Design methodology and internal flow characteristics of a 20MWe supercritical carbon dioxide centrifugal compressor

Abstract

Due to the high density and low viscosity near the critical point, supercritical carbon dioxide (S-CO2) centrifugal compressors exhibit complex aerodynamic behaviours and significant non-linear thermophysical effects, which poses great challenges for design. Relevant design and analyses on the S-CO2 centrifugal compressors exceeding 20 MWe are scarce in China, and numerical simulation results are sensitive to the thermophysical property models adopted for CO2. In the present research, a high-fidelity numerical model was established for the originally designed 20MWe S-CO2 centrifugal compressor. Two typical CO2 models are adopted: the ideal CO2 gas model and NIST real gas model. The results show that during the three-dimensional design process of a S-CO2 compressor, the specific operating conditions, namely, a low rotational speed (less than 10,000 rpm), result in an impeller with a relatively large outer diameter, longer blades, and inlet and outlet angles that are significantly smaller than those of conventional compressors. After applying the three-dimensional computational fluid dynamics simulation, the NIST model presents the highest consistency with design targets. The design stage pressure ratio of 1.77 is achieved. The ideal gas is inapplicable to the design of S-CO2 compressors near the critical point.