【作者】 曹小玲；

【导师】 苏明；

【作者基本信息】 上海交通大学 ， 动力工程及工程热物理， 2006， 博士

【摘要】 汽包水位晃荡是联合循环余热锅炉在运行工况下出现的不良现象,但目前还缺乏有效的手段进行抑制和消除,随着联合循环系统对汽包水位控制要求的提高,如何建立基于水位晃荡的汽包水位动态仿真模型、研究水位晃荡规律以及如何消除水位晃荡给控制系统带来的负面影响已成为一个具有挑战性的研究。本文在国际合作项目[200310]和国家自然科学基金项目[5997022]的资助下,分析了汽包水位晃荡的机理,并针对汽包水位晃荡引起的原因,即水动力学和热力学性质,分别对应地建立了汽包水位水动力学模型和热力学模型,利用这两个模型的建模方法和知识,建立了基于水位晃荡的汽包水位动态仿真模型;基于该模型进行了动态仿真研究,得出了各种因素对水位晃荡的影响规律,并采用从研究中获得的知识对联合循环余热锅炉汽包水位的控制进行了探讨。本文主要进行的研究工作如下:1汽包水位水动力学模型的建模与动态仿真研究采用模块化建模的方法,将汽包沿长度方向进行模块划分,并根据质量守衡和动量守衡原理,建立了汽包子模块;基于Easy5仿真软件平台建立了汽包水位水动力模型,并基于该模型进行了动态仿真研究,结果表明:汽包水位与汽包长度对晃荡周期有很大的影响,晃荡液体密度对晃荡周期影响很小,晃荡振幅随液体密度增大而减小;就晃荡周期而言,模块非均匀划分方法对水动力学模型建模没有影响,且一定范围内模块划分数目对水动力学模型建模几乎没有影响。为建立基于水位晃荡的汽包水位动态仿真模型提供了重要的理论依据和方法。2汽包水位水动力学模型的实验验证设计了实验台架,并建立了实验装置,实验结果表明:就不同水位情况下晃荡周期的验证而言,实验结果与模型计算结果之间的数值误差在±10%以内;就有进出口流量的情况下模型的实验验证而言,模型仿真结果的变化趋势与实验结果基本上是一致的,尽管晃荡幅度和相位上还是存在一定的误差,但其数值误差在±20%以内。实验结果证明:水动力学模型能够有效地反映汽包中水位晃荡现象。3汽包水位热力学模型的建模与动态仿真研究采用集总参数法基于Easy5仿真软件平台对汽包建立了集总参数模型,并将该模型作为参考模型;根据汽包水位热力学模型的建模需要对汽包模块划分作了深入的处理,就所带来的问题进行了分析,并提出了四种解决问题的建模方法;同时对汽包中汽水混合物和蒸汽分别进行建模,获得蒸汽子模块和汽水子模块,基于这两类模块根据提出的四种建模方法进行建模得到相应的四种模型。为确定合适的热力学模型建模方法,采用这四种模型和参考模型,对汽包中典型的热力学性质-“虚假水位”现象的动态过程进行了动态仿真,结果表明:同时考虑汽包体积变化率和压力变化率的建模方法,其动态仿真结果完全可以正确地跟踪参考模型的仿真结果,并且数值误差在5%以内,故该建模方法可以用来建立汽包水位热力学模型。为建立基于水位晃荡的汽包水位动态仿真模型提供了重要的理论依据和方法。4基于水位晃荡的汽包水位动态仿真模型的建模与动态仿真研究基于汽包水位水动力学模型和热力学模型的建模方法和知识,并根据现场实际汽包结构对汽包水位动态仿真模型的模块划分进行了合理处理,基于质量、动量和能量守恒建立了基于水位晃荡的二维汽包水位动态仿真模型;分别从热力学角度和水动力学角度对该模型进行理论验证,结果表明:汽包水位动态仿真模型可以很好地反映汽包里面的热力学性质和水动力学性质。基于汽包水位动态仿真模型研究了各影响因素对汽包水位晃荡的影响规律,结果表明:随给水流量减小、出口蒸汽流量和加热量增大,水位晃荡频率减小;随给水流量增大、加热量和出口蒸汽流量减小,水位晃荡频率增大。5余热锅炉汽包水位控制的动态仿真研究建立了包括省煤器模块、过热器模块、容积模块、下降管模块和蒸发器模块等在内的基于汽包水位晃荡的余热锅炉动态仿真模型,并根据汽包水位晃荡的频率特性设计了汽包水位晃荡噪声滤波器。汽包水位控制的动态仿真研究结果表明:在考虑汽包水位晃荡噪声的情况下,引入晃荡噪声滤波器,在一定程度上滤去了水位晃荡噪声,并在一定程度上消除了水位晃荡噪声对PI控制器的影响,从而汽包“虚假水位”得到了有效地控制,并使控制系统的频繁动作得到了缓和,整体水位波动相对要平缓一些。更多还原

【Abstract】 Drum level sloshing is a negative phenomenon under the operation of Combined Cycle Heat Recovery Steam Generator(HRSG), but, at present there are still no effective means to control or eliminate it. With the increased requirements that the combined cycle has for drum level controlling, how to build the model of drum level sloshing, how to study the rules of drum level sloshing, and how to eliminate the negative effect that the drum level sloshing brings to the control system already become a challenging research object. Under the support of International Co-operation Project[200310] and National Natural Science Foundation[5997022], the mechanism of drum level sloshing was analyzed, according to hydrodynamics and thermodynamics characteristic in drum, corresponding hydrodynamics and thermodynamics models were set up respectively, so the drum level dynamic simulation model based on level sloshing was set up using the knowledge from the two models. Dynamic simulation was done based on the model, the influence rules that some factors bring to the level sloshing were got, simulation research of drum level controlling was carried out based on the model, how to eliminate the negative effect that the drum level sloshing brings to the level control system was discussed. Main research work done in the paper was listed as following:1 Modeling and Dynamic Simulation Research of Hydrodynamics Model of Drum LevelThe method of modular modeling was adopted in this paper, module dividing of drum was done alone drum length direction, and according to the mass and momentum conservation laws, drum sub-modules were built. And hydrodynamics model of drum level was also set up based on the Easy5 software platform, the simulation research was carried out on the model, conclusion and some rules of drum level sloshing were obtained as follows: The drum level and drum length have much influence on the drum level sloshing, liquid density has little effect on the period of drum level sloshing, but the amplitude of drum level sloshing increases as the liquid density decreasing. As the period of level sloshing, non-uniformity division of module has little effect on modeling, and the numbers of sub-modules almost has no effect on modeling within certain range too. The important theoretic base and method in this research were provided for building the drum level dynamic simulation model based on level sloshing.2 Experiment Validation of Hydrodynamics Model of Drum LevelThe experiment rig was designed, and the experiment equipment was also set up. The experiment results show: As the validation of sloshing period under different levels, maximum error between the results of the experiment and the model is within±10%. As the experiment validation of model under in-and-output flux, changing trends of results of the model and the experiment are consistent, though there is some error in sloshing amplitude, the numeric error is within±20%. So hydrodynamic characteristics in drum can be simulated reasonably by the hydrodynamics model.3 Modeling and Dynamic Simulation Research of Thermodynamics Model of Drum LevelBased on Easy 5 simulation software platform, the model of lumped parameter was set up using method of lumped parameter, and this model was taken as the reference model. Module division was deeply done according to the requirements of modeling of thermodynamics model of drum level, and the problem caused by module division was analyzed, and four methods of modeling were proposed to solve the problems. The modules were built for the mixture and the steam respectively, and the mixture sub-module and the steam sub-module were obtained, based on these two kinds of sub-modules, and according to the proposed four proposed methods, corresponding four kinds of models were obtained. In order to ensure the reasonable modeling method for thermodynamics model, by adopting these four kinds of models and the reference model, the typical thermodynamics characteristic in drum-the dynamic process of“false level”were dynamically simulated, the results of simulation indicate: The modeling method of considering the changing rates of pressure and volume simultaneously is more reasonable, it’s simulation result can be consistent with the result of the reference model, and the numeric error is within±5%, so, this method can be used to build thermodynamics model of drum level. Work done in this paper established an important foundation for modeling of drum level dynamic simulation model based on sloshing.4 Modeling and Dynamic Simulation Research of Drum Level Dynamic Simulation Model Based on Level SloshingBased on the modeling knowledge from hydrodynamics and thermodynamics models, and module division of drum level dynamic simulation model was considered reasonably according to configuration of field drum, 2-D drum level dynamic simulation model based on level sloshing was set up by adopting mass、momentum and energy conservation laws. Theoretical validations of the model were carried out respectively on thermodynamics and hydrodynamics, the result indicates that the thermodynamics and hydrodynamic characteristics in drum can be reflected well by the model.Based on the drum level dynamic simulation model, the influence rules that some factors bring to the drum level sloshing were studied, the results indicate: With the feed-water flowrate decreasing, and the main-steam flowrate and the heating quantity increasing, the frequency of level sloshing decreases, on the contrary, with the feed-water flowrate increasing, and the main-steam flowrate and the heating quantity decreasing, the frequency of level sloshing increases.5 Dynamic Simulation Research of Drum Level ControllingThe dynamic simulation model of HRSG based on level sloshing was set up, the model includes the Economizer module, superheater module, volume module, evaporator module etc, and the filter of drum level sloshing noise was designed according to the characteristics of drum level sloshing frequency. Based on the model, some simulation research was carried out for the drum level controlling, the results of simulation research indicate: With the noise of drum level sloshing being considered, and the filter of drum level sloshing noise being introduced, drum level sloshing noise is filtered to some degree, and the influence that the sloshing noise brings to the PI controller is eliminated in some extent, the“false level”is controlled effectively, and the frequent action of the control system become moderate, the wave action of whole drum level also get relatively milder.更多还原