Regenerative transcritical carbon dioxide two-stage compression system and control method

Abstract

The invention discloses a regenerative transcritical carbon dioxide two-stage compression system and a control method. A first outlet of a liquid storage tank of the system is connected with a cold side inlet of a first heat regenerator; the first heat regenerator is connected with working medium inlets of the second compressor and the third compressor through the first compressor and the precooler in sequence; working medium outlets of the second and third compressors are connected with a hot side inlet of the second heat regenerator through the air cooler; a hot side outlet of the second heat regenerator is connected with a working medium inlet of the flash tank through a first expansion valve; a cold side outlet of the second regenerator is connected with working medium inlets of the second and third compressors; a cold side inlet of the second heat regenerator is connected with a gas-phase working medium outlet of the flash tank; a liquid-phase working medium outlet of the flash tank is connected with a hot side inlet of the first heat regenerator; a hot side outlet of the first heat regenerator is connected with a first inlet of the liquid storage tank through a second expansion valve; and the liquid storage tank is connected with the ice rink coil pipe through a conveying pump. By introducing the low-pressure heat regenerator and the high-pressure heat regenerator, low-temperature carbon dioxide working medium energy is effectively recycled, and energy conservation and emission reduction are achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refrigeration and ice-making systems, in particular to the fields of industrial ice-making, cold chain transportation, food preservation and the like requiring efficient combined cooling and heating, and more particularly to a regenerative transcritical carbon dioxide two-stage compression system and control method. BACKGROUND

[0002] Carbon dioxide, as a natural refrigerant, has received widespread attention in the refrigeration field in recent years due to its environmental protection, non-toxicity and non-flammability. However, the traditional transcritical carbon dioxide refrigeration system has the following problems:

[0003] 1. Unbalanced cold and heat energy efficiency: In the transcritical cycle, the carbon dioxide gas is in a supercritical state in the gas cooler (so-called supercritical state refers to the state where the temperature and pressure of a substance are higher than the critical point, and the substance no longer has a liquid and gas state, but a uniform fluid state), and the heat release efficiency is low, resulting in low overall energy efficiency of the system.

[0004] 2. Large heat loss of low-temperature gas: The low-temperature gas flowing out of the low-pressure compressor outlet is usually not effectively utilized before entering the high-pressure compressor, resulting in energy waste.

[0005] Therefore, there is an urgent need to develop a technology that can solve the above technical problems. SUMMARY

[0006] The purpose of the present application is to provide a regenerative transcritical carbon dioxide two-stage compression system and control method to overcome the technical defects of the prior art.

[0007] To this end, the present application provides a regenerative transcritical carbon dioxide two-stage compression system, comprising a liquid storage tank, a first regenerator, a first compressor, a pre-cooler, a second compressor, a third compressor, a gas cooler, a second regenerator, a first expansion valve, a flash tank, a second expansion valve, a transport pump and an ice rink coil;

[0008] The first outlet a of the liquid storage tank is in communication with the cold side inlet b of the first regenerator;

[0009] The cold side outlet a of the first regenerator is in communication with the working medium inlet of the first compressor;

[0010] The working medium outlet of the first compressor is in communication with the working medium inlet of the pre-cooler;

[0011] The working medium outlet of the pre-cooler is in communication with the working medium inlet of the second compressor and the working medium inlet of the third compressor, respectively;

[0012] The working medium outlets of the second compressor and the third compressor are in communication with the working medium inlet of the gas cooler after converging and intersecting;

[0013] The working medium outlet of the gas cooler is connected with the hot side inlet c of the second regenerator;

[0014] The hot side outlet d of the second regenerator is connected with the working medium inlet b of the flash tank through the first expansion valve;

[0015] The cold side outlet a of the high-pressure regenerator is connected with the working medium inlet of the second compressor and the working medium inlet of the third compressor respectively;

[0016] The cold side inlet b of the second regenerator is connected with the gas phase working medium outlet c at the top of the flash tank;

[0017] The liquid phase working medium outlet a of the flash tank is connected with the hot side inlet c of the first regenerator;

[0018] The hot side outlet d of the first regenerator is connected with the first inlet b at the top of the liquid storage tank through the second expansion valve;

[0019] The second outlet c at the bottom of the liquid storage tank is connected with the working medium inlet of the transport pump;

[0020] The working medium outlet of the transport pump is connected with the working medium inlet of the ice rink coil;

[0021] The working medium outlet of the ice rink coil is connected with the second inlet d at the right end of the liquid storage tank.

[0022] In addition, the application also provides a control method of the regenerative transcritical carbon dioxide double-stage compression system as described above, which includes the following working modes:

[0023] Firstly, the low-pressure carbon dioxide working medium from the liquid storage tank is converted into a superheated state through the first regenerator, and then enters the first compressor to be compressed into a medium-low pressure state, and then is cooled through the pre-cooler and mixed with the high-pressure working medium flowing out from the second regenerator;

[0024] Then, the mixed carbon dioxide working medium enters the second compressor and the third compressor to be compressed into a high-temperature and high-pressure state, and then flows into the gas cooler to be cooled;

[0025] Then, the working medium cooled by the gas cooler enters the second regenerator for further cooling, and the working medium flowing out from the second regenerator enters the first expansion valve to be expanded and throttled to become medium-pressure working medium in a gas-liquid two-phase state, and then is introduced into the flash tank for gas-liquid separation to obtain gas phase working medium and liquid phase working medium, and then the gas phase working medium is output to the second regenerator, and the liquid phase working medium is output to the first regenerator;

[0026] Wherein, the gas phase working medium as the low temperature medium of the second regenerator is heated and then flows into the second compressor and the third compressor to be compressed into high temperature and high pressure working medium; then, the high temperature and high pressure working medium flowing out of the second compressor and the third compressor is cooled by the gas cooler and then enters the second regenerator to be cooled;

[0027] Wherein, the liquid phase working medium cooled by the first regenerator is throttled by the second expansion valve to become low pressure and low temperature liquid phase working medium;

[0028] Finally, the liquid phase working medium enters the liquid storage tank and is pumped into the ice rink coil by the transport pump to evaporate and absorb heat, so as to realize the refrigeration function and complete the whole cycle.

[0029] From the above technical scheme provided by the present application, compared with the prior art, the present application provides a regenerative transcritical carbon dioxide double-stage compression system and control method, which is scientific in design, effectively recovers the low temperature carbon dioxide working medium energy by introducing a low pressure regenerator and a high pressure regenerator, improves the overall energy efficiency of the system, and has great practical significance.

[0030] For the present application, a dynamic control strategy can be further combined to optimize the system operating state, so as to improve the cold and heat comprehensive energy efficiency of the carbon dioxide refrigeration system. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 A structure schematic view of a regenerative transcritical carbon dioxide double-stage compression system provided by the present application;

[0032] Figure 2 A control process schematic view of a regenerative transcritical carbon dioxide double-stage compression system provided by the present application in an embodiment;

[0033] In the figure, 1 is a liquid storage tank, 2 is a first regenerator (specifically a low pressure regenerator), 3 is a first compressor (specifically a low pressure stage compressor), 4 is a pre-cooler, 5 is a second compressor (specifically a high pressure stage compressor);

[0034] 6 is a third compressor (specifically a high pressure stage compressor), 7 is a gas cooler, 8 is a second regenerator (specifically a high pressure regenerator), 9 is a first expansion valve (specifically a high pressure expansion valve), and 10 is a flash tank;

[0035] 11 is a second expansion valve (specifically a low pressure expansion valve), 12 is a transport pump, and 13 is an ice rink coil. DETAILED DESCRIPTION

[0036] 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.

[0037] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0038] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0040] See Figure 1 , Figure 2 The present invention provides a regenerative transcritical carbon dioxide two-stage compression system, including a liquid storage tank 1, a first regenerator 2, a first compressor 3, a precooler 4, a second compressor 5, a third compressor 6, an air cooler 7, a second regenerator 8, a first expansion valve 9, a flash tank 10, a second expansion valve 11, a transport pump 12, and an ice rink coil 13.

[0041] The first outlet a of the liquid storage tank 1 is connected to the cold side inlet b of the first regenerator 2;

[0042] The cold side outlet a of the first regenerator 2 is connected to the working fluid inlet of the first compressor 3;

[0043] The working medium outlet of the first compressor 3 is communicated with the working medium inlet of the pre-cooler 4;

[0044] The working medium outlet of the pre-cooler 4 is communicated with the working medium inlets of the second compressor 5 and the third compressor 6 respectively;

[0045] The working medium outlets of the second compressor 5 and the third compressor 6 are communicated with the working medium inlet of the air cooler 7 after converging;

[0046] The working medium outlet of the air cooler 7 is communicated with the hot side inlet c of the second heat exchanger 8;

[0047] The hot side outlet d of the second heat exchanger 8 is communicated with the working medium inlet b of the flash tank 10 through the first expansion valve 9;

[0048] The cold side outlet a of the second heat exchanger 8 is communicated with the working medium inlets of the second compressor 5 and the third compressor 6 respectively;

[0049] The cold side inlet b of the second heat exchanger 8 is communicated with the gas phase working medium outlet c at the top of the flash tank 10;

[0050] The liquid phase working medium outlet a of the flash tank 10 is communicated with the hot side inlet c of the first heat exchanger 2;

[0051] The hot side outlet d of the first heat exchanger 2 is communicated with the first inlet b at the top of the liquid storage tank 1 through the second expansion valve 11;

[0052] The second outlet c at the bottom of the liquid storage tank 1 is communicated with the working medium inlet of the transport pump 12;

[0053] The working medium outlet of the transport pump 12 is communicated with the working medium inlet of the ice rink coil 13;

[0054] The working medium outlet of the ice rink coil 13 is communicated with the second inlet d at the right end of the liquid storage tank 1.

[0055] In the present application, the working medium of the system is carbon dioxide.

[0056] In the present application, the first compressor 3 is a low-pressure stage compressor, which is used to realize the pressure and temperature rising process of the carbon dioxide working medium on the low-pressure side and form high-temperature and high-pressure carbon dioxide working medium;

[0057] The second compressor 5 and the third compressor 6 are high-pressure stage compressors, which are used to realize the pressure and temperature rising process of the carbon dioxide working medium on the high-pressure side.

[0058] For example, the compressor with the exhaust pressure below 1 MPa is a low-pressure compressor, and the compressor with the exhaust pressure greater than 10 MPa is a high-pressure stage compressor.

[0059] In the present application, the first regenerator 2 is specifically a low-pressure regenerator (regenerator, also known as gas-liquid heat exchanger);

[0060] The second regenerator 8 is specifically a high-pressure regenerator;

[0061] It should be noted that the second regenerator 8 as a high-pressure regenerator is located in front of the first expansion valve 9 (specifically a high-pressure expansion valve) in the flow path of the working medium;

[0062] The first regenerator 2 is a low-pressure regenerator, which is located in front of the first compressor 3 (i.e. low-pressure stage compressor) in the flow path of the working medium.

[0063] The first regenerator 2 is used to cool the working medium entering the first compressor 3 (i.e. low-pressure stage compressor);

[0064] The second regenerator 8 is used to cool the working medium entering the second compressor 5 and the third compressor 6 (i.e. two high-pressure stage compressors).

[0065] In the present application, the pressure of the working medium in the second regenerator 8 (high-pressure regenerator) is greater than the pressure of the working medium in the first regenerator 2 (low-pressure regenerator).

[0066] In the present application, the first expansion valve 9 is specifically a high-pressure expansion valve;

[0067] The second expansion valve 11 is specifically a low-pressure expansion valve.

[0068] It should be noted that the first expansion valve 9 is a high-pressure expansion valve, which is the first expansion valve connected after the working medium passes through the two high-pressure stage compressors (second compressor 5 and third compressor 6);

[0069] The second expansion valve 11 is a low-pressure expansion valve, which is the second expansion valve connected after the working medium passes through the two high-pressure stage compressors (second compressor 5 and third compressor 6).

[0070] Specifically, the pressure of the working medium in the first expansion valve 9 is greater than the pressure of the working medium in the second expansion valve 11.

[0071] In the present application, the ice rink coil 13 is specifically a core heat exchange component of a traditional ice rink refrigeration system, which is located below the ice surface of the ice rink and is a hollow metal pipe (mostly copper pipe or steel pipe) located below the ice surface of the ice rink. It is a common component of the traditional ice rink refrigeration system, which will not be described here.

[0072] Specifically, the ice rink coil 13 is a metal pipe coiled and distributed below the ice surface of the ice rink, with its upper surface contacting the ice surface of the ice rink.

[0073] In the present application, specifically, any two intercommunicating devices are connected through a hollow connecting pipeline.

[0074] In order to more clearly understand the technical solutions of the present application, the functions of the main components in the present application and the working principle of mutual cooperation are described below.

[0075] The liquid storage tank 1 is used to collect the carbon dioxide working medium that has absorbed heat in the ice rink after flowing through the ice rink coil 13, and transport it to the first regenerator 2;

[0076] The first regenerator 2 is used to cool the working medium flowing out of the liquid storage tank 1 by using the working medium flowing out of the flash tank 10;

[0077] The first compressor 3 is used to compress the working medium from the first regenerator 2 and deliver it to the pre-cooler 4;

[0078] The pre-cooler 4 is used to cool the working medium from the first compressor 3 and deliver it to the second compressor 5 and the third compressor 6;

[0079] The second compressor 5 and the third compressor 6 are both used to compress the working medium from the pre-cooler 4 and deliver it to the air cooler 7;

[0080] The air cooler 7 is used to cool the working medium from the second compressor 5 and the third compressor 6 and deliver it to the second regenerator 8;

[0081] The second regenerator 8 is used to cool the working medium that needs to enter the second compressor 5 and the third compressor 6 in advance by using the working medium from the air cooler 7;

[0082] The first expansion valve 9 is used to expand, depressurize and cool the working medium from the first regenerator 8;

[0083] The flash tank 10 is used to separate the working medium from the first expansion valve 9 into gas and liquid, wherein the working medium gas enters the first regenerator 8 and the working medium liquid enters the second regenerator 2;

[0084] The second expansion valve 11 is used to expand, depressurize and cool the working medium from the second regenerator 2 and continue to deliver the working medium to the liquid storage tank 1;

[0085] The transport pump 12 is used to transport the working medium from the liquid storage tank to the ice rink coil 13;

[0086] The ice rink coil 13 is used to absorb heat in the ice rink for the working medium flowing therethrough from the transport pump 12, and deliver the working medium after absorbing heat to the liquid storage tank 1.

[0087] It should be noted that the ice rink refers to a flat ice surface venue formed by artificial refrigeration or natural low temperature for ice skating, ice hockey, figure skating and other sports activities, or as a low-temperature environment for commercial entertainment and industrial use. The ice rink coil 13 is the core heat exchange component of the traditional ice rink refrigeration system, usually refers to the metal pipe (mostly copper pipe or steel pipe) laid under the ice surface of the ice rink, which exchanges heat with the ice surface of the ice rink through the circulating low-temperature refrigerant (such as carbon dioxide, or ethylene glycol solution, brine) to maintain the frozen state of the ice surface of the ice rink.

[0088] Based on the above-mentioned regenerative transcritical carbon dioxide two-stage compression system provided by the application, the application further provides a control method of the regenerative transcritical carbon dioxide two-stage compression system, which includes the following working modes:

[0089] Firstly, the low-pressure carbon dioxide working medium from the liquid storage tank 1 is converted into a superheated state by the first regenerator 2, and then enters the first compressor 3 to be compressed to a medium-low pressure state. Then, the carbon dioxide working medium is cooled by the pre-cooler 4 and mixed with the high-pressure working medium flowing out of the second regenerator 8.

[0090] Then, the mixed carbon dioxide working medium enters the second compressor 5 and the third compressor 6, and is compressed to a high-temperature and high-pressure state (at this time, the working medium has the highest temperature and pressure in the system) in the second compressor 5 and the third compressor 6, and then flows into the gas cooler 7 for cooling.

[0091] Then, the working medium cooled by the gas cooler 7 enters the second regenerator 8 for further cooling, and the working medium flowing out of the second regenerator 8 enters the first expansion valve 9 to be expanded and throttled, becomes medium-pressure working medium in gas-liquid two-phase state, and then enters the flash tank 10 for gas-liquid separation to obtain gas-phase working medium and liquid-phase working medium. Then, the gas-phase working medium is output to the second regenerator 8, and the liquid-phase working medium is output to the first regenerator 2.

[0092] Among them, the gas-phase working medium acts as the low-temperature medium of the second regenerator 8, is heated and then flows into the second compressor 5 and the third compressor 6 to be compressed to high-temperature and high-pressure working medium. Then, the high-temperature and high-pressure working medium flowing out of the second compressor 5 and the third compressor 6 is cooled by the gas cooler 7 and then enters the second regenerator 8 for cooling.

[0093] It should be noted that the gas-phase working medium acts as the low-temperature medium of the second regenerator 8, and the liquid-phase working medium acts as the high-temperature medium of the first regenerator 2 and is cooled.

[0094] Among them, the liquid-phase working medium cooled by the first regenerator 2 enters the second expansion valve 11 to be depressurized and throttled, becoming low-pressure and low-temperature liquid-phase working medium.

[0095] Finally, the liquid-phase working medium is introduced into the liquid storage tank 1 and pumped into the ice rink coil 13 by the transport pump 12 to evaporate and absorb heat, so as to realize the refrigeration function and complete the whole cycle.

[0096] In order to more clearly understand the technical solutions of the present application, refer to Figure 2 The technical solutions of the present application will be described below in combination with specific embodiments.

[0097] For the regenerative transcritical carbon dioxide double-stage compression system provided by the present application, the control working process can include the following three stages:

[0098] In the first stage, system starting and initialization: when the system starts, the components are first initialized and detected to ensure normal operation. Then, according to the preset environmental temperature, evaporation temperature and gas cooler outlet temperature and other parameters, the rotation speed of the first compressor 3 (specifically a low-pressure stage compressor), the rotation speed of the second compressor 5 and the third compressor 6 (two high-pressure stage compressors), the outlet temperature of the gas cooler 7, the opening degree of the second expansion valve 11 (specifically a low-pressure expansion valve) and the opening degree of the first expansion valve 9 (specifically a high-pressure expansion valve) are adjusted, so that the system enters an initial running state;

[0099] In the second stage, running parameter monitoring and adjustment: during the system running process, the key parameters of the system are monitored in real time, such as the back pressure of the flash tank 10, the liquid level of the liquid storage tank 1, the maximum running pressure of the system, the unit working medium refrigerating capacity, the compressor power consumption and the COP, etc. According to the monitored parameter changes, the rotation speed of the first compressor 3 (specifically a low-pressure stage compressor), the rotation speed of the second compressor 5 and the third compressor 6 (two high-pressure stage compressors), the outlet temperature of the gas cooler 7, the opening degree of the second expansion valve 11 (specifically a low-pressure expansion valve) and the opening degree of the first expansion valve (specifically a high-pressure expansion valve) are dynamically adjusted in real time, so that the system COP reaches the maximum value to optimize the system performance;

[0100] In the third stage, optimal running state maintenance: through further data analysis and modeling, the optimal running parameter combination of the system under different working conditions can be determined. In actual operation, according to the real-time monitoring data, the system parameters are adjusted, so that the system can quickly adapt to external load changes and always maintain the optimal running state (so that the system COP returns to the maximum value).

[0101] It should be noted that for the system of the present application, a closed-loop control strategy is adopted, the performance parameters of the system are monitored in real time (the real-time monitored parameters include the compressor outlet temperature, the gas cooler outlet temperature, the liquid level of the liquid storage tank, the system pressure and the load change), and then the performance parameters are feedback adjusted according to the energy efficiency index (such as COP), so as to ensure that the system always runs in the optimal state (so that the system COP remains the maximum value).

[0102] Example 1

[0103] The heat recovery transcritical carbon dioxide double-stage compression system is started under the condition that the ambient temperature is 15℃ and the evaporation temperature is -18.5℃.

[0104] At the beginning, the opening of the first expansion valve 9 (specifically a high-pressure expansion valve) is set to 50%, and the outlet temperature of the gas cooler 7 is set to 35℃.

[0105] After the system is operated, the back pressure of the flash tank 10, the highest operating pressure of the system, the unit refrigerant capacity, the compressor power consumption and the coefficient of performance (COP) are monitored in real time. Then, according to the monitoring data, the opening of the first expansion valve and the outlet temperature of the gas cooler 7 are dynamically adjusted.

[0106] When the COP of the system reaches the maximum value of 2.36 (at this time, the system is in the optimal operating state under the above environmental conditions), the back pressure of the flash tank 10 at this time is recorded as 4.18 MPa, the opening of the first expansion valve 9 is set to 47.6%, and the outlet temperature of the gas cooler 7 is set to 28℃. In subsequent operation, when it is monitored that the system deviates from the optimal operating state, the related parameters are automatically adjusted to make it return to the optimal operating state (that is, to make the COP of the system return to the maximum value of 2.36).

[0107] Example 2

[0108] The heat recovery transcritical carbon dioxide double-stage compression system is started under the condition that the ambient temperature is 15℃ and the evaporation temperature is -18℃.

[0109] At the beginning, the opening of the first expansion valve 9 (specifically a high-pressure expansion valve) is set to 50%, and the outlet temperature of the gas cooler 7 is set to 35℃.

[0110] After the system is operated, the back pressure of the flash tank 10, the highest operating pressure of the system, the unit refrigerant capacity, the compressor power consumption and the COP are monitored in real time. Then, according to the monitoring data, the opening of the high-pressure expansion valve and the outlet temperature of the gas cooler are dynamically adjusted.

[0111] When the COP of the system reaches the maximum value of 2.61 (at this time, the system is in the optimal operating state under the above environmental conditions), the back pressure of the flash tank 10 at this time is recorded as 4.52 MPa, the opening of the first expansion valve 9 is set to 54.3%, and the outlet temperature of the gas cooler 7 is set to 30℃. In subsequent operation, when it is monitored that the system deviates from the optimal operating state, the related parameters are automatically adjusted to make it return to the optimal operating state (that is, to make the COP of the system return to the maximum value of 2.61).

[0112] In summary, for the regenerative transcritical carbon dioxide two-stage compression system of the application, by introducing a regenerator and optimizing the control strategy, the deficiencies of the existing system in terms of cold and heat comprehensive energy efficiency are solved. In addition, the system of the application also has good adaptability and flexibility, and can automatically adjust the operating parameters according to different working conditions to achieve efficient and stable refrigeration effect.

[0113] Through testing, the application of the application can improve the energy efficiency and adaptability to variable working conditions of the existing carbon dioxide ice making system. The application provides a transcritical carbon dioxide multi-connected ejection ice making system and control method based on dynamic optimal operating pressure. By adjusting the speed of the low-pressure stage compressor and the high-pressure stage compressor, the outlet temperature of the air cooler, and the opening degree of the low-pressure expansion valve and the high-pressure expansion valve, the ice making system is operated at the dynamic optimal operating pressure, thereby improving the cold and heat comprehensive energy utilization efficiency of the ice making system in a wide working area. The calculation method of the cold and heat comprehensive energy utilization efficiency is: (refrigerating capacity + heat recovery capacity) / power consumption.

[0114] In summary, compared with the prior art, the application provides a regenerative transcritical carbon dioxide two-stage compression system and control method, which is designed scientifically. The application effectively recovers the energy of low-temperature carbon dioxide working medium by introducing a low-pressure regenerator and a high-pressure regenerator, thereby achieving energy saving and emission reduction, and having great practical significance.

[0115] For the application, a dynamic control strategy is further combined to optimize the system operating state, thereby improving the cold and heat comprehensive energy efficiency of the carbon dioxide refrigeration system.

[0116] The above description is only the preferred embodiments of the application, and it should be pointed out that for ordinary skilled persons in the art, without departing from the principles of the application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the application.

Claims

1. A recuperated transcritical carbon dioxide two-stage compression system, characterized by, The system comprises a liquid storage tank (1), a first regenerator (2), a first compressor (3), a pre-cooler (4), a second compressor (5), a third compressor (6), an air cooler (7), a second regenerator (8), a first expansion valve (9), a flash tank (10), a second expansion valve (11), a transport pump (12) and an ice rink coil (13). A first outlet a of the liquid storage tank (1) is connected to a cold side inlet b of the first regenerator (2). A cold side outlet a of the first regenerator (2) is connected to a working medium inlet of the first compressor (3). A working medium outlet of the first compressor (3) is connected to a working medium inlet of the pre-cooler (4). A working medium outlet of the pre-cooler (4) is connected to working medium inlets of the second compressor (5) and the third compressor (6) respectively. Working medium outlets of the second compressor (5) and the third compressor (6) are connected to a working medium inlet of the air cooler (7) after converging. A working medium outlet of the air cooler (7) is connected to a hot side inlet c of the second regenerator (8). A hot side outlet d of the second regenerator (8) is connected to a working medium inlet b of the flash tank (10) through the first expansion valve (9). A cold side outlet a of the high-pressure regenerator (8) is connected to working medium inlets of the second compressor (5) and the third compressor (6) respectively. A cold side inlet b of the second regenerator (8) is connected to a gas phase working medium outlet c at the top of the flash tank (10). A liquid phase working medium outlet a of the flash tank (10) is connected to a hot side inlet c of the first regenerator (2). A hot side outlet d of the first regenerator (2) is connected to a first inlet b at the top of the liquid storage tank (1) through the second expansion valve (11). A second outlet c at the bottom of the liquid storage tank (1) is connected to a working medium inlet of the transport pump (12). A working medium outlet of the transport pump (12) is connected to a working medium inlet of the ice rink coil (13). A working medium outlet of the ice rink coil (13) is connected to a second inlet d at the right end of the liquid storage tank (1).

2. The recuperated transcritical carbon dioxide two-stage compression system of claim 1, wherein, The working medium of the system is carbon dioxide.

3. The recuperated transcritical carbon dioxide two-stage compression system of claim 1, wherein, The first compressor (3) is a low-pressure stage compressor. The second compressor (5) and the third compressor (6) are high-pressure stage compressors.

4. The recuperated transcritical carbon dioxide two-stage compression system of claim 3, wherein, The low-pressure compressor is a compressor with an exhaust pressure below 1 MPa. The high-pressure stage compressor is a compressor with an exhaust pressure greater than 10 MPa.

5. The recuperated transcritical carbon dioxide two-stage compression system of claim 1, wherein, The pressure of the working medium in the second regenerator (8) is greater than the pressure of the working medium in the first regenerator (2).

6. The recuperated transcritical carbon dioxide two-stage compression system of claim 1, wherein, The pressure of the working medium in the first expansion valve (9) is greater than the pressure of the working medium in the second expansion valve (11).

7. The recuperated transcritical carbon dioxide two-stage compression system of claim 1, wherein, The ice rink coil (13) is a hollow metal pipe located below the ice surface of the ice rink, with its upper surface contacting the ice surface of the ice rink.

8. A control method of a recuperated transcritical carbon dioxide two-stage compression system according to any one of claims 1 to 7, characterized in that, The system comprises the following working modes: First, the low-pressure carbon dioxide working medium from the liquid storage tank (1) is converted into a superheated state through the first regenerator (2), and then enters the first compressor (3) to be compressed to a medium-low pressure state, and then cools through the pre-cooler (4) and mixes with the high-pressure working medium flowing out of the second regenerator (8); Then, the mixed carbon dioxide working medium enters the second compressor (5) and the third compressor (6), is compressed into a high-temperature and high-pressure state in the second compressor (5) and the third compressor (6), and then flows into the gas cooler (7) to be cooled; Then, the working medium cooled by the gas cooler (7) enters the second regenerator (8) to be further cooled, the working medium flowing out of the second regenerator (8) enters the first expansion valve (9) to be expanded and throttled, becomes medium-pressure working medium in a gas-liquid two-phase state, is introduced into the flash tank (10) to be gas-liquid separated, and obtains gas-phase working medium and liquid-phase working medium, then the gas-phase working medium is output to the second regenerator (8), and the liquid-phase working medium is output to the first regenerator (2); Wherein, the gas-phase working medium is taken as low-temperature medium of the second regenerator (8), is heated, and then flows into the second compressor (5) and the third compressor (6) to be compressed into high-temperature and high-pressure working medium; subsequently, the high-temperature and high-pressure working medium flowing out of the second compressor (5) and the third compressor (6) is cooled by the gas cooler (7), enters the second regenerator (8) to be cooled; Wherein, the liquid-phase working medium cooled by the first regenerator (2) is introduced into the second expansion valve (11) to be decompressed and throttled, and becomes low-pressure and low-temperature liquid-phase working medium; Finally, the liquid-phase working medium is introduced into the liquid storage tank (1), is pumped into the ice rink coil (13) by the delivery pump (12) to be evaporated and absorb heat, so as to realize the refrigeration function, and the whole cycle is completed.

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