Abstract: The direct reduction of iron was carried out by pellet preheating and one-step coal-based direct reduction process with the high grade magnetite concentrate from Mengku, Xinjiang, as raw material. The quality of preheated pellets at different preheating system conditions was examined in order to determine the effect of preheating process when magnetite concentrate pellets were reduced. Both the compressive strength and degradation index of preheated pellet are the important indicators to measure the preheating process. The green pellets could be preheated in a chain grate to improve the strength of the preheated pellets and reduce the degradation index of green pellet. Based on the preliminary analysis of results, the best preheating system was determined, that is, the preheating temperature was between 800 to 850℃, preheating time 15~18 min, preheating wind velocity from 1.5 to 1.8 m/s and the material layer thickness 100 mm, the preheated pellets produced would have the compressive strength as high as 600 N, which means that its compressive strength is obviously improved compared with the pellets produced at other preheated system. The experimental results of scale-up process show that the quality of directly reduced iron under these conditions could completely meet the following production requirement.

Key words: magnetite concentrate, preheating system, powder efficiency of dried balls, preheated pellets, compressive strength, directly reduced iron

摘要： 以新疆蒙库高品位磁铁精矿为原料，采用预热球团一步法煤基直接还原工艺制取铁. 考察了不同预热制度下预热球的质量，以研究预热工艺在磁铁精矿球还原中的作用效果，其中预热球的抗压强度和粉未率是衡量预热工艺作用效果的重要指标. 通过链篦机预热处理生球以提高预热球强度，有效降低干球粉末率. 由实验结果确定最佳预热制度. 在预热温度800~850℃、预热时间15~18 min、预热风速1.5~1.8 m/s、料高100 mm的预热条件下，得到的预热球团抗压强度为600 N/个以上，比其他预热制度下得到的预热球团抗压强度有较大提高. 由扩大型全流程实验可知，在该条件下得到的直接还原铁质量完全达到生产要求.

关键词: 磁铁精矿, 预热制度, 干球粉末率, 预热球, 强度, 直接还原铁