【作者】 赵永椿；

【导师】 张军营； Mercedes D.S.； 郑楚光；

【作者基本信息】 华中科技大学 ， 热能工程， 2008， 博士

【摘要】 煤炭是我国主要能源资源,大量煤炭的消耗对环境造成了严重的污染,汞、砷、铬等重金属和飞灰颗粒物的排放已对人类健康造成了巨大的危害。矿物质是煤的重要组成部分,其在燃煤过程中迁移转化行为对煤炭的安全有效利用和污染物的排放有着重大甚至决定性的影响。由于煤中矿物组分的复杂性,传统的经典燃烧学理论已很难准确深入的揭示其转化过程,因此,采用各种新兴的研究方法和技术手段系统研究矿物质演化过程已成为本领域目前研究的热点问题之一。本文以飞灰形成过程中矿物质的迁移转化为主线,将矿物学和煤岩学相关理论融入到经典燃烧学中,综合利用磁选、筛分、浮沉实验等分选方法对飞灰进行了系统分选处理,结合X射线衍射矿物定量分析、场发射扫描电镜结合X射线能谱、X射线荧光探针分析等对飞灰中主要的、典型的单组分高铝灰（铝质）、高钙灰（钙质）和磁性灰（铁质）颗粒的物理化学特性、微区结构特征和形成演化过程进行了详细的研究;建立了矿物定量熔融热分析方法,分析了矿物演化对灰熔融和颗粒物形成的影响:探讨了不挥发性元素铬和半挥发性元素砷与矿物的相互作用机制;调查了易挥发性元素汞与飞灰中各组分的相互作用机制,建立了飞灰吸附汞的动力学模型,为廉价飞灰脱除烟气中汞的技术奠定了理论基础。通过系统的沉降炉实验,分析了典型铝质矿物的转化规律,综合运用热分析、矿物学和晶体学等多学科理论,揭示了矿物晶格转变对超细颗粒物形成的影响,建立了微观晶体学结构特征与宏观颗粒物排放的关联和关系。勃姆石脱水形成γ-Al₂O₃,随着温度升高γ-Al₂O₃转化为过渡态θ-Al₂O₃,θ-Al₂O₃微晶在高温下形核长大形成α-Al₂O₃,随着温度的进一步升高,α-Al₂O₃进一步长大粗化,形成约100nm的小晶粒;α-Al₂O₃微晶的粗化长大对0.7μm左右的亚微米细颗粒的形成有重要影响。采用低温灰化、高温煅烧、热重分析研究了含钙矿物的迁移转化,揭示了不同钙质组分的形成演化机制;钙氧化物相主要源于煤中含钙碳酸盐的分解;钙硅铝酸盐相组成复杂,主要源于内在矿物的融合凝并以及外在含钙矿物与外在硅铝质矿物的烧结;钙硫酸盐相和Ca-S-X相是含钙矿物的自脱硫产物;外在含钙矿物易形成钙硫酸盐相;而内在含钙矿物易形成Ca-S-X相;Ca-S-X相主要源于脱硫产物CaSO₄与硅铝质的结合。综合采用HSC软件热力学和动力学模型计算预测了不同形态典型矿物的迁移转化行为,基于已有的动力学参数对单个黄铁矿颗粒的分解、氧化进行了全过程模拟,详细分析了铁质组分的演化机制,从理论上揭示了含铁矿物易沉积的主要原因;外在含铁矿物在燃煤过程中大都直接氧化形成铁氧化物相;内在含铁矿物与其他内在矿物在高温下熔合形成含Fe、Al、Si的复杂的玻璃相,玻璃相的化学组成主要取决于单个煤颗粒中内在含铁矿物与粘土矿物的含量比例。结合低温灰化X射线衍射矿物定量分析和经典热分析理论,发展了一种矿物熔融动力学方法,计算获得了矿物熔融曲线,与常规煤灰熔融性测定方法测出的灰熔点相比,采用该方法计算的灰熔融特征曲线能更好地反映灰熔融变化规律;揭示了煤中矿物熔融多阶段反应过程,从理论上证明了矿物熔融是逐渐加剧的过程。分析了矿物迁移转化对灰熔融的影响,揭示了灰熔融对颗粒物形成的影响。以典型高砷煤和高铬煤为研究对象,系统研究半挥发性重金属元素砷和不挥发性元素铬在煤燃烧后飞灰颗粒的富集行为及其与矿物组分的相互作用。煤中砷、铬的赋存形态对其在飞灰中的富集分布有重要影响;灰中主要元素钙、铁对重金属元素的迁移转化有重要影响。将煤岩学相关理论应用到飞灰颗粒分类,构建了飞灰碳质有机岩相组分的分类方法,并采用固定床反应系统调查了飞灰与汞的作用机制,分析了飞灰脱汞能力的影响因素,揭示了不同飞灰碳颗粒类型脱汞能力的差异;飞灰捕获汞能力与LOI含量并无明显关联,各向异性碳颗粒尤其是多孔网状结构碳含量是决定飞灰脱汞能力的主要因素;烟气中汞浓度、烟气流量、温度等反应工况对汞的捕获和氧化有重要影响;计算了三种动力学机理模型的动力学参数,分析调查了飞灰吸附Hg⁰速率的控制机理,化学吸附是飞灰吸附汞的主要机理;揭示了飞灰对汞的氧化反应机制,识别了飞灰与汞作用的四类活性位,即:低能催化氧化活性位FA①、催化氧化活性位FA②、吸附活性位FA③和高能吸附活性位FA④;飞灰对汞的氧化机制以Mars-Maessen机制为主,无机组分中活性晶格氧是Hg⁰氧化的重要的氧化剂。全文系统的分析了燃煤典型矿物演化成灰机制,从单矿物入手深入系统的揭示了煤燃烧过程中颗粒物的形成机理,发展了基于矿物定量熔融热分析方法,阐述了灰熔融动力学机理;探讨了重金属与矿物组分的作用机制,并揭示了飞灰对汞的吸附氧化机理,为廉价燃煤污染物联合脱除控制技术开发奠定了基础。更多还原

【Abstract】 Coal is the mainly energy source in China, huge amount of coal utilization cause serious pollution to the environment. Especially for the emission of mercury and particulate matter which have caused damage to human health. Mineral matter is the mainly composition of the coal, the partition and transformation of minerals during coal combustion are responsible to the safe utilization and pollutant emission. The transformation process of mineral during coal combustion is still not well understood because of the complex mineral composition in coal. More and more novel methods and techniques are using to study the mineral partition.The object of the thesis is to clarify the transformation mechanism of minerals and trace elements during coal combustion. At the first, magnetic separation, seizing, and float-sinking procedures were used to separate the fly ash. X-ray diffraction, field scanning emission microscopy combine energy dispersive spectroscopy and X-ray fluorescence were used to analyze the physical-chemical characteristics and microstructures evolution mechanism of high aluminum fly ash, high-calcium fly ash, and ferrospheres. A mineral melting thermodynamic simulation method was developed to analyzer the influence of mineral transformation on ash melting and particle formation. The interactions of trace elements arsenic, chromium and mineral elements were studied, the capture and oxidation of mercury by fly ash was investigated, a mercury adsorption dynamic model was developed, which provide basement for pollution control in coal-fired power plants.The transformation of typical aluminum minerals in high temperature was investigated by systematic drop tube furnace （DTF） experiments and thermo gravimetric analysis. The phase transformation of boehmite in coal during high temperature treatment is undergone four stages include: boehimte dehydroxylation, transition phaseθ-Al₂O₃ formation, crystal nucleation andα-Al₂O₃ formation, and growth ofα-Al₂O₃ crystal. The DTF experimental results indicated that the growth ofα-Al₂O₃ crystal has significant impact on PM₁ emission. Mineralogy, crystallography and other multi-disciplinary theories were combined to reveal the influence of mineral lattice changes on the formation of ultra-fine particles, and establish the relationship of micro crystal structure and macro PM emission. Besides, lower temperature ashing, high temperature thermal gravimetric analysis was conducted to describe the formation mechanism of different calcium-bearing compounds. Calcium oxide phase is mainly derived from the decomposition of excluded calcium-bearing mineral, while calcium aluminosilicate phase is formed by the fusion of included calcium-bearing minerals. And both of calcium sulphate phase and Ca-S-X phase are the self-desulphurization production of calcium-bearing mineral, calcium sulphate phase is formed by the excluded calcium-bearing minerals easily; while Ca-S-X phase may derive from the fusion of included calcium-bearing minerals’ self-desulphurization production and other minerals in coal. Then, thermodynamic calculation software HSC was used to calculate and predict the transformation of different mineral speciation during coal combustion. A kinetic model for describing single pyrite partition during coal combustion was developed. The partition process of iron-bearing mineral was studied and the influence factors on pyrite oxidation and sulfur release were discussed. The results show that pyrite particle can rise to the eutectic point in a short time in furnace, excluded iron-bearing minerals oxidized to form ferro-oxides, included iron-bearing minerals mixed with other minerals to form complicated Fe-Al-Si solid solutions, the transformation processes of Fe-bearing minerals were related to temperature, atmosphere, and the occurrence of Fe-bearing minerals. The formation of Fe²⁺ intermediate products and Fe-S-0 eutectic ash particles were the important sources of the initial layer which occur in deposits formed in coal burning systems. Based on the X-ray diffraction mineral quantitative analysis of low temperature ash and classical thermal analysis theory, a mineral melting dynamic method （MQRLSTA method） was developed to calculate mineral melting curve. Compared to the ash melting points measured by conventional methods, the mineral melting curve calculated using MQRLSTA method can reflect the melting process better. Mineral melting characteristic curves indicated mineral melting is multi-stage reaction process. The influences of mineral evolutions on ash melting and particle formation were described.With the aim of better understanding partition of semi-volatile trace element arsenic and non-volatile element chromium, combustion of two kinds of high-arsenic coals and high chromium coals was studied in a bench-scale drop tube furnace （DTF）. The occurrences of arsenic and chromium in coal have significant effects on their enrichments on particles. The distribution of mainly mineral elements calcium and iron in the particles is also an important influence factors for the emission of trace elements during coal combustion. Petrography classification standard was applied to distinguish fly ash carbon, systematic experiments of fly ash capture mercury were conducted on a fixed-bed reactor to investigated the interaction between fly ash and mercury, the results imply that the carbon content is not the only variable that controls mercury capture in fly ashes, there are likely to be significant differences between the mercury-sorbing capacities of these various carbon forms. Hg capture capacity mainly depends on the content of anisotropy carbon particles with porous network structure. Compared to the organic carbon, the inorganic composition has less influence on Hg capture capacity of fly ash. Temperature, flow and Hg concentration in flue gas and other conditions has significant effect on Hg capture and oxidation. Three dynamic models were used to calculate mercury adsorption on fly ash, the oxidation mechanism was clarified. The reaction mechanism of mercury oxidation by fly ash is mainly Mars-Maessen reaction, the lattice oxygen in inorganic component of fly ash is the mainly oxidant.In summary, the evolution mechanisms of typical minerals in coal have been revealed; a mineral melting dynamic analysis method has been established, which would provide a theoretical basis to study mineral ash deposition in-depth. The interaction of mineral, fly ash, and trace elements is helpful for cheap pollution emission control technology development.更多还原