【作者】 初云涛；

【导师】 周怀春；

【作者基本信息】 华中科技大学 ， 热能工程， 2007， 博士

【摘要】 锅炉是火电机组中最重要的部件之一,锅炉安全一直以来都是具有重大实用价值的研究课题。壁温、热流、质量流速等热力参数是影响锅炉安全性的重要因素,这些热力参数在锅炉受热面上的分布是不均匀的,常用的热电偶、热流计等只能逐点测量,难以实现实时的、分布式的检测,从而不能全面评价机组的安全性。本文在对烟气传热、工质流动等物理过程分析的基础上,利用实时的炉内三维温度场以及颗粒黑度等燃烧检测信息,开展了电站锅炉分布参数建模的研究,获得的模型可全面反映锅炉热力参数分布特性。同时,针对目前用于动态特性分析及控制系统研究的锅炉简化模型由于普遍忽略各控制系统相互影响而精度不高的现状,从复现水位控制系统、主汽温度控制系统对负荷压力特性的实际影响出发,对汽包锅炉简化建模方法进行了探讨。本文开展的研究工作和创造性成果如下:考虑水位控制系统及主汽温度控制系统对负荷压力特性的影响,开展了汽包锅炉简化建模的研究。利用系统压力变动焓的概念把锅炉给水量与减温水量的影响引入汽包锅炉简化模型,该模型体现了控制系统间的耦合关系。同时,提出了一种新的水位控制系统和过热汽温控制系统前馈信号,可更好的削弱耦合回路的影响,进一步改善控制效果。开展了基于三维燃烧检测的蒸发系统分布参数建模的研究。利用燃烧检测系统提供的实时的炉内三维温度场和颗粒相黑度,计算水冷壁的二维热流分布。同时提出用火焰黑度修正系数对黑度进行修正,以反映气体辐射和对流对炉膛传热的影响。考虑了汽包水空间含汽对水位的影响,同时注意到代表过热系统阻力特性的汽包出口蒸汽流量方程系数随负荷变化,提出一种根据汽包压力和汽机调门开度计算该系数的经验公式。利用蒸发系统分布参数模型进行仿真,结果表明该模型不仅可以准确反映汽包压力、水位以及汽包出口蒸汽流量的动态特性,而且还可全面反映热流、壁温、质量流速等参数的二维分布特性,从而为有效评价锅炉蒸发系统安全性和可靠性提供了重要依据。利用蒸发系统分布参数模型对水冷壁水循环特性进行了仿真研究。结果表明,相对于其它因素,上升管管径和水冷壁热负荷偏差对水冷壁流量偏差有重要影响。存在上升管管径的最优设计值,在该管径下,机组可以有效适应热负荷、汽包压力、给水比焓等运行条件的变化,保持较好的水循环状态。当上升管管径等结构参数确定时,锅炉在较高汽包压力、较低给水比焓以及适当大循环泵增压的工况下运行,流量偏差小同时质量流速大,最有利于水循环。开展了过热系统分布参数建模的研究。根据热量来源,对过热系统传递的能量进行分类,并利用烟窗把各种类型的传热归结到一个封闭的系统内,进而建立了一种形式统一的过热系统分布式传热模型。在前人对三通集箱静压分布研究的基础上,考虑了宽度方向热负荷不均匀性对集箱静压以及并联管组流量分配的影响,得到了并联管组流量分配的热态模型。在此基础上,获得了过热系统/再热系统的分布参数模型,并通过仿真验证了模型的有效性。该模型在揭示过热系统和再热系统的同屏热力参数分布特性以及屏间热力参数分布特性方面具有独特的优越性。利用过热系统/再热系统分布参数模型对过热器和再热器壁温分布特性进行了仿真研究。结果表明:对于U型布置的后屏过热器及屏式再热器,高度方向烟温偏差较小时,外侧管圈存在出口段和水平段两个高壁温区域,内侧管圈则仅存在出口段一个高壁温区域。随着烟气偏差的增大,各管圈出口段壁温下降,而水平段壁温显著升高。对于蛇形布置的高温过热,当烟气偏差较小时,壁温最高点位于管圈尾部上升段内。随着烟气偏差的增大,壁温最高点由出口逆工质流程向管屏下部移动。这些结论可为锅炉的设计优化及运行优化提供有益的指导。更多还原

【Abstract】 Boiler is an important part of the power plant. The boiler security is still a valuable research. The temperature, heat flux and mass velocity heavily affect the boiler safety, which are non-uniformly distributed on the heated surface. Traditional methods such as thermocouple and heat flow meter are pointwise and hardly used for distributed measurements, so the boiler safety can’t be effectively evaluated. In this paper, based on the combustion monitoring information such as the 3-D temperature distribution and the emissivity of particle phase, the distributed parameter modeling for power plant boiler is studied, which can comprehensively descript the distributed parameter characteristics. In addition, considering the coupling relationship of the control systems, a new modeling method for drum boiler is developed to reflect the effect of the water level control system and the main steam temperature control system to load-pressure characteristics. The detailed description is as below.In the study, considering the coupling relationship of the control systems, a research on simplified model for drum boiler is performed. Using the system pressure deviation enthalpy, a model is developed, which can reflect the influence of feed water and spray water to the load-pressure characteristics. And a new type feedforword signal in water level control system and main steam temperature contol system is constructed, which can effectively weaken the influenc of other coupling control systems and further improve the control effects.Based on the 3-D combustion monitoring in furnace, a distributed parameter modeling method for evaporation system is developed. The transient, 2-D radiation flux is obtained by using the 3-D temperature distribution and the emissivity of the particle phase inside its furnace. And a factor of equivalent flame emissivity is proposed to reflect the gases radiation and convection to the heat transfer in furnace. The effect of the steam below liquid level to the drum level is considered, and an empirical express is proposed to calculate the coefficient of the equation of the steam mass flow rate at the outlet of drum, which varies with the boiler load.Then we obtain a distributed parameter model for the evaporation system. A simulation is made to validate the model by the comparison of the simulated value with the measured data of the drum pressure, the drum level and the steam mass flow rate at the outlet of drum. The transient, 2-D distribution of thermodynamic parameters, such as the wall temperature, the steam quality and the mass velocity can be predicted by the model, which forms an important basis to effectively evaluate the security and the reliability of the epaporation system.A simulation research on water circulation characteristics is performed by using the distributed parameter model for evaporation system. The results show that the diameter of risers and the thermal load deviation have the greatest influence on the deviation in flow rates. The diameter of the risers has an optimum design value, under the condition of such a diameter, a boiler can adapt to any changes in operation parameters, maintaining a comparatively good water circulation state. Moreover, when the structural parameters of a boiler have been determined, the boiler unit can secure a small deviation in flow rates favorable to water circulation while operating under the condition of a relatively high boiler drum pressure, relatively low feedwater specific enthalpy and moderately high boost-prssure of circulating pumps.A distributed parameter modeling for superheater/reheater system is performed. According to heat sources, the energies transferred in the superheater system are classified. By using the smoke vent plane, the heat transfers occur in an enclosure system, and then a distributed parameter model for the heat transfer of superheater panel is deduced. Based on the research of predecessors about the pressure distribution in headers, the effect of heat load distribution along the width to the pressure distribution in headers and flow distribution of parallel tubes is studied in this paper. Then, a distributed parameter model for superheater and reheater system is obtained, which is validated by the simulation and is useful to reflect the thermodynamic parameter distribution on the same platen or between the platens.A simulation study is made on the wall temperature characteristics of superheater and reheater system by using the distributed parameter model for superheater/reheater system. For the rear platen superheater or platen reheater, under the small gas deviation, there exist two high wall temperature zones for the outer tubes, one is at the horizontal part of U-tube, and the other is at the outlet of U-tube, however, there exists only one high wall temperature zone at the outlet of U-tube for the inner tubes. With the increase of gas deviation, the wall temperature at the tube’s outlet decreases, and the wall temperature of horizontal part of U-tube increases remarkably. For the high temperature superheater, the maximum wall temperature is at the tail part of the snake-tube. With the increase of gas deviation, the maximum wall temperature moves toward the bottom. These results are helpful for design and modification of the superheaters and reheaters.更多还原