COOLING SYSTEM FOR A HIGH-SPEED COMPRESSOR

Abstract

COOLING SYSTEM FOR A HIGH-SPEED COMPRESSOR The invention relates to a cooling system for a high-speed compressor (60) comprising a refrigerant inlet and outlet, said system comprising: a network of circulating pipes for said refrigerant; a condenser (20) fluidly connected to said refrigerant outlet of said centrifugal compressor by said network of pipes; an evaporator (40) fluidly connected to said condenser by said network of pipes; said cooling system being characterized in that it further comprises a heat exchanger, referred to as a superheat exchanger (50) fluidly connected by said network of pipes to said evaporator on the one hand, and to said refrigerant inlet of the high-speed compressor (60) on the other hand, so as to ensure superheating of said refrigerant upstream of said high-speed compressor (60). Figure for the abstract: Figure 1

Description

Title of the invention: COOLING SYSTEM FOR A HIGH-SPEED COMPRESSOR Technical field of the invention

[0001] The invention relates to the field of compressor cooling. More specifically, the invention concerns a cooling system for a high-speed compressor such as a centrifugal or screw compressor, comprising a heat exchanger dedicated to superheating downstream of an evaporator. Technological background

[0002] Steam cooling systems equipped with motorized volumetric compressors are known, in which the cooling of the motor is ensured by a direct circulation of the refrigerant fluid around the motor and the pivoting elements before the refrigerant is drawn in for compression.

[0003] In the case of a high-speed compressor, this cooling solution is not suitable.

[0004] Indeed, the direct circulation of refrigerant fluid around the motor results in significant pressure losses at the suction, which is prohibitive for the cooling capacity of the fluid and the overall coefficient of performance of the cooling cycle.

[0005] In addition, circulating refrigerant directly around the motor requires high compression ratios, and is not suitable for high-speed compressors due to the compactness of the components.

[0006] High-speed compressors are generally cooled by injecting liquid refrigerant, which significantly impacts the overall cycle performance. Furthermore, this solution makes the system more complex, notably requiring the addition of means to control the injected liquid flow rate to ensure complete vaporization.

[0007] In a conventional system, the refrigerant superheating is provided directly by the evaporator. In liquid loop or two-phase / conductive loop cooling systems, the thermal coefficient of the liquid or phase-change fluids results in small temperature differences between the fluids, which do not allow for sufficient superheating.

[0008] To ensure sufficient superheating, it is then necessary to reduce the efficiency of the evaporator to fully ensure this function, which is prohibitive for the performance of the cooling system.

[0009] There are systems incorporating subcoolers and heaters, but these do not directly provide cooling for the compressor.

[0010] In addition, most compressor cooling systems do not allow for a satisfactory balance between compactness and cooling. Objectives of the invention

[0011] The invention aims to provide a cooling system that avoids the disadvantages of liquid injection for cooling a high-speed compressor.

[0012] The invention aims to provide a cooling system designed to separate the superheating and evaporator functions.

[0013] The invention aims to provide a cooling system with a heat exchanger exclusively dedicated to the superheating function at the evaporator outlet.

[0014] The invention also aims to provide, in at least one embodiment, a cooling system that allows the size of the evaporator to be greatly reduced.

[0015] The invention also aims to provide, in at least one embodiment, a cooling system enabling a reduction in pressure losses

[0016] The invention also aims to provide, in at least one embodiment, a cooling system designed to effectively protect the compressor.

[0017] The invention also aims to provide, in at least one embodiment, a cooling system allowing the injection of hot gas while limiting pressure losses. Description of the invention

[0018] To this end, the invention relates to a cooling system for a high-speed compressor comprising a refrigerant inlet and outlet, said system comprising:

[0019] - a network of circulation pipes for said refrigerant fluid;

[0020] - a condenser fluidically connected to said refrigerant outlet of said centrifugal compressor via said network of pipes;

[0021] - an evaporator fluidically connected to said condenser by said network of pipes;

[0022] said cooling system being characterized in that it further comprises a heat exchanger, said superheat exchanger fluidically connected by said network of pipes to said evaporator on the one hand, and to said refrigerant inlet of the high speed compressor on the other hand, so as to ensure superheating of said refrigerant upstream of said high speed compressor.

[0023] Throughout the following text, the high-speed compressor is defined as a compressor comprising compact pivoting elements such as a compressor centrifugal or screw compressor, and having a rotational speed greater than or equal to 8000 revolutions per minute

[0024] Throughout the text, the high-speed compressor can be selected from centrifugal compressors and screw compressors, said compressors being capable of being driven electrically or via an air turbine. Preferably, the high-speed compressor is a centrifugal compressor capable of including pivoting elements such as bearings and gas thrust bearings.

[0025] Preferably, the high-speed compressor is a screw compressor comprising pivoting elements of the radial and axial bearing type with ball bearings or any other bearing known to a person skilled in the art.

[0026] The cooling system according to the invention does not include injection of coolant or direct circulation of refrigerant fluid around the motor and / or the compressor pivot before suction notwithstanding the possible circulation of a leakage flow from the compression stage to the bearings.

[0027] By superheat exchanger, we mean a heat exchanger dedicated to the superheat function, arranged between the evaporator and the high-speed compressor.

[0028] The term "a superheat exchanger fluidly connected by said network of pipes on the one hand, and to said refrigerant inlet of the high-speed compressor on the other hand" means a pipe from said network of pipes fluidly connecting the superheat exchanger and the compressor or a direct connection between said superheat exchanger and said compressor.

[0029] By "direct connection" between said superheat exchanger and said casing is meant a connection other than a pipe belonging to said pipe network. For this purpose, a pipe integrated into a dedicated compartment of the casing or an integration of said superheat exchanger on the periphery of the casing may be envisaged.

[0030] This advantageous arrangement of the cooling system according to the invention makes it possible to maintain good performance of the cooling cycle by avoiding the disadvantages of injecting liquid refrigerant into the compressor.

[0031] Advantageously, the evaporator can directly connect the superheat exchanger, and the superheat exchanger can directly connect to the centrifugal compressor. "Directly connect" means a direct fluid connection without intermediaries between the components concerned.

[0032] Furthermore, the internal pressure of the high-speed compressor, particularly at the pivot, is generally higher than the suction pressure and does not allow for a satisfactory refrigerant charging capacity of the bearings for a high-speed compressor when the refrigerant circulates around the pivot. The invention thus makes it possible to redirect the motor and / or pivot cooling of the compressor in a superheat exchanger before suction to overcome these disadvantages.

[0033] The cooling system, according to the invention, makes it possible, thanks to the superheat exchanger, not only to ensure the cooling of a high-speed compressor, but also to improve the efficiency and compactness of the evaporator. Advantageously, and according to the invention, the superheat exchanger comprises two fluid circuits in thermal interaction with each other, referred to respectively as the primary circuit and the secondary circuit, said primary circuit being supplied by the refrigerant from the piping network and supplying said refrigerant inlet of the high-speed compressor, and said secondary circuit being supplied by a thermal circuit supplied by said high-speed compressor.

[0034] Thus and according to the invention, the system makes it possible to generate a greater temperature difference between the elements to be cooled and said refrigerant fluid in order to generate sufficient superheating.

[0035] Advantageously and according to the invention, the superheat exchanger is further arranged peripherally on said high-speed compressor.

[0036] Preferably said superheat exchanger is an integral part of said high-speed compressor and can be arranged in a dedicated compartment on said compressor or in the casing skin of the latter.

[0037] Thus and according to the invention, this arrangement makes it possible to reduce the distance between the superheat exchanger and said compressor.

[0038] Advantageously and according to the invention, the thermal circuit comprises a conductive or two-phase heat transport means configured to thermally connect said superheat exchanger and said high-speed compressor.

[0039] Thus and according to the invention, the system makes it possible to reduce the heat transport distance to be covered by the heat transport means.

[0040] Advantageously and according to the invention, the conductive or two-phase heat transport means is configured to thermally connect said superheat exchanger and a motorized assembly of said high-speed compressor.

[0041] Thus and according to the invention, the system makes it possible to cool the most heat-generating parts of the compressor.

[0042] It is understood that the motorized assembly may include an electric motor, or a turbine or an equivalent means known to a person skilled in the art configured to drive the mechanism of said high-speed compressor in rotation, including pivoting elements such as bearings, stops or bushings.

[0043] Advantageously and according to the invention, the pipe network further comprises a pipe, called a bypass pipe, fluidly connecting the refrigerant outlet said high-speed compressor and said piping network upstream of the superheat exchanger and downstream of the evaporator.

[0044] Thus and according to the invention, the system makes it possible to connect the compressed refrigerant fluid from the compressor to the inlet of the superheat exchanger in order to obtain a mixture with the flow of refrigerant fluid from the evaporator while limiting the pressure losses of said fluid.

[0045] The system thus makes it possible to limit the pressure loss of the refrigerant at the evaporator outlet while offering a flow rate from the bypass.

[0046] Advantageously and according to the invention, the bypass line includes a control valve configured to regulate the flow of the refrigerant circulating in said bypass.

[0047] Thus and according to the invention, said valve makes it possible to ensure a flow of refrigerant adapted to the level of the compressor, in order to avoid pumping and discharge of fluid into the latter.

[0048] Advantageously and according to the invention, the cooling system further comprises at least one regulating valve arranged on said network of pipes between the condenser and the evaporator.

[0049] The invention also relates to a cooling system for a centrifugal compressor characterized in whole or in part by the characteristics mentioned above and / or below. List of figures

[0050] Other objects, features and advantages of the invention will become apparent from the following description, given by way of non-limiting example only, and which refers to the accompanying figures in which: • [Fig.1] schematically represents a cooling system according to an embodiment of the invention. • [Fig.2] schematically represents the thermal interaction carried out by the superheat exchanger of the cooling system according to an embodiment of the invention. • [Fig.3] represents a motorized assembly of the high-speed compressor according an embodiment of the invention.

[0051] Detailed description of an embodiment of the invention

[0052] In the figures, the scales and proportions are not strictly respected, for the purposes of illustration and clarity.

[0053] In the entire detailed description that follows with reference to the figures, unless otherwise indicated, each element of the cooling system according to the invention is described as it is arranged during its use. Furthermore, the embodiment described below- The following relates to a cooling system for a high-speed compressor of the centrifugal type with an electric motor.

[0054] Identical, similar or analogous elements are designated by the same references in all figures.

[0055] Figures [Fig.1] and [Fig.2] both relate to the same embodiment of the cooling system of the invention.

[0056] Fig. 1 describes a cooling system intended to cool an electric centrifugal compressor 60.

[0057] The system comprises a network of pipes 10, 11, 12, 13, 14 for circulating a refrigerant fluid to cool said compressor 60. The cooling system according to the described embodiment relates to a closed cooling circuit in which a refrigerant fluid circulates. For this purpose, said system comprises a condenser 20, an evaporator 40, and a compressor 60 fluidically connected by said network of pipes 10, 11, 12, 13, 14 in series.

[0058] In this embodiment, said compressor 60 comprises a motorized assembly 62 and at least one centrifugal impeller 61 configured to compress said refrigerant. The motorized assembly 62 and the centrifugal impeller 61 are arranged within the housing of said compressor 60. The motorized assembly 62 comprises, in this embodiment, an electric motor and the pivoting elements of said compressor. The electric motor may be a motor known to those skilled in the art and includes, among other things, a rotor and a stator.

[0059] The pivoting elements of the motorized assembly can be, in a known manner, the bearings and / or gas thrust bearings of the centrifugal compressor 60. These pivoting elements and the electric motor of the motorized assembly 62 constitute a heat source that must be cooled. The compressor 60 therefore includes a refrigerant inlet and outlet.

[0060] The system includes a first line 10 fluidly connecting the refrigerant outlet of the compressor 60 with the inlet of a condenser 20. The line 10 is thus configured to circulate a compressed refrigerant from the compressor 60 to said condenser 20.

[0061] The system also includes a line 11 fluidly connecting an outlet of said condenser 20 with a first regulating valve 30 in order to reduce the pressure of the refrigerant at the outlet of the condenser 20 before it enters the evaporator 40. The valve 30 is further fluidly connected to an inlet of the evaporator 40 by a line 12. The valve 30 is thus arranged between the condenser 20 and the evaporator 40 of said cooling system.

[0062] The evaporator 40 is fluidly connected to a heat exchanger, referred to as a superheat exchanger 50, by means of a pipe 13. Said pipe 13 supplies The superheat exchanger 50 is connected to the refrigerant from the evaporator 40 of the system. The superheat exchanger 50 is fluidly connected to the centrifugal compressor 60 and supplies the latter with superheated refrigerant at the refrigerant inlet of said compressor 60 by means of a line 14.

[0063] However, in a preferred embodiment, the superheat exchanger 50 is arranged directly on the compressor housing 60 such that the fluid connection can be made directly between said superheat exchanger 50 and said compressor 60 in a dedicated section of the housing and not via said line 14, said refrigerant inlet then being provided in the housing. The housing is thus configured to ensure the fluid connection between the superheat exchanger 50 and the compressor 60.

[0064] In the described embodiment, the superheat exchanger 50 is arranged between the evaporator 40 and the refrigerant inlet of the compressor 60. In addition, the pipe 13 of the pipe network connects the downstream of the evaporator 40 and the upstream of the superheat exchanger 50.

[0065] In the described embodiment, the superheat exchanger 50 is arranged on the centrifugal compressor 60.

[0066] The cooling system further includes a heat transport means 70 configured to thermally connect the motorized assembly 62 of the compressor 60 with said superheat exchanger 50. The heat transport means 70 may include conductive or two-phase means known to those skilled in the art, such as heat pipes, capillary jet loops (CJL) or pulsating heat pipes (PHP), or a combination of these means.

[0067] In order to limit the distance of heat transport to be ensured by the heat transport means 70, the superheat exchanger 50 can be integrated peripherally around said compressor 60, in particular in a circular manner.

[0068] The superheat exchanger 50 thus advantageously allows the superheating of the refrigerant circulating upstream of the compressor 60 to be carried out in place of the evaporator 40 or according to the thermal dissipation of said compressor 60.

[0069] In the event that the heat dissipation of said compressor 60 is very high, the evaporator 40 does not completely evaporate the refrigerant. The superheat exchanger 50 thus completes the evaporation and performs all the superheating.

[0070] In the case where the heat dissipation of said compressor 60 is intermediate, that is to say at the optimal operating point of said compressor 60, the evaporator 40 achieves complete evaporation of the refrigerant but does not superheat it. The superheat exchanger 50 thus performs all the superheating.

[0071] In the case where the heat dissipation is low, the evaporator 40 starts superheating and the superheat exchanger 50 finishes superheating.

[0072] The system thus benefits from an exchanger solely dedicated to the superheat function for cooling the compressor 60. It is understood that the superheat exchanger 50 includes the means necessary to allow an operator to measure the level of superheat at the outlet of said superheat exchanger, such as a temperature sensor.

[0073] The cooling system of the described embodiment further includes a line, referred to as a bypass line 15. Said bypass line 15 is configured to fluidly connect the refrigerant outlet of the compressor 60 with the line 13 fluidly connecting the evaporator 40 with the superheat exchanger 50. In addition, the compressed refrigerant from the refrigerant outlet of the compressor 60 flows in a line 10 on which the bypass line 15 is arranged.

[0074] Said bypass pipe 15 thus fluidly connects pipe 10 with pipe 13 of the pipe network. A control valve 31 is further arranged on the bypass pipe.

[0075] The bypass line 15 fluidly connects the piping network at the level of the line 13 located upstream of the heat exchanger 50 and downstream of the evaporator 40. The bypass of the described embodiment thus makes it possible to mix the refrigerant in the form of hot gas at the outlet of the compressor 60 with the flow of refrigerant at the outlet of the evaporator 40 while limiting the pressure losses of the refrigerant.

[0076] Fig. 2 schematically represents the detail of the thermal interaction of the two fluid circuits of the superheat exchanger 50 of the cooling system according to the embodiment described.

[0077] In this figure, a first fluid circuit, called the primary circuit, is shown with solid arrows. This primary circuit includes the fluid connection between the evaporator 40 and the superheat exchanger 50. This fluid connection is provided by the pipe 13 of the piping network described [Fig. 1]. Said primary circuit also includes the fluid connection between said superheat exchanger 50 and the compressor 60, in particular at the refrigerant inlet of said compressor 60.

[0078] In this figure, a second fluid circuit, called the secondary circuit, is shown in particular with a thermal circuit supplying said secondary fluid circuit, indicated by a dashed arrow. This secondary circuit includes a thermal connection between a motorized assembly 62 of the compressor 60 and said heat exchanger. superheat 50. This thermal connection is made with a conductive or two-phase means 70 configured to thermally connect the motorized assembly 62 of the compressor 60 with the superheat exchanger 50.

[0079] The superheat exchanger 50 thus ensures the thermal connection of the two fluid circuits of the centrifugal compressor 60 cooling system.

[0080] Fig. 3 schematically represents an embodiment of a high-speed compressor 60 driven by an air turbine.

[0081] In this embodiment, the motorized assembly includes an air turbine 62a in a compartment separate from the housing of the high-speed compressor 60. The compressor 60 includes pivoting elements 62b. The pivoting elements 62b may be the bearings and / or the axial thrust bearings of said compressor 60.

[0082] The air turbine 62a is playfully connected to another external pressurized air circuit (not shown in the diagram), the expansion of which drives said turbine 62a. The turbine 62a drives the compressor 60 via a magnetic coupling that maintains the compressor's airtightness through static sealing. The turbine 62a and the pivot 62b are cooled by the external pressurized air circuit, and the superheat exchanger 50 cools only the pivot 62b. Furthermore, the superheat exchanger 50 is directly integrated into a dedicated part of the compressor housing 60 and does not require a line 14 to fluidly connect said superheat exchanger 50 to the refrigerant inlet of the compressor 60.

[0083] The particular arrangement of the superheat evaporator of the cooling system according to the invention makes it possible to obtain, to limit the pressure losses of the evaporator and also to protect the compressor by ensuring that the circulating refrigerant is completely evaporated before entering said compressor.

Claims

Demands

1. Cooling system for a high-speed compressor (60) comprising a refrigerant inlet and outlet, said system comprising: • a network of circulating pipes for said refrigerant; • a condenser (20) fluidly connected to said refrigerant outlet of said centrifugal compressor by said network of pipes; • an evaporator (40) fluidly connected to said condenser by said network of pipes; said cooling system being characterized in that it further comprises a heat exchanger, said superheat exchanger (50) fluidly connected by said network of pipes to said evaporator (40) on the one hand, and to said refrigerant inlet of the high-speed compressor (60) on the other hand, so as to ensure superheating of said refrigerant upstream of said high-speed compressor (60).

2. System according to claim 1, characterized in that the superheat exchanger (50) comprises two fluid circuits in thermal interaction with each other, referred to respectively as primary circuit and secondary circuit, said primary circuit being supplied by the refrigerant from the piping network and supplying said refrigerant inlet of the high-speed compressor (60), and said secondary circuit being supplied by a thermal circuit supplied by said high-speed compressor (60).

3. System according to claim 2, characterized in that said thermal circuit comprises a conductive or two-phase heat transport means (70) configured to thermally connect said superheat exchanger (50) and said high-speed compressor (60).

4. System according to the preceding claim, characterized in that the conductive or two-phase heat transport means (70) is configured to thermally connect said superheat exchanger (50) and a motorized assembly (62) of said high-speed compressor (60).

5. System according to any one of the preceding claims, characterized in that the piping network further comprises a pipe, called a bypass pipe (15) fluidically connecting the refrigerant outlet of said high-speed compressor (60) and said piping network upstream of the superheat exchanger (50) and downstream of the evaporator (40).

6. System according to claim 5, characterized in that the bypass line (15) includes a control valve (31) configured to regulate the flow of the refrigerant circulating in said bypass.

7. System according to any one of the preceding claims, characterized in that it further comprises at least one control valve (30) arranged on said network of pipes between the condenser (20) and the evaporator (40).

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