Thermo-Structural Analysis of Steam Turbine Startup With and Without Integrated Prewarming System Using Hot Air

Abstract

In this paper, the transient thermal and structural analyses of a 19-stage IP steam turbine in various start-up operating modes are discussed. The research utilises a hybrid (HFEM - numerical FEM and analytical) approach to efficiently determine the time-dependent temperature distribution in the components of the steam turbine. The simulation strategy of the HFEM model applies analytical correlations to describe heat transfer in the turbine channel. These are developed by means of unsteady multistage conjugate heat transfer simulations for both start-up turbine operation with steam and pre-warming operation with hot air. Moreover, the numerical setup of the HFEM model considers the thermal contact resistance (TCR) on the surfaces between vane and casing as well as blades and rotor. Prior to the analysis of other turbine start-up operating modes, the typical start-up turbine process is calculated and validated against an experimental data as a benchmark for subsequent analysis. In addition to heat transfer correlations, the simulation of a turbine start-up from cold state uses an analytic pressure model to allow for a consideration of condensation effects during first phase of start-up procedure. Finally, the presented thermal investigation focuses on the comparison of transient temperature fields in the turbine for different start-up scenarios after pre-warming with hot air and provides the subsequent structural investigation with boundary conditions. As a result, the values of the highest stress are numerically determined and compared to the values obtained by means of cold start-up simulation.