【作者】 邹冲；

【导师】 温良英； 张生富；

【作者基本信息】 重庆大学 ， 冶金工程， 2014， 博士

【摘要】 由于国家对钢铁行业节能减排要求的不断严格和企业炼铁成本压力的不断加大，优化高炉效能成为提高钢铁企业竞争力的重要途径。其中，高炉喷煤是优化高炉原燃料结构，降低原燃料消耗的重要措施，该措施不但能节约炼铁成本，还可降低炼焦工艺对环境的污染。因此，提高高炉煤比已成为钢铁企业共同追求的目标。喷吹煤粉在风口前的燃烧率是目前限制喷煤量提高的决定性因素。研究者已采用诸多措施强化喷吹煤粉在此区域的燃烧。尽管如此，目前我国钢铁企业的高炉平均煤比与国外先进水平仍存在一定差距。在化石燃料燃烧涉及的相关领域，催化燃烧技术是改善燃料燃烧性能的重要手段。尽管煤的催化燃烧研究工作起步较晚，但近年来发展迅速。根据高炉喷吹煤粉的燃烧特点和未燃煤粉生成原因，在喷吹煤中加入适量添加剂可提高燃料利用效率，改善料柱透气/液性，提高喷煤量。将催化燃烧技术应用于高炉喷煤工艺前需要评估的核心问题是添加剂的作用效果和适用性，即高炉喷煤添加剂既要有催化强化煤粉燃烧的功效，又要对高炉炼铁无富集损坏作用，还应具有较低廉的成本。而高炉喷吹煤粉的催化强化燃烧机理研究可为添加剂的选择提供理论依据。本文围绕高炉喷吹煤粉催化强化燃烧机理及应用基础，采用实验和理论计算相结合的方式开展了催化燃烧行为及动力学、催化燃烧过程中的氧传递/释放机理、高温催化燃烧机制及复合添加剂及应用基础等方面的研究。采用以热分析法为主的实验方法，研究了不同添加剂对煤粉的催化强化燃烧行为及机理。首先，研究了不同升温速率对煤粉燃烧规律的影响，建立了煤粉燃烧过程的非等温动力学机理模型；在此基础上，考察了适合高炉喷吹的典型催化剂对煤粉燃烧特征和动力学参数的影响规律，并根据实验现象分析了产生此规律的原因。基于喷吹煤粉燃烧特点，发展了喷煤添加剂的种类：①经筛选和热分析实验得出含有Fe2O3、CaO等催化活性物质的转炉除尘灰在8种含铁冶金粉料中的助燃催化效果最佳；②基于过氧化钙分解温度（362~456℃）与煤粉热分解温度相近，提出以过氧化钙作为复合添加剂配方组分的思路，通过实验研究表明过氧化钙在煤粉燃烧过程具有分解释氧、改善半焦结构和催化半焦燃烧的多重作用，对促进煤粉燃烧反应性和提高燃烧效率作用效果明显。采用基于密度泛函理论（DFT）的第一性原理（First principles）系统地研究了CaO、-Fe2O3等催化剂在强化煤粉燃烧过程中促进氧传递的机理过程。研究结果表明：①CaO(001)面的Ca-O桥键位、Fe2O3(0001)面及Fe2O3(1102)面的氧空穴位、FeO(001)面的Fe原子上方是催化反应的活性位，O2可在这些位置稳定吸附并生成活性氧物种；②C或CO优先与生成的活性氧物种反应，产物的脱附过程容易进行；③Fe2O3(0001)面及Fe2O3(1102)面的氧空穴生成原因为表面被C或CO还原。解释了催化剂促进碳-氧反应的微观机理，丰富了煤粉催化燃烧机理关于“氧传递理论”内容。利用滴管炉(DTF)模拟高炉风口喷吹煤粉的快速升温过程，考察了三种催化剂对煤粉燃烧率和气体产物组成的影响。结果表明：催化剂对烟煤的催化活性顺序为：CaO> Fe2O3> MnO2，对无烟煤的催化活性顺序为：Fe2O3> CaO> MnO2；催化剂对无烟煤的催化作用明显优于烟煤。通过比较分析添加催化剂前后未燃煤粉的微观结构、微晶结构和反应性变化，解释了快速升温条件下的煤粉催化燃烧机制为：①催化剂促进半焦表面和内孔的碳氧化学反应进行，加快内孔的塌陷、交联、破碎和粒径缩小速度；②催化剂加快了半焦的不饱和脂肪类结构燃烧，使未燃煤粉中脂肪类结构比例降低，晶格尺寸增加，燃烧后期碳原子有序性排列趋势增强。通过热分析结果发现，催化燃烧生成的未燃煤粉的气化反应性也高于普通的未燃煤粉，有利于未燃煤粉在高炉内的后续消耗。针对喷吹煤粉燃烧产物在高炉内的衍变规律，采用FactSage软件对催化燃烧产物的高温熔融及粘温特征进行了理论计算，通过实验考察了燃烧产物对焦炭性质的影响。结果表明：①Fe2O3和CaO在原煤中添加量低于1.5%条件下，降低了煤灰全液相温度和粘度。②煤粉燃烧产物在焦炭表面均不润湿，但含有催化剂的煤灰（简称“催化煤灰”，下同）对焦炭的侵润性强于原煤灰。③未燃煤粉与焦炭表面反应较弱，对焦炭表面形貌影响不大；原煤灰与焦炭反应导致焦炭表面孔径增加，对焦炭结构影响只停留在焦炭表面及孔隙入口处；催化煤灰熔融后则会浸入焦炭内部，与焦炭反应后造成焦炭孔径增加。④原煤灰和未燃煤粉降低了焦炭的反应性；催化煤灰则提高了焦炭的反应性，其中添加Fe2O3的影响强于添加CaO。⑤高炉喷煤催化强化燃烧应用中应考虑喷吹煤自身的性质，使用灰熔点高且灰分流动性较差的煤粉，并应控制添加剂的加入量。采用实验室扩大的喷煤设备分别进行了3组分和含有转炉除尘灰的4组分复合添加剂的研制。由Fe2O3、CaO2、CaO组成的三组分添加剂按最佳配比添加后，对高炉喷吹煤粉的燃烧具有良好的催化强化效果；采用转炉除尘灰替代部分化学试剂Fe2O3后，在添加量为0.6%条件下，可提高煤粉燃烧率8.94%。利用COMSOLMultiphysics多物理场耦合仿真软件对加入复合添加剂后煤粉燃烧速率、温度、气体组分进行了数值模拟计算。分析了本采用催化强化燃烧技术对高炉生产相关指标的影响。本研究成果对强化高炉喷吹煤粉燃烧具有较好的指导意义。更多还原

【Abstract】 Due to the higher requirements of government on energy conservation andemission reduction for iron and steel industry as well as the cost increase of ironmaking,optimizing energy efficiency of BF become an important measure for improving thecompanies’ competiveness. Pulverized coal injection (PCI) is a primary solution foroptimizing the structure of fuels and reducing the fuels consumption. This technologycould not only benefit the cost saving for ironmaking process, but could reduce thepollution of the environment from coke making process. Thus, increasing the PCI rate isthe objective for iron and steel companies. The burnout rate of pulverized coal (PC) inthe tuyere and raceway is an especially important restriction in BF. Researchers takemany measures to enhance the PC combustion in these zones. However, there arecertain gaps for China in PCI rate when compared with international advanced levels.Catalytic combustion is an important technique for utilization of fossil fuels.Although the research of catalytic combustion on coal started late, it developed rapidlyin recent years. Depending on the features of PC combustion in BF and the generationfor unburnt char (UBC), adding an adequate additive in the PC before injection into theBF could increase the utilization efficiency of fuel, and improve the gas/liquidpermeability of charging column, leading to a higher PCI rate. The effect and adaptationof additives are the innermost core that need to be evaluated before application ofcatalytic combustion for PCI coal. The PCI additive should have these featuresincluding obvious catalytic effect, no negative on iron-making process and inexpensive.The research results of catalytic combustion mechanism of PCI coal could provide abasis for selecting the PCI additives.This paper centered on the research target of catalytic combustion-ralted issues andits foundamental application on PCI technology. A careful theoretical analysis and anumber of experiments were carried out for investigating the catalytic combusitionbehavior, oxygen reserve/transmit during catalytic combusiton process, catalyticmechanism at high temperature, and compound additives for application in PCI.Firstly, the catalytic effect of different of additives on pulverized coal combustionwas investigated by Thermal analysis (TA). The effect of heating rate on pulverized coalcombustion process was investigated, and the isoconversional and Melak method is applied to establish the pulverized coal kinetics model. Combustion characteristic andkinetic study was carried out for investigating the typical catalyst, and the experimentalphenomena was explained by the microcosmic mechanism. Two novel additives wereproposed and the catalytic mechanism was analyzed:①Due to the active compoundin the dust such as Fe2O3, CaO and its special microstructure, BOF dust is the bestsubstance for catalytic combustion in the eight iron-containing powder;②Due to thedecomposition temperature of CaO2approached the coal pyrolysis, CaO2supports thecoal combustion based on its three effects, including the released oxygen, improving thechar morphology and catalyzing char combustion.To solve the insufficiency understand of the “oxygen transmit theory”, a Firstprinciple study of CaO,-Fe2O3and its derivative-FeO on catalytic combustion basedon density functional theory (DFT) was employed. The storage/transmit oxygen lawwas proposed based on DFT, and the results showed that:①The top of Ca-O bonds ofCaO(001) surface, the oxygen vacancies of Fe2O3(0001) and Fe2O3(1102) surface, andtop of Fe atoms on FeO(001) surface are the catalytic active sites, where have strongability of adsorption of O2result in generation of active oxygen species;②The carboncluster and CO preferentially reacted with these active oxygen species, and the productscould easily desorbed from catalytsts surface;③The reduction of Fe2O3(0001) andFe2O3(1102) surface by C and CO, leading the generation of active oxygen species.Then the catalytic route and discipline of oxygen reserve/transmit were proposed, andoxidation reaction mechanism was analyzed.In order to investigate the influences of applying catalysts on PCI and BFoperations, the catalytic combustion was simulated by using a drop tube furnace (DTF),and variation of structures as well as the reactivity of unburnt chars (UBC) wereexamined. For bituminous, the relative active sequence of catalysts to the burnout ratewas: CaO> Fe2O3> MnO2. For anthracite, it as follows: Fe2O3> CaO> MnO2. Ingeneral, these three catalysts exhibited better catalytic effect on anthracite thanbituminous coal. The catalytic features can be analyzed by these aspects:①Thestructural study shows that a decrease in particle size and surface area of unburnt charsformed form catalytic combustion, implying that the chemical reactions on char particleand pore surface were enhanced greatly by catalysts;②the X-ray diffraction analysisshows that chars became more ordered with catalysts addition. Nevertheless, the TGAand kinetic study results indicates that unburnt chars formed from catalytic combustionstill have a higher reactivity than pure unburnt char, these results imply that the catalytic combustion in PCI operation facilitates the combustion process of pulverized coal inraceway, as well as the following consumption of unburnt char out of raceway.To analysis the catalytic products in the following evolution in BF, the fusion andviscosity were investigated by the FactSage software, and the effect of products on cokeproperties was discussed based on experiment. It can be found that:①Fe2O3and CaOcould decrease the liquid temperature and viscosity below the1.5%of addition in coal;②The coal combustion products has not wettability on the coke surface, however, thecatalytic combustion product could infiltrated in the coke surface;③The reactionbetween UBC and coke is slow, therefore, there was little change on the morphology ofcoke. The pore diameter increased by coal ash, however, the effect only appeared on theentrance of pores and coke surface. The catalytic product could enter into the inside ofcoke, leading to the pore diameter increase.④The reactivity of coke prepared by coalash and UBC was decreased, while the catalytic products increased the coke reactivity,and this effect of Fe2O3is more remarkable than CaO.⑤Based on this results, itshould consider the intrinsic property of PCI and control the addition.Finally, a three component additive and a four component additives weredeveloped by the expand experiment. In the three component additive, the bestproportion of Fe2O3、CaO2and CaO was presented, which has obvious effect on PCIcoal combusion. In addition, when part of Fe2O3was replaced by BOF dust, thecombustion rate was increased by8.94%at the addition content of0.6%. The softwarewas used to forecasting the effect of catalytic combustion on the properties of tuyereand raceway, such as combustion kinetics, temperature, and gas composition. A forecastabout the operating parameter of BF after adopting the technique of catalyticcombustion was presented.To sum up the above results, in this paper, author carried out an exploratoryresearch on the catalytic combustion of PCI coal, and proposed a complex additivewhich is suitable for BF. Moreover, the influence of catalytic combustion on BFoperation was analyzed. These results could give a guidance on the combustionenhancement of PCI.更多还原