【作者】 宋文佳；

【导师】 朱子彬；

【作者基本信息】 华东理工大学 ， 化学工艺， 2011， 博士

【摘要】 煤灰在高温下的熔融性、流动性与流变性对煤气化炉的设计、稳定运行、操作参数的确定以及评价煤种适应性有着重要的意义。相关问题广泛地存在于气化炉的实际操作过程中。本论文利用本课题组自主研发的多气氛灰熔融仪、高温粘度计和高温流变仪及世界著名的热力学软件FactSage、X-射线衍射仪、X-荧光分析仪和电子扫描电镜对我国53种典型煤种中煤灰样的高温特性、化学组分、矿物组成和微观结构进行了系统而深入的研究。在本篇论文中系统研究了化学组分对煤灰熔融温度、临界温度与全液相温度的影响,揭示了不同液相相对含量下对应温度分别与熔融温度和临界温度之间存在的相关性；通过矿物分析、微观结构和元素分析发现了不同气氛对煤灰熔融温度影响的主要原因；利用热力学软件FatSage计算出的热力学数据,建立了多套煤灰高温特性模型用于预测其熔融温度、临界温度和在不同剪切速率下的粘度；系统研究了煤灰高温流变特性,并对其流型进行数学模拟；考察了来自同一煤种的灰烬与灰渣的差异性与相似性,论证了用实验室制得的灰烬预测从真实气化炉中排出灰渣高温特性的合理性。(1)利用多气氛灰熔融仪测定了氧化物CaO、Fe2O3、MgO和SiO2/Al2O3对煤灰熔融温度的影响,并利用热力学软件FactSage计算了添加有上述氧化物后煤灰样品的全液相温度和不同温度下的矿物组成,绘制了不同组分的三元相图。研究结果表明：煤灰样品的熔融温度随上述氧化物含量增加的变化趋势与热力学软件FactSage计算出的煤灰样品全液相温度的变化趋势相似,但计算得到的全液相温度均高于其熔融温度。(2)测定了我国21种煤灰样品在惰性气氛(Ar>99.99 vo1.%)和强还原气氛(H2>99.99 vo1.%)下的熔融温度。研究结果表明：由于在强还原气氛下煤灰样品中熔点较低的氧化铁全部被还原为熔点较高的单质铁,同时煤灰样品在高温下的微观结构由网状结构变为钢架结构使得三角灰锥在高温下不易变形,以上两个因素使得煤灰样品在强还原气氛(H2>99.99 vo1.%)下的熔融温度总是高于在惰性气氛(Ar>99.99 vo1.%)下的熔融温度。(3)利用热力学软件FactSage计算得到的60组人工配灰样品在惰性气氛(Ar>99.99vo1.%)和强还原气氛(H2>99.99 vo1.%)下的全液相温度与样品在这两种气氛下的熔融温度进行线性回归,得到了全液相熔融温度模型,在本模型中充分考虑了煤灰中矿物质对熔融温度影响这一因素,最后利用该模型成功的预测了我国煤灰样品在在惰性气氛(Ar>99.99 vo1.%)和强还原气氛(H2>99.99 vo1.%)中的熔融温度。(4)利用高温粘度计测定了氧化物CaO、Fe2O3、MgO和SiO2/Al2O3对煤灰样品临界温度的影响,比较了由热力学软件FactSage计算得到的不同液相相对含量下对应温度与煤灰样品临界温度的关系。研究结果表明：煤灰样品的临界温度均随着CaO、Fe2O3、MgO和SiO2/Al2O3含量的增加先减小达到最低值而后又增大,呈凹形曲线变化。(5)借助主要化学组分相同的人工配灰样品与煤灰样品在高温下流动特性具有相似性这一特点,利用高温粘度计测定了40组人工配灰样品的临界温度,并将热力学软件FactSage计算出的人工配灰样品在不同液相相对含量下对应的温度与其临界温度进行线性相关性比较,利用相关性最好的模型预测了我国煤灰样品的临界温度。研究结果表明：人工配灰样品在高温下的临界温度与热力学软件FactSage计算得到的不同液相相对含量对应的温度的线性相关性随着液相相对含量的增加在不断增加,其中人工配灰样品的全液相温度与其临界温度的线性相关性最好(R>0.900),同时具有良好的精度(σ=29℃),获得的全液相临界温度模型也成功的对我国煤灰样品的临界温度进行了很好的预测性。(6)利用高温流变仪测定了我国45种煤灰样品在不同固体结晶粒子相对含量和不同剪切速率下的粘度,利用热力学软件FactSage计算了煤灰样品的全液相温度、在不同温度下煤灰样品中固体结晶粒子的相对体积含量和矿物组成,根据煤灰样品在不同温度下固体结晶粒子的相对体积含量的不同,将其粘温曲线图进行分段模拟。研究结果表明：对煤灰样品在高温下形成的熔渣中的固体粒子体积相对含量分别为0 vo1.%、0-10.00vo1.%和10.00-40.00 vo1.%三个区间段的粘度分别进行模拟,得到的高温粘度模型可以很好的预测我国煤灰样品高温粘度,其中多数煤灰样品高温粘度的实验值与预测值的绝对差值在实验误差范围之内。(7)利用高温流变仪测定了煤灰的高温流变特性,研究了温度对煤灰流型的影响,剪切速率对粘度的影响,以及温度对煤灰屈服应力的影响。研究结果表明：当温度高于煤灰的全液相温度时,煤灰的流型均表现为牛顿型流体,然而随着温度的降低,固体结晶粒子的不断析出,其流型变为Bingham流体、Casson流体和Herschel-Bulkley流体,同时随着固体结晶粒子相对含量的增加,煤灰样品在高温下剪切稀化现象越来越明显,同时煤灰样品的屈服应力也随着温度的降低在不断增加。(8)利用多气氛灰熔融仪和高温粘度计研究了来自同一煤种经实验室制的灰烬与经气化炉直接排出灰渣的高温熔融性与流行性的差异性与相似性。研究结果表明：取白同一煤种的灰烬与灰渣的化学组分与物相结构有一定的差异性,其中灰烬中的主要氧化物A12O3和Fe2O3与微量氧化物TiO2、Na2O、K2O和SO3均高于灰渣,同时灰烬的物相结构为晶态特征,而灰渣为非晶态特征,并且在灰烬的微观结构中颗粒是成团聚状,而灰渣中的颗粒无团聚呈几何形分布,灰烬的熔融温度与临界温度总是高于灰渣,同时灰烬粘度滞后性比灰渣的更加明显,但两者在高温下的差异性均在气化炉操作条件浮动范围内,同时助熔剂对灰烬与灰渣的高温熔融性与流动性的影响是相似的,因此利用实验室制的灰烬可以较好的反映从气化炉中排出灰渣的高温熔融性与流动性。更多还原

【Abstract】 The development of next generation of coal fired power stations using integraed gasification-combined cycle addressed a number of problems concerning the increase of emissions of greenhouse gases, sulphur dioxide, nitrogen oxides and particulates from pulverised coal fired power stations. In entrained flow gasifiers the coal ash should be liquid and fluid enough to be tapped. The fusiblity, flow charactersitics and rheological properites of the molten coal ash are, therefore, very important factors affecting the gasification regimes and operating costs. It is, therefore, important to study the properties of coal ash at ultra high temperature for selection of coals, flux additions and coal blending to optimise industrial operations, and to reduce operating costs. In this work, we studied the fusibility, flow characteristic and rheological properties of various ashes derived from fifty-three Chinese coal ash at the ultra high temperature. The Chemical analysis, mineralogical analysis, microstructural analysis, and the other physical properties at high temperature were ananlzed with X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), fusion temperature furance, the high temperature rotational viscometer, the high temperature rheometer, and thermodynamic software package FactSage. The effect of chemical composition on ash fusion temperature, the temperature of critical viscosity, and liquidus temperature of coal ash samples were systematically studied. The main contents are listed as follows:(1) The ash fusion temperatures (AFTs) of coal mineral matter at high temperature are important parameters for all gasifiers. Experiments have been conducted in which mixtures of selected coal ashes and SiO2, Al2O3, CaO, Fe2O3, MgO were subjected to the standard test for ash fusibility. The computer software package FactSage has been used to calculate the liquidus temperatures of coal ash samples and the proportions of the various phases present as a function of temperature. The results show that the AFTs of coal ash samples first decrease with increasing CaO, Fe2O3, and MgO contents, then reach a minimum value, before increasing again. However, for the effect of S/A ratio, its AFTs are always increased with increasing S/A ratios. The measured AFTs all show variations with mixture composition that correlated closely with liquidus temperatures for the appropriate pseudo-ternary phase diagrams. The liquidus and AFTs generally showed parallel compositional trends, but are displaced from each other because of the influence of additional basic components in the coal ash. The liquidus temperatures of coal ash samples are always higher than its AFTs.(2) The ash fusion temperatures of twenty-one typical Chinese coal ash samples were measured in Ar and H2 atmospheres. Since the iron oxides in coal ash samples fused under a H2 atmosphere are reduced to metallic iron, and lead to changes of mineral species and micro-morphology, the AFTs in a H2 atmosphere are always higher than those with an Ar atmosphere.(3) The computer software package FactSage was used to calculate the temperatures corresponding to different proportions of liquid phase and predict phase the equilibria of and sixty synthetic ash samples. Empirical liquidus models were derived to correlate the AFTs under both Ar and H2 atmospheres of sixty synthetic ash samples with their liquidus temperatures calculated by FactSage. These models were used to predict the AFTs of twenty-one Chinese coal ash samples in Ar and H2 atmospheres and then the AFT differences between the atmospheres was analyzed. The results show that for both atmospheres, there was an apparently linear correlation and good agreement between the AFTs of synthetic ash samples and the liquidus temperatures calculated by FactSage (R> 0.89,σ<30℃). These models predict the AFTs of coal ash samples with a high level of accuracy (SE<30℃).(4) The viscosity and the temperature of critical viscosity values of eighteen synthetic slag samples formed from mixtures of five oxides (SiO2, Al2O3, CaO, Fe2O3, and MgO) have been measured. Moreover, the effects of these oxides on the temperature of critical viscosity values and the microstructure seen in metallurgical microscopy of synthetic slag samples have been analyzed. The computer software package FactSage has been used to calculate the temperatures corresponding to different proportions of liquid phase of synthetic slag samples. The results show that the temperature of critical viscosity values of synthetic slag samples decrease with increasing CaO, Fe2O3 and MgO contents and with increasing SiO2/Al2O3 ratio (named S/A ratio), then reach a minimum value, before increasing again. These curves are similar to the variations in the temperatures corresponding to liquid phase contents> 80.00 wt.% seen with increasing contents of these oxides and with an increase in the S/A ratio. Moreover, most of the temperature of critical viscosity values of the synthetic slag samples lie between the temperatures corresponding to liquid phase contents of 80.00 wt.% and 100.00 wt.%, respectively.(5) The temperatures of critical viscosity of eight coal ash samples and forty synthetic ash samples have been measured. The computer software package FactSage has been used to calculate the temperatures corresponding to different proportions of liquid phase of synthetic ash samples. Empirical liquidus model has been derived to correlate the temperature of critical viscosity of the forty synthetic ash samples with their liquidus temperatures calculated by FactSage. The liquidus model was then used to predict the temperature of critical viscosity of the eight coal ash samples. The results show that there was an apparently linear correlation and good agreement between the temperature of critical viscosity of the synthetic ash samples and the liquidus temperatures calculated by FactSage (R> 0.900,σ< 30℃). This model predicts the temperature of critical viscosity of coal ash samples with a high level of accuracy. Meanwhile, the temperature of critical viscosity is a result of many complex factors; hence, the adequacy of liquidus model in the paper is limited by a range of conditions.(6) The viscosities of forty-five coal ash samples at high temperature have been measured under different temperatures and shear rates. The computer thermodynamic software package FactSage has been used to predict liquidus temperatures, volume fractions of crystallized solid particles (φ), and the compositions of remaining liquid phase for 45 coal ash samples. The flow properties of completely liquid and partly crystallized coal ash samples have been predicted by three viscosity models. The Urbain formalism has been modified to describe the viscosities of fully liquid slag and homogeneous remaining liquid phase in coal ash samples. The modified Einstein equation and Einstein-Roscoe equation have been used to describe the viscosities of heterogeneous coal ash samples ofφ<10.00 vol.% andφ≥10.00 vol.%, respectively. These three models provided a good description of the experimental data of fully liquid and heterogeneous coal ashes samples. The new models also predicted flow properties of mixtures of coal ashes with CaO, Fe2O3, MgO, SiO2, and Al2O3.(7) The rheological characteristic of two coal ash from entrained gasifiers at high temperature was studied. Slag samples have been analyzed by X-ray fluorescence, X-ray diffraction, and scanning electron microscopy. The rheological behavior of the slag has been investigated experimentally using a high-temperature rheometer at temperatures. The effects of the shear rate and temperature on the rheological behavior of the slags have been explored. Moreover, the observed rheological behavior of the slag has been correlated with its solid-phase content, as calculated with the aid of the computer software package FactSage. The results show that the sensitivity of the slag viscosity to temperature decreases with increasing rotation speed. Above its liquidus temperature calculated by FactSage, the slags behave as a Newtonian fluid; below its liquidus temperature, however, the rheological behavior of the slags becomes non-Newtonian owing to its increased solid-phase content. Meanwhile, Slags containing a number of crystalline particles shows dramatic shear-thinning and thixotropic behavior. Moreover, the shear-thinning behavior of the slags becomes ever more distinct as the temperature is decreased. The yield stress values of the slag and the number and particle size of the crystalline particles in the slag increase with decreasing temperature.(8) The physical properties of ash and slag were analyzed with X-ray fluorescence, X-ray diffraction and scanning electron microscopy. The fusion temperature and the experiment viscosity were measured for the ash and slag with the addition of fluxing CaO. Ash and slag have properties that were approximated by the SiO2-Al2O3-FeO-CaO system. The computer software package FactSage was used to predict the proportion of solid phase and the mineral phase formed as a function of the composition and the temperature of the SiO2-Al2O3-FeO-CaO system. The results show that the fusion temperatures and the temperature of critical viscosity (Tcv) of ash are always higher than that of slag. Also, the viscosity of ash is always higher than that of slag at the slag tapping temperature range of 1400-1500℃, and the hysteresis between the heating and cooling cycles for ash is more obvious than that of slag because of different physical properties. The fusion temperature and Tcv of ash and slag decrease with increasing CaO content, whereas those values increase rapidly with CaO content higher than 35%. Also, the sensitivity of the viscosity of the ash and slag with temperature decreases with increasing CaO content because the sensitivity of the phase equilibria of in the SiO2-Al2O3-FeO-CaO system to temperature excursions decreases with increasing CaO content.更多还原