Assessment of turbine performance variability in response to power block design decisions for SF6 and CO2 solar thermal power plants

Abstract

All Solar Thermal Power (STP) systems are exposed to the variability of solar insolation. Due to the heliocentric nature of the system, seasonal and continuous time variations, investigation of operating point selection is a continuing concern for STP systems. This paper explores the relationship between cycle design, operating conditions and off-design performance; exploring the response that several turbines have to a wide range of operating conditions.By systematically developing radial turbines for each cycle design and evaluating each turbine over a range of operating conditions, the study found that for previously indistinguishable radial inflow turbine designs – both cycle design and operational factors have a significant influence on performance. Furthermore, the performance is made more sensitive under certain cycle designs. Specifically, there exists an optimal combination of specific power, temperature and pressure that will optimise both on- and off-design performance. For example, when using the new approach developed in this paper, it was found that the maximum specific power that may be generated by the radial inflow turbines developed for CO2 was 142.27 kJ/kg. Previous methods focussed on the off-design performance of turbomachinery alone, the present work extends the application to incorporate more in-depth analysis of the interaction between design parameters and off-design performance of cycles and turbomachinery. The new map-based method developed in this study can be easily integrated into existing power block design codes and may be used in the early cycle design phase to ensure that performance is consistently high by considering the actual operating conditions.