Analysis On Steam Turbine Rotor Thermal Stress For Peak Load Condition

As China now witnesses the great changes in social power consumption, thereis an increasingly large difference between the peak load and the value. With theconstant increase in the power generation ratio of intermittent clean sources ofenergy, such as wind power and photovoltaic, it has become increasingly difficult forthe grid to contain and consume power types. As a result, the wind power enterpriseshave given up this kind of power, which leads to great economic loss as well aswaste of social resources. At the same time, the low economic efficiency of thermalpower units under low load condition has forced the large-scaled ones to initiateStar-Stop Peak Modulation. Therefore, the study of the thermal stress and life loss ofthe peak-modulation turbines is of great importance to guarantee safety andmaneuverability for the large-capacity thermal power units involving the peakmodulation.The changes in power load and frequent start-stop in the peak-modulationturbines leads to the changes of the steam parameter inside the turbines, causing theviolent changes of rotors, especially of the metal temperatures of the governing stage.This has increases its temperature gradient and thermal stress, which posing a threaton the safe operation, and at the same time, limiting its capability of fast peakmodulation. This paper first conducts a theoretical analysis of the generation anddistribution of the thermal stress as well as the mechanical stress of the rotor; it thenestablishes the2D finite dynamic elements model for the rotors, choosing theappropriate grid number and proper refined grids so as to complete grid division; thishas become the calculation of the changes in steam temperatures in different parts aswell as the heat transfer coefficients variation as the starting time changes. Thus, ithas been set as the third kind boundary condition: ANSYS is used to calculate thetemperature field, thus getting the temperature distribution at different time. The temperature at the key point as well as the temperature difference between the rotorsurface and centerline change with time, therefore, the distribution of stress for therotors can be obtained through thermal-structural coupling analysis. Based on theresults of stress analysis, the detailed analysis of the stress at cross, vertical and axialaspects as well as the combined stress and be gained; at the same time, in the lastsection, it analyses the factors influencing the thermal stress in details and optimizesthe thermal starting process by changing the load-increasing ratio of the low load,which increases the safety and maneuverability for the large-scale thermal powerunits in start-stop peak modulation.