Method and device for obtaining energy using a cryogenic medium

Abstract

The invention relates to a method for obtaining energy using a cryogenic medium, comprising the following steps: withdrawing a cryogenic fluid from a vessel; compressing the cryogenic fluid to a supercritical pressure; heating the cryogenic fluid of supercritical pressure to a supercritical temperature range such that a cryogenic gas is produced; expanding the supercritical cryogenic gas in a turbine to a subcritical range to produce energy; returning the cryogenic gas from the turbine to the vessel; withdrawing the cryogenic gas from the vessel; liquefying the cryogenic gas in a separate circuit and returning the cryogenic fluid to the vessel; wherein liquefying is carried out in a range of less than 20 °C, preferably less than 10 °C, particularly preferably less than 5 °C below the critical temperature of the cryogenic medium, for example at -149.5 °C. The invention also relates to a corresponding device.

Description

[0001] Method and device for energy generation using a cryogenic medium

[0002] The present invention relates to a method for generating energy using a cryogenic medium, comprising the steps of: withdrawing a cryogenic fluid from a container; compressing the cryogenic fluid to a supercritical pressure; heating the cryogenic fluid to a supercritical temperature range to generate a cryogenic gas; and expanding the supercritical cryogenic gas in a turbine to a subcritical range to generate energy. The invention further relates to a corresponding device.

[0003] Thermal power plants generate large amounts of high-temperature heat and convert it into mechanical energy with an efficiency of up to 38%. This poor efficiency is due to the high enthalpy of vaporization of the working fluid used (water) at 2,256 kJ / kg. This "heat of change of state" is lost, so that while the turbine's efficiency is over 90%, the enthalpy of vaporization reduces the power plant's efficiency to 38%.

[0004] From the publication US 2015 / 0000280 Ai, a method for generating energy using a cryogenic medium is known, in which a cryogenic fluid is taken from a storage tank and compressed using a fluid pump and then converted into the gas phase in an evaporator. The gas is fed to a first turbine. After leaving the first turbine, the gas is reheated in an intermediate heater and fed to a second turbine. The exhaust gas from the second turbine is split into a first and a second path. The first portion of the exhaust gas is passed through a first outlet to the environment, and the second portion of the exhaust gas is passed along to an inlet of the evaporator, so that thermal energy is exchanged with the cryogenic fluid within the evaporator.After passing through the evaporator, the second exhaust stream is recompressed and fed into the exhaust gas from the first turbine, so that the compressed second exhaust stream and the gas discharged from the first turbine are combined and fed into the reheater. The disadvantage of the prior art process, however, is that it does not provide a recirculation process in which the cryogenic medium is returned to the initial vessel.

[0005] It is therefore intended to further develop a method and device for energy generation using a cryogenic medium in such a way that its efficiency is increased and its effectiveness improved.

[0006] The problem is solved by the features of the independent patent claims. Advantageous embodiments are described in the dependent patent claims.

[0007] Accordingly, the method further comprises returning the cryogenic gas from the turbine to the vessel. Furthermore, the method comprises removing the cryogenic gas from the vessel, liquefying the cryogenic gas in a separate circuit, and returning the cryogenic fluid to the vessel. The liquefaction takes place in a range of less than 20°C, preferably less than 10°C, particularly preferably less than 5°C below the critical temperature of the cryogenic medium, for example, at -149.5°C.

[0008] For example, when using nitrogen as a cryogenic medium, the process provides that the liquid nitrogen stored in the container is heated to 30 bar and -

[0009] It is stored at 149.5 °C because, close to the critical temperature, there is only a low heat of change of state of 65.26 kJ / kg. Below 30 bar and -149.5 °C, the heat of change of state is removed from the gas, and the nitrogen becomes liquid.

[0010] It can be provided that the cryogenic fluid withdrawn from the container has a subcritical pressure and / or a subcritical temperature, for example, if nitrogen is used as the cryogenic medium, a pressure of 30 bar and a temperature of -149.5 °C. Furthermore, it can be provided that the compression of the cryogenic fluid to a supercritical pressure takes place by means of a pump. The pressure can be increased to 240 bar. It is conceivable that the heating of the cryogenic fluid from supercritical pressure to a supercritical temperature range initially comprises the evaporation of the fluid in a first heat exchanger and then the further heating of the now gaseous cryogenic medium with a second heat exchanger. For example, the temperature can be increased by 40 °C by means of the first heat exchanger to, for example, -

[0011] 109.5 °C and then in the second heat exchanger by a further 109.5 °C to, for example, 0 °C. Furthermore, it can be provided that the expansion of the supercritical cryogenic gas in a turbine into a subcritical region occurs adiabatically. Furthermore, it can be provided that the expansion occurs without a phase transition. For example, using nitrogen as an example, it can be provided that the temperature is reduced to -149.5 °C and the pressure to 30 bar by the expansion.

[0012] It can be provided that when the cryogenic gas is removed from the container, the cryogenic gas is fed to the separate Linde circuit. The gas removed from the container and fed to the separate circuit can have a temperature of -149.5 °C and a pressure of 30 bar. The liquefaction can comprise compressing the cryogenic gas to a supercritical temperature and a supercritical pressure. After compression, the gas can have a pressure of 90 bar and a temperature of -109.5 °C. The liquefaction can further comprise isobaric cooling of the compressed cryogenic gas. Heating can precede the compression. The precedent heating can take place in a heat exchanger, through which the returning compressed cryogenic gas to be cooled flows at the rear. The cooling may comprise flowing through a first heat exchanger through which the compressed cryogenic fluid to be evaporated flows in the opposite direction.The cooling may further comprise flowing through the second heat exchanger, which, as mentioned above, is flowed through at the front by the not yet compressed cryogenic gas to be liquefied. The cooling may comprise a temperature reduction to -149.5°C. Furthermore, it may be provided that the gas is expanded upon re-entering the vessel and is thereby liquefied. The pressure in the expanded state may be 30 bar.

[0013] The liquefaction takes place in a range of less than 20 °C, preferably less than 10 °C, particularly preferably less than 5 °C below the critical temperature of the cryogenic medium, for example at -149.5 °C if the cryogenic medium is nitrogen. The critical temperature of nitrogen is -147.05 °C. Thus, it can further be provided that the liquefaction takes place in a range of less than 3 °C below the critical temperature. Furthermore, it can be provided that the cryogenic medium, after liquefaction, has a pressure of less than 10 bar, preferably less than 5 bar, below the critical pressure of the cryogenic medium. The critical pressure of nitrogen is 33.94 bar. It can be provided that the heating of the cryogenic fluid takes place by means of a heat exchange with ambient heat.For example, a heat exchanger can be provided through which ambient air or water from a body of water such as a lake or river flows. Alternatively, the heat exchange can be carried out using the waste heat from a thermal power plant, so that both power plants are coupled.

[0014] It is conceivable that heating the cryogenic fluid involves vaporizing the cryogenic fluid. Evaporation can be achieved by heat exchange with the separate circuit for liquefying the cryogenic gas.

[0015] It may be provided that the cryogenic medium is brought to ambient temperature at a constant volume. For example, when using nitrogen, after heating, it can have a temperature of 0 °C and a pressure of 240 bar.

[0016] Expanding the supercritical cryogenic gas in the turbine to a subcritical range can involve expanding it to a subcritical temperature and pressure. For example, the high-pressure gas can be expanded adiabatically from approximately 240 bar to 30 bar via the turbine.

[0017] When using nitrogen, energy is generated at 235.3 kJ / kg, with the expansion being converted into mechanical work with an efficiency of approximately 90%. After expansion, the gas can be brought back to cryogenic temperature before the heat of the change in state is removed using cryogenic technology, e.g., the Linde process, and the liquid nitrogen can be injected back into the cryogenic tank. Since the expansion energy is many times the energy of the heat of mass change, the cycle according to the invention is profitable.

[0018] It can be provided that the compression of the cryogenic fluid takes place isothermally. Furthermore, it can be provided that the heating of the cryogenic fluid takes place isobarically.

[0019] It is conceivable that the expansion of the supercritical cryogenic gas in the turbine occurs without phase transition. The liquefaction of the cryogenic gas may further include compression to a supercritical pressure and to a supercritical temperature. Liquefaction in the Linde cycle may further include isobaric cooling to a subcritical temperature and subsequent expansion to a subcritical pressure. The expansion may include a phase transition from gaseous to liquid.

[0020] It can also be provided that the system is flushed once or several times with dry, clean nitrogen before initial commissioning to prevent water vapor or carbon dioxide from remaining in the system, which could lead to ice buildup. It is also conceivable that the system is brought to a pressure of less than 30 bar before commissioning and liquid nitrogen is pumped into the tank. It can be provided that the compressor and pump are then started. The heat exchanger Kl can then be started to create the desired pressure conditions in the system. When the pressure reaches the desired value of 240 bar at the outlet of the heat exchanger Kl, the turbine can be started. This completes the commissioning of the system.

[0021] The system can be equipped with an automatic control system. The control system can monitor the ambient temperature, and the system's performance can be regulated by controlling the pump. The amount of heat that can be extracted from the environment can be controlled by the volume of the medium flowing through the heat exchanger Kl, so that this volume can be adjusted to the ambient temperature.

[0022] Pressure gauges can be installed on the inlet and outlet sides of the heat exchangers so that any blockages in the heat exchanger system can be detected by monitoring the respective pressure difference.

[0023] For the shutdown procedure, it can be planned that the Szi pump is first stopped and liquid nitrogen is pumped from the KTi condensation tank. A Linde auxiliary circuit coupled to the tank can pump the remaining gaseous nitrogen out of the system and liquefy it. It is conceivable that the system pressure could be reduced to below 30 bar, after which the system could be shut down.

[0024] The invention further relates to a device for generating energy using a cryogenic medium, in particular for carrying out a method according to one of the preceding claims, comprising a container for storing a partially gaseous and partially liquid cryogenic medium; a pump for compressing cryogenic fluid taken from the container to a supercritical pressure; at least one device for evaporating and heating the cryogenic fluid at supercritical pressure to a supercritical temperature; at least one turbine for expanding the supercritical cryogenic gas into a subcritical region, wherein the subcritical cryogenic gas is returned from the turbine to the container; further comprising a circuit for liquefying the subcritical cryogenic gas, which circuit is fed from the container and from which the cryogenic fluid is returned to the container.wherein the circuit for liquefying the cryogenic gas takes place in a range of less than 20 °C, preferably less than 10 °C, particularly preferably less than 5 °C below the critical temperature of the cryogenic medium, for example at -149.5 °C;

[0025] The device for heating and evaporating the cryogenic medium may comprise at least one ambient heat-fed heat exchanger for heating the cryogenic gas. The heating and evaporating device may further comprise a heat exchanger coupled to the circuit for liquefying the subcritical cryogenic gas for evaporating the cryogenic fluid.

[0026] The Linde cycle for liquefying the cryogenic gas may include a compressor for compressing the cryogenic gas to a supercritical pressure and to a supercritical temperature.

[0027] Furthermore, the circuit for liquefying the cryogenic gas may further comprise at least one heat exchanger for isobarically cooling the compressed cryogenic gas to a subcritical temperature for expansion to a subcritical pressure and into a liquid state.

[0028] Further details of the invention are explained with reference to the following figures.

[0029] Fig. 1 is a flow diagram of an embodiment of the process according to the invention; Fig. 2 is a flow diagram of a supplementary auxiliary process for supplementing the process according to the invention;

[0030] Fig. 3 is a pV diagram of the process according to the invention;

[0031] Fig. 4 a Ts diagram of the method according to the invention.

[0032] Fig. 1 shows a flow diagram of an embodiment of the process according to the invention. The device essentially comprises, on the one hand, an outer Rankine cycle and, on the other hand, an inner Linde cycle. The Rankine cycle comprises, in succession in the direction of flow, a tank KTi, a pump Szi, a first heat exchanger Hi, a nitrogen heating system Kl, an inlet valve Si, a turbine Ti, and a generator G connected to the latter. The Linde cycle is also fed from the tank, or the process medium liquefied in the Linde cycle is fed back into the tank after liquefaction. The Linde cycle comprises, in succession in the direction of flow, a second heat exchanger H2 downstream of the tank KTi, a compressor Koi, the first heat exchanger Hi, and, in counterflow, again the heat exchanger H2, after flowing through which the process medium, now liquefied, is fed back into the tank KTi.Behind the turbine, the process medium is returned to the KTi tank.

[0033] In a first step of the process, subcritical liquid nitrogen is taken from the KTi tank and fed to the Szi pump (point 5), where the pressure is isothermally increased to a supercritical range. Liquid nitrogen at -149.5 °C and 30 bar is fed to the Szi pump. After passing through the Szi pump (point 1), the nitrogen remains liquid and has a temperature of -149.5 °C, while the Szi pump has increased the pressure to 240 bar. The liquid nitrogen then flows through the Hi heat exchanger (point 2), which is counterflowed by the Linde circuit, with the temperature of the counterflowing gas being -109.5 °C. In the Hi heat exchanger, the nitrogen is evaporated, the temperature is isobarically increased to -109.5 °C, and the pressure remains at 240 bar.The gaseous nitrogen then flows through the nitrogen heating system Kl (point 3), a heat exchanger fed by ambient heat, in which the temperature of the nitrogen is increased to at least 0°C. The pressure here remains at 240 bar. The highly pressurized nitrogen then drives a turbine Ti, in which the nitrogen is adiabatically expanded (point 4). The turbine Ti is in turn coupled to a generator G, which provides electrical energy. The nitrogen loses most of its pressure and temperature through expansion, so that the temperature of the nitrogen downstream of the turbine is -149.50°C and the pressure is 30 bar. The nitrogen is in a gaseous state here. The heat required to change the state of the nitrogen is then extracted by the Linde cycle to return the nitrogen to the liquid state.The advantage of performing the heat removal at 30 bar is that it is close to the critical temperature of -147.05 °C of nitrogen, since in this range the energy required for phase transformation is only low, namely 65.26 kJ / kg.

[0034] The Hampson-Linde cycle provides a regenerative cooling system, or a positive feedback cooling system. The arrangement of the heat exchangers makes it possible to exceed the absolute temperature difference (e.g., 0.27 °C / atm J - T cooling to air) in a single cooling stage and achieve the low temperatures required for liquefaction of gaseous nitrogen. Gaseous nitrogen is fed to the Linde cycle from the KTi vessel at -149.50 °C and 30 bar (point 6). It passes through the second heat exchanger H2 and absorbs heat from the returning 90-bar nitrogen gas (point 7). The compressor K01 increases the pressure and temperature of the nitrogen to -109.50 °C and 90 bar (point 8). In the subsequent first heat exchanger Hi, the liquid nitrogen from the Rankine cycle cools the gas from the Linde cycle (point 9).The cooled nitrogen is further cooled in the second heat exchanger H2 by the gas from the condensation tank to a temperature of approximately -149.50°C (point 10). The liquid nitrogen now has a temperature of -149.50°C and a pressure of 90 bar, from where it is fed to a throttle valve located at the tank inlet (point 11). As it passes through the throttle valve, it loses pressure and cools, extracting heat from the gas volume and condensing part of it in the condensation tank KTi, while the rest of the nitrogen remains in the circuit. The liquid nitrogen is then fed back to pump S. zi supplied.

[0035] Before initial commissioning, the system is purged several times with dry, clean nitrogen to prevent water vapor or carbon dioxide from remaining in the system, which can lead to ice buildup. During commissioning, the system is brought to a pressure below 30 bar, liquid nitrogen is pumped into the condensation tank KTi, then the compressor Ki and the pump Szi are started. The heat exchanger Kl is then started to establish the desired pressure conditions in the system. When the pressure reaches the desired value of 240 bar at the outlet of the heat exchanger Kl, the turbine T t started and the system commissioning is complete.

[0036] The system features an automatic control system. The control system monitors the ambient temperature, and the system's performance can be regulated by controlling the Szi pump. The amount of heat that can be extracted from the environment is controlled by the volume of the medium flowing through the Kl heat exchanger, allowing this volume to be adjusted to the ambient temperature.

[0037] Pressure gauges are installed on the inlet and outlet sides of the heat exchangers Hi, H2, Kl so that any blockages in the heat exchanger system can be detected by monitoring the pressure difference.

[0038] During shutdown, the Szi pump is stopped and liquid nitrogen is pumped from the KTi condensation tank. The Linde auxiliary circuit shown in Fig. 2 liquefies the remaining gaseous nitrogen in the system and pumps it out. The system pressure is reduced to below 30 bar, and the system can then be shut down.

[0039] The first law of thermodynamics states that the change in internal energy of a closed system is equal to the sum of the change in heat and the change in work. The cycle according to the invention does not violate this law of conservation of energy because the internal energy of the cycle is constant, i.e. the amount of energy Qbe absorbed from the environment is equal to the sum of heat added, heat removed, and work done. This gives rise to: Qbe = Qin + Qout + WKR. This fulfills the first law of thermodynamics. The second law of thermodynamics states that there is no process that leads to heat being transferred from a system with a lower temperature to a system with a higher temperature. In other words, heat cannot be transferred from a body with a lower temperature to a body with a higher temperature.Since the nitrogen used as the working fluid in the inventive process always has a lower temperature than the ambient temperature, this proves the second law of thermodynamics. The third law of thermodynamics states that the entropy of a perfect crystalline substance is zero at absolute zero. One of the most important consequences of this law is that the temperature of absolute zero (0 K) cannot be reached by any process with a limited number of steps. Since the proposed process does not approach absolute zero, the third law is irrelevant for the present process.

[0040] The cryogenic thermal power plant according to the invention is a heat pump that generates electricity from ambient heat. It has the significant advantage of drawing its energy from the environment, thus avoiding environmental pollution and even having a positive effect on climate change by cooling the environment. For example, in combination with thermal power plants, their waste heat can be successfully recovered, eliminating the need for large cooling systems and preventing the environment from heating up. Alternatively, in hot climates, the thermal power plant can cool the environment and provide electricity and air conditioning.

[0041] Fig. 2 shows a flow diagram of the auxiliary circuit. This is connected to the tank KTi of the circuit shown in Fig. 1 via valve S4. The pumped-out nitrogen is fed to an external buffer tank Pi. The buffer tank P tis connected via a valve S2 to an outlet valve N2 for adding or removing nitrogen. Furthermore, the buffer tank Pi is connected to another Linde circuit, realized by the heat exchangers H4, H5, the compressor Ko2, and the external unit HO O i, in which the remaining gaseous nitrogen can be liquefied. The liquefied nitrogen is released via a sequence valve F2 and fed into the buffer tank Pi, where it is cooled.

[0042] Fig. 3 shows a pV diagram and Fig. 4 a Ts diagram of the process. From Fig. 4 it is clearly evident that a large part of the process takes place in the supercritical range. After leaving the vessel KTi (point 5), the liquid nitrogen has a pressure of 30 bar and a temperature of -149.5 °C, and the enthalpy is 5 kJ / kg. After passing through the pump Szi (point 1), the pressure is 240 bar, the temperature is -149.5 °C, and the enthalpy is 0 kJ / kg. After passing through the first heat exchanger Hi and the heat exchanger Kl (points 2 and 3), the pressure is 240 bar, while the temperature has increased to 0 °C and the enthalpy to 236.3 kJ / kg. After expansion in the turbine Ti (point 4), the gaseous nitrogen has a pressure of 30 bar, a temperature of -149.5 °C, and an enthalpy of 65.2 kJ / kg. The thermal efficiency of the process is thus W / Qbe=H3-H4 / H3-H2=236.3-65.2 / 236.3-O=72.4%.The features of the invention disclosed in the above description, in the drawings and in the claims may be essential for the realization of the invention both individually and in any combination.

[0043] List of reference symbols

[0044] KTi container

[0045] Szi Pump

[0046] Hi heat exchanger

[0047] Ki nitrogen heating system

[0048] 51 Inlet valve

[0049] Ti Turbine

[0050] G Generator

[0051] H2 heat exchanger

[0052] Ka compressor

[0053] HOoi external unit

[0054] H4 heat exchanger

[0055] H5 heat exchanger

[0056] K02 compressor

[0057] F2 sequence valve

[0058] 52Valve

[0059] 53Valve

[0060] 54Valve

[0061] N2Hahn

[0062] Pi external buffer memory

[0063] K03 Compressor

Claims

Claims 1. A method for generating energy using a cryogenic medium, comprising the steps: Removing a cryogenic fluid from a container (KTi); Compressing the cryogenic fluid to a supercritical pressure; Heating the cryogenic fluid at supercritical pressure to a supercritical temperature range to produce a cryogenic gas; Expanding the supercritical cryogenic gas in a turbine (Ti) to a subcritical region to generate energy; Returning the cryogenic gas from the turbine (Ti) to the vessel (KTi); Removing the cryogenic gas from the container (KTi), liquefying the cryogenic gas in a separate circuit, and returning the cryogenic fluid to the container (KTi); wherein the liquefaction takes place in a range of less than 20 °C, preferably less than 10 °C, particularly preferably less than 5 °C below the critical temperature of the cryogenic medium, for example at -149.5 °C.

2. The method of claim 1, wherein heating of the cryogenic fluid is effected by means of heat exchange with ambient heat.

3. The method of claim 1 or 2, wherein heating the cryogenic fluid comprises vaporizing the cryogenic fluid.

4. A method according to any one of the preceding claims, wherein the evaporation is carried out by means of heat exchange with the separate circuit for liquefying the cryogenic gas.

5. A method according to any one of the preceding claims, wherein the expansion of the supercritical cryogenic gas in the turbine (Ti) into a subcritical region comprises expansion to a subcritical temperature and to a subcritical pressure.

6. A method according to any one of the preceding claims, wherein the compression of the cryogenic fluid is carried out isothermally.

7. A method according to any one of the preceding claims, wherein the heating of the cryogenic fluid is carried out isobarically.

8. Method according to one of the preceding claims, wherein the expansion of the supercritical cryogenic gas in the turbine (Ti) takes place without phase transformation.

9. A method according to any one of the preceding claims, wherein liquefying the cryogenic gas comprises compressing it to a supercritical pressure and to a supercritical temperature 10. A process according to any one of the preceding claims, wherein the liquefaction further comprises isobaric cooling to a subcritical temperature and subsequent expansion to a subcritical pressure, wherein the expansion comprises a phase transformation from gaseous to liquid.

11. A device for generating energy using a cryogenic medium, in particular for carrying out a method according to one of the preceding claims, comprising a container (KTi) for storing a partially gaseous and partially liquid cryogenic medium; a pump (Szi) for compressing cryogenic fluid taken from the container (KTi) to a supercritical pressure; at least one device for evaporating and heating the cryogenic fluid at supercritical pressure to a supercritical temperature; at least one turbine (Ti) for expanding the supercritical cryogenic gas into a subcritical region, wherein the subcritical cryogenic gas is returned from the turbine (Ti) to the container (KTi); further comprising a circuit for liquefying the subcritical cryogenic gas, which circuit is fed from the container (KTi) and from which the cryogenic fluid is returned to the container (KTi);wherein the circuit for liquefying the cryogenic gas is in a range of less than 20 °C, preferably less than 10 °C, particularly preferably less than; 5 °C below the critical temperature of the cryogenic medium, for example at -149.5 °C.

12. Apparatus according to claim 11, wherein the means for heating and vaporizing the cryogenic medium comprises a heat exchanger (Kl) fed by ambient heat for heating the cryogenic gas.

13. Device according to one of claims 11 or 12, wherein the means for heating and evaporating comprises a heat exchanger (Hi) coupled to the circuit for liquefying the subcritical cryogenic gas for evaporating the cryogenic fluid.

14. Device according to one of claims 11 to 13, wherein the circuit for liquefying the cryogenic gas comprises a compressor (K01) for compressing the cryogenic gas to a supercritical pressure and to a supercritical temperature.

15. Device according to one of claims 11 to 14, wherein the circuit for liquefying the cryogenic gas further comprises at least one heat exchanger (H 2 ) for isobarically cooling the compressed cryogenic gas to a subcritical temperature for expansion to a subcritical pressure and into a liquid state.

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