循环流化床内多组分颗粒流化特性的数值研究

发布时间：2018-04-09 01:05

  本文选题：多组分颗粒　切入点：循环流化床　出处：《哈尔滨工业大学》2016年硕士论文

【摘要】：循环流化床锅炉(CFB)技术是一项近20年来才发展起来的燃煤技术,因其燃烧效率高、污染物排放低和燃料适应性强等契合能源发展趋势的特色优势,受到广泛的关注和研究。然而在其内部稠密气固两相流动过程中,高随机性、多种作用耦合和固相属性不均等复杂因素给数值研究带来了很大的困难。目前的数值研究中,由于模拟条件的限制和实际物性的复杂,对于宽筛分的煤炭颗粒进行理想化处理已经成为共识。大多数的循环流化床内的流动、燃烧传热反应模拟主要基于平均颗粒属性(包括粒径和密度)的假设,极大减少了计算量和对数学模型的要求。然而实际床料颗粒的粒径和密度等属性存在明显差异,单组分颗粒的模拟过度简化,将对模拟结果产生很大的影响。在多组分颗粒流化模拟方面,尽管有双组分颗粒模拟的先例,然而模型依旧很不完善,忽略了颗粒间碰撞的动量交换,且两种颗粒的假设并不够典型。因此有必要建立一套基于多组分颗粒假设的模拟模型,并对循环流化床内的流动和燃烧进行数值模拟研究,进行气固两相流向实际宽筛分颗粒体系发展的探索,为循环流化床甚至内部存在气固流动的化工设备的发展提供数值借鉴。根据煤炭颗粒粒径符合Rosin-Rammler分布的特点,将颗粒粒径细化为典型的细、中、粗三组分颗粒群进行研究,以颗粒动力学理论为出发点,考虑多组分颗粒间的各种相互作用,运用双流体模型,建立基于气体-多组分颗粒的数值模拟模型。模拟采用多相流程序软件,由于其开源特性,更便于根据需要搭配模型。文中详细分析了固相应力模型和关键的颗粒动力学相关理论,之后考虑多组分煤炭颗粒燃烧的主要反应,编写并调试了完整的模拟程序。本文进行了三维流化床提升管的模型验证对比、二维冷态循环流化床流动模拟和热态流化床燃烧模拟。提升管的模拟验证了模型的可行性,对比了多组分颗粒假设相比于单组分颗粒的优点,并对比了两种主要固相应力模型的区别。冷态循环流化床模拟得出关于多组分颗粒存在时浓度场、速度场、湍动度等流场特性,并分析颗粒密度、流化气速对多组分颗粒群的流动影响。最后进行了二维流化床热态燃烧模拟,燃烧主要考虑了煤的热解、煤焦燃烧、挥发分和CO燃烧以及CO2的还原反应,着重分析了组分场分布、各相颗粒相关的反应速率和温度场特性等参数。探讨了一二次风配比对燃烧的影响,对比了挥发分差异较大的烟煤和无烟煤的燃烧情况,分析各类颗粒的燃烧特点及其对整体燃烧的影响。
[Abstract]:Circulating Fluidized bed Boiler (CFB) is a coal-fired technology developed in recent 20 years. Because of its high combustion efficiency, low pollutant emission and strong fuel adaptability, it has attracted extensive attention and research.However, in the process of dense gas-solid two-phase flow, the complex factors of high randomness, interaction coupling and imparity of solid properties bring great difficulties to numerical research.In the present numerical research, due to the limitation of simulation conditions and the complexity of actual physical properties, it has become a consensus to idealize the treatment of coal particles with wide sieving.In most circulating fluidized beds, the simulation of combustion heat transfer reaction is based on the assumption of average particle size and density, which greatly reduces the computational complexity and the requirement of mathematical model.However, there are obvious differences in the particle size and density of the actual bed particles, and the simplification of the simulation of the single component particles will have a great impact on the simulation results.In the multi-component particle fluidization simulation, although there is a precedent of two-component particle simulation, the model is still imperfect, ignoring the momentum exchange between particles, and the assumption of the two particles is not typical enough.Therefore, it is necessary to establish a simulation model based on the assumption of multi-component particles, and to simulate the flow and combustion in a circulating fluidized bed, and to explore the development of gas-solid two-phase flow to the actual wide sieve particle system.It provides a numerical reference for the development of chemical equipment with gas-solid flow in circulating fluidized bed and even inside.According to the characteristics of coal particle size according to Rosin-Rammler distribution, the particle size is refined into typical fine, medium and coarse three component particle groups. Based on the theory of particle dynamics, various interactions between multicomponent particles are considered.A numerical simulation model based on gas-multi-component particles was established by using two-fluid model.The multiphase flow software is used in the simulation, because of its open source feature, it is more convenient to match the model according to the need.The solid stress model and the relevant theory of particle dynamics are analyzed in detail. After considering the main reaction of multi-component coal particle combustion, a complete simulation program is compiled and debugged.In this paper, the model verification and comparison of three-dimensional fluidized bed riser, two-dimensional cold circulating fluidized bed flow simulation and hot fluidized bed combustion simulation are carried out.The simulation of the riser validates the feasibility of the model, compares the advantages of the multicomponent particle hypothesis over that of the single component particle, and compares the differences between the two main solid stress models.The characteristics of concentration field, velocity field and turbulence degree in the presence of multi-component particles are obtained by cold circulating fluidized bed simulation, and the effects of particle density and fluidized gas velocity on the flow of multi-component particle groups are analyzed.Finally, the thermal combustion simulation of a two-dimensional fluidized bed is carried out. The combustion mainly considers the pyrolysis of coal, the combustion of coal char, the combustion of volatile matter and CO, and the reduction reaction of CO2. The distribution of compositional field is emphatically analyzed.The parameters of reaction rate and temperature field related to each phase particle.The influence of the ratio of primary and secondary air on combustion was discussed. The combustion conditions of bituminous coal and anthracite with big difference in volatile content were compared, and the combustion characteristics of various kinds of particles and their effects on the overall combustion were analyzed.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TK229.66
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本文编号：1724142