Development of Highly Efficient Nuclear HP Steam Turbines Using Physics Based Moisture Loss Models

Abstract

Turbines operating under wet steam conditions experience efficiency losses caused by the presence of moisture. A full understanding of these loss mechanisms is required for an accurate prediction of turbine performance. However, due to the extremely complicated nature of the wet steam flow, full numerical simulations are time consuming and expensive and have limited value for the turbine designers. The traditional empirical approach, though simple, generally offers no insight into the moisture loss mechanisms. As a result, little guidance is provided for design improvements. This paper presents a physics-based moisture loss prediction system that has been developed specifically for industrial applications. Three main categories of moisture losses are considered: homogeneous nucleation, thermodynamic (supersaturation) loss and mechanical loss. Two new correlations have been developed that provide a quick means for determining the Wilson Point location, resulting equilibrium moisture deficit and average size and number of the condensed moisture (fog). The thermodynamic losses produced by the non-equilibrium expansion of the wet steam beyond the Wilson Point are modeled using Young’s semi-analytical approach [23]. The mechanical moisture losses are modeled using the myriad of loss models available from the public domain. The combination of this new moisture loss model with existing steam path design tools has greatly improved our understanding of the moisture loss that occurs in wet steam expansions. In particular, it has provided significant insight into flow path design optimization for nuclear high pressure (HP) turbines. As a result, a new design methodology, Nuclear HP Dense Pack™, has been developed for the nuclear HP turbines. Preliminary results have shown this new design methodology has the capability of improving the section efficiency of existing nuclear HP steam turbines by 2-4% points.