WO2013034139A1 - Method and device for storing and recovering thermal energy - Google Patents

Abstract

In known methods for storing and recovering thermal energy, provision is made at surplus energy times for a heated heat transfer medium to communicate via a heat exchanger with a heat storage medium. On account of the customary behaviour of steam, said method, which is carried out with synthetic oil, is not directly transferrable to a solar steam generator because the steam used as a heat transfer medium therein can absorb or output large amounts of energy around boiling temperature, without the temperature changing as a result. A heat transfer to the heat storage medium would only be possible to an unsatisfactory degree. The invention solves said problem in that the heat storage medium is divided in accordance with a low temperature heat exchanger, such that part of the heat storage medium can be heated much more intensely in a high temperature heat exchanger. The capacity of the vapour is considerably better utilised hereby, and the operation of connected steam turbines is hence considerably more effective.

Description

 METHOD AND DEVICE FOR STORING AND RECOVERING THERMAL ENERGY

The present invention relates to a process for the spoke ^¬ tion of thermal energy, a method for recovering thermal energy and a device for the storage and recovery of thermal energy with a too in a bypass line between a heat transfer medium inlet and a heat transfer medium return line or by a steam turbine, which is a Assigned to the heat exchanger is passed through the primary side of the heat transfer medium, while through the secondary side, a heat storage medium between a hot storage and a cold storage and can be derived.

Such methods and apparatus are be ^¬ already known from the prior art in many ways. Such systems are, for example, in solar thermal power plants ^¬ as Andasol 1, 2 and 3 in Spain used for electricity generation ^¬ supply after sunset.

The basic operation of such a system is that with an excess of thermal energy, this is not directly converted into the hard-to-store, elec ^¬ cal energy, but is stored directly in the form of thermal ^¬ shear energy. For this purpose, the heat transfer ^¬ medium, in the art usually a synthetic oil, using a heat exchanger transferred to a heat storage medium, which is transferred in the course of the transfer of a cold storage in a hot storage. The thermal storage ^¬ chermedium is thereby heated by the heat transfer and maintained in the hot storage until further notice. As soon as a need for energy is produced, the opposite approach is ge ^¬ go, so out the hot heat storage medium through the heat exchanger back into the cold storage and heated this primary side run through the heat exchanger heat transfer medium again. With this heated heat transfer medium in turn, for example, turbines can be operated, which provide the desired electrical energy available.

The use of such a system for water or steam Instead of the use of synthetic oil as the heat transfer medium is still in development and brings various ^¬ dene technical and economic challenges. For example, in the procedure outlined above, the maximum achievable temperature of the heat storage medium would be approximately 310 ° C. when the hot storage medium is charged by means of superheated steam at 450 ° C. This, in turn, the maxi ^¬ times attainable temperature of the discharge at the Spei ^¬ chers, say, the recovery of the energy resulting vapor is limited to about 305 ° C. In a power plant process, this would severely limit the performance and efficiency of the steam cycle.

The background of this situation lies in the typical behavior of steam, which in the region of its boiling temperature can absorb energy in the form of heat energy to a great extent, before a further increase in the temperature, and thus in the area of the superheated steam, takes place. Since at the same time the temperature of the heat storage medium in these areas increases uniformly, but always lower than the temperature of the energy ^¬ rich steam, the high energy of the superheated steam could be insufficient use. Against this background, the prior art systems, in which different heat storage media are provided for the different areas of the boiling curve of the steam. For example, the German Aerospace Center (DLR) is working on dual-fuel storage systems to solve these problems. Was such systems with several different union under ^¬ heat storage media are, however, considered to be expensive and technically complex, so look for a cheaper alternative.

The present invention therefore has as its object to provide a method and a device for storing and recovering thermal energy, especially in solar thermal power plants, which makes the existing solutions with steam as the only heat storage medium significantly more efficient than a mere takeover of the known Lö ^¬ sungen, and at the same time dispensed with the use of additional, additional heat storage media.

This is achieved by the present invention by a method for storing thermal energy according to the features of claim 1, a method for recovering thermal energy according to the features of independent claim 5 and by a device for storing and recovering thermal energy according to the features of the independent claim 9 Further useful embodiments of the method and the device can be taken from the respectively associated subclaims.

According to the invention, the solution of the prior art to a so-called intermediary memory, so an additional, arranged in the middle temperature range memory to supplement, in which the storage thermal energy heated heat storage medium is introduced. A portion of this heat storage medium will, however OF INVENTION ^¬ dung according diverted and further heated again through another, designed as a high temperature heat exchanger additional heat exchanger again. Due to the fact that the heating only refers to a partial flow of the heat storage medium in this second heat exchanger, a much stronger heating is possible. In addition, it is provided (vapor) and heat storage medium adjacent to lead heat transfer medium (usually a medium of liquid salt) in the opposite direction over, so that the first heating stage of the thermal storage medium is gleichzei ^¬ tig the second cooling step of the steam. This allows pre-heated heat storage medium are particularly strongly heated in the second stage by using the superheated steam, which is provided for heat storage, which already carried the cooled steam, a very high heating of this part-stream of the heat storage medium is made possible due to the ge ^¬ ringeren amount of heat storage medium.

Thus, all areas are you used ^¬ dekurve the steam efficiently in accordance with the invention, namely the high Tem ^¬ temperatures of the superheated steam to the strong heating of a portion of the heat storage medium and, after cooling of the superheated steam to normal steam, the use of long time constant temperature of this Steam for heating the bulk of the heat storage medium in a range of about 310 ° C.

The use of the heat transfer medium in a steam turbine is in these embodiments, a possible, but not the only possible use. The present patent Avoidance explicitly refers to all possible applications.

In the reverse way, the recovery of energy, which can be done in case of a need for energy, works. In this case, the process water, which is normally pumped approximately into a solar steam generator, heated as a heat transfer medium using the heat storage medium from the In ^¬ termediärspeicher, and thereby resulting from the process water vapor over the high-temperature heat exchanger using the highly heated heat storage medium from the hot storage overheated. This allows a much more efficient use of steam turbines, which then have to work with the recovered energy.

In a continuation of this idea, a fourth memory, that is to say a second intermediate memory, can also be added, as can a third heat exchanger. This makes it possible to use the rise of the boiling curve before the boiling point also more effectively by anticipating a corresponding preheating of the bulk of the heating in the boiling range of the vapor.

Purely structurally, it is possible the storage te both as separate to provide individual containers such as to also provide a type layer ^¬ heat storage in which each separable

Layer can be regarded as a single memory.

According to the invention, it is also possible to use the individual

To operate heating or cooling stages in two or three separate secondary circuits with different mass flows, so that this results in a simplified Handha ^¬ exercise, but also a slightly lower efficiency. The Solution with the merged stages, however, is the preferred embodiment described below.

The invention described above will be explained in more detail below with reference to an exemplary embodiment.

1 is a schematic representation of a prior art two-tank salt storage system;

Figure 2 is a graph relating to the curves for

Loading and unloading of the vapor stream and for comparison the curve of the molten salt ^¬ flow in a device according to the prior art and simultaneous use of steam as the heat transfer medium, Figure 3 is a schematic representation of he ^¬ inventive storage system, and

Figure 4 is a graph relating to the curves for

Loading and unloading of the vapor stream and the curve of the molten salt stream in egg ^¬ ner device according to the present invention.

FIG. 1 shows a schematic representation of a bypass between a line which leads from a solar steam generator 1 to a steam turbine 2. Such an arrangement is usually operated with synthetic oil and not with steam. It is now, however, the effect of an operation with steam as a heat transfer medium be ^¬ wrote to then he ^¬ invention to illustrate the operation of the.

The bypass line 8 includes a heat exchanger 12, through the primary side 9 of the initially superheated steam from the solar steam generator 1 emits its heat energy in the Wärmetau ^¬ shear 12 to a heat storage medium. The heat storage medium is simultaneously pumped in the opposite direction of a cold storage 6 through the secondary side 10 of the heat exchanger 12 in a hot accumulator 5, wherein it takes heat energy of the heat transfer medium, ie the steam, in the heat exchanger 12 ^¬ .

During the discharge of the hot accumulator 5, therefore, the heat ^¬ storage medium flows through the heat exchanger 12 in the cold accumulator 6 and thereby outputs the heat contained in the Wärmeträgermedi ^¬ from. The heated heat transfer medium then flows to the steam turbine 2 and is used to generate electrical energy. In order to ensure the heat transfer in the heat exchanger 12 when loading the hot accumulator 5, the heat transfer medium must have a higher temperature than the heat storage medium. When discharging the hot accumulator 5, this is exactly the opposite. Accordingly, the temperatures of the heat transfer medium before loading and after discharge are always different.

This has an effect according to the diagram in FIG. The vapor flow discharge curve represents the temperature of the vapor stream above the transmitted thermal energy, showing a distinct kinking shape. In this The example in the range between approximately 3000 and 4000 kW is superheated steam, which leads to a decrease in temperature when energy is released. In the range of about 300 to 3000 kW, a temperature change is virtually unnoticeable, while below 300 kW, the temperature drops further.

Similarly, but with somewhat different vertices, the curve relating to the loading of the steam stream 14 behaves between these two cures, the corresponding curve of the salt ^¬ melt stream 15, ie the characteristic of the heat storage medium ^¬ ums shown. This lies between the other two curves, after one hand, the heat storage medium from the heat transfer medium can not be heated more than its own temperature and vice versa, this also applies to the recovery of energy also.

Figure 3 shows the arrangement according to the invention, which provides an additional intermediate memory 7 between the hot storage 5 and the cold storage 6. Also, this is no longer a solution with a heat exchanger 12, but rather with two heat exchangers 3 and 4. With respect to the heat transfer medium is at its discharge or loading of the heat storage medium initially the superheated steam via the bypass line 8 in the high-temperature heat ^¬ 4 enter. After crossing it, the meanwhile cooled steam is then transferred again in the low-temperature heat exchanger 3 heat to the heat storage medium and condense. In the reverse direction, during the loading of the heat storage medium, this first pumped from the cold storage 6 in the low-temperature heat exchanger 3 and then divided into two mass flows. A mass flow leads to the intermediate memory 7, in which the through the Low-temperature heat exchanger 3 preheated heat storage medium is stored. However, a portion is passed further into the high-temperature heat exchanger 4, in which it can exchange the heat with the superheated steam in the line of the primary side 9, so that this portion of the heat storage medium can be heated significantly further. This significantly further heated heat storage medium is then stored in the hot accumulator 5.

Accordingly, does the recovery of energy, in ^¬ which the now current in the opposite direction and entering first in the low-temperature heat exchanger 3, the water is vaporized at the primary side 9, and then later in the high temperature heat exchanger 4 can be overheated. This is achieved in that the overheating due to the thermal storage ^¬ cap- tured can be done from the hot accumulator 5, wherein the cooling in the course of this heat transfer heat storage medium then connects with a second mass flow from the Intermediärspeicher 7 and then supplies the Niedertemperaturwärmetau ^¬ shear. 3

Accordingly, the efficiency of the overall arrangement can be improved according to the graph in Figure 4, after it is pos ^¬ lich to bend the curve of the molten salt stream in the range from about 3500 kW upwards, so with the entry into the heat exchanger 4 a much greater heating too realize. This has a significant effect on the vapor flow loading curve, as a result of which the result is a significantly higher steam temperature, which markedly improves the efficiency of the steam turbines 2. In the graph, a vertical line at 3500 kW separates the area passing through the heat exchanger 3 is reached by the area of the heat exchanger 4. Described above thus provides a process and apparatus for the storage and recovery of thermal energy, which in result by a splitting of the mass ^¬ flow of the heat storage medium and the repeated Further ^¬ overheating, only a portion of this mass flow over ^¬ superheated steam to store significantly more heat and thereby a much better efficiency in the recovery of energy is able to achieve.

E N G L I S H E S T E

1 solar steam generator

 2 steam turbine

 3 low-temperature heat exchanger

 4 high temperature heat exchanger

 5 hot storage

 6 cold storage

 7 intermediary spies

 8 bypass line

 9 primary side

 10 secondary side

 11 distributors

 12 heat exchangers

 13 Curve discharging the steam flow

 14 Curve loading of the steam flow

 15 curve salt melt stream

Claims

P A T E N T A N S P R E C H E Method for storing thermal energy, preferably in a solar thermal power plant, in which a heat transfer medium, with the release of thermal energy to a heat storage medium, through the primary side (9) of a heat exchanger (3, 4) is passed while the heat ^¬ mespeichermedium of a cold storage (6) via the secondary side (10) of the heat exchanger (3, 4) in a hot ^¬ memory (5) is passed, characterized in that in a second stage, a second heat exchanger (4, 3) is provided, which is pri märseitig upstream or downstream of the first heat exchanger ^¬ (3, 4) is located and through which a larger ^¬ or smaller mass flow of heat storage medium than in the first stage from a cold storage (6) in a hot storage (5) is passed, wherein the first heat exchanger is a low-temperature heat exchanger (3), and the heat storage medium before reaching the hot storage (5) in two mass flows un ^¬ is tert approaches, one of which SpeI ^¬ cher in an intermediary (7) and the other on the secondary side (10) of an additional high temperature heat exchanger (4) whose primary side (9) upstream of the primary side (9) of the low temperature heat exchanger (3) is and also flows through the heat transfer medium with the release of thermal energy to the heat storage medium in the Heißs (5) is passed, and wherein the high ^¬ temperature heat exchanger (4) is flowed through by superheated steam on the primary side. 2. The method according to claim 1, characterized in that the heat storage medium in addition before reaching the Intermediärspeichers (7) from two mass flows together ^¬ , one of which is fed from a second intermediate storage and the other from the secondary side of the low-temperature heat exchanger (3) , and by the secondary side (10) of an additional means ^¬ temperature heat ^exchanger whose primary side (9) between the primary sides (9) of the high-temperature heat exchanger (4) and the low-temperature heat exchanger (3) and also from the heat transfer medium with the release of thermal energy to the heat storage medium is passed through. Process for the recovery of thermal energy from a heat storage medium, preferably in a solar thermal power plant, in which the heat storage medium with release of thermal energy to a heat transfer medium from a hot storage (5) through the secondary side (10) of a heat exchanger (4, 3) in a cold storage ( 6) ge ^¬ passes is characterized in that in a second stage, a second heat exchanger (3, 4) is provided, which primary side upstream or downstream of the first heat ^¬ exchanger (4, 3) and through which a larger or smaller mass flow of heat storage medium than in the first stage from a hot storage (5) in a cold storage (6) is passed, wherein the first heat exchanger is a high-temperature heat exchanger (4), and the heat storage medium as a first mass flow after passing through the secondary side (10) of the high-temperature heat exchanger (4) with a second mass flow of the heat storage medium from an intermediate accumulator (7) is united and through the secondary side (10) of an additional low-temperature heat exchanger (3), the primary side (9) upstream of the primary side (9) of the high-temperature heat ^exchanger (4) and just ^¬ if from the heat transfer medium with absorption of thermal energy of the heat storage medium is flowed through, is passed, and wherein in the low-temperature ^¬ heat exchanger (3) is a heating of the heat transfer medium, preferably water, up to the boiling temperature, while in the high-temperature heat exchanger (4) overheating of the heat transfer medium, preferably superheated ^¬ tem water vapor, he follows. 4. The method according to claim 3, characterized in that the heat storage medium flows through the merge of the first and second mass flow, the secondary side (10) of an additional medium-temperature heat exchanger whose primary side (9) between the primary sides (9) of the high-temperature heat exchanger (4) and the Niedertempera ^¬ turwärmetauschers (3) is located and is also traversed by the heat ^¬ carrier medium taking in thermal energy from the heat storage medium, the mass flow before entering the low-temperature heat exchanger (3) and thereby a third mass flow of the heat storage medium into a second Interme ^¬ diärspeicher is passed. 5. A device for storing and recovering thermal energy, preferably in solar thermal power plants, with a in a bypass line (8) between a heat carrier supply line and a heat carrier return line, which is associated with a heat exchanger (4, 3), through its primary side (9) the heat transfer medium directed is, while by the secondary side (10) a heat storage ^¬ chermedium between a hot storage (5) and a cold storage (6) back and can be derived, characterized in that in a second stage, a second heat exchanger (3, 4) is provided, which is pri märseitig upstream or downstream of the first heat ^¬ exchanger (4, 3) and through which a larger or smaller mass flow of heat storage medium as in the first stage between a hot storage (5) and a cold storage (6) can be derived and derived. Apparatus according to claim 5 with two combined stages, wherein the first heat exchanger is a low-temperature heat exchanger (3) whose secondary side, the hot storage (5) facing connection with a secondary connection of an additional high-temperature heat exchanger (4), which Also flows through the heat transfer medium on the primary side, so ^¬ as with an additional intermediate memory (7) is connected. Apparatus according to claim 6, characterized in that between the low-temperature heat exchanger (3) and the high-temperature heat exchanger (4) an additional middle-temperature heat exchanger is arranged, which is also flowed through by the heat transfer medium on the primary side and whose secondary side connections each with either the intermediate memory (7) or a additional, second intermediate memory and with the secondary terminals of each adjacent heat exchanger (3, 4) are connected. 8. Device according to one of claims 6 or 7, characterized in that the memory (5, 6, 7) are formed in a ge ^¬ common container as layers within a layer heat storage. 9. Device according to one of claims 6 or 7, characterized in that the memory (5, 6, 7) are formed as separate containers. 10. Device according to one of claims 6 to 9, characterized in that it is the heat storage medium is liquid salt. 11. Device according to one of claims 6 to 10, characterized in that it is the heat transfer medium is water, which is present depending on the degree of heating as liq ^¬ siges water, steam or superheated steam.