Direct reduction of iron ore pellets using hydrogen gas has the potential to significantly reduce CO2 emissions from the ironmaking process. In this work, green pellets of titanomagnetite ironsand from New Zealand were oxidatively sintered to form titanohematite. These sintered pellets were then reduced by H2 gas at temperatures ≥ 1043 K, and a maximum reduction degree of ~ 97 pct was achieved. Fully reduced pellets contained metallic Fe as the main product phase, but several different (Fe, Ti) oxides were also present as minor inclusions. The phase distribution of these oxides depended on the reduction temperature. With increasing temperature, the relative proportion of pseudobrookite in the final product increased, while the proportion of residual ilmenite and rutile decreased. The reduction kinetics were found to be well described by a pellet-scale single-interface shrinking core model, for reduction degrees up to 90 pct. At temperatures above 1143 K, the rate-limiting step was found to be solely an interfacial chemical reaction process, with a calculated apparent activation energy of 31.3 kJ/mol. For pellet sizes from 5.5 to 8.5 mm, the reaction rate was observed to increase linearly with decreasing pellet diameter, and this linear correlation extrapolated to intercept the axis at a pellet diameter of 2.5 mm. This is interpreted as the minimum length required for a shrinking core interface to develop within the pellet.

中文翻译：

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在高达 1443 K 的温度下在 H2 中氧化新西兰铁砂颗粒的还原动力学

使用氢气直接还原铁矿石球团有可能显着减少炼铁过程中的二氧化碳排放。在这项工作中，来自新西兰的钛磁铁矿铁砂生球团被氧化烧结形成钛赤铁矿。这些烧结球团随后在 ≥ 1043 K 的温度下用 H2 气体还原，最大还原度达到 ~ 97 pct。完全还原的球团包含金属 Fe 作为主要产物相，但也存在几种不同的（Fe、Ti）氧化物作为少量夹杂物。这些氧化物的相分布取决于还原温度。随着温度的升高，最终产品中假板钛矿的相对比例增加，而残留钛铁矿和金红石的比例下降。还原动力学被发现由颗粒规模的单界面收缩核心模型很好地描述，还原度高达 90 pct。在高于 1143 K 的温度下，发现限速步骤仅仅是一个界面化学反应过程，计算出的表观活化能为 31.3 kJ/mol。对于 5.5 至 8.5 毫米的颗粒尺寸，观察到反应速率随着颗粒直径的减小而线性增加，并且这种线性相关性外推到在 2.5 毫米的颗粒直径处截取轴。这被解释为收缩的核心界面在颗粒内形成所需的最小长度。计算出的表观活化能为 31.3 kJ/mol。对于 5.5 至 8.5 毫米的颗粒尺寸，观察到反应速率随着颗粒直径的减小而线性增加，并且这种线性相关性外推到在 2.5 毫米的颗粒直径处截取轴。这被解释为收缩的核心界面在颗粒内形成所需的最小长度。计算出的表观活化能为 31.3 kJ/mol。对于 5.5 至 8.5 毫米的颗粒尺寸，观察到反应速率随着颗粒直径的减小而线性增加，并且这种线性相关性外推到在 2.5 毫米的颗粒直径处截取轴。这被解释为收缩的核心界面在颗粒内形成所需的最小长度。