Self-cooling type subcritical carbon dioxide refrigerating system

Abstract

The invention discloses a self-cooling type subcritical carbon dioxide refrigeration system which comprises an absorption refrigeration subsystem and a carbon dioxide mechanical compression refrigeration subsystem, and the absorption refrigeration subsystem comprises a heat absorption concentration unit and a dilution refrigeration unit. Compression heat of the carbon dioxide mechanical compression refrigeration subsystem is used for driving operation of the heat absorption concentration unit, a cold source generated by the dilution refrigeration unit is used for condensing a high-pressure refrigerant in the compression refrigeration subsystem into a liquid phase in a subcritical pressure state, and subcritical carbon dioxide refrigeration is achieved. High-temperature sensible heat of the carbon dioxide mechanical compression refrigeration subsystem serves as generation heat of the absorption refrigeration subsystem to concentrate a dilute solution, and then a cold source generated by the absorption refrigeration subsystem condenses a high-pressure refrigerant at an outlet of a compressor at a low temperature under subcritical pressure. The condensation temperature of the carbon dioxide mechanical compression refrigeration subsystem and the outlet pressure of a compressor are reduced, self-cooling of the carbon dioxide refrigeration system is achieved, and meanwhile efficient operation of the carbon dioxide mechanical refrigeration subsystem under the subcritical condition is achieved.

Description

Technical Field

[0001] The invention relates to the field of carbon dioxide refrigeration systems, and in particular to a self-cooling subcritical carbon dioxide refrigeration system. Background Art

[0002] Under ambient cooling conditions, the condensation temperature of traditional carbon dioxide compression refrigeration systems is usually higher than the critical temperature and can only operate in a transcritical state. At the same output temperature, the system has technical defects such as compressor outlet pressure higher than the critical pressure and low system efficiency. Compared with the transcritical state, the carbon dioxide compression refrigeration system in the subcritical state has a lower system pressure and lower cost, but requires additional artificial cooling, which reduces the coefficient of performance. How to reduce the condensation temperature to below the critical temperature, achieve self-cooling of subcritical carbon dioxide, and improve system efficiency is a technical difficulty of the subcritical carbon dioxide refrigeration system.

[0003] The absorption refrigeration system driven by thermal energy greatly reduces the dependence on electrical energy or high-quality thermal energy. Figure 1 As shown, in the existing closed absorption-compression cascade refrigeration system, the condensation heat of the compression refrigeration subsystem is all taken away by the evaporator of the absorption refrigeration subsystem, converted into low-grade heat, and finally discharged from the system by the cold source of the condenser and absorber of the absorption refrigeration subsystem, resulting in a heavy load on the absorption refrigeration subsystem; what is more serious is that the heat generated by the absorption refrigeration subsystem needs to be provided by additional thermal energy, resulting in low energy utilization efficiency of the entire system. Summary of the invention

[0004] In view of this, the present invention aims to overcome the shortcomings of the prior art and provide a self-cooling subcritical carbon dioxide refrigeration system, which drives its own condensation through the compression heat of the carbon dioxide compression refrigeration system, thereby realizing efficient operation of the self-cooling carbon dioxide refrigeration system under subcritical conditions, effectively reducing the waste of mechanical compression energy, and improving the overall energy utilization efficiency of the system.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A self-cooling subcritical carbon dioxide refrigeration system comprises an absorption refrigeration subsystem and a carbon dioxide mechanical compression refrigeration subsystem. The absorption refrigeration subsystem comprises an endothermic concentration unit and a dilution refrigeration unit. The compression heat of the carbon dioxide mechanical compression refrigeration subsystem is used to drive the operation of the endothermic concentration unit. The cold source generated by the dilution refrigeration unit is used to condense the high-pressure refrigerant in the compression refrigeration subsystem into a liquid phase under a subcritical pressure state, thereby realizing subcritical carbon dioxide refrigeration.

[0007] As one of the preferred schemes of the present invention, in the absorption refrigeration subsystem, the heat absorption concentration unit includes a generator, the dilution refrigeration unit includes an absorber and an absorption evaporator; the carbon dioxide mechanical compression refrigeration subsystem includes a compressor and a compression evaporator; the generator is coupled to the compressor; the compression heat at the compressor outlet is used to drive the generation and concentration of the dilute solution in the generator, and the refrigeration generated in the absorption evaporator condenses the high-pressure refrigerant at the compressor outlet into a liquid phase under a subcritical pressure state, thereby realizing subcritical carbon dioxide refrigeration.

[0008] As one of the preferred solutions of the present invention, the absorption refrigeration subsystem includes a generator, an absorber, and an absorption evaporator, and the carbon dioxide mechanical compression refrigeration subsystem includes a compressor and a compression evaporator; the generator is coupled to the compressor;

[0009] The compression heat at the compressor outlet is used to drive the concentration of the dilute solution in the generator, and the cold source generated by the absorption evaporator is used to absorb the heat released by the condensation of the refrigerant of the compression refrigeration subsystem at a lower temperature under subcritical pressure, thereby reducing the condensation temperature of the compression refrigeration subsystem.

[0010] As one of the preferred solutions of the present invention, the carbon dioxide mechanical compression refrigeration subsystem also includes a first regenerator, a throttle valve and a second regenerator; the compressed refrigerant at the compressor outlet passes through the generator of the heat absorption and concentration unit, the second regenerator, the absorption evaporator, the first regenerator, the throttle valve, the compression evaporator, the first regenerator, the second regenerator and then returns to the compressor inlet.

[0011] As one of the preferred solutions of the present invention, the compressor is coupled to the generator through a solution heater, and the compressed refrigerant at the compressor outlet releases heat through the solution heater and then enters the second regenerator to heat the refrigerant sucked into the compressor.

[0012] As one of the preferred solutions of the present invention, the generator is an open generator, and the compression heat at the compressor outlet and the ambient air together drive the generation and concentration of the dilute solution in the open generator.

[0013] As one of the preferred solutions of the present invention, the solution heater is arranged outside the generator, and the dilute solution at the absorber outlet is pumped into the solution heater through a solution pump, and after being heated by the compressed refrigerant in the solution heater, it enters the generator to exchange heat and mass with the ambient air.

[0014] As one of the preferred solutions of the present invention, the solution heater is arranged inside the generator, and the dilute solution at the absorber outlet is pumped into the generator through the solution pump, and simultaneously exchanges heat with the compressed refrigerant in the solution heater and exchanges heat and mass with the ambient air.

[0015] As one of the preferred solutions of the present invention, the absorption refrigerant in the absorption evaporator is environmental water.

[0016] As one of the preferred solutions of the present invention, the generator is a closed generator, and the absorption refrigeration subsystem also includes an absorption condenser and a solution heat exchanger. The dilute solution at the absorber outlet passes through a solution pump and a solution heat exchanger and then enters the generator; the absorption refrigerant at the generator outlet is condensed by the absorption condenser and then enters the absorption evaporator.

[0017] As one of the preferred solutions of the present invention, the solution heater is arranged inside the closed generator, and the dilute solution in the generator exchanges heat with the compressed refrigerant in the solution heater.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] (1) The present invention uses the high-temperature sensible heat of the carbon dioxide mechanical compression refrigeration subsystem as the generated heat of the absorption refrigeration subsystem to concentrate the dilute solution, and uses the low-temperature sensible heat of the compressed refrigerant at the compressor outlet as the suction heating heat source of the compressor. The low-temperature cold source generated by the absorption refrigeration subsystem is then used to condense the high-pressure refrigerant at the compressor outlet under subcritical pressure, thereby reducing the condensation temperature of the carbon dioxide mechanical compression refrigeration subsystem and the compressor outlet pressure, thereby realizing self-cooling of the carbon dioxide refrigeration system and realizing efficient operation of the carbon dioxide refrigeration system under subcritical conditions.

[0020] (2) The carbon dioxide mechanical compression refrigeration subsystem adopted by the present invention has its high-pressure and high-temperature refrigerant released heat twice before entering the absorption evaporator, which greatly reduces the cold source burden of the absorption refrigeration subsystem, thereby reducing the cost of the absorption system; at the same time, part of the released heat is used as the heat source of the absorption refrigeration subsystem, avoiding the waste of additional heat from the outside, and the other part of the recovered heat is used to heat the intake air of the compression refrigeration subsystem, increasing the energy of the CO2 gas at the outlet of the compression refrigeration subsystem, increasing the heat source of the absorption refrigeration subsystem, and increasing the refrigeration capacity of the absorption refrigeration subsystem, thereby improving the refrigeration source and efficiency of the compression refrigeration subsystem.

[0021] (3) The absorption refrigeration subsystem of the present invention can use an open generator. While fully utilizing the compression heat, the open generator can also use the vapor partial pressure difference between the ambient air and the solution to exchange heat and mass, further reducing the waste of mechanical compression energy; the absorption refrigerant comes from the environment and is discharged into the environment after heat exchange. It has a simple structure, generates at normal pressure without leakage risk, and has a lower manufacturing cost than a closed generator. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 It is a schematic diagram of the flow of an existing closed absorption-compression refrigeration system;

[0024] Figure 2 This is a schematic diagram of the self-cooling subcritical carbon dioxide refrigeration system of the present invention;

[0025] Figure 3 This is a schematic diagram of a self-cooling subcritical carbon dioxide refrigeration system using an open generator according to Embodiment 1 of the present invention;

[0026] Figure 4 This is a schematic diagram of a self-cooling subcritical carbon dioxide refrigeration system using an open generator according to the second embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of a self-cooling subcritical carbon dioxide refrigeration system using a closed generator as described in Example 3 of the present invention.

[0028] Figure 6 Transcritical CO2 compression refrigeration systems for conventional ambient cooling;

[0029] Figure 7 When the ambient temperature is 30°C and the evaporation temperature is from -45 to -25°C, the first to third embodiments are Figure 1 and Figure 6 System performance comparison chart.

[0030] Figure 8 When the evaporation temperature is -25°C and the ambient temperature changes between 30 and 45°C, the first to third embodiments are Figure 1 and Figure 6 System performance comparison chart.

[0031] Description of reference numerals:

[0032] 1- compressor, 2- compression evaporator, 3- first regenerator, 4- second regenerator, 5- throttle valve; 6- generator, 7- absorber, 8- absorption evaporator, 9- solution pump, 10- solution heater, 11- flow valve, 12- absorption throttle valve, 13- absorption condenser, 14- solution heat exchanger. DETAILED DESCRIPTION

[0033] In order to make the technical means, objectives and effects of the present invention easy to understand, the embodiments of the present invention are described in detail below with reference to specific drawings.

[0034] It should be noted that all the terms used in the present invention for directional and positional indications, such as "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "inside", "outside", "top", "low", "lateral", "longitudinal", "center", etc., are only used to explain the relative positional relationship and connection status between the components in a certain state (as shown in the accompanying drawings), and are only for the convenience of describing the present invention, rather than requiring the present invention to be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes, and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features.

[0035] In the description of the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0037] like Figure 2 As shown, the present invention proposes a self-cooling subcritical carbon dioxide refrigeration system, including an absorption refrigeration subsystem and a carbon dioxide mechanical compression refrigeration subsystem; the absorption refrigeration subsystem includes an endothermic concentration unit and a dilution refrigeration unit, the compression heat of the carbon dioxide mechanical compression refrigeration subsystem is used to drive the operation of the endothermic concentration unit, and the cold source generated by the dilution refrigeration unit is used to condense the high-pressure refrigerant in the compression refrigeration subsystem into a liquid phase under a subcritical pressure state, thereby realizing subcritical carbon dioxide refrigeration.

[0038] The self-cooling subcritical carbon dioxide refrigeration system of the present invention utilizes the compression heat of the mechanical compression refrigeration subsystem itself to indirectly drive its own subcritical condensation without consuming an external heat source, thereby achieving self-cooling of the carbon dioxide refrigeration system.

[0039] Embodiment 1

[0040] As an embodiment of the present invention, Figure 3 In the self-cooling subcritical carbon dioxide refrigeration system shown, the absorption refrigeration subsystem includes a generator 6, an absorber 7, and an absorption evaporator 8, and the carbon dioxide mechanical compression refrigeration subsystem includes a compressor 1 and a compression evaporator 2; the generator 6 is coupled to the compressor 1; the compression heat at the outlet of the compressor 1 is used to drive the dilute solution in the generator 6 to concentrate, and the concentrated solution enters the absorber 7 to absorb moisture and release heat to form a dilute solution, which is heated again by the compression heat and then sent to the generator, thereby circulating. The absorption refrigerant in the absorption evaporator 8 condenses the compressed refrigerant in the compression evaporator 2 at a subcritical pressure (<7.38MPa) at a temperature lower than the critical temperature (31°C).

[0041] The carbon dioxide mechanical compression refrigeration subsystem further includes a first regenerator 3, a throttle valve 5, and a second regenerator 4; after the compressed refrigerant at the outlet of the compressor 1 releases latent sensible heat through the generator of the heat absorption and concentration unit, it returns to the inlet of the compressor 1 through the second regenerator 4, the absorption evaporator 8, the first regenerator 3, the throttle valve 5, the compression evaporator 2, the first regenerator 3, and the second regenerator 4 in sequence, forming a closed cycle of the compressed refrigerant. The compressed refrigerant is carbon dioxide.

[0042] The compressor 1 is coupled to the generator 6 through the solution heater 10, and the compressed refrigerant at the outlet of the compressor 1 releases sensible heat through the solution heater 10 and enters the second regenerator 4. The exhaust gas of the compressor 1 is integrated with the generator 6, and no additional energy is consumed, the structure is simple, and the energy-saving effect is significant.

[0043] In this embodiment, the generator 6 is an open generator, and the solution heater 10 is arranged outside the generator 6 .

[0044] In the absorption refrigeration subsystem, the concentrated solution in the generator 6 enters the absorber 7 through the flow valve 11, absorbs the ambient water at a lower vapor pressure, and the ambient water enters the absorber 7 to be absorbed by the concentrated solution after phase change and evaporation in the absorption evaporator 8 and absorbing heat. The heat of the absorption process is taken away by the ambient water. The dilute solution with a lower temperature after absorption is pumped into the solution heater 10 by the solution pump and heated by the high-temperature refrigerant vapor of the compression refrigeration subsystem, and then enters the generator 6 to exchange heat and mass with the ambient air and be concentrated. This cycle continues.

[0045] In the mechanical compression refrigeration subsystem, the high-temperature refrigerant vapor at the compressor outlet enters the solution heater 10 to release sensible heat, then enters the second regenerator 4 to heat the compressed refrigerant before suction, and then enters the absorption evaporator 8 to be condensed into CO2 liquid. The CO2 liquid enters the first regenerator 3 to be supercooled. The supercooled CO2 refrigerant passes through the throttle valve 5 and enters the compression evaporator 2 to evaporate and refrigerate at a lower pressure to output the cold source. The evaporated refrigerant is heated for the first time by the first regenerator 3, and then heated for the second time by the second regenerator 4, and then enters the compressor 1 to be compressed. This cycle is repeated.

[0046] The idea is to recover the high-temperature sensible heat at the outlet of the compressor of the carbon dioxide mechanical compression refrigeration subsystem through an open absorption refrigeration subsystem, and then recover part of the low-temperature sensible heat before condensation through suction gas, making full use of the heat of the refrigerant at the compressor outlet and the cold source of the refrigerant after evaporation. This ensures that the open absorption refrigeration subsystem can provide a stable and sufficient cold source to the compression refrigeration subsystem under the premise of relying solely on the sensible heat of the refrigerant, and at the same time ensures that the mechanical compression refrigeration subsystem can achieve high-efficiency subcritical refrigeration with the assistance of the absorption refrigeration subsystem.

[0047] Embodiment 2

[0048] As another embodiment of the present invention, Figure 4 In the self-cooling subcritical carbon dioxide refrigeration system shown, the generator 6 is an open generator, and the solution heater 10 is arranged inside the generator 6.

[0049] In this embodiment, in the absorption refrigeration subsystem, the concentrated solution in the generator 6 enters the absorber 7 through the flow valve 11, absorbs the ambient water at a lower vapor pressure, and the ambient water enters the absorber 7 and is absorbed by the concentrated solution after phase change, evaporation and heat absorption in the absorption evaporator 8. The heat of the absorption process is taken away by the ambient water. The dilute solution with a lower temperature after absorption enters the generator 6, is heated by the high-temperature refrigerant vapor in the solution heater 10, and simultaneously exchanges heat and mass with the low-pressure ambient air, and is concentrated. This cycle is repeated.

[0050] In the open absorption-compression refrigeration system adopted in Example 1 and Example 2, the open generator can fully utilize the compression heat and at the same time utilize the vapor partial pressure difference between the ambient air and the solution to exchange heat and mass, further reducing the waste of mechanical compression energy. The absorption refrigerant comes from the environment and is discharged into the environment after heat exchange. The structure is simple, and normal pressure manufacturing can meet the use requirements, and the cost is low.

[0051] Embodiment 3

[0052] As another embodiment of the present invention, Figure 5In the self-cooling subcritical carbon dioxide refrigeration system shown, the generator 6 is a closed generator, and the solution heater 10 is arranged inside the generator 6. The dilute solution in the generator 6 exchanges heat with the compressed refrigerant in the solution heater 10.

[0053] The absorption refrigeration subsystem also includes an absorption condenser 13 and a solution heat exchanger 14. The dilute solution at the outlet of the absorber 7 passes through the solution pump 9 and the solution heat exchanger 14, and then enters the generator 6, where it is heated and concentrated by the high-temperature compressed refrigerant in the solution heater 10, and then enters the absorber 7 through the flow valve 11 after releasing heat through the solution heat exchanger 14 to absorb moisture and release heat. The absorption refrigerant at the outlet of the generator 6 is condensed by the absorption condenser 13 and then enters the absorption evaporator 8 through the absorption throttle valve 12 to cool the compressed refrigerant of the compression refrigeration subsystem.

[0054] In the mechanical compression refrigeration subsystem, the high-temperature refrigerant vapor at the compressor outlet enters the solution heater 10 to release sensible heat, then enters the second regenerator 4 to heat the compressed refrigerant before suction, and then enters the absorption evaporator 8 to be condensed into CO2 liquid. The CO2 liquid enters the first regenerator 3 to be supercooled. The supercooled CO2 refrigerant passes through the throttle valve 5 and enters the compression evaporator 2 to evaporate and refrigerate at a lower pressure to output the cold source. The evaporated refrigerant is heated for the first time by the first regenerator 3, and then heated for the second time by the second regenerator 4, and then enters the compressor 1 to be compressed.

[0055] Compared with the traditional closed generation-compression refrigeration system, the generation heat source required by the system of the present invention does not require additional thermal energy to provide, and the cold source generated by the absorption refrigeration subsystem can also be fully utilized by the compression refrigeration subsystem, so the system performance is higher.

[0056] Figure 7 and Figure 8 The self-cooling subcritical carbon dioxide refrigeration system described in Examples 1 to 3 obtained by simulation calculation and Figure 1 The traditional closed-loop compression refrigeration system shown in Figure 6 The performance comparison of the conventional ambient cooling transcritical carbon dioxide compression refrigeration system is shown, where the compressor exhaust pressure of the conventional ambient cooling transcritical carbon dioxide compression refrigeration system is the optimal pressure with the maximum COP as the target. The compression working fluid in the calculation system is CO2, the absorption working fluid pair is H2O / LiBr, the ambient pressure is 101.3kPa, and the ambient relative humidity is 60%. Figure 7 When the ambient temperature is 30°C and the evaporation temperature is from -45 to -25°C, the first to third embodiments are Figure 1 and Figure 6 System performance comparison chart. Figure 8 When the evaporation temperature is -25°C and the ambient temperature changes between 30 and 45°C, the first to third embodiments are Figure 1 and Figure 6 System performance comparison chart. Figure 8 In the embodiment 3, when the ambient temperature is higher than 34°C, the closed absorption refrigeration subsystem cannot provide enough cooling capacity for the compression refrigeration subsystem because the ambient cooling temperature is too high, and the system stops working. In embodiments 1 and 2, because the driving force for solution concentration is the vapor pressure difference, when the ambient temperature rises, the system can increase the flow rate of ambient air with lower vapor partial pressure to maintain the refrigeration capacity and refrigeration temperature of the absorption subsystem. It can be seen that under the same environmental conditions, the COP values ​​of the systems described in embodiments 1 to 3 are higher than those of the traditional closed generation compression refrigeration system and the traditional environmental cooling transcritical carbon dioxide compression refrigeration system. This fully demonstrates that the self-cooling subcritical carbon dioxide refrigeration system described in the present invention has high system performance and can achieve efficient refrigeration in the subcritical state.

[0057] Under the same absorption working fluid pair, the performance of the open system described in Example 1 / 2 is better than that of the closed system described in Example 3.

[0058] The self-cooling subcritical carbon dioxide refrigeration system of the present invention realizes the efficient operation of the subcritical carbon dioxide refrigeration system through the organic coupling of the carbon dioxide mechanical compression refrigeration subsystem and the absorption refrigeration subsystem. The absorption refrigeration subsystem uses the sensible heat of the high-temperature and high-pressure carbon dioxide at the compressor outlet as a heat source to drive the operation of the absorption system, and outputs a low-temperature cold source. After the low-temperature refrigerant evaporated from the mechanical compression refrigeration subsystem is supercooled by the second regenerator to the refrigerant before throttling, part of the sensible heat before condensation is recovered again through the first regenerator, thereby reducing the burden on the absorption evaporator, and at the same time, part of the sensible heat is recovered by heating the suction air. It is ensured that the absorption refrigeration subsystem can provide sufficient condensation cold sources for the mechanical compression refrigeration subsystem under the premise of relying only on the sensible heat of the carbon dioxide at the compression outlet, and that the mechanical compression refrigeration subsystem can output cold sources stably and efficiently in a subcritical state with the help of the absorption refrigeration subsystem.

[0059] In the refrigeration system using an open generator, the condensation heat of the low-pressure ambient air and the compression refrigeration system drives the concentration of the solution, and then the concentrated solution absorbs the ambient water to undergo phase change and absorbs heat. The generated cold load is used again for condensation in the mechanical compression refrigeration subsystem. The system has a simple structure, water and air are easy to use as cold sources, and the operating cost is low.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Self-cooling subcritical carbon dioxide refrigeration system, characterized by: The invention comprises an absorption refrigeration subsystem and a carbon dioxide mechanical compression refrigeration subsystem. The absorption refrigeration subsystem comprises an endothermic concentration unit and a dilution refrigeration unit. The compression heat of the carbon dioxide mechanical compression refrigeration subsystem is used to drive the operation of the endothermic concentration unit. The cold source generated by the dilution refrigeration unit is used to condense the high-pressure refrigerant in the compression refrigeration subsystem into a liquid phase under a subcritical pressure state, thereby realizing subcritical carbon dioxide refrigeration.

2. The self-cooling subcritical carbon dioxide refrigeration system according to claim 1, characterized in that: In the absorption refrigeration subsystem, the heat absorption concentration unit includes a generator, the dilution refrigeration unit includes an absorber and an absorption evaporator; the carbon dioxide mechanical compression refrigeration subsystem includes a compressor and a compression evaporator; The high-temperature compression heat generated by the compressor is used to drive the concentration of the dilute solution in the generator. The absorption refrigerant in the absorption evaporator condenses the high-pressure refrigerant at the compressor outlet into a liquid phase under a subcritical pressure state, thereby realizing subcritical carbon dioxide refrigeration.

3. The self-cooling subcritical carbon dioxide refrigeration system according to claim 2, characterized in that: The carbon dioxide mechanical compression refrigeration subsystem also includes a first regenerator, a throttle valve and a second regenerator; the compressed refrigerant at the compressor outlet passes through the generator of the heat absorption and concentration unit, the second regenerator, the absorption evaporator, the first regenerator, the throttle valve, the compression evaporator, the first regenerator, the second regenerator in sequence and then returns to the compressor inlet.

4. The self-cooling subcritical carbon dioxide refrigeration system according to claim 3, characterized in that: The compressor is coupled to the generator through a solution heater. The compressed refrigerant at the compressor outlet releases heat through the solution heater and then enters the second regenerator to heat the refrigerant sucked into the compressor.

5. The self-cooling subcritical carbon dioxide refrigeration system according to claim 4, characterized in that: The generator is an open generator, and the compression heat at the compressor outlet and the ambient air together drive the generation and concentration of the dilute solution in the open generator.

6. The self-cooling subcritical carbon dioxide refrigeration system according to claim 5, characterized in that: The solution heater is arranged outside the generator, and the dilute solution at the outlet of the absorber is pumped into the solution heater through a solution pump, and after being heated by the compressed refrigerant in the solution heater, it enters the generator to exchange heat and mass with the ambient air.

7. The self-cooling subcritical carbon dioxide refrigeration system according to claim 5, characterized in that: The solution heater is arranged inside the generator, and the dilute solution at the outlet of the absorber is pumped into the generator through the solution pump, and simultaneously exchanges heat with the compressed refrigerant in the solution heater and exchanges heat and mass with the ambient air.

8. The self-cooling subcritical carbon dioxide refrigeration system according to any one of claims 5 to 7, characterized in that: The absorption refrigerant in the absorption evaporator is environmental water.

9. The self-cooling subcritical carbon dioxide refrigeration system according to claim 4, characterized in that: The generator is a closed generator, and the absorption refrigeration subsystem also includes an absorption condenser and a solution heat exchanger. The dilute solution at the absorber outlet enters the generator after passing through a solution pump and a solution heat exchanger. The absorption refrigerant at the generator outlet enters the absorption evaporator after being condensed by the absorption condenser, and the concentrated solution at the generator outlet enters the absorber after passing through the solution heat exchanger and the solution valve.

10. The self-cooling subcritical carbon dioxide refrigeration system according to claim 9, characterized in that: The solution heater is arranged inside the closed generator, and the dilute solution in the generator exchanges heat with the compressed refrigerant in the solution heater.

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