System and method for utilizing geothermal energy

Abstract

To provide a system for utilizing geothermal energy.SOLUTION: The system comprises: a storage device installed to store carbon dioxide, which is at a first temperature level and a first density level, in a subterranean reservoir; a retrieving device installed to retrieve carbon dioxide, which is at a second temperature level and a second density level, from the subterranean reservoir; a heat pump comprising a first heat exchanger, a compressor, a second heat exchanger, and an expander or throttle; and an introduction device installed to introduce carbon dioxide of a carbon dioxide source downstream of the retrieving device and upstream of the heat pump into the system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a system and method for utilizing geothermal energy.

Background Art

[0002] Patent Document 1 discloses a system for utilizing geothermal energy. The system for utilizing geothermal energy disclosed therein includes a storage device installed to store carbon dioxide at a first temperature level in an underground storage container. The system for utilizing geothermal energy disclosed therein includes a recovery device installed to recover carbon dioxide at a second temperature level from the underground storage container, and the second temperature level is higher than the first temperature level. Further, this system for utilizing geothermal energy includes an expander, a compressor, and a cooling device. In the expander, the carbon dioxide recovered from the storage container with the assistance of the recovery device can be expanded to generate mechanical energy from thermal energy, and this mechanical energy is converted into electrical energy by a generator. The compressor contributes to compressing the carbon dioxide expanded in the expander and compressing the carbon dioxide supplied by a carbon dioxide source. The cooling device contributes to cooling the carbon dioxide in order to store the cooled carbon dioxide in the storage container again.

[0003] Patent Documents 2, 3, and 4 disclose further prior art related to systems for utilizing geothermal energy.

[0004] Citation 5 discloses a system for converting geothermal energy into mechanical energy, which can be preferentially used in geothermal power plants. The system disclosed therein includes a pump for delivering a flowing medium through means for converting the flowing medium from a liquid state to a gaseous state, a turbomachine for converting the thermal energy of the flowing medium into mechanical energy, a condenser for condensing the gaseous flowing medium into a liquid state, and a cooling unit for cooling the liquid flowing medium.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0006] There is a need for a system and method for utilizing geothermal energy that enables improved efficiency and / or improved utilization of heat as compared to the prior art.

Means for Solving the Problems

[0007] Starting from this, the present invention aims to create a new type of system and method for utilizing geothermal energy. This object is achieved through the system for utilizing geothermal energy according to claim 1 and through the method according to claim 6.

[0008] The system for utilizing geothermal energy according to the present invention includes a storage device installed for storing carbon dioxide at a first temperature level and a first density level in an underground storage container.

[0009] The system for utilizing geothermal energy according to the present invention includes a recovery device installed for recovering carbon dioxide at a second temperature level and a second density level from the underground storage container, where the second temperature level is higher than the first temperature level and the second density level is lower than the first density level.

[0010] The system for utilizing geothermal energy according to the present invention includes a heat pump having a first heat exchanger, a compressor, a second heat exchanger, and an expander or throttle valve. The first heat exchanger of this heat pump is installed for transferring the thermal energy of carbon dioxide downstream of the recovery device and upstream of the storage device to the process medium of the heat pump. The compressor of the heat pump is installed for compressing the process medium of the heat pump downstream of the first heat exchanger and upstream of the second heat exchanger. The second heat exchanger of the heat pump is installed for transferring the thermal energy of the process medium of the heat pump to the consumer. The expander or throttle valve of the heat pump is installed for expanding the process medium of the heat pump downstream of the second heat exchanger and upstream of the first heat exchanger.

[0011] The system for utilizing geothermal energy according to the present invention includes an introduction device installed for introducing carbon dioxide from a carbon dioxide source downstream of the recovery device and upstream of the heat pump into the system for utilizing geothermal energy.

[0012] Regarding the invention presented herein, a system for utilizing geothermal energy comprises a heat pump. By means of the heat pump, the thermal energy of carbon dioxide extracted from an underground storage container can be efficiently transferred to the process medium of the heat pump. The process medium of the heat pump can be utilized by at least one consumer, for example, as heating energy or as process heat. Furthermore, the efficiency of the geothermal process can be increased, and the efficiency depends on the temperature difference and density difference of carbon dioxide between the storage device and the recovery device.

[0013] Preferably, a system for utilizing geothermal energy is a turbine installed to expand carbon dioxide downstream of the recovery device and upstream of the introduction device, and the turbine is provided for converting thermal energy into mechanical energy and / or into electrical energy through a generator driven by the turbine. By integrating a turbine within a system for utilizing geothermal energy, the geothermal energy can not only be used by consumers as heating energy or process heat, for example, within the region of the heat pump, but the geothermal energy can also be converted into mechanical energy and / or electrical energy. This also contributes to an increase in efficiency and an improvement in the utilization of thermal energy.

[0014] Preferably, a system for utilizing geothermal energy comprises a separation tank installed for separating liquid from carbon dioxide downstream of the recovery device and upstream of the introduction device. In particular, the separation tank is connected between the recovery device and the turbine. The separation tank enables ensuring that liquid is separated from the carbon dioxide recovered from the underground storage container through the recovery device in order to supply only gas or supercritical carbon dioxide, especially in the direction of the turbine. This also contributes to increasing the efficiency of the system for utilizing geothermal energy.

[0015] Further advantages of the present invention can be derived from the dependent claims and the following description. Exemplary embodiments of the present invention will be described in more detail by the drawings without being limited thereto.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Mode for Carrying Out the Invention

[0017] FIG. 1 schematically shows a system 10 for utilizing geothermal energy with an underground storage container 11, in which carbon dioxide can be stored and heated by geothermal energy. The underground storage container 11 can be arranged, for example, at a depth of 1 km to 5 km underground from the ground surface 12.

[0018] The system 10 for utilizing geothermal energy according to the present invention includes a storage device 13, which is installed to store carbon dioxide at a first temperature level and a first density level in the underground storage container 11.

[0019] Furthermore, the system 10 for utilizing geothermal energy includes a recovery device 14, which is installed to recover carbon dioxide at a second temperature level and a second density level from the underground storage container 11. The second temperature level is higher than the first temperature level. Therefore, the carbon dioxide recovered from the underground storage container 11 through the recovery device 14 is at a higher temperature than the carbon dioxide stored in the underground storage container 11 through the storage device 13. The second density level is lower than the first density level. Therefore, the carbon dioxide recovered in the area of the recovery device 14 is at a lower density than the carbon dioxide stored in the underground storage container 11 in the area of the storage device 13.

[0020] The carbon dioxide recovered from the underground storage container 11 through the recovery device 14 can be guided in the direction of the storage device 13 through the pipeline 15, and the system 10 for utilizing geothermal energy includes a heat pump 16. The heat pump 16 includes a first heat exchanger 17, a compressor 18, a second heat exchanger 19, and an expander 26 in FIG. 1. Instead of the expander 26, a throttle valve can also be employed. The first heat exchanger 17 of the heat pump 16 is integrated within the pipeline 15 for carbon dioxide, and the first heat exchanger 17 of the heat pump 16 cools the carbon dioxide downstream of the recovery device 14 and upstream of the storage device 13, and is installed to transfer the thermal energy of the recovered carbon dioxide to the process medium of the heat pump 16 in the process. The compressor 18 of the heat pump 16 is installed to compress the process medium of the heat pump 16 heated within the region of the first heat exchanger 17, that is, downstream of the first heat exchanger 17 and upstream of the second heat exchanger 19. The second heat exchanger 19 of the heat pump 16 is installed to transfer the thermal energy of the process medium of the heat pump 16 to consumers, thereby utilizing heat, particularly as process heat or heat. Within the region of the expander 26, the process medium of the heat pump 16 is then expanded in order to be supplied again to the first heat exchanger 17 of the heat pump 16 as the expanded process medium.

[0021] The motor 20 contributes to driving the compressor 18 of the heat pump 16. In particular, as shown in FIG. 1, when the heat pump 16 includes an expander, mechanical energy is obtained within the expander 26 during the expansion of the process medium of the heat pump 16, and this mechanical energy can be utilized to drive the compressor 18. In this case, it is possible to remove the motor 20. When there is simply a throttle valve instead of the expander 26, all the driving force for driving the compressor 18 of the heat pump 16 needs to be provided by the motor 20.

[0022] System 10 for utilizing geothermal energy further includes an introduction device 21 for introducing carbon dioxide from a carbon dioxide source 22 downstream of the recovery device 14 and upstream of the heat pump 16 into the system 10 for utilizing geothermal energy, i.e., into the pipeline 15. A compressor 23 drivable by a motor 24 is connected between the introduction device 21 and the carbon dioxide source 22. By the compressor 23, the carbon dioxide from the carbon dioxide source 22 is compressed to a pressure level corresponding to the pressure level of the carbon dioxide in the region of the pipeline 15 downstream of the recovery device 14 and upstream of the heat pump 16. Further, FIG. 1 shows a pressure control valve 25, and together with the assistance of this valve, the pressure in the pipeline 15 can be directly controlled downstream of the recovery device 14.

[0023] FIG. 2 shows a further improvement of the system 10 of FIG. 1. For the system 10 for utilizing geothermal energy in FIG. 2, the same reference numerals as in FIG. 1 are used for the same assemblies. In the following, only the details in which the exemplary embodiment of FIG. 2 differs from the exemplary embodiment of FIG. 1 are discussed. For all other details, the exemplary embodiment of FIG. 2 is consistent with the exemplary embodiment of FIG. 1, and thus it is possible to refer to the description of the exemplary embodiment of FIG. 1.

[0024] In the exemplary embodiment of FIG. 2, the system 10 for utilizing geothermal energy includes a turbine 27, which expands the carbon dioxide downstream of the recovery device 14 and upstream of the introduction device 21 to convert the enthalpy of the carbon dioxide into mechanical energy, thereby contributing to generating electrical energy, for example, driving a generator 28 installed for this purpose. Then, the compressor 23 compresses the carbon dioxide from the carbon dioxide source 22 to the pressure level downstream of the turbine 27.

[0025] In the exemplary embodiment of FIG. 2, not only is geothermal energy accessible to the consumer within the region of the second heat exchanger 19 of the heat pump 16, but geothermal energy can also be utilized within the region of the turbine 27 and the generator 28 in order to generate mechanical energy and electrical energy. Although it is preferred, it is optional to convert the mechanical energy obtained within the region of the turbine 27 into electrical energy.

[0026] The system 10 can be defined to comprise a separation tank not shown in FIGS. 1 and 2. Within the separation tank, it is possible to separate the liquid from the carbon dioxide recovered from the underground storage container 11 through the recovery device 14. Accordingly, the efficiency of the system 10 for utilizing geothermal energy can be increased. Accordingly, the storage container 11 dries out. Mixing of the carbon dioxide stream with water or other liquids, which can reduce efficiency, can be avoided. Accordingly, extracting foreign matter unrelated to the subject from the carbon dioxide stream contributes to an increase in efficiency and complete preservation of function.

[0027] The placement of the separation tank depends on the individual components of the system 10. Primarily, it depends on the corrosiveness and agglomeration state of the foreign matter unrelated to the subject within the carbon dioxide stream, as well as the corrosion resistance of the corresponding components, and in the case of the turbine 27, it depends on the resistance to the liquid components in the material stream. In the turbine 27, in the case of the liquid components in the material stream, the cavitation effect can significantly reduce the durability of the turbine 27. This depends on the specific design of the turbine 27.

[0028] If there is no compatibility with the individual components or a plurality of components within the system 10, it is preferred to place them upstream of the corresponding components. At the same time, direct separation before the storage device 13 and after the turbine 27 and the first heat exchanger 17 increases efficiency because the enthalpy flow of the foreign matter unrelated to the subject within the turbine 27 and / or the first heat exchanger 17 is available.

[0029] Furthermore, the system 10 for utilizing geothermal energy can include a pump for carbon dioxide connected between a heat pump 16, i.e., a first heat exchanger 17 of the heat pump, and a storage device 13. Such a pump is optional. Depending on the pressure of carbon dioxide within the regions of the storage device 13 and the recovery device 14, as well as the pressure within the storage vessel 11 and the geodetic head, such a pump can be omitted.

[0030] Furthermore, the present invention also relates to a method of operating the system 10 for utilizing geothermal energy.

[0031] The carbon dioxide at a first temperature level and a first density level is stored within the underground storage vessel 11 by the storage device 13.

[0032] Within the region of the recovery device 14, the carbon dioxide is recovered from the underground storage vessel 11 at a second temperature level and a second density level, and the carbon dioxide within the region of the recovery device 14 can particularly have supercritical state aggregates, and in the corresponding case, can have partially gaseous state aggregates.

[0033] The carbon dioxide is cooled by the first heat exchanger 17 of the heat pump 16, whereby the density of the carbon dioxide increases.

[0034] The present invention enables effective operation and increased efficiency of the system for utilizing geothermal energy, and enables improved utilization of geothermal energy.

Explanation of Reference Numerals

[0035] 10 ··· System 11 ··· Underground storage vessel 12 ··· Earth's surface 13 ··· Storage device 14 ··· Recovery device 15 ··· Pipeline 16 ··· Heat pump 17 ··· First heat exchanger 18 ··· Compressor 19 ··· Second heat exchanger 20 ··· Motor 21 ··· Introduction device 22 ··· Carbon dioxide source 23 ··· Compressor 24 ··· Motor 25 ··· Pressure control valve 26 ··· Expander 27 ··· Turbine 28 ··· Generator

Claims

Claim 1 A system (10) for utilizing geothermal energy, comprising: a storage device (13) installed for storing carbon dioxide at a first temperature level and a first density level in an underground storage container (11); a recovery device (14) installed for recovering carbon dioxide at a second temperature level and a second density level from the underground storage container (11), wherein the second temperature level is higher than the first temperature level and the second density level is lower than the first density level; a heat pump (16) comprising a first heat exchanger (17), a compressor (18), a second heat exchanger (19), and an expander (26) or a throttle valve, wherein the first heat exchanger (17) of the heat pump (16) is installed for transferring the thermal energy of the carbon dioxide downstream of the recovery device (14) and upstream of the storage device (13) to the process medium of the heat pump (16), the compressor (18) of the heat pump (16) is installed for compressing the process medium of the heat pump (16) downstream of the first heat exchanger (17) and upstream of the second heat exchanger (19), the second heat exchanger (19) of the heat pump (16) is installed for transferring the thermal energy of the process medium of the heat pump (16) to a consumer, and the expander (26) or the throttle valve of the heat pump (16) is installed for expanding the process medium of the heat pump (16) downstream of the second heat exchanger (19) and upstream of the first heat exchanger (17); and an introduction device (21) installed for introducing carbon dioxide from a carbon dioxide source (22) downstream of the recovery device (14) and upstream of the heat pump (16) into the system (10) for utilizing geothermal energy. Claim 2 The system (10) according to claim 1, characterized by a turbine (27) installed downstream of the recovery device (14) and upstream of the introduction device (21) for expanding the carbon dioxide, the turbine (27) converting thermal energy into mechanical energy and / or into electrical energy through a generator (28) driven by the turbine (27).

3. The system (10) according to claim 1 or 2, characterized by a separation tank installed for separating liquid from the carbon dioxide downstream of the recovery device (14) and upstream of the introduction device (21).

4. The system (10) according to claim 3, dependent on claim 2, characterized in that the separation tank is connected between the recovery device (14) and the turbine (27).

5. The system (10) according to any one of claims 1 to 4, characterized by a pump for the carbon dioxide connected between the heat pump (16) and the storage device (13).

6. A method for operating the system (10) according to any one of claims 1 to 5, comprising the following a step in which the storage device (13) stores gaseous and / or liquid carbon dioxide in the underground storage container; a step in which the recovery device (14) recovers supercritical carbon dioxide from the underground storage container; a step in which the first heat exchanger (17) of the heat pump (16) cools supercritical and / or gaseous carbon dioxide; A method including these steps.

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