Refrigeration system and circulation method for realizing low temperature refrigeration

Abstract

The present invention relates to the technical field of refrigeration cycle, and specifically to a refrigeration system and circulation method for realizing low-temperature refrigeration, wherein the refrigeration system comprises a high-temperature cycle system and a low-temperature cycle system, wherein the high-temperature cycle system comprises a high-temperature low-pressure compressor, a high-temperature high-pressure compressor, a high-temperature condenser, a high-temperature intermediate cooler, a high-temperature low-pressure economizer and a condensing evaporator connected in series in sequence, wherein the high-temperature intermediate cooler is connected to the pipeline between the high-temperature low-pressure compressor and the high-temperature high-pressure compressor through a pipeline, and the high-temperature low-pressure economizer is connected to the high-temperature low-pressure compressor through a pipeline; and the low-temperature cycle system comprises an evaporator, a regenerator, a low-temperature low-pressure compressor, a low-temperature high-pressure compressor, a condensing evaporator and a liquid storage device connected in series, wherein the outlet of the liquid storage device is connected to the regenerator, and the regenerator is connected to the evaporator through a pipeline, so that the refrigerant circulates and refrigerates in a subcritical state, thereby improving the refrigeration efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of refrigeration cycles, and in particular to a refrigeration system and a circulation method for realizing low-temperature refrigeration. Background Art

[0002] In the prior art, multi-stage compression refrigeration is usually used to achieve low-temperature refrigeration above -50°C, while the general two-stage cascade system can achieve low-temperature refrigeration above -90°C. When the refrigeration temperature is lower than -100°C, three-stage cascade refrigeration is generally required. For the three-stage cascade, the refrigeration cycle is composed of three sets of different refrigerant cycles. Generally, the refrigerants used are R507A, R23 and R14, that is, the first cycle is R507A refrigeration, which provides a cold source on the condensation side for the second cycle, the second cycle is R23 refrigeration, which provides a cold source on the condensation side for the third cycle, and the third cycle is R14 low-temperature refrigeration, which provides a cold source for the low-temperature heat source. Since the system needs to use three refrigerants, three lubricants, and three cycles, the structure is complex, and the three cycles restrict and influence each other, making the control and adjustment difficult, and the operation is cumbersome. Therefore, the three-stage cascade is particularly complex in terms of both the refrigerant cycle and the lubricant cycle, and at the same time causes relatively poor control stability. If the conventional two-stage cascade of R507A / R23 is used, it is limited by the standard boiling point of the low-temperature refrigerant and cannot achieve a low temperature of -110℃ to -125℃. If the conventional two-stage cascade of R507A / R14 is used, although the standard boiling point is feasible in theory, both the high and low temperature stages have problems of excessive pressure ratio and low efficiency. At the same time, due to the high pressure of the low-temperature refrigerant, the low-temperature stage refrigeration is very easy to operate in a transcritical cycle, and the refrigeration efficiency is extremely low when the liquid is directly expanded. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a refrigeration system and a circulation method for realizing low-temperature refrigeration.

[0004] The technical solution of the present invention to solve the above technical problems is as follows: a refrigeration system for realizing low-temperature refrigeration, comprising a high-temperature stage circulation system and a low-temperature stage circulation system,

[0005] The high-temperature circulation system comprises a high-temperature low-pressure compressor, a high-temperature high-pressure compressor, a high-temperature condenser, a high-temperature intermediate cooler, a high-temperature low-pressure economizer and a condenser evaporator which are sequentially connected in series to form a circulation loop, the high-temperature intermediate cooler is connected to the high-temperature low-pressure compressor and the pipeline between the high-temperature high-pressure compressor through a pipeline, the high-temperature low-pressure economizer is connected to the high-temperature low-pressure compressor through a pipeline, and a throttle valve 1 is provided on the pipeline between the high-temperature low-pressure economizer and the condenser evaporator;

[0006] The low-temperature circulation system includes an evaporator, a regenerator, a low-temperature low-pressure compressor, a low-temperature high-pressure compressor, a condensing evaporator and a liquid storage tank connected in series, the outlet of the liquid storage tank is connected to the regenerator, and the regenerator is connected to the evaporator through a pipeline.

[0007] On the basis of the above technical solution, the present invention can also make the following improvements to the above technical solution:

[0008] Preferably, the low-temperature stage circulation system also includes an intercooler, the outlet of the regenerator is connected to the intercooler, the outlet of the intercooler is connected to the evaporator, and a throttle valve 2 is provided on the pipeline between the intercooler and the evaporator.

[0009] Preferably, the intercooler is connected to the pipeline between the low-temperature and low-pressure compressor and the low-temperature and high-pressure compressor through a pipeline.

[0010] Preferably, the refrigerant in the high-temperature circulation system is R507A, and the refrigerant in the low-temperature circulation system is R14.

[0011] The beneficial effects of the refrigeration system for achieving low-temperature refrigeration of the present invention are: the high-temperature stage of the present invention innovatively adopts a dual-machine two-stage compressor unit, and selects high-pressure refrigerant to reduce the evaporation temperature of the high-temperature stage, thereby reducing the condensation temperature of the low-temperature stage, so that the low-temperature stage cycle enters a subcritical cycle, and at the same time, by adding a heat recovery cycle, the overall refrigeration efficiency of the -110°C to -125°C system is further improved.

[0012] The present invention also discloses a circulation method for realizing low-temperature refrigeration, which adopts the refrigeration system as described above and specifically comprises the following steps:

[0013] High-temperature cycle: the high-temperature refrigerant evaporates in the condenser evaporator to take away the heat rejection load on the low-temperature condensation side. After evaporation, the high-temperature refrigerant is pressurized by the high-temperature low-pressure compressor. The pressurized high-temperature refrigerant is mixed with the supplementary air from the high-temperature intercooler and then enters the high-temperature high-pressure compressor to be pressurized to the saturation pressure corresponding to the high-temperature condensation temperature, and then enters the high-temperature condenser. The high-pressure refrigerant liquid in the high-temperature condenser flows out, and after being supercooled by the high-temperature intercooler and the high-temperature low-pressure economizer, it enters the condenser evaporator after throttling by the throttle valve to evaporate, completing a complete cycle of high-temperature refrigeration.

[0014] Low-temperature stage cycle: After the low-temperature refrigerant absorbs the heat of the low-temperature heat source from the evaporator and evaporates at a temperature of -110℃ to -125℃, it enters the regenerator for heat recovery, and then enters the low-temperature low-pressure compressor for pressurization. The pressurized low-temperature refrigerant is mixed with the supplementary air from the intercooler for cooling, and then enters the low-temperature high-pressure compressor for pressurization to the saturation pressure corresponding to the optimal intermediate temperature, and enters the condensing evaporator for condensation. The condensed high-temperature and high-pressure refrigerant liquid enters the liquid receiver, and enters the regenerator from the outlet of the liquid receiver for supercooling, and then enters the intercooler for further supercooling, and finally enters the evaporator for evaporation after throttling and pressure reduction by throttle valve two, completing a complete cycle of low-temperature refrigeration.

[0015] The circulation method for realizing low-temperature refrigeration of the present invention has the following beneficial effects: both the two-stage cascade high and low temperature stages adopt a two-stage compression cycle, which greatly reduces the compression ratio of each stage compressor and improves the overall energy efficiency. The system is simple, the control is simple, and the operation stability is high; the high-temperature stage adopts a refrigeration cycle with a first-stage throttling intermediate incomplete cooling low-pressure stage and air replenishment and enthalpy increase, and the low-temperature stage adopts a refrigeration cycle with a first-stage throttling intermediate incomplete cooling and a heat recovery cycle; by optimizing the low-temperature stage cycle, an intermediate cooler is introduced into the low-temperature stage to improve the supercooling of the low-temperature refrigerant and improve the operating energy efficiency of the low-temperature stage, so that the -10°C to -125°C two-stage cascade low-temperature refrigerant runs a refrigeration cycle in a subcritical state, while reducing the amount of flash gas after throttling of the low-temperature refrigerant, thereby improving the refrigeration efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The block diagram of the refrigeration system for realizing low temperature refrigeration according to the present invention.

[0017] The accompanying drawings are marked as follows: 1. High-temperature, low-pressure compressor; 2. High-temperature, high-pressure compressor; 3. High-temperature condenser; 4. High-temperature intermediate cooler; 5. High-temperature, low-pressure economizer; 6. Condenser evaporator; 7. Low-temperature, low-pressure compressor; 8. Low-temperature, high-pressure compressor; 9. Evaporator; 10. Regenerator; 11. Intercooler; 12. Liquid storage tank; 13. Throttle valve one; 14. Throttle valve two; 15. Throttle valve three; 16. Throttle valve four; 17. Throttle valve five. DETAILED DESCRIPTION

[0018] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0019] like Figure 1As shown, the present invention discloses a refrigeration system for realizing low-temperature refrigeration, including a high-temperature stage circulation system and a low-temperature stage circulation system, the refrigerant in the high-temperature stage circulation system is R507A, the high-temperature stage circulation system includes a high-temperature stage low-pressure stage compressor 1, a high-temperature stage high-pressure stage compressor 2, a high-temperature stage condenser 3, a high-temperature stage intermediate cooler 4, a high-temperature stage low-pressure economizer 5 and a condenser evaporator 6 which are sequentially connected in series to form a circulation loop, the high-temperature stage intermediate cooler 4 is connected to the pipeline between the high-temperature stage low-pressure stage compressor 1 and the high-temperature stage high-pressure stage compressor 2 through a pipeline, the high-temperature stage intermediate cooler 4 replenishes air to the air outlet of the high-temperature stage low-pressure stage compressor 1, reduces the gas temperature after the first stage of compression, and reduces the power of the next stage of compression. Consumption is reduced, compression efficiency is improved, the high-temperature low-pressure economizer 5 is connected to the high-temperature low-pressure compressor 1 through a pipeline, the suction temperature and exhaust temperature of the high-temperature low-pressure compressor 1 are reduced, the load of the high-temperature low-pressure compressor 1 is reduced, and its service life is extended. A throttle valve 13 is provided on the pipeline between the high-temperature low-pressure economizer 5 and the condenser evaporator 6. The refrigerant flow rate is adjusted by the throttle valve 13 to ensure that the condenser evaporator 6 has an appropriate amount of refrigerant for evaporation and heat absorption, thereby ensuring the stability of the refrigeration effect. The opening of the throttle valve 13 can be adjusted to control the superheat of the refrigerant at the outlet of the condenser evaporator 6 to avoid excessive or low superheat, thereby improving the operating efficiency and stability of the system.

[0020] Furthermore, the high temperature intercooler 4 is connected to a throttle valve 3 15 to adjust the flow of the refrigerant in the high temperature intercooler 4 and the pressure of the high temperature intercooler 4 to adapt to different working conditions and system requirements and ensure the stable operation of the multi-stage compression system.

[0021] Furthermore, the high-temperature stage low-pressure economizer 5 is connected to a throttle valve 16 to accurately adjust the refrigerant flow entering the high-temperature stage low-pressure economizer 5 to adapt to different operating conditions and system load changes, thereby ensuring that the high-temperature stage low-pressure economizer 5 can function effectively, controlling the vaporization degree of the refrigerant, and ensuring that the high-temperature stage low-pressure economizer 5 can provide sufficient subcooling to improve the refrigeration efficiency of the system.

[0022] The refrigerant of the low-temperature cycle system is R14. The low-temperature cycle system includes an evaporator 9, a regenerator 10, a low-temperature low-pressure compressor 7, a low-temperature high-pressure compressor 8, a condensing evaporator 6 and a liquid storage tank 12 connected in series. The outlet of the liquid storage tank 12 is connected to the regenerator 10, and the outlet of the regenerator 10 is connected to the evaporator 9 through a pipeline. The regenerator 10 further cools the refrigerant flowing out of the evaporator 9, increases its supercooling, and reduces the flash gas of the refrigerant in the subsequent throttling process, thereby improving the cooling capacity and energy efficiency ratio of the refrigeration system, and the regenerator 10 can make the state of the refrigerant closer to the ideal thermodynamic cycle, improving the overall efficiency of the system. The liquid storage tank 12 is used to store the refrigerant, and helps to maintain the pressure stability of the refrigerant in the system, reducing the impact of pressure fluctuations on the operation of the system.

[0023] In this embodiment, the low-temperature circulation system also includes an intercooler 11. The outlet of the regenerator 10 is connected to the intercooler 11, and the outlet of the intercooler 11 is connected to the evaporator 9. By setting the intercooler 11, the temperature of the refrigerant can be further reduced, which helps to increase the refrigeration capacity per unit mass in the evaporator 9, improve the refrigeration effect, and enable the refrigerant to enter the evaporator 9 at a lower temperature, which can reduce the heat load of the evaporator 9 and reduce the energy consumption of the system. A throttle valve 14 is provided on the pipeline between the intercooler 11 and the evaporator 9. By adjusting the opening of the throttle valve 14, the refrigerant flow rate from the intercooler 11 to the evaporator 9 can be accurately controlled to adapt to different refrigeration loads and working conditions, ensuring that there is an appropriate amount of refrigerant in the evaporator 9 for evaporation and heat absorption, thereby ensuring the stability of the refrigeration effect. In addition, the throttle valve 14 reduces the pressure of the refrigerant when passing through, forming a suitable pressure difference, which helps the refrigerant to evaporate rapidly in the evaporator 9 and improve the heat exchange efficiency.

[0024] Furthermore, the intercooler 11 is connected to the pipeline between the low-temperature low-pressure compressor 7 and the low-temperature high-pressure compressor 8 through a pipeline. The intercooler 11 mixes the refrigerant after the pressure is increased by the low-temperature low-pressure compressor 7, reduces the temperature of the refrigerant entering the low-temperature high-pressure compressor 8, reduces the power consumption of the high-pressure compression, and thus improves the energy efficiency ratio of the entire refrigeration system.

[0025] Furthermore, the intercooler 11 is connected to a throttle valve 5 17. By adjusting the opening of the throttle valve 5 17, the ratio of the refrigerant flow rate flowing into the intercooler 11 and directly flowing to the subsequent process can be accurately adjusted to adapt to different working conditions and system requirements. The opening of the throttle valve 5 17 can be adjusted in time according to changes in the system load to avoid over-cooling or insufficient cooling of the refrigerant, thereby achieving the purpose of energy saving.

[0026] The present invention also discloses a circulation method for realizing low-temperature refrigeration, which adopts the refrigeration system as described above and specifically comprises the following steps:

[0027] High-temperature cycle: The high-temperature refrigerant R507A evaporates in the condenser evaporator 6 and takes away the heat rejection load on the low-temperature condensation side. After evaporation, the high-temperature refrigerant is pressurized by the high-temperature low-pressure compressor 1. The pressurized high-temperature refrigerant is mixed with the supplementary air of the high-temperature intermediate cooler 4 and enters the high-temperature high-pressure compressor 2 to be pressurized to the saturation pressure corresponding to the high-temperature condensation temperature, and then enters the high-temperature condenser 3. The high-temperature condenser 3 converts the high-temperature and high-pressure gaseous refrigerant into liquid. The high-pressure refrigerant liquid in the high-temperature condenser 3 flows out, and after being supercooled by the high-temperature intermediate cooler 4 and the high-temperature low-pressure economizer 5, it enters the condenser evaporator 6 after throttling by the throttle valve 13 to evaporate, completing a complete cycle of high-temperature refrigeration;

[0028] Low-temperature stage cycle: The low-temperature refrigerant R14 absorbs heat from the low-temperature heat source from the evaporator 9, evaporates at -110℃ to -125℃, and then enters the regenerator 10 for heat recovery. The low-temperature refrigerant is further supercooled before entering the compressor through heat recovery, which reduces the flash gas of the refrigerant in the subsequent throttling process, thereby improving the refrigeration capacity and energy efficiency ratio of the refrigeration system. After heat recovery, it enters the low-temperature low-pressure compressor 7 for pressurization. The pressurized low-temperature refrigerant R14 is mixed with the supplementary air from the intercooler 11 for cooling. The supplementary air can reduce the temperature of the refrigerant gas after the first stage of compression, reduce the power consumption of the next stage of compression, and improve the compression efficiency. The low-temperature refrigerant R14 is mixed with the supplementary air and enters the low-temperature high-pressure compressor 8 for pressurization to the saturation pressure corresponding to the optimal intermediate temperature, and then Then it enters the condenser evaporator 6 for condensation. Specifically, the high-temperature refrigerant R507A and the low-temperature refrigerant R14 exchange heat in the condenser evaporator 6 to condense the gaseous refrigerant R14 into a liquid state. The high-temperature and high-pressure refrigerant R14 liquid produced by the condensation enters the liquid storage tank 12, and enters the regenerator 10 from the outlet of the liquid storage tank 12 for supercooling, and then enters the intercooler 11 for further supercooling. The refrigeration capacity of the refrigeration system is significantly increased twice, the supercooling reduces the flash gas in the throttling process, and reduces the power consumption of the compressor, so that the system can generate more cooling capacity under the same input power, improves the energy utilization efficiency, and improves the energy efficiency ratio of the system. Finally, it enters the evaporator 9 for evaporation after throttling and reducing the pressure through the throttle valve 2 14, completing a complete cycle of low-temperature refrigeration.

[0029] Taking the evaporation temperature of -120℃ and the high temperature condensation temperature of +36℃ as an example, the low temperature stage operating cycle is -120℃ to -53℃, and the high temperature stage operating cycle is -58℃ to +36℃. The key parameters of the operation process are shown in Table 1:

[0030] Table 1

[0031]

[0032] COP represents the energy efficiency ratio of the system. The selection of the best intermediate temperature requires not only the optimal theoretical cycle COP, but also the comprehensive operating pressure ratio of the high and low temperature stages and the difference in the thermophysical properties of the refrigerant to ensure the best actual operating efficiency. The best intermediate pressure for the high and low temperature stages is also determined according to the principle of the theoretical optimal intermediate pressure. Configuration is performed, where Pm represents the optimal intermediate pressure, Pc represents the condensing pressure, and Pe represents the evaporating pressure, to ensure optimal operating efficiency of the high-temperature stage and the low-temperature stage.

[0033] The two-stage cascade high and low temperature stages of the present invention both adopt a two-stage compression cycle, simplifying the system and improving system stability. By introducing an intercooler 11 in the low temperature stage, the subcooling degree of the low temperature refrigerant is increased, and the low temperature stage operation energy efficiency is improved, so that the -110℃ to -125℃ two-stage cascade low temperature refrigerant circulates and refrigerates in a subcritical state, while reducing the amount of flash gas after throttling of the low temperature refrigerant, thereby improving the refrigeration efficiency. This solves the problem that each stage of the two-stage cascade in the prior art uses a single-stage compression, and the low temperature stage cycle is in a transcritical cycle. Even if a certain degree of subcooling is increased by the regenerator 10, a large amount of flash gas still exists after throttling, resulting in low refrigeration efficiency.

[0034] 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 principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A refrigeration system for realizing low-temperature refrigeration, comprising a high-temperature circulation system and a low-temperature circulation system, characterized in that: The high-temperature circulation system comprises a high-temperature low-pressure compressor (1), a high-temperature high-pressure compressor (2), a high-temperature condenser (3), a high-temperature intermediate cooler (4), a high-temperature low-pressure economizer (5) and a condenser evaporator (6) which are connected in series to form a circulation loop. The high-temperature intermediate cooler (4) is connected to the pipeline between the high-temperature low-pressure compressor (1) and the high-temperature high-pressure compressor (2) through a pipeline. The high-temperature low-pressure economizer (5) is connected to the high-temperature low-pressure compressor (1) through a pipeline. A throttle valve 1 (13) is provided on the pipeline between the high-temperature low-pressure economizer (5) and the condenser evaporator (6). The low-temperature circulation system comprises an evaporator (9), a regenerator (10), a low-temperature low-pressure compressor (7), a low-temperature high-pressure compressor (8), a condenser evaporator (6) and a liquid storage tank (12) which are connected in series. The outlet of the liquid storage tank (12) is connected to the regenerator (10), and the regenerator (10) is connected to the evaporator (9) through a pipeline.

2. A refrigeration system for realizing low temperature refrigeration according to claim 1, characterized in that: The low-temperature stage circulation system further comprises an intercooler (11), the outlet of the regenerator (10) is connected to the intercooler (11), the outlet of the intercooler (11) is connected to the evaporator (9), and a throttle valve 2 (14) is provided on the pipeline between the intercooler (11) and the evaporator (9).

3. A refrigeration system for realizing low temperature refrigeration according to claim 2, characterized in that: The intercooler (11) is connected to a pipeline between the low-temperature and low-pressure compressor (7) and the low-temperature and high-pressure compressor (8) through a pipeline.

4. A refrigeration system for realizing low temperature refrigeration according to claim 1, characterized in that: The refrigerant in the high-temperature circulation system is R507A, and the refrigerant in the low-temperature circulation system is R14.

5. A circulation method for realizing low temperature refrigeration, using the refrigeration system according to any one of claims 1 to 4, characterized in that: The specific steps include: High-temperature cycle: the high-temperature refrigerant evaporates in the condenser evaporator (6) to remove the heat rejection load on the low-temperature condensation side. After evaporation, the high-temperature refrigerant is pressurized by the high-temperature low-pressure compressor (1). The pressurized high-temperature refrigerant is mixed with the supplementary air from the high-temperature intermediate cooler (4) and enters the high-temperature high-pressure compressor (2) to be pressurized to a saturation pressure corresponding to the high-temperature condensation temperature. The high-pressure refrigerant then enters the high-temperature condenser (3). The high-pressure refrigerant liquid in the high-temperature condenser (3) flows out and is supercooled by the high-temperature intermediate cooler (4) and the high-temperature low-pressure economizer (5). After being throttled by the throttle valve 1 (13), the high-pressure refrigerant enters the condenser evaporator (6) to evaporate, completing a complete cycle of high-temperature refrigeration. Low-temperature stage cycle: The low-temperature refrigerant absorbs heat from the low-temperature heat source from the evaporator (9), evaporates at a temperature of -110°C to -125°C, and enters the regenerator (10) for heat recovery. After heat recovery, it enters the low-temperature stage low-pressure compressor (7) for pressurization. The pressurized low-temperature refrigerant is mixed with the supplementary air from the intercooler (11) and cooled. It then enters the low-temperature stage high-pressure compressor (8) for pressurization to the saturation pressure corresponding to the optimal intermediate temperature, and then enters the condensing evaporator (6) for condensation. The high-temperature and high-pressure refrigerant liquid generated by the condensation enters the liquid storage tank (12), and enters the regenerator (10) from the outlet of the liquid storage tank (12) for supercooling, and then enters the intercooler (11) for further supercooling. Finally, it enters the evaporator (9) for evaporation after throttling and pressure reduction by the throttle valve 2 (14), completing a complete cycle of low-temperature stage refrigeration.

Images