WO2015189452A1

WO2015189452A1 - Energy storage method and system for storing energy

Info

Publication number: WO2015189452A1
Application number: PCT/ES2015/070454
Authority: WO
Inventors: Antonio Lecuona Neumann; Pedro Acisclo RODRÍGUEZ AUMENTE; José Ignacio NOGUEIRA GORIBA; Mathieu Legrand; Rubén VENTAS GARZÓN; María del Carmen RODRÍGUEZ HIDALGO
Original assignee: Universidad Carlos Iii De Madrid; Universidad Politécnica de Madrid
Priority date: 2014-06-13
Filing date: 2015-06-10
Publication date: 2015-12-17
Also published as: ES2554133B1; ES2554133A1

Abstract

The invention describes an energy-storage system which is based on the phenomenon of sorption/desorption of a vapour in a sorbent, and includes: a) a first thermally insulated tank (2) which houses a sorbent having an affinity for a vapour; b) a second thermally insulated tank (3) which also houses a sorbent having an affinity for said vapour; c) a compressor device (4) connected between the first tank (2) and the second tank (3) in order to compress the vapour by making same pass from the first tank (2) to the second tank (3) in an energy-accumulation phase; and d) an expander device (5) connected between the first tank (2) and the second tank (3) in order to expand the vapour, enabling same to return from the second tank (3) to the first tank (2) in an energy-depletion phase.

Description

DESCRIPTION

Procedure and energy storage system OBJECT OF THE INVENTION

The present invention pertains to the field of electrical energy storage systems intended, for example, to balance distribution networks, service isolated networks or soften the intermittent production of electricity generators based on renewable sources.

A first object of the present invention is a novel energy storage system based on the phenomenon of the sorption / desorption of a vapor in a sorbent. A second object of the present invention is the energy storage process carried out by the previous system.

BACKGROUND OF THE INVENTION Storing energy, and more specifically electric energy, is a priority objective in many research plans and is subject to intense activity. In the context of an electricity distribution network, it is interesting to store electricity when the sale price or consumption needs fall, and it is interesting to distribute the energy stored otherwise. This is especially interesting in electrical networks with a high penetration of renewable energy sources that have great variability, as is the case of the Spanish electricity system. On the other hand, the storage of electrical energy is also of great interest in the case of isolated networks to be able to cover the demand when the energy source has ceased or is insufficient against the demand. Currently, the most frequently used solution for the storage of electrical energy in this area are electrochemical batteries, also called accumulators. Electrochemical batteries are capable of storing electricity for a certain period of time in chemical form. However, conventional electrochemical batteries have a number of drawbacks that prevent their widespread use for many applications, since they are expensive, have an excessively short duration, and present various operational problems when the size of the installation is large, among others.

DESCRIPTION OF THE INVENTION The present invention solves the above problems, allowing to store electrical energy using low environmental impact materials, with a power density similar to those of current Lithium-ion batteries and allowing to use much larger sizes. In addition, the invention can increase its storage capacity by taking advantage of residual, solar or geothermal heat. An additional advantage is that its duration turns out to be much greater than electrochemical accumulators.

A first aspect of the invention is directed to a system for the storage of energy that essentially comprises the following elements: a) A first thermally insulated tank that houses a sorbent with physical and / or chemical affinity for a vapor, called sorbate for being the substance that is sipped by the sorbent.

The sorbent may be in a solid state, in which case the phenomenon of adsorption would occur, or in a liquid state, in which case the phenomenon of absorption would occur. Examples of solid sorbents are zeolite, a silica gel or activated carbon. Examples of liquid sorbents are water or a salt which, when dissolved in the substance constituting the vapor (sorbate) reaches the liquid state from a certain mass fraction of sorbate.

As for steam or sorbate, some examples are ammonia, water, hydrogen, ammonia, alcohol, acetone or a hydrocarbon.

On the other hand, in order to simplify the description in this document, there will always be general talk of sorption / desorption regardless of the physical state of the sorbent. b) A second thermally insulated tank that also houses a sorbent with affinity for said vapor. Normally, the sorbent of the second deposit is the same as that of the first deposit, although this does not necessarily have to be the case. c) A compressor device connected between the first tank and the second tank to compress the steam by passing it from the first tank to the second tank in a phase of energy accumulation. d) An expander device connected between the first tank and the second tank to expand the steam allowing its return from the second tank to the first tank in a phase of energy de-accumulation.

During the energy accumulation phase, the compressor device drives the steam from the first tank to the second tank. As a consequence of this mass transfer, there is a decrease in pressure in the first tank and an increase in pressure in the second tank. In this phase of the process, the steam (sorbate) is desorbed from the sorbent in the first tank, absorbing heat, and is sipped in the sorbent in the second tank with heat release. Because of this, there is a cooling in the first tank and a heating in the second tank that contribute to further increase the pressure difference that is created as a result of the action of the compressor device. As is evident, during this accumulation phase the compressor consumes work, which can come from an electrical supply by coupling it to an electric motor, or it can be a compressor device directly moved by electricity.

The energy is thus accumulated in the system for an indeterminate period of time that constitutes the so-called storage stage. When the energy is needed again, a decumulation stage is carried out where the expander allows the expansion of steam in its return from the second high pressure tank to the first low pressure tank, recovering a large part of the energy consumed by the compressor during the accumulation stage. The work generated by the expander device at this stage of decumulation can be converted into electrical energy by coupling it to an electric generator, or it can be an expander device that integrates the work extracted from steam into electrical energy.

Defining efficiency as the recovered electrical energy divided by the electrical energy invested in storage, the current efficiencies of the various known electricity storage methods are around 80% for batteries (including the necessary electrical conditioning and the complete cycle), 70 % for pumping in reversible hydroelectric plants, and between 20% and 50% for hydrogen as an energy vector with its storage. The proposed system is able to reach efficiencies similar to the best, resulting in competitive.

On the other hand, as with electrochemical batteries or accumulators, energy storage in the system of the invention is not permanent. The heat transfer between the tanks and abroad is gradually decreasing the stored energy, although it is never completely lost due to the fact that in the second tank there is steam absorbed in greater proportion than in the first tank, so it exerts greater pressure . To minimize energy losses, therefore, it will be essential to provide both tanks with an effective thermal insulation.

In the system of the invention, the compressor device and the expander device can be implemented as separate elements connected in parallel between the two tanks. In that case, the expander device would be canceled during the accumulation stage, while during the decumulation stage it would be the compressor device that would cancel out. Another alternative option is that the compressor device and the expander device consist of a single reversible device capable of acting alternatively as a compressor and also as an expander by means of a change.

Occasionally, the pressure in the second tank may increase excessively, the pressure in the first tank may drop excessively, or even the pressure difference between the first tank and the second tank may be excessive. To solve it, according to a preferred embodiment, the system of the present invention further comprises a means of heat exchange between the first tank and the second tank that can be activated and deactivated at will. This heat exchange acts as a moderator that tends to reduce the pressure and temperature difference between the first tank and the second tank. This heat exchange can also serve to avoid unwanted crystallization of the absorbent substance, if it is solid in its pure state, for example, a salt. In principle, the heat exchange medium can be implemented in different ways. For example, it may comprise a thermal contact area between the first tank and the second tank that can be activated at the will of the system operator, or another option is to use a closed circuit filled with a heat transfer fluid and in thermal contact with the first tank and with the second deposit, which can be activated voluntarily. This heat transfer fluid can be the fluid of either of both deposits. In another preferred embodiment of the invention, the first tank and / or the second tank comprise a means for stirring steam. The stirring of the steam in the first and / or the second tank can serve to respectively stimulate desorption / sorption in each of them, as well as to control the rate of heat transfer between the first tank and the second tank through the medium. Heat exchange described above. Note that, if the sorbent is liquid, the steam agitation medium would not only circulate the steam but also the sorbent itself, encouraging the transfer of mass and heat. One possibility of causing this agitation may be the bubbling of steam into the liquid.

Additionally, the system of the invention preferably comprises a means of providing heat to the second tank during the energy accumulation stage, during the static storage stage, or during the energy decumulation stage. The contribution of heat helps to increase the pressure in the second tank, thus increasing the capacity for energy accumulation and even compensates for heat losses to the environment. This heat can come from heat from some other process, from solar collectors or from geothermal sources, thus allowing the system of the invention to take advantage of surplus or unused energy in the form of residual heat. Another preferred embodiment of the system of the invention intended to improve the efficiency of the invention comprises means for reducing, canceling or reversing the increase in steam temperature that occurs during compression. That is, the temperature increase during compression can be reduced to the point of achieving isothermal compression, or even until the temperature drops during compression. As a result, it is possible to reduce the work required for compression, thus obtaining an improvement in efficiency.

This can be done in different ways. For example, it can be achieved directly by cooling the steam, either continuously or staggered. Another option is to evacuate part of the heat generated during steam compression to the environment. A further option involves the aggregation of fluid from one of the two steam tanks that is being compressed, with the consequent effect of reducing compression work. Note that, if the sorbent is solid, the active fluid for the absorption / desorption of the deposits will be only the steam itself, while if the sorbent is liquid, the fluid from the tanks may be the dissolution of the vapor itself in the liquid sorbent A different liquid could also be used that is compatible and that is housed in one of the two tanks with that specific purpose In any case, this fluid absorbs at least a part of the increase in thermal energy as a result of compression, reducing compression work.

A second aspect of the present invention is directed to an energy storage process carried out by the system described. This storage procedure basically comprises the following stages:

1) A stage of energy accumulation, where a steam is compressed by passing it from a first thermally insulated tank that houses a sorbent with affinity for said steam to a second thermally insulated tank that houses a sorbent with affinity for steam.

2) A static storage stage in which the system conserves the accumulated energy. During this stage heat can be added to the second tank in order to compensate for heat losses and even increase the stored energy.

3) An energy deacumulation stage, where the steam expands allowing its return from the second tank to the first tank.

In a preferred embodiment, the method further comprises exchanging heat between the first tank and the second tank in order to control its pressures and / or temperatures.

In another preferred embodiment, the method further comprises stirring the steam of the first tank and / or the second tank for the purpose, either of encouraging the sorption and / or desorption, or of controlling the heat transfer between the first tank and the Second deposit

In another preferred embodiment of the invention, the method further comprises providing heat to the second tank during the accumulation stage, during the static accumulation stage and / or during the de-accumulation stage to increase its energy storage capacity.

Another particular embodiment of the invention comprises the step of reducing, canceling or even reverse the increase in the temperature of the steam that occurs during compression to ensure that it is carried out with a smaller amount of work. As mentioned above, this can be done in several ways, such as directly cooling the steam before or during compression. Another option is to evacuate part of the heat generated during steam compression to the environment. A further option involves the aggregation of fluid from one of the two vapor deposits that is being compressed.

BRIEF DESCRIPTION OF THE FIGURES Fig. 1 shows a general scheme of the system of the present invention.

Figs. 2a and 2b respectively show a scheme of the accumulation stage and a scheme of the decumulation stage PREFERRED EMBODIMENT OF THE INVENTION

A particular example of the present invention is described below with reference to the attached figures where the different parts that make up the system (1) are appreciated and the main steps of the process are simplified.

Fig. 1 shows a diagram of the energy storage system (1) formed by a first tank (2) and a second tank (3). Both tanks are thermally insulated with the outside and with each other and contain a sorbent or mixture of sorbents with physical, chemical affinity or combination of both, by a vapor. In this specific example, a solid state sorbent has been represented, although as mentioned above in this document it would also be possible for the sorbent to be in a liquid state or to evolve from a solid state to a liquid upon sipping the sorbate. The tanks (2, 3) also house a certain amount of said steam. Initially it can be considered that both tanks (2, 3) are in a state of equilibrium with a part of free steam and another part of steam absorbed by the sorbent.

The two tanks (2, 3) are connected through a reversible compressor / expander device (4, 5), installed so that the direction of compression is directed to the second tank (3) and the direction of expansion is directed to the first deposit (2). Note that, as described above, it would also be possible to use two devices separated and installed in parallel between both tanks (2, 3): a compressor device (4) for compression and an expander device (5) for expansion.

Fig. 1 also shows a means (6) for exchanging heat between the first tank (2) and the second tank (3), which can be activated or deactivated voluntarily. Although previously described in this document different implementation possibilities have been described for this heat exchange means (6), in this figure a closed circuit filled with a heat transfer fluid whose exchange capacity can be accelerated by driving it with a pump has been represented. The heat exchanged by this heat exchange means (6) has been represented as

Steam agitation means (7) in the form of stirring blades have been arranged inside each tank (2, 3), although it may be installed in only one of them, to force the circulation of steam and thus favor both Sorption / desorption phenomena that occur in its interior such as the heat exchange that is carried out through the heat exchange means (6).

A means (8) of heat input to the second tank (3) has also been represented, which has been represented as a circuit through which a heat transfer fluid whose temperature is higher than that of the second tank (3) passes. This heat supply means (8) can be fed by a geothermal source, solar collectors or use heat from another process. The heat contributed to the second tank (3) has been represented as Q ₂ . The operation of this system (1) has been schematically represented in Figs. 2a and 2b. The accumulation stage shown in Fig. 2a comprises the operation of the reversible compressor / expander device (4, 5) in compression mode (4) to drive steam from the first tank (2) to the second tank. As a consequence, the pressure and temperature in the first tank (2) decrease, while the pressure and temperature in the second tank (3) increase. Simultaneously the concentration of sorbate in the first deposit (2) decreases and increases in the second deposit (3).

Optionally, the heat transfer medium (6) can be activated if said increase, or the difference in pressure between both tanks (2, 3), is excessive, or if the concentration of sorbate in the solution is so low that may occur a crystallization of the sorbent or excessive viscosity of the solution. There would then be a heat exchange Q that would normally pass from the second tank (3), hotter, to the first tank (2), colder. Also optionally, the steam agitation means (7) of the first tank (2) and / or the second tank (3) can be operated. The circulation of steam in one or both tanks (2, 3) has the effect of both favoring the desorption / sorption process that is carried out inside it, and of favoring the heat exchange process in case it is being using the heat exchange medium (6).

In another option, the means (8) of heat input to the second tank (3) could be activated to maximize its energy storage capacity, providing a quantity of heat Q _{2 to it} . In any case, in the final state the pressure and temperature in the second tank (3) would be much higher than in the first tank (2). Both deposits (2, 3) would remain stationary in a stage called static state storage for as long as it was necessary to store the energy. Optionally, during this stage the stored energy could be increased by providing external heat to the second tank (3) by means of the device (8). During the energy accumulation stage, the compressor device (4) has consumed a job W

Fig. 2b schematically shows the decumulation stage. In this case, the reversible compression / expansion device (4, 5) operates as an expander (5), allowing the return of steam that was confined in the second tank (3) at high pressure and temperature to the first tank ( 2) whose pressure and temperature at that time are much lower. In this return process, a W ₂ job is produced, which can be recovered in the form of electrical energy if the expander (5) is connected to an electric generator (not shown). In addition, the pressure drop that occurs during this stage in the second tank (3) can be recovered at least partially by adding external heat by means of the device (8). It is thus possible to store additional energy in thermal form that the system can convert into electricity through the expander.

Claims

1. Energy storage system (1), characterized in that it comprises:

- a first thermally insulated tank (2) housing a sorbent with affinity for a vapor;

- a second thermally insulated tank (3) that also houses a sorbent with affinity for said vapor;

- a compressor device (4) connected between the first tank (2) and the second tank (3) to compress the steam by passing it from the first tank (2) to the second tank (3) in a phase of energy accumulation; Y

- an expander device (5) connected between the first tank (2) and the second tank (3) to expand the steam allowing its return from the second tank (3) to the first tank (2) in a phase of energy de-accumulation.

2. Energy storage system (1) according to claim 1, further comprising a means (6) for heat exchange between the first tank (2) and the second tank (3), which can be activated and deactivated at Will.

3. Energy storage system (1) according to claim 2, wherein the heat exchange means (6) comprises a closed circuit filled with a heat transfer fluid and in thermal contact with the first tank (2) and with the second deposit (3).

4. Energy storage system (1) according to claim 2, wherein the heat exchange means (6) comprises a thermal contact area between the first tank (2) and the second tank (3).

5. Energy storage system (1) according to any of the preceding claims, wherein the first tank (2) and / or the second tank (3) comprises a means (7) for steam agitation.

6. Energy storage system (1) according to any of the preceding claims, wherein the compressor device (4) and the expander device (5) are constituted by a single reversible type device.

7. Energy storage system (1) according to any of the preceding claims, further comprising a means (8) of heat input to the second deposit (3) that can be activated and deactivated at will.

8. Energy storage system (1) according to any of the preceding claims, further comprising a means for reducing, canceling or reversing the increase in steam temperature during compression.

9. Energy storage system (1) according to any of the preceding claims, wherein the sorbent is chosen from water, a salt, zeolite, silica gel and activated carbon, and the vapor is chosen from ammonia, water, hydrogen, alcohol, acetone and a hydrocarbon.

10. Energy storage method carried out by the system (1) of any of the preceding claims, characterized in that it comprises the following steps:

- a stage of energy accumulation, where a steam is compressed by passing it from a first thermally insulated tank (2) that houses a sorbent with affinity for said steam to a second thermally insulated tank (3) that houses a sorbent with affinity for the steam.

- a stage of static storage of the accumulated energy; Y

- an energy deacumulation stage, where the steam is expanded allowing its return from the second tank (3) to the first tank (2).

11. Energy storage method according to claim 10, further comprising exchanging heat between the first tank (2) and the second tank (3) in order to control their pressures and / or temperatures.

12. Energy storage method according to any of claims 10-11, further comprising stirring the steam of the first tank (2) and / or the second tank (3) in order to encourage sorption and / or desorption or control of heat transfer between the first tank (2) and the second (3) tank.

13. Energy storage method according to any of claims 10-12, further comprising providing heat to the second tank (3) during the accumulation stage, during the static storage stage and / or during the de-accumulation stage for Increase your energy storage capacity.

14. Energy storage method according to any of claims 10-13, further comprising reducing, canceling or reversing the increase in steam temperature that occurs during compression.

15. Energy storage method according to claim 14, which comprises cooling the steam.

16. Energy storage method according to claim 14, which comprises evacuating heat to the environment.

17. Energy storage method according to claim 14, which comprises adding fluid from one of the tanks (2, 3) to the vapor that is compressed.