Cascade refrigerating system of medicinal experimental freeze dryer

Abstract

The utility model provides a cascade refrigeration system of a medicinal experimental freeze dryer, which comprises a high-temperature-stage refrigeration unit and a low-temperature-stage refrigeration unit, and the high-temperature-stage refrigeration unit comprises a high-temperature-stage compressor, a condensation precooler, a first dry filter, a first electromagnetic valve, an expansion valve and a condensation evaporator which are sequentially connected in series and form a closed loop; the low-temperature-stage refrigeration unit comprises a gas-liquid separator, a low-temperature-stage compressor, an oil separator, a condensation precooler, a condensation evaporator, a high-pressure liquid storage device, a second drying filter, a front box electromagnetic valve, a front box expansion valve, a front box heat exchanger, a cold trap electromagnetic valve, a cold trap expansion valve, a cold trap, a check valve and a hot gas bypass branch. According to the utility model, the hot gas bypass branch is arranged in the system, and controllable additional load is added to the cold trap, so that the suction pressure is regulated and controlled, the compression ratio and the refrigeration working condition are improved, meanwhile, the flow of refrigerant in the cold trap is increased when the load is small, the cooling effect of the low-temperature-stage compressor is enhanced, and overhigh temperature and fault shutdown are avoided.

Description

Technical Field

[0001] The utility model relates to the field of freeze-drying machine refrigeration systems, in particular to a cascade refrigeration system of a medicinal experimental freeze-drying machine. Background Art

[0002] Pharmaceutical experimental freeze dryers are small freeze-drying equipment, mainly used for pharmaceutical process development and process optimization. As experimental equipment, in addition to being easy to install and use, compact in structure, and easy to move, due to the high value of the drugs, there are also high requirements for the performance and reliability of the equipment.

[0003] As a key component of a pharmaceutical laboratory freeze dryer, the refrigeration system's performance and reliability play a decisive role in its operation. The maximum operating temperature is generally -85°C. Therefore, the refrigeration system of pharmaceutical laboratory freeze dryers generally adopts a two-stage cascade refrigeration cycle, a direct expansion cold trap for cooling, and is equipped with a fully enclosed commercial compressor and an air-cooled condenser.

[0004] The freeze-drying cycle of a laboratory freeze dryer is typically long, and the refrigeration system's operating conditions and loads vary greatly, even to extremes, during a single freeze-drying cycle. During much of the latter part of the freeze-drying cycle, the refrigeration load is very low and continues to decline, causing the compressor suction pressure to continuously drop to the compressor's limit. This can lead to oil return difficulties, excessive compression ratios, overheating of the compressor motor, and even thermal shutdowns. Consequently, when ambient temperature and humidity are slightly elevated or the operating time is prolonged, pharmaceutical laboratory freeze dryers are prone to compressor oil shortages and oil degradation. This shortens the compressor's lifespan, reduces reliability, and makes the system prone to failures and shutdowns, resulting in freeze-drying failures and serious economic losses. Utility Model Content

[0005] In order to solve the problems in the prior art of reduced compressor life, reduced reliability, and easy failure and shutdown resulting in freeze-drying failure caused by low refrigeration load in the latter part of the freeze-drying cycle, the utility model provides a cascade refrigeration system for a pharmaceutical experimental freeze dryer;

[0006] The utility model provides a cascade refrigeration system for a medicinal experimental freeze dryer adopts the following technical solutions:

[0007] A cascade refrigeration system for a pharmaceutical experimental freeze dryer comprises a high-temperature refrigeration unit and a low-temperature refrigeration unit, wherein the high-temperature refrigeration unit is used to refrigerate the low-temperature refrigeration unit.

[0008] The high-temperature refrigeration unit comprises a high-temperature compressor, a condenser precooler, a drying filter, a solenoid valve, an expansion valve and a condenser evaporator connected in series to form a closed loop;

[0009] The low-temperature refrigeration unit includes a gas-liquid separator, a low-temperature compressor, an oil separator, a condenser precooler, a condenser evaporator, a high-pressure liquid storage device, a second drying filter, a front box solenoid valve, a front box expansion valve, a front box heat exchanger, a cold trap solenoid valve, a cold trap expansion valve, a cold trap, a check valve and a hot gas bypass branch;

[0010] The return air pipe of the gas-liquid separator is connected to the input port of the low-temperature compressor, the output port of the low-temperature compressor is connected to the oil separator, the oil separator is connected to the condenser precooler, the condenser precooler is connected to the condenser evaporator, the refrigerant in the low-temperature refrigeration unit performs heat exchange with the refrigerant in the high-temperature refrigeration unit in the condenser evaporator, the condenser evaporator is connected to the input end of the high-pressure liquid storage device, the output end of the high-pressure liquid storage device is respectively connected to the front box solenoid valve and the cold trap solenoid valve through the second drying filter to form a parallel pipeline, the front box solenoid valve is connected to the front box expansion valve, the front box expansion valve It is connected to the input end of the front box heat exchanger, the cold trap solenoid valve is connected to the cold trap expansion valve, the cold trap expansion valve is connected to the input end of the cold trap, the output end of the cold trap is connected to the input end of the check valve, the output end of the check valve is connected in parallel with the output end of the front box heat exchanger and then connected to the air inlet pipe of the gas-liquid separator; a hot gas bypass branch is provided between the condensing precooler and the cold trap, and a solenoid valve 2 and a pressure reducing valve are provided in the hot gas bypass branch, the output end of the condensing precooler is connected to the input end of the hot gas bypass branch, and the output end of the hot gas bypass branch is connected in parallel with the output end of the cold trap expansion valve and then connected to the input end of the cold trap.

[0011] Furthermore, the low-temperature refrigeration unit also includes a pressure relief valve and an expansion tank, the input end of the expansion tank is connected after the output end of the oil separator, and the output end of the expansion tank is connected before the input port of the low-temperature compressor, and a pressure relief valve is arranged between the expansion tank and the oil separator.

[0012] Furthermore, the condensing precooler is an air-cooled heat exchanger with a fan, which has two independent sets of heat exchange pipes inside. The two sets of heat exchange pipes share a set of cooling fans. One set of heat exchange pipes is used to cool the refrigerant in the high-temperature refrigeration unit into high-pressure liquid refrigerant and store it, and the other set of heat exchange pipes is used to cool the refrigerant in the low-temperature refrigeration unit.

[0013] Furthermore, the interfaces of the condensation precooler and the cold trap are both configured as a top-in and bottom-out structure.

[0014] Furthermore, the high-temperature stage compressor and the low-temperature stage compressor are any one of a piston compressor, a scroll compressor and a rolling rotor compressor.

[0015] Furthermore, the condenser evaporator and the front box heat exchanger are any one of a plate heat exchanger, a sleeve heat exchanger, a shell and tube heat exchanger and a microchannel heat exchanger.

[0016] Furthermore, the expansion valve, front box expansion valve, cold trap expansion valve and pressure reducing valve are all any one of a thermal expansion valve, a pulse width expansion valve, an electromagnetic expansion valve and an electric expansion valve.

[0017] In summary, the beneficial effects of the present invention are as follows:

[0018] This utility model incorporates a condenser precooler that operates simultaneously in both the high- and low-temperature refrigeration units. This allows the refrigerant in the low-temperature refrigeration unit to be precooled before entering the condenser evaporator for further cooling until liquefaction. This effectively reduces the area of the condenser evaporator and the system capacity of the high-temperature refrigeration unit, lowering the average temperature difference during the cooling process and thus improving the system's economic efficiency. By providing a hot gas bypass branch in the system, a controllable additional load is added to the cold trap, thereby regulating suction pressure, improving the compression ratio, and refrigeration conditions. This also increases the refrigerant flow rate in the cold trap under low load conditions, thereby improving the return of lubricating oil from the cold trap. Furthermore, this increased refrigerant flow rate enhances the cooling efficiency of the low-temperature compressor, preventing overheating and shutdowns. When the circulation flow rate of the low-temperature refrigeration unit increases, the refrigerant flow rate in the high-temperature refrigeration unit also increases, thereby simultaneously improving oil return and compressor cooling in the high-temperature refrigeration unit system. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the high-temperature refrigeration unit of the utility model;

[0020] Figure 2 This is a schematic diagram of the cascade refrigeration system of the present invention.

[0021] As shown in the figure: 1-high-temperature compressor, 2-condenser precooler, 3-drier filter 1, 4-solenoid valve 1, 5-expansion valve, 6-condenser evaporator, 7-low-temperature compressor, 8-oil separator, 9-high-pressure liquid receiver, 10-drier filter 2, 11-front box solenoid valve, 12-front box expansion valve, 13-front box heat exchanger, 14-cold trap solenoid valve, 15-cold trap expansion valve, 16-cold trap, 17-check valve, 18-gas-liquid separator, 19-pressure relief valve, 20-expansion tank, 21-solenoid valve 2, 22-pressure reducing valve, 23-hot gas bypass branch. DETAILED DESCRIPTION

[0022] The following is combined with Figure 1 , Attachment Figure 2 The utility model is further described in detail:

[0023] The present invention discloses a cascade refrigeration system for a pharmaceutical experimental freeze dryer. Figure 1 、 Figure 2 As shown, the cascade refrigeration system of a pharmaceutical experimental freeze dryer of the present invention is divided into two cycles: a high-temperature refrigeration unit and a low-temperature refrigeration unit. The high-temperature refrigeration unit and the low-temperature refrigeration unit use different refrigerants. The condensation side of the high-temperature refrigeration unit is the environment in which the freeze dryer is located, and the evaporation side is the condenser evaporator 6. The condensation side of the low-temperature refrigeration unit is the condenser evaporator 6, and the evaporation side is the front box heat exchanger 13 and the cold trap 16. In the front box heat exchanger 13, the refrigerant of the low-temperature refrigeration unit cools the heat carrier, which then transfers the cold energy to the plate layer in the front box of the freeze dryer to cool the material. The refrigerant evaporates in the cold trap 16 and absorbs heat, so that the heat exchanger surface of the cold trap 16 remains at a low temperature, capturing and freezing water vapor in the nearby space.

[0024] The high-temperature refrigeration unit mainly consists of a high-temperature compressor 1, a condenser precooler 2, a filter dryer 3, a solenoid valve 4, an expansion valve 5, and a condenser evaporator 6. The high-temperature compressor 1 is a fully enclosed compressor, and the expansion valve 5 can automatically adjust the liquid supply. The condenser precooler 2 is an air-cooled heat exchanger with a fan. It is equipped with two independent heat exchange pipes. One set is used to cool the refrigerant in the high-temperature refrigeration unit to a liquid state and has a certain capacity to store high-pressure liquid refrigerant; the other set is used to cool the refrigerant in the low-temperature refrigeration unit. The two sets of heat exchange pipes share a set of cooling fans, and the refrigerant flow order is arranged according to the top-in and bottom-out. It is worth noting that the interfaces of the condenser precooler 2 in the prior art are all bottom-in and top-out structures. The interfaces of the condenser precooler 2 in this embodiment are all configured as top-in and bottom-out structures. The use of this structure facilitates the return of lubricating oil entrained in the condenser precooler 2.

[0025] The low-temperature refrigeration unit mainly consists of a gas-liquid separator 18, a low-temperature compressor 7, an oil separator 8, a condenser precooler 2, a condenser evaporator 6, a high-pressure liquid storage tank 9, a drying filter 10, a front box solenoid valve 11, a front box expansion valve 12, a front box heat exchanger 13, a cold trap solenoid valve 14, a cold trap expansion valve 15, a cold trap 16, a check valve 17, a hot gas bypass branch 23, a pressure relief valve 19, an expansion tank 20, a solenoid valve 21, and a pressure reducing valve 22. The low-temperature compressor 7 is a fully enclosed compressor, the oil separator 8 is an optimized high-efficiency oil separator 8 and can automatically return oil, the front box expansion valve 12, the cold trap expansion valve 15 and the pressure reducing valve 22 can automatically adjust the flow rate, the gas-liquid separator 18 has an oil return function, and the refrigerant flow direction of the cold trap 16 is top in and bottom out. It is worth noting that the interfaces of the cold trap 16 in the prior art are all bottom-in and top-out structures, while the interfaces of the cold trap 16 in this embodiment are all set to a top-in and bottom-out structure, which is conducive to the backflow of the lubricating oil entrained by the cold trap 16.

[0026] Preferably, the high-temperature stage compressor 1 and the low-temperature stage compressor 7 are any one of a piston compressor, a scroll compressor and a rolling rotor compressor.

[0027] Preferably, the condenser evaporator 6 and the front box heat exchanger 13 are any one of a plate heat exchanger, a shell and tube heat exchanger, a shell and tube heat exchanger and a microchannel heat exchanger.

[0028] Preferably, the expansion valve 5 , the front box expansion valve 12 , the cold trap expansion valve 15 and the pressure reducing valve 22 are any one of a thermal expansion valve, a pulse width expansion valve, an electromagnetic expansion valve and an electric expansion valve.

[0029] The return air pipe of the gas-liquid separator 18 is connected to the input port of the low-temperature stage compressor 7, the output port of the low-temperature stage compressor 7 is connected to the oil separator 8, the oil separator 8 is connected to the condenser precooler 2, the condenser precooler 2 is connected to the condenser evaporator 6, the refrigerant in the low-temperature stage refrigeration unit is heat exchanged with the refrigerant in the high-temperature stage refrigeration unit in the condenser evaporator 6, the condenser evaporator 6 is connected to the input end of the high-pressure liquid storage 9, the output end of the high-pressure liquid storage 9 is respectively connected to the front box solenoid valve 11 and the cold trap solenoid valve 14 through the drying filter 2 10 to form a parallel pipeline, the front box solenoid valve 11 is connected to the front box expansion valve 12, the front box expansion valve 12 is connected to the front box heat exchanger 13 The input end is connected, the cold trap solenoid valve 14 is connected to the cold trap expansion valve 15, the cold trap expansion valve 15 is connected to the input end of the cold trap 16, the output end of the cold trap 16 is connected to the input end of the check valve 17, the output end of the check valve 17 is connected in parallel with the output end of the front box heat exchanger 13 and then connected to the air inlet pipe of the gas-liquid separator 18; a hot gas bypass branch 23 is provided between the condensing precooler 2 and the cold trap 16, and a solenoid valve 21 and a pressure reducing valve 22 are provided in the hot gas bypass branch 23, the output end of the condensing precooler 2 is connected to the input end of the hot gas bypass branch 23, and the output end of the hot gas bypass branch 23 is connected in parallel with the output end of the cold trap expansion valve 15 and then connected to the input end of the cold trap 16. The low-temperature refrigeration unit also includes a pressure relief valve 19 and an expansion tank 20. The input end of the expansion tank 20 is connected after the output end of the oil separator 8, and the output end of the expansion tank 20 is connected before the input port of the low-temperature compressor 7. A pressure relief valve 19 is provided between the expansion tank 20 and the oil separator 8.

[0030] The implementation principle of the embodiment of the present utility model is:

[0031] After being compressed by the high-temperature compressor 1, the high-temperature gaseous refrigerant enters the condenser precooler 2 and flows from top to bottom, facilitating the return of entrained lubricating oil. In the condenser precooler 2, the high-temperature, high-pressure gaseous refrigerant undergoes heat exchange with the fan-driven air and is cooled into a liquid state. When the solenoid valve 4 opens, the high-pressure liquid refrigerant passes through the expansion valve 5 and becomes a low-pressure gas-liquid two-phase mixture before entering the condenser evaporator 6, where it transfers its cooling capacity to the refrigerant on the low-temperature refrigeration unit side. Simultaneously, the high-temperature refrigeration unit refrigerant vaporizes and is withdrawn by the high-temperature compressor 1, starting a new cycle. The expansion valve 5 automatically controls the refrigerant flow rate based on the load of the condenser evaporator 6, thereby regulating the cooling capacity.

[0032] After the high-temperature gaseous refrigerant is compressed by the low-temperature compressor 7, it passes through the oil separator 8, and most of the entrained lubricating oil is separated and automatically returned to the low-temperature compressor 7. After passing through the oil separator 8, the refrigerant enters the condenser precooler 2 and flows from top to bottom to facilitate the reflux of the entrained lubricating oil. In the condenser precooler 2, the high-temperature and high-pressure gaseous refrigerant undergoes heat exchange with the fan-driven air and is cooled before entering the condenser evaporator 6. The high-pressure gaseous refrigerant of the low-temperature refrigeration unit is cooled to a high-pressure liquid by the refrigerant on the high-temperature refrigeration unit side and then flows into the high-pressure liquid reservoir 9. After pre-cooling, the refrigerant of the low-temperature refrigeration unit enters the condenser evaporator 6 to continue cooling until it is liquefied. This can effectively reduce the area of the condenser evaporator 6 and the system configuration capacity of the high-temperature refrigeration unit, reduce the average temperature difference of the heat exchange during the cooling process, and thus improve the economy of the system. When the front box requires cooling, the front box solenoid valve 11 opens. The high-pressure refrigerant liquid stored in the high-pressure accumulator 9 flows through the second filter drier 10 and the front box expansion valve 12, becoming a low-pressure gas-liquid two-phase mixture. It then enters the front box heat exchanger 13, where it transfers its cooling energy to the heat carrier fluid on the other side, which then delivers the cooling energy to the materials in the front box. The front box expansion valve 12 automatically controls the refrigerant flow rate based on the cooling demand of the front box, thereby adjusting the cooling capacity. When the cold trap 16 requires cooling, the cold trap solenoid valve 14 opens. The high-pressure refrigerant liquid in the high-pressure accumulator 9 flows through the second filter drier 10 and the cold trap expansion valve 15, becoming a low-pressure gas-liquid two-phase mixture. It then flows from top to bottom through the cold trap 16, facilitating the return of the lubricating oil contained in the refrigerant. The refrigerant transfers its cooling energy to the trapped water vapor, freezing it. The cold trap expansion valve 15 automatically controls the refrigerant flow rate based on instructions, thereby adjusting the cooling capacity and controlling the water capture efficiency of the cold trap 16. A check valve 17 is installed on the refrigerant outlet line of cold trap 16, just before its intersection with the refrigerant outlet line of headbox heat exchanger 13, to prevent refrigerant in headbox heat exchanger 13 from flowing back into cold trap 16. The low-pressure refrigerant vaporized in headbox heat exchanger 13 and cold trap 16 passes through gas-liquid separator 18 and is then withdrawn by low-temperature compressor 7 to begin a new cycle. Gas-liquid separator 18 ensures that the refrigerant return air does not contain a large amount of liquid that could cause a liquid hammer accident. Gas-liquid separator 18 also collects lubricating oil from the system and returns it to low-temperature compressor 7 via the return air.

[0033] After system shutdown, the low-temperature refrigeration unit heats up, and a large amount of liquid refrigerant on the high-pressure side vaporizes, causing excessive system pressure. When the pressure exceeds the set value of pressure relief valve 19, the vaporized refrigerant is released through pressure relief valve 19 into expansion tank 20, thereby maintaining the system pressure within a safe range. When the cold trap 16 is under low load and the suction pressure of the low-temperature compressor 7 is too low, solenoid valve 21 is opened to release a portion of the high-pressure hot gas from the low-temperature compressor 7 through pressure reducing valve 22. This gas is mixed with the refrigerant flowing through the cold trap expansion valve 15 and supplied to the cold trap 16. Pressure reducing valve 22 automatically adjusts the refrigerant gas flow rate according to the command. This effectively adds a controllable additional load to the cold trap 16, thereby regulating the suction pressure, improving the compression ratio, and refrigeration conditions. It also increases the refrigerant flow rate in the cold trap 16 during low load conditions, thereby improving the return of lubricating oil in the cold trap 16. Furthermore, the increased refrigerant flow rate enhances the cooling effect of the low-temperature compressor 7, preventing overheating and shutdown. Under the condition that the circulation flow of the low-temperature refrigeration unit increases, the circulation of the high-temperature refrigeration unit will also increase the refrigerant flow, thereby improving the oil return and compressor cooling of the high-temperature refrigeration unit system at the same time.

[0034] The above shows and describes the basic principles, main features and advantages of the present invention. The various components mentioned in the present invention are common technologies in the existing field. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and improvements may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and improvements fall within the scope of the present invention. The scope of protection claimed in this utility model is defined by the appended claims and their equivalents.

Claims

1. A cascade refrigeration system for a pharmaceutical laboratory freeze dryer, comprising a high-temperature refrigeration unit and a low-temperature refrigeration unit, wherein the high-temperature refrigeration unit is used to refrigerate the low-temperature refrigeration unit, characterized in that: The high-temperature refrigeration unit comprises a high-temperature compressor (1), a condenser precooler (2), a drying filter (3), a solenoid valve (4), an expansion valve (5), and a condenser evaporator (6) which are sequentially connected in series to form a closed loop; The low-temperature refrigeration unit comprises a gas-liquid separator (18), a low-temperature compressor (7), an oil separator (8), a condenser precooler (2), a condenser evaporator (6), a high-pressure liquid storage device (9), a second drying filter (10), a front box solenoid valve (11), a front box expansion valve (12), a front box heat exchanger (13), a cold trap solenoid valve (14), a cold trap expansion valve (15), a cold trap (16), a check valve (17), and a hot gas bypass branch (23); The return air pipe of the gas-liquid separator (18) is connected to the input port of the low-temperature compressor (7), the output port of the low-temperature compressor (7) is connected to the oil separator (8), the oil separator (8) is connected to the condenser precooler (2), the condenser precooler (2) is connected to the condenser evaporator (6), the refrigerant in the low-temperature refrigeration unit performs heat exchange with the refrigerant in the high-temperature refrigeration unit in the condenser evaporator (6), the condenser evaporator (6) is connected to the input end of the high-pressure liquid storage device (9), the output end of the high-pressure liquid storage device (9) is respectively connected to the front box electromagnetic valve (11) and the cold trap electromagnetic valve (14) through the drying filter 2 (10) to form a parallel pipeline, the front box electromagnetic valve (11) is connected to the front box expansion valve (12), the front box expansion valve (12) is connected to the front box heat exchanger (13) The input end is connected, the cold trap solenoid valve (14) is connected to the cold trap expansion valve (15), the cold trap expansion valve (15) is connected to the input end of the cold trap (16), the output end of the cold trap (16) is connected to the input end of the check valve (17), the output end of the check valve (17) is connected in parallel with the output end of the front box heat exchanger (13), and then connected to the air inlet pipe of the gas-liquid separator (18); a hot gas bypass branch (23) is provided between the condensing precooler (2) and the cold trap (16), a solenoid valve 2 (21) and a pressure reducing valve (22) are provided in the hot gas bypass branch (23), the output end of the condensing precooler (2) is connected to the input end of the hot gas bypass branch (23), the output end of the hot gas bypass branch (23) is connected in parallel with the output end of the cold trap expansion valve (15), and then connected to the input end of the cold trap (16).

2. The cascade refrigeration system of a pharmaceutical experimental freeze dryer according to claim 1, characterized in that: The low-temperature refrigeration unit further comprises a pressure relief valve (19) and an expansion tank (20), wherein the input end of the expansion tank (20) is connected after the output end of the oil separator (8), and the output end of the expansion tank (20) is connected before the input port of the low-temperature compressor (7), and a pressure relief valve (19) is provided between the expansion tank (20) and the oil separator (8).

3. The cascade refrigeration system of a pharmaceutical experimental freeze dryer according to claim 2, characterized in that: The condensing precooler (2) is an air-cooled heat exchanger with a fan, and is internally provided with two sets of independent heat exchange pipes, which share a set of cooling fans. One set of heat exchange pipes is used to cool the refrigerant in the high-temperature refrigeration unit into high-pressure liquid refrigerant and store it, and the other set of heat exchange pipes is used to cool the refrigerant in the low-temperature refrigeration unit.

4. The cascade refrigeration system of a pharmaceutical experimental freeze dryer according to claim 1, characterized in that: The interfaces of the condensing precooler (2) and the cold trap (16) are both configured as a top-in, bottom-out structure.

5. The cascade refrigeration system of a pharmaceutical experimental freeze dryer according to claim 1, characterized in that: The high-temperature stage compressor (1) and the low-temperature stage compressor (7) are each any one of a piston compressor, a scroll compressor, and a rolling rotor compressor.

6. The cascade refrigeration system of a pharmaceutical experimental freeze dryer according to claim 1, characterized in that: The condenser evaporator (6) and the front box heat exchanger (13) are any one of a plate heat exchanger, a shell and tube heat exchanger, a shell and tube heat exchanger and a microchannel heat exchanger.

7. The cascade refrigeration system of a pharmaceutical laboratory freeze dryer according to claim 1, characterized in that: The expansion valve (5), the front box expansion valve (12), the cold trap expansion valve (15) and the pressure reducing valve (22) are all any one of a thermal expansion valve, a pulse width expansion valve, an electromagnetic expansion valve and an electric expansion valve.

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