Compressed air energy storage system utilizing two-phase flow to facilitate heat exchange
View Patent ↗A compressed-air energy storage system according to embodiments of the present invention comprises a reversible mechanism to compress and expand air, one or more compressed air storage tanks, a control system, one or more heat exchangers, and, in certain embodiments of the invention, a motor-generator. The reversible air compressor-expander uses mechanical power to compress air (when it is acting as a compressor) and converts the energy stored in compressed air to mechanical power (when it is acting as an expander). In certain embodiments, the compressor-expander comprises one or more stages, each stage consisting of pressure vessel (the “pressure cell”) partially filled with water or other liquid. In some embodiments, the pressure vessel communicates with one or more cylinder devices to exchange air and liquid with the cylinder chamber(s) thereof. Suitable valving allows air to enter and leave the pressure cell and cylinder device, if present, under electronic control.
1. A method for releasing stored energy, the method comprising:
in an expansion cycle, transferring a quantity of air to a chamber having a piston disposed therein;
allowing the quantity of air to expand and drive the piston;
communicating mechanical power from the piston through a mechanical linkage; and
introducing a determined quantity of liquid to the quantity of air to provide thermal energy absorbed by the expanding air and thereby maintain the quantity of air in a first temperature range during the expansion, wherein the introducing comprises bubbling the air through liquid in the chamber.
2. The method of claim 1 wherein the determined quantity of liquid is based upon one or more control parameters.
3. The method of claim 1 wherein the control parameter is calculated from a measured physical property.
4. The method of claim 1 wherein the control parameter is selected from a maximum decrease in a temperature of the quantity of air during the expansion, an amount of the liquid inside the chamber, an efficiency, a power input to the piston, a speed of the piston, or a force of the piston.
5. The method of claim 1 wherein the first temperature range is reflected by a change in a temperature of the first quantity of air from a first temperature to a second temperature, the change less than a determined value.
6. The method of claim 5 wherein the lower temperature is greater than a freezing point of the liquid.
7. The method of claim 1 wherein at an end of an expansion stroke of the piston, the quantity of air is configured to produce a pressure on the piston substantially equal to a desired pressure.
8. The method of claim 7 , wherein the desired pressure is an input pressure of a next lowest pressure stage, or is ambient pressure.
9. The method of claim 7 wherein the desired pressure is calculated to maximize an efficiency of expansion.
10. The method of claim 7 wherein the desired pressure is calculated to produce a desired level of power output.
11. The method of claim 1 wherein the mechanical linkage is configured to convert reciprocating motion to shaft torque.
12. The method of claim 11 wherein the mechanical linkage comprises a crankshaft.
13. The method of claim 12 wherein the crankshaft is coupled to a piston rod.
14. The method of claim 1 wherein the mechanical power is communicated through the mechanical linkage to a generator.
15. The method of claim 14 wherein the generator comprises a motor-generator.
16. The method of claim 1 wherein the piston comprises a single-acting piston.
17. The method of claim 1 wherein the piston comprises a double-acting piston.
18. The method of claim 1 wherein the determined quantity of liquid comprises water.