Dynamic study of the extraction ratio and interstage pressure ratio distribution in typical layouts of SCO2 Brayton cycle under temperature fluctuations

Supercritical CO₂ Brayton cycle is widely used in industry because of its small compression work and considerable cycle efficiency. In this work, dynamic simulation numerical models of Supercritical CO₂ Brayton cycle with three typical layouts (recompression, reheating, intercooling) and a newly proposed layout are developed using thermodynamic equations. After verifying the simulated steady-state values with the experimental ones, key parameters in the recompression and the new layout, as well as their responses under temperature perturbations, are calculated for different extraction ratios. It has been found that larger extraction ratios correspond to lower efficiency but higher stability, and similarly, the new proposed layout is 4.1% less efficient but with a 34% smaller fluctuation amplitude compared to the recompression layout. Then system parameters are calculated for different interstage pressure ratio assignments for the turbine in the reheating model and for the compressor in the intercooling model. The results show the 1st-stage with a pressure ratio of 1.2 has higher power generation and cycle efficiency, as well as more stable generated power. For the newly proposed layout, the pre-compressor power, as well as the fluctuation amplitude of the (RC + IC + PC) model, is much larger than the other compression powers, and the fluctuation amplitude from largest to smallest are IC, (RC + IC + PC), RC, RH. The effects of extraction ratio on efficiency and generated power are much greater than the distribution of interstage pressure ratio, and the maximum efficiency is obtained at the small extraction ratio and the equal pressure ratio of the two stages.