HIGH POWER STEAM TURBINE LIFETIME INCREASE BY MEANS OF FRONT END SEAL ARRANGEMENT AND START-UP HEATING CONDITIONS IMPROVEMENT

摘要

Use of high power steam turbines in maneuver regimes by power plants became a widely-distributed practice in chase of short-term economic benefits. At the same time, these actions resulted in much higher levels of lifetime consumption for turbines which are not designed for high numbers of start-ups. The purpose of the present study is to improve operational flexibility for 325 MW steam turbine through design modifications. For the accurate simulation of rotor thermo-structural state and lifetime, an improved methodology was developed. The approach allows engineers to account for the steam film condensation process and the steam flow physics for regions with the anticipated high-stress levels at front-end seal zone, and the influence of the inter-casing space steam film condensation on the flow parameters in the front-end seals chambers. Based on the simulation results for the 325 MW supercritical steam turbine HP rotor, the design changes of the front-end seal arrangement and heating conditions modification during the pre-warming phase are proposed. The results show that the proposed changes make it possible to provide a more uniform heating and lower thermo-stress level for the high-pressure cylinder rotor at the front-end seal region during the pre-warming phase, which results in an increased allowable number of turbine start-ups. The influence of heating conditions on thermo-stresses and low cycle fatigue lifetime for the baseline and modified designs as well as modeling details for transient thermo-structural analysis have been discussed.