Abstract:
The invention relates to a compressor unit, in particular for underwater operations, comprising a compressor with a rotational axis and an electric motor. Said compressor unit has a housing with an automation unit for control and regulation tasks. The aim of the invention is to improve the co-operation of the automation unit and the compressor unit and in particular to reduce the complexity of the cooling of the automation unit and signal and energy transmission. To achieve this, an additional housing, which contains the automation unit, is attached to the housing.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the US National Stage of International Application No. PCT/EP2007/051474, filed Feb. 15, 2007 and claims the benefit thereof. The International Application claims the benefits of European application No. 06006059.7 filed Mar. 24, 2006, both of the applications are incorporated by reference herein in their entirety. 
     
    
     FIELD OF INVENTION 
       [0002]    The invention relates to a compressor unit, in particular for underwater operation, comprising a compressor with a rotation axis and an electric motor, which compressor unit has a housing which has an inlet and an outlet for a pumping medium, having an automation unit which is designed such that it carries out open-loop and closed-loop control tasks for the compressor unit. 
       BACKGROUND OF THE INVENTION 
       [0003]    Recent developments in the field of compressor design have also been concentrated on undersea arrangements of large compressors which are intended to be used for the pumping of natural gases. 
         [0004]    Because of the particular operating conditions, in particular because of the greatly restricted accessibility both for maintenance purposes and by means of supply lines, the specialists are confronted with major requirements. The relevant environmental regulations forbid any exchange of substances between the equipment to be installed and the surrounding seawater. Furthermore, seawater is an aggressive medium and extreme pressure and temperature conditions can be found at the various depths in the sea. A further requirement is that the equipment should on the one hand have an extremely long life and on the other hand must be designed to be virtually free of maintenance. An additional exacerbating factor is not-inconsiderable contamination of the medium to be pumped which in some cases is chemically aggressive. 
         [0005]    Compressor units normally require numerous electrical connections for their operation, in particular for the power supply and for transmission of control signals between a higher-level automation unit and the compressor unit. The higher-level automation units are in this case arranged separately from the compressor unit, at some distance away, on the one hand in order to achieve a high level of modularity of design, and on the other hand to ensure optimum operating conditions for the electronics of the automation unit. Particularly when using active magnetic bearings, numerous signal lines are required between the automation unit and the compressor unit, and transmit various measured values to the automation unit, and transmit corresponding control parameters to the magnetic bearings. 
         [0006]    The transmission of the power for operation of the compressor unit and of the signals between the compressor unit and the automation unit necessitates a considerable amount of complexity since the numerous lines must be designed, inter alia, to be disconnectable by means of a very costly plug connection. The cost aspect becomes many times more important when this relates to an installation which is suitable for undersea operation, since the plug connection has to comply with particular requirements for this purpose. 
         [0007]    Furthermore, the automation unit must be provided with a cooling system by means of which the not-inconsiderable lost power from the components, some of which are in the form of power electronics, must be dissipated. 
         [0008]    The document WO-A-2005/003512 has already disclosed a compressor unit for underwater operation in which the compressor together with an electric motor is accommodated in a common, gas-tight housing. An automation unit, which controls the operation of magnetic bearings, is connected for signal transmission purposes to these bearings. 
       SUMMARY OF INVENTION 
       [0009]    Against the background of the problems of the prior art, the object of the invention is to provide a better interaction between the automation unit and the compressor unit and, in particular, to reduce the complexity for cooling the automation unit and of the signal and power transmission. 
         [0010]    A compressor unit is proposed in order to achieve the object according to the invention. 
         [0011]    The arrangement of an additional housing, in which the automation unit is arranged, on the housing of the compressor unit has, in particular, the advantage that appropriate power supply lines and signal lines between the automation unit and the compressor unit need no longer be designed to comply with a standard which is suitable for direct contact with the environmental conditions. In fact, these lines can be designed such that they merely satisfy the always reproducible and exactly predictable operating conditions in the interior of the additional housing and of the housing of the compressor unit. Furthermore, no special plug connections are required for disconnection of lines between the automation unit and the compressor unit. Surprisingly, it was also found that some areas on the housing of the compressor unit satisfy the thermal constraints required for operation of the automation unit, without any additional modification. This major advantage means that there is no longer any need for a separate cooling system for the automation unit. This advantage is particularly evident when the additional housing for the automation unit is thermally conductively fitted to the housing in the area of an intake connecting stub of the inlet such that the power lost from the automation unit is dissipated by means of thermal conduction to the housing. Although this advantage is fundamentally relevant for compressor units, it is additionally important in the field of underwater operation since, in this case, the accessibility to the compressor unit is very greatly restricted and, for this reason, additional cooling media are available only with difficulty, if at all. It is virtually impossible to use seawater as a cooling medium, because of the aggressive chemical characteristics. When pumping natural gas, the lost power can be absorbed without any problems by the cold pumping medium. However, one problem in this case is the introduction of the heat into the pumped flow. 
         [0012]    Particularly when a compressor unit is of a single-shaft design with a motor and a compressor unit along a single rotation axis, it is normally in an elongated form thus resulting in a temperature profile in the longitudinal extent during operation. The temperature in the axial area of the inlet or of the intake connecting stub is particularly advantageous for thermally conductive fitting of the additional housing for the automation unit. According to the invention, the heat is dissipated from the automation unit by means of thermal conduction in the area of the intake connecting stub of the housing, and introduced into the pumping medium flowing through the compressor unit. A person skilled in the art can decide the circumferential position in the axial area of the intake connecting stub at which the additional housing is fitted, depending on the thermal-conduction conditions between the housing of the compressor unit and the additional housing. 
         [0013]    In this case, the automation unit is expediently connected to components of the compressor unit by means of internal signal lines and/or internal power supply lines. These internal lines can expediently be designed to be disconnectable by means of a plug connection, such that elements can be replaced without any problems even during the course of maintenance tasks. The plug connections need be designed only to satisfy the always reproducible and predictable operating conditions in the housing interior. The components which are connected to the automation unit are, in particular, magnetic bearings for the rotor of the compressor and of the motor, and the electric motor. In addition, various temperature measurements and pressure measurements can be provided. 
         [0014]    The automation unit is expediently connected to a base station by means of an external signal line or an external power supply line, or by means of both. 
         [0015]    One advantageous development of the invention provides for the additional housing to be connected to the housing of the compressor unit by means of welding, which on the one hand ensures good thermal conduction between the housings and on the other hand provides the required gas-tightness, in particular for underwater operation. In order to ensure that the components in the additional housing are nevertheless accessible for maintenance tasks, it is advantageous for the additional housing to have an opening which can be closed. This opening which can be closed can be sealed by means of a conventional seal. For relatively long underwater operation phases, it is also feasible for this additional opening to be sealed by means of a weld seam, which in any case withstands the adverse operating conditions. 
         [0016]    In order to reliably dissipate on the one hand the lost power from the automation unit and on the other hand that from the operation of the compressor unit, it is expedient for the compressor unit itself to have a high-performance cooling system. This cooling system may, in particular during the pumping of natural gas during underwater operation, be designed such that the pumping medium flows around various components of the compressor unit, and the lost heat is in this way emitted to the pumping medium. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The invention will be described in more detail in the following text using one specific exemplary embodiment for illustrative purposes, and with reference to drawings. The embodiment shown should be regarded only as being illustrative, as one example of the invention. In the FIGURE: 
           [0018]      FIG. 1  shows a longitudinal section through a compressor unit with an automation unit fitted according to the invention, in the form of a schematic illustration. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0019]      FIG. 1  shows a section along a compressor unit  1  according to the invention which has, as major components, a motor  2  and a compressor  3  in a housing  4  which is designed to be gas-tight. The housing  4  accommodates the motor  2  and the compressor  3 . In the area of the junction between the motor  2  and the compressor  3 , the housing  4  is provided with an inlet  6  and an outlet  7 , with the fluid to be compressed being sucked in through the inlet  6  by means of an intake connecting stub  8 , and with the compressed fluid flowing out through the outlet  7 . 
         [0020]    The compressor unit  1  is arranged vertically during operation, with a motor rotor  15  of the motor  2  being combined via a compressor rotor  9  of the compressor  3  to form a common shaft  19 , which rotates about a common vertical rotation axis  60 . 
         [0021]    The motor rotor  15  is mounted in a first radial bearing  21  at the upper end of the motor rotor  15 . 
         [0022]    The compressor rotor  9  is mounted in a second radial bearing  22  at a lower position. 
         [0023]    An axial bearing  25  is therefore provided at the upper end of the motor rotor  15 , at the upper end of the common shaft  19 . The radial bearings  21 ,  22  and the axial bearing  25  operate electromagnetically, and are each designed to be encapsulated. The radial bearings  21 ,  22  in this case extend in the circumferential direction around the respective bearing point of the shaft  19 , and in this case are designed to revolve through 360° and not to be split. 
         [0024]    The compressor  3 , which is in the form of a centrifugal compressor, has three compressor stages  11  which are each connected by means of an overflow  33 . The pressure differences which result across the compressor stages  11  ensure a thrust on the compressor rotor  9 , which is transmitted via a coupling to the motor rotor  15  and is in the opposite direction to the force produced by the weight of the entire resultant rotor comprising the compressor rotor  9  and the motor rotor  15 , such that this results in a very high degree of thrust matching during rated operation. This allows the axial bearing  25  to be designed to be comparatively smaller than in a horizontal arrangement. 
         [0025]    The electromagnetic bearings  21 ,  22 ,  25  are cooled to operating temperature by means of a cooling system  31 , with the cooling system  31  providing a tap  32  in an overflow of the compressor  3 . A portion of the pumping medium, which is preferably natural gas, is passed from the tap  32  by means of pipelines through a filter  35 , and is then passed through two separate pipelines to the respective outer bearing points (first radial bearing  21  and second radial bearing  22  as well as the axial bearing  25 ). This cooling by means of the cold pumping medium saves additional supply lines. 
         [0026]    The motor rotor  15  is surrounded by a stator  16  which has an encapsulation  39 , such that the aggressive pumping medium does not damage the windings of the stator  16 . The encapsulation  39  is in this case preferably designed such that it can withstand the full operating pressure. This is also because a separate stator cooling arrangement  40  is provided, which pumps a dedicated cooling medium  41  via a heat exchanger  43  by means of a pump  42 . At least the encapsulation  39  is designed such that the section which extends between the stator  16  and the motor rotor  15  admittedly has a thin wall thickness, but is able to withstand the design pressure when the stator cooling arrangement  40  is completely filled by means of the cooling medium  41 . This avoids relatively major eddy current losses in this area, and improves the efficiency of the overall arrangement. 
         [0027]    The compressor rotor  9  expediently has a compressor shaft  10  on which the individual compressor stages  11  are mounted. This can preferably be achieved by means of a thermal shrink fit. An interlock, for example by means of polygons, is likewise possible. Another embodiment provides for the various compressor stages  11  to be welded to one another, thus resulting in an integral compressor rotor  9 . 
         [0028]    An additional housing  56  is thermally conductively fitted to the housing  4  of the compressor unit  1  by means of a weld seam  58 . The additional housing  56  has an opening  57  through which the interior of the additional housing  56  is accessible, and which is closed by means of screws  59  and a cover  70 . The cover  70  is welded by means of a sealing joint  63  to the adjacent elements of the additional housing  56  in order that the surrounding medium cannot enter during underwater operation. An automation unit  51 , comprising power electronics  52  and further components, is located in the interior of the additional housing  56 . The automation unit  51  is thermally conductively connected to the housing  4  of the compressor unit by means of a thermal-conduction element  64 , such that the lost power that is created is dissipated by means of thermal conduction to the housing  4 . 
         [0029]    The additional housing  56  is arranged in the axial area  50  of the inlet  6 , or of the intake connecting stub  8 , of the compressor unit such that the thermal conditions which prevail there ensure particularly efficient cooling of the automation unit  51 . A specific temperature profile occurs along the rotation axis  60  of the compressor unit during operation, and essentially has a low point in the area of the intake connecting stub  8 . 
         [0030]    The automation unit  51  is connected by means of external signal lines  66  and external power supply lines  68  to a station  65  which on the one hand controls, and on the other hand supplies, the compressor unit  1 . The external signal lines  66  and power supply lines  68  are designed such that they can be disconnected by means of external plug connections  69 . A bushing  53  seals the inlet of the external lines ( 66 ,  68 ) into the additional housing  56 . 
         [0031]    The automation unit  51  is connected to components of the compressor unit  1  by means of internal signal lines  55  and internal power supply lines  67 . The components comprise an axial bearing  25 , radial bearings  21 ,  22  and the motor  2 . In addition, further sensors and components are also provided and are connected to the automation unit  51 , although they will not be explained in any more detail here. 
         [0032]    The additional housing is formed from stainless steel, in particular for underwater operation. The power supply originating from the base station  65  is 400 V.