WO2019116210A1

WO2019116210A1 - Compressed air energy system

Info

Publication number: WO2019116210A1
Application number: PCT/IB2018/059852
Authority: WO
Inventors: Warwick LEAPER
Original assignee: Leaper Innovate Green Technologies (Proprietary) Limited
Priority date: 2017-12-11
Filing date: 2018-12-11
Publication date: 2019-06-20
Also published as: EP3701617A1; EP3701617A4

Abstract

This invention relates to an energy system and apparatus and more particularly relates to a compressed air energy system (10) and apparatus which includes a power supply means in drive communication with an output demand means via a motor/pump combination (14), a piston assembly (18) powered by and in drive communication with the motor/pump combination (14), and storage means (15) in flow communication with the piston assembly (18) and the motor/pump combination (14).

Description

COMPRESSED AIR ENEGERY SYSTEM

FIELD OF THE INVENTION

[001] This invention relates to an energy system and apparatus and more particularly relates to a compressed air energy system and apparatus.

BACK GROUND TO THE INVENTION

[002] Compressed air energy storage (CAES) is a way to store energy generated at one time for use at another time using compressed air.

[003] At utility scale, energy generated during periods of low energy demand (off-peak) can be released to meet higher demand (peak load) periods. [004] Small scale systems have long been used in such applications as propulsion of mine locomotives. Large scale applications must conserve the heat energy associated with compressing air; dissipating heat lowers the energy efficiency of the storage system.

[005] Compression of air creates heat and in turn does expansion remove heat. If no extra heat is added, the air will be much colder after expansion. If the heat generated during compression can be stored and used during expansion, the efficiency of the storage improves considerably.

[006] Generally there are three methods of dealing with heat in CAES systems namely adiabatic, diabatic, or isothermal.

[007] Adiabatic storage continues to keep the heat produced by compression and returns it to the air as it is expanded to generate power. [008] The theoretical efficiency of adiabatic storage approaches 100% with perfect insulation, but in practice round trip efficiency is expected to be 70%. Heat can be stored in a solid such as concrete or stone, or more likely in a fluid such as hot oil (up to 300 °C) or molten salt solutions (600 °C). [009] Diabatic storage dissipates much of the heat of compression with intercoolers (thus approaching isothermal compression) into the atmosphere as waste; essentially wasting, thereby, the renewable energy used to perform the work of compression. [0010] Upon removal from storage, the temperature of this compressed air is the one indicator of the amount of stored energy that remains in this air. Consequently, if the air temperature is low for the energy recovery process, the air must be substantially re-heated prior to expansion in the turbine to power a generator. This reheating can be accomplished with a natural gas fired burner for utility grade storage or with a heated metal mass. As recovery is often most needed when renewable sources are quiescent, fuel must be burned to make up for the wasted heat. This degrades the efficiency of the storage-recovery cycle; and while this approach is relatively simple, the burning of fuel adds to the cost of the recovered electrical energy and compromises the ecological benefits associated with most renewable energy sources. Nevertheless, this is thus far the only system which has been implemented commercially.

[0011] Isothermal compression and expansion approaches attempt to maintain operating temperature by constant heat exchange to the environment. They are only practical for low power levels, without very effective heat exchangers. The theoretical efficiency of isothermal energy storage approaches 100% for perfect heat transfer to the environment. In practice neither of these perfect thermodynamic cycles is obtainable, as some heat losses are unavoidable. [0012] Near isothermal compression (and expansion) is a process in which air is compressed in very close proximity to a large incompressible thermal mass such as a heat absorbing and releasing structure (HARS) or a water spray. A HARS is usually made up of a series of parallel fins. As the air is compressed the heat of compression is rapidly transferred to the thermal mass, so the gas temperature is stabilised. An external cooling circuit is then used to maintain the temperature of the thermal mass. The isothermal efficiency (Z) is a measure of where the process lies between an adiabatic and isothermal process. If the efficiency is 0%, then it is totally adiabatic; with an efficiency of 100%, it is totally isothermal. Typically with a near isothermal process an efficiency of 90-95% can be expected. [0013] One implementation of isothermal CAES uses high, medium and low pressure pistons in series, with each stage followed by an airblast venturi pump that draws ambient air over an air-to-air (or air-to-seawater) heat exchanger between each expansion stage. Early compressed air torpedo designs used a similar approach, substituting seawater for air. The venturi warms the exhaust of the preceding stage and admits this preheated air to the following stage. This approach was widely adopted in various compressed air vehicles such as H. K. Porter, Inc.'s mining locomotives and trams. Here the heat of compression is effectively stored in the atmosphere (or sea) and returned later on.

[0014] Compression may be achieved with electrically powered turbo- compressors and expansion with turbo 'expanders' or air engines driving electrical generators to produce electricity.

[0015] The storage system of a CAES (Compressed Air Energy Storage) is one of the most interesting characteristics of this technology, and it is strictly related to its economic feasibility, energy density and flexibility. There are a few categories of air storage vessels, based on the thermodynamic conditions of the storage, and on the technology chosen:

1. Constant Volume Storage (Solution mined caverns, aboveground vessels, aquifers, automotive applications, etc.)

2. Constant Pressure Storage (Underwater pressure vessels, Hybrid Pumped Hydro - Compressed Air Storage) [0016] Constant Volume Storage uses a chamber with rigid boundaries to store large amounts of air. This means from a thermodynamic point of view, that this system is a Constant Volume and Variable Pressure system. This causes some operational problems to the compressors and turbines operating on them, so the pressure variations have to be kept below a certain limit, as do the stresses induced on the storage vessels.

[0017] The storage vessel is often an underground cavern created by solution mining (salt is dissolved in water for extraction) or by utilizing an abandoned mine; use of porous rock formations (rocks which have holes through which liquid or air can pass) such as those in which reservoirs of natural gas are found has also been studied.

[0018] In some cases also an above ground pipeline was tested as a storage system, giving some good results. Obviously the cost of the system is higher, but it can be placed wherever the designer chooses, while an underground system needs some particular geologic formations (salt domes, aquifers, depleted gas mines, etc.).

[0019] In this case the constant pressure storage the vessel is kept at a constant pressure, while the gas is contained in a variable volume vessel. Many types of storage vessel have been proposed, but the operating conditions follow the same principle, the storage vessel is positioned hundreds of meters underwater, the hydrostatic pressure of the water column above the storage vessel allows to keep the pressure to the desired level.

[0020] This configuration allows to: · Improve the energy density of the storage system, because all the air contained can be used (the pressure is constant in all charge conditions, full or empty, the pressure is the same, so the turbine has no problem exploiting it, while with constant volume systems after a while the pressure goes below a safety limit and the system needs to stop)

• Improve the efficiency of the turbomachinery, which will work under constant inlet conditions.

• Opens to the use of different geographic locations for the positioning of the CAES plant (coastal lines, floating platforms, etc.)

[0021] On the other hand, the cost of this storage system is higher, due to the need of positioning the storage vessel on the bottom of the chosen water reservoir (often the sea or the ocean) and due to the cost of the vessel itself. [0022] Plants operate on a daily cycle, charging at night and discharging during the day. Heating of the compressed air using natural gas or geothermal heat to increase the amount of energy being extracted has been studied by the Pacific Northwest National Laboratory. [0023] Compressed air energy storage can also be employed on a smaller scale such as exploited by air cars and air-driven locomotives, and can use high-strength carbon-fiber air storage tanks. In order to retain the energy stored in compressed air, this tank should be thermally isolated from the environment; else, the energy stored will escape under the form of heat since compressing air raises its temperature.

OBJECT OF THE INVENTION [0024] It is an object of the current invention to at least partially alleviate some of the aforementioned problems by providing a more effective apparatus and systems of compressed air energy using renewable energy such as Solar and/or wind turbines, alternatively Grid linked mains power input.

SUMMARY OF THE INVENTION

[0025] The invention provides for a compressed air energy storage system which includes a power supply means in drive communication with an output demand means via a motor/pump combination, a piston assembly powered by and in drive communication with the motor/pump combination, and storage means in flow communication with the piston assembly and the motor/pump combination. [0026] The piston assembly may include a two-stage recuperating piston compressor having a double rod cylinder, at least one large cylinder and one small cylinder in communication with the double rod cylinder. [0027] The storage means may comprise a heat storage means and a compressed air storage means, or any combination of the aforementioned. [0028] The heat storage means may include any conventional known insulated reservoir to store excess heat.

[0029] The compressed air storage means may include at least one pressure reservoir and in a preferred embodiment of the invention may include a battery of pressure reservoirs.

[0030] The invention may include a heat exchanger in communication with the heat storage reservoir, the heat exchanger capable to remove excess heat from at least the piston assembly and store the excess heat in the heat storage reservoir and reintroducing same into the main systems as required.

[0031] The invention may yet further include a water trap, capable to remove water from compressed air. The water may be used for any purpose, and in a preferred embodiment of the invention is use during any cooling stage to control temperatures.

[0032] The system may be controlled by means of multiple valves which are in communication with and controlled with an automation controller means which generally includes a computer program.

[0033] The system may be designed to remain isothermal at minus 35 °C - 100 °C, the compressed air to be between 10 - 800Bar. [0034] The power supply means may generate a rotational force by means of solar energy, electrical, electromechanically, gasification plant, renewable energy resources or any combination of the aforementioned, which rotational force may be transmitted via an output shaft provided on power supply means.

[0035] The motor/pump combination may be hydraulically alternatively pneumatically operable. [0036] The motor/pump combination may be an electrical driven, hydraulic variable positive displacement bidirectional over centre pump/motor and may be driven by the rotating force generated by the output shaft of the power supply means. [0037] The output demand means may be an AC generator of which a stable output may be maintained regardless of the input power or demand. The stable output may be achieved by means of an offset of the motor/pump combination and controller.

[0038] The stable output demand may be maintained through at least one fly- wheel and one-way bearing combination which may be interspaced between the motor/pump combination and output demand means to act as a compensator for fluctuations to produce a stable load regulated AC output source. [0039] It will be appreciated by a person skilled in the art that once the input power is greater than the output demand, surplus energy/power may be generated, which surplus energy/power may be utilised to drive the piston assembly.

[0040] It will further be appreciated that once the input power is less than the output demand an energy/power shortage stage may be created. During an energy shortage stage, stored energy may be reintroduced into the system (generating mode) in the form of stored compressed air, which compressed air may be heated by means of the heat exchanger and redirected back into the motor/pump allowing the motor/pump combination to now function as a motor.

[0041] In a preferred embodiment of the invention, the system may operate in a two-stroke manner.

[0042] During a first stage (charging mode) the bidirectional over centre motor/pump combination may be driven by the rotating force supplied from an output shaft associated with the power supply.

[0043] During the first stage, flow of hydraulic oil may be directed through a change over-valve, alternatively a swash plate, provided in the motor/pump combination, to a port of a hydraulic piston forcing the remaining oil from the opposite side of the piston to the return leg of the motor/pump combination to generate a resulting force, commonly known as a closed circuit. [0044] The resulting force may drive pistons of at least two air compressors in the same direction to a maximum, at which point a dead space may be created (commonly known in the art.) It will be appreciated by those skilled in the art that the resulting dead space causes a loss in efficiency.

[0045] At the point when the compression in each direction is at maximum, a valve may release the undelivered waste pressure to the opposite side of the piston nullifying the dead space created. [0046] During a second stage (generating mode), the same cycle may be repeated in the opposite direction during which a change-over valve may be activated to redirect the flow of air, from the storage reservoirs, to the various pistons and related hydraulics. [0047] The directional movement of the piston shaft may be controlled by means of a change-over proximity switch.

[0048] During the second stage (generation mode) the air driving pressure is derived from the storage reservoirs and directed to the piston assembly via at least one valve, driving the motor/pump combination, which in turn may support the AC generator acting as the output demand means.

[0049] Any Compressors may be plated with nickel to prevent water damages, alternatively may be manufactured form a suitable material such as stainless steel, ceramic or nickel, further alternatively may be lined to prevent corrosion. BRIEF DESCRIPTION OF INVENTION

[0050] The invention is now further described by way of example with particular reference to the following drawings.

Figure 1 is a flow diagram of the compression stage according to the invention;

Figure 2 is a flow diagram of the de-compression stage according to the invention;

DESCRIPTION OF PREFERRED EMBODIMENTS

[0051] In the following embodiments individual characteristics, given in connection with specific embodiments, may actually be interchanged with other different characteristics that exist in other embodiments.

[0052] Figure 1 illustrates a compressed air energy storage system 10 which includes a power supply means 12 in drive communication with an AC generator via a hydraulic motor/pump combination 14, a piston assembly 18 powered by and in communication with the hydraulic motor/pump combination 14 and storage means 15. [0053] The piston assembly 18 typically consists of a piston 18a movable within a cylinder 18b to define at least two chambers 19a and 19b respectively. [0054] The power supply means 12, is an electric motor powered by solar P.V as DC input, three phase 380V AC, renewable energy resources such as turbines, alternatively any combination of the aforementioned.

[0055] The system includes a heat exchanger (not shown) in communication with at least one heat storage reservoir (not shown), the heat exchanger capable to remove excess heat and store same in the heat storage reservoir.

[0056] In a preferred embodiment of the invention, the heat exchanger is positioned in a coil extending about the outer peripheral of at least one cylinder provided in the piston assembly 18.

[0057] The system further includes a water trap (not shown) capable to remove excess water from compressed air. The water may be used for any purpose and in a preferred embodiment of the invention is used during any cooling stage as a cooling medium.

[0058] In this embodiment of the invention, the system is designed to remain isothermal at 25 °C - 40 °C, the compressed air to be 250 Bar and the average storage capacity in Kwh at 350L water volume to be 9.5Kwh at 25 °C.

[0059] However it must be appreciated by those skilled in the art that the system may operate between minus 35 °C to 100 °C, and between 10 - 800 Bar of pressure. [0060] The system is controlled by means of multiple valves 22 which are in communication and controlled with an automation controller means, which is computer aided. The controller means is not shown in the accompany drawings and does the operation thereof fall beyond the scope of the current invention.

[0061] The hydraulic motor/pump 14 is an electrically driven, hydraulic variable positive displacement bidirectional over centre motor/pump.

[0062] The piston assembly 18 includes a two-stage recuperating piston compressor having a double rod cylinder 24, at least one large cylinder 26 and one small cylinder 28 in communication with the double rod cylinder 24. A shaft 30 is provided which shaft 30 extends via the double rod cylinder 24 between the larger cylinder 26 and the small cylinder 28.

[0063] The bidirectional over centre hydraulic pump/motor 14 is in drive communication with an output shaft 32 of the power supply 12 and is driven by a rotating force generated by an output shaft 32 of the power supply 12. In a preferred embodiment of the invention, output shaft is designed to remain at 1500 RPM.

[0064] The AC generator 16 generates output power equal to 220V and in a preferred embodiment is regulated by an offset of the hydraulic motor/pump 14 and controller to maintain a stable output regardless of the input power or demand. [0065] It will be appreciated that once the input power is greater than the output demand of the AC generator (surplus power), the surplus energy/power is utilised to drive the piston assembly 18 by means of the motor/pump combination 14.

[0066] It will further be appreciated that during a stage when stored energy is required (generating mode), the system releases stored air which may be warmed up by means of the heat exchanger and redirected back into the motor/pump combination 14 now functioning as a motor. The rotational direction does not change. The AC generator may now be powered.

[0067] A fly-wheel and one-way bearing (not shown) may be interspaced between the hydraulics and generator to act as a compensator for fluctuations and produces a stable load regulated AC output source.

[0068] In a preferred embodiment of the invention, the system operates in a two-stroke manner.

[0069] During the first stage (charging mode) the bidirectional over centre hydraulic pump/motor combination 14 is driven by the rotating force supplied from an output shaft 32 associated with the power supply 14.

[0070] The AC generator 16 which is in drive communication with the same output shaft 32, generates power at 220V and may be regulated by the offset of the hydraulic motor and controller to maintain a stable output regardless of input power or supply. [0071] It will be appreciated that in the event that the power available at the input shaft 32 is greater (surplus) than required by the generator 16, the surplus power/energy is used to drive the air piston assembly 18 by means of the motor/pump combination 14.

[0072] The flow of hydraulic oil is directed through a change-over valve 22 to the a port (not shown) of the hydraulic piston 24 forcing the remaining oil from the opposite side of the piston to the return leg 38 of the hydraulic pump to tank.

[0073] The resulting force drives the shaft 30 extending between the pistons 28 and 26 respectively, in the same direction and in turn receives air into a receiving side (chamber) and compressing the opposite side (chamber) to the heat exchanger and the smaller air compressor piston 28 receiving side (chamber).

[0074] It will be appreciated by those skilled in the art that resulting dead space causes a loss in efficiency. At the point when the compression in each direction is at its maximum, an electrically driven valve releases undelivered waste pressure to the opposite side of the chamber nullifying the dead space. The pressure at this point may be approximately 10Bar.

[0075] The same cycle is repeated in the opposite direction when the shaft 32 reaches a change-over proximity switch 40, utilsed to control the movement of the shaft 32, a change-over valve is activated to redirect the flow of air to the various pistons. [0076] During the second stage (generating mode) the sequence of events as hereinbefore set out is very similar but for the difference that the air driving pressure is now approximately 10Bar derived from a reducer valve and the pressure directed to the piston assembly.

[0077] The hydraulic motor/pump is now driven, which in turn may drive the AC generator 16. The control of delivered power may be regulated by the variable displacement controller provided at the hydraulic motor/pump 14. [0078] It will be appreciated by those skilled in the art that during this stage, the motor/pump 14 is effectively driven by the stored air redirected through the system.

[0079] Any excess air is stored in air storage reservoirs 42, which in a preferred embodiment of the invention is stored above ground.

[0080] It will be appreciated by those skilled in the art that the entire system is controlled and monitored by computer aiding. [0081] The hereinbefore system includes the following outputs namely heat to storage for use during power generation and cooling of the system; water extraction and provision to utilisation as a water generator; power storage into compressed air reservoirs above ground, alternatively air cleaning as a by- product of the air utilisation of atmospheric air.

Claims

CLAIMS:

1. A compressed air energy storage system which includes a power supply means in drive communication with an output demand means via a motor/pump combination, a piston assembly powered by and in drive communication with the motor/pump combination, and storage means in flow communication with the piston assembly and the motor/pump combination.

2. A compressed air energy storage system as claimed in claim 1 wherein the piston assembly includes at least one two-stage recuperating piston compressor having a double rod cylinder and at least one large cylinder and one small cylinder in communication with the double rod cylinder.

3. A compressed air energy storage system as claimed in any one of claim 1 to

2 wherein the system includes a heat exchanger in communication with a heat storage tank, the heat exchanger capable to remove excess heat and store same in the heat storage means and reintroducing same into the main systems as required.

4. A compressed air energy storage system as claimed in any one of claims 1 to

3 wherein the system includes a water trap, capable to remove water from compressed air.

5. A compressed air energy storage system as claimed in any one of claims 1 to

4 wherein the system is controlled by means of multiple valves which are in communication and controlled with an automation controller means.

6. A compressed air energy storage system as claimed in any one of claims 1 to

5 wherein the system is designed to remain isothermal at minus 35 °C to 100 °C, the compressed air to be between 10 to 800Bar.

7. A compressed air energy storage system as claimed in any one of claims 1 to

6 wherein the power supply means generate a rotational force by means of solar energy, electrical, electromechanically, gasification plant, renewable energy resources or any combination of the aforementioned.

8. A compressed air energy storage system as claimed in any one of claims 1 to

7 wherein the motor/pump combination is hydraulically alternatively pneumatically operable.

9. A compressed air energy storage system as claimed in any one of claims 1 to

8 wherein the motor/pump combination is an electrically driven, hydraulic variable positive displacement bidirectional over centre pump/motor.

10. A compressed air energy storage system as claimed in any one of claims 1 to

9 wherein the bidirectional over centre hydraulic pump/motor is driven by a rotating force generated by an output shaft of the power supply means.

11. A compressed air energy storage system as claimed in any one of claims 1 to

10 wherein the output demand means generates an output which is regulated by an offset of the hydraulic motor and controller to maintain a stable output regardless of the input power or demand.

12. A compressed air energy storage system as claimed in any one of claims 1 to

11 wherein once the input power is greater than the output demand, the surplus energy/power is utilised to drive the piston assembly.

13. A compressed air energy storage system as claimed in any one of claims 1 to

12 wherein during a stage when stored energy is required (generating mode), the system reintroduces stored energy which is heated by means of the heat exchanger and directed into the hydraulic motor/pump now functioning as a motor.

14. A compressed air energy storage system as claimed in any one of claims 1 to

13 wherein a fly-wheel and one-way bearing is interspaced between the hydraulics and generator to act as a compensator for fluctuations and produces a stable load regulated AC output source.

15. A compressed air energy storage system as claimed in any one of claims 1 to

14 wherein the system operates in a two-stroke manner.

16. A compressed air energy storage system as claimed in any one of claims 1 to 16 wherein during the strokes (compression) the bidirectional over centre hydraulic motor/pump is driven by the rotating force supplied from an output shaft associated with the power supply.

17. A compressed air energy storage system as claimed in any one of claims 1 to

16 wherein the output demand is an AC generator which is in drive communication with the same output shaft generates power and is regulated by the offset of the hydraulic motor/pump and controller to maintain a stable output regardless of input power or supply.

18. A compressed air energy storage system as claimed in any one of claims 1 to

17 wherein the power available at the input shaft the can be greater (surplus) than that required by the load in which instance the surplus power/energy is used to drive the air piston assembly.

19. A compressed air energy storage system as claimed in any one of claims 1 to

18 wherein the flow of hydraulic oil is directed through a change-over valve, alternatively a swash plate, to the left port of the hydraulic piston forcing the remaining oil from the opposite side of the piston to the return leg of the hydraulic motor/pump to tank, commonly known as a close circuit.

20. A compressed air energy storage system as claimed in any one of claims 1 to

19 wherein the resulting force drives pistons of at least two air compressors in the same direction and in turn receives air into the created negative volume and compressing the opposite side to the heat exchanger and the smaller air compressor piston receiving side.

21. A compressed air energy storage system as claimed in any one of claims 1 to

20 wherein at the point when the compression in each direction is at maximum, a valve releases the undelivered waste pressure to the opposite side of the chamber, nullifying a dead-space created.

22. A compressed air energy storage system as claimed in any one of claims 1 to

21 wherein the same cycle is repeated in the opposite direction when the shaft reaches a change-over proximity switch, used to control the movement of the shaft, a change-over valve is activated to redirect the flow of air to the various pistons and the hydraulics.

23. A compressed air energy storage system as claimed in any one of claims 1 to

22 wherein during the generation mode the air driving pressure is derived from the storage pressure system and directed to the smaller piston/compressor and larger piston/compression via at least one valve, driving the motor/pump.

24. A compressed air energy storage system as claimed in any one of claims 1 to

23 wherein any excess energy is stored in at least one air storage container.