A transcritical CO2 ultra-high temperature heat pump system and its temperature control method

Abstract

The application discloses a transcritical CO2 ultra-high temperature heat pump system and a temperature control method, wherein supercritical CO2 is a high-temperature and high-pressure fluid at the outlet of a gas cooler, throttles to an evaporation pressure, and a large amount of throttling loss exists, which leads to the decrease of the heating energy efficiency ratio of the transcritical CO2 heat pump system, and is not conducive to the best energy-saving benefit of the ultra-high temperature heat pump. In view of the above problems, the application innovatively couples gas-electric dual-drive technology, two-stage compression intermediate cooling technology and mechanical supercooling technology, which can effectively reduce the high-pressure fluid temperature before the throttling valve of the CO2 working medium, reduce the throttling loss, drive the supercritical compressor through the adjustable turbine expander, reduce the power consumption of the compressor, improve the heating energy efficiency of the CO2 heat pump system, and flexibly and efficiently and stably supply steam in a wide range of variable working condition adjustment, improve the full working condition operation efficiency, achieve the purposes of energy saving and emission reduction and production cost reduction, and further widen the application range and application prospect of the high-temperature heat pump system.

Description

Technical Field

[0001] This invention patent relates to the field of industrial heat pump technology, specifically to a transcritical CO2 ultra-high temperature heat pump system and temperature control method that employs transcritical CO2 working fluid coupled gas-electric dual drive technology, two-stage compression intercooling technology, and mechanical subcooling technology. Background Technology

[0002] Heat pumps are a key technology for recovering waste heat. They utilize high-grade energy sources (such as electricity or heat) to transfer heat from a low-temperature heat source to a high-temperature supply, making them highly efficient energy-saving devices. This technology is widely used in refrigeration systems for cooling and in HVAC systems for space heating, cooling, and hot water supply. Currently, with further technological advancements, more and more heat pumps are being applied in industrial fields for high-temperature heating to meet the needs of industrial applications.

[0003] However, because ultra-high temperature heat pumps operate under ultra-high temperature conditions (condensing temperature > 160℃), the manufacturing of the unit places higher demands on the compressor, motor, materials, working fluid, and lubricating oil. Selecting a suitable working fluid and optimizing the cycle design are key to reducing compressor power consumption and improving COP and waste heat recovery efficiency while meeting the requirements of high-temperature processes.

[0004] Currently, ultra-high temperature heat pumps with output temperatures above 160℃ are still in the theoretical research and laboratory verification stage. CO2 (R744) is the preferred working fluid. For transcritical CO2 ultra-high temperature heat pumps, the transcritical cycle can achieve a higher COP at high temperatures. Multiple heat pump cycles can be connected in series to achieve a higher temperature rise and meet ultra-high temperature requirements. However, compared to traditional refrigerants where the refrigerant is already a relatively cool liquid at the condenser outlet with less throttling loss, CO2 remains a high-temperature, high-pressure fluid at the gas cooler outlet, directly throttling to the evaporation pressure. This means the compressor needs to provide more electrical energy to compensate for this loss, essentially wasting a large amount of available energy. The huge pressure difference signifies a significant irreversible loss; this lost energy is not used for heating or cooling, thus reducing cycle efficiency. Furthermore, the throttled working fluid is closer to the saturated gas phase, reducing the heat absorption of the latent heat of vaporization in the evaporator's phase change zone. These multiple adverse factors combined lead to a decrease in the heating efficiency ratio of the transcritical CO2 heat pump system, hindering the market promotion and economical, reliable operation of ultra-high temperature heat pumps, and restricting the industrialization of ultra-high temperature heat pump technology. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a transcritical CO2 ultra-high temperature heat pump system and its temperature control method to solve the problem of poor energy efficiency in ultra-high temperature heat pump systems. This invention combines the advantages and disadvantages of transcritical CO2 heat pump cycle technology, innovatively coupling adjustable gas-electric dual-drive technology, two-stage compression intercooling technology, and mechanical subcooling technology. This effectively reduces the high-pressure fluid temperature before the CO2 working fluid throttling valve, minimizing throttling losses, and drives the supercritical compressor through an adjustable turbine expander, reducing compressor power consumption. This improves the heating efficiency of the CO2 heat pump system and enhances the flexibility, efficiency, and stability of steam supply during wide-range variable operating conditions, improving overall operating efficiency and achieving energy conservation, emission reduction, and lower production costs. Furthermore, it broadens the application scope and prospects of high-temperature heat pump systems, demonstrating significant technological advancement.

[0006] The technical problem to be solved by the present invention can be achieved by the following technical solution: a transcritical CO2 ultra-high temperature heat pump system, comprising a closed transcritical CO2 heat pump cycle module and an open steam generation module; The closed-loop transcritical CO2 heat pump cycle module consists of a two-stage compression gas-electric dual-drive unit, a regenerative subcooling unit, a cold-end storage mixing unit, a matching control and regulating valve group, and a control system. The low-pressure saturated carbon dioxide working fluid is split into two paths after passing through the cold-end storage mixing unit and the two-stage compression gas-electric dual-drive unit. One path is the pre-cooled medium-high temperature supercritical CO2 working fluid, which is controlled by the flow regulating valve at the turbine expander inlet to drive the turbine expander and then discharged into the gas mixing chamber of the cold-end storage mixing unit. The turbine expander drives the supercritical compressor in the two-stage compression gas-electric dual-drive unit, reducing the power consumption of the compression system. The other path enters the liquid phase buffer tank through the regenerative subcooling unit. The regenerative subcooling unit uses organic working fluid heat pump coupled ejector technology to subcool the high-pressure CO2 working fluid before throttling, reducing the enthalpy of the CO2 working fluid before throttling, thereby increasing the latent heat of vaporization absorbed by the working fluid in the saturated region of the evaporator in the cold-end storage mixing unit and reducing the throttling loss of the working fluid. The open-loop steam generation module consists of a two-stage series feedwater preheating unit, a two-stage parallel steam superheating unit, a matching pipeline regulating valve group, and a control system. The inlet liquid-phase low-temperature water is preheated by the two-stage series feedwater preheating unit to form saturated steam, which is then processed by the two-stage parallel steam superheating unit to produce high-temperature steam that meets the quality requirements of users.

[0007] Furthermore, the two-stage compression gas-electric dual-drive unit of the closed transcritical CO2 heat pump cycle module mainly includes a transcritical compressor, a medium-pressure superheater, a supercritical compressor, a high-pressure superheater, and auxiliary control valves and pipelines. The supercritical compressor is a gas-electric dual-drive type, with one end connected to an electric motor and the other end connected to a turboexpander via a coupling. The electric motor drives the supercritical compressor during the start-up and shutdown phases of the transcritical CO2 ultra-high temperature heat pump system. During normal operation, the turboexpander dynamically adjusts the speed and flow rate parameters to drive the supercritical compressor to achieve the temperature and pressure increase of the circulating working fluid.

[0008] Furthermore, the regenerative subcooling unit of the closed-loop transcritical CO2 ultra-high temperature heat pump cycle module includes a regenerator, an ejector, an organic working fluid heat pump, a liquid phase buffer tank, and auxiliary control valves and pipelines. The organic working fluid heat pump subcooler consists of a low-temperature gas cooler, an organic working fluid compressor, a feed water preheater, an organic working fluid throttling valve, and auxiliary control valves and pipelines. After cooling, the gaseous working fluid separated from the CO2 working fluid in the liquid phase buffer tank is entrained by the ejector into the organic working fluid heat pump for secondary cooling, ensuring that the working fluid before the liquid phase CO2 throttling valve of the cold end storage mixing unit is a liquid working fluid with a certain degree of subcooling.

[0009] Furthermore, the cold-end storage mixing unit of the closed-loop transcritical CO2 ultra-high temperature heat pump cycle module includes a liquid phase CO2 throttling valve, a low-temperature evaporator, a medium-temperature evaporator, a gas storage mixing chamber, and auxiliary control valves and pipelines. The gas storage mixing chamber is used to mix the low-pressure superheated working fluid at the outlet of the medium-temperature evaporator with the low-pressure superheated working fluid discharged from the turbine expander, so that it reaches the optimal inlet temperature of the transcritical compressor.

[0010] Furthermore, the two-stage series feedwater preheating unit includes a feedwater preheater of an organic working fluid heat pump, a regenerator of a regenerative subcooling unit, a steam-water separator, a feedwater recirculation pump, and auxiliary control valves and pipelines. After being preheated by the organic working fluid heat pump, the liquid-phase low-temperature water flows downstream to the regenerator for further heating. After being heated to the saturation temperature under the feedwater working pressure, it is discharged into the steam-water separator to achieve steam-water separation. The liquid-phase working fluid is pressurized by the feedwater recirculation pump and pumped into the regenerator for secondary heating. The vapor-phase working fluid is discharged into the two-stage parallel steam superheating unit.

[0011] Furthermore, the two-stage parallel steam superheating unit includes a high-pressure superheater, a medium-pressure superheater, and auxiliary control valves and pipelines. The two superheaters are connected in parallel, and the steam temperature is ensured to meet the user's requirements by controlling the opening of the regulating valve, thus providing the user with a stable and reliable steam supply.

[0012] On the other hand, the present invention provides a temperature control method for a transcritical CO2 ultra-high temperature heat pump, the method comprising the following steps: 1) Start-up and operation mode: The bypass regulating valves of the transcritical compressor and supercritical compressor are opened first, and the organic working fluid compressor is delayed in starting to maintain feedwater self-circulation. After the preheating temperature reaches the saturation temperature corresponding to the feedwater working pressure, the inlet regulating valve of the medium-pressure superheater is opened to generate superheated steam. Then the supercritical compressor is started and the supercritical compressor bypass regulating valve is closed. The inlet regulating valve of the high-pressure superheater is then opened. After the CO2 working fluid temperature at the outlet of the high-pressure superheater reaches a certain set value, the turbine inlet regulating valve is gradually opened, the turbine expander is put into operation, and the motor and the turbine expander jointly drive the supercritical compressor. Then the supercritical compressor motor is turned off, and the compressor load is driven by the turbine expander. The ultra-high temperature heat pump unit enters normal operation mode. 2) Normal operating mode: The transcritical compressor is driven by an electric motor, and the supercritical compressor is driven by a turbine expander. The output of the turbine expander is adjusted to match the load of the supercritical compressor by adjusting the turbine inlet regulating valve. The supercritical compressor bypass regulating valve is in the closed state. The organic working fluid heat pump is in operation. The steam flow and temperature are adjusted and matched by the high-pressure superheater inlet regulating valve and the medium-pressure superheater inlet regulating valve. 3) Shutdown and maintenance mode: First, reduce the output of the turbine expander by closing the turbine inlet regulating valve, open the supercritical compressor bypass regulating valve to maintain the no-load heat dissipation of the supercritical compressor and turbine expander, then shut down the transcritical compressor, and after the CO2 inlet temperature of the low-temperature gas cooler is lower than a certain value, shut down the organic working fluid heat pump compressor, and finally delay shutting down the feedwater recirculation pump.

[0013] The beneficial effects of this invention are: Compared to traditional refrigerants, which are already in a subcooled liquid state at the condenser outlet with relatively small throttling losses, supercritical CO2 remains a high-temperature, high-pressure fluid at the gas cooler outlet. Throttling to the evaporation pressure results in significant throttling losses, leading to a decrease in the heating efficiency ratio of transcritical CO2 heat pump systems. This hinders the optimal energy-saving benefits of ultra-high temperature heat pumps. To address these issues, this invention innovatively couples gas-electric dual-drive technology, two-stage compression intercooling technology, and mechanical subcooling technology. The proposed transcritical CO2 ultra-high temperature heat pump system and temperature control method effectively reduce the high-pressure fluid temperature before the CO2 working fluid throttling valve, minimizing throttling losses. Furthermore, by driving the supercritical compressor with an adjustable turboexpander, it reduces compressor power consumption, improving the heating efficiency of the CO2 heat pump system and enhancing the flexibility, efficiency, and stability of steam supply during wide-range variable operating conditions. This improves overall operating efficiency, achieving energy conservation, emission reduction, and lower production costs, further expanding the application scope and prospects of high-temperature heat pump systems. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a process flow diagram of the transcritical CO2 ultra-high temperature heat pump system of the present invention; Figure 2 This is the temperature entropy diagram (TS diagram) of the transcritical CO2 ultra-high temperature heat pump system of the present invention. In the diagram: 1. Low-pressure saturated CO2 working fluid; 2. Low-pressure superheated working fluid at the evaporator outlet; 3. Low-pressure superheated working fluid at the turbine expander exhaust; 4. Low-pressure superheated working fluid at the gas storage mixing chamber outlet; 5. Medium-pressure superheated working fluid at the transcritical compressor outlet; 6. Medium-pressure superheated working fluid at the medium-pressure superheater outlet; 7. High-pressure superheated working fluid at the supercritical compressor outlet; 8. High-pressure superheated working fluid at the high-pressure superheater outlet; 9. Supercritical liquid-phase working fluid at the ejector inlet; 10. Supercritical liquid-phase working fluid at the ejector outlet; 11. Subcooled mixed-phase working fluid at the condenser outlet; 12. Saturated gas phase working fluid at the top of the liquid phase buffer tank; 13. Saturated liquid phase working fluid at the bottom of the liquid phase buffer tank; A1. Low-temperature evaporator; A2. Medium-temperature evaporator. B. Gas mixing chamber; C. Transcritical compressor; D. Intermediate-pressure superheater; E. Supercritical compressor; F. High-pressure superheater; G. Turbine expander; H. Coupling; I. Regenerator; J. Cryogenic gas cooler; K. Liquid phase buffer tank; L. Feedwater preheater; M. Organic working fluid compressor; N. Gas-liquid separator; O. Feedwater recirculation pump; f1. Liquid phase CO2 throttle valve; f2. Turbine inlet regulating valve; f3. Ejector; f4. Organic working fluid throttle valve; f5. Preheated water check valve; f6. Pressure reducing valve; f7. Circulating water pump outlet control valve; f8. High-pressure superheater inlet regulating valve; f9. Intermediate-pressure superheater inlet regulating valve; f10. Supercritical compressor bypass regulating valve. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. In order to illustrate the principle of the patent, the present invention only uses key valves and pipelines as embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1As shown, this invention provides a transcritical CO2 ultra-high temperature heat pump system and temperature control method, mainly composed of a closed-loop transcritical CO2 heat pump circulation module and an open-loop steam generation module. This invention can effectively reduce the high-pressure fluid temperature before the CO2 working fluid throttling valve, reducing throttling losses, and can also drive a supercritical compressor through an adjustable turbine expander, reducing compressor power consumption, improving the heating efficiency of the CO2 heat pump system, and providing flexible, efficient, and stable steam supply during wide-range variable operating condition adjustments.

[0018] The circulating working fluid in the closed-loop transcritical CO2 heat pump circulation module is CO2. Under normal operating conditions, the temperature and entropy changes of the circulating working fluid are as follows: Figure 2 As shown. Low-pressure saturated carbon dioxide working fluid 1 sequentially passes through low-temperature evaporator A1, medium-temperature evaporator A2, gas storage mixing chamber B, transcritical compressor C, medium-pressure superheater D, supercritical compressor E, and high-pressure superheater F. At this point, the high-pressure superheated working fluid 8 at the outlet of the high-pressure superheater is split into two streams with mass flow rates m1 and m2, respectively. The stream with mass flow rate m1 is controlled by the turbine expander inlet regulating valve f2 to drive the turbine expander G and then discharged into the gas storage mixing chamber B to complete the top cycle with mass flow rates of m1 + m2. The working fluid state changes in this heat pump cycle as follows: turbine expander exhaust low-pressure superheated working fluid 3 - gas storage mixing chamber outlet low-pressure superheated working fluid 4 - transcritical compressor outlet medium-pressure superheated working fluid 5 - medium-pressure superheater outlet medium-pressure superheated working fluid 6 - supercritical compressor outlet high-pressure superheated working fluid 7 - high-pressure superheater outlet high-pressure superheated working fluid 8 - turbine expander exhaust low-pressure superheated working fluid 3. A flow rate of m2 passes through the regenerator I, ejector f3, cryogenic gas cooler J, and liquid buffer tank K to complete a bottom circulation with a flow rate of m2. The working fluid state changes as follows: low-pressure saturated CO2 working fluid 1 - evaporator outlet; low-pressure superheated working fluid 2 - turbine expander exhaust; low-pressure superheated working fluid 3 - high-pressure superheater outlet; high-pressure superheated working fluid 8 - ejector inlet and outlet; supercritical liquid phase working fluid 9 - 10 - low-pressure saturated CO2 working fluid 1.

[0019] In the closed-loop transcritical CO2 heat pump cycle module, only three core valves are listed: the liquid phase CO2 throttling valve f1, the supercritical compressor bypass regulating valve f10, and the turbine inlet regulating valve f2, to illustrate the core control process of this invention. The temperature, pressure, flow rate, and control valve groups used for variable load, variable operating conditions, and functional regulation of the cycle system are not listed. All embodiments including key valves and working fluid circulation are within the scope of protection of this invention.

[0020] The working fluid in the open-type steam generator module is water. The inlet is low-temperature liquid water, and the outlet is high-temperature superheated steam. Feedwater sequentially passes through the feedwater preheater L, regenerator I, steam-water separator N, and feedwater recirculation pump O to preheat the feedwater and form saturated steam. This saturated steam then passes through the intermediate-pressure superheater D and high-pressure superheater F in parallel, controlled by regulating the inlet regulating valves f8 and f9 of the high-pressure and intermediate-pressure superheaters, respectively, to produce high-temperature steam meeting user requirements. The open-type steam generator module also includes three core valves: a preheating water check valve f5, a pressure reducing valve f6, and a circulating water pump outlet control valve f7, to fulfill the functional requirements for feedwater preheating. This patent only provides a principle description; other embodiments with added or removed valve groups are within the scope of this invention.

[0021] To effectively reduce the high-pressure fluid temperature before the CO2 working fluid throttling valve, minimize throttling losses, and simultaneously improve the system waste heat in the low-temperature gas cooler, an ejector-coupled organic working fluid heat pump technology is employed to subcool the CO2 working fluid and preheat the feedwater, achieving complementary advantages between ultra-high temperature and high-temperature heat pumps. The organic working fluid heat pump consists of a low-temperature gas cooler J, an organic working fluid compressor M, a feedwater preheater L, an organic working fluid throttling valve f4, and auxiliary control valves and pipelines. An ejector f3, a low-temperature gas cooler J, and a liquid buffer tank K are connected in a series circuit. The low-temperature gas cooler J serves as the evaporator end of the organic working fluid heat pump, cooling the supercritical liquid-phase carbon dioxide working fluid 10 at the ejector outlet. The feedwater preheater L serves as the condenser end of the organic working fluid heat pump, preheating the feedwater. A simple organic working fluid heat pump is constructed through the organic working fluid compressor M, the organic working fluid throttling valve f4, and related piping accessories. The heat pump circulating working fluid is an organic working fluid, such as R134a, R245fa, or a mixture of organic working fluids. The supercritical liquid-phase carbon dioxide working fluid 10 at the inlet of the low-temperature gas cooler J is condensed into a subcooled mixed-phase working fluid 11 at the condenser outlet after heat exchange with a low-temperature organic working fluid. The saturated gas phase working fluid 12 separated in the liquid buffer tank K is entrained by the ejector f3 to the ejector throat and mixed with the supercritical liquid-phase working fluid 9 at the outlet of the regenerator I, forming the supercritical liquid-phase working fluid 10 at the ejector outlet. This achieves subcooling coupling between the ejector and the organic working fluid heat pump. Secondary cooling by the subcooler J ensures that the working fluid 13 before the liquid CO2 throttle valve is a liquid-phase working fluid with a certain degree of subcooling. In this patent, the organic working fluid heat pump is only described in principle using the four core components of the heat pump to illustrate the functional requirements of the organic working fluid heat pump technology presented in this patent. Any other adjustments to the organic working fluid heat pump embodiment based on this are within the scope of protection of this invention, such as multi-stage compression of the organic working fluid, gas injection for enthalpy increase, ejector coupling, and cascade circulation, etc.

[0022] The working principle and process of this invention are as follows: The basic principle of the transcritical CO2 ultra-high temperature heat pump system and temperature control method proposed in this invention is as follows: A pre-cooled medium-high temperature supercritical CO2 working fluid is used to power the turbine expander G and drive the supercritical compressor E, reducing the power consumption during the compression and heating process of the CO2 working fluid; conventional organic working fluid heat pump coupled ejector technology is used to subcool the high-pressure CO2 working fluid before throttling, reducing the enthalpy of the CO2 working fluid before throttling, thereby increasing the latent heat of vaporization absorbed by the working fluid in the saturated region of the evaporator and reducing the throttling loss of the working fluid. Simultaneously, the feedwater preheater L on the condenser side of the organic working fluid heat pump can be used to preheat the feedwater, further recovering the system's waste heat; a gas mixing chamber is used to mix the low-pressure superheated working fluid at the outlet of the medium-temperature evaporator A2 with the low-pressure superheated working fluid discharged from the turbine expander G, achieving the optimal inlet temperature of the transcritical compressor and reducing the power consumption of the transcritical compressor C; a two-stage parallel configuration of a high-pressure superheater and a medium-pressure superheater is adopted, and the steam temperature is ensured to meet user requirements by controlling the opening of the regulating valve, providing a stable and reliable steam supply to the user.

[0023] The main operating modes of the transcritical CO2 ultra-high temperature heat pump system and temperature control method proposed in this invention can be summarized as follows: (1) Start-up and operation mode: The transcritical compressor C starts up, and the CO2 stored in the gas mixing chamber B is heated and pressurized. The supercritical compressor bypass regulating valve f10 is opened. Since there is no saturated steam during the start-up stage, there is no cooling steam in the intermediate-pressure superheater D and the high-pressure superheater F. The heat exchanger is made of high-temperature resistant high-quality alloy steel and has a certain dry-burning capacity. The organic working fluid compressor M starts up with a delay. The low-temperature gas cooler J and the regenerator I are used to preheat the feedwater. The feedwater recirculation pump O maintains the water side self-circulation. After the preheating temperature reaches the saturation temperature corresponding to the feedwater working pressure, the intermediate-pressure superheater inlet regulating valve f9 is gradually opened to prepare superheated steam. Then the supercritical compressor E is gradually opened and the supercritical compressor bypass valve is closed. After the supercritical compressor E reaches a certain set power, the supercritical compressor bypass regulating valve f10 is completely closed. Then, the high-pressure superheater inlet regulating valve f8 is opened to cool it with saturated steam. After the CO2 working fluid temperature at the outlet of the high-pressure superheater F reaches a certain set value, the turbine inlet regulating valve f2 is gradually opened, and the turbine expander G is put into operation. After the load of the turbine expander G reaches a certain set value, it is connected to the load of the supercritical compressor E. The motor and the turbine expander G jointly drive the supercritical compressor E. After the ultra-high temperature heat pump load reaches a certain design value, the motor of the supercritical compressor E is turned off, and the load of the supercritical compressor E is driven by the turbine expander G. The ultra-high temperature heat pump unit enters the normal operation mode.

[0024] (2) Normal operation mode: The transcritical compressor C is driven by a motor, and the supercritical compressor E is driven by a turbine expander G. The output of the turbine expander G is adjusted to match the load of the supercritical compressor E by adjusting the turbine inlet regulating valve f2. The supercritical compressor bypass regulating valve f10 is in the closed state. The organic working fluid heat pump compressor M is put into operation. The steam flow and temperature are adjusted and matched by the high pressure superheater inlet regulating valve f8 and the medium pressure superheater inlet regulating valve f9.

[0025] (3) Shutdown and maintenance mode: First, reduce the output of turbine expander G by adjusting turbine inlet regulating valve f2. After the expander output is lower than a certain value, start the motor of supercritical compressor E, open supercritical compressor bypass regulating valve f10, maintain the no-load heat dissipation of supercritical compressor E and turbine expander G, then gradually shut down transcritical compressor C. After the carbon dioxide temperature at the inlet of low temperature gas cooler J is lower than a certain value, shut down organic working fluid heat pump compressor M, and finally delay shutting down feedwater recirculation pump O.

[0026] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A transcritical CO2 ultra-high temperature heat pump system, characterized in that: It includes a closed-loop transcritical CO2 heat pump cycle module and an open-loop steam generation module; The closed-loop transcritical CO2 heat pump cycle module consists of a two-stage compression gas-electric dual-drive unit, a regenerative subcooling unit, a cold-end storage mixing unit, a matching control and regulating valve group, and a control system. The low-pressure saturated carbon dioxide working fluid is split into two paths after passing through the cold-end storage mixing unit and the two-stage compression gas-electric dual-drive unit. One path is the pre-cooled medium-high temperature supercritical CO2 working fluid, which is controlled by the flow regulating valve at the turbine expander inlet to drive the turbine expander and then discharged into the gas mixing chamber of the cold-end storage mixing unit. The turbine expander drives the supercritical compressor in the two-stage compression gas-electric dual-drive unit, reducing the power consumption of the compression system. The other path enters the liquid phase buffer tank through the regenerative subcooling unit. The regenerative subcooling unit uses organic working fluid heat pump coupled ejector technology to subcool the high-pressure CO2 working fluid before throttling, reducing the enthalpy of the CO2 working fluid before throttling, thereby increasing the latent heat of vaporization absorbed by the working fluid in the saturated region of the evaporator in the cold-end storage mixing unit and reducing the throttling loss of the working fluid. The open-loop steam generation module consists of a two-stage series feedwater preheating unit, a two-stage parallel steam superheating unit, a matching pipeline regulating valve group, and a control system. The inlet liquid-phase low-temperature water is preheated by the two-stage series feedwater preheating unit to form saturated steam, which is then processed by the two-stage parallel steam superheating unit to produce high-temperature steam that meets the quality requirements of users.

2. The transcritical CO2 ultra-high temperature heat pump system according to claim 1, characterized in that: The two-stage compression gas-electric dual-drive unit of the closed-loop transcritical CO2 ultra-high temperature heat pump cycle module mainly includes a transcritical compressor, a medium-pressure superheater, a supercritical compressor, a high-pressure superheater, and auxiliary control valves and pipelines. The supercritical compressor is a gas-electric dual-drive type, with one end connected to an electric motor and the other end connected to a turboexpander via a coupling. The electric motor drives the supercritical compressor during the start-up and shutdown phases of the transcritical CO2 ultra-high temperature heat pump system. During normal operation, the turboexpander dynamically adjusts the speed and flow rate parameters to drive the supercritical compressor to achieve the temperature and pressure increase of the circulating working fluid.

3. The transcritical CO2 ultra-high temperature heat pump system according to claim 1, characterized in that: The regenerative subcooling unit of the closed-loop transcritical CO2 ultra-high temperature heat pump cycle module includes a regenerator, an ejector, an organic working fluid heat pump, a liquid phase buffer tank, and auxiliary control valves and pipelines. The organic working fluid heat pump subcooler consists of a low-temperature gas cooler, an organic working fluid compressor, a feed water preheater, an organic working fluid throttling valve, and auxiliary control valves and pipelines. After cooling, the gaseous working fluid separated from the CO2 working fluid in the liquid phase buffer tank is entrained by the ejector into the organic working fluid heat pump for secondary cooling, ensuring that the working fluid before the liquid phase CO2 throttling valve of the cold end storage mixing unit is a liquid working fluid with a certain degree of subcooling.

4. The transcritical CO2 ultra-high temperature heat pump system according to claim 1, characterized in that: The cold-end storage mixing unit of the closed-loop transcritical CO2 ultra-high temperature heat pump cycle module includes a liquid phase CO2 throttling valve, a low-temperature evaporator, a medium-temperature evaporator, a gas storage mixing chamber, and auxiliary control valves and pipelines. The gas storage mixing chamber is used to mix the low-pressure superheated working fluid at the outlet of the medium-temperature evaporator with the low-pressure superheated working fluid discharged from the turbine expander, so that it reaches the optimal inlet temperature of the transcritical compressor.

5. A transcritical CO2 ultra-high temperature heat pump system according to claim 4, characterized in that: The two-stage series feedwater preheating unit includes a feedwater preheater of an organic working fluid heat pump, a regenerator of a regenerative subcooling unit, a steam-water separator, a feedwater recirculation pump, and auxiliary control valves and pipelines. After being preheated by the organic working fluid heat pump, the liquid phase low-temperature water flows downstream to the regenerator for further heating. After being heated to the saturation temperature under the feedwater working pressure, it is discharged into the steam-water separator to achieve steam-water separation. The liquid phase working fluid is pressurized by the feedwater recirculation pump and pumped into the regenerator for secondary heating. The vapor phase working fluid is discharged into the two-stage parallel steam superheating unit.

6. The transcritical CO2 ultra-high temperature heat pump system according to claim 1, characterized in that: The two-stage parallel steam superheating unit includes a high-pressure superheater, a medium-pressure superheater, and auxiliary control valves and pipelines. The two superheaters are connected in parallel, and the steam temperature is ensured to meet the user's requirements by controlling the opening of the regulating valve, thus providing the user with a stable and reliable steam supply.

7. A temperature control method based on the transcritical CO2 ultra-high temperature heat pump according to any one of claims 1-6, characterized in that, This method includes the following steps: 1) Start-up and operation mode: The bypass regulating valves of the transcritical compressor and supercritical compressor are opened first, and the organic working fluid compressor is delayed in starting to maintain feedwater self-circulation. After the preheating temperature reaches the saturation temperature corresponding to the feedwater working pressure, the inlet regulating valve of the medium-pressure superheater is opened to generate superheated steam. Then the supercritical compressor is started and the supercritical compressor bypass regulating valve is closed. The inlet regulating valve of the high-pressure superheater is then opened. After the CO2 working fluid temperature at the outlet of the high-pressure superheater reaches a certain set value, the turbine inlet regulating valve is gradually opened, the turbine expander is put into operation, and the motor and the turbine expander jointly drive the supercritical compressor. Then the supercritical compressor motor is turned off, and the compressor load is driven by the turbine expander. The ultra-high temperature heat pump unit enters normal operation mode. 2) Normal operating mode: The transcritical compressor is driven by an electric motor, and the supercritical compressor is driven by a turbine expander. The output of the turbine expander is adjusted to match the load of the supercritical compressor by adjusting the turbine inlet regulating valve. The supercritical compressor bypass regulating valve is in the closed state. The organic working fluid heat pump is in operation. The steam flow and temperature are adjusted and matched by the high-pressure superheater inlet regulating valve and the medium-pressure superheater inlet regulating valve. 3) Shutdown and maintenance mode: First, reduce the output of the turbine expander by closing the turbine inlet regulating valve, open the supercritical compressor bypass regulating valve to maintain the no-load heat dissipation of the supercritical compressor and turbine expander, then shut down the transcritical compressor, and after the CO2 inlet temperature of the low-temperature gas cooler is lower than a certain value, shut down the organic working fluid heat pump compressor, and finally delay shutting down the feedwater recirculation pump.

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