Experimental study on microwave heating performances of soybean straw briquettes

Soybean straw briquettes were used in this study to explore the impacts of fuel length (10–50 mm) and microwave power (400–800 W) on the heating performances, with incremental steps of 10 mm and 100 W, respectively. The relationships between average heating rate and affect factors (fuel length and microwave power) were established. Also, the changes in the microstructure, specific surface area, and pore size of the soybean straw briquettes were presented. The results indicate that for fuel lengths of 10–50 mm, the average heating rate of the soybean straw briquettes were 20.83–53.53 °C/min. At microwave powers of 400–800 W, the average heating rates were 15.63–38.46 °C/min. After microwave heating, the microstructure of the soybean straw briquettes showed significant improvements. The specific surface area and pore volume exhibited a tendency that initially ascended and thereafter descended, while the average pore size followed the opposite trend when the fuel length or microwave power increased. At 600 W microwave power, 30 mm fuel length, and a final heating temperature of 250°C, the specific surface area and pore volume reached their maximum values of 0.769 m²/g and 0.0034 cm³/g, respectively, while the average pore size was minimized at 11.073 nm. These results demonstrate that microwave pretreatment significantly enhances the thermochemical conversion potential of soybean straw briquettes by optimizing pore structure and heating efficiency. The study provides critical theoretical guidance for scalable, energy-efficient biomass valorization, advancing sustainable bioenergy production aligned with carbon neutrality goals.