Dynamic model of supercritical CO₂ brayton cycles driven by concentrated solar power

Supercritical carbon dioxide (sCO₂) Brayton cycle is an emerging technology to be used as a power block with concentrated solar power (CSP) systems, tower type. sCO₂ Brayton cycle has the potential to be competitive with traditional Rankine steam cycle. Most of the studies have been focused on the steady state analysis of this technology. This research has developed numerical models for five configurations of sCO₂ Brayton cycles operating under quasi steady state conditions. The studied cycles are connected directly to the solar central receiver tower, which is used to provide heat input to the cycles; consequently, the heat addition is changing over time as a function of solar radiation. During the off load operation, the mass flow rate of the cycle is changing with the goal of keeping the turbine inlet temperature at 700°C. The compressor and turbine use a partial load model to adjust velocities according to the new mass flow rate. Also, the heat exchangers effectiveness are adjusted as they present off-design operation. In the recompression cycle, the model permits to explore the relationship between recompression fraction and the ambient temperature. It is demonstrated that the power generated by the cycle may be improved more than 6 % if the recompression fraction is continuously changed and controlled as a function of the ambient temperature.