System and method for utilizing geothermal energy

Abstract

A system (10) for utilizing geothermal energy, comprising a storage device (13) configured to store carbon dioxide present at a first temperature level and a first density level in an underground reservoir (11), a withdrawal device (14) configured to withdraw carbon dioxide present at a second temperature level and a second density level from the underground reservoir, wherein the second temperature level is greater than the first temperature level and the second density level is less 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, wherein the first heat exchanger (17) is configured,to transfer thermal energy of the carbon dioxide downstream of the withdrawal device (14) and upstream of the storage device to a process medium of the heat pump (16), wherein the compressor (18) is configured to compress the process medium downstream of the first heat exchanger (17), wherein the second heat exchanger (19) is configured to transfer thermal energy of the compressed process medium to a consumer, and wherein the expander (26) or the throttle is configured to expand the process medium downstream of the second heat exchanger (19), and with an introduction device (21) configured to introduce carbon dioxide from a carbon dioxide source (22) downstream of the withdrawal device (14) and upstream of the heat pump (16) into the system (10).

Description

The invention relates to a system and a method for utilizing geothermal energy.EP 2 406 562 B1 discloses a system for utilizing geothermal energy. The system disclosed therein for utilizing geothermal energy comprises a storage device which is configured to store carbon dioxide present at a first temperature level into an underground reservoir. Furthermore, the system for utilizing geothermal energy disclosed therein has a storage device which is configured to store carbon dioxide present at a second temperature level from the underground reservoir, wherein the second temperature level is greater than the first temperature level. Furthermore, this system for utilizing geothermal energy has an expander, a compressor and cooling devices. In the expander, that carbon dioxide which is stored out of the reservoir by means of the storage device can be expanded in order thus to generate mechanical energy from thermal energy, which is converted into electrical energy in a generator. The compressor serves for compressing the carbon dioxide expanded in the expander and for compressing carbon dioxide which provides a carbon dioxide source. The cooling devices serve for cooling the carbon dioxide in order to store cooled carbon dioxide again in the reservoir.U.S. Pat. No. 8 316 955 B2, U.S. Pat. No. 8 833 475 B2 and U.S. Pat. No. 8 991 510 B2 disclose further prior art relating to systems for utilizing geothermal energy.WO 2021 / 013 465 A1 discloses a system for converting thermal energy into mechanical energy, which can preferably be used in a geothermal power plant. The system disclosed therein has a pump for conveying a flow medium, an arrangement for converting the flow medium from a liquid to a gaseous state, a turbomachine for converting the thermal energy of the flow medium into mechanical energy, a condenser for condensing the gaseous flow medium into a liquid state and a cooling unit for cooling the liquid flow medium.There is a need for a system and a method for utilizing geothermal energy which enable an improvement in the efficiency and / or an improved utilization of the heat compared to the prior art.On the basis of this, the object of the present invention is to create a novel system and method for utilizing geothermal energy. This object is achieved by a geothermal energy utilization system according to claim 1 and by a method according to claim 6.The geothermal energy utilization system according to the invention has a storage device which is designed to store carbon dioxide present at a first temperature level and a first density level in an underground reservoir.The geothermal energy utilization system according to the invention has a storage device which is configured to store carbon dioxide present at a second temperature level and a second density level from the underground reservoir, wherein the second temperature level is greater than the first temperature level and the second density level is less than the first density level.The system according to the invention for utilizing geothermal energy has a heat pump with a first heat exchanger, a compressor, a second heat exchanger and an expander or a throttle, wherein the first heat exchanger of the heat pump is configured to transfer thermal energy of the carbon dioxide downstream of the storage device and upstream of the storage device to a process medium of the heat pump, wherein the compressor of the heat pump is configured to compress the process medium of the heat pump downstream of the first heat exchanger and upstream of the second heat exchanger, wherein the second heat exchanger of the heat pump is configured to transfer thermal energy of the process medium of the heat pump to a consumer, and wherein the expander or the throttle of the heat pump is configured to expand the process medium of the heat pump downstream of the second heat exchanger and upstream of the first heat exchanger.The geothermal energy utilization system according to the invention has an introduction device which is configured to introduce carbon dioxide of a carbon dioxide source into the geothermal energy utilization system downstream of the storage device and upstream of the heat pump.In the sense of the present invention, the system for utilizing geothermal energy has a heat pump. By means of the heat pump, thermal energy of the carbon dioxide removed from the underground reservoir can be effectively transferred to the process medium of the heat pump. The process medium of the heat pump can be brought to a temperature level which can be used by at least one consumer, for example as heating energy or as process heat. Further, the efficiency of the geothermal process, the efficiency of which depends on the temperature difference and the density difference of the carbon dioxide between the storage device and the storage device, can be increased.The system for utilizing geothermal energy preferably has a turbine which is configured to expand the carbon dioxide downstream of the storage device and upstream of the introduction device and to convert thermal energy into mechanical energy and / or into electrical energy via a generator driven by the turbine. By incorporating the turbine into the system for utilizing geothermal energy, the geothermal energy can be utilized not only in the area of the heat pump by a consumer, for example as heating energy or process heat, but rather the geothermal energy can also be converted into mechanical energy and / or electrical energy. This also serves to increase the efficiency and to improve the utilization of geothermal energy.The system for utilizing geothermal energy preferably has a separation container which is configured to separate liquid from the carbon dioxide downstream of the storage device and upstream of the introduction device. In particular, the separation container is connected between the storage device and the turbine. The separation container can ensure that liquid is separated from the carbon dioxide, which is stored from the underground reservoir via the storage device, in order to convey exclusively gaseous or supercritical carbon dioxide, in particular in the direction of the turbine. This also serves to increase the efficiency of the geothermal energy utilization system.Preferred developments of the invention are evident from the dependent claims and the following description. Exemplary embodiments of the invention are explained in more detail with reference to the drawings, without being restricted thereto. The following shows: FIG. 1 is a block diagram of a first system according to the invention for utilizing geothermal energy, FIG. 2 is a block diagram of a second geothermal energy utilization system according to the present invention.FIG. 1 shows a highly schematic view of a system 10 for utilizing geothermal energy together with an underground reservoir 11 in which carbon dioxide can be stored and heated by geothermal energy. The underground reservoir 11 may be located at a depth of 1 km to 5 km below the surface of the earth 12, for example.The geothermal energy utilization system 10 according to the invention has a storage device 13 which is designed to store carbon dioxide present at a first temperature level and a first density level in the underground reservoir 11.Furthermore, the geothermal energy utilization system 10 has a storage device 14 which is configured to store carbon dioxide present at a second temperature level and a second density level from the underground reservoir 11. The second temperature level is greater than the first temperature level. The carbon dioxide to be stored from the underground reservoir 11 via the storage device 14 is accordingly warmer than the carbon dioxide to be stored into the underground reservoir 11 via the storage device 13. The second density level is less than the first density level. The carbon dioxide to be stored in the region of the storage device 14 accordingly has a smaller density than the carbon dioxide to be stored in the underground reservoir 11 in the region of the storage device 13.The carbon dioxide stored from the underground reservoir 11 via the storage device 14 can be directed via a pipeline 15 in the direction of the storage device 13, wherein the system 10 for utilizing geothermal energy has a heat pump 16. The heat pump 16 has a first heat exchanger 17, a compressor 18, a second heat exchanger 19 and, in FIG. 1, an expander 26. Instead of an expander 26, a throttle can also be used. The first heat exchanger 17 of the heat pump 16 is integrated into the pipeline 15 for the carbon dioxide, wherein the first heat exchanger 17 of the heat pump 16 is configured to cool the carbon dioxide downstream of the storage device 14 and upstream of the storage device 13 and in the process to transfer thermal energy of the stored carbon dioxide to a process medium of the heat pump 16. The compressor 18 of the heat pump 16 is configured to compress the process medium of the heat pump 16 heated in the region of the first heat exchanger 17, namely downstream of the first heat exchanger 17 and upstream of the second heat exchanger 19, wherein the second heat exchanger 19 of the heat pump 16 is configured to transfer thermal energy of the process medium of the heat pump 16 to a consumer which can use the heat in particular as process heat or heating heat. In the region of the expander 26, the process medium of the heat pump 16 is expanded in order to be provided again to the first heat exchanger 17 of the heat pump 16 as expanded process medium subsequently.A motor 20 is used to drive the compressor 18 of the heat pump 16; if, as shown in FIG. 1, the heat pump 16 has the expander 19, mechanical energy is obtained in the expander 19 during the expansion of the process medium of the heat pump 16, which can be used to drive the compressor 18. In this case, the motor 20 can then be unloaded. If only one throttle is present instead of the expander 19, all the drive power for driving the compressor 18 of the heat pump 16 must be provided by the engine 20.The geothermal energy utilization system 10 further comprises an introduction device 21, which is configured to introduce carbon dioxide of a carbon dioxide source 22 downstream of the storage device 14 and upstream of the heat pump 16 into the geothermal energy utilization system 10, namely into the pipeline 15. The carbon dioxide of the carbon dioxide source 22 is compressed via the compressor 23 to a pressure level which corresponds to the pressure level of the carbon dioxide in the region of the pipeline 15 downstream of the storage device 14 and upstream of the heat pump 16. Furthermore, FIG. 1 shows a pressure regulating valve 25, with the aid of which the pressure within the pipeline 15 can be regulated directly downstream of the storage device 14.FIG. 2 shows a development of the system 10 of FIG. 1, wherein the same reference numerals as in FIG. 1 are used for the system 10 for utilizing thermal energy of FIG. 2 for the same assemblies. With regard to all other details, the exemplary embodiment of FIG. 2 corresponds to the exemplary embodiment of FIG. 1, so that reference can be made to the explanations relating to the exemplary embodiment of FIG. 1.In the exemplary embodiment of FIG. 2, the geothermal energy utilization system 10 has a turbine 27, which is designed to expand the carbon dioxide downstream of the storage device 14 and upstream of the introduction device 21 and thus convert enthalpy of the carbon dioxide into mechanical energy, in order to drive, for example, a generator 28, which is used to generate electrical energy. The compressor 23 then compresses the carbon dioxide of the carbon dioxide source 22 to a pressure level which prevails downstream of the turbine 27.In the exemplary embodiment of FIG. 2, the geothermal energy can be made accessible to a consumer not only in the region of the second heat exchanger 19 of the heat pump 16, but rather the geothermal energy can be used in the region of the turbine 27 and of the generator 28 for generating mechanical energy and electrical energy. Although the conversion of the mechanical energy obtained in the region of the turbine 27 into electrical energy is preferred, it is optional.It can be provided that the system 10 has a separation container, which is not shown in FIGS. 1, 2. Liquid can be separated in the separation container from the carbon dioxide which has been stored from the underground reservoir 11 via the storage device 14. This allows the efficiency and thus the efficiency of the geothermal energy utilization system 10 to be increased. The reservoir 11 is thereby dried. Mixing of the carbon dioxide stream with water or other liquids, which would reduce efficiency, can be avoided. Extraction of foreign constituents from the carbon dioxide stream thus serves to increase efficiency and to maintain the function without limitations.The location of the deposition vessel is dependent upon the individual components of the system 10 and is primarily dependent upon the corrosiveness and aggregate state of the foreign constituents in the carbon dioxide stream as well as the corresponding corrosion resistance of the components and, in the case of the turbine 27, the resistance to liquid constituents in the material stream. In the turbine 27, cavitation effects in the case of liquid constituents in the stream of material could significantly reduce the durability of the turbine 27. This depends on the specific design of the turbine 27.Given corresponding incompatibility of individual or multiple components within system 10, placement upstream of the corresponding component is preferred. At the same time, separation directly upstream of the storage device 13 and downstream of the turbine 27 and the first heat exchanger 17 increases efficiency, since the enthalpy flow of the foreign constituents in the turbine 27 and / or in the first heat exchanger 17 can thereby be used.The system 10 for utilizing geothermal energy can furthermore have a pump for the carbon dioxide connected between the heat pump 16, namely the first heat exchanger 17 thereof, and the storage device 13. Such a pump is optional. Depending on the pressures of the carbon dioxide in the region of the storage device 13 and the storage device 14 and the pressure in the reservoir 11 and the geodetic height, such a pump can be dispensed with.The invention further relates to a method for operating a system 10 for utilizing geothermal energy.Carbon dioxide present at the first temperature level and the first density level is stored in the underground reservoir 11 via the storage device 13.In the region of the storage device 14, the carbon dioxide is stored at the second temperature level and the second density level from the underground reservoir 11, wherein the carbon dioxide present in the region of the storage device 14 can have in particular a supercritical aggregate state and optionally partially a gaseous aggregate state.Carbon dioxide is cooled via the first heat exchanger 17 of the heat pump 16 and the density of the carbon dioxide is thus increased.The invention permits efficient operation and thus an improvement in the efficiency of a system for utilizing geothermal energy and an improved utilization of geothermal heat.List of reference characters10 System 11 underground reservoir 12 Earth surface 13 Storage device 14 Storage 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 regulating valve 26 Expander 27 Turbine 28 GeneratorReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedEP 2 406 562 B1

[0002] U.S. Pat. No. 8,316,955 B2

[0003] U.S. Pat. No. 8,833,475 B2

[0003] U.S. Pat. No. 8,991,510 B2

[0003] WO 2021 / 013 465 A1

[0004]

Claims

A system (10) for utilizing geothermal energy, comprising a storage device (13), which is configured to store carbon dioxide present at a first temperature level and a first density level, in an underground reservoir (11), comprising a storage device (14), which is configured to store carbon dioxide present at a second temperature level and a second density level, from the underground reservoir (11), wherein the second temperature level is greater than the first temperature level and the second density level is less than the first density level, comprising 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, wherein the first heat exchanger (17) of the heat pump (16) is configured, Thermal energy of the carbon dioxide downstream of the storage device (14) and upstream of the storage device (13) to be transferred to a process medium of the heat pump (16), wherein the compressor (18) of the heat pump (16) is configured to compress the process medium of the heat pump (16) downstream of the first heat exchanger (17) and upstream of the second heat exchanger (19), wherein the second heat exchanger (19) of the heat pump (16) is configured to be transferred thermal energy of the process medium of the heat pump (16) to a consumer, and wherein the expander (26) or the throttle of the heat pump (16) is configured to expand the process medium of the heat pump (16) downstream of the second heat exchanger (19) and upstream of the first heat exchanger (17), with an introduction device (21) configured to expand the process medium of the heat pump (16), In an embodiment, carbon dioxide of a carbon dioxide source (22) is introduced into the geothermal energy utilization system (10) downstream of the storage device (14) and upstream of the heat pump (16).System (10) according to Claim 1, characterized bya turbine (27) which is designed to expand the carbon dioxide downstream of the storage device (14) and upstream of the introduction device (21) and to convert thermal energy into mechanical energy and / or into electrical energy via a generator (28) driven by the turbine.System (10) according to claim 1 or 2, characterised bya separation container which is configured to separate liquid from the carbon dioxide downstream of the storage device (14) and upstream of the introduction device (21).System (10) according to Claims 2 and 3, characterized in that the separation vessel is connected between the storage device (14) and the turbine (27).System (10) according to one of Claims 1 to 4, characterized bya pump for the carbon dioxide connected between the heat pump (16) and the storage device (13).Method for operating a system (10) according to one of Claims 1 to 5, having the following steps: gaseous and / or liquid carbon dioxide is stored in the underground reservoir via the storage device (13), supercritical carbon dioxide is stored out of the underground reservoir via the storage device (14), supercritical and / or gaseous carbon dioxide is cooled via the first heat exchanger (17) of the heat pump (16).

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