【作者】 张延辉；

【导师】 张秋民； 何德民；

【作者基本信息】 大连理工大学 ， 化学工艺， 2018， 硕士

【摘要】 直接还原工艺作为非高炉炼铁的主要方法,因其摆脱了对炼焦煤资源的依赖、更符合目前节能减排的要求,受到世界各国的关注。半焦是煤热解产物,具有作为铁矿石还原剂的潜力。本文选用半焦作为直接还原的还原剂,探究了不同因素对铁矿石球团成型结果的影响,考察了还原温度、时间、焦矿比、还原气氛、气体浓度对直接还原结果的影响。对朝阳铁矿测试表征表明,该铁矿铁品位为66.10%,属于高品位磁铁矿,有害杂质元素S的含量低,是一种可以直接应用于直接还原工艺的优质铁矿石。还原剂半焦由红柳林长焰煤低温热解得到,通过固定床热解实验确定制取还原剂半焦温度为550°C。利用热重分析仪对铁矿石和半焦混合物进行非等温热重分析,考察样品在不同气氛及不同气体浓度下的还原行为,结果表明:N₂气氛下的反应过程可分为三个阶段,反应机理分别为三维扩散、随机成核和随后生长和界面化学反应。CO₂气氛下的反应过程分为两个阶段,反应机理分别为三维扩散和界面化学反应。H₂和CO气氛下的反应均分为三个阶段,反应机理分别为化学反应、随机成核和随后生长和三维扩散。对铁矿石球团成型过程,本文探究了成型压力、焦矿比、粘结剂添加量和铁矿石粒度对铁矿石球团强度的影响。实验结果表明,在本实验范围内,铁矿石粒径0.075⁰.09mm,半焦粒径小于0.05mm,粘结剂添加量10%,成型压力为60kN,焦矿比为0.4:1（质量比）时,能够制备符合本实验强度要求的铁矿石球团。对铁矿石球团直接还原过程,本文探究了还原温度、还原时间、焦矿比、还原气氛和气体浓度对直接还原结果的影响,利用化学分析法测定全铁化率和金属化率,采用X射线衍射和扫描电镜表征还原产物物相组成和微观结构。直接还原实验结果表明,N₂气氛下,在温度为950°C、反应时间1.0h、焦矿比0.4:1条件下得到金属化率为81.39%直接还原铁（DRI）,说明半焦作铁矿石还原剂是可行的。相同条件下CO₂气氛下得到了金属化率为84.30%的DRI,略微高于N₂气氛下结果,说明布多尔反应（C+CO₂=2CO）发生但作用不明显,金属化率均低于90%,无法直接用于电炉炼钢。引入还原性气体进行气-固协同还原,结果表明H₂和CO气氛下,还原温度为1000°C,还原时间1.0h,体积浓度为50%时,金属化率分别为91.43%和91.17%。升高还原温度和延长还原时间都可以使金属化率增加,且在较低温度范围内还原结果优于N₂和CO₂气氛下结果;增加气体浓度可以提高还原产物金属化率,但当浓度超过50%后,金属化率增加效果不明显。更多还原

【Abstract】 As the main method of non-blast furnace ironmaking,the direct reduction process has attracted worldwide attention due to its free from reliance on coking coal resources and its compliance with the current requirements for energy conservation and emission reduction.Char,as a product of coal pyrolysis,possesses the potential of being the reducing agent for iron ore.In this paper,char is used as reducing agent for direct reduction,and the influence of different factors on the formation of iron ore pellets is investigated.The effects of reduction temperature,time,ratio of char and ore,atmosphere and gas concentration on the direct reduction results are investigated.The characterization of Chaoyang Iron Ore shows that the iron grade of the iron ore is66.10%,which belongs to high-grade magnetite.The content of harmful impurity element S is low,which makes it a kind of high-quality iron ore that can be directly applied to the direct reduction process.The reductant char was obtained by low-temperature pyrolysis of Hongliulin sub-bituminous coal,and the pyrolysis temperature of the reductant was determined to be 550°C by the fixed-bed pyrolysis test.Non-isothermal thermogravimetric analysis of iron ore and char mixtures was conducted using a thermogravimetric analyzer to investigate the reduction behavior of samples under different atmospheres and different gas concentrations.The results show that the reaction process under N₂ atmosphere can be divided into three stages.The reaction mechanisms are three-dimensional diffusion,random nucleation and subsequent growth and interfacial chemical reactions.The reaction process in CO₂ atmosphere is divided into two stages.The reaction mechanism is three-dimensional diffusion and interface chemical reaction.The reaction under H₂ and CO atmosphere is divided into three stages.The reaction mechanisms are chemical reaction,random nucleation and subsequent growth and three-dimensional diffusion.For the formation process of iron ore pellets,the effects of molding pressure,ratio of char and ore,amount of binder addition and particle size of iron ore on the strength of iron ore pellets were investigated.The test results show that within the scope of this test,the particle size of iron ore is 0.075⁰.09mm,the particle size of char is less than 0.05mm,amount of the binder addition is 10%,the molding pressure is 60kN,and the ratio of char and coal is 0.4:1（mass ratio）,can prepare iron ore pellets that meet the strength requirements of this test.For the direct reduction process of iron ore pellets,the effects of reduction temperature,reduction time,ratio of char and ore,reducing atmosphere and gas concentration on the direct reduction results were investigated.The total ironification rate and metallization rate were determined by chemical analysis method.X-ray diffraction and scanning electron microscopy characterized the phase composition and microstructure of the reduced products.The results of the direct reduction test show that at the temperature of 950°C,reaction time of 1.0h and char-to-coal ratio of 0.4:1,the metallization rate was 81.39%under N₂ atmosphere,which proved the feasibility of char being reduing agent for iron ore.DRI with a metallization rate of 84.30%was obtained under CO₂ atmosphere at the same condion,slightly higher than that under N₂ atmosphere,indicating that the Boudouard reaction（C+CO₂=2CO）occurred but the effect was not obvious.Both the metallization rates were lower than 90%which can not be directly used for electric furnace steelmaking.The reduction gas was introduced into gas-solid synergistic reduction.The results showed that the metallization rates were 91.43%and 91.17%when the reduction temperature was 1000°C,the reduction time was 1.0h,and the volume concentration was 50%under H₂ and CO atmospheres.Increasing the reduction temperature and prolonging the reduction time can increase the metallization rate,and the reduction results are superior to N₂ and CO₂ in the lower temperature range.Increasing gas concentration can promote the metallization rate of reduction product,but when the gas concentration exceeds50%,the increase of metallization rate is not obvious.更多还原