Title : i Integrated motor-compressor unit having a cooling circuit and a depressurization system configured to reduce pressure of the cooling fluid

Background!

[1] The field of the invention relates to integrated motor-compressor units for processing a working fluid, and more particularly to an integrated motor- compressor having a cooling system.

[2] Generally, a motor-compressor unit comprises a centrifugal compressor and a motor integrated in a common housing.

[3] A centrifugal compressor with multiple compression stages generally comprises a plurality of impellers supported by a driven shaft coupled to a rotor driven by a motor or a turbine in order to generate a flow of compressed process gas.

[4] The shaft used to directly drive such a centrifugal compressor is required to rotate at relatively high speeds which generate heat. Furthermore, operating the motor-compressor at high speeds increases windage frictional losses resulting from components operating in pressurized gas.

[5] If this heat is not properly dissipated, it may negatively affect the performance of the motor, as well as damage the electrical insulation of the stator. Increased temperatures can also adversely affect the rotor-bearing systems of both the compressor and motor, thus leading to bearing damage and/or failure.

[6] In orderto regulate the heat and cool such an integrated motor-compressor unit, it is known to use a cooling circuit which may be an open loop cooling circuit or a quasi-closed loop cooling circuit where gas is drawn from the process stream at some point in the compression process. The process gas is then circulated through the motor and the bearings to absorb heat.

[7] For example, only a small amount of process gas is fed into the cooling circuit from the process stream. The cooling gas may be driven by a pressure difference between the source of the cooling gas and the place where the gas is allowed to flow to. [8] Alternatively, it is known to use a blower located before the cooling loop to circulate the cooling gas in said cooling circuit and thus im prove the fa n com pression efficiency. However, such solution increases sign ificantly the windage losses, even more when the machine works at high pressure.

[9] Reference can be made to document US 9, 200, 643 - B2 which describes a system for cooling a motor-compression with a closed-loop cool ing circuit. However, the motor is sealed from the com pressor processed gas by dry gas seal or carbon rings in order to avoid contam ination, which increases the maintenance of the seals.

Brief Description of Invention

[10] One benefit afforded by em bodiments of the integrated motor-com pressor unit described herein is to reduce windage losses.

[11] I ndeed, the high speed motor, the coupl ing and the bear ings being im merged in the process gas, windage losses may be high, especial ly for com pressors with high suction pressure.

[12] It is therefore proposed a depressurization system for an integrated motor - com pressor unit having a motor and a compressor coupled to said motor. The depressurization system is configured to depressurize the pressure of the motor.

[13] It is further proposed an integrated motor-com pressor u nit configured to process a working flu id, such as for example gas, and com prising a motor and a com pressor coupled to said motor via a rotatable shaft and mounted in a single com mon housing, a cool ing fl uid is circulated throughout sa id housing in a cooling circuit.

Summary

[14] The integrated motor-com pressor unit com prises a depressurization system configured to depressurize the pressure of the motor.

[15] The depressurization system is thus configured to reduce pressu re of the cooling flu id circulating in the cool ing circuit.

[16] Such a depressurization system creates a significant pressure d rop of at least 10 ba rs. The efficiency of the motor is thus significa ntly increased. [17] According to an embodiment, the depressurization system comprises an expansion device, for example before the cooling circuit, and an auxiliary compressor, for example, after the cooling circuit, configured to recover the suction pressure.

[18] The expansion device may be, for example, a cooling expansion valve configured to receive the working fluid via a main compressor suction inlet of the compressor and to transmit expanded cooled fluid to the cooling circuit, and the auxiliary compressor may be configured to receive the cooling fluid after having cooled notably the motor and/or the bearings and to compress the cooling fluid.

[19] According to another embodiment, the expansion device is an expansion wheel.

[20] The expansion wheel may be mounted in various suitable locations further described and claimed herein.

[21] In an embodiment of operation of the integrated motor-compressor unit the motor rotates the shaft and thereby drives the compressor. A process gas to be compressed is introduced via a main compressor suction inlet provided in the housing. The compressor then compresses the process gas through successive stages of impellers to thereby produce a compressed process gas. The compressed process gas then exits the compressor via a process discharge outlet provided in the housing.

Brief Description of the Drawings

[22] Other aims, features and advantages of embodiments of the invention will become apparent on reading the following description, given purely as a non limiting example, and with reference to the attached drawings in which:

Figure 1 very schematically represents an integrated motor-compressor unit according to a first embodiment of the invention;

Figure 2 very schematically represents an integrated motor-compressor unit according to a second embodiment of the invention;

Figure 3 very schematically represents an integrated motor-compressor unit according to a third embodiment of the invention; and Figure 4 very schematically represents an integrated motor-compressor unit according to a fourth embodiment of the invention.

Detailed description

[23] The Figures very schematically illustrate an integrated motor-compressor unit 10 configured to process a working fluid, such as gas. The integrated motor- compressor unit 10 comprises a motor 12 and a compressor 14 coupled to said motor 12 via a rotatable shaft 16 and mounted in a single common housing 18 configured to circulate a cooling fluid in a cooling circuit 27.

[24] The integrated motor-compressor unit 10 further comprises a depressurization system 30 configured to depressurize the pressure of the motor 12 and thus configured to reduce pressure of the cooling circulating in the cooling circuit.

[25] Such a depressurization system 30 creates a significant pressure drop of at least 10 bars. The efficiency of the motor 12 is thus significantly increased thanks to such pressure drop.

[26] The shaft extends substantially the whole length of the housing 18 and comprises a motor section 17 coupled to the motor 12 and a driven section 19 coupled to the compressor 14. The motor section 17 and the driven section 19 of the rotatable shaft 16 are connected via a coupling 20, such as for example a flexible or rigid coupling.

[27] As illustrated, the motor section 17 and the driven section 19 are supported at each end, respectively, by one or more radial bearings 22. As way of a non- limitative example, four sets of radial bearings 22 are shown. The bearings 22 may be directly or indirectly supported by the housing 18.

[28] The motor 12 may be an electric motor, such as a permanent magnet motor having permanent magnets mounted on the rotor (not depicted on the figures) and a stator (not depicted on the figures). As an alternative, other types of electric motors, such as for example synchronous, induction, brushed DC motors, etc... may be used.

[29] The compressor 14 may be a multi-stage centrifugal compressor with one or more compressor stage impellers (not shown). [30] In order to cool or otherwise regulate the temperature of the motor 12 and the bearings 22, a cooling gas is circulated throughout the housing 18 in the cooling circuit 27 having cooling conducts 28 and hot conducts 29.

[31] The depressurization system 30 comprises an expansion device 32 before the cooling circuit 27 and an auxiliary compressor 34 after the cooling circuit 27 configured to recover the suction pressure.

[32] A first embodiment of the depressurization system 30 is shown on Figure 1. In this embodiment, the expansion device 32 is a cooling expansion valve receiving process gas via the main compressor suction inlet 24 and transmitting expanded cooled process gas to the cooling circuit 27. The auxiliary compressor 34 receives the cooling fluid after having cooled the bearings 22 and the motor 12 and compresses it before transmitting to the main compressor suction inlet 24.

[33] The embodiment of Figure 2, where the same elements bear the same reference differs from the embodiment of Figure 1 by the structure of the expansion device 32. In this embodiment, the expansion device 32 is an expansion wheel mounted on the motor shaft end. Alternatively, the expansion wheel may be mounted on the compressor shaft end, between bearings or on a dedicated turbo-expander. The auxiliary compressor 34 is, in this embodiment, mounted on the compressor shaft end. Alternatively, the auxiliary compressor 34 may be mounted on the motor shaft end, between bearings, on a dedicated turbo-expander, or on a dedicated compressor.

[34] The embodiment of Figure 3, where the same elements bear the same reference differs from the embodiment of Figure 1 by the structure of the expansion device 32. In this embodiment, the expansion is created by voluntary compressor 14 leakages that are compressed by the auxiliary compressor 34. In other words, calibrated gas leakages on the compressor end 14 are used to generate the cooling flow. In this embodiment, and as a non-limitative example, the auxiliary compressor 34 is mounted on the motor shaft end.

[35] The embodiment of Figure 4, where the same elements bear the same reference differs from the embodiment of Figure 1 by the structure of the depressurization system 30. In this embodiment, the depressurization system 30 comprises a blower device 36 mounted upstream the compressor 14 and configured to circulate the cooling fluid in a closed loop cooling circuit 27. The depressurization system 30 further comprises a depressurization auxiliary compressor 34 configured to compensate for the main compressor gas leakages. The depressurization system 30 also comprises a cooler 38 mounted on the cooling circuit 27 after the blower device 36.

[36] The depressurization auxiliary compressor 34 may be a low pressure compressor or a dedicated equipment.

[37] In an embodiment of operation of the integrated motor-compressor unit 10, the motor 12 rotates the shaft 16 and thereby drives the compressor 14. A process gas to be compressed is introduced via a main compressor suction inlet 24 provided in the housing 18. The compressor 14 then compresses the process gas through successive stages of impellers to thereby produce a compressed process gas. The compressed process gas then exits the compressor 14 via a process discharge outlet 26 provided in the housing 18.

[38] Thanks to the depressurization system of the invention, windage losses are reduced in the integrated motor-compressor unit, especially in compressors having high suction pressure.