COMPRESSED GAS ENERGY STORAGE SYSTEM
Embodiments of the present invention use compressed air to store and deliver electrical, mechanical, and/or thermal power with high round-trip efficiency. Various embodiments may be scalable for use in a variety of environments—from wind farms to power plants to motor vehicles. An energy storage system according to the present invention can operate as a stand-alone storage system that connects electrically to the grid, it can be tightly integrated with a wind turbine, and/or it can be co-located with a thermal power generation facility and operate with even higher efficiency by scavenging low-grade waste heat.
1 . An apparatus comprising:
an expander comprising an inlet valve configured to receive a pressurized gas, the expander further comprising an element configured to introduce liquid to effect gas-liquid heat exchange with gas being expanded;
a proportional-integral-derivative (PID) controller configured to adjust a timing of the inlet valve to close when a percentage of the expander filled is a quotient of downstream and upstream pressures;
a gas-liquid separator configured to separate the liquid from a gas-liquid mixture received from the expander; and
an insulated thermal storage unit in thermal communication with the separated liquid.
2 . An apparatus as in claim 1 wherein the insulated thermal storage unit is configured to store the separated liquid.
3 . An apparatus as in claim 1 wherein the insulated thermal storage unit is configured to store a second liquid in thermal communication with the separated liquid through a heat exchanger.
4 . An apparatus as in claim 3 wherein the second liquid is maintained at a lower pressure than the gas-liquid mixture.
5 . An apparatus as in claim 3 wherein the separated liquid and the second liquid comprise water.
6 . An apparatus as in claim 3 wherein the separated liquid comprises water and the second liquid comprises an oil.
7 . An apparatus as in claim 1 wherein the inlet valve is configured to receive the pressurized gas from a compressed gas storage unit.
8 . An apparatus as in claim 7 wherein inlet valve comprises an active valve having a valve timing changed as the compressed gas storage unit depletes.
9 . An apparatus as in claim 1 wherein the inlet valve is configured to receive the pressurized gas from a higher pressure expansion stage.
10 . An apparatus as in claim 1 wherein the expander comprises a reversible compressor/expander.
11 . An apparatus as in claim 10 wherein the insulated thermal storage unit is in thermal communication with a heat source when the reversible compressor/expander is operating as an expander.
12 . An apparatus as in claim 11 wherein the heat source is internal.
13 . An apparatus as in claim 11 wherein the heat source is external.
14 . An apparatus as in claim 10 further comprising a second insulated thermal storage unit configured to be in thermal communication with the separated liquid when the reversible compressor/expander is operating as a compressor.
15 . An apparatus as in claim 14 wherein the second insulated thermal storage unit is in thermal communication with a heat source.
16 . An apparatus as in claim 10 further comprising a second insulated thermal storage unit configured to be in thermal communication with liquid separated by a second gas-liquid separator when the reversible compressor/expander is operating as a compressor.
17 . An apparatus as in claim 10 wherein the insulated thermal storage unit comprises a moveable partition defining,
a first chamber receiving the separated liquid when the reversible compressor/expander is operating as a compressor, and
a second chamber receiving the separated liquid when the reversible compressor/expander is operating as an expander.
18 . An apparatus as in claim 10 wherein the reversible compressor/expander is in selective communication with a Variable Frequency Drive (VFD).
19 . An apparatus as in claim 1 wherein a majority of the gas-liquid heat exchange is sensible heat.
20 . An apparatus as in claim 1 wherein the element comprises a pre-mixing chamber.