Optimization of operating parameters for tar reforming/hydrogen upgrading in corn straw pyrolysis polygeneration

Regulation of operating parameters is crucial in biomass pyrolysis polygeneration. A two-stage reaction system was used to investigate the biochar catalytic reforming of corn straw pyrolysis tar. The effects of pyrolysis temperature (500 °C–800 °C), catalytic temperature (600 °C–750 °C) and steam content (0 vol%∼40 vol%) were studied and analyzed. GC-MS, Raman, FTIR, N₂ adsorption and TG were used in the analysis of tar and biochar. The most suitable operating parameters were finally determined, namely, pyrolysis temperature of 800 °C, catalytic temperature of 700 °C and addition of 30 vol% steam. With these parameter settings, tar is almost completely removed, and the H₂ yield reaches the highest 0.197 L/g. As the pyrolysis temperature increases, the tar yield decreases continuously and the yields of CH₄, CO and H₂ increase significantly. 600 °C–700 °C is the preferred catalytic temperature range for biochar, and 650 °C is the most suitable catalytic temperature for biochar, at which the tar yield is reduced to 0.15%. The H₂ yield gradually increases with increasing catalytic temperature, while the CH₄ and CO yields reach their highest values at 700 °C. The addition of steam reduces the tar yield to a much lower level and its value is no longer available by laboratory methods. Styrene, Indene and Naphthalene are completely converted. When 30 vol%∼40 vol% of steam is added, the Toluene peak area drops to less than 30% of that without steam. The addition of steam also promotes the methane steam reforming and the water-gas shift reaction. The H₂ yield is significantly increased.