Abstract:
A motor-compressor includes a compressor, an electric motor directly connected to the compressor, magnetic bearings and one gas support located adjacent to a magnetic bearing to seal and support an end of the compressor&#39;s rotor. The compressor and the electric motor are integrated in a single unit, being housed in a single box or casing.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a motor-compressor used for the compression of process gas, in particular used for applications in which a reduced maintenance and high reliability are required, and more specifically used in applications in underwater environments. 
     BACKGROUND OF THE INVENTION 
     A motor-compressor normally comprises a compressor of process gas and an electric motor for activating said compressor. 
     These are typically coupled with each other by means of a joint, which connects a portion of a shaft of the compressor, extending from its box or casing, to a corresponding portion of a rotor of an electric motor, which in turn extends from the box or casing of the same electric motor. 
     Both the motor and the compressor are equipped with at least a pair of radial bearings for supporting the corresponding rotor. 
     In certain cases, these bearings are lubricated with oil: this has the disadvantage of the use of control and management systems of the lubricating oil with consequent high encumbrances and significant maintenance interventions. 
     In the case of submarine applications this type of configuration (non-integrated) requires a series of sealing washers to insulate the internal parts of the compressor and electric motor, and above all the parts of the respective shafts extending therefrom for coupling. 
     This however consequently increases the number of components and complexity of the motor-compressor. 
     BRIEF DESCRIPTION OF THE INVENTION 
     An objective of the present invention is to provide a motor-compressor which is reliable with time and has reduced maintenance times and costs. 
     Another objective is to provide a motor-compressor which has a reduced number of components to increase the reliability and availability. 
     A further objective is to avail of a motor-compressor which is compact, light and easily transportable. 
     Yet another objective is to provide a motor-compressor which is simple and economical. 
     These objectives according to the present invention are achieved by providing a motor-compressor as specified in claim  1 . 
     Further characteristics of the invention are indicated in the subsequent claims. 
     The characteristics and advantages of a motor-compressor according to the present invention will appear more evident from the following illustrative and non-limiting description referring to the enclosed schematic drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially sectional raised side schematic view of a preferred embodiment of a motor-compressor according to the present invention; 
         FIG. 2  is a schematic view of an internal detail of the compressor. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the figures, these show a motor-compressor  10  comprising a compressor  20  and an electric motor  30  directly connected to said compressor  20 , which are integrated in a single unit. 
     In particular, said motor-compressor  10  comprises a single box or casing  12  in which said compressor  20  and said electric motor  30  are housed. 
     Said compressor  20  and said electric motor  30  are preferably not separated and the same type of gas (process gas processed by the compressor) pass through both. 
     Although process gas contains potentially corrosive/erosive agents, capable of degrading the electric parts in an extremely rapid time, (in particular the motor  30  coils and magnetic bearings  70  of the rotor), the motor-compressor  10  according to the present invention comprises a protection system of the motor windings and magnetic bearings from the process gas based on the use of barriers. 
     Said motor-compressor  10  preferably comprises three active radial magnetic bearings  70  for supporting both a rotor  32  of the electric motor  30  and a rotor  22  of the compressor  20 . 
     A first and a second bearing of said three active magnetic bearings  70  are preferably positioned and support said shaft  32  of said electric motor  30  close to its ends. 
     A third bearing of said three active magnetic bearings  70  preferably supports and is positioned on a free end of said rotor  22  of said compressor  20 . In this way, the necessity of lubricating oil and relative maintenance interventions is advantageously avoided, at the same time reducing the number of bearings for supporting the electric motor  30  and compressor  20  to the minimum possible, as three supporting bearings  70  are used. 
     According to the invention, it is in fact superfluous to resort to a configuration of the traditional type with four transporting bearings  70 . 
     Even if, on the other hand, the solution according to the invention enables resort to be made to a configuration in which only two radial bearings are used, it has been verified that in particularly difficult application contexts, such as for example in submarine applications, where the maximum reliability of the system is required and where the functioning scenarios require a high number of centrifugal disc wheels, the solution with two bearings does not guarantee the necessary reliability. 
     Said motor-compressor  10  preferably comprises a further active magnetic bearing  80  suitable for supporting axial thrusts, in particular situated on said rotor  32  of said electric motor  30 . 
     In addition to the three active radial magnetic bearings  70 , the rotor is provided with a fourth gas support  85  situated close to the bearing of the compressor. 
     This support is capable of increasing the stability of the rotor and substituting the magnetic bearing in the case of its malfunctioning. 
     In particular, said motor-compressor  10  comprises a suitable direct coupling  50  with a front toothing (Hirth type), which connects said compressor  20  to said electric motor  30 . 
     In particular, said direct coupling  50  connects and makes integral said rotor of said compressor  20  and said rotor  32  of said electric motor  30 . 
     In other words, an end portion of said rotor  32  of said electric motor  30  is connected by means of a front coupling  50  with a corresponding end portion  22  of said rotor of said compressor  20 . 
     Said direct coupling  50  connects in particular said rotor  32  of said electric motor  30  to said rotor  22  of said compressor  20  by means of a tie-rod, not shown, fixed to said rotor  32  of said electric motor  30  and passing through said rotor  22  of said compressor  20 . 
     Said tie-rod is assembled by acting on the accessible side of said centrifugal compressor  20  and this avoids other openings in the side surface of the outer casing excluding those for the passage of service/process fluids and wires for the electrical connection, as on the contrary is necessary according to the known art, wherein the connection between the motor shaft and compressor shaft requires an access opening through the casing. 
     Said casing  12  consequently does not have any connections in the connection point between the motor and compressor but, on the side surface, comprises a series of openings exclusively suitable for the passage of service/process fluids and for the passage of wires for the electrical connection: this aspect is particularly advantageous in applications in which a reduction in possible leakages between the inner environment of the machine and the outside environment is of great importance (especially submarine applications). 
     With reference to  FIG. 2 , according to a preferred embodiment of the present invention, said rotor  22  of said compressor  20  comprises a series of portions  22 ′ and a series of direct couplings  51  with a front toothing, of the Hirth type, to make said portions  22 ′ integral with each other. 
     Each portion  22 ′ is equipped with a respective disc wheel  26  and is also suitable for being coupled with at least another portion  22 ′ by means of a respective analogous direct coupling  51  with a front toothing. 
     The number of disc wheels is preferably adapted to the particular compression service requirements. 
     The presence of a series of sections  22 ′ also allows the following advantages: the diaphragms which enclose the disc wheels  26  can be produced in a single piece; internal washer seals can be avoided. 
     In this way, the probability of internal leakages is reduced to the minimum. 
     Said rotor  22  of said compressor  20  can be completely assembled to the stator parts (diaphragms) on the outside of the casing  12  thus facilitating assembly operations. 
     Finally, each disc wheel  26  situated in each portion  22 ′ is produced integrally with the shaft. 
     The cooling of the electric parts is preferably effected as follows. 
     For the electric motor  30  there is a closed circuit  40  equipped with an external exchanger  41  and disc wheel  45  situated at the end of the rotor  32  of said electric motor  30 , to circulate the cooling gas through the stator and rotor parts. The gas used is the same process gas which is inserted in the motor volume in the ignition phase. 
     The magnetic bearings of the motor side are cooled by the same gas which is circulating in the motor, by means of the system  40  and the disc wheel  45 . 
     For the magnetic bearing of the compressor side, the cooling is guaranteed by means of a gas discharge  60  from the first compressor phase sent to the magnetic bearing through a channeling  61 . The same discharge, by exploiting a different channeling  65 , also reaches the motor, where it effects a compensation (part of the gas flows from the motor chamber to the compressor chamber). 
     The configuration of said motor-compressor  10  can be either horizontal or vertical depending on the particular installation demands. 
     As it is more compact, the motor-compressor is advantageously easy to transport. 
     It can therefore be seen that a motor-compressor according to the present invention achieves the objectives indicated above. 
     The motor-compressor of the present invention thus conceived can undergo numerous modifications and variants, all included in the same inventive concept. 
     Furthermore, in practice, the materials used as also the dimensions and components, can vary according to technical requirements.