Compressed gas energy storage and harvesting system and method with storage of the heat by heat transfer fluid

Abstract

The present invention relates to an AACAES system and method in which a heat transfer fluid makes it possible to store heat. The heat transfer fluid, which comprises balls of heat storage material, circulates between two tanks: a hot tank and a cold tank, and passes through at least one heat exchanger.

Claims

1. A compressed gas energy storage and harvesting system, the system comprising: at least one gas compression means, storage means for compressed gas, at least one expansion means for the compressed gas, at least one heat exchange means arranged at the output of the at least one gas compression means and/or at the input of at least one expansion means, the at least one heat exchange means being configured to transfer energy between the compressed gas and a heat transfer fluid, the heat transfer fluid comprising heat storage balls, first storage means for the heat transfer fluid, second storage means for the heat transfer fluid, and means for circulating the heat-transfer fluid from the first storage means for the heat transfer fluid to the second storage means for the heat transfer fluid through the at least one heat exchange means.

2. The system as claimed in claim 1, wherein the heat storage balls have a diameter of between 10 nm and 50 nm.

3. The system as claimed in claim 1, in which the heat storage balls comprise alumina, metal, or micro or nanocapsules of phase change material.

4. The system as claimed in claim 1, wherein the heat storage balls withstand temperatures of between 20 and 700 C.

5. The system as claimed in claim 1, wherein the heat transfer fluid comprises oil, air, water, or molten salts.

6. The system as claimed in claim 1, wherein the at least one gas compression means comprises a several staged gas compression means, the at least one expansion means comprises a several staged expansion means, and a heat exchange means of the at least one heat exchange means is arranged between each stage of the several staged gas compression means and/or each stage of the several staged expansion means.

7. The system as claimed in claim 6, wherein the first storage means for heat transfer fluid comprises a first storage drum and the second storage means for heat transfer fluid comprises a second storage drum, the heat transfer fluid circulating from the first storage drum to the second storage drum through each heat exchange means of the at least one heat exchange means.

8. The system as claimed in claim 6, wherein the first heat transfer fluid storage means comprises a first storage drum for each heat exchange means of the at least one heat exchange means, the second heat transfer fluid storage means comprises a second storage drum for each heat exchange means the at least one heat exchange means, the heat transfer fluid circulating from the first storage drum to the second storage drum through a respective heat exchange means of the at least one heat exchange means.

9. The system as claimed in claim 3, wherein the heat storage balls comprise the phase change material, and the phase change material is selected from paraffins, metals or salts.

10. A compressed gas energy storage and harvesting method comprising steps of: a) compressing a gas; b) cooling the compressed gas by heat exchange with a heat transfer fluid; c) storing the cooled compressed gas; d) heating the stored compressed gas by heat exchange with the heat transfer fluid; and e) expanding the heated compressed gas to generate an energy, wherein the heat transfer fluid is made to circulate between storage means for the heat transfer fluid for at least one heat exchange with the gas and wherein the heat transfer fluid comprises heat storage balls.

11. The method as claimed in claim 10, wherein the heat storage balls have a diameter of between 10 nm and 50 mm.

12. The method as claimed in claim 10, wherein the heat storage balls comprise aluminas, metals, or micro or nanocapsules of phase change material.

13. The method as claimed in claim 10, in which the heat storage balls withstand temperatures of between 20 and 700 C.

14. The method as claimed in claim 10, wherein the heat transfer fluid comprises oil, air, water, or molten salts.

15. The method as claimed in claim 10, in which the steps a) and b) and/or the steps d) and e) are reiterated.

16. The method as claimed in claim 15, in which all the heat exchanges are produced by means of the heat transfer fluid circulating from a first heat transfer fluid storage drum to a second heat transfer fluid storage drum.

17. The method as claimed in claim 15, in which each heat exchange is produced separately by means of the heat transfer fluid circulating from a first storage drum for the heat transfer fluid to a second storage drum for the heat transfer fluid.

18. The method as claimed in claim 12, wherein the heat storage balls comprise the phase change material, and the phase change material is selected from paraffins, metals or salts.

19. A compressed gas energy storage and harvesting system, the system comprising: a turbine for compression and expansion of gas, a vessel for storing compressed gas emitted from the turbine, a heat exchanger configured to transfer energy between the compressed gas and a heat transfer fluid, the heat transfer fluid comprising heat storage balls, a first vessel for storing the heat transfer fluid in a heated state, and a second vessel for storing the heat transfer fluid in a cooled state, the heat exchanger being connected between the first vessel and the second vessel to allow the heat transfer fluid to flow through the heat exchanger when the heat transfer fluid flows between the first vessel and the second vessel.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other features and advantages of the method according to the invention will become apparent on reading the following description of nonlimiting exemplary embodiments, with reference to the figures attached and described herein below.

(2) FIG. 1 illustrates a compressed gas energy storage and harvesting system, according to a first embodiment of the invention, in energy storage mode of operation.

(3) FIG. 2 illustrates a compressed gas energy storage and harvesting system, according to the first embodiment of the invention, in stored energy restoration mode of operation.

(4) FIG. 3 illustrates a compressed gas energy storage and harvesting system, according to a second embodiment of the invention, in energy storage mode of operation.

DETAILED DESCRIPTION OF THE INVENTION

(5) The present invention relates to a compressed gas energy storage and harvesting system equipped with a heat storage means (AACAES). The system according to the invention comprises: at least one gas compression means (or compressor), preferably the system comprises several staged gas compression means, the gas compression means can be driven by a motor, notably an electric motor, at least one means for storing gas compressed by the gas compression means, the compressed gas storage means can be a tank, an underground cavity or equivalent, etc. at least one gas expansion means (or expansion valve) making it possible to expand the compressed and stored gas, the system preferably comprises several staged gas expansion means, the gas expansion means makes it possible to generate an energy, notably an electrical energy by means of a generator, at least one heat exchange means, or heat exchanger, between the compressed gas and a heat transfer fluid for cooling the compressed gas at the output of the gas compression means and/or for heating the compressed gas at the input of the gas expansion means, heat transfer fluid storage means, circuits for circulating the heat transfer fluid between the heat transfer fluid storage means by passing through at least one heat exchange means.

(6) The terms staged compression or expansion means are used when a plurality of compression or expansion means are mounted in succession one after the other in series: the compressed or expanded gas at the output of the first compression or expansion means then passes into a second compression or expansion means, and so on. A compression or expansion stage is then called a compression or expansion means of the plurality of staged compression or expansion means. Advantageously, when the system comprises a plurality of compression and/or expansion stages, a heat exchange means is arranged between each compression and/or expansion stage. Thus, the compressed air is cooled between each compression, which makes it possible to optimize the efficiency of the next compression, and the expanded air is heated between each expansion, which makes it possible to optimize the efficiency of the next expansion. The number of compression stages and the number of expansion stages can be between 2 and 10, preferably between 3 and 5. Preferably, the number of compression stages is identical to the number of expansion stages. Alternatively, the AACAES system according to the invention can contain a single compression means and a single expansion means.

(7) The system according to the invention is suited to any type of gas, notably air. In this case, the air at the input used for the compression can be taken from the ambient air and the air at the output after the expansion can be released into the ambient air. Hereinafter in the description, only the variant embodiment with compressed air will be described, but the system and the method are valid for any other gas.

(8) The heat exchange means make it possible, upon the storage of the compressed gas (compression), to recover a maximum of heat deriving from the compression of the gas at the output of the compressors and to reduce the temperature of the gas before the transition to the next compression or before the storage. For example, the compressed gas can switch from a temperature higher than 150 C. for example approximately 190 C., to a temperature lower than 80 C., for example approximately 50 C. The heat exchange means make it possible, in the restoration of the energy to restore a maximum of stored heat by increasing the temperature of the gas before the transition to the next expansion. For example, the gas can switch from a temperature lower than 80 C., for example approximately 50 C., to a temperature higher than 150 C., for example approximately 180 C.

(9) According to the invention, the heat transfer fluid circulates between two heat transfer fluid storage means and passes through at least one heat exchange means. Thus, the heat transfer fluid storage means comprise at least one hot heat transfer fluid storage tank, called hot drum and one cold heat transfer fluid tank, called cold drum. The hot drum stores the heat deriving from the heat exchanges in the compression and the cold drum stores the heat transfer fluid cooled upon the expansion. For the cooling of the compressed air (energy storage), the heat transfer fluid circulates from the cold drum, passes through at least one heat exchanger situated at the output of a compression means for cooling the air, then is stored in the hot drum. For the reheating of the air (energy restoration), the heat transfer fluid circulates from the hot drum, passes through at least one exchanger situated at the input of an expansion means for heating the air, then is stored in the cold drum. According to the invention, the hot and cold drums have no direct link; to go from one to the other the heat transfer fluid systematically passes through at least one heat exchange means.

(10) Ideally, upon the storage of the compressed air, the input temperature of the ball-filled heat transfer fluid is at the temperature of the output of the exchanger on the compressed air side and the output temperature of the heat transfer fluid is at the temperature of the input of the exchanger on the compressed air side (compressor output).

(11) This arrangement of the heat transfer fluid storage means with a cold drum and a hot drum allows for a separate storage of the cold heat transfer fluid and of the hot heat transfer fluid, which allows for an effective storage of the heat energy, with a minimum of losses.

(12) The control of the compressor input temperature is ensured by the control of the flow rate of the heat transfer fluid mix.

(13) Furthermore, the system according to the invention provides flexibility of operation.

(14) According to the invention, the heat transfer fluid includes heat storage balls. The heat storage balls are elements of small dimensions capable of storing up and restoring heat. The heat storage balls have a high heat capacity and more specifically a high energy density (or storage capacity) expressed in MJ/m.sup.3. The balls can be substantially spherical and have a diameter of a few tens of nanometers to a few tens of millimeters depending on the nature thereof, preferably, the diameter of the balls is between 10 nm and 50 mm, in particular between 50 m and 10 mm. The balls according to the invention are produced in materials that can be used in temperature ranges of between 20 and 700 C. The balls used can be produced by aluminas, or in metal or phase change materials (PCM) encapsulated or non-encapsulated within the operating temperature range. The nature of the phase change materials PCM can be of different types, including: salts (with a storage capacity of between 300 to 1000 MJ/m.sup.3) : for example NaCl, NaNO.sub.3, KNO.sub.3, etc., metals (with a storage capacity of between 100 and 2000 MJ/m.sup.3): for example magnesium, aluminum, copper, antimony, etc.

(15) The heat storage balls make it possible to store up a greater quantity of heat than the fluid alone, so the volume needed for heat transfer fluid containing balls is less than the volume needed for a conventional heat transfer fluid. Thus, it is possible to reduce the storage volumes of the TES.

(16) The heat transfer fluid can be of different kinds: molten salts (for example NaNO.sub.2, NaNO.sub.3, KNO.sub.2, etc.), oil, air, water, etc., so that it is easy to implement from a heat exchange and hydraulic point of view according to the type of balls used and the type of exchanger installed.

(17) The choice of the nature of the heat transfer fluid and of the balls depends on the temperature range in which it will be used, which is directly linked to the configuration of the compression (number of stages and compression rate) storage pressure of the compressed air of the TES. Upon the storage of the compressed air, the ball-filled heat transfer fluid can be transferred from a cold storage drum to a hot storage drum via a pump. The pump can also be used to place the balls in suspension in the drums. In the energy restoration phase, the ball-filled heat transfer fluid can be transferred from the hot storage drum to the cold storage drum via a pump. The pump can be the same as that used in the storage of the compressed air.

(18) According to a first embodiment of the invention, the heat transfer fluid storage means comprise only two storage drums: a hot drum and a cold drum. The heat transfer fluid circulates between these two drums by passing through all the heat exchange means. If the AACAES system is a staged system (with several compressions and/or expansions), in the heat transfer fluid circuit, the flow of the heat transfer fluid is divided into parallel branches. Each parallel branch comprises a single air heat exchanger. The direction of circulation of the heat transfer fluid is the same in all the branches. This embodiment makes it possible to limit the number of heat transfer fluid storage drums to two.

(19) FIG. 1 presents an AACAES system according to a nonlimiting example of the first embodiment of the invention, for an energy storage operation (i.e. by air compression). As illustrated, the AACAES system according to the invention comprises four compression stages produced by air compressors 2 which successively compress the air taken from the ambient air 1. Between each compression stage, there is a heat exchanger 3, within which the air compressed and heated (by the compression) is cooled by the heat transfer fluid. At the output of the last compression stage, the compressed air is stored in a compressed air storage means 4. For the compression mode of operation, the heat transfer fluid circulates from a cold storage drum 5 by means of a pump 7 to a hot storage drum 6 by passing through four heat exchangers 3 by means of four parallel circuit branches.

(20) FIG. 2 presents an AACAES system according to a nonlimiting example of the first embodiment of the invention, for an energy restoration operation (by air expansion). As illustrated, the AACAES system according to the invention comprises four expansion stages produced by expansion means 9 which successively expand the compressed air contained in the compressed air storage means 4. Between each expansion stage 9, there is a heat exchanger 3, within which the air cooled by the expansion is heated by the heat transfer fluid. At the output of the last expansion stage, the expanded air is released into the ambient environment. For the expansion mode of operation, the heat transfer fluid circulates from the hot storage drum 6 by means of a pump 8 to the cold storage drum 5 by passing through the four heat exchangers 3 by means of four parallel circuit branches. The hot storage drum contains the hot heat transfer fluid which was used to cool the air compressed in the compression.

(21) According to a second embodiment of the invention, the heat transfer fluid storage mean comprise two heat transfer fluid storage drums (a hot drum and a cold drum) for each compression or expansion stage. The heat transfer fluid circulates between these two storage drums by passing through a single heat exchange means (that of the stage concerned). This embodiment makes it possible to limit the size of the heat transfer fluid storage drums, because the volume of fluid to be stored is reduced because the heat transfer fluid passes only in a single heat exchanger. In the case where the number of compression stages is identical to the number of expansion stages, the energy storage and harvesting system comprises as many cold storage drums and hot storage drums as there are compression and expansion stages.

(22) FIG. 3 presents an AACAES system according to a nonlimiting example of the second embodiment of the invention, for an energy storage operation (i.e. by air compression). As illustrated, the AACAES system according to the invention comprises four compression stages produced by air compressors 2 which successively compress air taken from the ambient air 1. Between each compression stage there is a heat exchanger 3, within which the air compressed and heated (by the compression) is cooled by the heat transfer fluid. At the output of the last compression stage, the compressed air is stored in a compressed air storage means 4. The system comprises four cold drums 51, 52, 53, 54, four hot drums 61, 62, 63, 64 and four pumps 71, 72, 73, 74. For each stage, the heat transfer fluid circulates from a cold storage drum 51, 52, 53, 54 to a hot storage drum 61, 62, 63, 64 by passing through a single heat exchanger 3 by means of a pump 71, 72, 73, 74.

(23) For an energy restoration operation, i.e. by air expansion (not represented), the AACAES system according to this second embodiment of the invention comprises four expansion stages produced by expansion means which successively expand the compressed air contained in the compressed air storage means. Between each expansion stage there is a heat exchanger, within which the compressed air is heated by the heat transfer fluid. At the output of the last expansion stage, the expanded air is released into the ambient environment. The system comprises four cold storage drums, four hot storage drums and four pumps. The heat transfer fluid circulates from a hot drum to a cold drum by passing through a single heat exchanger by means of a pump. Each hot drum contains the hot heat transfer fluid which was used to cool the compressed air in the compression.

(24) Other embodiments of the invention can be envisaged, in particular by the combination of the two embodiments described previously. For example, the heat transfer fluid can be used for two compression or expansion stages. Thus, it is possible to limit both the number of heat transfer fluid storage drums and their dimensions.

(25) The invention can therefore allow for the cross-over of the temperatures in the inter-stage exchangers, notably by means of a double-pipe exchanger, a spiral-wound exchanger, several exchangers in series. The use of the heat transfer fluid filled with heat storage materials also makes it possible to be able to operate with different cycle times, that is to say that the AACAES system can continue to function even if the air storage cycle time and the air withdrawal cycle time are different. Furthermore, the system according to the invention allows for operational flexibility and simplicity; the regulation is done with the output temperature on the compressed air side, and the system requires a pump, two storage drums and heat exchangers.

(26) The present invention also relates to a compressed gas energy storage and harvesting method, in which the following steps are carried out: a) a gas is compressed, notably by means of an air compressor; b) the compressed gas is cooled by heat exchange with a heat transfer fluid, in particular by means of a heat exchanger; c) the cooled compressed gas is stored, notably by a compressed gas storage means; d) the stored compressed gas is heated by heat exchange with the heat transfer fluid heated in the step b); and e) the heated compressed gas is expanded to generate an energy, for example by means of a turbine to generate an electrical energy.

(27) According to the invention, the heat transfer fluid is made to circulate between heat transfer fluid storage means for at least one heat exchange with the gas. Furthermore, the heat transfer fluid includes heat storage balls.

(28) The method according to the invention can be implemented by the system according to the invention, in particular the heat transfer fluid can be as described previously.

(29) According to an aspect of the invention, the method comprises several successive compression steps, by means of air compressors placed in series. In this case, the steps a) and b) are reiterated for each compression stage.

(30) According to a feature of the invention, the method comprises several successive expansion stages, by expansion means placed in series. In this case, the steps d) and e) are reiterated for each expansion step.

(31) According to the first embodiment of the invention, illustrated in FIGS. 1 and 2, the heat transfer fluid is made to circulate between two storage drums (a cold drum and a hot drum), the heat transfer fluid being used for all the steps of heat exchange with the compressed gas. The heat transfer fluid is distributed in parallel branches which each comprise a single heat exchanger.

(32) According to the second embodiment of the invention, illustrated in FIG. 3, for each heat exchange step, the heat transfer fluid is made to circulate between two storage drums (a cold drum and a hot drum), the heat transfer fluid being used for a single step of heat exchange with the gas. For each compression/expansion step, a heat transfer fluid is therefore made to circulate in a closed circuit.