煅烧白云石铝热法原位脱硫的基础研究

Magnesium is an excellent desulfurizing agent, aluminothermic reduction in situ desulfurization of calcined dolomite with its realizing conditions has the potential advantage in the future industrial applications in atmospheric pressure and in the normal high-temperature range of molten iron, but the low utilization rate of magnesium is the main problem to limit the wide application of this method. In situ desulfurization is an important means to improve the utilization of magnesium. At present, there is little research on the mechanism of the motion and mass transfer of magnesium bubbles during the desulfurization of magnesium, which hinders the development of in situ desulfurization technology. In situ desulfurization of calcined dolomite is proposed. The interaction mechanism between Al2O3 and composition of calcined dolomite MgO and CaO is studied. The change and growth of magnesium bubbles in liquid iron and the contributory factors of temperature, time, and addition of aluminum, etc., on the rate of in situ desulfurization reaction are determined. With the help of water model experiment, the mechanism of supergravity strengthening is studied, and the coupling model between bubble floating velocity and mass transfer is established. A theoretical and technical prototype of calcining aluminite in situ desulfurization will be formed, and a new method different from dolomite-metal magnesium-passivated magnesium particles-liquid iron pretreating desulfurization will be established which will improve the utilization rate of magnesium from the source. The research of the project is of great significance to the new desulfurization technologies development and engineering amplification process.

金属镁能够在常压和正常液态铁水温度范围内实现深度脱硫，在未来的工业应用上具有潜在的优势，但镁利用率较低。镁原位脱硫是提高镁利用率的重要手段，目前对镁原位脱硫过程中镁气泡的运动和传质强化机理研究甚少。项目提出对煅烧白云石铝热法原位脱硫过程中还原反应变化规律，提高镁利用率的影响因素进行较为系统的研究。探明铝热还原产物Al2O3与煅烧白云石主要成分MgO、CaO的相互作用机制，镁气泡在铁水中产生、长大的变化规律，液态铁水温度、反应时间、铝加入量等因素与脱硫反应速率的内在联系，确定镁原位脱硫反应速度控速步骤；借助水模型试验研究超重力强化的微观机理，揭示镁脱硫的反应历程和多相传质机理，建立气泡上浮速度与传质之间的耦合模型，形成煅烧白云石铝热法脱硫的理论与技术原型，从源头上解决镁利用率低的问题。为以煅烧白云石为原料开发新的脱硫工艺，及工程放大提供理论基础和技术支撑。

传统的铁水脱硫工艺采用皮江法利用煅烧白云石、75硅铁和萤石制备金属镁，然后再经过精炼、浇铸、制粉、钝化等工序制备镁脱硫剂，工艺繁琐，且镁利用率低。课题提出将铝颗粒和煅烧白云石直接放入铁水中，在铝热还原制备金属镁的同时，得到的镁直接脱硫，省去了精炼、浇铸、制粉、钝化等制备镁脱硫剂的工序，并对新工艺进行了研究。课题主要研究了铝热还原过程MgO、Al2O3、CaO的相互作用规律；铝还原剂的制备与表征；铝热还原煅烧白云石脱硫实验；脱硫过程的物理模拟与数值模拟；脱硫废渣的综合利用等内容。. 研究发现，MgO会与Al2O3结合生成MgO·Al2O3，抑制氧化镁的还原，加入CaO后可以降低铝热还原MgO的温度。随着CaO/MgO值的增加，MgO还原率逐渐增加，较多的氧化钙不能确保MgO完全还原。采用气雾化和真空蒸馏方法能够得到粒度较小的铝粉，碳热还原粉煤灰制备铝硅合金的同时还可以得到AlN-SiC陶瓷。常压下铝热还原反应为外扩散控制，不脱硫时在铁水中转变为化学反应控制，脱硫时为准二级吸附动力学控制。脱硫废渣制备微晶玻璃时，较小的Fe3+/ Fe2+值有利于降低析晶温度。偏心搅拌能够改善搅拌器底部铁水的流动状态，有利于减小死区的大小。圆形底部钢包有利于脱硫剂的卷吸，提高脱硫速率。铁水中硫的分布几乎是均匀的，顶部和底部硫含量差小于10-6。数值模拟过程中发现全局尺寸为0.5mm和1mm的两套网格非常接近，可以认为当网格全局尺寸为1mm时数值解与网格大小无关。搅拌桨边缘两侧流动最为活跃。圆底钢包的死区小于平底钢包的死区，在相同的混合条件下，圆底钢包的混合时间比平底钢包的短。频繁的轴向速度变化有助于提高脱硫剂颗粒的均匀性。课题研究对于解析金属镁脱硫机理和数值模拟的网格划分具有重要的科学意义