Ambient temperature thermal adapter for supercritical carbon dioxide power cycle
A refrigeration cycle is connected to a supercritical carbon dioxide (sCO2) power cycle by incorporating a CO2 condenser which is also the refrigeration cycle evaporator. The heat rejected by the carbon dioxide is absorbed by the refrigerant in the CO2 condenser. Work is done on the refrigerant to raise its temperature above the local ambient temperature. The heat absorbed from the power cycle and the work required to raise the refrigerant temperature is rejected to the ambient environment, which may be either air, earth, or water. This results in improved efficiencies in carbon dioxide power cycles without regard to the ambient temperature by forcing a transcritical phase change even when ambient temperatures are above the carbon dioxide critical point. A two-phase heat transfer on both sides of the CO2 condenser further improves efficiency of the sCO2 power cycle.
1 . A supercritical carbon dioxide (sCO2) power system comprising:
a thermal energy source;
a turbine configured to receive supercritical CO2 from the thermal energy source and expand the supercritical CO2;
a recuperator configured to receive CO2 from the turbine;
a condenser configured to receive CO2 from the recuperator;
a refrigeration system in thermal communication with the condenser, the refrigeration system configured to provide a heat sink for the CO2 at a temperature below a critical temperature of CO2 to condense the CO2 to a liquid state regardless of an ambient temperature being above or below the critical temperature of CO2;
a pump configured to pump liquid CO2 existing the condenser; and
a carbon dioxide (CO2) fluid loop configured to convey CO2 through the fluid loop such that the CO2 transitions from a supercritical state upstream of the turbine, to a gaseous state downstream of the turbine, to a liquid state downstream of the condenser, and back to the supercritical state after being heated by the thermal energy source.
2 . The sCO2 power system as in claim 1 , further comprising a refrigerant flowing through the refrigeration system, and wherein the refrigerant undergoes a phase change from a liquid phase to a vapor phase as it passes through the condenser, thereby providing two-phase heat transfer on both a CO2 side and a refrigerant side of the condenser.
3 . The sCO2 power system as in claim 2 , wherein the refrigerant is one of propane and ammonia.
4 . The sCO2 power system as in claim 1 , wherein the refrigeration system comprises a refrigerant compressor, a refrigerant condenser, and an expansion valve, wherein the expansion valve is configured to reduce pressure and temperature of refrigerant exiting the refrigerant condenser before the refrigerant enters the condenser to absorb heat from the CO2.
5 . The sCO2 power system as in claim 1 , wherein the recuperator is located and configured to receive hot CO2 in a gaseous state from the turbine and transfer heat to cold liquid CO2 after it exits the condenser, thereby preheating the liquid CO2 before the liquid CO2 is heated by the thermal energy source.
6 . The sCO2 power system as in claim 1 , further comprising a generator operatively coupled to the turbine and configured to receive kinetic energy from the turbine and use the kinetic energy to generate electricity.
7 . The sCO2 power system as in claim 1 , further comprising a compressor operatively coupled to the turbine to receive kinetic energy from the turbine and compress refrigerant in a refrigeration system.
8 . The sCO2 power system as in claim 1 , further comprising a CO2 compressor operatively coupled to the turbine to receive kinetic energy from the turbine and compress CO2 within the CO2 fluid loop.
9 . The sCO2 power system as in claim 1 , wherein the refrigeration system is configured to be selectively disengaged from the condenser.
10 . The sCO2 power system as in claim 9 , further comprising an auxiliary cooling system in selective engagement with the condenser and configured to supplant the refrigeration system in response to ambient temperature falling below a threshold.
11 . The sCO2 power system as in claim 1 , wherein the thermal energy source is a nuclear reactor, and wherein the condenser supplies CO2 at a temperature below an ambient temperature.
12 . The sCO2 power system as in claim 11 , wherein the condenser supplies CO2 to the nuclear reactor at a temperature that is predetermined and stable.
13 . The sCO2 power system as in claim 1 , further comprising a heat exchanger that thermally couples the thermal energy source with the CO2 fluid loop.
14 . A method, comprising:
operating a heat generator to raise CO2 to a temperature and pressure above its critical point to a supercritical phase to result in supercritical CO2 (sCO2);
causing the sCO2 to flow through a turbine, wherein CO2 exits the turbine in a gaseous state;
operating a refrigeration cycle and causing a refrigerant to flow through a carbon dioxide (CO2) condenser to provide a heat sink at a temperature below a critical temperature of CO2 regardless of whether an ambient temperature is above or below the critical temperature of CO2;
causing the CO2 that exits the turbine to flow through the CO2 condenser and condense to a liquid CO2; and
pumping the liquid CO2 to the heat generator to cause it to become supercritical, whereby the CO2 undergoes a transcritical cycle transitioning through supercritical, gaseous, and liquid phases.
15 . The method of claim 14 , wherein operating the refrigeration cycle comprises providing a refrigerant at a temperature below an ambient temperature and causing a heat exchange between the CO2 and the refrigerant to cause the CO2 to undergo a phase change from a vapor to a liquid.
16 . The method of claim 14 , further comprising the step of disengaging the refrigeration cycle in response to an ambient temperature falling below a threshold temperature.
17 . The method of claim 14 , further comprising transferring heat from the CO2 exiting the turbine to the liquid CO2 exiting the condenser in a recuperator before the CO2 exiting the turbine enters the condenser.