Changing the Heating Conditions of the Rotor of High Pressure Cylinder in the Region of End Seals in the Cold Start Mode

Анотація

The steam flows in the front end seal (FES) of the high pressure cylinder of the turbine К-325-23.5 operated by PJSC "Turboatom" were studied to get prepared for the cold start at the time interval from the beginning of picking up the vacuum to the rotor push. The purpose of this research was to analyze the rotor heating in the FES region in the cold start mode and find the solution that would enable a more uniform rotor heating. Consideration was given to the superheated steam motion in FES sections. The FES length is equal to approximately one third of that of high pressure rotor. It has been shown that for the adopted seal scheme and high pressure cylinder heating only small end section is heated. Up to the point of steam supply through control valves at the rotor push about 80 % of the FES have low surface temperature and when the steam of 290^оС reaches the surface it results in the thermal shock and as a consequence in high thermal stresses in stress concentration regions, in particular at the angular points of cavities of a stepwise type.  To provide the uniform rotor heating in the entire time interval from the beginning of picking up the vacuum to the rotor push we proposed to modify the initial FES structure. This enables the creation of an additional chamber using holding inserts and their connection to increased pressure sources (the collector of 1.3 MPa, cold industrial superheating when the high pressure cylinder is heated through the exhaust nozzle) and decreased pressure sources (the capacitor). The steam flow rate for every other seal segment and the boundary conditions for the computation investigation of thermal and thermostressed states of the rotor of high pressure cylinder in the cold start mode of the turbine have been defined.