Supercritical carbon dioxide reverse Brayton cycle heat pump system and control method thereof

Abstract

The invention discloses a supercritical carbon dioxide reverse Brayton cycle heat pump system and a control method thereof, and relates to the technical field of heat pump systems. The heat pump system comprises a compressor, a carbon dioxide cooler, a high-temperature heat regenerator, a flow dividing element, a low-temperature heat regenerator, a high-temperature expansion machine, a low-temperature expansion machine and a carbon dioxide heater. The outlet end of the compressor, the carbon dioxide cooler and the high-temperature side inlet end of the high-temperature heat regenerator are sequentially communicated; a high-temperature side outlet of the high-temperature heat regenerator is divided into two paths through a flow dividing element, one path communicates with the inlet end of the high-temperature expansion machine, and the other path communicates with the high-temperature side inlet end of the low-temperature heat regenerator, the low-temperature expansion machine and the inlet end of the carbon dioxide heater in sequence. The outlet end of the high-temperature expansion machine communicates with the outlet end of the carbon dioxide heater and communicates with the low-temperature side inlet end of the low-temperature heat regenerator. The heat recovery efficiency and the COP (coefficient of performance) of the system can be improved, and a higher heat release temperature can be achieved to meet the continuous supply requirement of high-temperature water vapor.

Description

Technical Field

[0001] This invention relates to the field of heat pump system technology, and in particular to a supercritical carbon dioxide reverse Brayton cycle heat pump system and its control method. Background Technology

[0002] Industrial sectors consume enormous amounts of energy, and numerous production processes generate substantial heat dissipation demands. This results in a significant amount of energy being released into the environment as low-quality heat, leading to considerable energy waste. Simultaneously, industrial production demands substantial heating, requiring long durations, wide temperature ranges, and high steam parameters. Traditional heating systems generally rely on direct heating from fossil fuel combustion devices such as coal-fired and gas-fired boilers. This method not only generates large amounts of carbon dioxide emissions but also faces the dual pressures of rising fuel costs and energy structure adjustments. Utilizing high-temperature heat pump technology to meet the high-temperature heating needs of industrial sectors is a heating solution that can better satisfy the "dual carbon" (carbon dioxide, carbon sequestration, and carbon emissions) objectives.

[0003] Traditional heat pump cycle configurations, such as the reverse Rankine cycle and the simple regenerative reverse Brayton cycle, have limitations in temperature rise capability and applicable scenarios. The reverse Rankine cycle uses a low-boiling-point organic working fluid, such as R245fa, to increase heat output through evaporation heat absorption and compression temperature rise. However, its working fluid critical temperature is relatively low, making it difficult to reach high heat release temperatures without changing the cycle configuration, thus limiting the heat pump's ability to stably generate high-temperature steam. Using multi-stage compression and throttling designs would significantly increase the complexity and energy consumption of the reverse Rankine cycle heat pump system. The simple regenerative reverse Brayton cycle lacks the heat absorption stage in the two-phase region found in the reverse Rankine cycle; the working fluid remains in the gaseous state throughout, offering a wider operating temperature range. However, the gas has a low specific heat capacity, requiring a high compression ratio to achieve a significant temperature rise, which leads to excessive compressor power consumption and a large equipment size. In summary, traditional reverse Rankine cycle and simple regenerative reverse Brayton cycle heat pumps cannot achieve high heat release temperatures under reasonable energy efficiency conditions, such as COP > 3, making it difficult to meet the continuous supply demand for high-temperature steam.

[0004] In view of the problems existing in the prior art, those skilled in the art urgently need a supercritical carbon dioxide reverse Brayton cycle heat pump system and its control method. Summary of the Invention

[0005] The purpose of this invention is to provide a supercritical carbon dioxide reverse Brayton cycle heat pump system and its control method to solve the problems existing in the prior art, improve the system's regenerative efficiency and energy efficiency ratio (COP), and achieve a higher heat release temperature to meet the continuous supply demand of high-temperature steam.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] This invention provides a supercritical carbon dioxide reverse Brayton cycle heat pump system, comprising a compressor, a carbon dioxide cooler, a high-temperature regenerator, a flow divider, a low-temperature regenerator, a high-temperature expander, a low-temperature expander, and a carbon dioxide heater. The compressor is used to compress supercritical carbon dioxide as the working fluid. The outlet end of the compressor, the high-temperature cooler, and the high-temperature side inlet end of the high-temperature regenerator are sequentially connected. The high-temperature side outlet of the high-temperature regenerator is divided into two paths by the flow divider: one path is connected to the inlet end of the high-temperature expander, and the other path is sequentially connected to the high-temperature side inlet end of the low-temperature regenerator, the inlet end of the low-temperature expander, and the inlet end of the carbon dioxide heater. The outlet end of the high-temperature expander is connected to the outlet end of the carbon dioxide heater and to the low-temperature side inlet end of the low-temperature regenerator. The low-temperature side outlet end of the low-temperature regenerator, the low-temperature side of the high-temperature regenerator, and the inlet end of the compressor are sequentially connected.

[0008] In some embodiments, the diversion element is a diversion valve; the inlet end of the diversion valve is connected to the high-temperature side outlet end of the high-temperature regenerator via a pipeline, the first outlet end of the diversion valve is connected to the inlet end of the high-temperature expander via a pipeline, and the second outlet end of the diversion valve is connected to the high-temperature side inlet end of the low-temperature regenerator via a pipeline; the diversion valve is used to regulate the mass flow rate of supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator.

[0009] In some embodiments, a mixer is also included; the first inlet of the mixer is connected to the outlet of the carbon dioxide heater via a pipeline, the second inlet of the mixer is connected to the outlet of the high-temperature expander via a pipeline, and the outlet of the mixer is connected to the low-temperature side inlet of the low-temperature regenerator via a pipeline; the mixer is used to mix the supercritical carbon dioxide working fluid flowing out of the high-temperature expander and the carbon dioxide heater.

[0010] In some embodiments, both the high-temperature regenerator and the low-temperature regenerator are printed circuit heat exchangers.

[0011] In some embodiments, a generator is also included; both the high-temperature expander and the low-temperature expander are connected to the generator, and the expansion of the supercritical carbon dioxide working fluid in the high-temperature expander and the low-temperature expander can drive the generator to generate electricity.

[0012] In some embodiments, the heat release temperature of the carbon dioxide cooler is greater than or equal to 150°C.

[0013] In some embodiments, the flow divider valve can adjust the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator to adjust the pinch position of the low-temperature regenerator; and the pinch position of the low-temperature regenerator is located at the inlet or outlet position of the low-temperature regenerator.

[0014] In some embodiments, a temperature sensor is also included; multiple temperature sensors are provided inside the low-temperature regenerator, at the inlet position and the outlet position, and the multiple temperature sensors are used to detect the pinch position of the low-temperature regenerator.

[0015] This invention also provides a control method for the above-mentioned supercritical carbon dioxide reverse Brayton cycle heat pump system, comprising the following steps: compressing supercritical carbon dioxide working fluid using a compressor, and the compressed supercritical carbon dioxide working fluid flowing into a carbon dioxide cooler to heat the heating medium; performing a first heat recovery on the supercritical carbon dioxide working fluid flowing out of the carbon dioxide cooler using a high-temperature regenerator; dividing the supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator into two paths using a flow splitting element, one path flowing through a high-temperature expander for expansion and work, and the other path flowing sequentially through the high-temperature side of a low-temperature regenerator for a second heat recovery, through a low-temperature expander for expansion and work, and through a carbon dioxide heater for heat exchange; mixing the supercritical carbon dioxide working fluid flowing out from the high-temperature expander and the carbon dioxide heater, and then sequentially flowing through the low-temperature side of the low-temperature regenerator, the low-temperature side of the high-temperature regenerator, and the inlet end of the compressor.

[0016] In some embodiments, the diversion element is a diversion valve; the step of "using the diversion element to divide the supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator into two separate streams" includes: using the diversion valve to divide the supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator into two separate streams and adjusting the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator.

[0017] Compared with the prior art, the present invention has achieved the following technical effects:

[0018] The supercritical carbon dioxide reverse Brayton cycle heat pump system and its control method of this invention utilize supercritical carbon dioxide, which has a density much greater than water vapor, a viscosity less than liquid, high heat transfer efficiency, and low compressibility, effectively reducing the volume of system components. Furthermore, this invention employs a two-stage split-flow expansion design, combined with a two-stage split-flow regeneration design, optimizing the expansion compressor's pressure energy recovery efficiency, reducing heat pump system power consumption, and significantly improving the system's COP. Moreover, this invention utilizes a carbon dioxide heater to absorb medium- and low-temperature industrial waste heat; carbon dioxide can reach a high exothermic temperature, simultaneously solving the waste heat utilization problem in chemical industrial production processes. The carbon dioxide heater can exchange heat with medium- and low-temperature heat sources to utilize medium- and low-temperature industrial waste heat to supply heat to other production processes with heat requirements, effectively reducing carbon emissions and energy consumption caused by industrial heating demands. Furthermore, this invention adjusts the mass flow rate at both ends of the low-temperature regenerator through a split-flow element, optimizing the heat exchange efficiency reduction caused by the difference in carbon dioxide heat capacity at the hot and cold ends of the heat exchanger, thereby improving the system's regeneration efficiency and COP. Attached Figure Description

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a connection diagram of a supercritical carbon dioxide reverse Brayton cycle heat pump system in some embodiments of the present invention.

[0021] Figure 2 This is a flowchart of the main steps of the control method for a supercritical carbon dioxide reverse Brayton cycle heat pump system in some embodiments of the present invention.

[0022] In the diagram: 1-Compressor; 2-Carbon dioxide cooler; 3-High temperature regenerator; 4-Diverter valve; 5-Low temperature regenerator; 6-Low temperature expander; 7-High temperature expander; 8-Carbon dioxide heater; 9-Mixer. Detailed Implementation

[0023] 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. 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.

[0024] The purpose of this invention is to provide a supercritical carbon dioxide reverse Brayton cycle heat pump system and its control method to solve the problems existing in the prior art, improve the system's regenerative efficiency and energy efficiency ratio (COP), and achieve a higher heat release temperature to meet the continuous supply demand of high-temperature water vapor.

[0025] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] This invention provides a supercritical carbon dioxide reverse Brayton cycle heat pump system, such as... Figure 1 As shown, it includes a compressor 1, a carbon dioxide cooler 2, a high-temperature regenerator 3, a flow divider element, a low-temperature regenerator 5, a high-temperature expander 7, a low-temperature expander 6, and a carbon dioxide heater 8. The compressor 1 is used to compress supercritical carbon dioxide working fluid and raise its temperature. The outlet end of the compressor 1 is connected to the inlet end of the carbon dioxide cooler 2 through a pipeline. The outlet end of the carbon dioxide cooler 2 is connected to the high-temperature side inlet end of the high-temperature regenerator 3 through a pipeline. The carbon dioxide cooler 2 uses the heated carbon dioxide working fluid to heat the heating medium and cool the carbon dioxide working fluid. The high-temperature regenerator 3 is used to perform the first heat recovery on the high-temperature carbon dioxide flowing out of the carbon dioxide cooler 2.

[0027] The high-temperature side outlet of the high-temperature regenerator 3 is divided into two paths by a diverting element. One path is connected to the inlet of the high-temperature expander 7, and the other path is connected to the high-temperature side inlet of the low-temperature regenerator 5. The high-temperature side outlet of the low-temperature regenerator 5 is connected to the inlet of the low-temperature expander 6, and the outlet of the low-temperature expander 6 is connected to the inlet of the carbon dioxide heater 8. The high-temperature expander 7 is used for the first expansion of the carbon dioxide working fluid, the low-temperature expander 6 is used for the second expansion of the carbon dioxide working fluid, and the carbon dioxide heater 8 is used for heat exchange with the medium and low temperature heat source.

[0028] The outlet end of the high-temperature expander 7 is connected to the outlet end of the carbon dioxide heater 8 and is connected to the inlet end of the low-temperature side of the low-temperature regenerator 5. The outlet end of the low-temperature side of the low-temperature regenerator 5 is connected to the inlet end of the low-temperature side of the high-temperature regenerator 3. The outlet end of the low-temperature side of the high-temperature regenerator 3 is connected to the inlet end of the compressor 1, thereby forming a circulation loop.

[0029] It should be noted that the high-temperature regenerator 3 and the low-temperature regenerator 5 of the present invention form a two-stage split-flow regeneration, and the high-temperature expander 7 and the low-temperature expander 6 form a two-stage split-flow expansion; and the high-temperature side outlet of the high-temperature regenerator 3 is divided into two paths. By adjusting the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator through the split-flow element, the heat exchange efficiency caused by the difference in carbon dioxide heat capacity at the hot and cold ends of the heat exchanger, i.e., the low-temperature regenerator 5, can be optimized, thereby improving the system regeneration efficiency and COP.

[0030] In some embodiments, the diversion element is a diversion valve 4; the inlet end of the diversion valve 4 is connected to the outlet end of the high-temperature side of the high-temperature regenerator 3 through a pipeline, the first outlet end of the diversion valve 4 is connected to the inlet end of the high-temperature expander 7 through a pipeline, and the second outlet end of the diversion valve 4 is connected to the inlet end of the high-temperature side of the low-temperature regenerator 5 through a pipeline; the diversion valve 4 is used to regulate the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander 7 and the high-temperature side of the low-temperature regenerator 5.

[0031] It should be noted that the embodiments of the present invention are illustrated using a diversion valve 4 as an example. Those skilled in the art can also set other components that can play a diversion role, and the present invention does not specifically limit them.

[0032] In some embodiments, a mixer 9 is also included; the first inlet end of the mixer 9 is connected to the outlet end of the carbon dioxide heater 8 via a pipeline, the second inlet end of the mixer 9 is connected to the outlet end of the high-temperature expander 7 via a pipeline, and the outlet end of the mixer 9 is connected to the inlet end of the low-temperature side of the low-temperature regenerator 5 via a pipeline; the mixer 9 is used to mix the supercritical carbon dioxide working fluid flowing out of the high-temperature expander 7 and the carbon dioxide heater 8.

[0033] It should be noted that the present invention can uniformly mix the working fluids flowing out of the high-temperature expander 7 and the carbon dioxide heater 8 by setting the mixer 9; and those skilled in the art can also use other components with mixing functions, which are not specifically limited in the present invention.

[0034] In some embodiments, both the high-temperature regenerator 3 and the low-temperature regenerator 5 are printed circuit heat exchangers. Obviously, the high-temperature regenerator 3 and the low-temperature regenerator 5 of the present invention can also employ other types of heat exchangers, which can be selected by those skilled in the art according to the specific circumstances.

[0035] In some embodiments, a generator is also included; both the high-temperature expander 7 and the low-temperature expander 6 are connected to the generator, and the expansion of the supercritical carbon dioxide working fluid in the high-temperature expander 7 and the low-temperature expander 6 can drive the generator to generate electricity.

[0036] It should be noted that the high-temperature expander 7 and the low-temperature expander 6 of the present invention can be turbine expanders, which can drive the generator to rotate and discharge when the supercritical carbon dioxide working fluid expands; thus, the present invention can recover pressure energy by expanding the carbon dioxide working fluid to do work.

[0037] In some embodiments, the heat release temperature of the carbon dioxide cooler 2 is greater than or equal to 150°C.

[0038] In some embodiments, the diversion valve 4 adjusts the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander 7 and the high-temperature side of the low-temperature regenerator 5 to adjust the pinch position of the low-temperature regenerator 5; and the pinch position of the low-temperature regenerator 5 is located at the inlet or outlet position of the low-temperature regenerator 5.

[0039] It should be noted that the pinch point is the location where the minimum temperature difference occurs between the cold and hot fluids within a heat exchanger. Because supercritical carbon dioxide undergoes drastic property changes near the critical point, the minimum temperature difference between the cold and hot fluids may occur in the middle of the heat exchanger. This could lead to adverse effects such as increased heat exchanger size and deteriorated heat exchange efficiency, increasing the complexity of heat exchanger design. This problem of heat exchange deterioration due to the pinch point being located in the middle of the heat exchanger is called the pinch point problem. This invention regulates the mass flow rate of supercritical carbon dioxide working fluid entering the high-temperature expander 7 and the high-temperature side of the low-temperature regenerator 5 through the diversion valve 4. This allows for the adjustment of the temperature at the cold and hot ends of the heat exchanger (i.e., the low-temperature regenerator 5), thereby adjusting the pinch point temperature difference to occur at the inlet and outlet positions of the heat exchanger. This enhances the ability to recover high-temperature waste heat from the circulating air cooler (i.e., the carbon dioxide cooler 2) and significantly improves the energy utilization rate of the heat pump cycle.

[0040] In some embodiments, a temperature sensor is also included; multiple temperature sensors are provided inside the low-temperature regenerator 5, at its inlet and outlet positions, and the multiple temperature sensors are used to detect the pinch position of the low-temperature regenerator 5.

[0041] It should be noted that the present invention can detect the temperature changes of the cold and hot ends inside the low-temperature regenerator 5 by means of multiple temperature sensors installed inside the low-temperature regenerator 5 and at the inlet and outlet positions, thereby adjusting the clamp position of the low-temperature regenerator 5 according to the temperature changes, so that the clamp of the low-temperature regenerator 5 is located at the inlet and outlet positions.

[0042] The working principle of the supercritical carbon dioxide reverse Brayton cycle heat pump system of this invention is as follows:

[0043] Carbon dioxide enters carbon dioxide compressor 1, is compressed and heated to the required heating temperature, and then discharges heat from carbon dioxide cooler 2 to heat the heating medium required for industrial production. The high-temperature carbon dioxide flowing out of cooler 2 enters high-temperature regenerator 3 for the first heat recovery. The cooled carbon dioxide is divided into two streams, with mass flow rates of m·x and m·(1-x) from the two outlets of diversion valve 4, where m is the mass flow rate of carbon dioxide flowing through compressor 1 and x is the diversion ratio of diversion valve 4. The carbon dioxide with a mass flow rate of m·x flows into high-temperature carbon dioxide expander 7, where it is expanded... The work recovers part of the pressure energy; carbon dioxide with a mass flow rate of m·(1-x) flows into the low-temperature regenerator 5 to further recover heat energy, and after flowing out of the low-temperature regenerator 5, it enters the low-temperature carbon dioxide expander 6 to expand and do work, recovering pressure energy; the carbon dioxide flowing out of the outlet of the low-temperature carbon dioxide expander 6 enters the carbon dioxide heater 8 to absorb the heat of the medium and low temperature heat source, and then mixes with the carbon dioxide flowing out of the outlet of the high-temperature carbon dioxide expander 7 in the mixer 9, and flows out of the outlet of the mixer 9 sequentially into the low-temperature regenerator 5 and the high-temperature regenerator 3 to absorb the heat energy of the high-pressure side carbon dioxide, and returns to the inlet of the carbon dioxide compressor 1, and so on.

[0044] Compared with traditional heat pump cycles, the present invention has at least the following advantages:

[0045] This invention relates to a supercritical carbon dioxide re-expansion inverse Brayton system, which uses supercritical carbon dioxide, which has a density much greater than that of water vapor, a viscosity less than that of liquids, high heat transfer efficiency, and low compressibility, thus effectively reducing the volume of system components.

[0046] This invention adopts a two-stage split-flow regeneration design of high-temperature regenerator 3 and low-temperature regenerator 5. By adjusting the mass flow rate at both ends of the low-temperature regenerator 5, the heat exchange efficiency reduction caused by the difference in carbon dioxide heat capacity at the hot and cold ends of the heat exchanger is optimized, thereby improving the system's regeneration efficiency and COP.

[0047] This invention employs a two-stage split expansion design (high-temperature expander 7 - low-temperature expander 6) combined with a two-stage split regeneration design to optimize the pressure energy recovery efficiency of the expanders, reduce the power consumption of the heat pump system, and significantly improve the system COP.

[0048] The high-temperature regenerator 3 and the low-temperature regenerator 5 use printed circuit heat exchangers, such as the PCHE type, to provide the largest possible heat exchange area within a limited volume, making the regeneration process more complete.

[0049] The heat release temperature of the carbon dioxide cooler 2 exceeds 150°C. The diverted carbon dioxide expands and does work in the high-temperature expander 7 and the low-temperature expander 6 respectively, recovering part of the pressure energy and reducing the overall energy consumption of the system.

[0050] The supercritical carbon dioxide re-expansion reverse Brayton high-temperature heat pump cycle can achieve a higher COP than the traditional reverse Rankine cycle and reverse Brayton cycle at a lower operating pressure, effectively reducing the safety pressure requirements of the heat pump system.

[0051] This invention relates to a supercritical carbon dioxide recompression reverse Brayton heat pump for absorbing medium- and low-temperature industrial waste heat. Carbon dioxide can reach a high heat release temperature, and at the same time, it can solve the problem of waste heat utilization in the chemical industry production process. It utilizes medium- and low-temperature industrial waste heat to provide heat for other production processes with heat demand, effectively reducing carbon emissions and energy consumption caused by industrial production heating demand.

[0052] This invention also provides a control method for a supercritical carbon dioxide reverse Brayton cycle heat pump system, such as... Figure 2 As shown, it includes the following steps:

[0053] Step S1: Compress supercritical carbon dioxide working fluid using compressor 1, and the compressed supercritical carbon dioxide working fluid flows into carbon dioxide cooler 2 to heat the heating medium.

[0054] Step S2: Use the high-temperature regenerator 3 to perform the first heat recovery on the supercritical carbon dioxide working fluid flowing out of the carbon dioxide cooler 2.

[0055] Step S3: The supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator 3 is divided into two streams using a diversion element. One stream flows through the high-temperature expander 7 to perform expansion work, and the other stream flows through the high-temperature side of the low-temperature regenerator 5 for a second heat recovery, through the low-temperature expander 6 to perform expansion work, and through the carbon dioxide heater 8 for heat exchange.

[0056] Step S4: The supercritical carbon dioxide working fluid flowing out of the high-temperature expander 7 and the carbon dioxide heater 8 is mixed and then flows sequentially through the low-temperature side of the low-temperature regenerator 5, the low-temperature side of the high-temperature regenerator 3, and the inlet end of the compressor 1.

[0057] In some embodiments, the diversion element is a diversion valve 4; the step of "using the diversion element to separate the supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator 3 into two separate paths" includes:

[0058] The supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator 3 is divided into two streams by the diversion valve 4 and the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander 7 and the high-temperature side of the low-temperature regenerator 5 is adjusted.

[0059] In some embodiments, the supercritical carbon dioxide reverse Brayton cycle heat pump system of the present invention further includes a mixer 9; in step S4:

[0060] The supercritical carbon dioxide working fluid flowing from the high-temperature expander 7 and the carbon dioxide heater 8 is mixed using mixer 9.

[0061] This invention employs supercritical carbon dioxide as the heat pump working fluid and innovatively designs a supercritical re-expansion reverse Brayton heat pump configuration. The re-expansion layout of the high-temperature expander 7 and the low-temperature expander 6 effectively improves the efficiency of heat pump cycle pressure energy recovery, achieving a reduction in the overall energy consumption of the heat pump system and effectively improving the heat pump heating COP. The staged regeneration design of the high-temperature regenerator 3 and the low-temperature regenerator 5 controls the proportion of carbon dioxide flowing into the low-temperature regenerator 5 and the low-temperature expander 6 by proportionally splitting the flow, thereby matching the specific heat capacity of carbon dioxide on both sides of the low pressure. This ensures that the pinch temperature difference of the heat exchanger appears at the inlet and outlet of the heat exchanger, enhancing the ability to recover high-temperature waste heat after the air cooler and significantly improving the energy utilization rate of the heat pump cycle. In addition, the high density and high specific heat characteristics of carbon dioxide in the supercritical region can efficiently absorb low-grade waste heat, reducing the overall size of heat exchange components and compressors, which helps to achieve installation or modification in limited spaces such as factories. Meanwhile, carbon dioxide as a working medium has environmental and safety advantages such as zero ozone depletion potential (ODP=0), low global warming potential (GWP=1), and being non-toxic and non-flammable, which meet the stringent requirements of chemical plants for safety and sustainability.

[0062] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only intended to help understand the method and core concept of the present invention. At the same time, those skilled in the art will find that the specific implementation methods and application scopes may vary based on the concept of the present invention. In summary, the contents of this specification should not be construed as limiting the present invention.

Claims

1. A supercritical carbon dioxide reverse Brayton cycle heat pump system, characterized in that, This includes compressors, carbon dioxide coolers, high-temperature regenerators, flow dividers, low-temperature regenerators, high-temperature expanders, low-temperature expanders, and carbon dioxide heaters; The compressor is used to compress supercritical carbon dioxide working fluid, and the outlet end of the compressor, the carbon dioxide cooler, and the high-temperature side inlet end of the high-temperature regenerator are connected in sequence. The high-temperature side outlet of the high-temperature regenerator is divided into two paths by the diversion element. One path is connected to the inlet end of the high-temperature expander, and the other path is connected in sequence to the high-temperature side inlet end of the low-temperature regenerator, the inlet end of the low-temperature expander, and the inlet end of the carbon dioxide heater. The outlet end of the high-temperature expander is connected to the outlet end of the carbon dioxide heater and to the low-temperature side inlet end of the low-temperature regenerator; the low-temperature side outlet end of the low-temperature regenerator, the low-temperature side of the high-temperature regenerator, and the inlet end of the compressor are connected in sequence.

2. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 1, characterized in that, The flow-diverting element is a flow-diverting valve; The inlet end of the diversion valve is connected to the high-temperature side outlet end of the high-temperature regenerator via a pipeline; the first outlet end of the diversion valve is connected to the inlet end of the high-temperature expander via a pipeline; and the second outlet end of the diversion valve is connected to the high-temperature side inlet end of the low-temperature regenerator via a pipeline. The diversion valve is used to regulate the mass flow rate of supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator.

3. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 1, characterized in that, It also includes a mixer; The first inlet end of the mixer is connected to the outlet end of the carbon dioxide heater through a pipeline, the second inlet end of the mixer is connected to the outlet end of the high-temperature expander through a pipeline, and the outlet end of the mixer is connected to the low-temperature side inlet end of the low-temperature regenerator through a pipeline. The mixer is used to mix the supercritical carbon dioxide working fluid flowing from the high-temperature expander and the carbon dioxide heater.

4. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 1, characterized in that, Both the high-temperature regenerator and the low-temperature regenerator are printed circuit heat exchangers.

5. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 1, characterized in that, It also includes generators; Both the high-temperature expander and the low-temperature expander are connected to the generator, and the expansion of the supercritical carbon dioxide working fluid in the high-temperature expander and the low-temperature expander can drive the generator to generate electricity.

6. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 1, characterized in that, The heat release temperature of the carbon dioxide cooler is greater than or equal to 150°C.

7. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 2, characterized in that, The flow divider valve regulates the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator, thereby adjusting the pinch position of the low-temperature regenerator. Furthermore, the pinch point of the low-temperature regenerator is located at either the inlet or outlet of the low-temperature regenerator.

8. The supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 2, characterized in that, It also includes a temperature sensor; Multiple temperature sensors are installed inside the low-temperature regenerator, at its inlet and outlet positions, and these multiple temperature sensors are used to detect the pinch point positions of the low-temperature regenerator.

9. A control method for a supercritical carbon dioxide reverse Brayton cycle heat pump system according to any one of claims 1-8, characterized in that, Includes the following steps: A compressor is used to compress supercritical carbon dioxide working fluid, and the compressed supercritical carbon dioxide working fluid flows into a carbon dioxide cooler to heat the heating medium. The supercritical carbon dioxide working fluid flowing out of the carbon dioxide cooler is recovered for the first time using a high-temperature regenerator. The supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator is divided into two streams by a diversion element. One stream flows through the high-temperature expander to perform expansion work, and the other stream flows through the high-temperature side of the low-temperature regenerator for a second heat recovery, through the low-temperature expander to perform expansion work, and through the carbon dioxide heater for heat exchange. The supercritical carbon dioxide working fluid flowing from the high-temperature expander and the carbon dioxide heater is mixed and then flows sequentially through the low-temperature side of the low-temperature regenerator, the low-temperature side of the high-temperature regenerator, and the inlet end of the compressor.

10. The control method for the supercritical carbon dioxide reverse Brayton cycle heat pump system according to claim 9, characterized in that, The flow-diverting element is a flow-diverting valve; The step of "using a flow splitter to divide the supercritical carbon dioxide working fluid flowing from the high-temperature side of the high-temperature regenerator into two separate streams" includes: The supercritical carbon dioxide working fluid flowing out from the high-temperature side of the high-temperature regenerator is divided into two streams by the diversion valve and the mass flow rate of the supercritical carbon dioxide working fluid entering the high-temperature expander and the high-temperature side of the low-temperature regenerator is adjusted.

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