Method and assembly for generating electrical energy using an ORC circuit process with cooling potential

Abstract

The present invention relates to a method and assembly for generating electrical energy using an ORC circuit process with respect to a cooling potential, and more specifically, to a case where a heat sink is present and its temperature gradient is substantially higher than the temperature gradient of a heat source. Therefore, an object of the present invention is to provide an energy generation method that overcomes the shortcomings of the prior art, reduces energy loss during the power generation process, and maximizes system efficiency. Furthermore, an object of the present invention is to provide an assembly for carrying out this method, which is achieved by the features specified in the claims.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for generating electrical energy by an ORC cycle process using thermal potential, and more particularly, to the case where a heat sink exists and its temperature gradient is significantly higher than that of the heat source.

Background Art

[0002] The organic Rankine cycle (ORC) represents a clockwise cycle process used to generate electricity from low-temperature heat.

[0003] The organic Rankine cycle represents a method of operating a steam turbine, and these steam turbines are driven not using steam but using an alternative working medium having more favorable evaporation characteristics at a temperature and pressure lower than that of water. Organic liquids such as isobutane, ethanol, or toluene are used.

[0004] This method is used when the available temperature gradient between the heat source and the heat sink is too low for the operation of a turbine driven by steam. This is the case, for example, when electricity is generated using geothermal technology, cogeneration, and ocean thermal energy conversion power plants.

[0005] ORC represents a method consisting of at least two circuits. In the first circuit, a pressurized liquid working medium absorbs thermal energy from an optimal heat source through a heat exchanger and evaporates. The resulting steam expands in an expander, thus generating torque for driving a turbine and generating electricity by a generator coupled to the turbine. In the second circuit, the gaseous working medium is cooled by a condenser, i.e., a heat exchanger using an optimal heat sink as a coolant, thereby converting it to its liquid state. Then, the liquid working medium is pressurized again by a pump and returned to the heat exchanger. This process starts again.

[0006] Further internal circuits can be integrated. For example, the expanded steam may be fed to a third heat exchanger known as a regenerator before condensation, and thus used for internal heat recovery for the evaporation process, resulting in improved electrical efficiency.

[0007] The working medium used in the ORC process may exist in both pure form and as a mixture of materials.

[0008] When a pure substance is used as a working fluid, the phase transition, that is, the transition between the liquid and gaseous states of the substance, occurs isothermally, that is, at a constant temperature.

[0009] When a mixture of substances is used as a working fluid, so-called non-azeotropic mixtures are used. These are mixtures whose components have different boiling points. As a result, in contrast to pure substances, the phase transition is not isothermal. During condensation and evaporation, a so-called thermal glide occurs, the magnitude of which depends on the composition of the mixture.

[0010] In this case, the mixture composition may be adapted during the ORC process, and continuous and discontinuous adaptation systems are distinguished.

[0011] In a discontinuous system, this composition is the same throughout the plant. When operating conditions change, the composition is adapted by separating and storing a portion of the working fluid. This composition is changed only at a specific point in time, i.e., discontinuously. The objective in this case is to adapt the cyclic process to changes in operating conditions.

[0012] In a continuous system, various compositions exist at different locations within the plant. This compositional adaptation occurs continuously. The purpose is to optimize the cycle process, for example, by utilizing heat sources and heat sinks in a more favorable manner (reducing exergy losses during heat transfer), or to achieve more favorable pressure conditions.

[0013] The composition is altered using a separator (passive system) or a rectification column (active system).

[0014] This problem can also be represented by a temperature entropy diagram (Ts diagram), where a specific cycle process operation corresponds to the area enclosed by the ORC cycle process. This area must be as large as possible to achieve maximum power yield. The area between the heat source and the heat sink, not filled by the ORC cycle process, corresponds to exergy losses.

[0015] Therefore, the objective of cycle process design is to fill the area between the heat source and the heat sink in the Ts diagram as completely as possible.

[0016] If a heat sink exists for the ORC process, and its temperature gradient is significantly higher than that of the heat source, then this corresponds to a right triangle in the Ts diagram in an idealized form, where the hypotenuse is the heat sink.

[0017] One example of the existence of such constraints is the supercritical evaporation of liquefied natural gas (also referred to as LNG below) using seawater as a heat source. Further examples involving heat sources and heat sinks with similar behavior include latent heat sources (among many, heat transfer involving a phase transition during condensation of vapor), supercritical evaporation of heat sinks, and combinations of multiple heat sinks connected in series at different temperature levels (for example, for simultaneous low-temperature heating and hot water requirements).

[0018] For this reason, conventional technology has described various plant circuits.

[0019] Patent Document 1 discloses an energy generation system using an organic Rankine cycle with a high-slip working fluid. Specifically, this disclosure relates to a system that separates the components of the working fluid to improve the effectiveness of the condenser, improve the thermal efficiency of the system, and reduce the cost of the condenser compared to the cost of the condenser required for an unseparated flow.

[0020] Patent document 2 discloses a device having a closed circuit for generating electricity from a low-temperature heat source.

[0021] Patent Document 3 discloses a Carina circulation system having a two-stage expansion machine equipped with a heating device, a separation device, an expansion machine, a generating device, an absorption and cooling device, and a pressurizing device.

[0022] Non-patent document 1 describes the use of a non-azeotropic mixture for an ORC circuit with LNG as a heat sink. Since this publication involves three consecutive ORC cycles, the complexity associated with the plant is a disadvantage in this case. This involves relatively high investment costs. At the same time, a high amount of working fluid is expected, which also represents a high cost factor.

[0023] Non-patent document 2 explores the objective of dynamically adapting the composition of the working medium as a reaction to seasonally fluctuating conditions in a heat sink. These describe the active and discontinuous adaptation of the working medium, where the column is not directly integrated into the ORC circuit but rather housed in a separate control circuit. As a result of rectification, the two mixed components of the working medium may be stored separately and supplied to the ORC process as needed, with both components evaporating together.

[0024] Patent documents 4 and 5 disclose further developments of a simplified method for adapting the composition of a working medium by a modified condenser (liquid separation condenser). These describe a passive and discontinuous adaptation of the working medium. In this case, a partial mass flow rate with a relatively high proportion of volatile components is supplied directly to the second condenser without further expansion, resulting in a disadvantage that a considerable portion of the exergy remains unused.

[0025] Patent document 6 discloses a system for reducing exergy loss in an ORC process, where a passive and continuous adaptation of the working medium occurs. After separation by the separator, more volatile mixture components are not used to generate power.

[0026] Patent Document 7 discloses a plant circuit in which a passive and continuous adaptation of a working medium occurs. In this case, after separation by a separator, the more volatile mixture components are sent to an expansion machine and then mixed with the saturated liquid flowing out of the separator.

[0027] Patent Document 8 discloses a plant circuit intended to independently adapt the mixture composition on the high-pressure and low-pressure sides to accommodate fluctuations in the heat source and heat sink.

[0028] Non-Patent Document 3 describes an ORC process using LNG as a heat sink. In this case, the working medium is separated into a liquid phase and a gas phase after passing through the first turbine stage. Then, a portion of the gas phase is expanded again in the second turbine stage and subsequently condensed. This two-stage condensation enables a better match of the ORC cycle to the temperature gradient of the LNG, resulting in a reduction in exergy loss. However, this configuration requires the expansion of the working medium into wet steam, which leads to a material-related load on the turbine (risk of droplet erosion). Furthermore, the working medium used is a pure substance, and as a result, the temperature profile of the ORC cycle process during condensation does not conform to the temperature profile of the heat sink as in the case of azeotropic mixtures, and higher exergy losses occur compared to that.

Prior Art Documents

Patent Documents

[0029]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Non-Patent Documents

[0030]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

[0031] The object of the present invention is to provide an energy generation method that eliminates the drawbacks of the prior art, reduces exergy loss while generating energy, and maximizes plant efficiency. Another object of the present invention is to provide an apparatus for carrying out this method.

[0032] This objective is achieved by the features described in the claims.

[0033] This objective is achieved by a method of generating energy by an ORC cycle process having a heat sink and a heat source, and the following method steps are performed: a) Extracting heat from a working fluid x in a heat sink, wherein the working fluid x is a non-azeotropic mixture having at least two mixture components with different boiling points. The working fluid x exists with a mixture composition xM. In the heat sink, heat is extracted by a condenser KM. After passing through the condenser KM, the working fluid x exists as wet vapor. b) Separating a working fluid x having a mixture composition xM by at least one separation device T. In this case, the mixture composition xM is changed into a first subflow A and a second subflow B. The first subflow A has a subflow composition xA, and the second subflow B has a subflow composition xB, such that xA ≠ xM ≠ xB. c) The first sub-flow A is expanded by the first sub-flow expander EA2, and then the first sub-flow A is condensed by the second condenser KA. d) Increase the pressure in the two sub-flows A and B using pumps PA and PB. e) In the heat source, evaporate the liquefied and separated partial flows A and B in evaporators VA and VB. f) Expand partial flows A and B by at least one expander EM. Subsequently, partial flows A and B are again supplied to the condenser KM, and this method is repeated from step a).

[0034] In partial flow A, the proportion of the more volatile mixture component (lower boiling point) of the working fluid x is large. In partial flow B, the proportion of the less volatile mixture component (higher boiling point) of the working fluid x is large.

[0035] According to various embodiments, after step b) of the method is performed, the second partial flow B exists as a liquid phase and / or the first partial flow A exists as a gas phase.

[0036] According to various embodiments, after step c) of the method is performed, the first partial flow A exists as a liquid phase.

[0037] According to various embodiments, the heat sinks used are liquefied natural gas and / or liquefied hydrogen. Other heat sinks are also possible. Furthermore, combinations of multiple heat sinks at different temperature levels connected in series are also possible, for example, for simultaneous low-temperature heating and hot water requirements. The use of supercritical heat sinks, for example, for the regasification of liquefied hydrogen (LH2) for supply to pipelines, is also possible.

[0038] According to various embodiments, the heat sources used are seawater and / or heat from the earth and / or the outside air. Other heat sources are also possible. For example, waste heat from agricultural and / or industrial processes, such as from a biogas plant, may be used. The heat sources used may also be appropriately temperature-controlled waste gases, such as from lime kilns and cement kilns. Solar thermal technology may also be used. Heat transfer from latent heat sources, i.e., heat sources involving phase transitions in the condensation of steam, for example, may also be used.

[0039] According to various embodiments, at least one separation apparatus T has at least one separator and / or one rectification column.

[0040] According to various embodiments, the first partial-flow expander EA2 and / or expander EM is in the form of a turbine driving a generator for generating electricity. Other configurations of the (one or more) expansion machines are possible, for example, in the form of a screw expander and / or a steam motor / reciprocating piston expander.

[0041] This objective is also achieved by an apparatus for generating energy, comprising a heat sink, a heat source, and an ORC circuit. The ORC circuit has a working fluid x, which is a non-azeotropic mixture having at least two mixture components with different boiling points. The working fluid x exists with a mixture composition xM. The ORC circuit also has a condenser KM located in the heat sink, and at least one separator T for separating the working fluid x into at least a first subflow A having composition xA and a second subflow B having composition xB. Furthermore, the ORC circuit has a first subflow expander EA2, a second condenser KA for liquefying subflow A, and two pumps PA and PB for increasing the pressure of the two subflows A and B. Furthermore, the ORC circuit has two evaporators VA and VB located in the heat source to evaporate subflows A and B, and at least one expander EM for expanding subflows A and B.

[0042] According to various embodiments, a heat sink is a storage container for liquefied natural gas or liquefied hydrogen. Other types of heat sinks are also conceivable. Furthermore, combinations of multiple heat sinks connected in series at different temperature levels are also conceivable, for example, for simultaneous low-temperature heating and hot water requirements. The use of supercritical heat sinks, for example, for the regasification of liquefied hydrogen (LH2) for supply to pipelines, is also conceivable.

[0043] According to various embodiments, the heat source is a storage container containing seawater and / or earth and / or open air. Other heat sources are also possible. For example, waste heat from agricultural and / or industrial processes, such as from a biogas plant, may be used. The heat source used may also be appropriately temperature-controlled waste gas from, for example, lime kilns and cement kilns. Solar thermal technology may also be used. Heat transfer from latent heat sources, i.e., heat sources involving phase transitions in the condensation of steam, for example, may also be used.

[0044] According to various embodiments, at least one separation apparatus T has at least one separator and / or one rectification column.

[0045] According to various embodiments, at least one of the expanders EA2 / EM is in the form of a turbine driving a generator for generating electricity. Other configurations of the expansion machine (one or more) are possible, for example, in the form of a screw expander and / or a steam motor / reciprocating piston expander.

[0046] When considering plants based on the Carnot process (pure substances as working fluids with isothermal phase transitions), it becomes clear that the Ts diagram cannot achieve the optimal results for the desired purpose.

[0047] The use of non-azeotropic mixtures (non-isothermal phase transitions) as working fluids in ORC processes appears advantageous in that the cycle process can be adapted to the temperature gradient (difference between inlet and outlet temperatures) of the heat source and heat sink better than with pure materials. This reduces exergy losses and, therefore, further increases the efficiency of the cycle process. However, significant exergy losses also occur in such cycle processes (e.g., Lorentz cycle processes), but these losses can be minimized by adapting the composition of the working fluid.

[0048] The method and apparatus according to the present invention enable efficient energy generation by an ORC cycle process, particularly in the presence of a heat sink, with a temperature gradient significantly higher than that of the heat source. In this case, exergy losses are minimized compared to conventional methods.

[0049] In this case, the basic idea is to adapt the composition of the non-azeotropic working fluid in the plant so that the temperature glide on the low-pressure side is as high as possible and the temperature glide on the high-pressure side is as low as possible. The mixture composition is modified using a separation device in the plant. A further advantage of the method according to the present invention is the two-stage expansion of the partial flow A by the expander EA, which may result in the generation of power using a larger portion of the theoretically available exergy.

[0050] The present invention will be described in more detail based on one exemplary embodiment / multiple exemplary embodiments. [Brief explanation of the drawing]

[0051] [Figure 1] This is a diagram showing a device for generating energy. [Figure 2] This diagram shows alternative devices for generating energy. [Modes for carrying out the invention]

[0052] This description refers to the attached drawings, which illustrate specific embodiments of the configuration according to the present invention. In this regard, directional terms such as “at the top” and “at the bottom” are used in relation to the orientation of the drawings being described. Directional terms are presented for illustrative purposes only and are not limiting.

[0053] It goes without saying that other embodiments may be used and structural or logical modifications may be made without departing from the scope of protection of the present invention. Unless otherwise specifically mentioned, the features of the various exemplary embodiments described herein may be combined with each other. The following detailed description should therefore not be construed as restrictive, and the scope of protection of the present invention is defined by the appended claims.

[0054] In each figure, identical or similar elements are assigned the same reference numeral for convenience.

[0055] Figure 1 shows an embodiment of the apparatus according to the present invention for generating energy by an ORC cycle process, specifically in the case where a heat sink is present and its temperature gradient is significantly higher than that of the heat source. The apparatus comprises a heat sink, a heat source, and an ORC circuit. The ORC circuit has a working fluid x, which is a non-azeotropic mixture having at least two mixture components with different boiling points. The working fluid x exists with a mixture composition xM. The ORC circuit also has a condenser KM located on the heat sink, and at least one separator T for separating the working fluid x into at least a first subflow A having composition xA and a second subflow B having composition xB. Furthermore, the ORC circuit has a first subflow expander EA2, a second condenser KA for liquefying subflow A, and two pumps PA and PB for increasing the pressure of the two subflows A and B. Furthermore, the ORC circuit has two evaporators VA and VB positioned in the heat source to evaporate partial flows A and B, and at least one expander EM to expand partial flows A and B. In this case, the partial mass flows A and B are combined downstream of evaporators VA and VB and expand together in expander EM. The advantage of this variant is that one expander can be eliminated.

[0056] In the condenser KM, a great deal of heat is removed from the working fluid having a mixture composition xM, so the mass ratio of the vapor decreases significantly. After leaving the condenser KM, the working fluid enters the separator T as wet vapor and is divided into a saturated liquid having composition xB and a saturated vapor having composition xA, where xA ≠ xM ≠ xB, and in particular xA > xB. The saturated vapor having composition xA then expands again in the first partial-flow expander EA2 (if the separator is a separator, the working fluid does not need to be completely condensed in the condenser KM, for otherwise the composition would not change). However, if a column is used, complete condensation in KM is possible, and as a result, the liquid and unsaturated vapor described may enter the separator. The saturated vapor having composition xA then expands again in the first partial-flow expander EA2 and is condensed in the condenser KA. Two mass flow rates, having mixture compositions xA and xB, which exist in liquid form, are subsequently increased to a higher pressure, separated from each other in pumps PA and PB, evaporated in evaporators VA and VB, and expanded in expander EM. The two partial mass flow rates are combined upstream of or within expander EM, resulting in a total mass flow rate M of working fluid x having mixture composition xM.

[0057] According to various embodiments, the heat sink is a storage container for liquefied natural gas or liquefied hydrogen. Also, combinations of multiple heat sinks connected in series at different temperature levels are conceivable, for example, for simultaneous low-temperature heating and hot water requirements. Furthermore, the use of supercritical heat sinks is also conceivable, for example, for the regasification of liquefied hydrogen (LH2) for supply to pipelines.

[0058] According to various embodiments, the heat source is a storage container containing seawater and / or earth and / or open air. Other heat sources are also possible. For example, waste heat from agricultural and / or industrial processes, such as from a biogas plant, may be used. The heat source used may also be appropriately temperature-controlled waste gas from, for example, lime kilns and cement kilns. Solar thermal technology may also be used. Heat transfer from latent heat sources, i.e., heat sources involving phase transitions in the condensation of steam, for example, may also be used.

[0059] According to various embodiments, at least one separation apparatus T has at least one separator and / or one rectification column. In the column, it is possible to achieve a significantly larger change in the mixture composition than in the separator, but heat must be supplied to the column during rectification, which leads to a loss of overall efficiency.

[0060] According to various embodiments, at least one of the expanders EA2 / EM is in the form of a turbine driving a generator for generating electricity. Other configurations of the expansion machine (one or more) are possible, for example, in the form of a screw expander and / or a steam motor / reciprocating piston expander.

[0061] According to various embodiments, the expander EM of the apparatus for generating energy has a second subflow expander EA for expanding subflow A and a third subflow expander EB for expanding subflow B. Figure 2 shows this alternative embodiment of the apparatus according to the present invention for generating energy by an ORC cycle process. In this case, Figure 2 shows a second subflow expander EA and a third subflow expander EB for expanding subflows A and B separately. In this case, subflows A and B are recombined only after passing through the expanders and then returned to the condenser KM as a working fluid x having a mixture composition xM. [Explanation of symbols]

[0062] A First partial flow of the working fluid A B Second partial flow of the working fluid B EA Second subflow expander for first subflow A EA2 First subflow expander for first subflow A EB Third subflow expander for second subflow B EM expander KA Second Condenser KM Condenser M Total mass flow rate of the working fluid Pump for PA partial flow A Pump for PB partial flow B T separation device Evaporator for VA partial flow A VB Evaporator for partial flow B x Working fluid xA Mixture composition of the first partial flow A xB Mixture composition of the second partial flow B Mixture composition of xM total mass flow rate

Claims

1. A method for generating electrical energy by an ORC cycle process having a heat sink and a heat source, using a cold potential, a) A step of extracting heat from a working fluid x having a mixture composition xM, which is a nonazeotropic mixture having at least two mixture components with different boiling points, wherein in the heat sink, heat is extracted by a condenser KM, and the working fluid x exists as wet vapor after passing through the condenser KM. b) A step in which the working fluid x in the mixture composition xM is separated by at least one separation device T, such that the mixture composition xM changes and xM is separated into a first partial flow A having partial flow composition xA and a second partial flow B having partial flow composition xB, wherein xA ≠ xM ≠ xB c) The first partial flow A is expanded by the first partial flow expander EA2 and the second condenser KA, followed by condensation. d) A step of increasing the pressure of the two partial flows A and B using pumps PA and PB, e) In the heat source, the step of evaporating the separated partial flows A and B in the evaporators VA and VB, f) The step of expanding the partial flows A and B by at least one expander EM, then supplying them again to the condenser KM, and repeating the method from step a). A method that includes this.

2. A method for generating electrical energy by an ORC cycle process using a cold potential, characterized in that, after step b) is performed, the second partial flow B exists as a liquid phase and / or the first partial flow A exists as a gas phase, according to claim 1.

3. A method for generating electrical energy by an ORC cycle process using a cold potential, according to claim 1, characterized in that the first partial flow A exists as a liquid phase after step c) is performed.

4. A method for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 1 to 3, characterized in that the heat sink used is liquefied natural gas and / or liquefied hydrogen.

5. A method for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 1 to 4, characterized in that the heat source used is seawater, and / or heat from the earth and / or the outside air, and / or heat from a heat source involving latent heat transfer.

6. A method for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 1 to 5, characterized in that the at least one separation device T is at least one separator and / or one rectification column.

7. A method for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 1 to 6, characterized in that the first partial flow expander EA2 and / or the expander EM is in the form of a turbine that drives a generator for generating electricity.

8. An apparatus for generating electrical energy by an ORC cycle process using a cold potential, according to the method of claim 1, comprising the following components, namely: It has a heat sink, a heat source, and an ORC circuit, and the ORC circuit has the following components, namely, The working fluid x is a non-azeotropic mixture having at least two mixture components with different boiling points, and the working fluid x exists in a mixture composition xA; the condenser KM is arranged in the heat sink; and the separation device T is for separating the working fluid x into at least a first partial flow A having the composition xA and a second partial flow B having the composition xB. Furthermore, it includes a first partial flow expander EA2, a second condenser KA for liquefying the partial flow A, and two pumps PA and PB for increasing the pressure of the two partial flows A and B. The apparatus also includes two evaporators VA and VB located in the heat source for evaporating the partial flows A and B, and at least one expander EM for expanding the partial flows A and B.

9. The apparatus for generating electrical energy by an ORC cycle process using a cold potential, as described in claim 8, characterized in that the heat sink is a storage container containing liquefied natural gas or liquefied hydrogen.

10. The apparatus for generating electrical energy by an ORC cycle process using a cold potential, as described in claim 8 or 9, characterized in that the heat source is a storage container containing heat from seawater and / or the earth and / or the outside air and / or a heat source involving latent heat transfer.

11. Apparatus for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 8 to 10, characterized in that the at least one separation apparatus T has at least one separator and / or one rectification column.

12. Apparatus for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 8 to 11, characterized in that at least one expander EA2 / EM is in the form of a turbine that drives a generator for generating electricity.

13. The apparatus for generating electrical energy by an ORC cycle process using a cold potential, according to any one of claims 8 to 12, characterized in that the expander EM comprises a second partial flow expander EA for expanding the partial flow A and a third partial flow expander EB for expanding the partial flow B.

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