【作者】 林伟宁；

【导师】 于广锁；

【作者基本信息】 华东理工大学 ， 化学工艺， 2011， 博士

【摘要】 气流床煤气化技术具有煤种适应性广、操作压力和操作温度高、碳转化率高、生产强度和规模大等特点,已成为煤基大容量、高效洁净的燃气与合成气制备的首选技术。水冷壁气化炉是气流床气化技术的重要类型,具有运行寿命长、维护费用低等优势,是气流床气化技术的发展方向。因此,对气化炉水冷壁技术进行研究具有重要意义。(1)基于实验室小型水冷壁气流床气化炉,以北宿煤为原料进行粉煤气化试验,考察气化炉内的熔渣沉积情况,并对附壁渣层的表面形态及组成进行分析研究。北宿煤灰分中碱性氧化物含量较高,灰熔点相应较低。气化渣样的XRD分析结果显示,气化过程中生成了熔点较低的复杂共熔体钙长石及磁赤铁矿。渣层形态与气化炉内的温度分布特征密切相关,总体上讲,渣层表面粗糙度随温度降低而增大。(2)神府煤灰渣的CaO含量相对较高,具有较低的熔融温度。试验条件下采用神府煤灰渣进料可以改善炉内结渣状况。气化过程中,渣层表面区域的煤渣处于熔融状态,形成液态渣层；渣层中存在大量气孔,气体受热膨胀,导致熔融的渣层发生变形、凸起,气体逸出后,该处渣层发生坍塌。气化渣样主要由钙长石、透辉石及钠长石组成,其孔隙率为36.6%。(3)建立气化炉水冷壁传热模型,采用有限元法对水冷壁的温度场进行模拟计算。气化炉正常运行状况下,采用稳态法可对水冷壁中的温度分布进行较为准确地预测,而气化炉变工况时,采用瞬态法的模拟结果则更为准确。水冷壁中的温度分布与材料的导热系数密切相关,导热系数较小的材料中存在较大的温度梯度。渣钉、水冷管及鳍片中的最高温度随渣层表面温度的升高而升高,随工质对流给热系数的增大而降低,而工质温度的影响并不明显。工业气化炉水冷壁传热稳态分析结果显示,水冷壁锥段抽出管附近区域的鳍片冷却效果较差,温度相应较高；对水冷壁结构进行优化、增设水冷管后,鳍片中的最高温度显著下降。(4)建立水冷壁热应力模型,对气化炉变工况水冷壁的应力场进行研究。升温阶段渣层中的热应力主要表现为压应力,而降温阶段则主要表现为拉应力。渣层的最大热应力随导热系数、孔隙率的增大而减小,随弹性模量、热膨胀系数、渣层厚度的增大而增大,渣层密度、比热的影响并不显著。初始固态渣层与新生固态渣层中的等效应力分布及其变化趋势均存在显著差异；初始固、液接触面处等效应力不连续分布。含裂纹的渣层中热应力的最大值出现在裂纹尖端,在裂纹尖端附近区域存在较大的应力梯度,而距裂纹尖端稍远处,应力梯度较小。裂纹尖端的应力强度因子与渣层温度分布、裂纹特征尺寸及断裂面与渣层表面法线夹角密切相关。当裂纹尖端的应力强度因子大于渣层的断裂韧性时,裂纹失稳扩展,且扩展具有定向性。(5)建立水冷壁冷却工质流动与传热模型,对冷却工质的水力特性进行研究。分配集箱中沿流向工质速度逐渐降低,静压逐渐升高。汇集集箱中沿流向工质速度逐渐增大,静压总体呈降低趋势。与集箱进口距离较远的冷却管的进、出口压差相对较大,因此具有较高的质量流量。缩小冷却管直径、增大管间夹角均可减小却冷管间流量差异,改善工质不均匀性。随集箱入口速度的增加,工质的不均匀性加剧。而在不发生相变的情况下,改变入口工质的温度对其不均匀性无显著影响。更多还原

【Abstract】 Entrained-flow gasification has become the preferred, efficient and clean technology for coal-based large-scale gas and syngas production due to its advantages, such as insensitivity to coal type, high operating pressure and temperature, high carbon conversion, high production intensity, large scale, etc. As one of the most important types of entrained-flow gasifier, membrane wall gasifier has the advantages of long service life and low maintenance cost, and hence, it has become the development tendency of entrained-flow gasification. Consequently, it is of great significance to study on the technology of membrane wall.(1) Gasification experiments were performed in a bench-scale membrane wall entrained-flow gasifier using Beisu coal and the slag deposition was studied. The surface morphology and composition of the slag layer were also investigated. Beisu coal ash has a low fusion temperature for its high alkaline oxide content. According to the XRD result, anorthite and maghemite generated during the gasification. The morphology of slag layer is strongly related to the temperature distribution in the gasifier. In general, the surface roughness of slag layer increases with the decrease of temperature.(2) Shenfu coal ash has a low fusion temperature due to its high content of CaO. The slagging in the gasifier is improved by using Shenfu coal ash as feed stock. During the gasification, a liquid slag layer was formed by molten slag over the solid slag layer. A large amount of pores were observed in the molten slag, and gas in the pores expanded with the increasing temperature, which resulted in the deformation of the molten slag layer. The bumped slag layer collapsed after the gas released from it. The slag sample mainly consists of anorthite, diopside and albite. The porosity of slag is 36.6%.(3) A heat transfer model of membrane wall was established and the temperature field was simulated using FEM. Under stable operation condition, the temperature distribution in the membrane wall can be accurately predicted with static method, while transient analysis gives more accurate results for variable conditions. The temperature distribution is closely related to the conductivities of materials. Great temperature gradient is observed in the material with a low conductivity. The maximum temperatures of stud, cooling tube and fin increase with the increase of slag surface temperature, while decrease with the increasing convection coefficient of working fluid. The effect of working fluid temperature on the maximum temperatures is insignificant. The static simulation result of an industrial membrane wall gasifier shows that the fin temperature in the region near the draw-out tube is higher for the poor cooling effect there. The maximum temperature obviously decreases after structure optimization by adding a cooling tube outside.(4) A thermal stress model of membrane wall was developed for the stress field study. The thermal stresses of the slag layer act as compressive stresses during temperature rising process, while tension during the cooling process. The maximum of thermal stresses decreases with the increase of conductivity and porosity, but increases with the increase of Young’s module, thermal expansive coefficient and slag thickness. The density and specific heat of slag have unconspicuous effects on the maximum thermal stresses. Both distribution and variation of thermal stresses are obviously different between the initial solid slag and the slag solidified, and the thermal stresses are discontinuous at the initial interface. For the slag layer with cracks, the maximum thermal stress is observed at the crack tip. There are great stress gradients in the region near the crack tip, while small gradients in others. The stress intensity factor of the crack tip has close relation with temperature distribution, feature size of crack and the angle between the crack face and the normal of slag surface. As the value of stress intensity factor exceeds fracture toughness of slag layer, the crack develops directionally.(5) A flow and heat transfer model of working fluid was built for the analysis of hydraulic characteristics of the membrane wall. The working fluid velocity gradually decreases along flow direction in the distribution header with the increase of static pressure. In the collection header, the velocity of working fluid gradually increases along flow direction, while the static pressure decreases in the same direction. Higher inlet-outlet pressure drop and flow rate are observed in the cooling tube which is farther from the header inlet. The maldistribution of working fluid can be reduced by diminishing the cooling tube diameter and enlarging the angle between the adjacent tubes. The maldistribution is enhanced by increasing the inlet velocity of working fluid. Changing the inlet temperature of working fluid has negligible effect on its maldistribution.更多还原