镁在水蒸气中着火特性和模型分析

Experimental and model study on ignition of magnesium in steam

为研究镁在水蒸气中着火特性,采用可视化密闭燃烧器对镁颗粒进行加热后,观测到颗粒表面重复着氧化层沉积、破碎并剥落的过程,表面光泽明暗交替,直至发生着火.在高温管式炉上,研究加热速率、水蒸气质量分数和粒径对镁颗粒着火温度和着火延迟时间的影响规律.镁在水蒸气中着火前的反应主要是镁蒸发控制的均相反应,表面反应可以忽略.计算得到水蒸气中镁着火的活化能为150kJ/mol.建立常压下水蒸气中镁颗粒着火的能量方程,采用突变理论中的尖点突变模型分析水蒸气中镁的着火动力学过程,计算不同粒径的镁颗粒在静止水蒸气环境中的着火温度和着火延迟时间.结果表明,对于粒径小于50μm的镁颗粒,着火延迟时间不超过20ms.

The ignition characteristics of magnesium particles in steam were studied. A magnesium particle was heated in a visualizing enclosed burner and the ignition process was observed. Depositing, breaking and peeling of the oxide cap happen repeatedly on the particle surface, and the surface becomes bright and dark alternately until the particle is ignited. The effects of heating rate, steam concentration and particle diameter on ignition temperature and ignition delay time of magnesium in steam were studied by using a tube reactor. The ignition of magnesium in steam is controlled by the homogeneous reaction and the heterogeneous reaction can be ignored. The energy equation of the magnesium ignition in steam on normal pressure was set up. The activity energy of ignition in steam was calculated and the value of 150 kJ/mol was gained. The ignition kinetics was analyzed by the catastrophic model. Ignition temperature and ignition time of magnesium particles with different diameter in stationary steam were predicted. The ignition delay time is less than 20 ms for the magnesium particles which are smaller than 50 μm.