Refrigerating system with low-pressure-ratio centrifugal compressor and screw compressor connected in series and matched

Abstract

The invention belongs to the technical field of refrigeration preparation equipment, and particularly discloses a low-pressure-ratio centrifugal compressor and screw compressor series matched refrigeration system. A low-compression-ratio centrifugal compressor is used as a supercharging device matched with a main compressor (or a second-stage compressor), and three sections of different pressures including low pressure at an outlet of an evaporator, medium pressure at an inlet of the main compressor (or the second-stage compressor) and high pressure at an outlet of the main compressor (or the second-stage compressor) are formed by increasing the low-compression-ratio centrifugal compressor; the original process requirements of the refrigerating unit are met, and the air suction capacity of the main compressor (or called a secondary compressor) is improved through the air supply advantage of the low-compression-ratio centrifugal compressor under the low-temperature and low-pressure conditions. According to the invention, the centrifugal compressor is connected in series in the screw compressor refrigeration system for use. The compression ratio of the centrifugal compressor is ingeniously reduced, so that the centrifugal compressor meets the pressurization working condition of a refrigerating system of the screw compressor. Through the cooperation, the efficiency of the refrigerating system under the low-temperature and low-pressure working conditions is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of refrigeration preparation equipment, and in particular relates to a refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series. Background Art

[0002] Traditional single refrigeration systems usually have a single compressor or two compressors of the same type connected in series. Traditional refrigeration compressors usually pursue high compression ratios to improve the cooling or heating efficiency of the compressor. In traditional single-system compressor refrigeration systems, the compressor has low suction capacity under low temperature or low pressure working conditions, which further affects the working efficiency of the compressor under low temperature or low pressure conditions. In traditional dual-compressor series refrigeration systems, the first-stage compressor has low suction capacity, high outlet pressure, and high temperature, resulting in high technical requirements for the ratio of the second-stage compressor, poor operating stability of the whole machine, and difficulty in ensuring efficiency. Therefore, the traditional dual-compressor series refrigeration system has been basically abandoned by the industry.

[0003] Patent publication number CN117968266A discloses a technical solution: a booster refrigeration unit includes: a compressor, a condenser, a dry filter, an expansion valve, an evaporator, a gas collecting tank, and a booster device. The compressor is connected to the condenser, and the refrigerant is compressed by the compressor to become a high-temperature and high-pressure gaseous refrigerant and discharged into the condenser; the condenser is connected to the dry filter, and the dry filter is connected to the expansion valve. The high-temperature and high-pressure gaseous refrigerant exchanges heat with an external cold source in the condenser and becomes a medium-temperature and high-pressure liquid refrigerant, and then enters the expansion valve after being dried by the dry filter. The expansion valve is used for the medium-temperature and high-pressure liquid refrigerant. The high-pressure liquid refrigerant is intercepted and depressurized; the expansion valve is connected to the evaporator, the outlet of the evaporator is connected to the gas collecting tank, and the outlet of the gas collecting tank is connected to the booster; the medium-temperature and high-pressure liquid refrigerant is depressurized by the expansion valve and enters the evaporator to become a low-temperature and low-pressure gaseous refrigerant for evaporation and cooling. The low-temperature and low-pressure gaseous refrigerant exchanges heat with the medium to be cooled in the evaporator. After the gaseous refrigerant exchanges heat in the evaporator, it enters the gas collecting tank, and the residual liquid refrigerant is evaporated again in the gas collecting tank to avoid liquid return. Then the gaseous refrigerant is pressurized to the required medium pressure by the booster and then transported to the compressor inlet. However, the content of the utility model patent does not specify the specific types and schemes of the booster and main compressor in the booster refrigeration system. Summary of the invention

[0004] In view of the problems existing in the traditional centrifugal compressor refrigeration system, such as poor performance of the high-pressure section, single refrigerant adaptability, and unsuitability for low-temperature conditions, the present invention proposes a refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series. The present invention innovates a pneumatic structure of a low-compression ratio centrifugal compressor and controls the speed of the impeller of the low-compression ratio centrifugal compressor through frequency conversion, so as to achieve different outlet pressures under different working conditions and cooperate with the traditional screw compressor to improve the stability of the whole machine operation and the unit efficiency.

[0005] To this end, the present invention adopts the following technical scheme: a refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series, comprising a screw compressor, a condenser, a dry filter, an expansion valve, an evaporator, a gas collecting tank and a low-compression ratio centrifugal compressor; The outlet of the screw compressor is connected to the inlet of the condenser, the outlet of the condenser is connected to the inlet of the dry filter, the outlet of the dry filter is connected to the inlet of the expansion valve, the outlet of the expansion valve is connected to the inlet of the evaporator, the outlet of the evaporator is connected to the inlet of the gas collecting tank, the outlet of the gas collecting tank is connected to the inlet of the low-compression ratio centrifugal compressor, and the inlet of the low-compression ratio centrifugal compressor is connected to the inlet of the screw compressor. By adding a low-compression ratio centrifugal compressor, three different pressures are formed, namely, low pressure at the evaporator outlet, medium pressure at the screw compressor 1 inlet, and high pressure at the screw compressor outlet, to form an overall refrigeration circuit.

[0006] The series-connected refrigeration system also includes a pressure controller, a screw compressor suction pressure gauge, an evaporator outlet pressure gauge, and a screw compressor exhaust pressure gauge; the pressure controller monitors the screw compressor suction pressure gauge, the evaporator outlet pressure gauge, and the screw compressor exhaust pressure gauge and has an alarm protection function; the gas screw compressor suction pressure gauge monitors the screw compressor suction pressure; the evaporator outlet pressure gauge monitors the evaporator outlet pressure; and the screw compressor exhaust pressure gauge monitors the screw compressor exhaust pressure.

[0007] The present invention can achieve the following beneficial effects: 1. The present invention uses a low compression ratio centrifugal compressor as a booster device, and forms three different pressures of low pressure at the evaporator outlet, medium pressure at the screw compressor inlet, and high pressure at the screw compressor outlet by adding a low compression ratio centrifugal compressor; the original process requirements of the refrigeration unit are met, and the air supply advantage of the low compression ratio centrifugal compressor under low temperature and low pressure conditions can be used to improve the air suction capacity of the screw compressor. Thereby, the compression ratio of the refrigerant in the refrigeration system is improved, the motor of the screw compressor is promoted to work more efficiently, and finally the efficiency of the entire refrigeration unit is improved.

[0008] 2. The present invention reduces the compression ratio of the centrifugal compressor in exchange for the compressor efficiency of the centrifugal compressor under low temperature or low pressure conditions, thereby solving the problems of poor performance of the traditional centrifugal compressor refrigeration system in the high pressure section, single refrigerant adaptability, and unsuitability for low temperature conditions; it solves the problem of low efficiency in the low pressure section caused by low suction capacity of the traditional refrigeration unit under low temperature conditions; the low compression ratio centrifugal compressor is used as a first-stage compressor in series with the refrigeration system. Compared with the traditional double compressors in series, the first-stage low compression ratio centrifugal compressor has a low compression ratio and strong suction capacity, and the centrifugal structure cooperates with the variable frequency control to load and unload more smoothly, which can ensure continuous and stable air supply to the main compressor (or secondary compressor), so it has better stability; and the main compressor (or secondary compressor) adopts a screw compressor in the high pressure section, which can give full play to its characteristics of high output pressure and good performance in the high pressure section.

[0009] This technology has created a precedent for the use of low compression ratio centrifugal compressors in series with screw compressors in refrigeration systems. By combining two different types of compressors, the respective advantages of low compression ratio centrifugal compressors and screw compressors are fully utilized, greatly improving the refrigeration efficiency and operational reliability of the refrigeration unit, and achieving the goal of energy conservation and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0011] The specific implementation modes of the present invention are described in detail below in conjunction with the accompanying drawings. The described embodiments are only for illustration and explanation of the present invention and do not constitute the sole limitation of the present invention.

[0012] like Figure 1As shown, the present invention includes a screw compressor 1, a condenser 2, a dry filter 3, an expansion valve 4, an evaporator 5, an air collecting tank 6, a low compression ratio centrifugal compressor 7, a pressure controller 8, a screw compressor suction pressure gauge 9, an evaporator outlet pressure gauge 10 and a screw compressor exhaust pressure gauge 11; the outlet of the screw compressor 1 is connected to the inlet of the condenser 2, the outlet of the condenser 2 is connected to the inlet of the dry filter 3, the outlet of the dry filter 3 is connected to the inlet of the expansion valve 4, the outlet of the expansion valve 4 is connected to the inlet of the evaporator 5, the outlet of the evaporator 5 is connected to the inlet of the air collecting tank 6, the outlet of the air collecting tank 6 is connected to the inlet of the low compression ratio centrifugal compressor 7, and the inlet of the low compression ratio centrifugal compressor 7 is connected to the inlet of the screw compressor 1. By adding the low compression ratio centrifugal compressor 7, three different pressures are formed, namely, a low pressure at the outlet of the evaporator 5, a medium pressure at the inlet of the screw compressor 1 and a high pressure at the outlet of the screw compressor 1, to form an overall loop. The pressure controller 8 monitors the pressure of the screw compressor suction pressure gauge 9, the evaporator outlet pressure gauge 10, and the screw compressor exhaust pressure gauge 11 and has an alarm protection function. The gas screw compressor suction pressure gauge 9 monitors the suction pressure of the screw compressor 1; the evaporator outlet pressure gauge 10 monitors the evaporator outlet pressure; the screw compressor exhaust pressure gauge 11 monitors the exhaust pressure of the screw compressor 1.

[0013] As a priority of this embodiment, the screw compressor 1 delivers refrigeration lubricating oil to the low compression ratio centrifugal compressor 7 through the refrigeration oil oil pipeline 12. The screw compressor 1 can also be a magnetic suspension compressor, a centrifugal compressor, a piston compressor, a turbine compressor or any other form of screw compressor. The condenser 2 is a water-cooled shell and tube condenser, an air-cooled fin condenser, an evaporative cooling condenser or any other form of condenser. The evaporator 5 is a shell and tube dry evaporator, a flooded evaporator, a falling film evaporator, a coil evaporator, an air-cooled machine, an air conditioner indoor unit, a plate evaporator or any other form of evaporator.

[0014] As a preference of this embodiment, the screw compressor 1 is preferably a screw compressor.

[0015] The medium-pressure gaseous refrigerant output by the low-compression ratio centrifugal compressor 7 is sucked into the screw compressor 1. After being compressed by the screw compressor 1, the refrigerant becomes a high-temperature and high-pressure refrigerant and is discharged into the condenser 2. The high-temperature and high-pressure refrigerant exchanges heat with the external cold source in the condenser 2 and becomes a medium-temperature and high-pressure liquid refrigerant. After being dried by the dry filter 3, it enters the expansion valve 4. The expansion valve 4 intercepts and releases the medium-temperature and high-pressure liquid refrigerant. After the medium-temperature and high-pressure refrigerant is released by the expansion valve 4, it enters the evaporator 5 and becomes a low-temperature and low-pressure gaseous refrigerant to achieve evaporation and cooling. The low-temperature and low-pressure gaseous refrigerant exchanges heat with the material to be refrigerated in the evaporator 5. After the gaseous refrigerant exchanges heat in the evaporator 5, it enters the gas collecting tank 6. The residual liquid refrigerant is evaporated twice in the gas collecting tank 6 and then pressurized to the required medium pressure by the low-compression ratio centrifugal compressor 7 and then transported to the screw compressor 1. The above process is continuously circulated to form a refrigeration process of a refrigeration system in which a low-compression ratio centrifugal compressor and a screw compressor are connected in series.

[0016] As the first-stage compressor of the booster refrigeration unit, the low-compression ratio centrifugal booster compressor adopts a single-stage low-compression ratio working condition design and a centrifugal structure. The compression ratio of the compressor inlet and outlet is generally between 1:1.2 and 1:1.8 according to different working conditions, and the maximum compression ratio does not exceed 1:2.5; the outlet absolute pressure is generally controlled at 2Bar to 4 Bar, and the maximum does not exceed 5Bar. The low-compression ratio centrifugal booster compressor has a significantly lower compression ratio and outlet absolute pressure than traditional centrifugal compressors (traditional centrifugal compressors usually have to reach more than 1:3, and the outlet absolute pressure is generally controlled at more than 8Bar), making the low-compression ratio centrifugal booster compressor more suitable for low-temperature and low-pressure working conditions, and more efficient under low-pressure or low-temperature working conditions. The screw compressor side has the characteristics of high output pressure and stable operation under high-pressure working conditions, so it is used as a secondary high-pressure compressor. The combination of the two can effectively increase the refrigerant exhaust temperature and pressure, and can ensure the unit's operating efficiency and stability. The refrigeration system that combines a low-compression ratio centrifugal compressor and a screw compressor in series fully utilizes the respective advantages of the two different types of compressors, greatly improving the refrigeration efficiency and operational reliability of the refrigeration unit and achieving the goal of energy conservation and emission reduction.

[0017] According to the above characteristics, the refrigeration system with low compression ratio centrifugal compressor and screw compressor in series is fully in line with the technical characteristics of booster refrigeration unit (patent publication number: CN117968266A, application number CN202410238799.1). It not only solves the pressure matching of high and low pressure matching of dual compressors, but also can adapt to R22, R407C, R507, R404A, R134A or other multi-type refrigerants, especially in medium and low temperature refrigeration systems, it has better performance.

[0018] Although this technology is currently mainly applied to low-temperature or low-pressure refrigeration systems, its effect in other working conditions needs to be further verified. Other working conditions of this technology should also be regarded as an extension of this technology.

[0019] Figure 1 The above are only core components. This technology includes but is not limited to the above components. Other refrigeration systems with the addition or subtraction of auxiliary refrigeration accessories that do not produce essential changes to the technical principles are included in the protection scope of this technology. The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. Technical personnel in this industry should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only illustrative of the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected. The scope of protection claimed by the present invention is defined by the attached claims and their equivalents.

Claims

1. A refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series, characterized in that: The refrigeration system in which the low-pressure ratio centrifugal compressor and the screw compressor are connected in series comprises a screw compressor (1), a condenser (2), a dry filter (3), an expansion valve (4), an evaporator (5), a gas collecting tank (6) and a low-compression ratio centrifugal compressor (7); The outlet of the screw compressor (1) is connected to the inlet of the condenser (2), the outlet of the condenser (2) is connected to the inlet of the dry filter (3), the outlet of the dry filter (3) is connected to the inlet of the expansion valve (4), the outlet of the expansion valve (4) is connected to the inlet of the evaporator (5), the outlet of the evaporator (5) is connected to the inlet of the gas collecting tank (6), the outlet of the gas collecting tank (6) is connected to the inlet of the low compression ratio centrifugal compressor (7), and the inlet of the low compression ratio centrifugal compressor (7) is connected to the inlet of the screw compressor (1). By adding the low compression ratio centrifugal compressor (7), three different pressures are formed, namely, the low pressure at the outlet of the evaporator (5), the medium pressure at the inlet of the screw compressor (1), and the high pressure at the outlet of the screw compressor (1), thereby forming an overall refrigeration circuit.

2. A refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series according to claim 1, characterized in that: The series-connected refrigeration system further includes, but is not limited to, a pressure controller (8), a screw compressor suction pressure gauge (9), an evaporator outlet pressure gauge (10), and a screw compressor exhaust pressure gauge (11); the pressure controller (8) monitors the pressures of the screw compressor suction pressure gauge (9), the evaporator outlet pressure gauge (10), and the screw compressor exhaust pressure gauge (11) and has an alarm protection function; the screw compressor suction pressure gauge (9) monitors the suction pressure of the screw compressor (1); the evaporator outlet pressure gauge (10) monitors the evaporator outlet pressure; and the screw compressor exhaust pressure gauge (11) monitors the exhaust pressure of the screw compressor (1).

3. A refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series according to claim 2, characterized in that: The screw compressor (1) delivers refrigeration lubricating oil to the low compression ratio centrifugal compressor (7) via a refrigeration oil delivery pipe (12).

4. A refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series according to claim 3, characterized in that: The screw compressor (1) may also be a magnetic suspension compressor, a centrifugal compressor, a piston compressor, a turbine compressor or any other form of gas compressor.

5. A refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series according to claim 4, characterized in that: The condenser (2) is a water-cooled shell and tube condenser, an air-cooled fin condenser, an evaporative cooling condenser or any other type of condenser.

6. A refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series according to claim 5, characterized in that: The evaporator (5) is a shell and tube dry evaporator, a flooded evaporator, a falling film evaporator, a coil evaporator, an air cooler, an air conditioner indoor unit, a plate evaporator or any other type of evaporator.

7. A method for operating a refrigeration system in which a low-pressure ratio centrifugal compressor and a screw compressor are connected in series, characterized in that: The screw compressor (1) sucks in the stable medium-pressure gaseous refrigerant output by the low-compression ratio centrifugal compressor (7), which is then compressed by the screw compressor (1) to become a high-temperature and high-pressure refrigerant and discharged into the condenser (2). The high-temperature and high-pressure refrigerant exchanges heat with an external cold source in the condenser (2) to become a medium-temperature and high-pressure liquid refrigerant, which is dried by a dry filter (3) and then enters the expansion valve (4). The expansion valve (4) intercepts and releases the pressure of the medium-temperature and high-pressure liquid refrigerant. The medium-temperature and high-pressure refrigerant is released by the expansion valve (4) and then enters the evaporator. (5) is converted into a low-temperature, low-pressure gaseous refrigerant to achieve evaporation cooling. The low-temperature, low-pressure gaseous refrigerant exchanges heat with the material to be refrigerated in the evaporator (5). After the heat exchange in the evaporator (5), the gaseous refrigerant enters the gas collecting tank (6). A small amount of residual liquid refrigerant is evaporated for the second time in the gas collecting tank (6) and is pressurized to the required medium pressure by the low-compression ratio centrifugal compressor (7) and then transported to the screw compressor (1). The above process is continuously circulated to form a refrigeration process of a refrigeration system in which a low-compression ratio centrifugal compressor and a screw compressor are connected in series.

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