Cascade backheating flash separation auto-cascade refrigeration system and control method

Abstract

The invention discloses a cascade regenerative flash evaporation separation auto-cascade refrigeration system and a control method. The auto-cascade refrigeration system comprises a compressor, a condenser, a regenerator, two gas-liquid separators, an electronic expansion valve, a cascade heat exchanger, an evaporator, a controller, a temperature sensor and a pressure sensor. A heat regenerator and a cascade heat exchanger are arranged in the auto-cascade refrigeration system to perform cascade heat regeneration, so that heat exchange loss is reduced. And a condenser outlet section and a compressor suction section heat regenerator are arranged, so that the inlet dryness of the gas-liquid separator is reduced, and the first-stage flash separation efficiency is improved. And the mass flow of low-boiling-point components and refrigerants in the evaporator is increased through two-stage flash separation. The controller collects signals of a compressor outlet pressure sensor, an evaporator outlet pressure sensor and signals of a compressor outlet temperature sensor, a condenser outlet temperature sensor, a heat regenerator hot side outlet temperature sensor and an evaporator outlet temperature sensor, and efficient operation of the refrigerating system is guaranteed by controlling the opening degree of each electronic expansion valve and adjusting the refrigerant flow and the component circulation concentration.

Description

Technical Field

[0001] This invention relates to the field of cryogenic refrigeration technology, specifically to a cascade regenerative flash separation self-cascade refrigeration system and its control method. Background Technology

[0002] Refrigeration technology below -40°C has significant application demands in fields such as medical storage, food science, and electronics. Traditional single-stage vapor compression refrigeration systems and absorption refrigeration systems experience a significant decrease in efficiency when operating below -40°C or under large temperature differences. Cascade refrigeration cycles, formed by connecting single-stage vapor compression cycles through cascade heat exchangers, involve complex system control strategies and face challenges in equipment maintenance costs and miniaturization. Therefore, self-cascade refrigeration systems that utilize a single compressor and the temperature glide characteristics between non-azeotropic working fluids to achieve low-temperature targets have attracted widespread attention.

[0003] Cascade refrigeration systems can meet low-temperature requirements; however, their low component separation efficiency and component misalignment characteristics result in relatively low coefficient of performance (COP). Furthermore, the cascade heat exchanger accounts for a large portion of the cooling capacity generated by the compressor, and the irreversibility of the cascade heat exchanger... The losses are significant. Furthermore, in a cascade refrigeration system, a refrigerant dryness of around 0.5 entering the gas-liquid separator from the condenser ensures uniform refrigerant distribution to achieve the target refrigeration temperature range. However, due to component misalignment, the condenser outlet is often in a high dryness state during actual operation. This state reduces component separation efficiency and leads to gas entrainment at the liquid outlet, weakening the throttling refrigeration effect and impacting system energy efficiency. Improving the regenerative layout and optimizing the separation method are key measures to improve component separation efficiency and system energy efficiency. Summary of the Invention

[0004] To address the actual operating conditions and problems of the aforementioned self-cascade refrigeration systems, the present invention aims to propose a cascade regenerative flash separation self-cascade refrigeration system and its control method. The system incorporates a regenerator and a cascade heat exchanger for cascade regenerative heat reduction. Heat loss. By incorporating regenerators at the condenser outlet and compressor suction sections, the dryness of the gas-liquid separator inlet is reduced, improving component separation efficiency. Considering the decrease in gaseous refrigerant flow rate due to reduced dryness, a two-stage flash separation process is used to increase the refrigerant mass flow rate and the concentration of low-boiling-point components in the evaporator. The refrigeration system proposed in this invention improves the energy efficiency of the self-cascade refrigeration system by increasing the content of low-boiling-point components and the refrigerant flow rate in the evaporator.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] This invention proposes a cascaded regenerative flash evaporation separation self-cascade refrigeration system, comprising a compressor 1, the outlet of which is connected to the inlet of a condenser 2; the outlet of the condenser 2 is connected to the hot-side inlet of a regenerator 3; the hot-side outlet of the regenerator 3 is connected to the inlet of a first gas-liquid separator 4 via a first electronic expansion valve 8; the liquid phase outlet of the first gas-liquid separator 4 is connected to the inlet of a second gas-liquid separator 5 via a second electronic expansion valve 9; the gas phase outlet of the first gas-liquid separator 4, after passing through a third electronic expansion valve 10 and merging with the gas phase outlet of the second gas-liquid separator 5, is connected to the hot-side inlet of a cascade heat exchanger 6; the hot-side outlet of the cascade heat exchanger 6 is connected to the inlet of an evaporator 7 via a fourth electronic expansion valve 11; the liquid phase outlet of the second gas-liquid separator 5, after passing through a fifth electronic expansion valve 12 and merging with the outlet of the evaporator 7, is connected to the cold-side inlet of the cascade heat exchanger 6; the cold-side outlet of the cascade heat exchanger 6 is connected to the cold-side inlet of the regenerator 3; the cold-side outlet of the regenerator 3 is connected to the inlet of the compressor 1; and the receiving end of a controller 13 is connected to a first temperature sensor 101 and a first pressure sensor 101 at the outlet of the compressor 1. The controller 13 is connected to the second temperature sensor 103 at the outlet of the condenser 2; the controller 13 is connected to the third temperature sensor 104 at the hot side outlet of the regenerator 3; the controller 13 is connected to the second pressure sensor 106 and the fourth temperature sensor 105 at the outlet of the first electronic expansion valve 8; the controller 13 is connected to the third pressure sensor 107 and the fifth temperature sensor 108 at the outlet of the evaporator 7; the controller 13 is connected to the control mechanism of the compressor 1; the control mechanism 13 is connected to the regulating mechanism of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10, the fourth electronic expansion valve 11, and the fifth electronic expansion valve 12; during operation, the controller 13 can control the opening of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10, the fourth electronic expansion valve 11, and the fifth electronic expansion valve 12 to regulate the flow rate and the concentration of the mixed working fluid components in the evaporator 7, thereby maintaining the efficient operation of the refrigeration system.

[0007] The self-cascade refrigeration system uses a binary hydrocarbon non-azeotropic mixture as its working fluid. The high-temperature, high-pressure gas, compressed by compressor 1, enters condenser 2 for partial condensation and then enters regenerator 3. In regenerator 3, it is cooled to reduce dryness. After cooling in regenerator 3, the two-phase mixed refrigerant is depressurized and cooled in the first electronic expansion valve 8 before entering the first gas-liquid separator 4, where it is separated into a gas phase rich in low-boiling-point working fluid and a liquid phase rich in high-boiling-point working fluid. The liquid phase is then depressurized and cooled by the second electronic expansion valve 9 before entering the second gas-liquid separator 5, where it is separated into a gas phase rich in low-boiling-point working fluid and a liquid phase rich in high-boiling-point working fluid. The gas phase from the first gas-liquid separator 4 is cooled and depressurized by the third electronic expansion valve 10 and then merges with the gas phase from the second gas-liquid separator 5 before entering the cascade heat exchanger 6 to release heat and cool down. The liquid phase, which has condensed to a subcooled state, is cooled and depressurized in the fourth electronic expansion valve 11 and then enters the evaporator 7 to absorb heat and become a low-temperature, low-pressure two-phase state. The liquid phase from the second gas-liquid separator 5 is cooled and depressurized by the fifth electronic expansion valve 12 and then mixes with the fluid at the outlet of the evaporator 7 before entering the cold side inlet of the cascade heat exchanger 6. It absorbs heat and heats up in the cascade heat exchanger 6. After that, it enters the regenerator 3 to absorb heat and heat up before entering the inlet of the compressor 1.

[0008] The control method for a cascade regenerative flash separation self-cascade refrigeration system involves using a controller 13 to collect signals from temperature and pressure sensors within the refrigeration system, as well as the system's operating time. The controller 13 controls the start and stop of compressor 1. It also adjusts the opening degrees of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10, the fourth electronic expansion valve 11, and the fifth electronic expansion valve 12 to ensure stable operation of the self-cascade refrigeration system. The safe outlet pressure of compressor 1 is P10 with a deviation of Δ10; the safe outlet temperature of compressor 1 is T12 with a deviation of Δ12; the setpoint for the outlet temperature of evaporator 7 is T20 with a deviation of Δ20; the start-up time is t0; and the setpoint for the dryness of the hot side outlet of regenerator 3 is q30 with a deviation of Δ30. The specific control method is as follows:

[0009] 1) The controller 13 collects the running time t of the self-cascade refrigeration system to determine whether it is in the start-up stage. When t < t0, the system is in the start-up stage. The controller 13 receives the compressor discharge pressure collected by the first pressure sensor 102 in real time. When the compressor 1 outlet pressure P1 > P10 + Δ10, the controller 13 reduces the compressor speed and adjusts the five electronic expansion valves to the fully open state. The two gas-liquid separators act as expansion containers to increase the internal volume, reduce the pressure in the start-up stage, and solve the problem of high compressor discharge pressure in the start-up stage of the self-cascade refrigeration system.

[0010] 2) Controller 13 acquires the running time t of the refrigeration system and the temperature signal T5 from the fifth temperature sensor 108 at the outlet of evaporator 7; determines whether the evaporator outlet temperature has reached the set temperature; when t≥t0 and T5>T20+Δ20, the refrigeration system is in the cooling stage; the controller 13 increases the compressor speed; the controller 13 increases the opening of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10 and the fifth electronic expansion valve 12, and decreases the opening of the fourth electronic expansion valve 11, increasing the total circulation flow of the system, increasing the cold side flow of the cascade heat exchanger 6, and decreasing the hot side flow, thereby accelerating the cooling rate by rapidly constructing regeneration; the controller 13, based on the pressure signal from the first pressure sensor 102 and the temperature signal from the third temperature sensor 108, determines whether the evaporator outlet temperature has reached the set temperature; when t≥t0 and T5>T20+Δ20, the refrigeration system is in the cooling stage; the controller 13 increases the compressor speed; the controller 13 increases the opening of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10 and the fifth electronic expansion valve 12, and decreases the opening of the fourth electronic expansion valve 11, thereby increasing the total circulation flow of the system, increasing the cold side flow of the cascade heat exchanger 6, and decreasing the hot side flow, thereby accelerating the cooling rate by rapidly constructing regeneration; the controller 13, based on the pressure signal from the first pressure sensor 102 and the temperature signal from the third temperature sensor 108, determines whether the evaporator outlet temperature has reached the set temperature ... The temperature signal from 04 is used to calculate the dryness value q3 at the hot side outlet of the regenerator 3. The controller 13 adjusts the opening of the fourth electronic expansion valve 11 and the fifth electronic expansion valve 12 to ensure that the dryness value q30-Δ30≤q3≤q30+Δ30 at the hot side outlet of the regenerator 3, thus guaranteeing the component separation efficiency of the self-cascade system and ensuring the regeneration construction and cooling rate. When q3≤q30-Δ30, the controller 13 increases the opening of the fourth electronic expansion valve 11 and the fifth electronic expansion valve 12; when q3≥q30+Δ30, the controller 13 decreases the opening of the fourth electronic expansion valve 11 and the fifth electronic expansion valve 12. The controller 13 adjusts the third electronic expansion valve 10 to balance the mixing point pressure. During the cooling stage, P1≤P10+Δ10 and T1≤T12+Δ12 are guaranteed.

[0011] 3) Controller 13 acquires the temperature signal T5 from the fifth temperature sensor 108 at the outlet of evaporator 7; when T20-Δ20≤T5≤T20+Δ20, the system is in a stable operating phase; controller 13 acquires the temperature signal T2 from the second temperature sensor 103 at the outlet of condenser 2; when changes in the ambient temperature cause T2 to increase, the evaporation temperature rises, and controller 13 reduces the opening of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10, the fourth electronic expansion valve 11, and the fifth electronic expansion valve 12 to reduce the evaporation pressure and lower the evaporation temperature; at the same time, it ensures that q30-Δ30≤q3≤q30+Δ30; when the temperature signal T5 increases, controller 13 increases the opening of the first electronic expansion valve 8 and the second electronic expansion valve 9 to reduce the amount of low-boiling-point fluid entering evaporator 7. The concentration of the component is increased; the opening of the fourth electronic expansion valve 11 is increased, the evaporation pressure increases, and the evaporation temperature rises; the opening of the fifth electronic expansion valve 12 is increased, the cold side inlet temperature of the cascade heat exchanger 6 is increased, and the evaporation temperature rises; when the temperature signal T5 decreases, the controller 13 decreases the opening of the first electronic expansion valve 8 and the second electronic expansion valve 9 to enhance the flash separation effect and increase the concentration of low-boiling-point components entering the evaporator 7; the opening of the fourth electronic expansion valve 11 and the fifth electronic expansion valve 12 is decreased, the evaporation pressure and the cold side inlet temperature of the cascade heat exchanger 6 are decreased, and the evaporation temperature is lowered; regardless of whether the temperature signal T5 increases or decreases, it is necessary to ensure that T20-Δ20≤T5≤T20+Δ20, T1≤T12+Δ12, P1≤P10+Δ10, and q30-Δ30≤q3≤q30+Δ30.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] 1. Considering the low energy efficiency of self-cascade refrigeration systems and the irreversibility of cascade heat exchangers... The invention addresses the issues of significant losses and decreased component separation efficiency due to the high dryness of the condenser outlet during actual operation. The system described in this invention utilizes a cascade heat exchanger and a regenerator for staged heat recovery to reduce heat loss. Heat loss. Cascaded regenerative cooling can achieve lower evaporation temperatures. The regenerator reduces the inlet dryness of the gas-liquid separator, improving component separation efficiency.

[0014] 2. Considering the reduction in gaseous refrigerant flow rate due to decreased dryness, the refrigerant mass flow rate and low-boiling-point component concentration in the evaporator are increased through two-stage flash separation, thereby improving system energy efficiency. Attached Figure Description

[0015] Figure 1 This is a flow chart of a cascade regenerative flash separation self-cascade refrigeration system according to the present invention.

[0016] 1. Compressor; 2. Condenser; 3. Regenerator; 4. First gas-liquid separator; 5. Second gas-liquid separator; 6. Cascade heat exchanger; 7. Evaporator; 8. First electronic expansion valve; 9. Second electronic expansion valve; 10. Third electronic expansion valve; 11. Fourth electronic expansion valve; 12. Fifth electronic expansion valve; 13. Controller; 101. First temperature sensor; 102. First pressure sensor; 103. Second temperature sensor; 104. Third temperature sensor; 105. Fourth temperature sensor; 106. Second pressure sensor; 107. Third pressure sensor; 108. Fifth temperature sensor. Detailed Implementation

[0017] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and an embodiment. It should be understood that the specific embodiment described herein is only for explaining the invention and is not intended to limit the invention.

[0019] Implementation Cases

[0020] like Figure 1As shown. A cascaded regenerative flash separation self-cascade refrigeration system includes a compressor 1, with the compressor 1 outlet pipe connected to the inlet of a condenser 2; the condenser 2 outlet connected to the hot-side inlet of a regenerator 3; the regenerator 3 hot-side outlet connected to the inlet of a first electronic expansion valve 8; the first electronic expansion valve 8 outlet connected to the inlet of a first gas-liquid separator 4; the first gas-liquid separator 4 liquid phase outlet connected to the inlet of a second electronic expansion valve 9; the second electronic expansion valve 9 outlet connected to the inlet of a second gas-liquid separator 5; and the first gas-liquid separator 4 gas phase outlet connected to the inlet of a third electronic expansion valve 10. The gas phase outlet of gas-liquid separator 5 is connected to the hot side inlet of cascade heat exchanger 6 after merging with the outlet of the third electronic expansion valve 10; the hot side outlet of cascade heat exchanger 6 is connected to the inlet of the fourth electronic expansion valve 11; the outlet of the fourth electronic expansion valve 11 is connected to the inlet of evaporator 7; the liquid phase outlet of second gas-liquid separator 5 is connected to the inlet of fifth electronic expansion valve 12; the outlet of evaporator 7 is connected to the cold side inlet of cascade heat exchanger 6 after merging with the outlet of the fifth electronic expansion valve 12; the cold side outlet of cascade heat exchanger 6 is connected to the cold side inlet of regenerator 3; the cold side outlet of regenerator 3 is connected to the inlet of compressor 1. The receiving end of controller 13 is connected to the first pressure sensor 102 and the first temperature sensor 101 at the outlet of compressor 1; the receiving end of controller 13 is connected to the second temperature sensor 103 at the outlet of condenser 2; the receiving end of controller 13 is connected to the third temperature sensor 104 at the hot side outlet of regenerator 3; the receiving end of controller 13 is connected to the second pressure sensor 106 and the fourth temperature sensor 105 at the outlet of first electronic expansion valve 8; the receiving end of controller 13 is connected to the third pressure sensor 107 and the fifth temperature sensor 108 at the outlet of evaporator 7; the transmitting end of controller 13 is connected to the compressor control mechanism; the transmitting end of control mechanism 13 is connected to the regulating mechanism of first electronic expansion valve 8, second electronic expansion valve 9, third electronic expansion valve 10, fourth electronic expansion valve 11 and fifth electronic expansion valve 12; during operation, the refrigeration system can control the opening degree of first electronic expansion valve 8, second electronic expansion valve 9, third electronic expansion valve 10, fourth electronic expansion valve 11 and fifth electronic expansion valve 12 through controller 13 to regulate the flow rate and mixed working fluid component concentration in evaporator 7 and maintain the efficient operation of the refrigeration system.

[0021] The present invention discloses a cascaded regenerative flash separation self-cascade refrigeration system, employing a binary non-azeotropic working fluid, specifically a binary hydrocarbon non-azeotropic working fluid. The high-temperature, high-pressure gas, compressed by compressor 1, enters condenser 2 for condensation and then enters regenerator 3 for cooling. The two-phase refrigerant mixture, after cooling in regenerator 3, is depressurized and cooled in first electronic expansion valve 8 before entering first gas-liquid separator 4 and separated into a gas phase rich in low-boiling-point working fluid and a liquid phase rich in high-boiling-point working fluid. The liquid phase is then depressurized and cooled by second electronic expansion valve 9 before entering second gas-liquid separator 5 for further separation. The gas phase and liquid phase; the gas phase from the first gas-liquid separator 4 is cooled and depressurized by the third electronic expansion valve 10 and then merges with the gas phase from the second gas-liquid separator 5 before entering the cascade heat exchanger 6 to release heat and cool down; then the subcooled liquid is cooled and depressurized in the fourth electronic expansion valve 11 and enters the evaporator 7 to absorb heat and become a low-temperature, low-pressure two-phase state; the liquid phase from the second gas-liquid separator 5 is cooled and depressurized by the fifth electronic expansion valve 12 and then mixes with the fluid at the outlet of the evaporator 7 before entering the cold side inlet of the cascade heat exchanger 6; it absorbs heat and heats up in the cascade heat exchanger 6; then it enters the regenerator 3 to absorb heat and heat up before entering the compressor 1 inlet.

[0022] The present invention discloses a control method for a cascade regenerative flash separation self-cascade refrigeration system.

[0023] The controller 13 collects signals from temperature sensors, pressure sensors, and system running time within the refrigeration system, and controls the start and stop of compressor 1. The controller 13 also adjusts the opening degrees of the first electronic expansion valve 8, second electronic expansion valve 9, third electronic expansion valve 10, fourth electronic expansion valve 11, and fifth electronic expansion valve 12 to ensure stable operation of the cascade refrigeration system. The safe outlet pressure of compressor 1 is P10 of 2.5 MPa, with a deviation of Δ10 of 0.02 MPa; the safe outlet temperature of compressor 1 is T12 of 125℃, with a deviation of Δ10 of 2℃; the setpoint for the evaporator outlet temperature is T20 of -70℃, with a deviation of Δ20 of 1℃; the start-up time is t0 of 20 minutes; and the setpoint for the dryness fraction q30 at the hot side outlet of regenerator 3 is 0.5, with a deviation of Δ30 of 0.05. The specific control method is as follows:

[0024] 1) Controller 13 collects the running time t of the self-cascade refrigeration system. When t < 20 min, the self-cascade refrigeration system is in the start-up phase. Controller 13 receives the compressor discharge pressure collected by the first pressure sensor 102 at the compressor outlet in real time. When the compressor outlet pressure P1 > 2.52 MPa, controller 13 reduces the compressor speed, adjusts the five electronic expansion valves to 100% opening, and uses the two gas-liquid separators as expansion containers to increase their internal volume, thereby reducing the pressure during the start-up phase and solving the problem of high compressor discharge pressure during the start-up phase of the self-cascade refrigeration system.

[0025] 2) Controller 13 calculates the dryness value q3 at the hot side outlet of regenerator 3 based on the pressure signal from the first pressure sensor 102 and the temperature signal from the third temperature sensor 104. Controller 13 collects the running time t of the refrigeration system and the temperature signal T5 from the fifth temperature sensor 108 at the outlet of evaporator 7. When t ≥ 20 min and T5 > -69℃, the refrigeration system is in the cooling stage. Controller 13 increases the compressor speed. Controller 13 adjusts the first electronic expansion valve to 80% opening, the second electronic expansion valve to 80% opening, and the third electronic expansion valve to 80% opening to balance the pressure. Controller 13 also adjusts the fourth electronic expansion valve 11 to 30% opening and the fifth electronic expansion valve 12 to 70% opening, increasing the total system circulation flow, increasing the cold side flow of the cascade heat exchanger 6, and decreasing the hot side flow. This rapidly builds up regeneration to accelerate the cooling rate. Simultaneously, it ensures that the dryness value at the hot side outlet of regenerator 3 is 0.45 ≤ q3 ≤ 0.55, improving component separation efficiency. When q3 < 0.45, controller 13 increases the opening of the fourth electronic expansion valve 11 to 50% and the opening of the fifth electronic expansion valve 12 to 80%; when q3 > 0.55, controller 13 decreases the opening of the fourth electronic expansion valve 11 to 20% and the opening of the fifth electronic expansion valve 12 to 60%; during the cooling process, P1 ≤ 2.52 MPa and T1 ≤ 127℃ are maintained.

[0026] 3) Controller 13 acquires the temperature signal T5 from the fifth temperature sensor 108 at the outlet of evaporator 7; when -71℃≤T5≤-69℃, the system is in a stable operating phase; controller 13 acquires the temperature signal T2 from the second temperature sensor 103 at the outlet of condenser 2; when changes in the ambient temperature cause T2 to increase, the evaporation temperature rises. Whenever T2 increases by 2℃, controller 13 controls the electronic expansion valve adjustment mechanism to reduce the opening of the first electronic expansion valve 8, the second electronic expansion valve 9, the third electronic expansion valve 10, the fourth electronic expansion valve 11, and the fifth electronic expansion valve 12 in a step of 5%, thereby reducing the evaporation pressure and lowering the evaporation temperature, while ensuring 0.45≤q3≤0.55; when the temperature signal T5 increases, whenever T5 increases by 2℃, controller 13 increases the opening of the first electronic expansion valve 8 and the second electronic expansion valve 9 in a step of 5%, thereby reducing the pressure entering evaporator 7. The concentration of low-boiling-point components in the evaporator 7 is increased; the opening of the fourth electronic expansion valve 11 is increased by a step size of 5%, which increases the evaporation pressure and the evaporation temperature; the opening of the fifth electronic expansion valve 12 is increased by a step size of 5%, which increases the cold-side inlet temperature of the cascade heat exchanger 6 and raises the evaporation temperature; when the temperature signal T5 decreases, the controller 13 decreases the opening of the first electronic expansion valve 8 and the second electronic expansion valve 9 by a step size of 5% whenever T5 decreases by 2℃, which enhances the flash separation effect and increases the concentration of low-boiling-point components in the evaporator 7; the opening of the fourth electronic expansion valve 11 and the fifth electronic expansion valve 12 is decreased by a step size of 5%, which decreases the evaporation pressure and the cold-side inlet temperature of the cascade heat exchanger 6, thus lowering the evaporation temperature; regardless of whether T5 increases or decreases, it is necessary to ensure that -71℃≤T5≤-69℃, T1≤127℃, P1≤2.52MPa, and 4.5≤q3≤5.5.

Claims

1. A cascaded regenerative flash separation self-cascade refrigeration system, characterized in that, The system includes a compressor (1), whose outlet is connected to the inlet of a condenser (2); the outlet of the condenser (2) is connected to the hot-side inlet of a regenerator (3); the hot-side outlet of the regenerator (3) is connected to the inlet of a first gas-liquid separator (4) via a first electronic expansion valve (8); the liquid phase outlet of the first gas-liquid separator (4) is connected to the inlet of a second gas-liquid separator (5) via a second electronic expansion valve (9); the gas phase outlet of the first gas-liquid separator (4) is connected to the hot-side inlet of a cascade heat exchanger (6) after passing through a third electronic expansion valve (10) and merging with the gas phase outlet of the second gas-liquid separator (5). The hot-side outlet of the cascade heat exchanger (6) is connected to the inlet of the evaporator (7) via the fourth electronic expansion valve (11); the liquid-phase outlet of the second gas-liquid separator (5) is connected to the cold-side inlet of the cascade heat exchanger (6) after merging with the outlet of the evaporator (7) via the fifth electronic expansion valve (12); the cold-side outlet of the cascade heat exchanger (6) is connected to the cold-side inlet of the regenerator (3); the cold-side outlet of the regenerator (3) is connected to the inlet of the compressor (1); the receiving end of the controller (13) is connected to the first temperature sensor (101) and the first pressure sensor (102) at the outlet of the compressor (1); the controller ( The receiving end of controller (13) is connected to the second temperature sensor (103) at the outlet of condenser (2); the receiving end of controller (13) is connected to the third temperature sensor (104) at the hot side outlet of regenerator (3); the receiving end of controller (13) is connected to the second pressure sensor (106) and the fourth temperature sensor (105) at the outlet of first electronic expansion valve (8); the receiving end of controller (13) is connected to the third pressure sensor (107) and the fifth temperature sensor (108) at the outlet of evaporator (7); the transmitting end of controller (13) is connected to the control mechanism of compressor (1). The controller (13) is connected to the regulating mechanism of the first electronic expansion valve (8), the second electronic expansion valve (9), the third electronic expansion valve (10), the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12). During operation, the refrigeration system controls the opening of the first electronic expansion valve (8), the second electronic expansion valve (9), the third electronic expansion valve (10), the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12) through the controller (13), adjusts the flow rate and the concentration of mixed working fluid components in the evaporator (7), and maintains the efficient operation of the refrigeration system.

2. The cascade regenerative flash separation self-cascade refrigeration system according to claim 1, characterized in that, The refrigeration system uses a binary hydrocarbon non-azeotropic mixture. The high-temperature, high-pressure gas, after being compressed by the compressor (1), enters the condenser (2) and is partially condensed before entering the regenerator (3). The regenerator (3) cools the mixture to reduce its dryness. After being cooled by the regenerator (3), the two-phase mixed refrigerant is cooled and depressurized in the first electronic expansion valve (8) and then enters the first gas-liquid separator (4), where it is separated into a gas phase rich in low-boiling-point refrigerant and a liquid phase rich in high-boiling-point refrigerant. The liquid phase is cooled and depressurized by the second electronic expansion valve (9) and then enters the second gas-liquid separator (5), where it is separated into a gas phase rich in low-boiling-point refrigerant and a liquid phase rich in high-boiling-point refrigerant. The gas phase of the liquid separator (4) is cooled and depressurized by the third electronic expansion valve (10) and then merged with the gas phase of the second gas-liquid separator (5) and enters the cascade heat exchanger (6); the liquid that is condensed to a subcooled state is cooled and depressurized in the fourth electronic expansion valve (11) and then enters the evaporator (7), where it absorbs heat and becomes a low-temperature, low-pressure two-phase state; the liquid phase of the second gas-liquid separator (5) is cooled and depressurized by the fifth electronic expansion valve (12) and then mixed with the fluid at the outlet of the evaporator (7) and enters the cold side inlet of the cascade heat exchanger (6); it absorbs heat and rises in temperature in the cascade heat exchanger (6); after that, it enters the regenerator (3) to absorb heat and rise in temperature and then enters the compressor (1) inlet.

3. The control method for a cascade regenerative flash separation self-cascade refrigeration system as described in claim 1 or 2, characterized in that, The controller (13) collects signals from temperature and pressure sensors in the refrigeration system and the system running time, and controls the start and stop of the compressor (1) through the controller (13); the controller (13) adjusts the opening of the first electronic expansion valve (8), the second electronic expansion valve (9), the third electronic expansion valve (10), the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12) to ensure the stable operation of the self-cascade refrigeration system; the safe pressure at the outlet of the compressor (1) is P10, and the deviation value is Δ10; the safe temperature at the outlet of the compressor (1) is T12, and the deviation value is Δ12; the set value of the outlet temperature of the evaporator (7) is T20, and the deviation value is Δ20; the start-up time is t0; the set value of the dryness of the hot side outlet of the regenerator (3) is q30, and the deviation value is Δ30; the specific control method is as follows: 1) The controller (13) collects the running time t of the self-cascade refrigeration system and determines whether it is in the start-up stage. When t < t0, the system is in the start-up stage. The controller (13) receives the compressor discharge pressure collected by the first pressure sensor (102) in real time. When the compressor (1) outlet pressure P1 > P10 + Δ10, the controller (13) reduces the compressor speed and adjusts the five electronic expansion valves to the fully open state. The first gas-liquid separator (4) and the second gas-liquid separator (5) increase the internal volume as expansion containers, reduce the pressure in the start-up stage, and solve the problem of high compressor discharge pressure in the start-up stage of the self-cascade refrigeration system. 2) The controller (13) collects the running time t of the refrigeration system and the temperature signal T5 of the fifth temperature sensor (108) at the outlet of the evaporator (7); determines whether the outlet temperature of the evaporator has reached the set temperature; when t≥t0 and T5>T20+Δ20, the refrigeration system is in the cooling stage; the controller (13) increases the compressor speed; the controller (13) increases the opening of the first electronic expansion valve (8), the second electronic expansion valve (9), the third electronic expansion valve (10) and the fifth electronic expansion valve (12), and decreases the opening of the fourth electronic expansion valve (11), increases the total circulation flow of the system, increases the cold side flow of the cascade heat exchanger (6), and decreases the hot side flow, and accelerates the cooling speed by rapidly constructing reheat; the controller (13) according to the pressure signal of the first pressure sensor (102) and the temperature signal T5 of the third temperature sensor (108) at the outlet of the evaporator (7); 04) The temperature signal is used to calculate the dryness value q3 at the hot side outlet of the regenerator (3); the controller (13) adjusts the opening of the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12) to make the dryness value q30-Δ30≤q3≤q30+Δ30 at the hot side outlet of the regenerator (3) to ensure the component separation efficiency of the self-cascade system and to ensure the regeneration construction and cooling rate; when q3≤q30-Δ30, the controller (13) increases the opening of the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12); when q3≥q30+Δ30, the controller (13) decreases the opening of the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12); the controller (13) adjusts the third electronic expansion valve (10) to balance the mixing point pressure; during the cooling stage, P1≤P10+Δ10 and T1≤T12+Δ12 are guaranteed; 3) The controller (13) collects the temperature signal T5 from the fifth temperature sensor (108) at the outlet of the evaporator (7); when T20-Δ20≤T5≤T20+Δ20, the system is in a stable operating phase; the controller (13) collects the temperature signal T2 from the second temperature sensor (103) at the outlet of the condenser (2); when the change in ambient temperature causes T2 to increase, the evaporation temperature rises, and the controller (13) reduces the opening of the first electronic expansion valve (8), the second electronic expansion valve (9), the third electronic expansion valve (10), the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12) to reduce the evaporation pressure and the evaporation temperature decreases; at the same time, it ensures that q30-Δ30≤q3≤q30+Δ30; when the temperature signal T5 increases, the controller (13) increases the opening of the first electronic expansion valve (8) and the second electronic expansion valve (9) to reduce the amount of gas entering the evaporator (7). The concentration of low-boiling-point components in the evaporator (7) is increased; the opening of the fourth electronic expansion valve (11) is increased, the evaporation pressure is increased, and the evaporation temperature is increased; the opening of the fifth electronic expansion valve (12) is increased, the cold-side inlet temperature of the cascade heat exchanger (6) is increased, and the evaporation temperature is increased; when the temperature signal T5 decreases, the controller (13) decreases the opening of the first electronic expansion valve (8) and the second electronic expansion valve (9) to enhance the flash separation effect and increase the concentration of low-boiling-point components entering the evaporator (7); the opening of the fourth electronic expansion valve (11) and the fifth electronic expansion valve (12) is decreased, the evaporation pressure and the cold-side inlet temperature of the cascade heat exchanger (6) are decreased, and the evaporation temperature is decreased; regardless of whether the temperature signal T5 increases or decreases, it is necessary to ensure that T20-Δ20≤T5≤T20+Δ20, T1≤T12+Δ12, P1≤P10+Δ10, and q30-Δ30≤q3≤q30+Δ30.

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