Insight into the production factors influencing the physicochemical properties of densified briquettes comprising wood shavings and rice husk

Abstract

The present work aims at elucidating the impact of various densification parameters on the physicochemical and combustion properties of fuel briquettes issued from the co-processing of wood shavings (W) and rice husks (RH) using a mechanical piston press machine. To that end, a design of experiments integrating three feeding speeds (15.76, 18.56, and 21.73 mm·s⁻¹), two wood particle sizes (< 7 mm and between 7 and 10 mm) and six different RH contents ranging from 0 to 100 wt% was built. The obtained results showed that all the above operating factors influence the apparent density of the produced briquettes. Values ranging from 1143 to 1247 kg·m⁻³ were notably measured, with the highest one determined when considering a low feeding speed, small wood particles and an RH proportion of 80 wt%. While increasing the RH content led to an increase in the briquette density, the obtained results also showed that the higher the RH content, the lower the water resistance index. Measured values indeed went from 94 % on average for pure wood to ⁓85 % for pure RH, attesting to the potential challenge associated with the storage of briquettes containing high RH contents. As for the net calorific value, it was shown to rise from ⁓11 to ⁓ 16 MJ·kg⁻¹ when varying the proportion of wood between 0 and 100 wt%. This trend was especially traced to an increase of the wt% of volatile matters in the produced briquettes accompanied by a decrease of their ash content. Combustion tests performed with different briquette samples then allowed inferring burning rates between 10.9 and 13.4 g·min⁻¹, specific fuel consumptions ranging from 115.8 to 138.4 g·l⁻¹ and combustion efficiencies of around 12 %. As highlights, these tests demonstrated that the higher the wood content, the higher the burning rate, the lower the specific fuel consumption and the higher the combustion efficiency. Finally, two tested briquette formulations containing 80 and 100 wt% of wood were shown to have better combustion properties than a commercial firewood used for comparison. Total greenhouse gas (CO₂ and CH₄) emissions were even found to be reduced by 9.4 % when burning the RH-containing sample instead of firewood, while providing the same amount of sensible heat to a 3-l volume of water. These findings thus highlight the potential interest of beneficiating biomass wastes into briquettes for heat generation, further noting that the development of this type of alternative energy carrier offers multiple advantages in terms of waste management, reduction of the deforestation induced by the intensive use of firewood and mitigation of climate change through a potential reduction greenhouse gas emissions.