Abstract:
A compressed air energy storage (CAES) system is disclosed for the generation of power. The system may include a compressor configured to receive inlet air and output compressed air to an air storage during an off-peak period. During a peak load period, compressed air from the air storage may be released to generate power. A heat exchanger fluidly coupled to the air storage may receive the released compressed air and transfer heat to the compressed air. An air expander may receive the heated compressed air from the heat exchanger, expand the heated compressed air to generate a first power output, and output an exhaust. The system may further include a bypass line configured to circumvent compressed air around the air expander. A second power output may be generated through a turbine configured to receive the compressed air from the air storage and the exhaust from the air expander.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 12/818,186, filed on Jun. 18, 2010, which is a continuation-in-part of U.S. application Ser. No. 12/632,841, filed on Dec. 8, 2009, which is a continuation-in-part of U.S. application Ser. No. 12/582,720, filed on Oct. 21, 2009, which is a division of U.S. application Ser. No. 12/285,404, filed on Oct. 3, 2008, now U.S. Pat. No. 7,614,237 which is a continuation-in-part of U.S. application Ser. No. 12/216,911 filed on Jul. 11, 2008, abandoned, which is a continuation of U.S. application Ser. No. 12/076,689, filed on Mar. 21, 2008, now U.S. Pat. No. 7,406,828, which is a division of U.S. application Ser. No. 11/657,661, filed on Jan. 25, 2007, abandoned. The content of each of these applications is hereby incorporated by reference into this specification. 
     
    
     BACKGROUND 
       [0002]    This invention relates to a Compressed Air Energy Storage (CAES) system and, more particularly, to an adiabatic CAES system that provides improved performance of renewable energy sources by operating a CAES plant with generally zero emissions and without burning any fuel. 
         [0003]    In my earlier U.S. Pat. No. 4,765,142, the content of which is hereby incorporated by reference into this specification, I disclosed a system that stores the heat of compression which is used as an alternative to produce steam for injection into a combustion process. The system theoretically offered high energy storage efficiently, but required new research and development efforts associated with high capital costs to implement. That is why such systems have never been implemented. 
         [0004]    There is a need to provide an adiabatic CAES system with improved storage and recovery of the heat of compression by employing practical implementation solutions. 
       SUMMARY 
       [0005]    Embodiments of the disclosure may provide a compressed air energy storage power generation system. The compressed air energy storage power generation system may include a compressor configured to receive inlet air and output compressed air. The system may further include an air storage fluidly coupled to the compressor and defining a volume configured to store the compressed air from the compressor. A heat exchanger may be fluidly coupled to the air storage via a feed line and may be configured to receive the compressed air from the air storage and transfer heat from a heat source to the compressed air. An air expander may be fluidly coupled to the heat exchanger via the feed line and configured to receive the heated compressed air from the heat exchanger, expand the heated compressed air to generate a first power output in an electric generator coupled to the air expander, and output an exhaust. A bypass line may be fluidly coupled to the feed line upstream of the air expander and downstream from the air expander, and configured to circumvent the compressed air around the air expander. The system may also include a turbine fluidly coupled to the air expander and the air storage and configured to receive the compressed air from the air storage and the exhaust from the air expander. 
         [0006]    Embodiments of the disclosure may further provide a method of operating a compressed air energy storage system. The compressed air energy storage system may include a compressor, an air storage fluidly coupled to the compressor, a heat exchanger fluidly coupled to the air storage via a feed line, an air expander fluidly coupled to the heat exchanger via the feed line, a bypass line fluidly coupled to the feed line upstream of the air expander and downstream from the air expander, and a turbine fluidly coupled to the air expander and the air storage. The method of operating the compressed air energy storage system may include compressing inlet air in the compressor and storing the compressed air in the air storage during an off-peak period. The method may further include releasing the compressed air from the air storage during a peak load period and heating a first portion of the compressed air from the air storage in the heat exchanger with heat from a heat source. The first portion of the heated compressed air may be directed from the heat exchanger to the air expander and expanded therein to produce a first power output and an exhaust. The method may also include directing a second portion of the compressed air from the air storage through the bypass line to the turbine, thereby circumventing the air expander. The method may include expanding the exhaust from the air expander and the second portion of the compressed air from the bypass line in the turbine to generate a second power output. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The invention will be better understood from the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts, in which: 
           [0008]      FIG. 1  is a view of an adiabatic CAES system provided in accordance with a first embodiment thereof, utilizing a first combustion turbine assembly having a debladed turbine and a second combustion turbine assembly having a debladed compressor. 
           [0009]      FIG. 2  is a view of the system of  FIG. 1 , and further including an additional expander downstream of the air storage and upstream of the second combustion turbine assembly. 
           [0010]      FIG. 3  is a view of an adiabatic CAES system provided in accordance with a second embodiment thereof, using a motor driven low pressure compressor and a motor driven high pressure compressor for off-peak energy storage and an expander for producing power. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    As noted above, the power plant of U.S. Pat. No. 4,765,142 has not been commercially implemented due to the high capital cost of providing components of the plant. In particular, there is a high capital cost of research and development of the low pressure compressor of the plant so as to have the required discharge pressure and temperature. A combustion turbine assembly comprises a compressor and a turbine on a single shaft, with a combustor feeding the turbine. The turbine is connected with an electric generator to produce power. The combustion turbine assembly compressor is effective for use in an adiabatic CAES plant due to the fact that the combustion turbine assembly is similarly to an adiabatic CAES plant capitalizing on both the low pressure compressor discharge pressure and temperature. Industrial compressors are not as attractive for use as the low pressure compressor in an adiabatic plant since they have intercoolers because they are targeting only the compressed air/gas specified pressure with minimum power consumption. 
         [0012]    With the above in mind,  FIG. 1  shows an advanced adiabatic CAES system, generally indicated at  10 , in accordance with an embodiment. The system  10  includes a first single shaft combustion turbine assembly  12 , having a low pressure compressor  14  receiving a source of inlet air and a turbine element  16  that is initially debladed since such turbine element is not to be utilized for the production of energy. Consequently, the inlet to the turbine element  16  is disconnected or closed and no fuel will be supplied to combustor  18  during this energy absorbing compression stage. In order to compensate for the axial loss of thrust balance due to deblading turbine element  16 , an externally located additional thrust bearing  20  is installed on shaft  22 . Shaft  22  serves to transmit rotational energy from a synchronous electrical generator/motor, illustratively, motor  24 , to debladed turbine element  16 , compressor  14  and thrust bearing  20 . 
         [0013]    A compressor discharge flange (not shown) is typically provided in the compressor of a conventional combustion turbine assembly to direct compressed air to combustor  18 . However, in the embodiment, such compressed air input to combustor  18  is disconnected and the compressed air is instead directed to a first heat exchanger  26  via interconnection  28 . 
         [0014]    In addition to the above modification to combustion turbine assembly  12  and heat exchanger  26 , an industrial high pressure compressor  30 , driven by motor  32 , and an aftercooler  34  are provided to complete the compression train. 
         [0015]    High pressure compressor  30  further compresses the air outputted by the low pressure compressor  14 . High pressure compressor  30  is preferably driven through clutch  37  by the motor  32 . Alternatively, high pressure compressor  30  may be driven by motor  24 . The high pressure compressor  30  provides the additional pressure increase of the compressed air that is optimized based on a number of considerations such as the effects on the compressed air storage design and costs, and the effects on energy recovery and generation during peak hours. To minimize power consumption, the high pressure industrial compressor  30  has at least one intercooler  31  resulting in a temperature of compressed air outputted there-from to be substantially less than the temperature of compressed air outputted by the low pressure compressor  14 . 
         [0016]    Since no heat is stored due to compression by the high pressure compressor, the aftercooler  34  is not associated with a thermal storage device but merely further cools the compressed air exiting high pressure compressor  30  before entering the air storage  36 . The aftercooler  34  can be air or water cooled. 
         [0017]    In the embodiment, the air storage  36  is preferably an underground air storage such as a geological structure. Alternatively, the air storage  36  can be an above-ground pressure vessel that also could be a tower of a wind power plant. Although in the embodiment, compressed air is preferably stored in the air storage  36 , the compressed air can be converted into a liquid air and stored in the air storage  36 . When needed, the liquid air can then be converted back to compressed air and used in the system  10 . 
         [0018]    The system  10  includes a second combustion turbine assembly  38  that comprises a turbine  40  and a compressor  42  connected to a single shaft  44 . Compressor  42  is initially debladed since such compressor is not to be utilized for the compression of air. In order to compensate for the axial loss of thrust balance due to deblading compressor  42 , an externally located additional thrust bearing  52  is installed on the shaft  44 . Shaft  44  serves to transmit rotational energy from the turbine  40  to a synchronous electrical machine, illustratively, generator  50 , debladed compressor  42 , and thrust bearing  52 . 
         [0019]    In addition to the above modifications to the combustion turbine assembly  38 , the compressed air output of the compressor  42  is disconnected or closed. The combustor  54  is also non-functioning. Further, a valve  56  and associated interconnection  58 , such as piping, are placed between the non-functioning combustor  54  and the air storage  36 . Valve  56  and air storage  36  serve as a compressed air source for the turbine  40 , in place of compressor  42 . 
         [0020]    The conventional combustion turbine assembly is ordinarily coupled to an electrical power generator of predetermined capacity. In accordance with the embodiment, the electrical generator of the conventional combustion turbine assembly is removed and replaced by an electrical generator  50  of approximately double capacity since combustion turbine assembly  38  has approximately twice its original output once the compressor is debladed. Although the second combustion turbine assembly  38  provides the turbine  40 , an industrial turbine can be used instead. 
         [0021]    Adiabatic compressed air storage is different from a conventional CAES system in that it captures, stores, and returns heat during the compression cycle in order to conserve and recover the stored energy. In that regard, a first thermal energy storage device  60 , preferably a hot oil storage tank for storing thermal energy by heated oil in the tank, is connected to an outlet of the first heat exchanger  26 . An outlet of the first thermal energy storage device  60  is connected, via piping  62 , with a second heat exchanger  64  to provide heat to compressed air released from the storage  36 , as will be explained more fully below. An outlet of the second heat exchanger  64  is connected via piping  66  to an inlet of the turbine  40 . A valve  68  is provided in piping  66  to control flow there-through. A second thermal energy storage device  70  is connected, via piping  72 , with the second heat exchanger  64 . The second thermal energy storage device  70  is preferably a cold oil storage tank for storing cooled oil in the tank. An outlet of the second thermal storage device  70  is connected to the first heat exchanger  26  to remove heat from the compressed air from compressor  14  and to heat the oil. 
         [0022]    In accordance with the embodiment, during off-peak hours energy (which is not currently needed) is used by the motor-driven compressor  30  and is stored in the form of the compressed air in the air storage  36 . The energy of the stored compressed air depends on a combination of the stored air pressure and stored air temperature. In addition, the size and cost of the compressed air storage  36  depends on the compressed air pressure and air temperature. In the case of an underground storage, the stored air temperature is very limited by geological limitations and at times should not exceeding 80.degree. F. In the conventional CAES plant, the compressed air is just cooled to an acceptable stored air temperature level and the heat is wasted. In the adiabatic CAES system  10 , during off-peak hours, oil in the cold oil tank  70  is heated in heat exchanger  26  by the exhaust heat of the compressed air from the low pressure compressor  14 . The heated oil is transferred and stored in the hot oil tank  60 . In the embodiment, the temperature of the compressed air outputted by the low pressure compressor  14 ′ was 776.degree. F. as compared to the temperature of 387.degree. F. of the compressed air outputted by the high pressure compressor  30 . The temperature of the compressed air was reduced further to 100.degree. F. upon exiting the aftercooler  34  and upon entering the air storage  36 . 
         [0023]    During peak hours, the stored energy is recovered and utilized for peak power generation by using the stored compressed air energy based on the most effective and optimized combination of the stored compressed air pressure and temperature. More particularly, during peak hours, compressed air is released from the air storage  36  at specific pressure and temperature and is routed through flow control and pressure reducing valve  74  through heat exchanger  64 . The hot oil stored in the hot oil tank  60  is directed to the heat exchanger  64  for heating the compressed air released from the air storage  36 . The heated compressed air is then sent via piping  66  to the inlet of the non-functioning combustor  54  or directly to the turbine  40  which expands the heated compressed air to produce electrical power via generator  50 . Cold oil resulting from transferring heat to the compressed air released from the air storage is transferred to and stored in the cold oil tank  70 . 
         [0024]      FIG. 2  shows another embodiment of an adiabatic CAES system, generally indicated at  10 ′. The system  10 ′ is identical to the system  10  of  FIG. 1 , but further includes an additional high pressure expander  78 . In particular, the expander  78  is connected with piping  66  such that compressed air can be routed from the air storage  36  through flow control valve  74 , be preheated in a heat exchanger  64  that utilizes the hot oil from hot oil tank  60  and be expanded through the green power generation expander  78  driving an electric generator  80  to produce additional electrical power. The expander  78  has air extraction via interconnection  82  and through valve  84  to supply the extracted air upstream of the turbine  40 . Although all exhaust air from expander  78  is sent to the turbine  40 , it can be appreciated that only a portion of the airflow expanded in the expander  78  can be sent to the turbine  40 , with the remaining airflow being expanded in a low pressure part of the expander  78  to atmospheric pressure, generating the additional green electrical power. 
         [0025]      FIG. 3  shows another embodiment of an adiabatic CAES system, generally indicated at  10 ″. Instead of using the combustion turbine assemblies  12  and  38 , to provide the low pressure compressor  14  and the turbine  40  of  FIG. 1 , the system  10 ″ uses a low pressure industrial compressor  14 ′ driven by motor  86  and an industrial turbine  40 ′ for driving the generator  50 ′. The system  10 ″ operates in a similar manner as the system  10  as discussed above with regard to  FIG. 1 . In the embodiment, the temperature of the compressed air outputted by the low pressure compressor  14 ′ was 775.degree. F. as compared to the 271.degree. F. temperature of the compressed air outputted by the high pressure compressor  30 . The temperature of the compressed air was reduced further to 116.degree. F. upon exiting the aftercooler  34  and upon entering the air storage  36 . 
         [0026]    Also, although not shown in  FIG. 3 , the additional expander  78  can be provided in the system  10 ″. Furthermore, the turbine  40 ′ can be replaced with the combustion turbine assembly  38  having the turbine  40  and the debladed compressor on the single shaft  44  of  FIG. 1 , or with a turbine from a conventional combustion turbine assembly that has its own shaft that is separated from compressor shaft via a flange  46  ( FIG. 1 ). It is noted that when flange  46  provided and is disconnected, there is no need to debladed compressor  42  since it can simply be removed. Similarly, the compressor  14 ′ can be replaced with the combustion turbine assembly  12  having the compressor  14  and the debladed turbine element on the single shaft  22  of  FIG. 1 , or with a compressor from a conventional combustion turbine assembly that has its own shaft that is separated from turbine shaft via a flange  17  of  FIG. 1 . It is noted that when flange  17  is provided and disconnected, there is no need to debladed turbine element  16  since it can simply be removed. Thus, any combination of the disclosed compressors  14 ,  14 ′ and turbines  40 ,  40 ′ can be used. 
         [0027]    Although the thermal energy storage devices  60  and  70  are shown as separate oil tanks, these devices can be incorporated into a single structure having the appropriate tanks. Also, instead of heavy oil, the thermal fill material can be molten salt or ceramics or other suitable material for storing thermal energy. 
         [0028]    The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.