生物质炭复合团块在高炉中的反应行为

Reaction behavior of the biochar composite briquette in the blast furnace

研究了生物质复合团块在高炉中的反应行为,该复合团块主要成分(质量分数)为:11.1%C、72.7%Fe_(3)O_(4)、11.25%FeO、0.77%Fe和4.67%脉石.并对高炉环境下复合团块的反应行为进行了建模,通过高炉气氛下的等温动力学实验确定模型参数并进行了模型验证.进一步,结合模型模拟,模拟高炉环境的实验和团块微观结构分析,对模拟高炉条件下和实际高炉条件下团块的反应行为进行了分析.研究结果表明:模拟高炉条件下,在60 min(973 K)到120 min(1273 K)期间,团块的微观结构发生明显变化,其微观结构由渣相网络结构向金属铁网络结构转变.在实际高炉中,复合团块的反应进程主要包括三个阶段:团块的高炉煤气还原(473~853 K)、团块的高炉煤气还原和部分自还原(853~953 K)以及团块的完全自还原(953~1150 K).在团块自还原参与阶段,与烧结矿相比,团块内氧化铁还原速率更快;与焦炭相比,团块内生物质炭气化速率更高.同时,在此阶段,团块有提高高炉煤气利用率和降低高炉热储备区温度的作用.

Blast furnace(BF)ironmaking is considered to be the most popular technology to meet the increasing steel demand worldwide,but it is responsible for the most CO_(2) emissions in the blast furnace-basic oxygen furnace production process.The utilization of biomass/biochar in BF ironmaking is an effective countermeasure to reduce its CO_(2) emission,as biomass/biochar is a renewable carbon source and environment neutron.Charging the biochar composite briquette(BCB)is a convenient method to introduce biomass/biochar into BF.The present research investigates the reaction behavior of the BCB in the BF.The BCB for the BF was prepared using cold briquetting followed by low-temperature heat treatment.The BCB was composed of 11.1%carbon,72.7%magnetite,11.25%wustite,0.77%metallic iron,and 4.67%gangue(all in mass fraction).The BCB reaction model in the BF was developed considering the step-wise gaseous reduction of iron-oxide particles,CO_(2) gasification of biochar particles,internal gas diffusion in the BCB,and mass transfer between the BCB and the environment.Isothermal BCB reaction tests were conducted for model validation.Using the model,the changes of the BCB iron-oxide reduction fraction and biochar conversion rate and the BCB microstructure evolution under simulated BF conditions were analyzed.The model was also applied to predict the change of the BCB iron-oxide reduction fraction,change of the BCB biochar conversion,change of the BCB CO generating rate,and change of the BCB CO_(2) generation rate along a solid flowing path near the mid-radius in an actual BF.Results showed that under simulated BF conditions,the BCB underwent fast self-reduction and structure changes(forming low-melting compounds and transforming from the slag matrix to the iron network)from 60 min(973 K)to 120 min(1273 K).In an actual BF,the BCB reaction route is mainly divided into three stages:(1)reduction by BF gas(473-853 K),(2)reduction by the BF gas and partial self-reduction(853-953 K),and(3)full self-reduction(953-1150 K).In the stages involving BCB self-reduction,the iron oxide in the BCB reduces faster than the sinter,and the biochar gasifies faster than the coke.Moreover,in these stages,the BCB has the functions of increasing the BF gas utilization efficiency and lowering the temperature level of the BF thermal reserve zone.