【作者】 梁钦锋；

【导师】 王辅臣；

【作者基本信息】 华东理工大学 ， 化学工艺， 2010， 博士

【摘要】 水冷壁气流床气化炉是大型煤气化技术发展的主要方向之一。水冷壁采用“以渣抗渣”原理,利用渣层保护水冷壁不受高温侵蚀,气化炉内的熔渣沉积和传热与气化炉操作温度、煤灰理化性质等密切相关。本文以水冷壁气流床气化技术为背景,研究了扩散火焰形态及气化炉内熔渣沉积与传热规律。(1)气化火焰是气流床气化炉的主要特征之一,气化火焰形态和特征影响炉内温度分布,火焰形态学是火焰研究的一个重要方向,本文通过研究发现,敞开空间下空气中氧气对扩散火焰形态有一定影响,但随着喷嘴自身携带氧气流量增大,扩散火焰整体形态转为受喷嘴氧气控制；采用多股射流组合的集束喷嘴有效强化了燃料与氧气的混合,扩散火焰绝对长度较两通道喷嘴火焰长度短；气流速度较低时,两通道气流式雾化喷嘴火焰形态与燃料初次雾化有关,热态与冷态下液体初次雾化规律相似,但燃烧过程中的初次雾化临界速度较冷态时高；撞击火焰在撞击前仍较好地保持着火焰湍流结构,撞击后火焰湍流结构迅速消失,随着撞击速度的增大,火焰撞击区域变大且不稳定,但单股火焰的分布更为均匀和连续；撞击火焰边缘具有分形特征,撞击火焰的分形维数在点火阶段逐渐降低,从两喷嘴向四喷嘴撞击过渡时火焰边缘曲线分形维数逐渐增大,随着操作负荷增大,分形维数增大,两喷嘴和四喷嘴撞击火焰分形维数相差逐渐减小(2)通过水冷壁气化炉小试和中试研究发现,熔渣沉积形态与气化炉流场结构、操作温度和煤灰理化性质等因素相关,水冷壁表面均能覆盖渣层,能有效保护水冷壁不受高温烧蚀,随着气化炉处理负荷的增大,气化炉内温度梯度减小,熔渣分布更为均匀；随着水冷壁单位面积处理负荷增大,水冷壁带走热量比例显著降低,煤粉流量、氧煤比和汽包压力等参数对水冷壁传热的影响程度各不相同。(3)建立水冷壁传热和应力模型,基于该模型分析了水冷壁结构温度和应力分布,计算结果与试验吻合良好,为进一步掌握气化炉水冷壁传热规律与渣层裂缝生成提供指导。计算结果表明,渣层内温度梯度大,可有效降低水冷壁结构内部温度；操作温度变化将导致水冷壁内部产生热应力,不同材料热应力差异显著,越接近渣层表面,热应力越大,靠近水冷管和渣钉处热应力相对较小；熔渣孔隙率越大,愈容易发生形变造成开裂；渣层表面存在裂纹时,与施加的拉力载荷相比,裂纹尖端附近的等效应力较高,最大值出现在裂尖,离开裂纹尖端稍远处,应力分布又趋于正常。更多还原

【Abstract】 The entrained flow gasification technology with water wall is a better choice in large coal gasification field. According to "principle of slag resistence", slag deposited on water wall can protect water wall from high temperature ablation. The slag deposit and heat transfer of water wall nearly have relations with flow field of gasifier, operating temperature and ash physicochemical property etc. Base on the background of water wall entrained flow gasification technology, the study on characteristic of diffusion flame and slag deposit and heat transfer was carried out.(1) The gasification diffusion flame is primary character in entrained flow gasifier and effect total temperature distribution of gasifier. The morphological analysis is mainly direction on flame investigation. The results indicate that in open space the effect of oxygen in air on flame configuration is finite, flame shape is gradually determined by oxygen from burner with increasing oxygen flux from burner. The burner structure of multi-jet can effectively improve mixture of fuel and oxygen, flame length of multi-jet burner is shorter than that of coaxial two-channel burner. In low oxygen velocity, the flame of two-channel burner is related to fuel primary atomization. The rule of primary atomization in combustion is similar with that in cold condition, but the critical velocity in combustion is higher. The structure of single flame is maintained before arriving to impinging region, but rapidly disappear in impinging region. With the increase of impinging velocity, impinging region become larger and unstable, the distribution of single flame is more continuous and homogeneous.There is a fractal characteristic in impinging gasification flame boundary. The fractal dimension decreases in ignition stage and increases from two-burners to four-burners. During the increase of load, the fractal dimension increases, however, the difference-value of the fractal dimension in two burner pattern reduces.(2) The results of study on bench-scale and pilot-scale water wall gasifier indicate that the slag deposit is related to flow filed, operating temperature and slag physicochemical property etc. Slag can deposit on all water wall surface and protect water wall from ablation. Compared with bench-scale study, slag deposit is more homogeneous in pilot-scale gasifier. With consumption scale per water wall surface increasing heat loss of water wall can play down. The dry feed flow, the ratio of oxygen and coal and drum pressure respectively can effect the heat transfer of water wall, but the level of effect is different. (3) The results of simulation based on water wall heat transfer and stress model is approximately consistent with experimental measure. According to simulation, the distribution of temperature and stress is achieved and further understand water wall heat transfer and slag cracking. The results show that the temperature gradient of slag layer is maximal, slag layer can effectively reduce bulk temperature of water wall. Temperature fluctuation in gasifier will result in thermal stress, the thermal stress is distinct for different material. The maximal thermal stress is located in slag layer, thermal stress of tube and pin is minimal. The possibility of slag crack increase with slag porosity increasing. When a load is applied in slag surface that there is a crack, stress distribution is very concentrative near crack tip and stress located in crack tip is several times than applied load. Once away from crack tip, stress distribution return to normal.更多还原