COMPARING DIFFERENT DESIGNS OF A GRID-VALVE FOR INDUSTRIAL STEAM TURBINES

The current energy market is characterized by the increasing split of energy produced with renewables, and by the strong push towards a sustainable use of the resources and a reduction of the global carbon footprint. Both these two aspects underline the importance of operating the energy production plants in an efficient and effective way not only at full but also at partial load. This paper presents the results obtained using a CFD commercial code to understand how the different design choices affect the performance of a grid-valve used for steam turbines in the industrial power generation market. Several different configurations were considered, mainly to understand the best trade-off in terms of performance and mechanical aspects. In fact, the grid valves are intended to have a certain modularity and are designed to operate within a given range of conditions and applied to different steam turbine architectures. At best, they should be able to deliver the same performance regardless of the operating conditions or the steam turbine architecture. Therefore, part of the activity focused on the criteria to be used to decide the size the grid valve with respect to the mass flow and the downstream flowpath. A significant part of the analytical efforts was also devoted to provide a set of rules to account for the performance variability. To this purpose, a significant number of cases was used to cover the most relevant factors affecting the performance of the grid valves. Considered factors include: the variability of the radial length of the stages downstream of the grid valve, the pressure ratio through the grid valve, and the amount of flow extracted upstream of the grid valve.