Density-Based Control of Air Coolers in Supercritical CO2 Power Cycles

In this paper, the problem of controlling the thermodynamic state at the outlet of the air cooling unit in a supercritical CO2 Brayton cycle is addressed. First-principle modelling analysis of the cooler model with boundary conditions representing the interaction with the full plant reveals that the dynamic response of the CO2 outlet density to small changes of the cooling air flow has a much higher gain and a much more regular behaviour across the whole operating range of the system than the outlet temperature, suggesting to use the former variable for feedback control instead of the latter. Furthermore, it is shown how adaptive density feedback controllers can be designed with simple gain scheduling policies based on the plant load level and on the cooling air temperature.