Effect of torrefaction conditions on the physicochemical characterization of agricultural waste (sugarcane bagasse)

Pakistan is an agricultural country whose agricultural sector employs 43% of the labour force. However, a substantial amount of agricultural waste contributes little economic benefit to the farmers. The annual production of agricultural waste studied in this work, i.e., sugarcane bagasse, is approximately 12 million tonnes per year, and most of that is burned inefficiently. The present work shows that agricultural waste is a significant energy resource that could be used to generate electricity after the application of a simple thermal processing technique (i.e., torrefaction). Torrefaction is a mild pyrolysis treatment in an inert atmosphere that is carried out to improve the physical and chemical properties of biomass. In this study, sugarcane bagasse was torrefied at five different temperatures (200 °C, 225 °C, 250 °C, 275 °C and 300 °C) for four different residence times (15, 30, 45 and 60 min). The physical and chemical properties, such as proximate and ultimate analysis, true density, grindability and hydrophobicity, of the raw and torrefied sugarcane bagasse were investigated. No significant improvement in the characteristics of torrefied waste was found at low torrefaction temperatures (200 °C and 225 °C). However, with the increase in the temperature and residence time torrefaction conditions to 300 °C and 60 min, respectively, a significant improvement was found. The Fourier transform infrared spectroscopy (FTIR) analysis showed that owing to torrefaction, the hydroxyl group content is decreased and carbonyl group content is increased within the fuel. Moreover, a scanning electron microscopy (SEM) study indicated that tiny dispersed particles in the raw sample fused together at a higher torrefaction temperature of 300 °C, forming a tubular structure due to lignin degradation, and the biomass became easy to grind. Thus, torrefaction is an effective approach for improving the characteristics of sugarcane bagasse.