Abstract: Thermal decomposition is the primary step to utilizing magnesite resources. Traditionally, it has been done in the shaft or rotary-type kilns using lumpy bulk raw materials, leaving a substantial amount of small or millimeter-sized particle materials unusable. In this work, the decomposition of millimeter-scale magnesite particles using high-temperature gas-solid fluidized beds is proposed. The thermal decomposition behavior of magnesite particles with four different sizes in the range of 0.3~3 mm at different temperatures using a laboratory fluidized bed reactor of 30 mm in diameter combined with an online mass spectrometry analyzer is reported in this work. The results showed that the thermal decomposition rate of magnesite particles accelerated with the increase in bed temperature and the decrease in particle size. As the decomposition progresses, three characteristic stages can be observed. At the initial stage of decomposition corresponding to conversions of less than about 0.1, the reaction was controlled by the interfacial chemical reaction kinetics, and the apparent activation energy decreased with increasing particle size. In the middle stage of the reaction (the conversion was 0.1~0.9), the decomposition reaction obeyed the shrinking core model, and the activation energy of the decomposition reaction remained almost unchanged with the conversion for the particle of 0.46 mm in diameter but increased with the conversion for other large-sized particles. In the later stage of the thermal decomposition reaction (after the conversion was greater than 0.9), the conversion varied slowly with time, and the reaction was affected significantly by heat transfer and gas diffusion. For each of the decomposition reaction stages, the reaction mechanisms and kinetic parameters were determined based on the experimental data. This study discussed the effects of bed temperature and particle size on the thermal decomposition of magnesite particles for a better understanding of the thermal decomposition behavior of millimeter-sized magnesite particles in fluidized beds. The study provided essential data support for the development of new products for the preparation of magnesite particles in fluidized beds, serving as a critical reference for the preparation of millimeter-sized high-density dead burned magnesia at high-temperature in fluidized beds.

Key words: thermal decomposition of magnesite, fluidized bed, kinetics, particle size, reaction mechanism

摘要： 流态化热分解毫米级菱镁矿颗粒是提高和促进小颗粒菱镁矿资源利用的有效途径，但有关基础研究尚处于空白阶段。对此，本工作选取粒径范围为0.3~3 mm的四种颗粒样品，利用直径为30 mm的实验室流化床反应器结合在线质谱分析仪，研究了不同温度下菱镁矿颗粒流态化热分解行为。结果表明，菱镁矿颗粒热分解速度随床层温度升高和粒径减小而加快。随着颗粒粒径增大，反应界面缩小，活化分子减少，表观活化能减小。随着反应程度加深，热分解反应控制机理逐渐由化学反应控制向颗粒内扩散和传热控制转变。本研究揭示了毫米级菱镁矿颗粒流态化热分解行为，对开发新型流态化制备菱镁矿颗粒热分解产品提供基础数据支持，对高温流态化制备毫米级尺寸高密度重烧镁砂技术也具有重要的参考价值。

关键词: 菱镁矿热分解, 流化床, 反应动力学, 粒径, 反应机理