Numerical modeling of gland seal erosion in a geothermal turbine

摘要

Excessive erosion of the low-pressure rotor end gland seal of a 25 MWe geothermal turbine produced a partial loss of turbine vacuum that degraded cycle efficiency. This study used computational fluid dynamics (CFD) to identify the causes of erosion and the optimal steam seal system flow conditions for reducing the erosion problem. The predictions were based upon a numerical calculation using a commercial CFD code (Adapco Star-CD) to model the rotor end gland seal with a steam flow containing hard solid particles. The results confirmed that flow conditions play a major role in rotor gland seal erosion. By changing steam seal flow pressures to vary flow, it was confirmed that there is a threshold seal flow condition below which erosion does not occur, or is minimized. Optimizing the rotor end gland seal supply pressure and intercondenser pressure reduced the turbulent flow kinetic energy by 49%, with a corresponding decrease in the erosion rate of the rotor gland seal surface. The erosion rate is related directly to the particle velocity and turbulent flow kinetic energy. Recommendations are provided for adjusting the rotor end gland seal system to avoid erosion.