No abstract

The supercritical carbon dioxide Brayton cycle is recognized as a promising candidate for the next generation of nuclear power and energy system. Among all the components in the cycle, the centrifugal compressor is one of the most important ones. This paper presents a streamline curvature throughflow method based on real gas properties and capable of dealing with condensation flows in the supercritical carbon dioxide compressors. A fluid thermodynamic property calculation method based on look-up tables is adopted to account for the real gas effects and fluid condensation and to reduce the computational time. For extending the simulation capability to the region below the saturation curve to assess the condensation possibility, the homogeneous equilibrium model is adopted. Finally, the real gas-based streamline curvature method is applied in the analysis of a supercritical carbon dioxide centrifugal compressor working near the critical point. Then, computational fluid dynamics calculations are performed to validate the method in detail. The results of the computational validation indicate that the real gas-based streamline curvature method presented in the paper can obtain an accurate enough flow field as that obtained by three-dimensional computational fluid dynamics simulations considering the coarse grid and the much less calculation time.

The inlet volute is one of the key components that guide the working fluid into the radial inflow turbine. It has a significant effect on the performance of the radial inflow turbine. The conventional design criteria for the vaneless inlet volute mainly focuses on the ideal gas, which does not apply to real gas cases, such as supercritical carbon dioxide(S-CO2). In this paper, an MW-class S-CO2 radial inflow turbine is studied. Firstly, the inlet volute design of the radial inflow turbine with a vaned stator is completed, and the flow in the whole machine is calculated using CFD simulations. Then, based on the inlet boundary conditions of the impellers, the vaneless inlet volute with different throat areas and cross-sectional area distributions are investigated. The results indicate that the size of the counter rotating vortexes in the vaneless inlet volute increases with the throat area increasing, and is also influenced apparently by the cross-sectional area distribution. The volute throat area has little effect on the circumferential distribution of the outlet airflow angle but changes the average value of the airflow angle. The cross-sectional area distribution of the volute influences the circumferential distribution of the outlet flow angle. The result indicates that volute with a small-scale convex profile has a uniform outlet flow field. Compared to the turbine with the vaned stator, the radial dimension of the vaneless volute turbine obtained in the final design is significantly reduced, and the total-total efficiency at the design point is 85.62%, which meets the design requirements. Moreover, it also has good performance at off-design operating conditions.

Compared with the traditional steam turbine, the supercritical H2O/CO2 turbine has a relatively high CO2 content in the working fluid. In the initial condensation zone, CO2 dissolves in the condensed water to form carbonic acid, which intensifies the corrosion of blade. In order to study the acid corrosion characteristics in the initial condensation zone of supercritical H2O/CO2 turbine, the acid corrosion rate of the blades in the initial condensation zone of supercritical H2O/CO2 turbine was calculated and analyzed based on the numerical model of non-equilibrium condensation flow and a numerical model of CO2 corrosion reaction. The results show that the temperature, pressure, proportion of CO2 in the gas phase and thickness of the solution on blade surface are the main factors affecting the acid corrosion rate in the initial condensation zone of the turbine. The influence of temperature and pressure is more significant. Overall, the acid corrosion rate decreases stage by stage.

A supercritical H2O/CO2 turbine is a key piece of equipment for the coal gasification in the supercritical water (CGSW) cycle to achieve conversion of heat into power. Compared with a traditional steam turbine, the working medium of an H2O/CO2 turbine has a relatively high CO2 concentration. In the initial condensation zone (ICZ), steam condenses into droplets on the turbine blades and the droplets combine with CO2 to form carbonic acid, which corrodes the turbine blades. In order to research the characteristics of acid corrosion in the ICZ of a H2O/CO2 turbine, the acid corrosion rate of the blades in the ICZ of the H2O/CO2 turbine was calculated and analyzed based on the three-dimensional CFD (3D CFD) method and a one-dimensional numerical model of CO2 corrosion. The results suggest that acid corrosion rates decrease stage by stage in the ICZ due to the reduction in temperature and pressure. Rotor blades in the first stage in the ICZ suffer the worst and form a corrosion zone at the trailing edge of the blade and on the pressure surface. The decline of efficiency caused by corrosion settles down to a relatively steady value of 0.6% for a 10 year service time. Moreover, the corrosion area for the last two stages shrinks with the service time due to the rearward movement of the ICZ.