Rankine cycle system and Rankine cycle method

Abstract

The present invention provides a Rankine cycle system. The Rankine cycle system includes a medium circuit formed by sequentially communicating a heater 1, an operating device 2, a cooler 3, and a pressurizing device 4. The circulating medium flows so as to circulate inside the medium circuit. The circulating medium flowing out from the heater 1 is in a supercritical state. The circulating medium is sufficiently expanded in the operating device 2 until it becomes a gas whose pressure is slightly higher than its triple point pressure. The circulating medium flowing out from the cooler 3 is a saturated liquid, and its temperature is 0 to 20°C higher than the triple point temperature of the circulating medium. The circulating medium is gradually expanded from a high-temperature and high-pressure supercritical state to a state in which it has its theoretical maximum amount of work, i.e., near the triple point pressure, thereby fully exerting its ability to do the work of the circulating medium.

Description

[Technical field]

[0001] The present invention relates to a Rankine cycle system and a Rankine cycle method in the field of power generation systems. [Background technology]

[0002] In industrial production, the exhaust temperature of some combustion engines is often relatively high. In order to further utilize the high-level heat source of the exhaust, it is common to combine a steam Rankine cycle with the lower layer of the combustion engine to realize efficient combined cycle power generation. The conventional steam Rankine cycle has the following four processes:

[0003] A heating process in which water is heated to steam in a boiler. Ideally, the heating process is a constant pressure reversible endothermic process.

[0004] A working process in which steam is expanded in a steam turbine. Ideally, the working process is a reversible adiabatic or isentropic expansion process.

[0005] A refrigeration process in which steam is cooled to saturated water in a condenser. Ideally, the refrigeration process is a reversible constant pressure refrigeration process.

[0006] A compression process in which water is compressed by increasing the pressure of a water pump. Ideally, the compression process is a reversible adiabatic compression process, i.e. an isentropic compression process.

[0007] According to Carnot's theorem, the efficiency of a reversible heat engine is related only to the maximum and minimum temperatures of the circulating medium. However, in the conventional steam Rankine cycle, water is heated to gas in the heating process and cooled to liquid close to the ambient temperature in the cooling process, so that the working efficiency of the Rankine cycle system is limited to a certain extent. Therefore, it is an urgent task in the technical field to further improve the working efficiency of the Rankine cycle system. Summary of the Invention [Problem to be solved by the invention]

[0008] SUMMARY OF THE PRESENT EMBODIMENTS The present invention aims to provide a Rankine cycle system with higher operating efficiency in view of the above-mentioned deficiencies of the prior art. [Means for solving the problem]

[0009] The Rankine cycle system includes a medium circuit formed by sequentially connecting a heater, an operating device, a cooler, and a pressurizing device, the circulating medium flows in a circulating manner inside the medium circuit, the circulating medium flowing out of the heater is in a supercritical state, the triple point temperature of the circulating medium is less than 0°C, the triple point pressure of the circulating medium is higher than standard atmospheric pressure, the circulating medium flowing out of the cooler is a saturated liquid and its temperature T1 is 0°C to 20°C higher than the triple point temperature Tgls of the circulating medium, and the pressure P1 of the gaseous circulating medium flowing out of the operating device is equal to the saturated vapor pressure of the circulating medium at temperature T1.

[0010] According to the technical solution, firstly, in the Rankine cycle system provided by the present invention, the circulating medium reaches a supercritical state in the heating device, and when the circulating medium is in a supercritical state, its density is high, and the number of turbine stages required for its expansion work is relatively small, so that the turbine device in the present invention is much more compact than the turbine structure in the traditional steam Rankine cycle, and the smaller turbine device volume leads to a smaller factory area and a more compact circulating flow.

[0011] Next, from a thermodynamic point of view, the circulation efficiency can be further improved by increasing the temperature of the heat source in the circulation process and decreasing the temperature of the cold source in the circulation process. However, if the temperature is lower than the triple point, the constant pressure cooling causes the circulation medium to change from gas to solid without passing through the liquid phase region, that is, sublimation occurs. However, since the solid circulation medium cannot flow, the utilization efficiency of the circulation medium in the Rankine cycle to the cold source supplied by the cooler is limited by the temperature of the triple point of the circulation medium. Therefore, according to Carnot's theorem, in the present invention, the circulation medium is heated to a supercritical state beyond the gas state, and is cooled in the cooler to a temperature slightly higher than the triple point (i.e., higher than the triple point of 0°C-20°C). The saturated vapor pressure of the circulation medium corresponding to this temperature is the exhaust pressure of the last stage operating device. As a result, the operating efficiency of the Rankine cycle system can be maximized. In addition, the triple point temperature of the circulating medium is lower than 0°C, so that the temperature of the circulating medium can be lowered, and the triple point pressure is higher than the standard atmospheric pressure, so that there is no need to maintain a vacuum in the condenser through an external device during the condensation process, and air leakage into the condenser is also avoided. In this way, by using a good low-temperature cold source, the circulation efficiency can be greatly improved from a thermodynamic perspective.

[0012] It is preferable that the Rankine cycle system further includes a regenerator, the heating side inlet of the regenerator being connected to a medium outlet of the operating device, the heating side outlet of the regenerator being connected to a heating side inlet of the cooler, the cooling side inlet of the regenerator being connected to a medium outlet of the pressurizing device, and the cooling side outlet of the regenerator being connected to a heater.

[0013] According to this technical solution, in the Rankine cycle system, a regenerator is added, and the gas circulating medium at the outlet of the operating device enters the regenerator and exchanges heat with the liquid circulating medium cooled and compressed in the regenerator. The gas circulating medium is pre-cooled in the regenerator and then introduced into the cooler to be cooled. The liquid circulating medium pressurized by the pressurizing device is pre-heated in the regenerator before entering the heater, thereby utilizing the residual heat of the circulating medium from the operating device, reducing the energy required by the heater and cooler, and improving the working efficiency of the Rankine cycle.

[0014] Wherein, the regenerator preferably comprises a high-temperature regenerator and a low-temperature regenerator. It is preferred that the heating side inlet of the high-temperature regenerator communicates with the medium outlet of the operating device, the heating side outlet of the high-temperature regenerator communicates with the heating side inlet of the low-temperature regenerator, the cooling side outlet of the high-temperature regenerator communicates with the heater, the cooling side inlet of the high-temperature regenerator communicates with the cooling side outlet of the low-temperature regenerator, the cooling side inlet of the low-temperature regenerator communicates with the medium outlet of the pressurizing device, and the heating side outlet of the low-temperature regenerator communicates with the cooler.

[0015] Preferably, the Rankine cycle system further includes a first three-way valve, a second three-way valve, and a compressor, the first three-way valve being connected to the compressor outlet, the cooling side outlet of the low-temperature regenerator, and the cooling side inlet of the high-temperature regenerator, respectively, and the second three-way valve being connected to the compressor inlet, the heating side outlet of the low-temperature regenerator, and the heating side inlet of the cooler, respectively.

[0016] According to this technical solution, by installing additional regenerators in the high-temperature regenerator and the low-temperature regenerator, the residual heat of the working medium flowing out of the operating device can be further utilized. In addition, the circulating medium flowing out of the low-temperature regenerator is branched, and a part of it is directly compressed by the compressor without passing through the cooler, and then it is combined with the cooled and pressurized liquid circulating medium and then flows into the heating device, thereby reducing the loss of the cold heat source of the Rankine cycle system and further improving the working efficiency of the Rankine cycle system.

[0017] The operating device preferably includes a first turbine, a second turbine, and a third turbine, the first turbine preferably performing work to the outside using a change in enthalpy value of the circulating medium in a supercritical state, the second turbine preferably receiving the circulating medium in a supercritical state from the first turbine and performing work to the outside using a phase transition of the circulating medium from a supercritical state to a gaseous state, and the third turbine preferably receiving the gaseous circulating medium from the second turbine and performing work to the outside using a change in enthalpy value of the gaseous circulating medium.

[0018] According to this technical solution, the operating device is installed in the multi-stage turbine, so that the thermal energy transmitted to the circulating medium in the heater is fully converted into mechanical energy by the multi-stage turbine, and the working efficiency of the entire circulation system is improved. Wherein, when the multi-stage turbine is a three-stage turbine, the circulating medium in the first turbine is maintained in a supercritical state, at this time, the density of the circulating medium is high, and the structure of the first turbine is more compact, and the circulating medium further expands in the second turbine, and then goes from the supercritical state to gas before entering the third turbine, and the residual heat of the circulating medium is further utilized in the third turbine, thereby improving the working efficiency of the entire circulation system.

[0019] Among them, the circulating medium of the Rankine cycle system is preferably CO2.

[0020] According to the technical proposal, currently CO2 is mainly used as the circulation medium in the supercritical CO2 (S-CO2) Brayton cycle, which has many advantages such as high high-temperature heat source circulation efficiency, small compression energy loss, compact turbine device structure and small footprint, and low corrosiveness, and is one of the potential options for efficient power generation using residual heat from gas turbine exhaust gas. However, in the supercritical CO2 (S-CO2) Brayton cycle, the cold source temperature cannot be lowered below the CO2 critical temperature (31.1°C), and this cold source temperature limits the working efficiency of the supercritical CO2 (S-CO2) Brayton cycle system.

[0021] Furthermore, the triple point of H2O is 0.01°C and 610.75 Pa, so the temperature of its cooling end cannot be reduced below 0°C, and the pressure of the triple point of H2O is too low (less than 1 kPa), so that the circulation is open, and in order to reduce the pressure close to the triple point, it is necessary to use a vacuum pump to extract the air and perform work, so there is a limit to improving the circulation efficiency. In contrast, the triple point of CO2 is -56.6°C and 0.52 MPa, so the temperature of the cold source can be reduced to a lower temperature, and the pressure of the triple point is above atmospheric pressure, the circulation form is a closed circulation, and there is no need to use a vacuum pump to evacuate, so that the entire circulation is above atmospheric pressure, and the infiltration of non-condensable gases into the low pressure part of the circulation is avoided. In this way, after combining and using good low-temperature cold sources, the circulation efficiency can be greatly improved from a thermodynamic point of view.

[0022] Finally, the corrosiveness of the CO2 circulating medium is significantly less than that of H2O steam, which significantly relaxes the corrosion resistance requirements for high-temperature component parts.

[0023] Preferably, the Rankine cycle system further includes an external cold heat source, an external heat source, and an organic media Rankine cycle circuit, the organic media Rankine cycle circuit including an organic media heater and an organic media cooler, the external heat source flows through the heater and then enters the organic media heater, and the external cold heat source is connected to the cooler and the organic media cooler respectively.

[0024] According to this technical solution, by adopting a circulation form that combines the Rankine cycle and the organic Rankine cycle, it is possible to achieve a higher circulation efficiency. With the same heat source, the combined cycle system of the present invention can generate more power and improve the energy utilization rate.

[0025] Wherein, the temperature of the external cold source is preferably -162℃ to 0℃. According to this technical solution, the temperature of the gas circulation medium can be quickly lowered to near the triple point by using a relatively low-temperature cold source. In addition, the low temperature of the cold source is advantageous for improving the operating efficiency of the Rankine cycle system.

[0026] Preferably, the external heat source is a gas unit, and the external cold source is liquefied natural gas.

[0027] According to this technical solution, the gas unit is used as a heat source, that is, the excess heat (e.g., high-temperature fumes) generated by the gas unit is reused. In addition, since the temperature of the cold source of liquefied natural gas is about -162°C, the gas circulation medium can be quickly cooled to a saturated liquid near the triple point, and the low temperature of the cold source is favorable for improving the working efficiency of the Rankine cycle system. In addition, the liquefied natural gas can be introduced into the cooler as a cold source and heat exchanged with the circulation medium, and then introduced into the gas unit as fuel, and the excess heat generated by the gas unit can be used as an external heat source to supply heat to the cycle, so that the cold source material can be fully utilized. [Brief description of the drawings]

[0028] [Figure 1] 1 is a structural schematic diagram of a Rankine cycle system according to an embodiment of the present invention. FIG. [Diagram 2] FIG. 2 is a structural schematic diagram of a Rankine cycle system according to another embodiment of the present invention. [Diagram 3] FIG. 2 is a structural schematic diagram of a Rankine cycle system according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present invention will be described in more detail with reference to the following specific embodiments and drawings. The content realized by the present invention is not limited to the following embodiments, and all various deformations, conversions, combinations, and improvements made within the scope of knowledge possessed by those skilled in the art based on the technical idea of the present invention belong to the protection scope of the present invention.

[0030] Overall configuration. As shown in FIG. 1, the Rankine cycle system according to this embodiment includes a medium circuit in which a heater 1, an operating device 2, a regenerator 5, a cooler 3, and a pressurizing device 4 are sequentially communicated. The circulating medium flows so as to circulate inside the medium circuit. Specifically, the temperature of the triple point of the circulating medium is less than 0°C, and the triple point pressure of the circulating medium is higher than the standard atmospheric pressure. The circulating medium absorbs thermal energy in the heater 1 to become a supercritical fluid, and then flows into the operating device 2, expands and does work, thereby converting the thermal energy into mechanical energy that is more easily utilized. The gaseous circulating medium that has passed through the operating device 2 enters the regenerator 5, reuses the waste heat of the circulating medium, and then enters the cooler 3 to lower the temperature. After cooling the gaseous circulating medium with a saturated liquid at a temperature T1 (Tgls < T1 < Tgls + 20°C) that is slightly higher than the triple point temperature Tgls of the circulating medium, the circulating medium enters the pressurizing device 4 and is pressurized. The pressurized liquid circulating medium enters the regenerator 5, absorbs the waste heat of the exhaust of the operating device, and enters the heater 1 again to perform a new cycle. In this way, the thermal energy is repeatedly converted into mechanical energy.

[0031] In addition, in this embodiment, the structure of each device or device is not limited. For example, in some embodiments, the operating device 2 may be a rotary turbine, and in other embodiments, the operating device 2 may be a cylinder device having a transmission rod. Similarly, on the premise that it does not violate the technical solution of the present invention, any simple replacement of the devices or devices in the present invention is considered not to exceed the protection scope of the present invention.

[0032] In this embodiment, the regenerator 5 is a device for reusing residual heat from the operating device 2. That is, in this embodiment, a preferred embodiment of the Rankine cycle to which the regenerator 5 is added has been described as an example, but as will be recognized by those skilled in the art, the Rankine cycle system according to the present invention may be configured by sequentially connecting the heater 1, the operating device 2, the cooler 3, and the pressurizing device 4 without including a regenerator.

[0033] In this embodiment, first, since the triple point temperature of the circulation medium is lower than 0°C, a cold heat source medium with a lower temperature can be used. In addition, since the triple point pressure is higher than the standard atmospheric pressure, it is not necessary to maintain a vacuum in the condenser, and it is energy-saving and prevents the intrusion of outside air into the circulation system. In this way, after combining and using good low-temperature cold sources, the circulation efficiency can be greatly improved according to Carnot's theorem.

[0034] Then, the circulating medium reaches a supercritical state in the heating device, and when the circulating medium is in a supercritical state, it has a high density and requires relatively fewer turbine stages to expand and perform work, so the high pressure turbine device in this embodiment is much more compact than the turbine structure in the traditional steam Rankine cycle. Smaller turbine device volume leads to smaller factory area and more compact circulating flow.

[0035] Finally, since the temperature of the circulating medium in the supercritical state is higher than that of the gas circulating medium, according to Carnot's theorem, when the cold source provided by the cooler 3 is fixed, the circulating medium in the Rankine cycle system of the present invention can reach a higher initial temperature, that is, the working efficiency of the Rankine cycle system of the present invention is higher than that of the conventional one.

[0036] Here, the circulating medium of the Rankine cycle system is preferably CO2.

[0037] In this embodiment, currently, CO2 is mainly applied to the supercritical CO2 (S-CO2) Brayton cycle as the circulating medium. The S-CO2 Brayton cycle has many advantages, such as high high-temperature heat source circulation efficiency, small compression energy loss, compact structure of the rotary turbine device, small footprint, and low corrosiveness, and is one of the potential options for efficient power generation using the residual heat of gas turbine exhaust gas. However, in the S-CO2 Brayton cycle, the cold heat source temperature does not fall below the CO2 critical temperature (31.1°C). This cold heat source temperature limits the working efficiency of the S-CO2 Brayton cycle system.

[0038] Furthermore, the triple point of H2O is 0.01°C and 610.75 Pa, and its cooling end temperature cannot be reduced below 0°C. Also, the triple point pressure of H2O is too low (less than 1 kPa), and the circulation form is open circulation, so that in order to cool it to a pressure close to the triple point, it is necessary to use a vacuum pump to extract air and perform work, which increases extra energy consumption and limits the improvement of circulation efficiency. In contrast, the circulation form of CO2 is closed circulation, and there is no need to use a vacuum pump to draw a vacuum. The triple point of CO2 is -56.6°C and 0.52 MPa, and the temperature of the cold source can be reduced to a lower temperature, and the triple point pressure is above atmospheric pressure, which avoids the penetration of the external condensable air into the circulation inside the condenser. In this way, after combining and using good low-temperature cold sources, the circulation efficiency can be greatly improved from a thermodynamic point of view.

[0039] In addition, the corrosiveness of the CO2 circulating medium is significantly weaker than that of H2O steam, which can significantly ease the corrosion resistance requirements for high-temperature component parts.

[0040] Finally, the specific volume of the CO2 circulating medium is much smaller than that of H2O, which can significantly reduce the size of the operating device and save factory area.

[0041] The Rankine cycle device according to this embodiment will be described in more detail below.

[0042] Heater. In this embodiment, the heater 1 may be any device capable of heating the circulating medium. Specifically, the heater 1 may be a heat exchanger that uses an external heat source 6 to heat the circulating medium. One end of the heat exchanger is provided for the introduction of the external heat source 6, and the other end is provided for the introduction of the circulating medium, so that the circulating medium absorbs the heat of the external heat source 6 through heat exchange, and is heated and undergoes a phase transition. This makes it easier to do work later. The external heat source 6 is preferably solar energy, nuclear energy, fossil fuels, etc. Furthermore, the external heat source 6 is preferably a gas unit. This allows the residual heat of the high-temperature fumes after combustion in the gas unit to be reused, thereby saving resources.

[0043] Operating device 2. In this embodiment, the operating device 2 may be a device capable of converting thermal energy into mechanical energy by utilizing the work caused by the expansion of a circulating medium, for example, a cylinder structure that reciprocates a transmission rod by gas expansion, or a rotary turbine structure that performs work by gas expansion and rotation. This embodiment will be further described by taking as an example that the operating device 2 is a rotary turbine.

[0044] The rotary turbine preferably includes a first turbine 21, a second turbine 22, and a third turbine 23. The first turbine 21 performs work to the outside by utilizing a change in the enthalpy value of the circulating medium in a supercritical state. The second turbine 22 receives the circulating medium in a supercritical state from the first turbine 21, and performs work to the outside by expansion by utilizing a phase transition of the circulating medium from a supercritical state to a gas state. The third turbine 23 receives the circulating medium that is a gas from the second turbine 22, and performs work to the outside by utilizing a change in the enthalpy value of the gas circulating medium.

[0045] In this embodiment, the operating device 2 is installed in a multi-stage turbine, so that the thermal energy transferred to the circulating medium in the heater 1 is fully converted into mechanical energy by the multi-stage turbine, thereby improving the working efficiency of the entire circulation system. As will be recognized by those skilled in the art, the effect of performing work by the circulating medium in the operating device 2 can be achieved even if a single or other number of turbines are installed. These do not exceed the scope of protection of the present invention. Here, when the multi-stage turbine is a three-stage turbine, the circulating medium in the first turbine 21 is maintained in a supercritical state. At this time, the density of the circulating medium is high, the structure of the first turbine 21 is more compact, and the circulating medium further expands adiabatically in the second turbine 22 and becomes gas from the supercritical state before entering the third turbine 23, and the residual heat of the circulating medium is further utilized in the third turbine 23, thereby increasing the working efficiency of the entire circulation system.

[0046] Regenerator 5. In this embodiment, the regenerator 5 may be a device having two flow paths, one for cold and one for hot, and exchanging heat between the media in the two flow paths. Specifically, the heating side inlet of the regenerator 5 is connected to the medium outlet of the operating device 2, the heating side outlet of the regenerator 5 is connected to the heating side inlet of the cooler 3, the cooling side inlet of the regenerator 5 is connected to the medium outlet of the pressurizing device 4, and the cooling side outlet of the regenerator 5 is connected to the heater 1.

[0047] In this embodiment, the gaseous circulating medium at the outlet of the operating device 2 enters the regenerator 5 and exchanges heat with the liquid circulating medium cooled and compressed in the regenerator 5, so that the gaseous circulating medium is pre-cooled in the regenerator 5, and then introduced into the cooler 3 to be cooled. The liquid circulating medium pressurized by the pressurizing device 4 is pre-heated in the regenerator 5 before entering the heater 1, thereby utilizing the residual heat of the circulating medium from the operating device 2, reducing the energy required by the heater 1 and the cooler 3, and improving the working efficiency of the Rankine cycle system.

[0048] 2, the regenerator 5 includes a high-temperature regenerator 51 and a low-temperature regenerator 52, the heating side inlet of the high-temperature regenerator 51 is connected to the medium outlet of the operating device 2, the heating side outlet of the high-temperature regenerator 51 is connected to the heating side inlet of the low-temperature regenerator 52, the cooling side outlet of the high-temperature regenerator 51 is connected to the cooling side inlet of the heater 1, the cooling side inlet of the high-temperature regenerator 51 is connected to the cooling side outlet of the low-temperature regenerator, and the cooling side inlet of the low-temperature regenerator 52 is connected to the medium outlet of the pressurizing device 4. The Rankine cycle system further includes a first three-way valve 91, a second three-way valve 92, and a compressor 8, the first three-way valve 91 is connected to the compressor 8 outlet, the cooling side outlet of the low-temperature regenerator 52, and the cooling side inlet of the high-temperature regenerator 51, respectively, and the second three-way valve 92 is connected to the compressor 8 inlet, the heating side outlet of the low-temperature regenerator 52, and the heating side inlet of the cooler 3, respectively.

[0049] As an example of operation, as shown in the Rankine cycle system in Fig. 2, the circulating medium first enters the cooling side inlet of the heater 1, the high-temperature exhaust gas from the gas unit enters the heating side inlet of the heater 1, the two air flows exchange heat in the heat exchanger, the cooled fumes are discharged from the heating side outlet of the heat exchanger, and the heated circulating medium flows out from the cooling side outlet of the heat exchanger and continues to enter the operating device 2 to expand and perform work. The operating device 2 has three turbines, and the circulating medium at the outlet of the first turbine 21 and the outlet of the second turbine 22 enters the heater 1 again to be heated, and then enters the second turbine 22 and the third turbine 23, respectively, to expand again and perform work. The circulating medium at the outlet of the third turbine 23 enters the heating side of the high-temperature regenerator 51, exchanges heat with the circulating medium at the cooling side of the high-temperature regenerator 51 to be cooled, the circulating medium that has been cooled once enters the heating side of the low-temperature regenerator 52 again to be cooled by heat exchange with the air flow at the cooling side of the low-temperature regenerator 52, the circulating medium that has been cooled twice is then branched into two by the second three-way valve 92, the main branch circulating medium is cooled to liquid by the cooler 3, enters the pressurizing device 4 to be pressurized, and then enters the low-temperature regenerator 52 again to be reheated and heated, and the sub branch circulating medium directly enters the compressor 8 to be pressurized. Next, the two branches of circulating medium are merged by the first three-way valve 91 to become one air flow, which then enters the cooling side of the high-temperature regenerator 51 to be reheated and heated, and then enters the heater 1 to absorb heat and continue the circulation process.

[0050] In this embodiment, further, by installing the regenerator 5 in a high-temperature regenerator 51 and a low-temperature regenerator 52, the residual heat of the working medium flowing out from the operating device 2 can be further utilized, and the circulating medium flowing out from the low-temperature regenerator 52 is branched, and a portion of it is compressed directly by the compressor 8 without passing through the cooler 3, and then merges with the cooled and compressed liquid circulating medium and flows into the heating device, thereby reducing the loss of the cold heat source in the Rankine cycle system and further improving the operating efficiency of the Rankine cycle system.

[0051] In this embodiment, the cooler 3 may be any device capable of cooling the circulating medium. Specifically, the cooler 3 may be a heat exchanger that cools the circulating medium by an external cold source 7, and one end of the heat exchanger is used to introduce the external cold source, and the other end is used to introduce the circulating medium, so that the gas circulating medium absorbs its own heat into the external cold source through heat exchange, and the temperature of the gas circulating medium is reduced to the vicinity of its triple point. This facilitates subsequent heat absorption. In addition, the temperature difference between the cooling end and the heating end of the Rankine cycle is increased, improving the circulation efficiency.

[0052] Here, the temperature of the external cold heat source is -162°C to 0°C. By using a relatively low-temperature cold heat source, the gas circulation medium can be cooled quickly and sufficiently to near the triple point, and the low cold heat source temperature is advantageous for improving the working efficiency of the Rankine cycle system. The external cold heat source 7 is preferably liquefied natural gas. The cold source temperature of liquefied natural gas is about -162°C, which is advantageous for improving the working efficiency of the Rankine cycle system. In addition, the liquefied natural gas can be continuously introduced into the gas unit as fuel after heat exchange with the circulation medium in the cooler 3, and the generated high-temperature fumes can be used as the external heat source 6, so that recycling of a good quality external cold heat source material, namely liquefied natural gas, can be realized.

[0053] Pressurizing device 4. In this embodiment, the pressurizing device 4 may be a liquid booster pump. Specifically, the pressurizing device 4 pressurizes the saturated liquid circulating medium that flows out of the cooler 3 and has a temperature close to the triple point of the circulating medium. Since the pressure of the circulating medium is close to its triple point, the energy that is converted by the circulating medium expanding in the operating device 2 and performing work in the primary Rankine cycle system is utilized as much as possible.

[0054] As shown in Figure 3, the Rankine cycle system further includes an organic media Rankine cycle circuit, which includes an organic media heater 1a and an organic media cooler 3a, and an external heat source 6 flows through the heater 1 and then enters the organic media heater 1a. An external cold source 7 is preferably connected to the cooler 3 and the organic media cooler 3a.

[0055] Furthermore, the organic Rankine cycle may include other devices in the Rankine cycle system. As shown in Fig. 3, the organic Rankine cycle further includes an organic medium operating device 2a, an organic medium pressurizing device 4a, and an organic medium regenerator 5a. The flow mechanism of the circulating medium in the organic Rankine cycle is the same as the flow mechanism of the Rankine cycle system according to the present invention, so a description thereof will be omitted here.

[0056] In this embodiment, a circulation form combining a Rankine cycle and an organic Rankine cycle is adopted, thereby realizing a higher circulation efficiency. For the same heat source, the combined cycle system of the present invention can generate more power and improve the energy utilization rate.

[0057] The Rankine cycle method applied to the Rankine cycle system according to this embodiment includes a heating step of providing an external heat source 6 and a circulating medium, and heating the circulating medium with the external heat source 6 to raise its temperature to a supercritical state; an operating step of causing the circulating medium in the supercritical state to perform work to the outside and change into a gas with a pressure close to the triple point pressure of the circulating medium; a cooling step of providing an external cold heat source 7, and cooling and lowering the temperature of the gas circulating medium with the external cold heat source 7 to obtain a saturated liquid circulating medium that is lower than 0°C and close to the triple point temperature; and a compression step of pressurizing the liquid circulating medium.

[0058] It is understood by those skilled in the art that the specific technical features in each embodiment can be adaptively divided or merged. The division or merging of the specific technical features does not cause the technical solution to deviate from the principle of the present invention, so that the divided or merged technical solution is all within the protection scope of the present invention.

[0059] Additionally, terms such as "first" and "second" are for descriptive purposes only and cannot be understood to indicate or imply the relative importance or number of the indicated technical features. Thus, a feature qualified as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "plurality" means two or more, unless otherwise specified.

[0060] Although the technical solutions of the present invention have been described above based on the embodiments shown in the drawings, it is obvious to those skilled in the art that the scope of protection of the present invention is not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent modifications or replacements to the relevant technical features, and all such modified or replaced technical solutions are within the scope of protection of the present invention. [Explanation of symbols]

[0061] 1...Heater, 2...Operating equipment, 21...First turbine, 22...Second turbine, 23...Third turbine, 3...Cooler, 4...Pressurization device, 5...Regenerator, 51...High temperature regenerator, 52...Low temperature regenerator, 6...External heat source, 7...External cold heat source, 8...Compressor, 91...First three-way valve, 92...Second three-way valve, 1a...Organic media heater, 2a...Organic media operating equipment, 3a...Organic media cooler, 4a...Organic media pressurization device, 5a...Organic media regenerator.

Claims

1. A Rankine cycle system including a medium circuit formed by sequentially communicating a heater, an operating device, a cooler, and a pressurizing device, and a circulating medium flows through the medium circuit, The operating device includes a first turbine that performs work to the outside by utilizing a change in the enthalpy value of the circulating medium in a supercritical state, and a second turbine that receives the circulating medium in a supercritical state from the first turbine and performs work to the outside by utilizing a phase transition of the circulating medium from a supercritical state to a gas state. a third turbine that receives the circulating medium, which is a gas, from the second turbine and performs work on an external device by utilizing a change in enthalpy value of the circulating medium, wherein a triple point temperature of the circulating medium is less than 0° C., and a triple point pressure of the circulating medium is higher than standard atmospheric pressure, the circulating medium exiting the heater is in a supercritical state; The circulating medium flowing out from the operating device is a gas, the circulating medium flowing out of the cooler is a saturated liquid, a temperature T1 is 0°C to 20°C higher than a triple point temperature Tgls of the circulating medium, and a pressure P1 of the circulating medium flowing out of the operating device is equal to a saturated vapor pressure of the circulating medium at the temperature T1.

2. 2. The Rankine cycle system according to claim 1, the medium circuit includes a reproducer; a heating side inlet of the regenerator connected to a medium outlet of the operating device, a heating side outlet of the regenerator connected to a heating side inlet of the cooler, a cooling side inlet of the regenerator connected to a medium outlet of the pressurizing device, and a cooling side outlet of the regenerator connected to the heater.

3. 3. The Rankine cycle system according to claim 2, The regenerator comprises a high-temperature regenerator and a low-temperature regenerator, A heating side inlet of the high-temperature generator communicates with a medium outlet of the operating device, a heating side outlet of the high-temperature generator communicates with a heating side inlet of the low-temperature generator, a cooling side outlet of the high-temperature generator communicates with the heater, and a cooling side inlet of the low-temperature generator communicates with a medium outlet of the pressurizing device, The Rankine cycle system includes a first three-way valve, a second three-way valve, and a compressor, the first three-way valve is connected to an outlet of the compressor, a cooling side outlet of the low-temperature regenerator, and a cooling side inlet of the high-temperature regenerator, respectively; and the second three-way valve is connected to an inlet of the compressor, a heating side outlet of the low-temperature regenerator, and a heating side inlet of the cooler, respectively.

4. The Rankine cycle system according to any one of claims 1 to 3, The Rankine cycle system is characterized in that the circulating medium is CO2.

5. The Rankine cycle system according to any one of claims 1 to 3, The Rankine cycle system includes an external cold source, an external heat source, and an organic media Rankine cycle circuit; the organic media Rankine cycle circuit includes an organic media heater and an organic media cooler; the external heat source flows through the heater and then enters the organic media heater; the external cold source is in communication with the cooler and the organic medium cooler, respectively.

6. 6. The Rankine cycle system according to claim 5, The Rankine cycle system is characterized in that the temperature of the external cold source is -162°C to 0°C.

7. 6. The Rankine cycle system according to claim 5, 1. A Rankine cycle system, comprising: a gas unit; and an external cold source that is a liquefied natural gas storage tank.

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