Steel slag waste heat-driven biomass gasification-mineralization for metallurgical syngas production

To integrate biomass valorisation, waste heat recovery from hot steel slag, and CO₂ mineralisation for carbon sequestration, a vertical high-temperature injection gasification system was established using bamboo chips and hot basic oxygen furnace steel slag as feed stocks. The effects of the CO₂ volume fraction in the carrier gas, steel slag particle size, and reaction temperature on syngas production and coupled carbon sequestration were systematically examined. Kinetic analysis and multiple characterisation techniques were combined to clarify the mechanisms of gas release and solid-phase evolution. The results show that temperature is the dominant factor governing CO formation and carbon sequestration behaviour. When the temperature increases from 700 ℃ to 1 100 ℃, the CO yield increases from 81.5 mL/g to 207.8 mL/g. At 1 000 ℃, the peak CO volume fraction reaches 10.48%, with the shortest reaction completion time. Kinetic analysis shows that the apparent activation energy during the high-temperature gasification stage is 222.50-268.69 kJ/mol. Increasing the CO₂ volume fraction in the carrier gas promotes bamboo char gasification, dry reforming, and CO₂ mineralisation by steel slag. The effect of steel slag particle size shows clear temperature dependence. Within the range of 900-1 100 ℃, fine steel slag is more effective in increasing the peak CO volume fraction and CO yield, and the peak CO volume fraction is reaching 12.16% at 1 100 ℃, bigger than 9.79% for coarse steel slag. In contrast, coarse steel slag better maintains gas-flow channels within the particle bed, thereby improving carbon sequestration. The carbon sequestration rate generally increases with temperature and reaches its maximum value of 16.60% at 1 000 ℃. After the reaction, carbonation, iron oxide reduction-reoxidation, and calcium silicate structural reconstruction occurs simultaneously in the steel slag. Considering both gas production and carbon sequestration, 1 000 ℃, a higher CO₂ partial pressure, and an appropriate steel slag particle size can be regarded as preferred process conditions for balancing CO release and CO₂ mineralisation. If maximising CO yield is the primary objective, 1 100 ℃ and fine steel slag are more favourable. This study provides experimental support for the synergistic resource utilization of biomass solid waste and metallurgical steel slag.