Performance Analysis And Numerical Simulation Of Heat Exchangers In Steam Turbine Unit Thermal System

To evaluate the performance of heat recovery system is an import aspect of thermal system performance analysis of steam turbine unit. And the most common reflect of heat recovery system performance is terminal temperature difference (TTD) and drain cooler approach (DCA) of heat exchangers. Influenced by various factors such as load, water level, area, TTD and DCA will change. This paper will analyse the steam turbine unit performance through studying TTD and DCA of heat exchangers. Theoretical modeling and numerical simulation are used to study heat exchangers, hence to have a more comprehensive understanding of them.To begin with, to build a simulation model of the steam turbine and heat recovery system of a 660MW coal-fired power units, and to verify its correctness by comparing it with design value. Based on the simulation model, influence of load, water level, area to temperature difference in the THA-40%THA is studied. The study of relationship between TTD, DCA and load indicate that they will all decrease when load decreases. Such relationship is identical to operating data. Variable condition characteristics when area decreases and tube plugs is also studied. Study of area decrease will help determine the reference value. Relationship of heat transfer coefficient, average logarithmic temperature difference, TTD, DCA with area is obtained. Considering water level is always low in actrual working condition, such low water level condistion was also studied. And change condition of void fraction, TTD, DCA between water level is got. And a water level setpoint is given to improve the efficiency and security of heat exchangers.According to above study, water level value that indicate low water level fault is also given. Then, to predict TTD and DCA through regression method and support vector machine to give a more reliable reference level to evaluate whether there is noncondensable water or fouling when there is tube plugging.Thereafter, numerical simulation is done about the heat exchangers. The flow field and temperature field of THA condition are carefully analysed to prove the reliability of the model. Thus to serve as the basis of the further variable condition simulation.Finally, variable condition simulation is done based on the above model to further explore the inside flow field of heaters and to supplement the previous theoretical model. Variable Conditions simulation focuses on tube plugging, corrosion of inlet baffle, steam containing at drain cooler inlet. The simulation result can modify, supplement and verify the theoretical model.