and African birch wood

Abstract

The development of solid fuels from biomass sources plays pivotal roles in the global transition towards sustainable energy systems. In this context, optimising solid fuel production processes and understanding the influence of key parameters on fuel quality are crucial. This study examined the development and process optimisation of combined torrefied and pelletised hybrid solid fuels derived from corncob and African birch wood (ABW). Residues of corncob and ABW blends were prepared gravimetrically and evaluated in both raw and torrefied forms to determine optimal combinations with enhanced combustion characteristics. A Box–Behnken experimental design was employed to investigate the effects of key operating parameters on physico-mechanical properties of the pellets. The statistical modelling demonstrated strong linear correlations, with coefficients of determination (R²) of 0.9362 for density, 0.9796 for shatter index, and 0.9736 for water uptake capacity. Analysis of variance confirmed that all continuous variables exerted statistically significant effects on the response variables. Optimal process parameters were identified at a torrefaction temperature of 259.39°C, particle size of 0.5 mm, binder content of 15%, and compacting pressure of 140 MPa. Under these conditions, the model predicted a pellet density of 1466.54 kg/m³, shatter index of 93.69%, and water uptake capacity of 2.37%. These experimental values compared favourably with the predicted outcomes, achieving a desirability factor of 1.00, thereby validating the robustness, reliability, and accuracy of the predictive model. They underscore the potential of combining corncob and ABW residues in the production of high-quality hybrid solid biofuels, with optimised processing conditions significantly enhancing their physico-mechanical performance.