石灰石在转炉中的分解与渣化特性及其冶金行为的研究

Energy consumption and environmental problem can not only be eliminated by using limestone instead of lime during BOF steelmaking process, but also the reduction of metallurgical effect caused by the slaking and pulverization of lime can be solved, and its prospect of industrial application is board. In the present proposed project, aiming at the current situation that few related theoretical basis and experimental research have been done, by using the combination of the high temperature experiment with simulation method, a systematic fundamental scientific research is to be carried out based on the metallurgical physical-chemistry, macro-kinetics and transport theory, including the decomposition behavior of limestone in converter and the evolvement rule of its microstructure, dissolution and slagging characteristics of limestone into molten slag, dephosphorization rate and effect of limestone in steelmaking process, oxidation behavior of CO2 generated during limestone decomposition, and analysis on the steelmaking process in converter by limestone slagging. The decomposition and slagging characteristics of limestone inside the melting bath, and the dephosphorization dynamics are to be clarified. Impacting law of CO2 on the compositions of molten steel, molten slag and burner gas is to be mastered. Furthermore, mathematical model of steelmaking in converter with limestone instead of lime will be developed. The research results are to be used as the theoretical basis for the development and application of feasible technics for the slagging in converter with limestone, in order to realize energy conservation and emission reduction, as well as cost decreasing and benefit increasing. The present proposed project is a research work with high scientific relevance and academic value.

采用石灰石替代石灰直接应用于转炉造渣冶炼，不仅可避免石灰煅烧所造成的能源消耗和环境污染，还可解决因烧成石灰潮解粉化所导致的冶金效果降低等问题，具有较好的工业应用前景。针对转炉采用石灰石造渣炼钢尚缺乏系统的理论体系和实验研究之现状，基于冶金物理化学、宏观动力学及冶金传输原理等相关理论，本申请项目拟采用高温实验与模拟研究相结合方法，对石灰石在转炉中的分解行为及其微观结构演变规律、石灰石溶解渣化特性及其动力学、转炉采用石灰石造渣脱磷的脱磷速率和脱磷效果、石灰石分解逸出CO2的供氧行为以及转炉石灰石造渣炼钢过程解析等相关科学问题进行深入系统研究，阐明石灰石在转炉中的分解和渣化特性及其脱磷动力学，掌握分解逸出CO2对熔渣、铁水和炉气成分影响规律，建立转炉石灰石炼钢过程数学模型。研究结果对于转炉采用石灰石造渣炼钢可行性工艺探索及推广应用、以实现炼钢生产的节能减排和降本增效具有重要学术意义和实际价值。

研究了转炉内石灰石原位分解动力学、产物微观结构演变、溶解渣化速率与脱磷效果、以及转炉石灰石造渣炼钢过程定量解析等主要科学问题，可为转炉采用石灰石造渣炼钢可行性工艺探索提供理论依据。转炉熔渣中石灰石分解过程限速环节为CaO产物层导热和界面化学反应联合控制，表观活化能为159kJ/mol。熔渣中石灰石分解速率常数为7.9*10^-4-6.3*10^-3 m/s，CaO产物层导热系数为0.21-2.51W/(m∙K)。石灰石分解产物CaO晶粒尺寸随熔渣温度升高而增大。1300~1400℃时，CaO晶粒度为0.594-0.919μm，CaO层孔隙率为36%-38%，且产物层有宏观裂纹产生。分解过程微观结构演变对石灰石溶解造渣有较大影响。转炉熔渣中石灰石溶解过程分为三个阶段：孕育期(石灰石分解)、中期(石灰石分解与所生成石灰溶解同时进行)及后期(石灰溶解)。中期由溶解反应与边界层扩散传质联合控制，后期仅由边界层扩散传质控制。溶解中期的表观活化能为293-345kJ/mol；溶解后期的表观活化能为116-183kJ/mol。分解产生CO2对中期溶解过程有一定促进作用。随温度升高和熔渣碱度降低，石灰石溶解速率增大，且溶解界面处的CaO-FeO富集带厚度也增加。溶解过程石灰石内部有渗渣带形成。采用石灰石替代部分石灰造渣脱磷时，熔池碳磷选择氧化转换温度约为1360℃。熔池温度高于1360℃时，增加石灰石加入量可降低铁水温度，提高铁水脱磷率。1350℃时，随石灰石替代比增加，石灰溶解速率减小，脱磷率减小；1400℃时，随石灰石替代比增加，石灰石分解吸热可改善脱磷热力学条件，脱磷率增大。 转炉石灰石造渣炼钢过程数学模型定量解析了石灰石替代比对转炉吹炼过程中钢水成分、熔渣组分、熔池温度及炉气成分的影响规律。1kg石灰石可提供0.08kg氧、冷却效果与1.2kg废钢相当。采用石灰石造渣炼钢应适当提高铁水温度及铁水硅含量，促进石灰石快速分解与溶解。随石灰石替代比增加，溶解速率降低，提高熔池温度及氧枪枪位可促进石灰石溶解。石灰石替代比由25%增至50%时，CO2所占供氧比例由10.7%增至19.7%，熔池温降分别为9~49℃与17~104℃，煤气中CO分别升高41%与44%。