磁铁矿球团等温氧化反应建模与数值模拟

Modeling and numerical simulation of isothermal oxidation reaction of magnetite pellet

针对磁铁矿球团在链箅机预热段中的氧化程度难以直接测量的难题,采用基于CFD、多孔介质传质、传热理论和未反应收缩核模型相结合的方法建立磁铁矿球团氧化反应模型,仿真得到球团表面及内部的氧化反应速率分布、生成物质量分数分布以及O2在球团内部的扩散情况,对不同预热温度、不同球团直径的氧化率及氧化速率进行数值模拟。结果表明:在单向流的作用下,O2从球团顶部的接触面逐渐向湍流尾部进行扩散,在球团内部呈现缩核模型现象;生成物质量分数分布呈现非均匀性;预热温度对氧化率影响显著,在973 K和1273 K温度工况下预热14 min,球团的氧化程度分别为67.6%和99.8%;氧化速率随氧化时间的延长而逐渐降低并趋于稳定;球团直径越大,氧化效果越差,获得的最佳球团直径范围为8~12 mm。研究计算结果与文献中的实验测量结果一致,其可用于预测球团预热过程的氧化率计算并优化相关工艺参数。

Aiming at the problem that the degree of oxidation of magnetite pellets in the preheating section of the grate is difficult to directly measure,a model for the oxidation of magnetite pellet is built based on a combination of CFD,porous media mass transfer,heat transfer theory and unreacted shrinking core model.The oxidation reaction rate distribution on the surface and inside of the pellet,the mass fraction distribution of the product and the diffusion of oxygen inside the pellet are simulated,while the oxidation rates and oxidation degree of pellets with different preheating temperatures and different diameters are imitated.The results show that under the influence of unidirectional flow,the oxygeninside the pellet gradually diffuses from the oxygen contact surface at the top of the pellet to the turbulent tail,and the phenomenon of shrinking core model appears inside the pellet.The mass fraction distribution of the product is inhomogeneous.The preheating temperature has a significant effect on the oxidation rate.Under the conditions of 973 K and 1273 K preheating for 14 minutes,the degree of oxidation of the two pellets is 67.6%and 99.8%respectively.The oxidation rate gradually decreases and becomes stable with the extension of the oxidation time.The larger the pellet diameter becomes,the lower the degree of oxidation will be,and the best pellet diameter range from 8 mm to 12 mm will be got.It is shown that the research calculation result is consistent with the experimental measurement result in the literature,which can be used to predict the oxidation rate of the pellet preheating process and to optimize related process parameters.