Optimization of Rice Straw Properties via Torrefaction for Solid Fuel Applications

This study investigated the potential of biochar produced via torrefaction of rice straw as a sustainable alternative to coal and coke in iron and steel production. The effects of process parameters, temperature (200–300 °C), residence time (20–60 min), and heating rate (10–30 °C/min) on torrefaction yield were evaluated. Following optimization, the biochar was characterized through ultimate, proximate, SEM, BET, EDS, and TG analyses, and its properties were compared to those of coal. The results indicated that the solid, Liquid, and syngas yields ranged from 44.67–96.43, 1.50–22.39, and 2.07–36.79%, respectively. The optimized process parameters achieved a solid yield of approximately 64% at an optimal temperature of 270 °C. The moisture, ash, volatile, and fixed contents of the biochar ranged from 7.43–8.80, 5.76–6.87, 21.75–28.26, and 56.83–63.82%, respectively. Among the optimized samples, O3 exhibited superior combustion performance, with a fixed carbon content of 63.82%, and morphological properties comparable to bituminous coal. The HHV (19.88 MJ/kg) of the optimized biochar falls within the upper range of lignite and approaches the lower range of bituminous coal. The optimized biochar showed a significantly higher BET surface area (58.845–59.572 m²/g) than lignite and anthracite (0.187–1.498 m²/g). Its BJH-specific surface area (47.423–48.194 m²/g) also far exceeds that of coal (0.178–1.985 m²/g), indicating superior adsorption capacity. Additionally, the total pore volume of the biochar (0.1366–0.1407 cm³/g) and average pore diameter (4.457–4.765 nm) surpass those of coal, supporting enhanced mass transfer and surface interactions.