Two-section compression type transcritical carbon dioxide heat pump system and control method thereof

Abstract

The invention discloses a two-section compression type transcritical carbon dioxide heat pump system and a control method thereof. An outlet of a second compressor sequentially passes through a high-temperature heat exchanger and a flow divider and then is divided into two paths; wherein one path is communicated with an inlet of a first expansion machine through a heat flow stream inlet valve of the first heat regenerator, the hot side of the first heat regenerator and the hot side of the second heat regenerator, and the other path is communicated with an inlet of a second expansion machine through a heat flow stream inlet valve of the third heat regenerator and the hot side of the third heat regenerator in sequence; the outlet of the second expansion machine is communicated with the inlet of the mixer through the cold side of the second heat regenerator, the cold stream inlet valve of the first heat regenerator and the cold side of the second heat regenerator in sequence; an outlet of the first expansion machine communicates with an inlet of the mixer through the low-temperature heat exchanger, a cold stream inlet valve of the third heat regenerator, the cold side of the third heat regenerator and the first compressor, an outlet of the mixer communicates with an inlet of the second compressor, and the comprehensive energy efficiency of the carbon dioxide heat pump system can be improved.

Description

Technical Field

[0001] This invention belongs to the field of industrial green electricity heating and cooling or thermal battery technology, and relates to a two-stage compression transcritical carbon dioxide heat pump system and its control method. Background Technology

[0002] With the large-scale grid connection of photovoltaic and wind power, the adoption of large-scale power storage technology is the only way to solve the problems of intermittency and volatility of renewable energy and matching user load demand. Carbon dioxide heat pumps are a promising new power conversion and storage technology, increasingly used for power storage due to their numerous advantages such as environmental friendliness, high-temperature heating performance, and adaptability to low ambient temperatures. This technology uses high-pressure carbon dioxide as the circulating working fluid, converting electrical energy into heat and cold energy through a reverse Brayton cycle and storing them in high-temperature heat storage media and low-temperature cold storage media for use during industrial processes or peak grid load periods. A carbon dioxide heat pump system generally consists of a high-temperature heat exchanger, a low-temperature heat exchanger, a regenerator, a compressor, and an expander. Within a certain power range, this technology offers advantages such as high system energy efficiency, compact equipment structure, and low initial infrastructure investment. However, industrial-grade heat pumps typically use the environment as a cold source. When a carbon dioxide heat pump (critical point parameters: 31℃, 7.38MPa) operates in the near-critical temperature region, its thermodynamic properties become distorted. The strong nonlinear changes in specific heat capacity, density, etc., with temperature lead to the deterioration of the flow and heat transfer process in the system, resulting in serious irreversible losses and energy dissipation, which greatly limits the improvement of the stability and energy efficiency of carbon dioxide heat pump operation. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a two-stage compression transcritical carbon dioxide heat pump system and its control method. This system and its control method can solve the technical problems of existing carbon dioxide heat pumps using the environment as a cold source, poor flow heat exchange matching in the near-critical temperature region of the system, and difficulty in regulation or inability to operate stably, thereby improving the overall energy efficiency of the carbon dioxide heat pump system.

[0004] To achieve the above objectives, the present invention discloses a two-stage compression transcritical carbon dioxide heat pump system, comprising a second compressor, a first expander, a second expander, and a mixer;

[0005] The outlet of the second compressor is divided into two paths after passing through a high-temperature heat exchanger and a distributor. One path is connected to the inlet of the first expander via the inlet valve of the hot stream of the first regenerator, the hot side of the first regenerator, and the hot side of the second regenerator. The other path is connected to the inlet of the second expander via the inlet valve of the hot stream of the third regenerator and the hot side of the third regenerator. The outlet of the second expander is connected to the inlet of the mixer via the cold side of the second regenerator, the inlet valve of the cold stream of the first regenerator, and the cold side of the second regenerator. The outlet of the first expander is connected to the inlet of the mixer via a low-temperature heat exchanger, the inlet valve of the cold stream of the third regenerator, the cold side of the third regenerator, the first compressor, and the mixer. The outlet of the mixer is connected to the inlet of the second compressor.

[0006] A further improvement of the two-stage compression transcritical carbon dioxide heat pump system of the present invention is as follows:

[0007] Furthermore, the cold-side outlet of the second regenerator is connected to the cold-side outlet of the first regenerator via a cold-side bypass valve of the first regenerator.

[0008] Furthermore, the outlet of the distributor is connected to the hot-side outlet of the first regenerator via the hot-side bypass valve of the first regenerator.

[0009] Furthermore, the outlet of the splitter is connected to the hot-side outlet of the third regenerator via the hot-side bypass valve of the third regenerator.

[0010] Furthermore, the outlet of the low-temperature heat exchanger is connected to the cold-side outlet of the third regenerator via the cold-side bypass valve of the third regenerator.

[0011] Furthermore, the on / off states of the inlet valve of the first regenerator heat flow stream and the hot side bypass valve of the first regenerator are mutually exclusive.

[0012] Furthermore, the on / off states of the first regenerator cold flow inlet valve and the first regenerator cold side bypass valve are mutually exclusive.

[0013] Furthermore, the on / off states of the inlet valve of the third regenerator hot flow stream and the hot side bypass valve of the third regenerator are mutually exclusive.

[0014] Furthermore, the on / off states of the cold flow inlet valve of the third regenerator and the cold side bypass valve of the third regenerator are mutually exclusive.

[0015] This invention discloses a control method for a two-stage compression transcritical carbon dioxide heat pump system, comprising the following steps:

[0016] When supplying heat to the medium-high temperature zone, the following steps are taken: First, the hot flow inlet valve of the first regenerator is opened, connecting the hot-side inlet of the first regenerator to the distributor; second, the hot-side bypass valve of the first regenerator is closed, disconnecting the hot-side inlet of the second regenerator from the distributor; third, the cold flow inlet valve of the first regenerator is opened, connecting the cold-side inlet of the first regenerator to the cold-side outlet of the second regenerator; fourth, the cold-side bypass valve of the first regenerator is closed, disconnecting the cold-side outlet of the second regenerator from the mixer; fifth, the hot flow inlet valve of the third regenerator is opened, connecting the hot-side inlet of the third regenerator to the distributor; sixth, the hot-side bypass valve of the third regenerator is closed, disconnecting the inlet of the second expander from the distributor; seventh, the cold flow inlet valve of the third regenerator is opened, connecting the cold-side inlet of the third regenerator to the cold-side outlet of the low-temperature heat exchanger; and eighth, the cold-side bypass valve of the third regenerator is closed, disconnecting the inlet of the first compressor from the cold-side outlet of the low-temperature heat exchanger.

[0017] When supplying heat to the medium and low temperature zone, the following steps are taken: The inlet valve of the hot stream of the first regenerator is closed, disconnecting the hot-side inlet of the first regenerator from the distributor; the hot-side bypass valve of the first regenerator is opened, connecting the hot-side inlet of the second regenerator to the distributor; the inlet valve of the cold stream of the first regenerator is closed, disconnecting the cold-side inlet of the first regenerator from the cold-side outlet of the second regenerator; the cold-side bypass valve of the first regenerator is opened, connecting the cold-side outlet of the second regenerator to the mixer; the inlet valve of the hot stream of the third regenerator is closed, disconnecting the hot-side inlet of the third regenerator from the distributor; the hot-side bypass valve of the third regenerator is opened, connecting the inlet of the second expander to the distributor; the inlet valve of the cold stream of the third regenerator is closed, disconnecting the cold-side inlet of the third regenerator from the cold-side outlet of the low-temperature heat exchanger; the cold-side bypass valve of the third regenerator is opened, connecting the inlet of the first compressor to the cold-side outlet of the low-temperature heat exchanger.

[0018] The present invention has the following beneficial effects:

[0019] In practical operation, the two-stage compression transcritical carbon dioxide heat pump system and its control method described in this invention fully utilize the regeneration method to supply heat to the medium and high temperature range by connecting the first and third regenerators to the heat pump system, thereby reducing the operating pressure of the system. By isolating the first and third regenerators from the heat pump system, the system can ensure efficient and stable heat supply to the medium and low temperature range. This solves the technical problems of existing carbon dioxide heat pumps that use the environment as a cold source, have poor flow heat exchange matching in the near-critical temperature range, and are difficult to control or cannot operate stably, thus improving the overall efficiency of the carbon dioxide heat pump system.

[0020] Furthermore, the present invention uses a first compressor to compress the carbon dioxide circulating working fluid to a medium temperature and medium pressure state, and then combines it with the circulating working fluid from the second regenerator and the cold side of the first regenerator in a mixer. After that, the circulating working fluid is compressed to a high temperature and high pressure state by the second compressor. By dividing the compression process of the carbon dioxide heat pump into two stages and adopting an intermediate self-cooling method, not only can the pressure ratio and energy consumption of the compressor be reduced, but it is also beneficial to reduce the design and manufacturing difficulty of the compressor.

[0021] Furthermore, the present invention uses a second expander to expand the carbon dioxide circulating working fluid to a low temperature state, and uses a second regenerator to precool the circulating working fluid at the inlet of the first expander to a liquid state, thereby preventing carbon dioxide from entering the two-phase region during the expansion process of the first expander (or significantly reducing the gas content at the outlet of the first expander), suppressing cavitation flow and cavitation phenomena in the first expander, and ensuring the safe operation of the first expander as well as the safety and stability of the carbon dioxide heat pump system. Attached Figure Description

[0022] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 This is a structural diagram of the present invention.

[0024] Wherein, 1 is the first compressor, 2 is the mixer, 3 is the second compressor, 4 is the high-temperature heat exchanger, 5 is the distributor, 6 is the first regenerator, 7 is the second regenerator, 8 is the first expander, 9 is the low-temperature heat exchanger, 10 is the third regenerator, 11 is the second expander, 12 is the first electric motor, 13 is the second electric motor, 14 is the first generator, 15 is the second generator, 61h is the hot flow inlet valve of the first regenerator, 61c is the cold flow inlet valve of the first regenerator, 62h is the hot side bypass valve of the first regenerator, 62c is the cold side bypass valve of the first regenerator, 101h is the hot flow inlet valve of the third regenerator, 101c is the cold flow inlet valve of the third regenerator, 102h is the hot side bypass valve of the third regenerator, and 102c is the cold side bypass valve of the third regenerator. Detailed Implementation

[0025] 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, not all, of the embodiments of the present invention. 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.

[0026] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0027] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0028] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0029] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0030] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0031] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0033] refer to Figure 1 The two-stage compression transcritical carbon dioxide heat pump system of the present invention includes a first compressor 1, a mixer 2, a second compressor 3, a high-temperature heat exchanger 4, a distributor 5, a first regenerator 6, a second regenerator 7, a first expander 8, a low-temperature heat exchanger 9, a third regenerator 10, a second expander 11, a first electric motor 12, a second electric motor 13, a first generator 14, a second generator 15, a first regenerator hot flow inlet valve 61h, a first regenerator cold flow inlet valve 61c, a first regenerator hot side bypass valve 62h, a first regenerator cold side bypass valve 62c, a third regenerator hot flow inlet valve 101h, a third regenerator cold flow inlet valve 101c, a third regenerator hot side bypass valve 102h, and a third regenerator cold side bypass valve 102c.

[0034] The outlet of the second compressor 3 is divided into two paths after passing through the high-temperature heat exchanger 4 and the distributor 5. One path is connected to the inlet of the first expander 8 via the hot flow inlet valve 61h of the first regenerator, the hot side of the first regenerator 6 and the hot side of the second regenerator 7. The other path is connected to the inlet of the second expander 11 via the hot flow inlet valve 101h of the third regenerator and the hot side of the third regenerator 10. The outlet of the second expander 11 is connected to the inlet of the mixer 2 via the cold side of the second regenerator 7, the cold flow inlet valve 61c of the first regenerator and the cold side of the second regenerator 7. The outlet of the first expander 8 is connected to the inlet of the mixer 2 via the low-temperature heat exchanger 9, the cold flow inlet valve 101c of the third regenerator, the cold side of the third regenerator 10 and the first compressor 1. The outlet of the mixer 2 is connected to the inlet of the second compressor 3.

[0035] The cold-side outlet of the second regenerator 7 is connected to the cold-side outlet of the first regenerator 6 via the cold-side bypass valve 62c of the first regenerator.

[0036] The outlet of the distributor 5 is connected to the hot side outlet of the first regenerator 6 via the hot side bypass valve 62h of the first regenerator.

[0037] The outlet of the distributor 5 is connected to the hot side outlet of the third regenerator 10 via the hot side bypass valve 102h of the third regenerator.

[0038] The outlet of the low-temperature heat exchanger 9 is connected to the cold-side outlet of the third regenerator 10 via the cold-side bypass valve 102c of the third regenerator.

[0039] The first expander 8 is connected to the first generator 14; the second expander 11 is connected to the second generator 15; the first compressor 1 is connected to the first electric motor 12; and the second compressor 3 is connected to the second electric motor 13.

[0040] The first compressor 1 is a turbine compressor; the second compressor 3 is a turbine compressor; the first expander 8 is a turbine expander; and the second expander 11 is a turbine expander.

[0041] The cold-side inlet of the high-temperature heat exchanger 4 is connected to the outlet of the high-temperature heat storage medium source, and the cold-side outlet of the high-temperature heat exchanger 4 is connected to the inlet of the high-temperature heat storage medium source. The high-temperature heat storage medium source stores a high-temperature heat storage medium, allowing it to exchange heat with the high-quality heat within the high-temperature heat exchanger 4, thereby storing high-quality heat. The high-temperature heat storage medium source can provide hot water to users, supplying them with hot water and steam. The hot-side inlet of the low-temperature heat exchanger 9 is connected to the outlet of the cold source, and the hot-side outlet of the low-temperature heat exchanger 9 is connected to the inlet of the cold source.

[0042] It should be noted that the on / off states of the first regenerator hot stream inlet valve 61h and the first regenerator hot side bypass valve 62h are mutually exclusive, as are the on / off states of the first regenerator cold stream inlet valve 61c and the first regenerator cold side bypass valve 62c. That is, when the heat pump system supplies heat to the medium-high temperature zone, when the first regenerator hot stream inlet valve 61h and the first regenerator cold stream inlet valve 61c are open, the first regenerator hot side bypass valve 62h and the first regenerator cold side bypass valve 62c are closed. When the heat pump system supplies heat to the medium-low temperature zone, while the first regenerator hot stream inlet valve 61h and the first regenerator cold stream inlet valve 61c are closed, the first regenerator hot side bypass valve 62h and the first regenerator cold side bypass valve 62c are open to ensure that the first regenerator 6 is completely isolated from the heat pump system.

[0043] Similarly, the on / off states of the hot stream inlet valve 101h and the hot side bypass valve 102h of the third regenerator are mutually exclusive, and the on / off states of the cold stream inlet valve 101c and the cold side bypass valve 102c of the third regenerator are mutually exclusive. That is, when the heat pump system supplies heat to the medium-high temperature zone, when the hot stream inlet valve 101h and the cold stream inlet valve 101c of the third regenerator are open, the hot side bypass valve 102h and the cold side bypass valve 102c of the third regenerator are closed. When the heat pump system supplies heat to the medium-low temperature zone, while the hot stream inlet valve 101h and the cold stream inlet valve 101c of the third regenerator are closed, the hot side bypass valve 102h and the cold side bypass valve 102c of the third regenerator are open to ensure that the third regenerator 10 is completely isolated from the heat pump system.

[0044] The control method of the two-stage compression transcritical carbon dioxide heat pump system of the present invention includes a medium-high temperature heating mode and a medium-low temperature heating mode; by adjusting the operation mode of the heat pump, it can adapt to providing heat within the required temperature range to different heating users; wherein, when the heating temperature is higher than 200°C, the medium-high temperature heating mode is activated; when the heating temperature is lower than 200°C, the medium-low temperature heating mode is activated.

[0045] When supplying heat to medium- and high-temperature areas, the specific procedures include:

[0046] The hot flow inlet valve 61h of the first regenerator is opened, connecting the hot side inlet of the first regenerator 6 with the distributor 5; the hot side bypass valve 62h of the first regenerator is closed, disconnecting the hot side inlet of the second regenerator 7 from the distributor 5; the cold flow inlet valve 61c of the first regenerator is opened, connecting the cold side inlet of the first regenerator 6 with the cold side outlet of the second regenerator 7; the cold side bypass valve 62c of the first regenerator is closed, disconnecting the cold side outlet of the second regenerator 7 from the mixer 2.

[0047] The hot flow inlet valve 101h of the third regenerator is opened, connecting the hot side inlet of the third regenerator 10 with the distributor 5; the hot side bypass valve 102h of the third regenerator is closed, disconnecting the inlet of the second expander 11 from the distributor 5; the cold flow inlet valve 101c of the third regenerator is opened, connecting the cold side inlet of the third regenerator 10 with the cold side outlet of the low-temperature heat exchanger 9; the cold side bypass valve 102c of the third regenerator is closed, disconnecting the inlet of the first compressor 1 from the cold side outlet of the low-temperature heat exchanger 9.

[0048] It should be noted that when supplying heat to the medium-high temperature zone, the carbon dioxide circulating working fluid is compressed to a high temperature and high pressure state by the first compressor 1 and the second compressor 3. The circulating working fluid flows through the high temperature heat exchanger 4 to transfer heat to the high temperature heat storage medium. Then, the circulating working fluid is divided into two streams by the splitter 5: the first stream of circulating working fluid recovers some heat through the first regenerator 6 and then enters the hot side of the second regenerator 7; the other stream of circulating working fluid recovers some heat through the third regenerator 10, expands and cools down through the second expander 11 and recovers the expansion work, and then enters the cold side of the second regenerator 7. After the two circulating working fluids exchange heat in the second regenerator 7, the temperature of the first circulating working fluid drops below the critical temperature and then enters the liquid expander (i.e., the first expander 8) to expand to a low temperature and low pressure state and recover the expansion work. The low temperature and low pressure circulating working fluid flows through the low temperature heat exchanger 9 to transfer the cold energy to the low temperature cold storage medium for storage, and then passes through the third regenerator 10 to be reheated to the inlet temperature of the first compressor 1. The temperature of the other circulating working fluid gradually increases, and then it is reheated through the first regenerator 6. Finally, it merges with the circulating working fluid at the outlet of the first compressor 1 in the mixer 2 to form a closed working cycle loop.

[0049] In this invention, by connecting the first regenerator 6 and the third regenerator 10 to the heat pump system, the heat pump system can achieve a large regenerative cycle, increasing the heating temperature of the heat pump system and ensuring that the heat pump system can continuously and stably supply heat to the medium and high temperature range. At the same time, connecting the third regenerator 10 to the heat pump system can increase the inlet temperature of the first compressor 1, thereby reducing the pressure ratio and the compressor load. Connecting the first regenerator 6 to the heat pump system can enable the circulating working fluid to achieve self-cooling in the mixer 2, reducing the inlet temperature of the second compressor 3 and further reducing the compressor load. Overall, the energy efficiency of the carbon dioxide heat pump system is effectively improved.

[0050] When supplying heat to medium and low temperature zones, the specific operations include:

[0051] The hot flow inlet valve 61h of the first regenerator is closed, disconnecting the hot-side inlet of the first regenerator 6 from the distributor 5; the hot-side bypass valve 62h of the first regenerator is opened, connecting the hot-side inlet of the second regenerator 7 to the distributor 5; the cold flow inlet valve 61c of the first regenerator is closed, disconnecting the cold-side inlet of the first regenerator 6 from the cold-side outlet of the second regenerator 7; the cold-side bypass valve 62c of the first regenerator is opened, connecting the cold-side outlet of the second regenerator 7 to the mixer 2.

[0052] The hot flow inlet valve 101h of the third regenerator is closed, disconnecting the hot side inlet of the third regenerator 10 from the distributor 5; the hot side bypass valve 102h of the third regenerator is opened, connecting the inlet of the second expander 11 to the distributor 5; the cold flow inlet valve 101c of the third regenerator is closed, disconnecting the cold side inlet of the third regenerator 10 from the cold side outlet of the low-temperature heat exchanger 9; the cold side bypass valve 102c of the third regenerator is opened, connecting the inlet of the first compressor 1 to the cold side outlet of the low-temperature heat exchanger 9.

[0053] It should be noted that when supplying heat to the medium and low temperature zone, the carbon dioxide circulating working fluid is compressed to a high temperature and high pressure state through the first compressor 1 and the second compressor 3. The circulating working fluid transfers heat to the high temperature heat storage medium through the high temperature heat exchanger 4. Then, the circulating working fluid is divided into two streams through the distributor 5: the first stream of circulating working fluid enters the hot side of the second regenerator 7 directly through the hot side bypass valve 62h of the first regenerator; the other stream of circulating working fluid enters the second expander 11 directly through the hot side bypass valve 102h of the third regenerator to expand and cool down and recover the expansion work, and then enters the cold side of the second regenerator 7. After the two circulating working fluids exchange heat in the second regenerator 7, the temperature of the first circulating working fluid decreases, and then it expands to a low temperature and low pressure state through the first expander 8 and recovers the expansion work. The low temperature and low pressure state of the circulating working fluid transfers the cold energy to the low temperature cold storage medium through the low temperature heat exchanger 9, and then enters the inlet of the first compressor 1 through the cold side bypass valve 102c of the third regenerator; the temperature of the other circulating working fluid gradually increases, and then it passes through the cold side bypass valve 62c of the first regenerator, and finally merges with the circulating working fluid at the outlet of the first compressor 1 in the mixer 2 to form a closed working cycle loop.

[0054] In this invention, by isolating the first regenerator 6 and the third regenerator 10 from the heat pump system, the operation and control process of the system is simplified, ensuring that the carbon dioxide heat pump system can efficiently and stably supply heat to the medium and low temperature range. Simultaneously, the second expander 11 in the heat pump system expands the circulating working fluid to a low temperature state, and the second regenerator 7 precools the circulating working fluid at the inlet of the first expander 8 to a liquid state, suppressing cavitation flow and cavitation phenomena in the first expander 8, thus ensuring the safe operation of the first expander 8 and the safety and stability of the heat pump system.

[0055] The two-stage compression transcritical carbon dioxide heat pump system with adjustable heating temperature range described in this invention can supply heat to the medium-high temperature range by connecting the first regenerator 6 and the third regenerator 10 to the circulation; and it can also supply heat to the medium-low temperature range by isolating the first regenerator 6 and the third regenerator 10 from the circulation, thus improving the energy efficiency and flexibility of the heat pump system when supplying heat to different users. By dividing the compression process of the heat pump system into two stages, the pressure ratio and energy consumption of the first compressor 1 are effectively reduced. The intermediate self-cooling method lowers the inlet temperature of the second compressor 3, which is very beneficial for reducing the design and manufacturing difficulty of the compressor. The second expander 11 expands the circulating working fluid to a low temperature state, and the second regenerator 7 precools the circulating working fluid at the inlet of the first expander 8 to a liquid state, avoiding the circulating working fluid from entering the two-phase region during the expansion process of the first expander 8, suppressing cavitation flow and cavitation phenomena in the first expander 8, and ensuring the stable and safe operation of the heat pump system.

[0056] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and disclosure of the invention. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the following claims.

[0057] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

[0058] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the present invention. Any simple modifications, alterations, or equivalent structural changes made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A two-stage compression transcritical carbon dioxide heat pump system, characterized in that, It includes a second compressor (3), a first expander (8), a second expander (11), and a mixer (2); The outlet of the second compressor (3) is divided into two paths after passing through the high-temperature heat exchanger (4) and the distributor (5). One path is connected to the inlet of the first expander (8) via the inlet valve (61h) of the first regenerator hot flow stream, the hot side of the first regenerator (6), and the hot side of the second regenerator (7). The other path is connected to the inlet of the second expander (11) via the inlet valve (101h) of the third regenerator hot flow stream and the hot side of the third regenerator (10). The second expander (11) The outlet of the first expander (8) is connected to the inlet of the mixer (2) via the cold side of the second regenerator (7), the cold flow inlet valve (61c) of the first regenerator, and the cold side of the first regenerator (6). The outlet of the first expander (8) is connected to the inlet of the mixer (2) via the low temperature heat exchanger (9), the cold flow inlet valve (101c) of the third regenerator, the cold side of the third regenerator (10), and the first compressor (1). The outlet of the mixer (2) is connected to the inlet of the second compressor (3).

2. The two-stage compression transcritical carbon dioxide heat pump system according to claim 1, characterized in that, The cold side outlet of the second regenerator (7) is connected to the cold side outlet of the first regenerator (6) via the cold side bypass valve (62c) of the first regenerator.

3. The two-stage compression transcritical carbon dioxide heat pump system according to claim 2, characterized in that, The outlet of the distributor (5) is connected to the hot side outlet of the first regenerator (6) via the hot side bypass valve (62h) of the first regenerator.

4. The two-stage compression transcritical carbon dioxide heat pump system according to claim 3, characterized in that, The outlet of the splitter (5) is connected to the hot side outlet of the third regenerator (10) via the hot side bypass valve (102h) of the third regenerator.

5. The two-stage compression transcritical carbon dioxide heat pump system according to claim 4, characterized in that, The outlet of the low-temperature heat exchanger (9) is connected to the cold side outlet of the third regenerator (10) via the cold side bypass valve (102c) of the third regenerator.

6. The two-stage compression transcritical carbon dioxide heat pump system according to claim 5, characterized in that, The on / off states of the first regenerator hot flow inlet valve (61h) and the first regenerator hot side bypass valve (62h) are mutually exclusive.

7. The two-stage compression transcritical carbon dioxide heat pump system according to claim 5, characterized in that, The on / off states of the first regenerator cold flow inlet valve (61c) and the first regenerator cold side bypass valve (62c) are mutually exclusive.

8. The two-stage compression transcritical carbon dioxide heat pump system according to claim 5, characterized in that, The on / off states of the inlet valve (101h) of the third regenerator hot flow stream and the hot side bypass valve (102h) of the third regenerator are mutually exclusive.

9. The two-stage compression transcritical carbon dioxide heat pump system according to claim 5, characterized in that, The on / off states of the cold flow inlet valve (101c) of the third regenerator and the cold side bypass valve (102c) of the third regenerator are mutually exclusive.

10. A control method for the two-stage compression transcritical carbon dioxide heat pump system as described in claim 5, characterized in that, Includes the following steps: When supplying heat to the medium-high temperature zone, the hot flow inlet valve (61h) of the first regenerator is opened, connecting the hot side inlet of the first regenerator (6) with the distributor (5); the hot side bypass valve (62h) of the first regenerator is closed, disconnecting the hot side inlet of the second regenerator (7) from the distributor (5); the cold flow inlet valve (61c) of the first regenerator is opened, connecting the cold side inlet of the first regenerator (6) with the cold side outlet of the second regenerator (7); the cold side bypass valve (62c) of the first regenerator is closed, disconnecting the cold side outlet of the second regenerator (7) from the mixer (2). ; Control the opening of the hot flow inlet valve (101h) of the third regenerator, so that the hot side inlet of the third regenerator (10) is connected to the distributor (5); Control the closing of the hot side bypass valve (102h) of the third regenerator, so that the inlet of the second expander (11) is disconnected from the distributor (5); Control the opening of the cold flow inlet valve (101c) of the third regenerator, so that the cold side inlet of the third regenerator (10) is connected to the cold side outlet of the low-temperature heat exchanger (9); Control the closing of the cold side bypass valve (102c) of the third regenerator, so that the inlet of the first compressor (1) is disconnected from the cold side outlet of the low-temperature heat exchanger (9); When supplying heat to the medium and low temperature zone, the hot flow inlet valve (61h) of the first regenerator is closed, disconnecting the hot side inlet of the first regenerator (6) from the distributor (5); the hot side bypass valve (62h) of the first regenerator is opened, connecting the hot side inlet of the second regenerator (7) to the distributor (5); the cold flow inlet valve (61c) of the first regenerator is closed, disconnecting the cold side inlet of the first regenerator (6) from the cold side outlet of the second regenerator (7); the cold side bypass valve (62c) of the first regenerator is opened, connecting the cold side outlet of the second regenerator (7) to the mixer (2). ; Control the hot flow inlet valve (101h) of the third regenerator to close, so that the hot side inlet of the third regenerator (10) is disconnected from the distributor (5); Control the hot side bypass valve (102h) of the third regenerator to open, so that the inlet of the second expander (11) is connected to the distributor (5); Control the cold flow inlet valve (101c) of the third regenerator to close, so that the cold side inlet of the third regenerator (10) is disconnected from the cold side outlet of the low temperature heat exchanger (9); Control the cold side bypass valve (102c) of the third regenerator to open, so that the inlet of the first compressor (1) is connected to the cold side outlet of the low temperature heat exchanger (9).

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