【作者】 甘敏；

【导师】 范晓慧；

【作者基本信息】 中南大学 ， 钢铁冶金， 2012， 博士

【摘要】 在全球气候变暖、生态环境恶化的时代背景下,钢铁工业节能减排成为当前亟待解决的重点难题。铁矿烧结作为钢铁生产第一道工序,其能耗居钢铁企业第二位,且排放大量含有多种污染物的烟气,是钢铁工业的能耗大户和主要大气污染源。应用清洁可再生的生物质能源替代煤炭类化石燃料进行烧结,其燃烧产生的CO2参与大气碳循环,加之生物质燃料低S、低N的特点,因而可从源头降低烧结CO2、 SOx及NOx的产生,对我国钢铁工业的可持续发展和实现“低碳经济”具有重要的意义。本文针对木质炭、秸秆炭、果核炭等三种生物质燃料,系统研究了生物质燃料的物化性能、微观结构特征及热化学行为,揭示了生物质燃料的基础特性；深入研究了生物质燃料对烧结燃烧前沿、燃料燃烧程度、烧结料层热状态等的影响规律,揭示了生物质燃料影响铁矿烧结的机理；在此基础上开发了强化生物质能烧结的关键技术及基于烟气循环的生物质能烧结新工艺,为生物质能成功应用于铁矿烧结提供理论依据和技术支持。(1)生物质燃料的基础特性生物质燃料的灰分低、挥发分高、孔隙率高、比表面积大,决定了其具有良好的燃烧性和反应性：与焦粉相比,生物质燃料燃烧和气化温度低,反应速度快,反应活化能低；三种生物质燃烧性和反应性的顺序为：秸秆炭>木质炭>果核炭。(2)生物质影响铁矿烧结的规律和机理生物质能烧结特征表明,随着生物质燃料替代焦粉比例的增加,烧结速度加快,但成品率、转鼓强度和利用系数都呈降低的趋势,三种生物质燃料对烧结过程的影响程度从大到小依次为：秸秆炭>木质炭>果核炭,它们替代焦粉的适宜值分别为20%、40%、40%。生物质能烧结实现了污染物减排：秸秆炭、木质炭和果核炭分别取代20%、40%、40%的焦粉时,COx排放分别减少7.19%、18.65%、22.31%,SOx减少31.79%、38.15%、42.77%,NOx减少18.31%、26.76%、30.99%。揭示了生物质影响烧结的机理：生物质燃料燃烧速度快使烧结燃烧前沿速度增加,破坏了燃烧前沿和传热前沿速度的协调性；生物质燃料良好的反应性使烧结过程燃料的不完全燃烧程度增加,降低了燃料的热利用效率；生物质替代焦粉后,烧结料层最高温度降低、高温保持时间缩短。当木质炭替代焦粉比例从0%提高到40%、100%,燃烧前沿速度从34.11mm/min提高到41.67mm/min、46.90mm/min,传热前沿速度保持35.71mm/min不变；燃烧比(CO/(CO+CO2)从12.17%提高到13.08%、14.85%；料层最高温度由1305℃下降到1255℃、1178℃,高温保持时间由2.67min下降到1.83min、0min。(3)强化生物质能烧结的关键技术研究了生物质燃料制备、生物质燃料改性、燃料预制粒、优化配矿等技术强化生物质能烧结。通过两段炭化工艺制备木质炭、果核炭,成型预处理-两段炭化制备秸秆炭,降低了生物质燃料的孔隙率和比表面积；采用液态的硼酸和硅溶胶、固体粉末硼砂和Si02钝化木质炭,降低反应表面积或起物理阻隔作用,都可使生物质燃烧性和反应性降低；采用预制粒技术控制生物质燃料分布在制粒小球内部,通过改善其二次燃烧的条件而提高生物质完全燃烧的程度；通过优化配矿,调控烧结矿熔融区的CaO/Fe2O3摩尔比、Si02含量、Al203含量和MgO含量等化学成分,提高了熔融区液相生成量和针柱状铁酸钙生成量,使烧结物料在较低温度下快速成矿而适合生物质烧结料层温度低、高温时间短的特点。在秸秆炭、木质炭、果核炭分别替代20%、40%、40%焦粉的条件下,上述关键技术都使烧结矿产量和质量不受影响。(4)基于烟气循环的生物质能烧结新工艺依据生物质能烧结和烟气循环烧结对燃料燃烧、料层传热的互补性,提出基于烟气循环的生物质能烧结新工艺。在循环烟气中O2含量15%、CO26%、H2O(g)氐于8%、热风温度150～250℃的条件下,燃烧前沿速度和传热前沿速度趋于一致,并且CO在料层中二次燃烧及烟气带入的物理热使料层温度提高、高温保持时间延长；在非选择性循环比例40%、面积覆盖比为100%,以及选择性循环比例40%、面积覆盖比为44.5%的工艺条件下,生物质替代40%焦粉的烧结指标与100%焦粉的指标相当；生物质能与烟气循环相结合可起到协同减排的作用,在生物质替代40%焦粉的条件下,两种循环方式分别降低COx排放30.04%和31.78%,SOx41.04%和44.51%,NOx42.25%和45.07%。更多还原

【Abstract】 Under the background of global warming and environmental deterioration, reducing energy consumption and pollutant emissions becomes a key issue in iron&steel industry. Sintering is the first procedure of iron&steel production. However, the energy consumption of sintering process ranks second, and the flue gas it emits contains diverse pollutants, so it is the large energy consumption and the main source of air pollution in iron&steel industry. Therefore, replacing fossil fuels with renewable and clean energy of biomass fuels, which is low in N and S content, and CO2participates in carbon cycle of atmosphere, can decrease the generations of COx, SOx, NOx et al. from the source, which is significant to the sustainable development of iron&steel industry and can realize low carbon economy.For such three biomass fuels as woodchar, strawchar and nutchar, their physico-chemical properties, microstructure characteristics and thermochemical behaviors have been studied systematically to illuminate the basic characteristics of biomass fuels in the dissertation. And then the fundamental theoretics of biomass affecting the flame front, the burning degree of fuels and the thermal state of sintering layer have been deeply discussed to reveal the mechanism of biomass fuels affecting sintering. Based on the research stated above, critical techniques to strengthen sintering with biomass fuels and new process of sintering with biomass energy based on flue gas recirculation have been exploited, so as to provide a theoretical basis and technical guidance for applying biomass in sintering successfully.(1) Basic characteristics of biomass fuelsBiomass fuel is low in ash content while high in volatile constituent, porosity and specific surface area, and these properties results to its good combustion and gasification, which perform as lower reaction temperatures, faster reaction speed, and lower activation energy than coke breeze does. The prior order of combustion and gasification is strawchar>woodcharl>nutchar. (2) Laws and mechanisms of using biomass as fuel affecting sinteringThe characteristics of biomass sintering indicate that, with the proportion of biomass replacing coke breeze increasing, vertical sintering speed is accelerated, while yield, tumble index and productivity are decreased. The effects of biomass types on sintering show that the order of affecting degree is strawchar>woodchar>nutchar. The appropriate proportions of three biomass fuels are20%,40%and40%respectively. Biomass replacing coke breeze realizes the pollutant emission reduction of sinter. When the replacement ratios of three biomass fuels are20%,40%and40%respectively, the emission of COx can be decreased by7.19%,18.65%and22.31%, SOx by31.79%,38.15%and42.77%, NOx by18.31%,26.76%and30.99%respectively.Mechanisms of using biomass as fuel affecting sintering were illuminated. The flame front speed is accelerated due to the excellent combustion property of biomass, which will ruin the consistency of heat front speed and flame front speed. Meanwhile, the degree of fuels combustion decreases because of the good reactivity of biomass, which will decrease the thermal utilization efficiency of fuel. In addition, the maximum temperature of sintering layer and high temperature duration time decrease as biomass replacing coke breeze. When the proportion of woodchar replacing coke breeze increases from0%to40%,100%respectively, the flame front speed rises from34.11mm/min to41.67mm/min,46.90mm/min but the heat front speed maintaining at35.71mm/min, and the combustion ratios increases from12.17%to13.08%,14.85%, the maximum temperature of sintering layer decreases from1305℃to1255℃,1178℃, and high temperature duration time decreases from2.67min to1.83min, Omin.(3) Key technologies of strengthening biomass sinteringTechnologies of strengthening biomass sintering with reinforcing the preparation of biomass fuels, modifying the properties of biomass, pregranulation technology of fuels and optimization technology of ore blending have been studied. The use of two carbonization process to strengthen the production of woodchar and nutchar, and the use of molding process combining two carbonization process to strengthen preparation of strawchar can decrease the porosity and specific surface area of biomass, and the use of liquid boric acid and silica sol, and solid powder borax and SiO2to passivate biomass can decrease the reactive suface area or take the action of physical obstruction, which result in lowering the combustion and reactivity of biomass. Taking the pregranulating technology, biomass distributes inside the balls, which can improve secondary combustion and result in increasing the combustion degree. On the base of optimization of ore blending, regulating the chemical compositions of melting zone of sinter, such as the molar ratio of CaO/Fe2O3, the contents of SiO2, Al2O3and MgO, can improve the liquid phase formation and needle-columnar SFCA generation to suit for the characteristics of sintering layer which is low in temperature and short in high temperature duration time. All the above technologies can make strawchar, woodchar and nutchar replace20%,40%and40%coke breeze respectively in the premise of not affecting the indexes of sintering yield and quality.(4)New process of sintering with biomass energy based on flue gas recirculationAccording to the complementary properties of the effect of biomass sintering and flue gas circulation sintering on combustion and heat transfer, the new process of combinating both technologies has been proposed. The results of the effects of circulating gas composition and temperature on biomass sintering show that, the re-consistent of flame front speed and heat front speed can be promoted on the conditions of15%O2content, CO26%, H2O(g) less than8%and150～250℃of circulating gas. And the maximum temperature and high temperature duration time can be improved by CO combustion and the physical heat transfer to the bed. On the appropriate cycling conditions, ie the circulating ratio of non-selective-circulation is40%and the area coverage ratio is100%, and the circulating proportion of selective-circulation is40%and the area coverage ratio is44.5%, the sintering indexes which the proportion of biomass replacing coke breeze is40%are comparative to that of using coke breeze completely. In addition, the emission of COx reduces by30.04%,31.78%, SO, by41.04%,44.51%, and NO, by42.25%,45.07%, which indicates that the combination of biomass sintering and flue gas circulating sintering may play a cooperative effect of energy saving and pollutant reduction.更多还原