Abstract A detailed char gasification model is developed using a multiphase Eulerian–Lagrangian algorithm and thermally thick treatment. The model is first validated by both gasification and combustion experiments of a millimeter-sized char particle. Temperature and mass loss histories as well as the particle morphology evolution correspond well with the existing results. Then the steam gasification of a 5 mm char particle is simulated and detailed physical and chemical conversion processes inside the particle are explored. During gasification, three distinct layers, i.e., the outer ash layer, the intermediate layer and the core layer, are identified based on the intraparticle porosity distribution. Simulation results show that the highest H2O and CO2 mass fractions locate in the ash layer, while the intermediate and core layers contain the highest H2 and CO mass fractions, respectively. Moreover, effects of several parameters are also explored. It is found that the Stefan flow caused by the mass transfer plays a key role in determining the diffusion and convection behavior during gasification. The strength of the Stefan flow in the intermediate layer appears to be two orders of magnitude smaller than that of the inflow and has an influence on the shifting from a kinetically-controlled mode to a diffusion-controlled mode. In addition, the char consumption rate in the intermediate layer increases with an increase in steam mass fraction, gasification temperature and inflow velocity while it decreases with increasing particle diameter. Meanwhile, the char consumption rate caused by CO2 is much smaller than that due to steam.

中文翻译：

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毫米级焦炭颗粒用热厚处理蒸汽气化的 CFD 模拟

摘要 使用多相欧拉-拉格朗日算法和热厚处理开发了详细的炭气化模型。该模型首先通过毫米大小的炭颗粒的气化和燃烧实验进行验证。温度和质量损失历史以及颗粒形态演变与现有结果非常吻合。然后模拟了 5 毫米炭颗粒的蒸汽气化，并探索了颗粒内部的详细物理和化学转化过程。在气化过程中，根据颗粒内孔隙度分布确定了三个不同的层，即外灰层、中间层和核心层。模拟结果表明，最高的 H2O 和 CO2 质量分数位于灰层，而中间层和核心层分别含有最高的 H2 和 CO 质量分数。此外，还探讨了几个参数的影响。发现由传质引起的斯特凡流动在决定气化过程中的扩散和对流行为中起着关键作用。中间层中的 Stefan 流的强度似乎比流入的强度小两个数量级，并且对从动力学控制模式到扩散控制模式的转变有影响。此外，中间层的焦炭消耗率随着蒸汽质量分数、气化温度和流入速度的增加而增加，而随着颗粒直径的增加而降低。同时，CO2 引起的焦炭消耗率远小于蒸汽引起的焦炭消耗率。