COMPRESSION DEVICE AND METHOD

Description

[0001] The invention relates to a compression device and method and to a refrigeration machine.

[0002] The invention relates more particularly to a device for centrifugal compression of a working gas, in particular for a refrigeration machine, comprising several centrifugal compressors forming several successive and / or parallel compression stages and several compressor drive motors, the device comprising a gas circuit comprising a first inlet pipe for gas to be compressed connected to an inlet of a first compressor to convey gas to be compressed into the first compressor, the circuit comprising a second pipe connected to an outlet of said first compressor to discharge the compressed gas therein, the second pipe being connected to an inlet of a second compressor to convey the compressed gas into the first compressor into the second compressor with a view to carrying out a second compression,the circuit comprising at least one third cooling pipe having one end connected to the outlet of at least one of the compressors and at least one second end connected to an inlet of at least one motor to transfer a fraction of the compressed gas in the at least one compressor to the at least one motor in order to limit the heating of the latter, the third cooling pipe comprising a first gas cooling member and two parallel branches respectively supplying two separate motors of the device for the purpose of their respective cooling, the circuit comprising fourth pipes connecting an outlet of the first motor and an outlet of the second motor to the inlet of the first compressor to recycle the gas used to limit the heating of the motors to the first compressor for the purpose of compressing it.,

[0003] A centrifugal compressor using direct drive between the (electric) motor and the compression wheel(s) (i.e. without a speed multiplier) requires a gas flow to remove the heat generated in the motor. This heat is generated mainly by motor losses and by friction of the rotor with the surrounding gas.

[0004] This cooling flow is usually injected into one side of the engine (at an inlet) and discharged out the other side (at an outlet) with a higher temperature. It can also be injected into the middle of the engine and discharged out of both sides of it.

[0005] A more or less significant portion of the heat is also usually evacuated by a heat transfer fluid circulating in a circuit surrounding the stator part of the motor (water or air or any other heat transfer fluid allowing the stator to be cooled).

[0006] In order not to lose or pollute the compressed gas, the gas circulating in the engine to cool it usually has the same composition as the compressed gas.

[0007] In order to limit the number of equipment, the driving force required to circulate the gas through the engine(s) is generated by one or more compression stages (i.e. by one or more of the compressors).

[0008] There are several known examples using this cooling technique.

[0009] US6464,469 describes the use of a portion of the gas exiting the first compression stage to cool the engine. This gas is then returned to the compressor inlet.

[0010] Document US5,980,218 describes the use of a portion of the gas leaving the cooling exchanger located downstream of the first compression stage to cool the engine. This gas is then returned to the compressor inlet.

[0011] US8,899,945 describes a multi-engine architecture

[0012] Document US 2017159665A1 describes prior art in accordance with the preamble of claim 1.

[0013] However, these solutions are not well suited to a multi-engine architecture and / or the performance is unsatisfactory.

[0014] An aim of the present invention is to overcome all or part of the drawbacks of the prior art noted above.

[0015] To this end, the device according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the circuit comprises fourth pipes connecting an outlet of the first motor and an outlet of the second motor to the inlet of the first compressor to recycle the gas used to limit the heating of the motors to the first compressor with a view to its compression, the circuit comprising at least one second gas cooling member arranged on the path of the fourth pipes to extract heat from the gas coming from the motors before its return to the first compressor.

[0016] Furthermore, embodiments of the invention may include one or more of the following features: the third cooling line comprises a set of valves for regulating the flow of gas allowed to circulate in the two parallel branches, the set of valves comprises two regulating valves located respectively in the two branches, the set of valves comprises a three-way regulating valve located at the junction of the two branches or a single valve located on the third line, upstream of the two branches, the first gas cooling member comprises a heat exchanger cooled by a heat transfer fluid, the compressors are driven in rotation directly by the corresponding motors, the device comprises one or more rotating joints between the motor(s) and the compressor(s) or one or more expansion stages so that the pressure in the cavities of the motor(s) is close to the lowest pressure of the compressor, i.e. the inlet pressure of the compressor,the device comprises at least one motor driving one or more compressors and at least one motor coupled to one or more expansion turbines,

[0017] The invention also relates to a low temperature refrigeration machine between -100°C and -273°C comprising a working circuit containing a working fluid, the working circuit comprising a centrifugal compression device and a device for cooling and expanding the compressed gas in the compression device, characterized in that the compression device conforms to any one of the characteristics above or below.

[0018] The invention also relates to a method for centrifugal compression of a working gas, in particular for a refrigeration machine using such a compression device, the method comprising: a step of compressing a working gas in a first compressor then in a second compressor arranged in series, a step of sampling a fraction of the compressed gas leaving at least one of the compressors and circulating this sampled gas in at least one engine for the purpose of cooling it, the method comprising a step of cooling the gas sampled at the outlet of the at least one compressor and a step of distributing and circulating in parallel this sampled and cooled gas in two separate engines for the purpose of their respective cooling.

[0019] The invention may also relate to any alternative device or method comprising any combination of the above or below features.

[0020] Other features and advantages will become apparent upon reading the following description, given with reference to the figures in which: THE figures 1 et 2 represent schematic and partial views illustrating firstly two examples of structure and operation of a compression device which is not according to the claimed invention and a second compression device according to the invention. figure 3 represents a schematic and partial view illustrating an example of structure and operation of a cooling machine comprising such a compression device.

[0021] The compression device 18 shown schematically in the figure 1 comprises two 1, 3 centrifugal compressors (i.e. two compressor wheels) forming two successive compression stages.

[0022] The two 1.3 compressors are each driven by a respective 5, 6 drive motor (preferably electric).

[0023] Preferably, the compressors 1, 3 are driven in rotation directly by their corresponding motors 5, 6.

[0024] The device 18 comprises a qaz circuit comprising a first inlet pipe 13 for gas to be compressed connected to the inlet of a first compressor 1, for conveying gas to be compressed into the first compressor 1.

[0025] The circuit comprises a second pipe 14 having an upstream end connected to an outlet of said first compressor 1 to discharge the compressed gas therein. The second pipe 14 has a downstream end connected to an inlet of the second compressor 3, to convey the gas which has been compressed in the first compressor 1 into the second compressor 3 in order to carry out a second compression (a second compression stage).

[0026] The circuit comprises a third cooling pipe 15 before an upstream end connected to the outlet of the first compressor 1 (for example via the second pipe 14) and two second downstream ends connected respectively to the inlets of the two motors 5, 6. That is to say that for example, the third pipe 15 has a common portion with the second pipe 14.

[0027] That is to say that the third line 15 forms a bypass of the second line 14 between the first 1 and second 3 compressors

[0028] This third pipe can therefore be a branch of the second pipe 14 (and / or a separate pipe).

[0029] That is to say that the third pipe 15 takes a fraction of the compressed gas intended to supply the second compressor 3 to sweep (cool) the two motors 5, 6. This fraction can correspond to one to forty percent of the gas flow leaving the first compressor 1.

[0030] The gas flow in each of the two branches supplying the engines 5, 6 respectively can be regulated by a set of valves 7, 8 (or any other suitable member, in particular a pressure reducing member such as an orifice, a capillary, etc.). In the example shown, two valves 7, 8 located respectively in the two parallel branches ensure these distributions of compressed cooling gas to the engines 5, 6.

[0031] Alternatively, the third single pipe 15 can be split. That is to say, two separate portions of pipe 15 are connected respectively to the two parallel branches and to the two valves 7, 8 or equivalent. Similarly, it is possible to envisage a single regulating valve located in the portion common to the two branches (in the portion of pipe between the second pipe 14 and the two parallel branches connected to the motors 5, 6).

[0032] In addition, the compressed gas leaving the first compressor 1 is cooled by a first gas cooling member 2 such as a heat exchanger in thermal exchange with a heat transfer fluid.

[0033] The cooling of the gas intended to supply the engines for their cooling can be provided on the third pipe 15 (between the second pipe 4 and the two parallel branches) and / or downstream (on the parallel branches). This cooling member (2 or other) can be sized to cool the gas to a lower temperature, for example 0°C (for example via a refrigeration unit) to improve the cooling of the engine(s).

[0034] Thus, the gas is cooled before being distributed to the two branches of the third pipe.

[0035] Thus, this cooling can be carried out via an exchanger 2 (or other) at the outlet of the compressor 1 as illustrated in the figure and / or downstream in the bypass 15 and / or in the branches via an exchanger or any other member ensuring even limited cooling of the gas.

[0036] That is to say that the circuit provides a parallel supply to the two motors 5, 6. After circulation in the motors 5, 6, this gas is then returned to the inlet of the first compressor 1 via fourth pipes 11, 12.

[0037] The fourth lines 11, 12 can also be used, if necessary, to recover gas from any leaks (for example, at joints located near the engines, such as rotating joints, for example).

[0038] In a possible non-limiting example, the mechanical power required to compress a flow rate of 1.26 kg / s of nitrogen gas initially at a pressure of 5 bar absolute and a temperature of 288 K at a pressure of 18.34 bar absolute is approximately 200 kW (100 kW per engine).

[0039] For example, nitrogen is compressed to 8.87 bar absolute in the first centrifugal compression stage (first compressor 1) with a power of 95 kW and a typical isentropic efficiency of 86%. The compressed gas is then cooled in exchanger 2. As described above, part of the gas is withdrawn via valves 7 and 8 to cool engines 5 and 6.

[0040] The main flow (stream) is then compressed again to a pressure of 18.34 bar absolute in the second centrifugal compression stage 3. This second compressor 3 has for example a power of 95 kW and a typical isentropic efficiency of 86%. Then the gas is cooled in an outlet heat exchanger 4 before being sent to the outlet 20 of the compression device 18.

[0041] Of the 100kW of work / power of the 5, 6 motors, typically 5% will be transformed into heat (electric motor losses and rotor friction losses with nitrogen) or approximately 5kW per 5, 6 motor.

[0042] A portion of the nitrogen flow at the outlet of the first cooling exchanger 2 is therefore sent through a first valve 7 and a first branch 9 to the first 5 engine for cooling.

[0043] The rise in gas temperature through engine 5 will typically be limited to 30 K (to limit the heating of engine 5) by controlling valve 7.

[0044] This can be translated as mass flow = Power / Cp / deltaT = 5000 / 1048 / 30=0.159 kg / s.

[0045] With Cp = heat capacity of the gas (nitrogen in this example) in J / kg / K.... delta T = the temperature variation of the gas between lines 9 and 11 in K.

[0046] Power = the engine losses to be evacuated by the gas in W. The gas which has circulated in the engine 5 will then leave the engine 5 via the third pipe 11 and reach the inlet of the first compressor 1.

[0047] The same process is carried out in parallel for the second motor 6 (via valve 8 and lines 10, 12).

[0048] Coming out of the two engines 5, 6 via the respective fourth lines 11, 12, the nitrogen at 318 K (288K+30K elevation) will be mixed with the nitrogen coming from the inlet 13 of the compressor 1. As illustrated schematically in figure 2 , according to the invention, a second cooling member 17 is provided in the circuit to cool the gas leaving the motors 5, 6 before its return to the first compressor 1.

[0049] That is to say that the cooling gas leaving the engine(s) 5, 6 can be cooled through, for example, a heat exchanger 17 before joining the main circuit of the compressor 1.

[0050] The efficiency of the device is improved by lowering the temperature of the cooling gas before returning it to the inlet of compressor 1.

[0051] This cooling gas coming from the engines 5, 6 via the third pipes 11, 12 is preferably cooled to a temperature close to or equal to the temperature of the gas at the inlet 13 of the compressor 1.

[0052] In the example of the figure 2 , the mechanical power required to compress a flow rate of 1.26 kg / s of gaseous nitrogen having an initial pressure of 5 bars absolute and a temperature of 288 K to 18.34 bars absolute is approximately 198 kW (98 kW for the first engine 5 and 100 kW for the second engine 6).

[0053] There is thus a 1% reduction in power consumption compared to the previous device.

[0054] Nitrogen is compressed to 8.87 bar absolute in the first centrifugal compression stage 1 having for example a power of 93 kW and a typical isentropic efficiency of 86%. Then the gas is cooled in the exchanger 2. Part of the gas is withdrawn via the valves 7, 8 to cool the engines 5, 6.

[0055] The main flow is then compressed to 18.34 bar absolute in the second centrifugal compression stage 3. This second compression stage has, for example, a power of 95 kW and a typical isentropic efficiency of 86%. Then the gas is cooled in the second heat exchanger 4 before being sent to the outlet 20 of the compression device (here outlet of the second compressor 3). Of the 98 kW and 100 kW of power supplied respectively by the motors 5, 6, typically 5% will be transformed into heat (electric motor losses, rotor friction losses with nitrogen, etc.), i.e. approximately 5 kW per motor 5, 6.

[0056] Part of the nitrogen flow at the outlet of the first cooling exchanger 2 will be sent through the first valve 7 and branch 9 to the engine 5 for cooling. The rise in the temperature of the gas through the engine 5 will typically be limited to 30 K (to limit the heating of the engine 5) by controlling the valve 7.

[0057] As before, this will result in a mass flow rate equal to Power / Cp / deltaT = 5000 / 1048 / 30=0.159 kg / s.

[0058] The nitrogen will then escape from the engine 5 via the fourth pipe 11 and join the heat exchanger 17 before returning to the inlet of the first compressor 1.

[0059] The same process is carried out for the other engine 6 (cooling gas via valve 8, lines 10 and 12 and exchanger 17).

[0060] Leaving the heat exchanger 17, the nitrogen at 288 K will be mixed with the nitrogen coming from the inlet 13 of the compressor 1. This will not have any impact on the temperature of the nitrogen at the inlet of the first stage 1 (unlike the previous device). The overall efficiency is improved.

[0061] Of course, the invention is not limited to these exemplary embodiments.

[0062] For example, the cooled gas used for cooling the engines 5, 6 may be taken from the outlet of a second 3 compression stage and / or subsequent compression stage.

[0063] In addition, several compression stages could be driven by a single engine. Similarly, one or more expansion stages (turbine(s)) can be coupled to at least one of the engines.

[0064] Furthermore, in addition to the compression stage(s) 1, 2, one or more expansion stages (preferably centripetal turbine(s)) may be mounted on the same drive shaft as one or more compressors.

[0065] Additionally, at least one bypass valve may be mounted on the cooling circuit so as to limit the flow through one or more engines.

[0066] The flow of cooling gas to an engine 5, 6 can be adjusted by one or more expansion members 7, 8. This or these members can advantageously be adjustable so as to control, for example, the temperature of one or more engines and / or the cooling flow rate and / or the temperature of the cooling gas.

[0067] In addition, these expansion organs 7, 8 can, if necessary, cool the gas before it enters the engine(s).

[0068] Thus, the valves 7, 8 can be replaced or associated with one or more turbines and / or Ranque tubes (Vortex tube). Likewise, these members 7, 8 can be located on the pipe 15 between the second pipe 14 and the two parallel branches.

[0069] In addition, rotating joints may be used between the motor(s) 5, 6 and the compression stage(s) 1, 3 or the expansion stage(s) so that the pressure in the motor cavities is close to the lowest pressure of the compressor, i.e. the compressor inlet pressure 13. This has the effect of lowering the friction losses between the rotor(s) and the gas because these losses are proportional to the pressure in the motor cavity.

[0070] As schematized in the figure 3, the compression device 18 may be part of a low-temperature refrigeration machine, for example between -100°C and -273°C, and comprising a working circuit 10 containing a working fluid, the working circuit comprising a centrifugal compression device 18 and a device 19 for cooling and expanding the compressed gas in the compression device 18.

[0071] The working gas may include all or part of: nitrogen, helium, hydrogen, neon, argon, carbon monoxide, methane, krypton, xenon, ethane, carbon dioxide, propane, butane, oxygen.

Claims

1. Centrifugal compression device for a working gas, notably for a refrigeration machine, including several centrifugal compressors (1, 3) forming several successive and / or parallel compression stages and several drive motors (5, 6) for the compressors (1, 3), the device having a gas circuit comprising a first inlet line (13) for the gas to be compressed that is linked to an inlet of a first compressor (1) to convey the gas to be compressed into the first compressor (1), the circuit having a second line (14) linked to an outlet of said first compressor (1) to discharge the gas compressed in the latter, the second line (14) being linked to an inlet of a second compressor (3) to convey the gas compressed in the first compressor (1) into the second compressor (3) in order to perform a second compression, the circuit having at least one third cooling line (15) with one end connected to the outlet of at least one of the compressors (1, 3) and at least one second end connected to an inlet of at least one motor (5, 6) for transferring a fraction of the gas compressed in the at least one compressor (1, 3) into the at least one motor (5, 6) in order to limit the heating of the latter, the third cooling line (15) including a first gas cooling member (2) and two parallel branches supplying respectively two separate motors (5, 6) of the device with a view to respectively cooling same, characterized in that the circuit includes fourth lines (11, 12) linking an outlet of the first motor (5) and an outlet of the second motor (6) to the inlet of the first compressor (1) to recycle the gas that was used to limit the heating of the motors to the first compressor (1) in order to compress said gas and in that the circuit includes at least one second gas cooling member (17) arranged on the path of the fourth lines (11, 12) to remove heat from the gas coming from the motors (5, 6) before said gas returns to the first compressor (1).

2. Device according to Claim 1, characterized in that the third cooling line (15) includes a set of control valves (7, 8) for the gas flow admitted into the two parallel branches.

3. Device according to Claim 2, characterized in that the set of valves (7, 8) includes two control valves positioned respectively in the two branches.

4. Device according to Claim 2, characterized in that the set of valves (7, 8) includes a three-way control valve positioned at the junction of the two branches or a single valve positioned on the third line (15), upstream of the two branches.

5. Device according to any one of Claims 1 to 4, characterized in that the first gas cooling member (2) includes a heat exchanger cooled by a heat-transfer fluid.

6. Device according to any of Claims 1 to 5, characterized in that the compressors (1, 3) are driven in rotation directly by the corresponding motors (5, 6).

7. Device according to any one of Claims 1 to 6, characterized in that it includes one or more rotary joints between the motor or motors (5, 6) and the compressor or compressors (1, 3) or one or more expansion stages such that the pressure in the cavities of the motor or motors is close to the lowest pressure in the compressor (1), i.e. the inlet pressure (13) of the compressor (1).

8. Device according to any one of Claims 1 to 7, characterized in that it includes at least one motor driving one or more compressors and at least one motor coupled to one or more expansion turbines.

9. Refrigeration machine at low temperature between - 100°C and -273°C including a working circuit (10) containing a working fluid, the working circuit including a centrifugal compression device (18) and a device (19) for cooling and expanding the gas compressed in the compression device (18), characterized in that the compression device (18) is according to any one of Claims 1 to 8.

10. Centrifugal compression method for a working gas, notably for a refrigeration machine using a compression device according to any one of Claims 1 to 8, the method comprising: - a step for compressing a working gas in a first compressor (1) then in a second compressor (3) that are arranged in series, - a step for drawing off a fraction of the compressed gas leaving at least one of the compressors and causing said gas drawn off to flow through at least one motor (5, 6) in order to cool same, characterized in that it includes a cooling step for the gas drawn off at the outlet of the at least one compressor (1) and a step in which said drawn off cooled gas is distributed and caused to flow in parallel through two separate motors (5, 6) in order to respectively cool same.