HK1159720B - Caes plant using humidified air in the bottoming cycle expander - Google Patents

Description

CAES plant using humidified air in a bottoming cycle expander

This application is a continuation-in-part application of U.S. application No. 12/285,404 filed on 3.10.2008, No. 12/285,404 is a continuation-in-part application of U.S. application No. 12/216,911 filed on 11.7.2008, No. 12/216,911 is a continuation-in-part application of U.S. application No. 12/076,689 filed on 21.3.2008, No. 12/076,689 is now U.S. patent No. 7,406,828, and is a division of U.S. application No. 11/657,661 filed on 25.1.2007 but now being abandoned.

Technical Field

These embodiments relate to Compressed Air Energy Storage (CAES) power plants and, more particularly, to reducing compressed air storage capacity of compressed air energy storage power plants.

Background

U.S. Pat. nos. 7,389,644 and 7,406,828 each disclose a CAES power plant in which compressed air is stored primarily in underground storage using salt, aquifer or hard rock geological formations. The location of large capacity CAES stations is dictated by acceptable geological formations for compressed air storage near large electrical grids. Small capacity CAES stations (e.g., 5-25MW) are used for load management of small wind farms and small distributed power generation grids. The multiple locations of small CAES stations are governed by the locations of energy consumers, usually located in urban areas as well as populated areas. Obviously, these urban areas do not necessarily have good geological formations for compressed air storage. Even with good geological formations, the storage volume of compressed air will be very small and it is very expensive to build such a reservoir in underground geological formations. Therefore, for small capacity CAES plants, the best option is to store the compressed air in pressure vessels and/or piping above ground. Above ground storage is still very expensive and its cost is proportional to its volume.

Disclosure of Invention

There is a need to reduce compressed air storage in CAES power plants, particularly in small CAES power plants that use above-ground compressed air storage.

The present invention aims to fulfill the above mentioned needs. In accordance with the principles of an embodiment, this object is achieved by providing a compressed air energy storage power generation system comprising: a gas turbine assembly having: a primary compressor constructed and arranged to receive ambient intake air; a main expansion turbine operatively associated with the main compressor; a primary combustion chamber constructed and arranged to preheat the received compressed air from the primary compressor and feed the primary expansion turbine; and an electrical generator associated with the main expansion turbine to produce electrical power. The air reservoir has a volume for storing compressed air associated with a certain amount of stored energy. The source of humidity humidifies the compressed air exiting the air reservoir and thereby provides humidified compressed air. A heat exchanger is constructed and arranged to receive a source of heat and to receive the humidified, compressed air so as to heat the humidified, compressed air. An air expander is constructed and arranged to expand the heated humidified compressed air to an exhaust atmospheric pressure to generate additional power, and is further constructed and arranged to allow a portion of the airflow expanded by the air expander to be injected into the gas turbine assembly under conditions to generate additional power as a result of the power augmentation of the gas turbine. A generator associated with the air expander generates additional electrical power. Due to the humidification of the compressed air, the volume of the air reservoir associated with a certain stored energy may be reduced, thereby reducing the size and cost of the air reservoir. For the compressor supplying the air reservoir, the size, cost and power consumed by the compressor are correspondingly reduced.

According to another aspect of an embodiment, a method of reducing the volume of an air reservoir in a compressed air energy storage power generation system is provided. The system includes a gas turbine assembly having: a primary compressor constructed and arranged to receive ambient intake air; a main expansion turbine operatively associated with the main compressor; at least one combustor constructed and arranged to preheat received compressed air from the primary compressor and feed to the primary expansion turbine; and an electrical generator associated with the main expansion turbine to produce electrical power. The air reservoir has a volume for storing compressed air associated with an amount of stored energy. The method provides moisture to humidify the compressed air exiting the air reservoir and thereby provides humidified compressed air. The humidified compressed air is then heated. The heated humidified compressed air is expanded in an air expander. Additional electricity is generated by a generator using air expanded by an air expander. The air expander is constructed and arranged to allow a portion of the airflow expanded by the air expander to be extracted and injected into the gas turbine assembly under conditions such that additional power is generated by the power augmentation of the gas turbine.

Other objects, features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification.

Drawings

The present invention will be better understood from the following detailed description of the preferred embodiments of the invention taken in conjunction with the accompanying drawings, in which like reference numerals refer to like parts, and in which:

FIG. 1 is a schematic diagram of a CAES power generation system of the type disclosed in U.S. Pat. No. 7,406,828 having a relatively large underground air storage for storing compressed air.

FIG. 2 is a schematic diagram of a CAES power generation system with a saturator as a source of humidity according to one embodiment, such that the volume of the air storage and the size of the compressor used to charge the air storage may be reduced due to the use of humidified compressed air.

FIG. 3 is a schematic diagram of a CAES power generation system having a heat recovery steam generator as a source of humidity according to another embodiment, such that the volume of the air storage and the size of the compressor used to charge the air storage may be reduced due to the use of humidified compressed air.

FIG. 4 is a schematic diagram of a CAES power generation system having steam external to the system as a source of humidity according to yet another embodiment of the present invention, such that the volume of the air reservoir and the size of the compressor used to charge the air reservoir may be reduced due to the use of humidified compressed air.

Detailed Description

U.S. Pat. Nos. 7,389,644 and 7,406,828, the contents of which are incorporated herein by reference, disclose that in a CAES system, stored compressed air is extracted from a compressed air storage, preheated by utilizing exhaust heat of a gas turbine, and then directed to an expander that produces bottoming cycle power in addition to the power augmented gas turbine power. The power generated by the bottoming cycle expander, among other features, is proportional to the flow of compressed air extracted from the reservoir and the inlet temperature and pressure of the expander. The compressed air flow and temperature of the expander are optimized based on the available exhaust heat/other heat sources of the gas turbine. For example, FIG. 1 shows a CAES power plant 10 of U.S. Pat. No. 7,406,828 having an extracted air stream of 47.5 pounds per second (lbs/sec) from a relatively large underground compressed air storage 18, producing 15.3MW net total power and 9.44MW bottoming cycle expander power. The net CAES power at around 15MW was chosen only for comparative analysis of the concept of this patent with the new embodiment. The range of net power is practically unlimited, but is based on the specific concept of above ground compressed air storage, and typical net power is expected to be in the range of 5-25 MW.

Referring to FIG. 2, a CAES power generation system with power augmentation in accordance with one embodiment of the present invention is shown and generally designated by the reference numeral 10'. The system 10' includes a conventional gas turbine assembly, generally indicated by reference numeral 11, having: a main compressor 12 receiving an intake air source at ambient temperature at an inlet 13 and feeding compressed air to a main fuel combustor 16 for preheating; a main expansion turbine 14 operatively associated with the main compressor 12, wherein the combustion chamber 16 feeds the main expansion turbine 14; and a generator 15 for generating electrical power.

For a compressed air energy storage power plant of 5-25MW, an air storage 18' is provided, preferably of the above-ground type, which utilizes pressure vessels and/or piping that store air compressed by at least one auxiliary compressor 20. The intercooler 19 may be associated with the compressor 20. In this embodiment, the auxiliary compressor 20 is driven by a motor 21, but may be driven by an expander or any other source. The auxiliary compressor 20 provides compressed air to the reservoir 18' during off-peak hours. According to this embodiment, a source of moisture is associated with the outlet 22 of the air reservoir 18'. As shown in fig. 2, the source of humidity is a saturator 23 constructed and arranged to receive compressed air from the air storage 18' and humidify the received compressed air with hot water. A conventional water heater 25 and pump 27 are associated with saturator 23. The heat exchanger 24 is constructed and arranged to receive a source of heat (e.g., exhaust gas 29 from the main expansion turbine 14) and to receive humidified compressed air from the saturator 23 so as to heat the received humidified compressed air. Instead of, or in addition to, the exhaust gas 29 from the main turbine 14, the heat exchanger 24 may receive any externally available heat source.

The outlet 26 of the heat exchanger 24 is connected to an optional combustor 28 feeding an expander 30, the function of which will be explained below. The expander 30 is preferably connected to a generator 30 to generate additional electrical power generated by the expander 30. A heat exchanger 24 for heating the compressed air sent to the expander 30 is also optional.

In the main power generating mode of operation during peak load times and during periods when the combustor 28 is not operating, compressed air from the air storage 18' is supplied through the saturator 23 to be humidified, preheated in the heat exchanger 24, and then sent to the expander 30. The humidified heated air is expanded by an expander 30, which is connected to a generator 31, and generates additional electrical power. The gas flow extracted from the expander 30 is injected into the gas turbine assembly 11, preferably upstream of the combustion chamber 16, with parameters determined by the limitations of the gas turbine and the optimization of the injection flow. As shown in fig. 2, structure 32 is in communication with structure 33 to facilitate the injection of air. In this embodiment, the structures 32 and 33 are preferably pipe structures. Under certain conditions, the implantation may be limited or restricted. For example, based on data published by the gas turbine manufacturer, injection at low ambient temperatures may not be allowed or possible, or injection may not be allowed or possible due to accessibility of the injection point, or injection may not occur due to operational judgments. The extracted gas stream injected into the gas turbine assembly 11 upstream of the combustor 16 provides a gas turbine power augmentation of approximately up to 20% to 25%. The remaining gas stream in expander 30 is expanded to atmospheric pressure through a plurality of low pressure stages. Thus, when injection is possible or desired, not all of the gas flow from the expander 30 is vented to atmospheric pressure.

Alternatively, in the main power producing mode of operation during peak load times and when the combustor 28 is not operating, the temperature of the compressed air is reduced as the expander 30 reduces the pressure of the preheated humidified compressed air. Thus, cold (sub-ambient temperature) air from the expander 30 may be connected with ambient air at the inlet 13 via structure 32' so that ambient intake air and cooler expander exhaust air mix to reduce the overall temperature of the intake air prior to being received by the main compressor 12. Reducing the overall temperature of the inlet air prior to receipt by the main compressor 12 provides a gas turbine power augmentation of approximately up to 20% to 25%. In this embodiment, the structure 32 'is a conduit connected between the discharge stage of the expander 30 and the inlet 13 of the main compressor 12, the structure 32' being an alternative to the conduit 32.

Since the compressed air is humidified via the saturator, the flow rate from the air reservoir 18' is reduced to 28 pounds per second (lbs/sec) compared to 47.5 lbs/sec in fig. 1 without the saturator 23. Since the flow rate from the air reservoir 18 'is reduced while substantially maintaining the net total power (e.g., 15MW of fig. 2 and 15.3MW of fig. 1), the volume of the air reservoir 18' may be advantageously reduced, thereby reducing the cost of the air reservoir. In the embodiment of fig. 2, the volume of the air reservoir 18' may be reduced to about 10/17 to provide the same amount of energy/capacity as compared to the volume of the air reservoir 18 of fig. 1. Furthermore, as the power consumption of the compressor 20 decreases, the size, and therefore the cost, of the compressor 20 may be reduced, because less air is required to be supplied to the air reservoir 18'.

In the synchronous stand-by power mode of operation, which is a very short duration emergency mode of operation, combustor 28 is operating while gas turbine assembly 11 is not operating. The heat exchanger 24 and the saturator 23 may not be operated. The compressed air from the reservoir 18' is preheated by the combustion chamber 28 which is used to combust the fuel supplied to the expander 30. The heated air is expanded by an expander 30 connected to a generator 31 to produce a direct immediate start for synchronous stand-by power operation independent of the operation of the gas turbine assembly 11.

Referring to FIG. 3, in the system 10 ", instead of the saturator 23, the source of humidity is a Heat Recovery Steam Generator (HRSG) 34. Thus, the compressed air from the air storage 18' is mixed with the steam produced by the HRSG 34, then further preheated by the heat exchanger 24 and expanded by the expander 30. The HRSG 34 preferably utilizes exhaust gases from the turbine 14 as a heat source. The duct burner 36 may be disposed upstream of the heat exchanger 24, or between the heat exchanger 24 and the HRSG 34, economizer 40, and air preheater 38. Because the compressed air is humidified via the HRSG 34, the flow rate from the air storage 18' is reduced to 28 pounds per second as compared to 47.5 pounds per second of FIG. 1 without utilizing the HRSG 34. Since the flow rate from the air reservoir 18' is reduced while substantially maintaining the net total power (e.g., 15MW of fig. 3 and 15.3MW of fig. 1), the volume of the air reservoir used to provide the same amount of energy storage/generation can be advantageously reduced, thereby reducing the cost of the air reservoir.

Referring to FIG. 4, in the system 10 '", instead of the HRSG 34, the source of moisture is steam 38 generated external to the system 10'". Since the compressed air is humidified via the added steam 38, the flow rate from the air reservoir 18' is reduced to 28 pounds per second compared to 47.5 pounds per second of fig. 1 without the added steam 38. Since the flow rate from the air reservoir 18' is reduced while substantially maintaining the net total power (e.g., 15MW of fig. 4 and 15.3MW of fig. 1), the volume of the air reservoir used to provide the same amount of energy storage/generation can be advantageously reduced, thereby reducing the cost of the air reservoir.

Thus, the system of these embodiments humidifies the stored compressed air for additional power generation before being directed to the expander 30. Humidification of the compressed air significantly increases the mass of the humidified compressed gas stream by a factor of about 1.5 to 2.5 (depending on the humidification temperature and pressure), and significantly increases the power of the expander 30. The flow of humidified, compressed air introduced to the expander 30 and the temperature of the air flow are optimized based on the available exhaust heat of the gas turbine assembly 11 and/or other heat sources. While producing substantially the same power via the expander 30 (as compared to the system 10 of fig. 1), the use of humidified compressed air flow by the expander 30 significantly reduces the stored "dry" compressed air flow mass to about 2/3 to 2/5, and correspondingly reduces the volume of the compressed air storage and its cost. Thus, for the compact CAES systems of figures 2, 3 and 4 which in fact provide the same net total power of about 15MW and the same stored/generated energy, the cost of the above ground storage 18' is now significantly reduced and is feasible.

The foregoing preferred embodiments have been shown and described to illustrate the structural and functional principles of the present invention and to illustrate the methods of practicing the preferred embodiments, and changes may be made to the described embodiments without departing from such principles. Accordingly, this invention includes all modifications encompassed within the scope of the following claims.

Claims (19)

1. A compressed air energy storage power generation system, comprising:

a gas turbine assembly, comprising: a primary compressor constructed and arranged to receive ambient intake air; a main expansion turbine operatively associated with the main compressor; a primary combustion chamber constructed and arranged to receive and preheat compressed air from the primary compressor and feed the primary expansion turbine; and a generator associated with the main expansion turbine to produce electrical power,

an air reservoir having a volume for storing compressed air;

a humidity source that humidifies the compressed air exiting the air reservoir and thereby provides humidified compressed air;

a heat exchanger constructed and arranged to receive a source of heat and to receive the humidified compressed air so as to heat the humidified compressed air;

a duct burner fluidly connected to the heat exchanger and disposed upstream of the heat exchanger;

an air expander constructed and arranged to expand the heated humidified compressed air to the discharged atmospheric pressure to generate additional power, and further constructed and arranged to allow a portion of the air stream expanded by the air expander to mix with the ambient intake air received by the main compressor;

a conduit configured and arranged to fluidly connect the air expander and an inlet of the main compressor such that all or the portion of the airflow is mixed with the ambient intake air before being received by the main compressor; and

a generator associated with the air expander to generate additional electrical power.

2. The compressed air energy-storing power generation system of claim 1, wherein the wet source is a saturator.

3. The compressed air energy storage power generation system of claim 1, wherein the moisture source is a heat recovery steam generator.

4. The compressed air energy storage power generation system of claim 1, wherein the source of moisture is steam from a source external to the compressed air energy storage power generation system.

5. The compressed air energy storage power generation system of claim 1, wherein the source of humidity is sufficient to provide the humidified compressed air such that the volume of the air reservoir can be reduced to 2/3 to 2/5 compared to the volume of the air reservoir in the system without a source of humidity when the compressed air energy storage power generation system produces the same net total power and stored energy as the system without a source of humidity.

6. The compressed air energy-storing power generation system of claim 1, wherein the heat source is exhaust gas from the main expansion turbine.

7. The compressed air energy storage and power generation system of claim 1, further comprising a compressor associated with the air reservoir to supply compressed air to the air reservoir.

8. The compressed air energy storage power generation system of claim 1, wherein the compressed air energy storage power generation system is constructed and arranged to provide a net total power of 5-25MW and the compressed air storage comprises a pressure vessel or piping.

9. The compressed air energy-storing power generation system of claim 1, further comprising an auxiliary combustion chamber between the air storage and the air expander, the auxiliary combustion chamber configured to receive compressed air from the air storage and to preheat the compressed air by combusting fuel to feed the air expander with preheated compressed air to provide synchronous back-up power when the gas turbine assembly is not operating.

10. A method of reducing a volume of an air reservoir of a compressed air energy storage power generation system having a gas turbine assembly comprising: a primary compressor constructed and arranged to receive ambient intake air; a main expansion turbine operatively associated with the main compressor; at least one combustor constructed and arranged to receive and preheat compressed air from said primary compressor and feed to said primary expansion turbine; and a generator associated with the main expansion turbine to produce electricity, the method comprising:

compressed air is released from the air reservoir and,

humidifying the compressed air discharged from the air reservoir,

heating the humidified compressed air, wherein the step of heating the humidified compressed air comprises using a duct burner as a heat source;

expanding the heated humidified compressed air in an air expander constructed and arranged to allow a portion of a gas stream expanded by the air expander to mix with the ambient intake air received by the main compressor,

mixing all or the portion of the airflow with the ambient intake air before being received by the main compressor, an

Using the air expanded by the air expander, generating additional electrical power via a generator,

wherein the step of humidifying the compressed air is such that the volume of compressed air stored in the air reservoir is reduced compared to the volume without the humidifying step.

11. The method of claim 10, wherein the compressed air energy storage and power generation system is constructed and arranged to provide a net total power of 5-25MW, and the method comprises using a pressure vessel or piping as the compressed air storage.

12. The method of claim 10, wherein a saturator humidifies the compressed air.

13. The method of claim 10, wherein a heat recovery steam generator humidifies the compressed air.

14. The method of claim 10, wherein the compressed air is humidified by steam from a source external to the compressed air energy storage power generation system.

15. The method of claim 10 wherein the step of humidifying ensures that the volume of the air reservoir can be reduced to 2/3 to 2/5 compared to the volume of the air reservoir in the system that does not humidify the released compressed air when the compressed air energy storage power generation system produces substantially the same net total power and has the same energy/power storage capacity as the system that does not humidify the released compressed air.

16. The method of claim 10, wherein the heating step includes using exhaust from the main expansion turbine as an additional heat source.

17. A compressed air energy storage power generation system, comprising:

a gas turbine assembly, comprising: a primary compressor constructed and arranged to receive ambient intake air; a main expansion turbine operatively associated with the main compressor; a main combustion chamber constructed and arranged to receive compressed air from the main compressor and combust fuel to preheat the compressed air prior to feeding the compressed air to the main expansion turbine; and a generator associated with the main expansion turbine to produce electrical power,

an air reservoir having a volume for storing compressed air;

a motor-driven compressor for supplying compressed air to the air reservoir;

a heat exchanger constructed and arranged to receive a heat source configured to not burn any additional fuel to preheat compressed air released from the air reservoir;

a duct burner fluidly connected to the heat exchanger and disposed downstream of the heat exchanger; a separate air expander located on a shaft separate from the shaft of the main expansion turbine and separate from any compressor shaft and constructed and arranged to expand the heated compressed air to the discharged atmospheric pressure to generate electricity;

a conduit configured and arranged to fluidly connect the independent air expander and the inlet of the main compressor such that all or a portion of the airflow expanded by the independent air expander mixes with the ambient intake air before being received by the main compressor; and

a generator associated with the air expander to generate electrical power.

18. The compressed air energy-storing power generation system of claim 17, wherein the heat source is exhaust gas from the main expansion turbine.

19. The compressed air energy storage power generation system of claim 17, further comprising a source of humidity that humidifies the compressed air exiting the air reservoir, thereby providing humidified compressed air, and the heat exchanger is constructed and arranged to heat the humidified compressed air.