基于流体网络理论的火电机组热力系统分析方法研究

发布时间：2018-07-17 01:13

【摘要】：目前,火力发电仍占我国电源结构的大部分,地位举足轻重。提高火电机组能源利用效率,对于提高国民经济的意义重大。火电机组运行的经济性取决于很多方面,本文的研究方向就是如何提高电能生产过程中能量利用的效率。为了提高热能的利用率,降低冷源损失,火电机组普遍采用再热循环和回热加热系统,来提高蒸汽循环的热效率。本文的研究目标就是如何分析或评价再热循环和回热加热系统对机组循环热效率的影响,包括在各种变工况条件下,再热循环和回热加热系统运行状态的分析。由于工质循环流动的通道,结构复杂,构成了一个复杂的热力系统,各分支之间互相影响,要研究回热系统或再热系统,无法将它们孤立出来,必须将它们放入大的热力系统中进行研究。因此,本文以某真实火电机组的热力系统为对象,研究热力系统的分析方法及回热系统和再热系统对工质循环热效率的影响。热力系统的计算和分析方法较多,本文根据自身的研究目的,将热力系统的分析计算方法简化,分解为热力系统流网计算和基于流网计算结果的焓值分布计算。将流体网络理论思想引入热力系统流网计算,通过合理假设,将热力系统流网的工质流动简化为不考虑工质换热对工质物性参数影响的一维、稳态流动问题,从而建立了热力系统流网的等值电路模型,将复杂流网的质量流量和压力分布求解,转化为直流电路的电流、电压分布求解,再应用基尔霍夫电压、电流定律建立等值电路的数学模型,通过求解该模型获得热力系统流网的质量流量和压力分布。再根据机组设计参数,建立热力系统焓值分布模型,在热力系统流网计算结果的基础上,得到热力系统焓值分布,进而得到机组循环热效率模型。通过研究,本文应用流体网络理论思想建立了热力系统流体网络计算模型,并建立了热力系统焓值分布模型,通过将100%负荷、75%负荷、50%负荷、40%负荷和30%负荷5个工况的流网计算结果和焓值分布计算结果与该机组汽轮机热力特性数据进行比对,验证了模型的准确性。在此基础上,本文给出了,应用该模型求解机组运行中典型问题的方法,包括热力系统流网支路流阻变化、给水泵或凝结水泵扬程变化、凝汽器压力变化、加热器水侧管路泄漏等。在分析再热蒸汽系统和回热加热系统对蒸汽循环热效率的影响时,本文定义了再热蒸汽系统和回热加热系统有效度的概念。该定义可以反映再热蒸汽系统和回热加热系统对蒸汽循环热效率的影响方向,以及影响程度的相对大小。通过应用本文建立的热力系统分析方法,对目前部分机组提出增加0号高加的改造方案,进行了分析计算。在计算结果中发现,增加0号高加,在5个不同负荷工况,都可以提高蒸汽循环热效率,但0段抽汽的循环有效度低于其他段抽汽。同时发现,本文研究机组的回热系统并未工作在最佳状态,在不增加0号高加,而单纯改变回热系统工作状态的情况下,仍有提高机组循环热效率的余地,这为我们提出了基于本文热力系统分析方法的热力系统优化计算的新方向。
[Abstract]:At present, thermal power generation still accounts for most of the power supply structure in China. It is of great importance to improve the energy utilization efficiency of thermal power units. The economy of the thermal power unit depends on many aspects. The research direction of this paper is how to improve the efficiency of energy utilization in the process of electric energy production. In order to improve the thermal efficiency of steam cycle, the aim of this paper is to analyze and evaluate the effect of reheat cycle and reheating system on the thermal efficiency of the unit cycle, including reheat cycle and return under various condition conditions. The analysis of the running state of the thermal heating system. Because of the complex structure of the circulating flow of the working fluid, the complex structure is made up of a complex thermodynamic system, which affects each other. It is necessary to study the regenerative system or reheat system. It is impossible to isolate them. They must be put into a large thermodynamic system. Therefore, this paper is based on a real fire. The analysis method of thermal system and the influence of the heat system and reheat system on the thermal efficiency of the working fluid are studied. There are many methods of calculation and analysis of the thermodynamic system. In this paper, the analysis and calculation method of the thermodynamic system is simplified and decomposed into a flow net calculation and a flow net based on the thermodynamic system. The calculation of the enthalpy distribution of the calculated results is introduced. The fluid network theory is introduced into the flow network calculation of the thermodynamic system. Through the reasonable assumption, the working fluid flow in the flow network of the thermodynamic system is simplified as one dimension without considering the effect of the heat transfer on the physical property parameters of the working material and the steady flow problem, thus the equivalent circuit model of the flow net of the thermodynamic system is established, which will be complex. The mass flow and pressure distribution of the flow net are solved, converted into the current of the DC circuit, the solution of the voltage distribution, and then the mathematical model of the equivalent circuit by using the Kirchhoff voltage and the current law. By solving the model, the mass flow and pressure distribution of the flow net of the thermodynamic system are obtained. Then the enthalpy points of the thermodynamic system are established according to the design parameters of the unit. On the basis of the calculation results of the thermodynamic system flow net, the distribution of enthalpy distribution of the thermodynamic system is obtained, and the heat efficiency model of the unit cycle is obtained. Through the study, the fluid network calculation model of the thermodynamic system is established by using the theory of fluid network, and the enthalpy distribution model of the thermodynamic system is established, through which the 100% load, the 75% load, and 50% are used. The calculation results of flow net calculation and enthalpy distribution of the load, 40% load and 30% load are compared with the steam turbine thermodynamic characteristics data, and the accuracy of the model is verified. On this basis, this paper gives the method to solve the typical problems in the operation of the unit, including the flow resistance change of the flow net branch of the thermodynamic system, In the analysis of the effect of reheat steam system and reheating system on the thermal efficiency of steam cycle, the concept of the reheat steam system and reheating system is defined. This definition can reflect the reheat steam system and the reheat addition. The influence of the thermal system on the thermal efficiency of the steam cycle and the relative size of the influence degree. Through the application of the thermal system analysis method established in this paper, an analysis and calculation for the increase of the 0 number of units at present is put forward. It is found that the increase of number 0 increases in the calculation results and can be improved in 5 different load conditions. The steam cycle heat efficiency, but the cycle efficiency of the 0 section extraction is lower than that of the other sections. It is found that the regenerative system of the unit does not work in the best state, and there is still a room for improving the thermal efficiency of the unit under the condition that the regenerative system is not increased and the working state of the regenerative system is simply changed. A new direction for optimization of thermodynamic system in text thermal system analysis.
【学位授予单位】：华北电力大学(北京)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM621.4

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