循环流化床锅炉的性能在很大程度上取决于床内物料品质，例如炉膛内颗粒粒径分布，沿床高的质量分布等。床料的粒径分布直接影响燃烧效率和脱硫效率，并决定燃烧室内的热负荷分布。本论文工作是在前人有关流化床锅炉燃煤成灰特性，磨耗特性研究的基础上，建立了宽筛分给煤条件下循环流化床锅炉的物料平衡模型，该模型考虑了物料磨耗的因素。通过模型预测工业规模循环流化床锅炉的灰平衡，为锅炉设计者提供分离器，受热面布置，煤粉制备系统的设计参数。该模型重点研究了影响物料平衡的几大因素，包括特定煤种的成灰特性和磨耗特性，颗粒停留时间模型，颗粒分层模型，分离器效率等，并通过工业循环流化床锅炉灰平衡测试数据进行了验证。本论文的第一部分工作是建立整体物料平衡模型，及影响物料平衡子模型。作者针对物料磨耗在平衡中的作用，提出物料即要按粒度分档， 同时也要按“年龄”分档。这个概念推演出物料在循环流化床内的停留时间是不同“年龄”的相同粒度物料的平均停留时间，该模型很好地解决了模型计算中如何考虑停留时间对物料磨耗量的影响问题。此部分是本工作的精华之一。作者处理的另一个难点是关于循环流化床物料分层对底渣粒度影响问题，作者根据有限的实验数据，以终端速度为颗粒分层强度指标，建立了一个半经验的模型。本论文的第二部分是对电厂煤样的成灰特性，磨耗特性的研究和工业锅炉灰平衡测试数据的采集。作者通过观察已有煤样灰份数据，提出将燃煤灰分为性质的不同的硬灰和软灰，进而提出了一种半理论半经验的成灰实验方法，进一步简化了已有的稳态燃烧冷态振筛的实验方法。在本论文的第三部分中，作者通过模型计算和锅炉测试数据的校和，确定了影响床内物料平衡的经验参数；讨论了几种运行参数和煤种特性对物料平衡的影响趋势；并针对特定蒸发量的锅炉燃用不同煤种进行了物料平衡预测，为改善物料平衡提出了几点建议。
The performance of CFB boiler mainly depends on the quality of the bed inventory, such as size distribution and vertical weight distribution in furnace. The size distribution of bed material will influence the combustion efficiency and desulfurization efficiency as well as the heat distribution along furnace. In this work, a mass balance model of Circulating Fluidized Bed (CFB) boiler is constructed based on the foundation of previous researches on coal ash formation and attrition. By predicting the ash balance in commercial CFB boilers, the model can provide suggestions on cyclone, heating surfaces and coal pulverization system to boiler designers. The mass balance model emphasizes on the important factors that influence ash balance, such as ash formation, attrition and size reduction, residence time and segregation, and it is verified by measurement from commercial boilers.The first part of the dissertation is to establish the CFB boiler mass balance model and the sub models.To study the influence of residence time on attrition, the evolution of particles and their attrition are analyzed by classifying particles in size cuts and age cuts. The residence time for a size cut particles is the average residence time of different age cuts particles. Using this concept, the influence of residence time on particle attrition can be easy solved in the calculation. This sub model is one of the innovations in the dissertation.Base on the limited experimental data, using the single particle terminal velocity as the decisive segregation characteristic, a semi-empirical segregation model is constructed. This model can effectively solve the segregation influence on the size distribution of bottom ash, which is one of the acknowledged difficulties in CFB model. The second part is to carry out the experiments on coal ash formation and attrition and conduct ash balance measurements in 3 Heat Power Plants. The analysis of the ash formation data shows that the ash particle size distribution from narrow size cut samples of coal has a bimodal nature, that are a fine soft component and a coarse hard component. And then a semi-empirical experimental technique combined with theory analysis is developed to predict the coal ash formation, which greatly simplifies the previous static combustion and cold sieving technique.In the third part, the mass balance model is verified by 3 CFB boilers in China, and the empirical parameters of segregation and axial decay under full load operation are optimized. More simulations of different operation and design parameters are carried out to investigate their influence on mass balance in CFB boiler. At last, using the operation conditions of 220t/h CFB boiler, the mass balances of other two coal types in 220t/h boiler are predicted. And several suggestions on how to improve mass balance are proposed.
