Off-design performance comparative analysis of a transcritical CO₂ power cycle using a radial turbine by different operation methods

Comparative analysis on off-design performance of a transcritical CO₂ (tCO₂) power cycle by different operation methods is conducted in this paper. The studied cycle is based on printed circuit heat exchangers (PCHEs) and a radial turbine with adjustable stator blades. A novel method for the optimal operation is proposed to obtain its maximal net power at given parameters of geothermal water. The optimal operation method is found by adjusting control variables including the evaporating pressure and the outlet angle of the adjustable stator. This paper compares the constant pressure operation method based on the adjustable stator, the optimal operation method, and the sliding pressure operation method. The results indicate that the ranges of control variables are narrower by the optimal operation method than by the sliding pressure operation method or by the constant pressure operation method. When the inlet temperature of geothermal water is fixed at the design value (125 °C), the method for optimal operation could generate 15.07% at most more net power than the sliding pressure operation method does and 3.49% more net power than the constant pressure operation method does at studied mass flow rate ratios of geothermal water. The increase of the net power per unit inlet temperature of geothermal water results in an increase of 1.19–1.98% by the optimal operation method compared with the net power at the design point.