Patent Application
20200386491
The present invention relates to the field of energy storage by compressed gas, notably air (CAES—Compressed Air Energy Storage). In particular, the present invention relates to an AACAES (Advanced Adiabatic Compressed Air Energy Storage) system wherein storage of the gas and storage of the heat generated is provided.
In a compressed-air energy storage (CAES) system, the energy that is desired to be used at a later time is stored as compressed air. For storage, the energy, in particular electrical energy, drives air compressors, and for de-storage, the compressed air drives turbines that may be connected to an electric generator. The efficiency of this solution is not optimal because part of the energy of the compressed air comes in form of heat that is not used. Indeed, in CAES methods, only the mechanical energy of the air is used, i.e. all of the heat produced upon compression is discharged. By way of example, compressed air at 8 MPa (80 bar) heats up during compression to about 150° C., but it is cooled prior to storage. Furthermore, the system requires heating the stored air to achieve expansion of the air. Indeed, if the air is stored at 8 MPa (80 bar) and at ambient temperature, and if it is desired to recover the energy by expansion, decompression of the air again follows an isentropic curve, but this time from the initial storage conditions (about 8 MPa and 300 K). The air thus cools down to temperatures that are not realistic (83 K, i.e. −191° C.). It is therefore necessary to heat it, which can be done using a gas burner, or another fuel.
Several variants currently exist for this system. The following systems and methods can notably be mentioned:
A first solution considered for the heat storage system TES consists in using a heat transfer fluid allowing to store the heat resulting from compression in order to release it into the atmosphere prior to expansion by means of heat exchangers. For example, patent application EP-2,447,501 describes an AACAES system where oil used as the heat transfer fluid circulates in a closed loop to exchange heat with air. Besides, patent applications EP-2,530,283 and WO-2011/053,411 describe an AACAES system where heat exchanges are carried out by a heat transfer fluid circulating in a closed loop, the closed loop comprising a single heat transfer fluid tank.
However, the systems described in these patent applications require specific means for storage and circulation of the heat transfer fluid. Furthermore, for these systems, significant pressure drops are generated by the heat exchangers used.
A second solution considered for the heat storage system TES is based on a static heat storage (without displacement of the bed of heat storage particles or of the heat transfer fluid). In this case, the heat storage means can be made up of one or more fixed bed(s) of heat storage particles. Upon charging, the hot compressed gas flows through the heat storage means. Through heat exchange between this gas and the storage particles, the latter are heated and the compressed gas is cooled. Likewise, when discharging, the heat exchange generated between the storage particles and the compressed gas cools the storage particles and heats the compressed gas. The fixed bed of storage particles is generally held in the storage means by a holding structure, which may directly be the wall of the storage means, or a structure mounted inside the storage means. When charging or discharging the heat storage system, the temperature of the fixed bed in a plane orthogonal to the compressed gas flow is substantially homogeneous, except in the vicinity of the holding structure. Indeed, the proximity of the wall induces, in the granular structure of the medium, a particular arrangement of the particles with respect to the wall (edge effect). This particular arrangement has an incidence on the velocity profile of the gas flows at the wall and, therefore, on the temperature profile of the particles.
As a result, the thermal gradient along a section orthogonal to the compressed gas flow is zero, or nearly zero, except at the holding structure juxtaposed with the fixed bed, on the periphery of the fixed bed: this shows that the temperature is homogeneous or nearly homogeneous in this section orthogonal to the axis of the compressed gas flow, except on the periphery of the fixed bed, at the holding structure. This temperature profile heterogeneity in the fixed bed induces a loss of the overall efficiency of the storage means and a loss of the overall performance of the system.
In order to overcome these drawbacks, and in particular to limit the efficiency loss related to the edge effect, the present invention relates to a heat storage means consisting of at least one fixed bed of heat storage particles. Inside the storage means, at least one obstacle, orthogonal or substantially orthogonal to the air flow, is positioned on the periphery of the bed of storage particles. This obstacle is arranged along the periphery of the fixed bed (continuously or discontinuously). It allows the compressed gas flow to be removed locally from the end of the fixed particle bed and, therefore, from the holding structure juxtaposed with the fixed bed, thus reducing the edge effect by the holding structure.
The invention relates to a heat storage and release system comprising at least one storage enclosure, at least one fixed bed of heat storage and release particles being arranged in said storage enclosure, and at least one fluid can flow through said fixed bed in said storage enclosure, said storage enclosure comprising at least one inlet of said fluid into said storage enclosure and at least one outlet of said fluid from said storage enclosure, characterized in that at least one obstacle is positioned in said fixed bed, substantially perpendicular to the circulating flow of said fluid, said obstacle being positioned on the periphery of said fixed bed of said heat storage and release particles, said obstacle being distributed around the periphery of said fixed bed of said storage particles.
According to a variant of the invention, the system comprises at least two obstacles evenly spaced along said circulating flow of said fluid.
Preferably, the spacing between two successive obstacles along said circulating flow of said fluid is at minimum twice the dimension of said obstacle, perpendicular to said circulating flow of said fluid.
According to an embodiment of the invention, said storage enclosure comprises at least one distributor for distributing said fluid into said fixed bed, and preferably at least two distributors.
Preferably, said obstacle is positioned at said distributor.
According to one implementation, said obstacle consists of a plate.
Advantageously, the dimension of said obstacle, perpendicular to said circulating flow of said fluid, ranges between 1 and 10 times the equivalent Sauter diameter of said heat storage and release particles of said fixed bed, preferably between 3 and 5 times the equivalent Sauter diameter of said heat storage and release particles of said fixed bed.
According to an embodiment, said storage enclosure is cylindrical or substantially cylindrical.
According to a variant embodiment, said circulating flow of said fluid within said storage enclosure occurs along the axis of said storage enclosure.
Advantageously, said obstacle consists of an annular plate arranged on the inner face of the cylindrical wall of said storage enclosure.
According to another variant embodiment, said circulating flow of said fluid within said storage enclosure occurs along an axis perpendicular to the axis of said storage enclosure, at least two trays supporting said fixed bed being positioned within said storage enclosure, said support trays being perpendicular to the axis of said storage enclosure.
Advantageously, said obstacle is positioned on said support trays, said obstacle thus forming a portion of a cylinder on each of the two trays supporting said fixed bed of said heat storage and release particles.
According to an embodiment, said obstacle is continuously distributed around the periphery of said fixed bed.
Alternatively, said obstacle is discontinuously distributed around the periphery of said fixed bed.
The invention also relates to a compressed-gas energy storage and recovery system, comprising at least one gas compression means, at least one compressed gas storage means, at least one means of expanding said compressed gas to generate energy and at least one heat storage means according to one of the above features.
The invention also relates to a heat storage and recovery method wherein the following steps are carried out:
a) storing the heat in a fixed bed of heat storage and release particles, by circulating a fluid in said fixed bed, and
b) releasing the heat recovered by said fixed bed, by circulating a fluid in said fixed bed.
To store and release the heat, said fluid is subjected to at least one obstacle positioned in the fixed bed, perpendicular or substantially perpendicular to the flow of said fluid, said obstacle being positioned on the periphery of said fixed bed of said heat storage and release particles, said obstacle being distributed around the periphery of said fixed bed of said heat storage and release particles.
According to a variant of the invention, said fluid flows through a stepped arrangement made up of a plurality of said fixed beds contained in said heat storage and release means.
According to an embodiment, said heat storage and release means has a substantially cylindrical shape.
According to a variant, said fluid flows radially through said fixed bed of said heat storage and release means.
Alternatively, said fluid flows axially through said fixed bed of said heat storage and release means.
The invention also relates to a compressed-gas energy storage and recovery method, wherein the following steps are carried out:
a) compressing a gas,
b) cooling said compressed gas by heat exchange with a fixed bed of heat storage and release particles,
c) storing said cooled gas,
d) heating said cooled compressed gas by releasing the heat of said fixed bed of said heat storage and release particles, and
e) expanding said heated compressed gas so as to generate energy, and wherein heat storage and release is carried out according to the heat storage and release method according to one of the above features.
Other features and advantages of the system and of the method according to the invention will be clear from reading the description hereafter of embodiments given by way of non-limitative example, with reference to the accompanying figures wherein:
The present invention relates to a heat storage and release system. In this implementation, a fluid (compressed gas for example) flows through a fixed bed of heat storage and release particles enabling thermal exchange between the fluid and the particles. The particles are selected from a material capable of storing and releasing heat.
The system according to the invention comprises:
Each fixed bed can comprise solid particles or particles containing a phase change material (PCM). The particles may thus come in form of capsules containing PCMs. Using PCM-containing particle beds allows to better control the thermal gradient in the tank by applying different melting temperatures. A compromise between efficiency and cost can also be found by mixing PCMs and sensible heat storage materials in the same bed. The following materials can be used for the PCMs: paraffins, whose melting temperature is below 130° C., salts melting at temperatures above 300° C., (eutectic) mixtures allowing to have a wide melting temperature range.
The solid particles (whether phase change particles or not) can have all the known forms of conventional granular media (balls, cylinders, extrudates, trilobes, etc.) and any other form allowing to maximize the surface of exchange with the gas. The particle size can range between 0.5 mm and 10 cm, preferably between 2 mm and 50 mm, and more preferably between 5 mm and 20 mm.
The temperature range within which the heat storage means can operate is between 0° C. and 500° C., preferably between 100° C. and 400° C., and more preferably between 100° C. and 350° C. The temperature levels depend both on the complete AACAES process and on the type of material used for the particles of the heat storage means.
According to an implementation of the invention, the system can comprise at least two obstacles evenly spaced along the circulating flow of the fluid. The presence of these evenly spaced obstacles improves the temperature homogeneity and therefore the performance. For example, the obstacles can be positioned at the inlets/outlets of the fixed bed and/or in the middle and, preferably, at the inlet, in the middle and at the outlet of the fixed bed. This configuration provides an optimized distribution of the heat flow in the fixed bed.
According to a variant embodiment of the invention, the spacing between the two successive obstacles can be at minimum equal to twice the dimension of the obstacle perpendicular to the circulating flow. Indeed, by observing this minimum spacing, the flow that is locally diverted by the obstacle towards the center of the fixed particle bed can again come close to the walls of the bed prior to encountering the next obstacle. Thus, the gas flow coming near to the next obstacle is very close to what it would be if the previous obstacle did not exist.
According to a variant embodiment of the invention, the storage enclosure can comprise at least one distributor. A distributor is understood to be a device allowing the fluid to be distributed as homogeneously as possible in the fixed bed of storage particles, so as to optimize thermal exchanges between the fluid and the fixed bed of storage particles. Preferably, at least two distributors can be provided, the first one at one end of the fixed bed of storage particles and the second at the other end of the fixed bed of storage particles. For example, when the fluid circulates in a given direction of flow (upon charging for example), the first distributor can be arranged at the inlet of the fixed bed of storage particles, just before the fluid enters the fixed bed of storage particles, and the second distributor can be arranged at the outlet of the fixed bed of storage particles, just after the fluid flows from the fixed bed of storage particles. When the fluid circulates upon discharging, in the opposite direction of flow, the second distributor is then located at the gas entry in the fixed bed of storage particles, just before the fluid enters the fixed bed of storage particles, and the first distributor is then at the gas exit from the fixed bed of storage particles, just after the outlet of the fixed bed of storage particles. Alternatively, other distributors may be added and positioned within the fixed bed of storage particles.
According to an embodiment of the invention, the obstacle can be positioned at the distributor. Thus, the local acceleration and the displacement of the gas flow by synergy between the presence of the obstacle and the presence of the distributor are improved.
According to an embodiment of the invention, the obstacle can consist of a plate. This design enables simple and inexpensive manufacturing of the obstacle. Besides, the plate needs not be mechanically fixed, which simplifies the implementation thereof and makes the invention usable when modernizing or revamping a unit. In this case, the plate lies on the fixed bed of particles.
According to a feature of the invention, the dimension of the obstacle perpendicular to the circulating flow of the fluid can be equal to a value between 1 and 10 times the equivalent Sauter diameter of the storage particles, preferably between 3 and 5 times the equivalent Sauter diameter of the storage particles. What is referred to as the equivalent Sauter diameter is the characteristic value of the storage particles d32 defined by:
with Vp the particle volume and Ap the particle surface area. This feature of the invention allows to limit the pressure drop induced by the obstacle while optimizing the effect of the presence of the obstacle on the temperature evolution in a plane perpendicular to the circulating flow of the fluid.
According to an embodiment of the invention, the storage enclosure may be cylindrical or substantially cylindrical.
Furthermore, the circulating flow of the fluid within the cylindrical or substantially cylindrical storage enclosure may occur along the axis of the storage enclosure. One speaks then of “axial flow” to designate this fluid circulation mode within the storage enclosure and of “axial flow system” to designate a heat storage and release system with an axial flow circulation mode of the fluid.
Moreover, the obstacle in the cylindrical or substantially cylindrical storage enclosure can be an annular plate. This type of obstacle is easy to manufacture, inexpensive, and it meets the requirement of local removal of the circulating fluid flow from the fixed bed periphery.
Alternatively, the circulating flow of the fluid within the cylindrical or substantially cylindrical storage enclosure may occur along an axis perpendicular to the storage enclosure axis. In this case, one speaks of “radial flow” for the fluid circulation within the storage enclosure and of “radial flow system” to designate a heat storage and release system with a radial flow circulation mode of the fluid. Trays referred to as “support trays” can therefore be used and positioned within the storage enclosure. Their purpose is to hold the fixed beds of storage particles and to orient the circulating flow of the fluid in the radial direction within the storage enclosure.
In the radial flow system, the obstacle can be positioned on the support trays. The obstacle is then divided into two parts, a first part positioned on the so-called “upper” support tray and a second part on the so-called “lower” support tray. On each of these two support trays, the obstacle represents for example a portion of a cylinder.
According to an embodiment, the obstacle can be continuously distributed around the periphery of the fixed bed, for example, by a plate or a flange (a collar). This allows to use an easily manufactured form.
Alternatively, the obstacle can be discontinuously distributed around the periphery of the fixed bed, for example by means of several obstacles distributed over the circumference. This affords the advantage of having several elements of smaller size, more easily transportable, which can be more readily set and positioned in the storage means.
These local temperature evolutions reflect a non-homogeneity of temperature profile 25 in a plane orthogonal to the direction of flow of the fluid. This lack of homogeneity induces a drop in performance of the heat storage and release system. The present invention allows to limit or even to avoid these local temperature evolutions in the fixed bed.
The present invention also relates to a compressed-gas energy storage and recovery system, comprising:
By using the heat storage and release means according to the invention, the thermal performances of the compressed-gas energy storage and recovery system are optimized and, therefore, the overall efficiency of the compressed-gas energy storage and recovery system is increased.
Preferably, several compression and expansion stages can be used in order to optimize the overall performances of the system. In this case, at least one heat storage and release means can be arranged between two compression or expansion stages. The number of stages and the ratio of each stage can be selected according notably to the gas and to the various constraints of the system to improve the cost/quality ratio.
The gas used may notably be air, for example air taken from the ambient medium.
Preferably also, several compressed gas storage tanks can be used. Each of these tanks may have different characteristics, for example different volumes and/or pressures.
Preferably, several heat storage and release means can also be used, and each of which may have different characteristics so as to optimize the overall operation of the system.
The compression means can notably be a compressor and the expansion means can notably be a turbine.
The present invention also relates to a heat storage and release method wherein the following steps are carried out:
a) storing the heat in a fixed bed of heat storage and release particles, by circulating a fluid in the fixed bed, and
b) releasing the heat recovered by the fixed bed, by circulating a fluid in the fixed bed,
and wherein, to store and release the heat, the fluid is subjected to at least one obstacle positioned in the fixed bed, perpendicular or substantially perpendicular to the circulating flow of the fluid, the obstacle being positioned on the periphery of the fixed bed of storage particles, the obstacle being distributed around the periphery of the fixed bed of storage particles, continuously or discontinuously. The presence of the obstacle thus positioned in the heat storage and release means allows to locally remove the circulating flow of the fluid from the fixed bed periphery. This generates a local change in the velocity field and therefore in temperature, which allows the temperature in the particle bed to be homogenized. Thus, the thermal performances of the method are improved.
The fluid used for heat release may be identical to or different from the fluid used for heat storage.
According to a variant embodiment of the method according to the invention, the fluid can flow through a stepped arrangement made up of a plurality of fixed beds contained in the heat storage and release means. The system can thus be optimized regarding various criteria such as, by way of non-limitative example, efficiency improvement or manufacturing cost minimization.
According to an embodiment of the method according to the invention, the fluid can circulate through a cylindrical or substantially cylindrical heat storage and release means. This particular geometric shape has the advantage of being easy to manufacture and it allows the circulating flow of the fluid to be readily and homogeneously directed through the heat storage and release means.
According to a variant embodiment of the method according to the invention, the fluid can flow radially through the fixed bed of the heat storage and release means, i.e. in a direction perpendicular to the axis of the cylindrical or substantially cylindrical heat storage and release means. The specific feature of the radial flow allows to better homogenize the temperatures inside the storage enclosure in relation to an axial flow and, therefore, to improve the thermal performances of the heat storage and release means.
Alternatively, the fluid can flow axially through the fixed bed of the heat storage and release means, i.e. the direction of flow of the fluid is colinear with the axis of the heat storage and release means. By using an axial-flow heat storage and release method, the method is easier to implement and the overall cost of the process can be minimized.
Furthermore, the present invention also relates to a compressed-gas energy storage and recovery method, wherein the following steps are carried out:
a) compressing a gas,
b) cooling said compressed gas by heat exchange with a fixed bed of storage particles,
c) storing the cooled gas,
d) heating the cooled compressed gas by release of the heat from the fixed bed of storage particles, and
e) expanding the heated compressed gas so as to generate energy,
wherein heat storage (compressed gas cooling) and release (compressed gas expansion) is carried out according to the heat storage and release method described above. Using the heat storage and release method according to at least one of the variants described above in the energy storage and recovery method allows the heat storage and release performances to be improved. Improving these performances allows the overall compressed-gas energy storage and recovery performances to be improved.
The gas used may notably be air, for example air taken from the ambient medium.
Steps b) and d) may be preferably implemented by the heat storage and release system according to at least one variant described above.
The compression and/or expansion steps can be broken down into several compression and/or expansion sub-steps. This can improve the overall performances of the system and/or optimize the overall cost/quality ratio according to the constraints of the system and the gas used. It is also possible to use standard compression and/or expansion means, which allows to limit the design and manufacturing costs of specific compression and/or expansion elements if necessary.
The compression and expansion steps can notably be carried out by a compressor and a turbine respectively. During expansion, the turbine can generate electrical energy. If the gas is air, the expanded air can be discharged into the ambient medium.
Step c) can be carried out within a compressed gas storage means which may be a natural reservoir or not (an underground cavity for example). The compressed gas storage means can be above or below ground. Furthermore, it can consist of a single volume or of a plurality of volumes, interconnected or not. During storage, the compressed gas storage means is closed.
The method and the system according to the invention can be used for storing intermittent energy, such as wind or solar power, so as to be able to use this energy at the desired time.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1761300 | Nov 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/081172 | 11/14/2018 | WO | 00 |
