基于阻抗匹配的微波强化含生物炭球团自还原

Biochar-bearing pellets are a material with bright prospect for direct reduction ironmaking. This project proposes the concept of intensifying self-reduction of biochar-bearing pellets using microwave energy based on impedance matching. The key point is to prepare double-layer pellets constituting by an impedance-matching layer and a core-reducing layer for improvement of impedance matching degree at pellet surface, and to optimize the pellet size which should satisfy the requirement of microwave penetration depth. By coupling microwave loss with reduction of pellets, efficient, fast and volumetric reduction with enhanced pellet quality can be expected. This project combines theories of metallurgy, electromagnetics, minerals science, materials science and heat transfer as well as technology of agglomeration. By studying effects of electromagnetic properties, microwave absorbing properties, impedance matching degree, microwave penetration depth, and reduction parameters on microwave reduction of biochar-bearing pellets, it reveals the mechanism for coupling microwave loss with self-reduction of biochar-bearing pellets and establishes the theory for intensifying microwave reduction of biochar-bearing pellets based on impedance matching. By exploring effects of pellet structure and size on reduction, pellet properties and pelletization, the project reveals the characteristics of pellets meeting the requirement for efficient and volumetric reduction. Developing technological prototype for construction of pellets with selectively distributed biochar will contribute to healthy and sustainable development of iron and steel industry.

含生物炭球团是一种具有广阔应用前景的直接还原炼铁原料。本项目提出基于阻抗匹配利用微波强化含生物炭球团自还原的技术思想。其关键是通过构建具有阻抗匹配层和核心还原层的双层球团结构提高球团表面阻抗匹配度，并根据微波穿透深度的匹配要求，优化球团尺寸，进而耦合微波损耗与球团还原，实现含生物炭球团的高效快速整体还原，同时提高还原球团质量。项目综合运用冶金学、电磁学、矿物学、材料学、传热学等原理，结合造块技术，通过研究原料电磁性质、微波吸收性能、阻抗匹配度、微波穿透深度、微波还原条件对含生物炭球团微波还原的影响，揭示微波损耗耦合含生物炭球团还原机理，建立基于阻抗匹配的微波强化含生物炭球团还原的基础理论；通过研究球团结构与尺寸对还原过程、球团性能及球团成型的影响，揭示满足快速整体还原的含生物炭球团条件，开发生物炭选择性分布球团构建关键技术原型，为钢铁工业的健康可持续发展作出贡献。

含生物炭球团是一种具有广泛应用前景的直接还原炼铁原料。本项目提出基于阻抗匹配利用微波强化含生物炭球团自还原的技术思想。项目首先揭示了微波在球团中的损耗机制。铁精矿和生物炭在常温下具有较强的介电损耗，并且随温度上升快速增加。生物炭在低温下的介电损耗弱于铁精矿，在高温下则强于铁精矿。由于高温条件下铁精矿的磁损耗消失，介电损耗是含生物炭球团微波还原过程中的主要生热机制和能量转化方式。其次，本项目阐明了含生物炭球团的微波还原机理。铁精矿和生物炭的阻抗匹配度和微波穿透深度随温度上升快速减小。在适宜的还原温度范围内生物炭的阻抗匹配度和微波穿透深度小于铁精矿，表明其微波反射损失和微波损耗均强于铁精矿。将生物炭全部分布于球核，铁精矿偏析分布于球团中形成核壳结构含生物炭球团可实现高效微波还原。在最佳还原温度为1050 ℃、保温时间为20 min、加热球团量为30 g、微波功率为1200 W、氮气流量为0.05 L/(m2.min)的条件下，获得的金属化球团全铁品位为91.74%、金属化率为94.04%、还原度为92.15%、残炭量为0.61%、抗压强度为203.63 N/p，完全满足直接还原铁的质量要求。最后，本项目构建了合理的含生物炭球团。在满足高效微波还原所需球团尺寸（10-13 mm）和核壳结构要求的前提下，获得了最佳的造球条件：球团中铁精矿B总配比为30%、造球时间为16 min、造球机转速为25 r/min、膨润土用量为2.3%、C/Fe质量比为0.225、球团水分含量为13.0%、球壳中铁精矿A和B配比分别为10%和0%。此时得到的含生物炭球团生球落下强度为3.3次/0.5m、抗压强度为11.1 N/p、爆裂温度为410 ℃，干球抗压强度达到33.9 N/p。基于以上工作，本项目揭示了满足高效整体还原的含生物炭球团条件，开发了生物炭选择性分布球团构建关键技术原型，为微波强化含生物炭球团自还原提供了重要理论和技术支撑。