Research On Thermodynamic System Anslysis Method Of Thermal Power Unit Based On Fluid Network Theory

At present,thermal power still accounts for the majority of the power structure of our country,its position is very important.Improving the energy utilization efficiency of thermal power units is of great significance to the improvement of the national economy.The economic performance of the thermal power unit operation depends on many aspects.The research direction of this paper was how to improve the efficiency of energy utilization in the process of electric energy production.To improve the efficiency of energy utilization and reduce the heat loss in the vapor congealing device,the reheating cycle and the regenerative heating system often are used.Then how to analyze and evaluate the influence of the reheating cycle and regenerative heating system on the cycle thermal efficiency of the unit and what changes will be produced in the running state of the reheating cycle and regenerative heating system under various changing conditions? Trying to find the answer to these questions is the purpose of this paper.The structure of working fluid's flow channels is very complicated,and comprises a complex thermal system,which branches influence each other.It's difficult to research the reheating steam system and heat regenerative system in isolation,they must be put into the thermal system to research.So the research object of this thesis was the thermal system of a real unit,and the emphasis was the analysis method of thermodynamic system,and the influence of regenerative system and reheating system on the cycle thermal efficiency.The calculation and analysis methods of thermodynamic system are many.Based on the research objectives a simple calculation method was put forward,thermodynamic system analysis and calculation were divided into the calculation of thermodynamic system net and the calculation of enthalpy value distribution of thermodynamic system based on calculation results of thermodynamic system net.Fluid network theory was introduced in the calculation of fluid network of thermodynamic system,through reasonable hypothesis fluid network of thermodynamic system is considered to be a one dimensional and steady flow,and the equivalent DC circuit model was established.Then solution of mass flow and pressure distribution in complex fluid network were translated into solution of current and voltage distribution in complex circuit.Kirchhoff's law of voltage and current were used to solve the equivalent circuit,and the mass flow and pressure distribution of fluid network were obtained.According to unit design data the enthalpy distribution model of thermodynamic system was established,the enthalpy distribution of thermodynamic system was obtained based on the calculation data of the fluid network of thermodynamic system.Then the model of cycle thermal efficiency was obtained.According to the research,the model of the fluid network and the model of enthalpy distribution of thermodynamic system were established,the accuracy of the model was verified through comparing the calculated results of fluid network and enthalpy distribution with the data of thermal characteristics of steam turbine under five conditions,100% load and 75% load and 50% load and 40% load and 30% load.Basing on the models the method of solving the flow resistance variation and node pressure change and branch change were proposed.The concept of the effective degree of reheating system and heat regenerative system were proposed on the basis of analysis of influence of reheating system and heat regenerative system to the cycle thermal efficiency.The effective degree could reflect the direction of the influence of the reheating steam system and the regenerative heating system to the cycle thermal efficiency,and the relative magnitude of the influence degree.The reconstruction schemes of adding No.0 high pressure heater of some units were calculated and analyzed using the analyzing method of thermal system proposed in this thesis.Found in the calculation results,adding No.0 high pressure heater,at different load conditions,could improve the cycle thermal efficiency.And the researched unit didn't work at the best condition,which cycle thermal efficiency could be improved;even No.0 high pressure heater was not added.That provided us a new research direction,namely thermodynamic system optimization calculation,based on the method proposed in this thesis.