生物质替代焦粉铁矿石烧结过程中的碱金属迁移行为

Migration behavior of alkali metals in an iron ore sintering process with the substitution of biomass for coke breeze

通过挥发-冷凝实验装置进行小型烧结实验,运用X射线荧光光谱(XRF)、扫描电镜-能谱仪(SEM-EDS)及电感耦合等离子体发射光谱仪(ICP-OES)等分析检测手段,结合Factsage热力学模拟,对比研究了以木炭和焦粉为燃料,配加含铁粉尘的铁矿石烧结过程中,床层碱金属随烟气挥发迁移的规律、烧结前后的碱金属脱除率以及工艺措施对碱金属脱除的影响.结果表明,K相对于Na更容易被脱除,挥发至烟气中的碱金属化合物主要是KCl,其次为NaCl.增加燃料配比促进了碱金属元素的脱除;在燃料配比相同的条件下,木炭烧结的碱金属脱除效果不及焦粉烧结.烧结过程中,排入废气中的碱金属化合物被下部混合料层大量捕获、吸附,下部床层内捕集的碱金属氯化物促进了碱金属的氯化脱除.添加CaCl2后,以木炭为燃料时K和Na的脱除率高于焦粉工况,且产物中K和Na的含量较低.配合氯化脱除工艺将生物质应用于铁矿石烧结是烧结生产发展的可行方向.

Iron ore sintering is a process in which iron ore powder,flux,iron-bearing dust,solid fuel(such as coke powder),and return fines are mixed in a certain proportion,granulated,and then processed into agglomerates by high-temperature generated by solidfuel combustion,which is an important process prior to blast furnace ironmaking.The iron ore sintering process is an important emitter of atmospheric particles in which alkali metal elements in a sinter bed contribute to the formation of fine particles during combustion,aggravating particulate emissions.Using biomass materials such as charcoal to replace coke in the sintering process can significantly alleviate the emission of both greenhouse gases and pollutants.However,owing to the high content of alkali metals in biomass and their poor combustion characteristics,alkali-metal-related problems inevitably arise.In this study,a small sintering experiment was conducted in a volatilization condensation test facility and analyses were performed based on data obtained by X-ray fluorescence spectroscopy,scanning electron microscopy energy dispersive spectrometer,and inductively coupled plasma-atomic emission spectrometry followed by thermodynamic simulation.The purpose of these analyses was to investigate the laws associated with alkali metal migration and enrichment,removal rate of alkali metal elements,and influence of technological measures on removal process in iron ore sintering using charcoal and coke as fuel with iron-bearing dust added.The results show that K is easier to remove than Na,and the alkali compounds volatilized into a flue gas mainly contain KCl with small amount of NaCl.With the same fuel mass fraction the removal rate of alkali metal in the sintering process using charcoal as fuel is less than that using coke.As the alkali metal compounds in the downstream flue gas migrate,they collide with the raw material particles because of the inertial effect.In addition,owing to the low temperature of the raw materials in the low bed,alkali metal compounds tend to condense and deposit on the particles’surface.During the sintering process,a large number of alkali metal compounds discharged into the waste gas are trapped and absorbed by the low bed,and the alkali metal chloride accumulated in the low bed promotes the removal of chloride from the alkali metal.With the addition of CaCl2,the removal rate of K and Na when using charcoal as fuel is higher than that using coke.Accordingly,the content of K and Na in sintering products with charcoal as fuel is lower than that using coke.The use of biomass as fuel in iron ore sintering in combination with chlorine removal process is feasible and has good prospects.