转炉尘泥含碳球团还原动力学研究

在1473~1573K的N2保护气氛下,通过还原失重实验研究了转炉尘泥所制含碳球团的还原特性.结果表明,还原得到的金属化球团全铁(TFe)在67%以上,金属化率(ηFe)在72%以上,可以作为高炉冶炼的原料;转炉尘泥所制含碳球团在0~100s时间内,反应分数受温度影响较小,在100s以后,受温度的影响逐渐增大,温度越高其值越大,转炉污泥球团还原反应分数随温度的变化更明显,反应结束时间在500s左右,比转炉细灰球团要早大约100s.含碳球团还原速度可由Mckwan方程所表达,还原速度由界面或局部反应控制.根据Arrhenius方程可以计算得出转炉细灰含碳球团的还原反应活化能为74.64kJ/mol,转炉污泥含碳球团的还原反应活化能为77.48kJ/mol.     

高炉瓦斯灰和转炉污泥造块制备金属化球团

用高炉瓦斯灰和转炉污泥造块后制备了金属化球团. 分析了两种尘泥的化学成分、物相组成及分布、粒度组成及堆密度等物化性质,考察了金属化处理温度、时间和原料C/O对球团金属化效果的影响. 结果表明,铁氧化物、熔剂氧化物及固体碳在两者中均含量较高,分布均匀,接触良好,锌以ZnFe2O4存在于CaO、MgO混合物相中. 两种尘泥堆密度均较小(<1.5 g/cm3),且含较多大于1.5 mm的粗颗粒. 提高金属化处理温度,延长处理时间及降低原料C/O,球团的金属化率、脱锌率均增大,其中温度的影响最为显著. 在C/O=1.0,金属化温度>1220℃,时间>30 min时,可获得金属化率大于85%,脱锌率大于90%的金属化球团.     

转底炉还原炼钢含锌粉尘球团的数值模拟

针对某钢铁厂处理含锌粉尘的转底炉直接还原工艺,建立了描述炉膛气体流动、燃烧和传热过程及炉内含碳球团理化反应和传热过程的数学模型,采用实际生产用球团在高温硅钼炉内进行还原实验验证模型的可靠性,得到转底炉炉膛内温度场、流场、压力场及球团内部的温度和组分分布,分析了转底炉主要操控参数对产品铁金属化和脱锌指标的影响. 结果表明,炉气流速沿流动方向逐渐增大,炉温最高点出现在还原二段(接近1350℃),球团还原20 min出炉后铁金属化率和脱锌率分别达77.9%和92.7%;要使产品铁金属化率达70%,生球碳氧摩尔比不得低于0.9,而配碳量对脱锌率影响不大;煤气供给减少1%将使产品铁金属化率和脱锌率分别降低0.8%和1.3%,二次风欠供20%时二者分别下降14%和24%;球团中锌还原脱除后在炉气中再次氧化,可通过转底炉烟气除尘系统将富锌粉尘回收并用于有色行业炼锌.     

回收高炉尘泥中的铁与锌

利用高炉尘泥以还原焙烧-磁选工艺获得高品位富铁矿,由醋酸回收液回收还原后的锌得到高纯度醋酸锌产品. 研究得出合理的焙烧工艺条件是：温度1373.2 K、时间60 min. 通过还原焙烧,高炉尘泥脱锌率可达98%,并得到含锌率仅为0.04%(w)、金属化率高的还原矿. 还原矿在150 mT的磁场强度下弱磁选可得铁品位在80%左右的富铁矿,回收液经浓缩结晶后得到纯度达98.7%的醋酸锌副产品. 所得富铁矿和醋酸锌可工业应用.     

含碳球团生产工艺参数优化及固结机理研究

实验研究了含碳球团高温自还原特性,考察了焙烧温度、C/O、焙烧时间等工艺参数对含碳球团还原后金属化率和强度指标的影响,利用XRD和SEM显微分析研究了球团还原过程和固结机理.正交实验结果表明,焙烧温度是影响两项指标的最重要因素,C/O次之,焙烧时间的影响不显著.在焙烧温度1350℃、C/O比1.15、焙烧时间25 min的最佳工艺条件下,金属化率最高为85.33%,球团的抗压强度达到2248 N.     

硼铁精矿含碳球团还原过程数学模型

通过等温热重实验分析CO/CO2/N2气氛中硼铁精矿还原和无烟煤气化的动力学特性,求得Fe3O4→Fe O和Fe O→Fe两个还原阶段及碳素溶损反应的活化能分别为74.72,65.74与194.72 k J/mol.建立了硼铁精矿含碳球团还原过程数学模型,并通过实验验证了模型的准确性.考察了球团尺寸、孔隙率、反应活化能对金属化率的影响,结果表明,球团尺寸从φ16 mm×8 mm增加至φ32 mm×16 mm,前期还原速率降低,但最终金属化率从85%上升至99.4%;球团孔隙率对还原过程影响较小;碳素溶损反应活化能上升抑制还原进行,但对最终金属化率没有影响,而当界面还原活化能从初始值的0.95倍上升至1.05倍时,不仅反应速率下降,最终金属化率也从99.59%降低至94.81%.从活化能对还原过程影响推断,反应前期还原过程受碳气化和铁氧化物还原联合控制,后期为铁氧化物还原反应控制.     

含碳球团还原机理研究

在1223~1473K的N2气氛下研究了石墨粉粒度、铁精矿粉粒度、温度、碳含量对含碳球团还原速度的影响．结果表明，石墨粉和铁精矿粉粒度越小，还原温度和碳含量越高，含碳球团还原速度越大．基于碳气化反应、气相扩散和界面反应的含碳球团还原速度方程均能较好地处理本研究的数据。根据Arrhenius方程计算出的碳气化反应和界面反应活化能分别为227．7和294．14kJ／mol；计算出的气相扩散为限制环节的含碳球团还原活化能为391．26～411．37kJ／mol．因此本研究条件下含碳球团还原似应由气相扩散所控制．     

钢铁厂典型粉尘的基本物性与利用途径分析

对钢铁生产流程中产生的几种典型粉尘采用化学分析,激光粒度仪,偏光显微镜,扫描电镜和XRD等手段进行了分析,结果表明,粉尘含铁量高,粒度细且含有多种杂质元素;高炉干灰碳含量为34.00%,锌含量为16.60%且以铁酸锌形式弥散分布;烧结三电场除尘灰钾含量为15.88%且以氯化钾形式存在.对比了烧结、球团、直接还原和炼钢处理粉尘的优缺点,着重分析转底炉直接还原处理粉尘的优势,并在实验室条件下模拟转底炉直接还原工艺,在1250℃下还原15min时,得到金属化率大于75%,脱锌率大于95%,脱钾、钠率大于80%和残碳量低于0.2%的金属化球团.     

金属化球团防止再氧化研究

研究了转炉尘泥和精矿含碳球团在氧化性气氛下还原、冷却和贮存过程中的再氧化问题，提出了有效防止再氧化的措施．高温（大于１２００℃）、快速（１０～２０ｍｉｎ）还原得到的金属化率大于９０％的金属化球团，采用炉内冷却、埋煤粉中、放密封罐内、炉内冷至９００～１０００℃后出炉冷却四种方式都是有效的，干燥清洁的室内堆存是简单有效贮存海绵铁的方法．     

高炉瓦斯泥碳热还原脱锌研究*

利用碳热还原方法,开展了高炉瓦斯泥焙烧脱锌实验研究。研究结果表明,碳热还原焙烧高炉瓦斯泥可有效脱除高炉瓦斯泥中的锌。最佳工艺条件为：焙烧温度为1 423 K,焙烧时间为180 min,物料粒径为9.5～10.5 mm。在最佳工艺条件下,高炉瓦斯泥脱锌率达99.2%,焙烧剩余渣中锌质量分数低于0.15%,可返回高炉使用。     

铜熔渣喷吹地沟油还原贫化

以地沟油为生物质还原剂,高温裂解后对铜火法冶炼铜渣进行还原贫化。结果表明,地沟油裂解产物主要是C, H2, CO和CH4等还原性小分子物质,1373, 1473和1573 K下裂解积碳的转化率分别为78.36%, 79.83%和80.07%,因此地沟油高温裂解时碳元素主要以积碳形式存在。热力学计算发现,高温下裂解产物均有良好的还原Fe3O4的活性,用地沟油替代传统化石类还原剂还原铜渣中磁性铁在热力学上是可行的。以N2为载气不仅有利于高温下地沟油顺利喷入铜熔渣中,且通过动量传递起到搅拌熔渣的作用,增大了微小铜滴碰撞聚集长大的机会。在熔炼温度1573 K、载气流量3 L/min、地沟油喷吹量2.055 mL/min、喷吹时间4 min、沉降时间50 min的最优还原贫化条件下,铜渣中Fe3O4含量从33.40wt%降至1.60wt%,含铜量从4.49wt%降至0.49wt%,渣中Fe3O4相转变为2FeO?SiO2相。根据Einstein?Roscoe方程分析,渣中Fe3O4含量减少有利于降低熔渣粘度,改善铜滴的沉降条件。继续增加地沟油喷吹时间沉降金属中杂质含量增加;沉降时间过长时,由于铜渣对铜的机械夹带和化学溶解作用,沉降效果不会更好。实验的铜回收率达89.09%。     

高温炉气中含碳团矿的还原和氧化过程研究

本文首次指出，在高温氧化性护气中焙烧含碳团矿时，还原反应开始前存在一脱碳期，其例证是，在表层的矿相照片上发现存在无碳无铁的浮氏体烧结层．因此，在高温炉气中焙烧含碳团矿时的化学反应过程可分为三段；前期为脱碳过程，中期为还原过程，后期为再氧化过程．后期的再氧化使金属化率随时间的变化由极大植逐渐下降，此金属化率极大值的高低主要决定于前期的脱碳程度．     

Measuring chemical heat production rates of biofuels by isothermal calorimetry for hazardous evaluation modelling

Biofuels are commonly stored in large stacks that may heat up and self‐ignite from microbiological and chemical heat production. This paper shows how isothermal (heat conduction) calorimetry can be used to measure heat production rates of biofuels at relatively low temperatures close to where self‐heating starts to become a problem. Measurements can be made to assess how the reaction rate is a function of such factors as temperature, extent of reaction, oxygen pressure, water content and the presence of catalytic compounds. In the present paper, measurements on pellets made of wood and bark are presented together with an analysis of how the reaction rate of the bark pellets depends on the oxygen pressure. It is also shown that 1% iron or copper ions increased the reaction rate of wood pellets by a factor of three. Copyright © 2006 John Wiley & Sons, Ltd.     

Mechanical Properties, Thermal Shock Resistance, and Thermal Stability of Zirconia-Toughened Alumina-10 vol% Silicon Carbide Whisker Ceramic Matrix Composite

Zirconia-toughened alumina (Al₂O₃–15 vol% Y-PSZ (3 mol% Y₂O₃)) reinforced with 10 vol% silicon carbide whiskers (ZTA-10SiC _w ) ceramic matrix composite has been characterized with respect to its room-temperature mechanical properties, thermal shock resistance, and thermal stability at temperatures above 1073 K. The current ceramic composite has a flexural strength of ∽550 to 610 MPa and a fracture toughness, K _IC , of ∽5.6 to 5.9 MPa·m^1/2 at room temperature. Increases in surface fracture toughness, ∽30%, of thermally shocked samples were observed because of thermal-stress-induced tetragonal-to-monoclinic phase transformation of tetragonal ZrO₂ grains dispersed in the matrix. The residual flexural strength of ZTA–10 SiC _w ceramic composite, after single thermal shock quenches from 1373–1573 to 373 K, was ∽10% higher than that of the unshocked material. The composite retained ∽80% of its original flexural strength after 10 thermal shock quenches from 1373–1573 to 373K. Surface degradation was observed after thermal shock and isothermal heat treatments as a result of SiC whisker oxidation and surface blistering and swelling due to the release of CO gas bubbles. The oxidation rate of SiC whiskers in ZTA-10SiC _w composite was found to increase with temperature, with calculated rates of ∽8.3×10⁻⁸ and ∽3.3×10⁻⁷ kg/(m²·s) at 1373 and 1573 K, respectively. It is concluded that this ZTA-10SiC _w composite is not suitable for high-temperature applications above 1300 K in oxidizing atmosphere because of severe surface degradation.     

Kinetic analysis of spinel formation from powder compaction of magnesia and alumina

A kinetic investigation into the formation of spinel from alumina (Al₂O₃) and magnesia (MgO) powder compaction with a stoichiometric mixing molar ratio of 1:1 was conducted in the temperature range of 1573 K to 1773 K over a certain time interval up to 25 h. The samples were pressed at pressures of 125, 375 and 750 MPa. The progress of the reaction was evaluated by monitoring the expansion ratio instead of the thickness of the spinel layer that was generated. The expansion ratio increases with increasing pressing pressure and holding time, and high temperature favored spinel formation. However, densification was observed at temperatures above 1673 K due to the occurrence of sintering between the powders. A kinetic model taking electrochemical potential as the driving force of the reaction was established, and the apparent activation energy was calculated to be 310.6 kJ/mol in the temperature range between 1573 K and 1673 K. The reaction was controlled by the inter-diffusion of Al³⁺ and Mg²⁺ ions in the spinel layer that was formed.     

Kinetics of isotopic exchange reaction between hydrogen and water vapor over platinum supported on a hydrophobic carrier

The isotopic exchange reaction between hydrogen and water vapor was studied for the temperature range 313 K to 353 K over platinum supported on hydrophobic styrene-divinylbenzene copolymer beads, and, for comparison, platinum supported on hydrophilic alumina pellets. The hydrophobic catalyst exhibited a high activity even with the gas saturated with water vapor, whereas the hydrophilic catalyst showed maximum exchange rate at a relative humidity of approximately 0.6. The dependences of the exchange rates on relative humidity, hydrogen partial pressure and temperature were extensively examined. The combined effect of surface reaction and intraparticle diffusion on the overall exchange reaction was analyzed to explain the kinetic behavior on the hydrophobic catalyst.