Process optimization and investigating the effects of torrefaction and pelletization on steam gasification of canola residue

• Canola residue pellets were gasified at 650–850 °C with an equivalence ratio of 0.2–0.4. • Highest syngas yields were obtained from gasification at optimal temperature (800 °C) and equivalence ratio (0.4). • Torrefaction and densification significantly improved the gas yields and quality. • Syngas from torrefied pellets had a greater lower heating value (1828–2396 kJ/Nm 3 ). • Tar content from gasification reduced remarkably due to torrefaction of pellets. In this study, steam gasification of pellets prepared from canola residue was carried out at varying temperatures (650–850 °C) and equivalence ratio (0.2–0.4). The optimal gasification temperature and equivalence ratio, based on syngas yield and its fuel quality, were found to be 800 °C and 0.4, respectively. Torrefaction and densification of canola residue significantly improved syngas yield. Torrefied pellets were obtained from torrefaction of canola residue at a microwave power, residence time and feeding load of 250 W, 10 min and 90 g, respectively. Pellets prepared with different bio-based additives were gasified to compare the effects of binder in gas compositions. The highest total gas yield (24.4 mol/kg), syngas yield (22.1 mol/kg), carbon conversion efficiency (85.1%), lower heating value of gases (2396 kJ/Nm 3 ) and gas energy recovery (29.2%) were reported from the gasification of torrefied canola residue pellet at optimal conditions. Tar yield decreased significantly when torrefied pellets were gasified. A comprehensive characterization of biochar and tar produced from gasification of raw and torrefied canola residue pellets was performed to determine their potential applications. The formation of aromatic carbon structures in biochar produced at higher gasification temperatures was noticed through FTIR spectroscopy. The aromaticity of biochar also resulted in its greater carbon content, heating value and thermal stability as evident from ultimate and thermogravimetric analyses. Tar obtained from gasification of canola residue pellets contained depolymerized products such as organic acids, phenolics, aldehydes, ketones, ethers and esters.