CO2 single-machine two-stage refrigeration system and regulation method

Abstract

The application relates to the refrigeration technical field and discloses a CO2 single-machine two-stage refrigeration system and a regulation and control method. The refrigeration system comprises a single-machine two-stage compressor, a staged condenser, an economizer, a first throttling element, a second throttling element and an evaporator. The staged condenser comprises a cooling medium flow path, a first-stage precooling flow path and a second-stage cooling flow path, and the economizer comprises a supercooling channel and a gas supplement channel. The first-stage exhaust port of the single-machine two-stage compressor is communicated with the first-stage precooling flow path, and CO2 output by the first-stage precooling flow path and CO2 output by the gas supplement channel are combined and then enter a second-stage suction port; CO2 output by the second-stage cooling flow path is divided into a first branch and a second branch, the first branch enters the evaporator through the supercooling channel of the economizer and the second throttling element, and the second branch enters the gas supplement channel through the first throttling element. Therefore, the first-stage exhaust gas can be precooled, the supercooling and intermediate gas supplement can be realized by using the economizer, the two-stage compression heat load can be reduced, and the system refrigeration efficiency and operation reliability can be improved.

Description

Technical Field

[0001] This invention relates to the field of refrigeration technology, and in particular to a single-unit two-stage CO2 refrigeration system and its control method. Background Technology

[0002] CO2 (R744), as a natural refrigerant, is increasingly being used in high and low temperature chambers, refrigeration and freezing systems, and industrial refrigeration equipment. In refrigeration scenarios that require coverage of a wide temperature range or the achievement of low evaporation temperatures, CO2 refrigeration systems often need to operate at high discharge pressures, and compression efficiency and heat dissipation capacity have a significant impact on the overall performance of the system.

[0003] Currently, most CO2 cryogenic refrigeration equipment uses cascade refrigeration systems. A typical cascade system consists of two relatively independent refrigeration cycles: a cryogenic stage and a high-temperature stage. The cryogenic stage uses CO2 as the refrigerant, while the high-temperature stage uses other refrigerants. The two stages are coupled through an intermediate heat exchanger to achieve cryogenic refrigeration in a relay manner.

[0004] However, cascade refrigeration systems require two compressors, heat exchangers, throttling elements, piping, and control components, resulting in complex circuits and consequently large system size and high manufacturing and installation costs. Therefore, using a single CO2 refrigeration cycle to achieve low-temperature or wide-temperature-range operation would simplify the system structure.

[0005] However, in a single CO2 refrigeration cycle, if a single-stage compression method is used to meet the requirements of lower temperature or wide temperature range operation, it is easy to have a large pressure ratio and high exhaust temperature. If a two-stage compression method is used, although it can reduce the burden of single-stage compression, if the refrigerant after the first stage compression is not effectively cooled before entering the second stage compression, it will still lead to high second-stage suction temperature and second-stage exhaust temperature.

[0006] Therefore, there is an urgent need to provide a single-unit two-stage CO2 refrigeration system that can simplify the structure of the cascade system and take into account the first-stage exhaust precooling, the second-stage compression cooling, and the improvement of the system's refrigeration efficiency. Summary of the Invention

[0007] One objective of this invention is to provide a single-unit two-stage CO2 refrigeration system to simplify the refrigeration system structure, reduce the heat load of the second-stage compression, and improve the system's refrigeration efficiency.

[0008] To achieve this objective, the present invention adopts the following technical solution: This invention provides a single-unit two-stage CO2 refrigeration system, comprising a single-unit two-stage compressor with a first-stage suction port, a first-stage discharge port, a second-stage suction port, and a second-stage discharge port; a staged condenser including a cooling medium flow path, a first-stage precooling flow path, and a second-stage cooling flow path, and having a first-stage precooling inlet and a first-stage precooling outlet connected to the first-stage precooling flow path, and a second-stage cooling inlet and a second-stage cooling outlet connected to the second-stage cooling flow path, wherein the cooling medium flow path is configured to exchange heat with the first-stage precooling flow path and the second-stage cooling flow path respectively; an economizer including a subcooling channel and a make-up gas channel for mutual heat exchange; and a first throttling device. The system comprises an element, a second throttling element, and an evaporator; wherein the primary exhaust port is connected to the primary precooling inlet, the primary precooling outlet and the outlet of the make-up air channel merge at a confluence point, and the confluence point is connected to the secondary intake port; the secondary exhaust port is connected to the secondary cooling inlet, and the secondary cooling outlet is connected to a first branch and a second branch respectively; the first branch is connected to the inlet of the evaporator via the subcooling channel and the second throttling element, and the outlet of the evaporator is connected to the primary intake port; the second branch is connected to the inlet of the make-up air channel via the first throttling element.

[0009] Optionally, the staged condenser includes a heat exchange core, and the cooling medium flow path, the primary precooling flow path, and the secondary cooling flow path are all formed within the heat exchange core; the cooling medium flow path passes through the heat exchange core, and the primary precooling flow path and the secondary cooling flow path are isolated from each other; the staged condenser also has a cooling medium inlet and a cooling medium outlet, and both the cooling medium inlet and the cooling medium outlet are connected to the cooling medium flow path.

[0010] Optionally, the economizer includes an economizer body, a subcooling inlet, a subcooling outlet, a make-up gas inlet, and a make-up gas outlet; the subcooling channel and the make-up gas channel are both located within the economizer body and are isolated from each other and heat exchanged; the subcooling inlet and the subcooling outlet are respectively connected to the subcooling channel, and the make-up gas inlet and the make-up gas outlet are respectively connected to the make-up gas channel.

[0011] Optionally, the CO2 single-unit two-stage refrigeration system further includes a first detection component and a controller; the first detection component is disposed at the outlet of the gas supply channel, and / or disposed between the outlet of the gas supply channel and the confluence; the first detection component is used to detect gas supply status parameters, the gas supply status parameters including gas supply temperature and gas supply pressure; the controller is communicatively connected to the first detection component and controllably connected to the first throttling element, the controller being configured to adjust the opening of the first throttling element according to the gas supply status parameters, so that the CO2 flowing out of the gas supply channel is in a superheated state.

[0012] Optionally, the CO2 single-unit two-stage refrigeration system further includes a second pressure detection element; the second pressure detection element is disposed on the outlet side of the second throttling element and is used to detect the pressure on the outlet side of the second throttling element; the controller is also communicatively connected to the second pressure detection element and control-connected to the second throttling element, and the controller is configured to adjust the opening of the second throttling element according to the detection result of the second pressure detection element so that the pressure on the outlet side of the second throttling element is not lower than a preset pressure.

[0013] Optionally, the CO2 single-unit two-stage refrigeration system further includes a mixing chamber, which is located in the upstream pipeline of the secondary suction port. The mixing chamber has a first inlet, a second inlet, and a mixing outlet. The first inlet is connected to the outlet of the primary precooling flow path, the second inlet is connected to the outlet of the make-up gas channel, and the mixing outlet is connected to the secondary suction port.

[0014] Optionally, the mixing chamber includes a filter, the filter includes a filter housing, the mixing chamber is formed inside the filter housing, the first inlet, the second inlet and the mixing outlet are all disposed in the filter housing and are all in communication with the mixing chamber.

[0015] Optionally, the CO2 single-unit two-stage refrigeration system further includes a second detection component, which is disposed at the mixing outlet of the mixing chamber or between the mixing outlet and the secondary intake port; the second detection component is used to detect the CO2 temperature and CO2 pressure before entering the secondary intake port.

[0016] Another objective of this invention is to provide a control method for a single-unit two-stage CO2 refrigeration system, which can adjust the opening degree of the first throttling element and the second throttling element to improve the stability of system operation.

[0017] To achieve this objective, the present invention adopts the following technical solution: This invention also provides a control method for a CO2 single-unit two-stage refrigeration system, which is applied to the CO2 single-unit two-stage refrigeration system. The control method includes: obtaining the gas supply temperature and gas supply pressure at the outlet of the gas supply channel and / or between the outlet of the gas supply channel and the confluence point; determining the saturation temperature of CO2 based on the gas supply pressure; determining the gas supply superheat based on the difference between the gas supply temperature and the saturation temperature; and adjusting the opening of the first throttling element based on the gas supply superheat to ensure that the gas supply superheat is not less than a preset superheat.

[0018] Optionally, the pressure at the outlet side of the second throttling element is obtained; the opening of the second throttling element is adjusted according to the pressure at the outlet side of the second throttling element so that the pressure at the outlet side of the second throttling element is not lower than a preset pressure.

[0019] Beneficial effects: The present invention provides a single-unit two-stage CO2 refrigeration system, which adopts a single CO2 refrigerant circuit and a single-unit two-stage compressor, and uses a staged condenser to achieve first-stage exhaust precooling and second-stage exhaust cooling. At the same time, an economizer is used to achieve subcooling and intermediate gas injection. This simplifies the system structure, reduces the heat load of the second-stage compression, and improves the system's refrigeration efficiency and operational reliability.

[0020] The present invention provides a control method for a single-unit two-stage CO2 refrigeration system. By determining the superheat of the supplementary gas based on the supplementary gas temperature and pressure, and adjusting the opening of the first throttling element according to the superheat of the supplementary gas, the superheat of the supplementary gas is not less than the preset superheat, thereby keeping the supplementary CO2 in a superheated state, reducing the risk of liquid entering the secondary suction port of the supplementary gas, and improving the reliability of system operation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the refrigeration circuit of a CO2 single-unit two-stage refrigeration system according to an embodiment of the present invention; Figure 2 This is a schematic flowchart of a control method for a CO2 single-unit two-stage refrigeration system according to an embodiment of the present invention.

[0022] In the picture: 1. Single-unit two-stage compressor; 101. First-stage suction port; 102. First-stage discharge port; 103. Second-stage suction port; 104. Second-stage discharge port; 2. Stage condenser; 3. Economizer; 4. First throttling element; 5. Second throttling element; 6. Evaporator; 7. Oil separator; 8. Liquid receiver; 9. Dryer filter; 10. Sight glass; 11. Gas-liquid separator; 21. Cooling medium inlet; 22. Cooling medium outlet; 23. Primary precooling inlet; 24. Primary precooling outlet; 25. Secondary cooling inlet; 26. Secondary cooling outlet; 31. Subcooled inlet; 32. Subcooled outlet; 33. Make-up gas inlet; 34. Make-up gas outlet. Detailed Implementation

[0023] Exemplary embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that these specific descriptions are for teaching those skilled in the art how to implement the invention, and are not intended to exhaustively describe all possible embodiments of the invention, nor to limit the scope of the invention.

[0024] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0025] Embodiments of the present invention provide a single-unit, two-stage CO2 refrigeration system, which will sometimes be referred to simply as a "refrigeration system" below. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] It should be noted that, Figure 1 The middle arrow schematically indicates the flow direction of CO2 refrigerant in the refrigerant circuit. The working medium circulating in the refrigerant circuit is CO2 (R744) refrigerant.

[0027] like Figure 1 As shown, the CO2 single-unit two-stage refrigeration system provided in this embodiment includes a refrigerant circuit for the circulation of CO2 refrigerant. The refrigerant circuit includes a single-unit two-stage compressor 1, a staged condenser 2, an economizer 3, a first throttling element 4, a second throttling element 5, and an evaporator 6. The single-unit two-stage compressor 1 has a first-stage suction port 101, a first-stage discharge port 102, a second-stage suction port 103, and a second-stage discharge port 104. In this embodiment, the first-stage compression section and the second-stage compression section of the single-unit two-stage compressor 1 are integrated into the same compressor body.

[0028] The staged condenser 2 includes a cooling medium flow path, a primary precooling flow path, and a secondary cooling flow path. It is equipped with a primary precooling inlet 23 and a primary precooling outlet 24 connected to the primary precooling flow path, and a secondary cooling inlet 25 and a secondary cooling outlet 26 connected to the secondary cooling flow path. The cooling medium flow path is configured to exchange heat with both the primary and secondary cooling flow paths. The economizer 3 includes a subcooling channel and a make-up gas channel for mutual heat exchange. The primary exhaust port 102 is connected to the primary precooling inlet 23. The primary precooling outlet 24 and the outlet of the make-up gas channel merge at a confluence point, which then connects to the secondary suction port 103. The secondary exhaust port 104 is connected to the secondary cooling inlet 25. The secondary cooling outlet 26 is connected to a first branch and a second branch. The first branch connects to the inlet of the evaporator 6 via the subcooling channel of the economizer 3 and the second throttling element 5. The outlet of the evaporator 6 connects to the primary suction port 101. The second branch connects to the inlet of the make-up gas channel via the first throttling element 4.

[0029] During operation, the low-temperature, low-pressure CO2 output from the evaporator 6 enters the single-unit two-stage compressor 1 through the primary suction port 101, where it undergoes primary compression. The CO2 after primary compression is discharged through the primary discharge port 102 and enters the primary pre-cooling flow path of the staged condenser 2 through the primary pre-cooling inlet 23. The primary pre-cooling flow path exchanges heat with the cooling medium flow path, pre-cooling the CO2 after primary compression. The pre-cooled CO2 flows out through the primary pre-cooling outlet 24 and merges with the CO2 flowing out of the economizer 3's make-up gas channel outlet at the confluence point before entering the secondary suction port 103 of the single-unit two-stage compressor 1.

[0030] Understandably, the primary precooling flow path precools the CO2 after primary compression and controls the degree of primary precooling to keep the CO2 in a gaseous state after primary precooling. The degree of primary precooling can be set according to the primary exhaust pressure and the corresponding saturation temperature of CO2 at that pressure.

[0031] The CO2, after two-stage compression, is discharged from the secondary exhaust port 104 and enters the secondary cooling flow path of the staged condenser 2 through the secondary cooling inlet 25, where it exchanges heat with the cooling medium flow path. The cooled CO2 flows out from the secondary cooling outlet 26 and splits into a first branch and a second branch. The first branch enters the subcooling channel of the economizer 3, where it exchanges heat with the CO2 in the make-up gas channel for further cooling. It then passes through the second throttling element 5 and enters the evaporator 6, where it absorbs heat and evaporates, achieving refrigeration. The second branch passes through the first throttling element 4 and enters the make-up gas channel, where it absorbs heat from the CO2 on the subcooling channel side. It then flows out from the make-up gas channel outlet and merges with the CO2 flowing out of the primary precooling outlet 24 at the confluence point before entering the secondary suction port 103.

[0032] Through the above configuration, this embodiment uses a single CO2 refrigerant loop to achieve two-stage compression refrigeration, which reduces the number of high-temperature stage cycles, low-temperature stage cycles, and corresponding pipelines and control components in the cascade system, thereby reducing the system's structural complexity. Furthermore, the CO2 after the first-stage compression is pre-cooled before merging with the make-up gas and entering the second-stage suction port 103, which helps to reduce the second-stage suction temperature and the second-stage discharge temperature, improving the operational reliability of the single-unit two-stage compressor 1. Simultaneously, the first branch is further subcooled in the economizer 3 before entering the evaporator 6, which helps to increase the subcooling degree of the CO2 before entering the evaporator 6, increasing the refrigeration capacity per unit mass of refrigerant, thereby improving the system's refrigeration efficiency.

[0033] Furthermore, in this embodiment, since a single-unit two-stage compressor 1 is used, the two-stage compression function is integrated into one compressor. Compared with the scheme of using two independent compressors in series, the number of compressors, connecting pipelines and installation space are further reduced, making the system structure more compact.

[0034] Optionally, in this embodiment, as Figure 1As shown, an oil separator 7 is installed between the secondary discharge port 104 and the secondary cooling inlet 25 of the single-unit two-stage compressor 1. The oil separator 7 is used to separate the lubricating oil in the secondary compression discharge. A liquid receiver 8, a dryer filter 9, and a sight glass 10 can also be installed sequentially between the secondary cooling outlet 26 and the economizer 3. Among them, the liquid receiver 8 is used to temporarily store CO2 cooled by the secondary cooling flow path to buffer refrigerant flow fluctuations; the dryer filter 9 is used to remove moisture and impurities in the refrigerant circuit; and the sight glass 10 is used to observe the refrigerant flow status. A gas-liquid separator 11 can be installed between the outlet of the evaporator 6 and the primary suction port 101 to reduce the risk of liquid CO2 entering the primary suction port 101.

[0035] It should be noted that the oil separator 7, liquid reservoir 8, dryer filter 9, sight glass 10 and gas-liquid separator 11 can all adopt common structures in the field, and will not be described in detail here.

[0036] Optionally, in this embodiment, the design pressure of the refrigeration system can be 90 MPa to meet the operating requirements of CO2 refrigerant under high pressure conditions.

[0037] Furthermore, the staged condenser 2 includes a heat exchange core. A cooling medium flow path, a primary pre-cooling flow path, and a secondary cooling flow path are all formed within this heat exchange core. The cooling medium flow path penetrates the heat exchange core and is respectively configured to exchange heat with the primary pre-cooling flow path and the secondary cooling flow path. Both the primary pre-cooling flow path and the secondary cooling flow path are refrigerant flow paths for CO2 refrigerant, and they are isolated from each other. In this way, the CO2 on the primary exhaust side and the CO2 on the secondary exhaust side can complete heat exchange separately within the same heat exchange core, without directly mixing within the staged condenser 2.

[0038] Specifically, the cooling medium flow path can be used for cooling water or other cooling media. When the cooling medium flows within the heat exchange core, it can exchange heat with the primary pre-cooling flow path and the secondary cooling flow path simultaneously or in sections.

[0039] In one embodiment, the staged condenser 2 can be a plate heat exchanger. The cooling medium flow path is a cooling water flow path that runs through the plate heat exchanger, and the primary precooling flow path and the secondary cooling flow path are two mutually isolated CO2 refrigerant flow paths formed within the plate heat exchanger. In other embodiments, the staged condenser 2 can also adopt other heat exchanger structures that can form a common cooling medium flow path and two mutually isolated CO2 refrigerant flow paths.

[0040] See Figure 1 The staged condenser 2 is provided with a cooling medium inlet 21 and a cooling medium outlet 22, both of which are connected to the cooling medium flow path. The staged condenser 2 is also provided with a primary precooling inlet 23, a primary precooling outlet 24, a secondary cooling inlet 25, and a secondary cooling outlet 26.

[0041] The primary precooling inlet 23 and primary precooling outlet 24 are both connected to the primary precooling flow path. The primary precooling inlet 23 receives CO2 from the primary exhaust port 102 of the single-unit two-stage compressor 1, and the primary precooling outlet 24 outputs CO2 precooled by the primary precooling flow path. The secondary cooling inlet 25 and secondary cooling outlet 26 are both connected to the secondary cooling flow path. The secondary cooling inlet 25 receives CO2 from the secondary exhaust port 104 of the single-unit two-stage compressor 1, and the secondary cooling outlet 26 outputs CO2 cooled by the secondary cooling flow path.

[0042] By integrating the primary precooling flow path and the secondary cooling flow path into the same heat exchange core, the staged condenser 2 can simultaneously achieve the precooling of the primary exhaust and the cooling of the secondary exhaust within a single component. This reduces the need for separate intercoolers and separate condensers, which helps to reduce the complexity of the system piping, save installation space, and make the overall structure of the refrigeration system more compact.

[0043] See Figure 1 The first throttling element 4 is used to regulate the CO2 flow rate entering the fuel supply channel of the economizer 3, and the second throttling element 5 is used to regulate the CO2 flow rate entering the evaporator 6. Optionally, in one embodiment, the first throttling element 4 is a first electronic expansion valve, and the second throttling element 5 is a second electronic expansion valve. In other embodiments, the first throttling element 4 and the second throttling element 5 may also employ other throttling structures capable of achieving throttling and pressure reduction functions.

[0044] like Figure 1 As shown, the economizer 3 includes an economizer body, a subcooling inlet 31, a subcooling outlet 32, a makeup air inlet 33, and a makeup air outlet 34. The economizer body contains a subcooling channel and a makeup air channel, which are isolated from each other and can exchange heat through a partition wall. The subcooling inlet 31 and the subcooling outlet 32 ​​are connected to both ends of the subcooling channel, and the makeup air inlet 33 and the makeup air outlet 34 are connected to both ends of the makeup air channel.

[0045] Specifically, the subcooling inlet 31 is connected to the first branch, and the subcooling outlet 32 ​​is connected to the second throttling element 5. (See also...) Figure 1Part of the CO2 flowing out of the secondary cooling outlet 26 enters the first branch, then enters the subcooling channel via the subcooling inlet 31. After heat exchange in the subcooling channel, it flows out from the subcooling outlet 32 ​​and then into the second throttling element 5. The makeup gas inlet 33 is connected to the second branch via the first throttling element 4, and the makeup gas outlet 34 is connected to the secondary intake port 103. Another part of the CO2 flowing out of the secondary cooling outlet 26 enters the second branch, first undergoes throttling and pressure reduction via the first throttling element 4, then enters the makeup gas channel via the makeup gas inlet 33. After heat exchange in the makeup gas channel, it flows out from the makeup gas outlet 34 and merges with the CO2 flowing out of the primary precooling outlet 24 at the confluence point.

[0046] In this embodiment, the economizer 3 can be a plate heat exchanger, with both the subcooling channel and the make-up gas channel used for CO2 flow. In other embodiments, the economizer 3 can also be a shell-and-tube heat exchanger, a microchannel heat exchanger, or other heat exchangers capable of achieving two-way CO2 heat exchange, as long as they can meet the pressure resistance requirements of the CO2 system.

[0047] Furthermore, the refrigeration system also includes a first detection component and a controller. The first detection component can be located at the outlet of the replenishment gas channel, or between the outlet and the confluence of the two CO2 channels. The first detection component is used to detect the replenishment gas status parameters before the two CO2 channels merge, including the replenishment gas temperature and replenishment gas pressure. The controller is communicatively connected to the first detection component and controllably connected to the first throttling element 4. The controller can adjust the opening of the first throttling element 4 according to the replenishment gas status parameters to ensure that the CO2 flowing out of the replenishment gas channel is in a superheated state. Here, the superheated state refers to the state where the actual temperature of the CO2 flowing out of the replenishment gas channel at the corresponding replenishment gas pressure is higher than the saturation temperature, thereby reducing the risk of liquid CO2 entering the secondary intake port 103 with the replenishment gas.

[0048] Specifically, the first detection component includes a first temperature detection element and a first pressure detection element. The first temperature detection element is used to detect the gas supply temperature, and the first pressure detection element is used to detect the gas supply pressure.

[0049] Optionally, in one embodiment, the controller can also set an upper and lower limit for the opening of the first throttling element 4. The upper limit is used to limit the CO2 flow rate entering the make-up gas channel, reduce the risk of insufficient CO2 evaporation in the make-up gas channel, and reduce the impact of excessive flow in the make-up gas branch on the refrigerant flow rate of the first branch. The lower limit is used to maintain the basic make-up gas volume while meeting the make-up gas superheat requirements, so as to balance the subcooling effect of the economizer 3 on the CO2 in the first branch and the system refrigeration efficiency.

[0050] Furthermore, the refrigeration system also includes a second pressure sensor. The second pressure sensor is located on the outlet side of the second throttling element 5 and is used to detect the pressure after throttling on the outlet side of the second throttling element 5. The controller is also communicatively connected to the second pressure sensor and controllably connected to the second throttling element 5 to adjust the opening of the second throttling element 5 according to the pressure after throttling, ensuring that the pressure on the outlet side of the second throttling element 5 is not lower than a preset pressure.

[0051] The preset pressure is a pressure threshold used to determine whether the pressure at the outlet side of the second throttling element 5 is too low. The preset pressure can be determined based on the phase change conditions of CO2, the operating pressure range of the evaporator 6, and the safety protection requirements of the refrigeration system. For example, in one embodiment, the preset pressure can be a gauge pressure of 5 MPa to reduce the risk of CO2 forming solid dry ice at the outlet side of the second throttling element 5.

[0052] Furthermore, in one embodiment, the controller can also set a minimum opening for the second throttling element 5 to ensure that the system still has sufficient CO2 flow through the evaporator 6 under low load conditions, thus maintaining normal system operation.

[0053] Optionally, the first temperature sensing element can be a temperature sensor, thermocouple, or other sensing element capable of detecting the refrigerant temperature; the first pressure sensing element and the second pressure sensing element can be a pressure sensor, pressure transmitter, or other sensing element capable of detecting the refrigerant pressure.

[0054] Furthermore, in this embodiment, the refrigeration system may also include a mixing chamber, which is disposed in the upstream pipeline of the secondary intake port 103. Figure 1 As shown, point M schematically represents the confluence or confluence area of ​​the primary precooling outlet 24 and the replenishment gas channel outlet. The CO2 flowing out of the primary precooling outlet 24 and the CO2 flowing out of the replenishment gas channel can converge at or near point M before entering the secondary intake port 103.

[0055] In this embodiment, the mixing chamber can be located at point M or between point M and the secondary intake port 103. The mixing chamber is used to receive CO2 flowing out of the primary precooling outlet 24 and CO2 flowing out of the make-up gas channel, so that the two CO2 streams merge and buffer before entering the secondary intake port 103.

[0056] Specifically, the mixing chamber includes a filter. The filter includes a filter housing, within which a mixing space is formed. A first inlet, a second inlet, and a mixing outlet of the mixing chamber are all located within the filter housing and communicate with the mixing space. The first inlet communicates with the primary pre-cooling outlet 24, the second inlet communicates with the outlet of the make-up air channel, and the mixing outlet communicates with the secondary intake port 103. Furthermore, the filter also includes a filter element disposed within the filter housing, located upstream of the mixing outlet.

[0057] During operation, the CO2 output from the primary precooling outlet 24 and the CO2 output from the make-up gas channel outlet converge at the confluence area indicated by point M and enter the mixing space within the filter housing. After further mixing in the mixing space, the two CO2 streams flow through the mixing outlet to the secondary intake port 103 of the single-unit two-stage compressor 1. The filter serves two purposes: firstly, it acts as a confluence and buffer space for the two CO2 streams; secondly, it filters the CO2 before it enters the secondary intake port 103, thereby reducing the risk of impurities entering the single-unit two-stage compressor 1.

[0058] Optionally, the volume of the filter housing can be set according to the suction flow rate, makeup gas volume, and system piping layout of the single-unit two-stage compressor 1. In one embodiment, the volume of the filter housing is approximately 1 liter to provide a buffer and mixing space for the CO2 output from the first-stage precooling outlet 24 and the CO2 output from the makeup gas channel. In other embodiments, the volume of the filter housing can also be adjusted according to the system cooling capacity and piping dimensions.

[0059] Optionally, a second detection component can be installed at the mixing outlet of the mixing chamber, or between the mixing outlet and the secondary intake port 103. The second detection component detects the CO2 temperature and pressure after mixing in the mixing chamber and before entering the secondary intake port 103. The controller can determine the overheating state of the CO2 before entering the secondary intake port 103 based on the detection results of the second detection component, thereby further reducing the risk of liquid carryover in the secondary intake.

[0060] With the above configuration, the CO2 single-unit two-stage refrigeration system in this embodiment integrates primary precooling, secondary cooling, economizer subcooling, and intermediate gas injection into the same refrigerant circuit. The primary exhaust gas is first cooled by the primary precooling flow path of the staged condenser 2, and then merges with the CO2 flowing out of the gas injection channel before entering the secondary suction port 103. This helps to reduce the secondary suction temperature and the secondary exhaust temperature, thereby reducing the heat load on the single-unit two-stage compressor 1. The CO2 flowing out of the secondary cooling outlet 26 is divided into a first branch and a second branch. The first branch is further subcooled by the subcooling channel of the economizer 3 before entering the evaporator 6, which increases the subcooling degree of the CO2 before entering the evaporator 6, thus increasing the refrigeration capacity per unit mass of CO2. The second branch is throttled by the first throttling element 4 before entering the gas injection channel. By controlling the superheat state of the CO2 at the outlet side of the gas injection channel, the risk of liquid entering the secondary suction port 103 with the gas injection gas can be reduced.

[0061] The present invention also provides a control method for a CO2 single-unit two-stage refrigeration system, which can be applied to the above-mentioned refrigeration system.

[0062] like Figure 2 As shown, in this embodiment, the control method includes the following steps.

[0063] S1: Obtain the gas replenishment temperature and gas replenishment pressure.

[0064] Specifically, the controller acquires the replenishment air temperature and pressure at the outlet of the replenishment air channel, or acquires the replenishment air temperature and pressure between the outlet and the confluence of the replenishment air channels. The replenishment air temperature can be obtained by a first temperature sensor, and the replenishment air pressure can be obtained by a first pressure sensor.

[0065] S2: Determine the saturation temperature corresponding to CO2 and determine the superheat of the supplementary gas.

[0066] Specifically, the controller determines the saturation temperature of CO2 at the replenishment pressure, and determines the replenishment superheat based on the difference between the replenishment temperature and the saturation temperature. The replenishment superheat is used to characterize whether the CO2 flowing out of the replenishment channel is in a superheated state.

[0067] S3: Adjust the opening degree of the first throttling element 4.

[0068] Specifically, the controller adjusts the opening of the first throttling element 4 according to the superheat of the supplementary gas to ensure that the superheat of the supplementary gas is not less than the preset superheat. This maintains the CO2 flowing out of the supplementary gas channel in a superheated state, reducing the risk of liquid entering the secondary suction port 103 during supplementary gas flow. Optionally, the preset superheat can be 5K, or it can be set according to the compressor's suction safety requirements and system operating conditions.

[0069] For example, when the superheat of the supplementary gas is less than 5K, it indicates that the CO2 flowing out of the supplementary gas channel may not be fully vaporized, posing a risk of liquid carryover during secondary intake. In this case, the controller can reduce the opening of the first throttling element 4 to reduce the CO2 flow rate into the supplementary gas channel, allowing the CO2 in the supplementary gas channel to fully absorb heat and vaporize, thereby increasing the superheat of the supplementary gas. When the superheat of the supplementary gas reaches or exceeds 5K, it indicates that the supplementary gas is in a safe superheated state. The controller can maintain the current opening of the first throttling element 4, or appropriately increase the opening of the first throttling element 4 according to the system's cooling requirements to ensure the amount of supplementary gas.

[0070] Furthermore, in this embodiment, the control method may also include the following steps.

[0071] S4: Obtain the pressure on the outlet side of the second throttling element 5.

[0072] Specifically, the controller acquires the pressure at the outlet side of the second throttling element 5. The pressure at the outlet side of the second throttling element 5 can be obtained by detecting the second pressure sensor.

[0073] S5: Adjust the opening degree of the second throttling element 5.

[0074] Specifically, the controller adjusts the opening of the second throttling element 5 according to the pressure at the outlet side of the second throttling element 5, so that the pressure at the outlet side of the second throttling element 5 is not lower than the preset pressure. The preset pressure can be determined according to the pressure conditions for CO2 to form solid dry ice. Optionally, the pressure at the outlet side of the second throttling element 5 can be controlled above 5 bar gauge pressure to reduce the risk of CO2 forming solid dry ice after throttling.

[0075] For example, when the pressure at the outlet side of the second throttling element 5 is lower than the preset pressure, the controller can enter a pressure protection control state and adjust the opening of the second throttling element 5 to restore the pressure at the outlet side of the second throttling element 5 to a range not lower than the preset pressure. When the pressure at the outlet side of the second throttling element 5 is not lower than the preset pressure, the controller can maintain the current opening of the second throttling element 5, or adjust the opening of the second throttling element 5 according to the cooling demand of the evaporator 6.

[0076] Through the above-mentioned control methods, on the one hand, the superheat of the supplementary gas can be controlled according to the supplementary gas temperature and pressure, reducing the risk of liquid CO2 entering the secondary suction port 103 with the supplementary gas; furthermore, the outlet pressure of the second throttling element 5 can be controlled to reduce the risk of solid dry ice forming due to excessively low pressure after CO2 throttling, thereby improving the operational stability of the CO2 single-unit two-stage refrigeration system and the reliability of the compressor.

[0077] It is understood that in this invention, when the number of components or members is not specifically limited, the number can be one or more, where multiple refers to two or more. For cases where the number of components or members shown in the drawings and / or described in the specification is, for example, two, three, four, etc., this specific number is generally exemplary and not limiting, and can be understood as multiple, i.e., two or more; however, this does not mean that the invention excludes the case of one.

[0078] It should be understood that the above-described embodiments, examples, or examples are merely exemplary and are not intended to limit the present invention. Those skilled in the art can make various modifications and changes to the above-described embodiments, examples, or examples under the guidance of the present invention, without departing from the scope of the present invention.

Claims

1. A single-unit, two-stage CO2 refrigeration system, characterized in that, include: A single-unit two-stage compressor (1) has a first-stage suction port (101), a first-stage discharge port (102), a second-stage suction port (103) and a second-stage discharge port (104). The staged condenser (2) includes a cooling medium flow path, a primary precooling flow path and a secondary cooling flow path, and is provided with a primary precooling inlet (23) and a primary precooling outlet (24) connected to the primary precooling flow path, and a secondary cooling inlet (25) and a secondary cooling outlet (26) connected to the secondary cooling flow path. The cooling medium flow path is configured to exchange heat with the primary precooling flow path and the secondary cooling flow path respectively. Economizer (3) includes a subcooling channel and a gas supply channel that exchange heat with each other; The first throttling element (4), the second throttling element (5), and the evaporator (6); Wherein, the primary exhaust port (102) is connected to the primary precooling inlet (23), the primary precooling outlet (24) and the outlet of the make-up air channel merge at the junction, and the junction is connected to the secondary intake port (103); the secondary exhaust port (104) is connected to the secondary cooling inlet (25), and the secondary cooling outlet (26) is connected to the first branch and the second branch respectively; the first branch is connected to the inlet of the evaporator (6) through the subcooling channel and the second throttling element (5), and the outlet of the evaporator (6) is connected to the primary intake port (101); the second branch is connected to the inlet of the make-up air channel through the first throttling element (4).

2. The CO2 single-unit two-stage refrigeration system according to claim 1, characterized in that, The staged condenser (2) includes a heat exchange core, and the cooling medium flow path, the primary precooling flow path and the secondary cooling flow path are all formed in the heat exchange core; The cooling medium flow path runs through the heat exchange core, and the primary precooling flow path and the secondary cooling flow path are isolated from each other; The staged condenser (2) is also provided with a cooling medium inlet (21) and a cooling medium outlet (22), both of which are connected to the cooling medium flow path.

3. The CO2 single-unit two-stage refrigeration system according to claim 1, characterized in that, The economizer (3) includes an economizer body, a subcooling inlet (31), a subcooling outlet (32), a make-up gas inlet (33), and a make-up gas outlet (34). The subcooling channel and the gas replenishment channel are both located within the economizer body and are isolated from each other and have heat exchange settings; the subcooling inlet (31) and the subcooling outlet (32) are respectively connected to the subcooling channel, and the gas replenishment inlet (33) and the gas replenishment outlet (34) are respectively connected to the gas replenishment channel.

4. The CO2 single-unit two-stage refrigeration system according to any one of claims 1 to 3, characterized in that, The CO2 single-unit two-stage refrigeration system also includes a first detection component and a controller; The first detection component is disposed at the outlet of the gas supply channel, and / or disposed between the outlet of the gas supply channel and the confluence; the first detection component is used to detect gas supply status parameters, the gas supply status parameters including gas supply temperature and gas supply pressure; The controller is communicatively connected to the first detection component and controlled by the first throttling element (4). The controller is configured to adjust the opening of the first throttling element (4) according to the gas replenishment state parameters so that the CO2 flowing out of the gas replenishment channel is in a superheated state.

5. The CO2 single-unit two-stage refrigeration system according to claim 4, characterized in that, The CO2 single-unit two-stage refrigeration system also includes a second pressure detection device; The second pressure detection element is disposed on the outlet side of the second throttling element (5) and is used to detect the pressure on the outlet side of the second throttling element (5); The controller is also communicatively connected to the second pressure sensor and controlled by the second throttling element (5). The controller is configured to adjust the opening of the second throttling element (5) according to the detection result of the second pressure sensor so that the pressure on the outlet side of the second throttling element (5) is not lower than the preset pressure.

6. The CO2 single-unit two-stage refrigeration system according to any one of claims 1 to 3, characterized in that, The CO2 single-unit two-stage refrigeration system also includes a mixing chamber, which is located in the upstream pipeline of the secondary intake port; The mixing chamber has a first inlet, a second inlet, and a mixing outlet. The first inlet is connected to the outlet of the primary precooling flow path, the second inlet is connected to the outlet of the replenishment channel, and the mixing outlet is connected to the secondary intake port.

7. The CO2 single-unit two-stage refrigeration system according to claim 6, characterized in that, The mixing chamber includes a filter, the filter includes a filter housing, the mixing chamber is formed inside the filter housing, the first inlet, the second inlet and the mixing outlet are all disposed in the filter housing and are all in communication with the mixing chamber.

8. The CO2 single-unit two-stage refrigeration system according to claim 6, characterized in that, The CO2 single-unit two-stage refrigeration system also includes a second detection component, which is located at the mixing outlet of the mixing chamber or between the mixing outlet and the secondary intake port; the second detection component is used to detect the CO2 temperature and CO2 pressure before entering the secondary intake port.

9. A method for controlling a single-unit two-stage CO2 refrigeration system, characterized in that, The control method, applied to any one of claims 1 to 8, in the CO2 single-unit two-stage refrigeration system, comprises: Obtain the gas supply temperature and pressure at the outlet of the gas supply channel and / or between the outlet of the gas supply channel and the confluence point; The saturation temperature corresponding to CO2 is determined based on the gas supply pressure, and the gas supply superheat is determined based on the difference between the gas supply temperature and the saturation temperature. Adjust the opening of the first throttling element (4) according to the superheat of the gas supply so that the superheat of the gas supply is not less than the preset superheat.

10. The control method for a single-unit two-stage CO2 refrigeration system according to claim 9, characterized in that, The control method also includes: Obtain the pressure on the outlet side of the second throttling element (5); Adjust the opening of the second throttling element (5) according to the pressure on the outlet side of the second throttling element (5) so that the pressure on the outlet side of the second throttling element (5) is not lower than the preset pressure.

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