System for converting thermal energy into mechanical energy
Patent Information
- Application Number
- EP2024708414
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-03-24
- Filing Date
- 2024-02-28
- Publication Date
- 2026-02-11
AI Technical Summary
Supercritical carbon dioxide (sCO2) cycles for thermal energy conversion face high compression work losses due to compressible properties of CO2, leading to inefficient energy conversion and increased energy costs for CO2 capture and storage, especially when using shallow geological formations.
Incorporating an additional heat exchanger to utilize waste heat from the compressor or pump unit to further heat the CO2 before it enters the turbomachine, enhancing the enthalpy gradient and increasing the power plant's output by leveraging thermal energy generated during the CO2 capture and storage process.
This approach significantly increases the performance of the turbomachine by a factor of 1.5 to 3, optimizing the compression process and reducing energy losses, while also optimizing the geothermal thermosiphon effect by utilizing waste heat effectively.
Smart Images
Figure EP2024055074_03102024_PF_FP_ABST
Abstract
Description
[0001] Description
[0002] System for converting thermal energy into mechanical energy
[0003] The invention relates to a system comprising a pump for conveying a flow medium, an arrangement for converting the flow medium from a liquid into a gaseous state, a turbomachine for converting the thermal energy of the flow medium into mechanical energy, and a condenser for condensing the gaseous flow medium into a liquid state.
[0004] Thermal power processes can be operated in a closed system. An example of a closed thermal power process is a water-steam cycle in a power plant for generating electrical energy. Water or steam is used as the heat transfer medium and the working medium. Such cycles are known as the Clausius-Rankine cycle.
[0005] At low process temperatures, these cycles are also operated with organic fluids. Such cycles are known as Organic Rankine Cycles.
[0006] Although the fluid in an Organic Rankine Cycle is not, strictly speaking, pure steam, the turbomachines used in these cycles to convert thermal energy into mechanical energy are called steam turbines. Another name for a turbomachine operating with CO2 as the fluid medium would be a CO2 expander.
[0007] Another flow medium that can be used in a cycle is carbon dioxide. One advantage of carbon dioxide over water is that the critical point is at a comparatively low pressure and temperature level. The critical point for carbon dioxide is at a pressure of approx. 74 bar and a temperature of approx. 31 °C. In comparison, the critical point for water is at a pressure of approx. 221 bar and a temperature of 385 °C. Such cycles are almost always supercritical cycles. For this reason, they are also called supercritical carbon dioxide cycles or sCCp cycles (sCCt = supercritical CO2). Although the flow medium here is not steam, the flow machine used to convert thermal energy into mechanical energy is called a steam turbine.
[0008] Figure 1 shows a cycle 1 according to the prior art, in particular a CO2 cycle. Before entering 2 the pump 3, the flow medium (CO2) is converted from a gaseous state to a liquid state in a condenser 4. The condenser 4 is operated with cooling water 8, on which the flow medium condenses. The cooling water 8 flows through pipes 9 in a condenser housing 10. The pump 3 conveys the liquid CO2 to an arrangement 5 which is designed to convert liquid CO2 into gaseous CO2. This is carried out using fuels, such as fossil fuels, or else through the use of geothermal energy, which is known under the term geothermal power plant. After leaving the arrangement 5, the gaseous CO2 flows to a steam turbine 6 which is designed to convert the thermal energy of the CO2 into mechanical energy.The cooled CO2 then reaches the condenser 4, which closes the cycle.
[0009] A key feature of such sCCp cycles is that the compression of the flow medium takes place in the near-liquid state region. This means that the working medium has compressible properties. In contrast to a Clausius-Rankine cycle, in which water as the flow medium can be described as incompressible. This means that the compressor or pump has to perform a comparatively large amount of compression work. Since compression is associated with losses, this means that small amounts of compression work, as in a water vapor cycle, lead to small losses, and large amounts of compression work, which in sCCp cycles leads to large losses.
[0010] One possibility to avoid or reduce carbon dioxide emissions would be through negative CO2 emissions, which are achieved by capturing and storing CO2 in geological formations (CCS).
[0011] For injection into these geological layers, a certain injection pressure of CO2S of 80 to 120 bar at the surface is necessary, which is composed of the hydrostatic pressure in the storage formation less the pressure due to the CO2 column in the injection well.
[0012] The capture of CO2 from the flue gases of power plants or industrial plants takes place at atmospheric pressure, so that compression is necessary before storage.
[0013] This compression requires a great deal of energy and cooling, which incurs costs and requires the use of additional fuel.
[0014] For CO2 capture and storage (CCS), geological formations with the shallowest possible depth (> 800 m) are usually selected. This limits the costs of injection wells and the costs of compaction associated with the injection pressure.
[0015] A simulation of such power plants shows that particularly high performance and economical operation would be possible if a geological formation at greater depth was chosen as the reservoir .
[0016] The lower energy yield from these flatter
[0017] Reservoirs result from a low thermosiphon effect and associated low turbine inlet pressures and a low turbine inlet temperature.
[0018] US 8,316,955 B2 discloses an application of sCCp cycles for geothermal power generation. The system described therein has an additional operating principle due to the significant difference in geodetic height. The heat is supplied in the ground, at depths of more than 730 m and frequently at depths of 2,000 m to 5,000 m. The average density of "cold" CO2 (at 10 °C to 40 °C) along the injection well differs significantly from the average density of warm CO2 (between approx. 60 °C and 260 °C). This density difference creates a natural circulation of the flow medium, which is also referred to as the thermosiphon effect. The working medium circulates without the addition of mechanical work. The extraction of thermal energy from the earth can be accelerated with a circulation pump.
[0019] For these geothermal cycles, it is also important to cool the cold flow medium as far as possible toward a liquid state, as this reduces the density at the inlet of the injection well and the compressibility of the flow medium, and thus reduces the required compression work at the inlet. The thermosiphon effect is thus enhanced.
[0020] The object of the invention is to improve a system with an SCO2 cycle.
[0021] This object is achieved by a system comprising a pump for conveying a flow medium, an arrangement for converting the flow medium from a liquid into 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, with an additional heat exchanger which is arranged between the arrangement and the turbomachine, with an additional heat exchanger which is arranged between the arrangement and the turbomachine, wherein the additional heat exchanger is designed to increase the temperature of the flow medium, wherein the increase in the temperature of the flow medium in the additional heat exchanger originates from the thermal energy of the waste heat from a compression or liquefaction process in a plant for separating and storing carbon dioxide.
[0022] Furthermore, the object is achieved by a method for operating a system in which a flow medium in the liquid state is conveyed by a pump to an arrangement, wherein in the arrangement the flow medium is converted from the liquid into a gaseous state, wherein the gaseous flow medium is guided into a turbomachine where the thermal energy of the flow medium is converted into mechanical energy, wherein after the turbomachine the flow medium is converted back into the liquid state in a condenser, wherein an additional heat exchanger is arranged between the arrangement and the turbomachine, wherein the increase in the temperature of the flow medium in the additional heat exchanger is caused by the thermal energy of the waste heat from a compression or liquefaction process from a plant for separating and storing carbon dioxide.
[0023] The invention thus solves the problem outlined by using the waste heat of a compressor or pump unit at a temperature level of 80 - 130 °C, which is too low for many power plant processes, to further heat the CO2 coming from the production wells of the geothermal power plant. This leads to a greater enthalpy gradient being available in the turbine and the output of the power plant increasing. In a plant for the capture and storage of carbon dioxide (CCS), compressor or pump units are used which heat up during operation. In particular, the medium to be compressed (carbon dioxide) is heated. It is therefore proposed according to the invention to harness the heat generated by the compressor or pump unit and to use it in a system to heat a flow medium.Before entering a turbomachine, the flow medium is further heated in a heat exchanger by the waste heat from the carbon dioxide capture and storage system.
[0024] Advantageous further developments are specified in the subclaims.
[0025] An essential feature of the invention is the use of thermal energy generated in a compressor or pump unit in a carbon capture and storage (CCS) plant.
[0026] The described process significantly increases the performance of the turbomachine. The increase in performance is also very significant, by a factor of between 1.5 and 3.
[0027] Without linking the compression or liquefaction process with the geothermal process, purely technical optimization of the compression or liquefaction process would result in a large number of compressor stages, each with an intermediate cooling stage. Utilizing the waste heat from the intermediate cooling system yields new optimization goals.
[0028] In an advantageous development, the cooling unit is designed as a heat exchanger. Another designation for the cooling unit would be subcooler. The cooling should advantageously be designed in such a way that the temperature reduction of the flow medium after condensation is 5 K. The temperature reduction can also be higher or lower than 5 K. In a further advantageous development, the further
[0029] The cooling unit is designed as a heat exchanger. Another name for the additional cooling unit would be desuperheater.
[0030] The turbomachine is designed as a steam turbine or CCp expander or can be called a steam turbine or CO2 expander.
[0031] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will be explained more clearly and in a more understandable manner in connection with the drawing.
[0032] An exemplary embodiment of the invention is described below with reference to the drawings. These are not intended to represent the exemplary embodiment in its entirety; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.
[0033] Identical parts or components or parts or components with the same function are marked with the same reference symbols.
[0034] It shows
[0035] Figure 1 shows a circuit according to the state of the art.
[0036] Figure 2 shows a circuit according to the invention.
[0037] Figure 3 is a representation of a TS diagram of the circuit according to the invention.
[0038] Figure 1 shows a conventional circuit 1, which has already been described above. Figure 2 shows a circuit 1 according to the invention. The difference between the circuit 1 according to Figure 1 and the circuit 1 according to the invention is described below. In the circuit 1 according to the invention, a cooling unit 7 is arranged in addition to the condenser 4. The cooling unit 7 is arranged between the condenser 4 and the pump 3.
[0039] The condenser 4 is operated with cooling water 8, on which the flow medium condenses. The cooling water 8 flows through pipes 9 in a condenser housing 10.
[0040] The cooling unit 7 is designed to further cool the liquid flow medium. In one embodiment, the liquid flow medium is operated with cooling water 8.
[0041] A heating unit 30, which can also be referred to as a desuperheater, is arranged in front of the condenser 4.
[0042] Furthermore, a further cooling unit 31 is arranged between the pump 3 and the arrangement 5.
[0043] A significant difference is the arrangement of an additional heat exchanger 32 between the arrangement 5 and the steam turbine 6 .
[0044] Figure 2 shows a system 41 for separating and storing carbon dioxide, which is operated in parallel to system 1. Carbon dioxide is passed from a flue gas 42 via a line 43 to a pump or compressor unit 40. The pressure of the carbon dioxide at the inlet is approximately 1 bar. In the pump or compressor unit 40, the pressure of the carbon dioxide is increased to approximately 80 to 120 bar. This increases the temperature of the carbon dioxide. According to the invention, the thermal energy thus generated is then fed via a line 33 into the additional heat exchanger 32. The thermal energy of the waste heat generated in the system 41 is thereby transferred to the flow medium in the system 1, with this transfer taking place in the additional heat exchanger 32.
[0045] The carbon dioxide cooled in the additional heat exchanger 32 is then led via a line 44 into a storage facility 45 (underground caverns or similar).
[0046] This results in a larger enthalpy gradient being available in the steam turbine 6 and the power output of the power plant increasing.
[0047] The flow medium is CO2, especially SCO2.
[0048] The circuit 1 shown in Figure 2 can be used in a geothermal application. For this purpose, the arrangement 5 is not designed as a separate component, but rather the geothermal energy present in the deep layers of the earth is utilized. At a first point 11 in the circuit 1, which is located upstream of the original generator 5, a line 12 is formed into a reservoir in the earth's interior (not shown). The essentially cold flow medium is heated in the reservoir by geothermal energy to such an extent that the flow medium undergoes a phase change from the liquid state to a gaseous state. The gaseous flow medium then returns to the circuit on the earth's surface via a feed line 13, wherein the flow medium is guided to the steam turbine 6.Although the steam turbine 6, as an embodiment of a turbomachine, is not strictly speaking powered by steam but by CO2, in particular SCO2, it is referred to here as a steam turbine 6 or CO2 expander. The steam turbine 6 or CO2 expander converts the thermal energy of the flow medium into mechanical energy, which can drive a generator, which in turn generates electrical energy.
[0049] Figure 3 shows a TS diagram of the above circuit 1 .
[0050] The letters A to J refer to points A to J in Figure 2. The temperature of the flow medium is shown on the Y-axis. The entropy of the flow medium is shown on the X-axis.
[0051] Starting with point A, the flow medium in pump 3 is brought to a higher pressure at constant temperature: Step A B . In step B C, the flow medium is cooled in the further cooling unit 31. The temperature and the entropy of the flow medium decrease. In the subsequent step C D the flow medium enters the injection bore 35 , whereby the temperature of the flow medium increases along the injection bore 35 up to the point D .
[0052] The flow medium is heated by the arrangement 5, which may be a geothermal reservoir with a high thermal energy, while simultaneously increasing the entropy. In the subsequent production well 36, the flow medium reaches an additional heat exchanger 32. The temperature of the flow medium drops in the process. In the additional heat exchanger 32, the thermal energy is used to further increase the temperature and entropy of the flow medium: Step F G . Finally, in the steam turbine 6, the thermal energy of the flow medium is converted into mechanical energy . The temperature, pressure, and entropy decrease in the process: Step G H .
[0053] In the subsequent step H I, the flow medium is cooled in a heat unit 30. In the condenser 4, the flow medium condenses: Step I J . In order to reduce the pump power, the flow medium is further cooled in a cooling unit 7 on the way to pump 3 : Step J A.
[0054] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.
Claims
Patent claims 1. System (1) comprising a pump (3) for conveying a flow medium, an arrangement (5) for converting the flow medium from a liquid into a gaseous state, a turbomachine (6) for converting the thermal energy of the flow medium into mechanical energy, a condenser (4) for condensing the gaseous flow medium into a liquid state, characterized by an additional heat exchanger (32) which is arranged between the arrangement (5) and the turbomachine (6), wherein the additional heat exchanger (32) is designed to increase the temperature of the flow medium, wherein the increase in the temperature of the flow medium in the additional heat exchanger (32) originates from the thermal energy of the waste heat from a compression or liquefaction process in a plant (41) for separating and storing carbon dioxide.
2. System according to claim 1, further comprising a cooling unit (7) designed to cool the liquid flow medium, wherein the cooling unit (7) is designed as a heat exchanger.
3. System according to claim 1 or 2, wherein the condenser (4) is fluidly connected to the pump (3) and the cooling unit (7) is arranged between the condenser (4) and the pump (3).
4. System according to one of the preceding claims, wherein the arrangement (5) is a generator which converts carbon dioxide from the liquid to the gaseous state by combustion of fuels.
5. System according to claims 1 to 3, wherein the arrangement (5) represents a reservoir in a geodetic layer of the earth, wherein the carbon dioxide arranged in the reservoir is converted from the liquid to the gaseous state by geothermal energy.
6. System according to one of the preceding claims, wherein the turbomachine (6) is designed as a steam turbine or CO2 expander.
7. System according to one of the preceding claims, wherein the turbomachine (6) is fluidically connected to the condenser (4) and a further cooling unit is arranged between the condenser (4) and the turbomachine (6), wherein the gaseous flow medium is cooled in the further cooling unit.
8. System according to claim 7, wherein the further cooling unit is designed as a heat exchanger.
9. System according to one of the preceding claims, wherein the cooling unit (7), the condenser (4) and the further cooling unit are arranged in a housing (17).
10. System according to one of claims 6, 7, 8 or 9, wherein a cooling medium flows first through the cooling unit (7), then through the condenser (4) and then through the further cooling unit.
11. System according to one of claims 6, 7, 8 or 9, wherein a cooling medium flows in parallel through the cooling unit (7), the condenser (4) and the further cooling unit.
12. System according to one of claims 1 to 8, wherein the cooling unit (7), the condenser (4) and the further cooling unit are arranged in separate housings.
13. System according to claim 12, wherein a cooling medium flows first through the cooling unit (7), then through the condenser (4) and then through the further cooling unit.
14. System according to claim 12, wherein a cooling medium flows in parallel through the cooling unit (7), the condenser (4) and the further cooling unit.
15. A method for operating a system designed according to one of claims 1 to 14, in which a flow medium in the liquid state is conveyed by a pump (3) to an arrangement (5), wherein in the arrangement (5) the flow medium is converted from the liquid into a gaseous state, wherein the gaseous flow medium is guided into a turbomachine (6), where the thermal energy of the flow medium is converted into mechanical energy, wherein after the turbomachine (6) the flow medium is converted back into the liquid state in a condenser (4), wherein between the arrangement (5) and the turbomachine (6) an additional heat exchanger (32) is arranged, wherein the increase in the temperature of the flow medium in the additional heat exchanger (32) is caused by the thermal energy of the waste heat by a compression or liquefaction process from a plant (41) for separating and storing carbon dioxide.
16. Method according to claim 15, wherein after the condenser (4) the temperature of the flow medium is reduced with a cooling unit (7) before the flow medium is fed back to the pump (3), wherein the flow medium is cooled in a further cooling unit before it flows into the condenser (4).
17. The method according to claim 15 or 16, wherein the flow medium is guided into a reservoir in the earth after the pump (3) and is heated by geothermal energy in such a way that the flow medium undergoes a phase change from liquid to gaseous and then the gaseous flow medium is guided from the earth to the flow machine (6).