Small Size Turbo-Machines for HTR Plants

This paper investigated the effects of working fluid, turbine inlet temperature and shaft rotation speed on the size, number of stages and performance of turbo-machines for high temperature reactor (HTR) plants with indirect Closed Brayton Cycles (CBCs). Working fluids considered are He and 15 g/mole He-Xe and He-N₂ binary mixtures. Analysis increased the shaft speed from 3000 to 9000 rpm and the turbine inlet temperature from 923 K to 1173 K. The number of compression and turbine stages for He-Xe and He-N₂ are significantly lower than for He. Increasing the shaft speed from 3000 to 5400 rpm decreases the number of compression stages for He by ∼ 44% to 47%, by ∼ 40% to 46% for He-N₂ and ∼ 40% to 43% for He-Xe over the range of inlet turbine temperatures considered. For He, the number of turbine stages decreases by ∼ 22% to 30%, but those for He-Xe and He-N₂ turbines either stay the same or decrease by one or two stages. For a shaft speed of 3000 rpm and turbine inlet temperature of 923 K, the number of compression and turbine stages for He are 27 and 9, while those for He-Xe are 7 and 2 stages, respectively. Increasing the turbine inlet temperature to 1173 K increases the number of compression stages for He-Xe to 10 (compared to 34 for He) and the number of turbine stages to 4 (compared to 13 for He). Even though He-Xe and He-N₂ have the same molecular weight, the latter requires more compression and turbine stages, though still considerably less than for He.