A Rankine cycle system and a Rankine cycle method

Abstract

The present invention provides a Rankine cycle system. The Rankine cycle system includes a medium loop formed by sequentially connecting a heater, a work device, a cooler, and a pressurization device. The circulating medium circulates inside the medium loop. The circulating medium flowing out of the heater is in a supercritical state. The circulating medium expands fully in the work device to a gaseous state slightly higher than its triple point pressure. The circulating medium flowing out of the cooler is in a saturated liquid state, and the temperature is 0-20 °C higher than the triple point temperature of the circulating medium. Since the circulating medium expands gradually from a supercritical state of high temperature and high pressure to its theoretical work limit state - near the triple point pressure, the work capacity of the circulating medium is fully exerted.

Description

Technical Field

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

[0002] In industrial production, some gas turbines often have a relatively high exhaust temperature. In order to further utilize the high-temperature exhaust heat source, people usually combine a steam Rankine cycle at the bottom of the gas turbine to achieve high-efficiency combined cycle power generation. The existing steam Rankine cycle has four processes:

[0003] Heating process: Water is heated to steam in a boiler, and the heating process can be idealized as a constant-pressure reversible endothermic process.

[0004] Work process: Steam expands in a steam turbine, and the work process can be idealized as a reversible adiabatic expansion process, that is, an isentropic expansion process.

[0005] Cooling process: Steam is cooled to saturated water in a condenser, and the cooling process can be idealized as a reversible constant-pressure cooling process.

[0006] Pressurization process: Water is compressed and pressurized in a water pump, and the pressurization process can be idealized as a reversible adiabatic compression process, that is, an isentropic compression process.

[0007] Among them, according to the Carnot principle, the efficiency of a reversible heat engine is only related to the highest temperature and the lowest temperature of the cycle medium. In the existing steam Rankine cycle, water is heated to a gaseous state during the heating process and cooled to a liquid state close to the ambient temperature during the cooling process, which to a certain extent limits the operating efficiency of the Rankine cycle system. Therefore, how to further improve the operating efficiency of the Rankine cycle system is an urgent problem to be solved in this field. Summary of the Invention

[0008] Aiming at the defects in the prior art, the purpose of the present invention is to provide a Rankine cycle system with higher operating efficiency.

[0009] The Rankine cycle system includes a medium loop formed by connecting a heater, a work device, a cooler, and a booster device in sequence. The circulating medium circulates inside the medium loop. The circulating medium flowing out of the heater is in a supercritical state. The triple point temperature of the circulating medium is lower than 0 °C, and the triple point pressure of the circulating medium is higher than the standard atmospheric pressure. The circulating medium flowing out of the cooler is in a saturated liquid state, and its temperature T1 is 0 °C - 20 °C higher than the triple point temperature Tgls of the circulating medium. The pressure P1 of the gaseous circulating medium flowing out of the work device is equal to the saturated vapor pressure of the circulating medium at temperature T1. According to this technical solution, firstly, in the Rankine cycle system provided by the present invention, the circulating medium reaches a supercritical state in the heating device. When the circulating medium is in a supercritical state, its density is relatively high, and the number of turbine stages required for its expansion work is relatively small. Therefore, in the present invention, the turbine device is much more compact than the turbine structure in the existing steam Rankine cycle. A smaller volume of the turbine device means a smaller plant area and a more compact circulation process.

[0010] Secondly, from a thermodynamic perspective, increasing the heat source temperature during the cycle process and decreasing the cold source temperature during the cycle process can further improve the cycle efficiency. However, when the temperature is lower than the triple point, constant-pressure cooling will cause the circulating medium to directly sublime from the gaseous state to the solid state without passing through the liquid phase region. But since the solid circulating medium cannot flow, the utilization ability of the cold source provided by the circulating medium to the cooler in the Rankine cycle is limited by the triple point temperature of the circulating medium. Therefore, according to the Carnot principle, in the present invention, the circulating medium is heated to a supercritical state higher than the gaseous state, and moreover, the circulating medium is cooled to a temperature slightly higher than the triple point (i.e., 0 °C - 20 °C higher than the triple point) in the cooler. The saturated vapor pressure of the circulating medium corresponding to this temperature is the exhaust pressure of the last-stage work device, which can maximize the operating efficiency of the Rankine cycle system; further, the triple point temperature of the circulating medium is lower than 0 °C, which can reduce the circulating medium to a lower temperature, and the triple point pressure is higher than the standard atmospheric pressure, so that it is not necessary to rely on external equipment to maintain the vacuum in the condenser during the condensation process, and it also avoids the leakage of air into the condenser. In this way, after combining the utilization of high-quality low-temperature cold sources, from a thermodynamic perspective, the cycle efficiency can be significantly improved.

[0011] Among them, preferably, the Rankine cycle system further includes a regenerator. The hot-side inlet of the regenerator is connected to the medium outlet of the work device, the hot-side outlet of the regenerator is connected to the hot-side inlet of the cooler, the cold-side inlet of the regenerator is connected to the medium outlet of the booster device, and the cold-side outlet of the regenerator is connected to the heater.

[0012] According to this technical solution, in this Rankine cycle system, a recuperator is added. The gaseous circulating medium at the outlet of the work device enters the recuperator and exchanges heat with the cooled and compressed liquid circulating medium in the recuperator, so that the gaseous circulating medium is pre-cooled in the recuperator and then sent to the cooler for cooling. The liquid circulating medium pressurized by the pressurizing device is pre-heated in the recuperator before entering the heater, so that the waste heat of the circulating medium after the work device can be utilized, the energy required to be provided by the heater and the cooler can be reduced, and the operating efficiency of the Rankine cycle system can be improved.

[0013] Among them, preferably, the recuperator includes a high-temperature recuperator and a low-temperature recuperator. The hot-side inlet of the high-temperature recuperator is communicated with the medium outlet of the work device, the hot-side outlet of the high-temperature recuperator is communicated with the hot-side inlet of the low-temperature recuperator, the cold-side outlet of the high-temperature recuperator is communicated with the heater, the cold-side inlet of the high-temperature recuperator is communicated with the cold-side outlet of the low-temperature recuperator, the cold-side inlet of the low-temperature recuperator is communicated with the medium outlet of the pressurizing device, and the hot-side outlet of the low-temperature recuperator is communicated with the cooler.

[0014] Among them, 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 is respectively communicated with the compressor outlet, the cold-side outlet of the low-temperature recuperator and the cold-side inlet of the high-temperature recuperator. The second three-way valve is respectively communicated with the compressor inlet, the hot-side outlet of the low-temperature recuperator and the hot-side inlet of the cooler.

[0015] According to this technical solution, the recuperator is further set as a high-temperature recuperator and a low-temperature recuperator, so that the waste heat of the working medium flowing out of the work device can be further utilized. And by diverting the circulating medium flowing out of the low-temperature recuperator, a part of it directly passes through the compressor for compression without passing through the cooler and then is aggregated with the cooled and pressurized liquid circulating medium and flows to the heating device, so that the cold source loss of the Rankine cycle system can be reduced, and the operating efficiency of the Rankine cycle system can be further improved.

[0016] Among them, preferably, the work device includes a first turbine, a second turbine and a third turbine. The first turbine uses the enthalpy change of the supercritical state circulating medium to do work externally. The second turbine receives the supercritical state circulating medium from the first turbine and uses the phase change of the circulating medium from the supercritical state to the gaseous state to do work externally. The third turbine receives the gaseous circulating medium from the second turbine and uses the enthalpy change of the gaseous circulating medium to do work externally.

[0017] According to this technical solution, by setting the work device as a multi-stage turbine, the thermal energy transferred to the circulating medium in the heater is fully converted into mechanical energy through the multi-stage turbine, improving the operating efficiency of the overall circulation system. Among them, when the multi-stage turbine is a three-stage turbine, the circulating medium in the first turbine remains in the supercritical state. At this time, the density of the circulating medium is relatively high, and the structure of the first turbine can be more compact. After the circulating medium further undergoes adiabatic expansion in the second turbine and changes from the supercritical state to the gaseous state, it enters the third turbine, where the waste heat of the circulating medium is further utilized, thereby increasing the overall operating efficiency of the circulation system.

[0018] Among them, preferably, the circulating medium of this Rankine cycle system is CO2.

[0019] According to this technical solution, the current application of CO2 as a circulating medium is mainly in the supercritical CO2 (S-CO2) Brayton cycle. The supercritical CO2 (S-CO2) Brayton cycle has many advantages such as high cycle efficiency of the high-temperature heat source, small compression work consumption, compact structure of the turbine equipment, small floor area, and low corrosion. It is one of the potential options for high-efficiency power generation from the exhaust waste heat of gas turbines. However, in the supercritical CO2 (S-CO2) Brayton cycle, the cold source temperature must not be lower than the CO2 critical temperature (31.1 °C), and this cold source temperature limits the operating efficiency of the supercritical CO2 (S-CO2) Brayton cycle system.

[0020] Furthermore, the triple point of H2O is 0.01 °C and 610.75 Pa, and its cold-end temperature can only be lowered to above 0 °C at the lowest. Moreover, due to the extremely low triple point pressure of H2O (only less than 1 kPa) and it being an open cycle, if it is to be lowered to near the triple point pressure, a vacuum pump needs to be used for pumping work, and the improvement of the cycle efficiency is relatively limited. In contrast, the triple point of CO2 is -56.6 °C and 0.52 MPa, its cold source temperature can be lowered to a lower level, and the triple point pressure is above atmospheric pressure. The cycle form is a closed cycle, and there is no need to use a vacuum pump to evacuate, enabling the whole cycle to be above atmospheric pressure, avoiding the infiltration of non-condensable gases at the low-pressure part of the cycle. In this way, after combining with the utilization of high-quality low-temperature cold sources, thermodynamically speaking, the cycle efficiency can be greatly improved.

[0021] Finally, the corrosiveness of the CO2 circulating medium is much milder than that of H2O steam, which can greatly reduce the corrosion resistance requirements for the materials of high-temperature component equipment.

[0022] Among them, preferably, this Rankine cycle system further includes an external cold source, an external heat source, and an organic Rankine cycle loop. The organic Rankine cycle loop includes an organic medium heater and an organic medium cooler. After the external heat source flows through the heater, it enters the organic medium heater, and the external cold source is respectively connected to the cooler and the organic medium cooler.

[0023] According to this technical solution, adopting a cycle form combining the Rankine cycle and the organic Rankine cycle can achieve a higher cycle efficiency. For the same heat source, using the combined cycle system of the present invention can generate more electricity and improve the energy utilization rate.

[0024] Among them, preferably, the temperature of the external cold source is -162°C - 0°C. According to this technical solution, using a cold source with a lower temperature can quickly cool the gaseous circulating medium to near the triple point, and the low temperature of the cold source is beneficial to improving the operating efficiency of the Rankine cycle system.

[0025] Among them, preferably, the external heat source is a gas turbine unit, and the external cold source is liquefied natural gas.

[0026] According to this technical solution, using the gas turbine unit as the heat source, that is, reusing the excess heat (such as high-temperature flue gas) generated by the gas turbine unit. In addition, the cold source temperature of liquefied natural gas is about -162°C, so that the gaseous circulating medium can be quickly cooled to the saturated liquid near the triple point, and the low temperature of the cold source is beneficial to improving the operating efficiency of the Rankine cycle system. Further, after liquefied natural gas is used as the cold source and passed into the cooler to exchange heat with the circulating medium, it can continue to be passed into the gas turbine unit as fuel, and the excess heat generated by the gas turbine unit can be used as an external heat source to supply heat to the cycle, thus realizing the full and reasonable utilization of the cold source material. Description of the Drawings

[0027] Figure 1 is a schematic structural diagram of a Rankine cycle system provided by an embodiment of the present invention;

[0028] Figure 2 is another schematic structural diagram of a Rankine cycle system provided by an embodiment of the present invention;

[0029] Figure 3 is still another schematic structural diagram of a Rankine cycle system provided by an embodiment of the present invention.

[0030] Description of the Reference Numerals

[0031] 1 - Heater; 2 - Work device; 21 - First turbine; 22 - Second turbine; 23 - Third turbine; 3 - Cooler; 4 - Boosting device; 5 - Regenerator; 51 - High-temperature regenerator; 52 - Low-temperature regenerator; 6 - External heat source; 7 - External cold source; 8 - Compressor; 91 - First three-way valve; 92 - Second three-way valve; 1a - Organic medium heater; 2a - Organic medium work device; 3a - Organic medium cooler; 4a - Organic medium boosting device; 5a - Organic medium regenerator. Detailed Embodiments

[0032] The present invention will be further described in detail with reference to the following specific embodiments and accompanying drawings. The implementation of the present invention is not limited to the following embodiments. All kinds of deformations, transformations, combinations and improvements under the technical concept of the present invention adopted within the knowledge scope of those skilled in the art belong to the protection scope of the present invention.

[0033] 1. Overall structure

[0034] As Figure 1 shown, a Rankine cycle system provided by this embodiment includes a medium loop formed by connecting a heater 1, a work device 2, a regenerator 5, a cooler 3, and a pressurization device 4 in sequence. The circulating medium circulates inside the medium loop. Specifically, the triple point temperature of the circulating medium is lower than 0 °C, and the triple point pressure of the circulating medium is higher than the standard atmospheric pressure. The circulating medium absorbs heat energy in the heater 1 and becomes a supercritical fluid, and then flows into the work device 2 to expand and do work, thereby converting the heat energy into mechanical energy that is more convenient to utilize. The gaseous circulating medium passing through the work device 2 enters the regenerator 5, and after the waste heat of the circulating medium is reused, it enters the cooler 3 for cooling. After the gaseous circulating medium is cooled to a saturated liquid at a temperature T1 (Tgls < T1 < Tgls + 20 °C) slightly higher than the triple point temperature Tgls of the circulating medium, the circulating medium enters the pressurization device 4 for pressurization. The pressurized liquid circulating medium enters the regenerator 5 to absorb the waste heat of the exhaust gas from the work device, and then re-enters the heater 1 for a new cycle, thereby cyclically converting heat energy into mechanical energy.

[0035] It should be noted that in this embodiment, the structures of each device or equipment are not limited. For example, in some embodiments, the work device 2 can be a rotary turbine, and in other embodiments, the work device 2 can also be a cylinder device with a transmission rod. Similarly, without violating the technical solution of the present invention, simple replacement of the devices or equipment in the present invention does not exceed the protection scope of the present invention.

[0036] In addition, those skilled in the art can understand that the regenerator 5 in this embodiment is a device for reusing the waste heat after the work device 2, that is, in this embodiment, an example of a preferred solution of the Rankine cycle with an added regenerator 5 is given. However, those skilled in the art can understand that the Rankine cycle system provided by the present invention may not include a regenerator and is directly composed of a heater 1, a work device 2, a cooler 3, and a pressurization device 4 connected in sequence.

[0037] In this embodiment, first, the triple point temperature of the circulating medium is lower than 0°C, enabling the use of a colder cold source medium. The triple point pressure is higher than the standard atmospheric pressure, eliminating the need to maintain a vacuum in the condenser. This not only saves energy but also prevents external air from leaking into the circulation system. After combining with a high-quality low-temperature cold source, according to the Carnot principle, the circulation efficiency can be significantly improved.

[0038] Secondly, the circulating medium reaches the supercritical state in the heating device. When the circulating medium is in the supercritical state, its density is relatively high, and the number of turbine stages required for its expansion work is relatively small. Therefore, in this embodiment, the high-pressure turbine equipment is much more compact than the turbine structure in the existing steam Rankine cycle. A smaller volume of the turbine equipment means a smaller plant area and a more compact circulation process.

[0039] Finally, the temperature of the circulating medium in the supercritical state is higher than that of the gaseous circulating medium. Therefore, according to the Carnot principle, with a certain cold source provided by the cooler 3, the circulating medium in the Rankine cycle system provided by the present invention can reach a higher initial temperature, that is, the operating efficiency of the Rankine cycle system in the present invention is higher.

[0040] Preferably, the circulating medium of the Rankine cycle system is CO2.

[0041] In this embodiment, the current application of CO2 as a circulating medium is mainly in the supercritical CO2 (S-CO2) Brayton cycle. The S-CO2 Brayton cycle has many advantages such as high cycle efficiency of the high-temperature heat source, small compression work consumption, compact structure and small footprint of the rotating turbine equipment, and low corrosivity. It is one of the potential options for efficient power generation from the exhaust waste heat of gas turbines. However, in the S-CO2 Brayton cycle, the cold source temperature cannot be lower than the critical temperature of CO2 (31.1°C), which limits the operating efficiency of the S-CO2 Brayton cycle system.

[0042] Furthermore, the triple point of H2O is 0.01°C and 610.75 Pa. The cold end temperature can only be reduced to above 0°C at the lowest. Moreover, due to the extremely low triple point pressure of H2O (only less than 1 kPa) and the open cycle form, if the pressure is to be cooled to near the triple point, a vacuum pump is required for pumping work, increasing additional energy consumption and having a limited improvement in the cycle efficiency. In contrast, the CO2 cycle form is a closed cycle, eliminating the need for a vacuum pump to evacuate. The triple point of CO2 is -56.6°C and 0.52 MPa, and its cold source temperature can be reduced to a lower level. Also, the triple point pressure is above the atmospheric pressure, preventing the leakage of external non-condensable air into the circulation at the condenser. In this way, after combining with a high-quality low-temperature cold source, from a thermodynamic perspective, the cycle efficiency can be significantly improved.

[0043] In addition, the corrosiveness of the CO2 cycle medium is much milder than that of H2O steam, which can greatly reduce the corrosion resistance requirements for the materials of high-temperature component equipment.

[0044] Finally, the specific volume of the CO2 cycle medium is much smaller than that of H2O, which can greatly reduce the size of the work equipment and save the plant area.

[0045] Next, the device of the Rankine cycle provided in this embodiment will be described in more detail.

[0046] 1. Heater 1

[0047] In this embodiment, the heater 1 can be any device capable of heating the cycle medium. Specifically, the heater 1 can be a heat exchanger that uses an external heat source 6 to heat the cycle medium. One end of the heat exchanger is connected to the external heat source 6, and the other end is connected to the cycle medium. Thus, the cycle medium absorbs the heat of the external heat source 6 through heat exchange, increases in temperature, and changes its phase state to facilitate subsequent work. Preferably, the external heat source 6 can be solar energy, nuclear energy, fossil fuels, etc. Further, the external heat source 6 is a gas turbine unit, so that the waste heat of the high-temperature flue gas after combustion in the gas turbine unit can be reused, saving resources.

[0048] 2. Work device 2

[0049] In this embodiment, the work device 2 can be a device that can convert thermal energy into mechanical energy by using the expansion work of the cycle medium. For example, a cylinder structure that uses gas expansion to push a transmission rod to reciprocate, or a rotary turbine structure that uses gas expansion to rotate and do work. In this embodiment, the work device 2 is taken as an example of a rotary turbine for further description.

[0050] Preferably, the rotary turbine includes a first turbine 21, a second turbine 22, and a third turbine 23. The first turbine 21 uses the enthalpy change of the supercritical state cycle medium to do external work. The second turbine 22 receives the supercritical state cycle medium from the first turbine 21 and uses the phase change of the cycle medium from the supercritical state to the gaseous state to expand and do external work. The third turbine 23 receives the gaseous cycle medium from the second turbine 22 and uses the enthalpy change of the gaseous cycle medium to do external work.

[0051] In this embodiment, by setting the work device 2 as a multi-stage turbine, the thermal energy transferred to the circulating medium in the heater 1 can be fully converted into mechanical energy through the multi-stage turbine, improving the operating efficiency of the overall circulation system. However, those skilled in the art can understand that setting a single or other number of turbines can also achieve the effect of the circulating medium doing work in the work device 2, and all are within the protection scope of the present invention. Among them, when the multi-stage turbine is a three-stage turbine, the circulating medium in the first turbine 21 remains in a supercritical state. At this time, the density of the circulating medium is relatively high, and the structure of the first turbine 21 can be more compact. After the circulating medium further undergoes adiabatic expansion in the second turbine 22, it changes from the supercritical state to a gaseous state and enters the third turbine 23, where the waste heat of the circulating medium is further utilized, thereby increasing the overall operating efficiency of the circulation system.

[0052] 3. Regenerator 5

[0053] In this embodiment, the regenerator 5 can be a device having two flow paths, a hot flow path and a cold flow path, and exchanging heat between the media in the two flow paths. Specifically, the hot-side inlet of the regenerator 5 can be connected to the medium outlet of the work device 2, the hot-side outlet of the regenerator 5 is connected to the hot-side inlet of the cooler 3, the cold-side inlet of the regenerator 5 is connected to the medium outlet of the pressurizing device 4, and the cold-side outlet of the regenerator 5 is connected to the heater 1.

[0054] In this embodiment, the gaseous circulating medium at the outlet of the work device 2 enters the regenerator 5 and exchanges heat with the cooled and compressed liquid circulating medium in the regenerator 5. Thus, the gaseous circulating medium is pre-cooled in the regenerator 5 and then introduced into the cooler 3 for cooling, while the liquid circulating medium pressurized by the pressurizing device 4 is pre-heated in the regenerator 5 before entering the heater 1. Thereby, the waste heat of the circulating medium after the work device 2 can be utilized, reducing the energy required to be provided by the heater 1 and the cooler 3, and thus improving the operating efficiency of the Rankine cycle system.

[0055] Further, as Figure 2As shown in the figure, the regenerator 5 includes a high-temperature regenerator 51 and a low-temperature regenerator 52. The hot-side inlet of the high-temperature regenerator 51 is communicated with the medium outlet of the work device 2. The hot-side outlet of the high-temperature regenerator 51 is communicated with the hot-side inlet of the low-temperature regenerator 52. The cold-side outlet of the high-temperature regenerator 51 is communicated with the cold-side inlet of the heater 1. The cold-side inlet of the high-temperature regenerator 51 is communicated with the cold-side outlet of the low-temperature regenerator. The cold-side inlet of the low-temperature regenerator 52 is communicated with 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 respectively communicated with the outlet of the compressor 8, the cold-side outlet of the low-temperature regenerator 52, and the cold-side inlet of the high-temperature regenerator 51. The second three-way valve 92 is respectively communicated with the inlet of the compressor 8, the hot-side outlet of the low-temperature regenerator 52, and the hot-side inlet of the cooler 3.

[0056] As an operating example, for the Rankine cycle system shown in Figure 2 the figure, the circulating medium first enters the cold-side inlet of the heater 1, and the high-temperature exhaust gas of the gas turbine unit enters the hot-side inlet of the heater 1. The two fluid streams achieve heat exchange in the heat exchanger. The cooled flue gas is discharged through the hot-side outlet of the heat exchanger. The heated circulating medium flows out from the cold-side outlet of the heat exchanger and then enters the work device 2 to expand and do work. The work device 2 has three turbines. The circulating medium at the outlets of the first turbine 21 and the second turbine 22 re-enters the heater 1 to be heated and then enters the second turbine 22 and the third turbine 23 respectively to expand and do work again. The circulating medium at the outlet of the third turbine 23 enters the hot side of the high-temperature regenerator 51 and exchanges heat with the circulating medium on the cold side of the high-temperature regenerator 51 to be cooled. The circulating medium cooled once then enters the hot side of the low-temperature regenerator 52 and exchanges heat with the fluid stream on the cold side of the low-temperature regenerator 52 to be cooled. Subsequently, the circulating medium cooled twice is divided into two streams by the second three-way valve 92: the main stream of the circulating medium is cooled to a liquid state by the cooler 3, enters the pressurizing device 4 to be pressurized, and then enters the low-temperature regenerator 52 for heat recovery and temperature rise; the sub-stream of the circulating medium directly enters the compressor 8 to be pressurized. Then, the two streams of circulating medium converge into one stream through the first three-way valve 91, then enter the cold side of the high-temperature regenerator 51 for heat recovery and temperature rise, and then enter the heater 1 to absorb heat, continuing the cycle process.

[0057] In this embodiment, the regenerator 5 is further set as the high-temperature regenerator 51 and the low-temperature regenerator 52, so that the waste heat of the working medium flowing out of the work device 2 can be further utilized. Moreover, by diverting the circulating medium flowing out of the low-temperature regenerator 52, a part of it directly passes through the compressor 8 for compression without passing through the cooler 3 and then is aggregated with the cooled and compressed liquid circulating medium and flows to the heating device, thereby reducing the cold source loss of the Rankine cycle system and further improving the operating efficiency of the Rankine cycle system.

[0058] 4. Cooler 3

[0059] In this embodiment, the cooler 3 can be any device capable of cooling the circulating medium. Specifically, the cooler 3 can be a heat exchanger that uses an external cold source 7 to cool the circulating medium. One end of the heat exchanger is connected to the external cold source, and the other end is connected to the circulating medium. Thus, through heat exchange, the heat of the gaseous circulating medium is absorbed by the external cold source, and the circulating medium is cooled to near its triple point, facilitating subsequent heat absorption. Moreover, the temperature difference between the cold end and the hot end of the Rankine cycle is increased, thereby improving the cycle efficiency.

[0060] Among them, the temperature of the external cold source is -162°C to 0°C; using a cold source with a lower temperature can quickly and fully cool the gaseous circulating medium to near the triple point, and a lower cold source temperature is beneficial to improving the operating efficiency of the Rankine cycle system. Preferably, the external cold source 7 can be liquefied natural gas. The cold source temperature of liquefied natural gas is about -162°C, which is beneficial to improving the operating efficiency of the Rankine cycle system. In addition, after liquefied natural gas exchanges heat with the circulating medium in the cooler 3, it can be further introduced into the gas turbine unit as fuel, and the generated high-temperature flue gas can be used as the external heat source 6, thus realizing the recycling of this high-quality external cold source material of liquefied natural gas.

[0061] 5. Boosting device 4

[0062] In this embodiment, the boosting device 4 can be a liquid booster pump. Specifically, the boosting device 4 boosts the saturated liquid circulating medium flowing out of the cooler 3 and having a temperature near the triple point of the circulating medium. Since the pressure of the circulating medium is close to its triple point, the energy that can be converted by the expansion work of the circulating medium in the work device 2 in the primary Rankine cycle system is utilized as much as possible.

[0063] Among them, preferably, as Figure 3 shown, the Rankine cycle system further includes an organic Rankine cycle loop, and the organic Rankine cycle loop includes an organic medium heater 1a and an organic medium cooler 3a. After the external heat source 6 flows through the heater 1, it enters the organic medium heater 1a, and the external cold source 7 is connected to the cooler 3 and the organic medium cooler 3a.

[0064] Furthermore, the organic Rankine cycle system can also include other devices in the above-mentioned Rankine cycle system. As Figure 3 shown, the organic Rankine cycle further includes an organic medium work device 2a, an organic medium boosting device 4a, and an organic medium regenerator 5a. The flow mode of the circulating medium in the organic Rankine cycle system is the same as that of the Rankine cycle system provided by the present invention, and will not be elaborated here.

[0065] In this embodiment, a combined cycle of the Rankine cycle and the organic Rankine cycle can achieve higher cycle efficiency. For the same heat source, the combined cycle system of the present invention can achieve more power generation and improve energy utilization.

[0066] In addition, in this embodiment, a Rankine cycle method applied to the above Rankine cycle system is also provided, comprising the following steps:

[0067] A heating step is to provide an external heat source 6 and a circulating medium, and utilize the external heat source 6 to heat the circulating medium to raise its temperature to a supercritical state; a work step is to perform external work on the circulating medium in a supercritical state and change it into a gaseous state with a pressure close to the triple point of the circulating medium; a cooling step is to provide an external cold source 7, and utilize the external cold source 7 to cool the gaseous circulating medium to obtain a saturated liquid circulating medium with a temperature close to the triple point and below 0°C; and a compression step is to pressurize the liquid circulating medium.

[0068] Those skilled in the art will appreciate that the specific technical features in each embodiment may be adaptively split or combined. Such splitting or combining of specific technical features will not cause the technical solution to deviate from the principle of the present invention, and therefore, the technical solutions after splitting or combining will fall within the protection scope of the present invention.

[0069] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0070] So far, the technical solutions of the present invention have been described in conjunction with the multiple embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A Rankine cycle system, comprising an external cold source, an external heat source, a medium loop formed by sequentially connecting a heater, a work device, a cooler, and a pressurizing device, and an organic medium Rankine cycle loop. The organic medium Rankine cycle loop includes an organic medium heater and an organic medium cooler. After the external heat source flows through the heater, it enters the organic medium heater. The external cold source is respectively connected to the cooler and the organic medium cooler. The circulating medium circulates inside the medium loop, and is characterized in that, The triple point temperature of the circulating medium is lower than 0°C, the triple point pressure of the circulating medium is higher than the standard atmospheric pressure, the circulating medium flowing out of the heater is in a supercritical state, the circulating medium flowing out of the working device is in a gaseous state, the circulating medium flowing out of the cooler is in a saturated liquid state, the temperature T1 is 0°C-20°C higher than the triple point temperature Tgls of the circulating medium, and the pressure P1 of the circulating medium flowing out of the working device is equal to the saturated vapor pressure of the circulating medium at the temperature T1.

2. The Rankine cycle system according to claim 1, wherein It also includes a regenerator, wherein the hot side inlet of the regenerator is connected to the medium outlet of the working device, the hot side outlet of the regenerator is connected to the hot side inlet of the cooler, the cold side inlet of the regenerator is connected to the medium outlet of the boosting device, and the cold side outlet of the regenerator is connected to the heater.

3. The Rankine cycle system according to claim 2, characterized in that, The regenerator comprises a high-temperature regenerator and a low-temperature regenerator, the hot side inlet of the high-temperature regenerator is connected to the medium outlet of the working device, the hot side outlet of the high-temperature regenerator is connected to the hot side inlet of the low-temperature regenerator, the cold side outlet of the high-temperature regenerator is connected to the heater, and the cold side inlet of the low-temperature regenerator is connected to the medium outlet of the supercharging device. The Rankine cycle system also includes a first three-way valve, a second three-way valve and a compressor. The first three-way valve is respectively connected to the compressor outlet, the cold side outlet of the low-temperature regenerator, and the cold side inlet of the high-temperature regenerator. The second three-way valve is respectively connected to the compressor inlet, the hot side outlet of the low-temperature regenerator, and the hot side inlet of the cooler.

4. The Rankine cycle system according to claim 1, characterized in that, The working device includes a first turbine, a second turbine and a third turbine. The first turbine uses the enthalpy change of the supercritical circulating medium to perform external work. The second turbine receives the supercritical circulating medium from the first turbine and uses the phase change of the circulating medium from the supercritical state to the gaseous state to perform external work. The third turbine receives the gaseous circulating medium from the second turbine and uses the enthalpy change of the gaseous circulating medium to act externally.

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

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

7. The Rankine cycle system according to claim 5, characterized in that, The external heat source is a gas unit, and the external cold source is a liquefied natural gas storage tank.

8. A Rankine cycle method, the Rankine cycle system applicable to the Rankine cycle method includes an external cold source, an external heat source, a medium circuit formed by sequentially connecting a heater, a work device, a cooler, and a pressurizing device, and an organic medium Rankine cycle circuit. The organic medium Rankine cycle circuit includes an organic medium heater and an organic medium cooler. After the external heat source flows through the heater, it enters the organic medium heater. The external cold source is respectively connected to the cooler and the organic medium cooler. The circulating medium circulates inside the medium circuit. The triple point temperature of the circulating medium is lower than 0 °C, and the triple point pressure of the circulating medium is higher than the standard atmospheric pressure. It is characterized in that, The steps include: A heating step, providing an external heat source and a circulating medium, and utilizing the external heat source to heat the circulating medium to raise its temperature to a supercritical state; In the work-doing step, the circulating medium in the supercritical state does work externally and fully expands to a gaseous circulating medium with a pressure close to its triple point; A cooling step, providing an external cold source, using the external cold source to cool the gaseous circulating medium to make it a saturated liquid circulating medium, the temperature T1 being 0°C-20°C higher than the triple point temperature Tgls of the circulating medium; The compression step pressurizes the liquid circulating medium to a pressure equal to the saturated vapor pressure of the circulating medium at temperature T1.

Images