Abstract:
A method for operating a compressor device and associated compressor device including a compressor chamber and a cooling chamber adjoining the compressor chamber is provided. The pressure of a cooling medium in the cooling chamber is held above the pressure of a compressor medium in the compressor chamber during operation of the compressor device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2008/064731, filed Oct. 30, 2008 and claims the benefit thereof. The International Application claims the benefits of European Patent Office application No. 07023293.9 EP filed Nov. 30, 2007. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF INVENTION 
     The invention refers to a method for operating a compressor device and to a compressor device with an electric drive, a compressor chamber and a cooling chamber which adjoins the compressor chamber, in which the compressor chamber is enclosed by a partition in the form of a tube which is provided between an electric stator of the drive and the rotor, which partition encapsulates the compressor chamber in relation to a cooling chamber, and in which the cooling chamber is part of a cooling device and contains a cooling medium which by means of a cooling circuit line can be transported out of and into this cooling chamber, wherein the cooling medium serves for dissipating heat which develops primarily as a result of a stator section of the electric drive. 
     BACKGROUND OF INVENTION 
     In known compression devices or compressor devices, it is customary to cool the compressor chamber and for this purpose to provide a cooling chamber which adjoins the compressor chamber. Thus, in known compressor devices with a common pressure casing for drive and compressor it is known to provide a comparatively thin partition for separating a compressor medium in the compressor chamber from the cooling medium in the adjoining cooling chamber. This partition can be a tube, for example, which is to be provided in a compressor device between its electric stator and the rotor. Such a tube should be designed as thin as possible for achieving the desired electrical functionality. Such a thin-walled tube, however, is limited in its pressure stability so that any hazard potential with regard to the existing pressure situation between compressor chamber and cooling chamber has to be excluded. 
     So that operation can be carried out with comparatively thin-walled tubes, even in the case of high compressor pressures, it is known to hold the pressure of the cooling medium, by means of a piston accumulator, lower than or equal to the compressor pressure. A system of this type, as is known for example from EP 1 482 179 B1, is very costly to adjust, however, and can possibly be seriously impaired in its function as a result of an inclusion of gases, such as air, in the media. 
     A multiphase pump for undersea operation is already known from WO 98/53182, in which a pressure compensating system ensures a positive pressure drop between a lubricating and cooling fluid and the process medium, wherein the driving electric motor is separated from the delivery pump by means of a shaft seal and the drive-side volume is filled completely with the lubricating and cooling fluid. WO 00/73621 A1, WO 2007/055589 A1, WO 2005/003512 A1, U.S. Pat. No. 2,423,436, and EP 0 550 381 A1 also deal with pumps or compressors which have a drive which is separated from the fluid flow unit by means of a seal so that the process fluid which is to be delivered does not come into contact with the drive. Such seals are expensive, especially with high demands for leak tightness. A compressor unit, in which a stator of an electric drive is separated from a compressor chamber by means of a cylindrical partition, is known from WO 2007/110281 A1. The strength requirements for such a partition are hard to fulfill, especially at a high pressure level, by means of conventional materials which also fulfill the requirement profile with regard to behavior in the electrical field and to chemical resistance. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to create a method for operating a compressor device and an associated compressor device, in which the aforementioned problems are solved in a cost-effective manner and in which overall a compressor which is to be operated in a risk-free manner, even for high compression pressures, is created. The solution according to the invention is to be applicable especially for compressor devices in the oil and gas industry. 
     The object is achieved according to the invention with a method for operating a compressor device according to the claims and a compressor device according to the claims. Advantageous developments of the solution according to the invention are described in the dependent claims. 
     According to the invention, the object is achieved by means of a method and a compressor device according to the independent claims. The dependent claims which are referred back to in each case contain advantageous developments of the invention. 
     By means of the solution according to the invention, the pressure of the cooling medium during operation of the compressor device is held above the pressure of the compression or compressor medium. According to the invention, it is consequently ensured that even in the case of leakages on a partition between compressor chamber and cooling chamber no gas can escape from the compressor device into the cooling medium. The compressor device according to the invention is protected particularly well with regard to the hazard situation on the partition between compressor chamber and cooling chamber. The gas volume of the compressor chamber is more reliably sealed as a result of the higher pressure in the cooling chamber and in the associated cooling circuit. 
     According to the invention, especially temperature-induced and/or pressure-induced volume changes in the cooling chamber are preferably compensated by means of a compensating device by admitting and releasing cooling media into or from the cooling chamber. In addition to the protecting of the pressure situation in the cooling chamber which is achieved therewith, the type of system according to the invention and the associated method are also independent with regard to the actual size or the volume of the cooling circuit of the compressor device. Regardless of whether there is a large or a small volume of the cooling circuit, the volume can always be completely filled by means of the compensating device according to the invention. 
     In the solution according to the invention, furthermore, gas bubbles are preferably dissipated from the cooling medium by means of a deaeration device. This deaeration device also contributes towards the safeguarding of the pressure according to the invention in the cooling chamber, which is higher in comparison to the compressor chamber. 
     According to the invention, the aforementioned compensating device is furthermore preferably designed with a differential pressure controller for controlling the pressure difference between the cooling chamber and the compressor chamber and has a control piston and a control valve which can be operated by this. In this case, the pressure of the compressor or the pressure which prevails in the compressor chamber advantageously acts upon the control piston on one side. On the other side of the control piston, especially the pressure of the cooling medium is applied, which pressure, so that it can be held higher than the pressure in the compressor chamber, is increased by means of a force which acts additionally on the control piston. 
     The pressure differential controller in this case is especially preferably designed with a control piston which has a first piston chamber, which is connected to the cooling chamber in a fluid-conductive manner, and a second piston chamber, which is connected to the compressor chamber in a fluid-conductive manner, and in which the control piston, on the side of the second piston chamber, is spring-preloaded in the direction towards the first piston chamber. The spring-preloading of this type creates in the first piston chamber a pressure increase in comparison to the second piston chamber, so that in this way the pressure of the cooling medium, as provided according to the invention, is held higher than the pressure of the compressor medium. 
     The compensating device according to the invention is furthermore preferably designed with a differential pressure measuring device for measuring the pressure difference between the cooling chamber and the compressor chamber. The differential pressure measuring device determines said pressure difference during operation of the compressor device according to the invention and generates a signal so that in the case of a small pressure difference or no pressure difference cooling medium in the cooling circuit is admitted into the cooling chamber by the aforesaid compensating device. 
     For this, the compensating device is preferably designed with a pressure generator for delivering cooling medium into the cooling chamber, which pressure generator, as explained above, can be operated especially by the differential pressure measuring device. 
     Furthermore, the compensating device is preferably designed with a pressure bleed for bleeding off cooling medium from the cooling chamber, which pressure bleed can be operated especially by the aforesaid control piston. As a pressure bleed, an overpressure valve and/or a safety valve can also be advantageously provided on the pressure generator. For protecting the compressor device according to the invention, so-called differential pressure protectors are also advantageously provided between the pressure side of the cooling medium and the pressure side of the compressor medium and, in the case of an increased pressure difference between these two sides of a compressor according to the invention, ensure a pressure balance after a prespecified pressure threshold by means of a movable wall. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       An exemplary embodiment of the solution according to the invention is explained in more detail below, with reference to the attached schematic drawings. 
       The FIGURE shows a greatly schematized functional diagram of an exemplary embodiment of a compressor device according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     A compressor device  10  is designed in the form of a turbocompressor and in this case has a compressor chamber  12  with a drive (not shown) of the turbocompressor partially integrated therein. In the compressor chamber  12 , there is a compressor medium (not illustrated in more detail). 
     The compressor chamber  12  is enclosed by a partition  14  in the form of a tube which encapsulates the compressor chamber  12  in relation to a cooling chamber  16 . The cooling chamber  16  is part of a cooling device  18  and contains a cooling medium (not illustrated in more detail) which by means of a cooling circuit line  20  can be transported out of and into this cooling chamber  16 . The cooling medium in this case serves for dissipating heat which develops primarily as a result of the stator section of the electric drive. For this, a cooling pump  22 , with an associated cooling pump drive  24 , and also a cooler  26  are connected in series into the cooling circuit line  20 . 
     A differential pressure control device  28 , which has a control piston  30 , is provided on the compressor device  10 . The control piston  30  separates a first piston chamber  32  from a second piston chamber  34 , wherein the pressure of the cooling medium is applied in the first piston chamber  32  and the pressure of the compressor medium is applied in the second piston chamber  34 . In the second piston chamber  34 , there is furthermore a spring element  36  by means of which the control piston  30  is displaced by spring action in the direction of the first piston chamber  32 . In this way, a higher pressure prevails in the first piston chamber  32  in comparison to the second piston chamber  34 . 
     A valve  38 , by means of which cooling medium can be released from the cooling circuit line  20 , can furthermore be operated by the control piston  30 . This releasing takes place if the volume of the cooling medium in the cooling circuit line  20  in the section between the cooling chamber  16  and the cooling pump  22  expands (particularly on account of heating of the cooling medium). Expansion like this of the cooling medium leads to the control piston  30  being displaced in the direction towards the second piston chamber  34  and, as a result, to the valve  38  being opened. The valve  38  then opens a line to a replenishment and storage device  40 , through which line cooling medium can flow out. 
     In the installed state, the valve  38  is arranged in the system at the highest point. Consequently, it is ensured that the valve  38  undertakes the function of a deaeration device and that the system is deaerated via the valve  38 . A differential pressure-measuring device  42  is provided for recording the pressure difference between the first piston chamber  32  and the second piston chamber  34  by a measurement technique. For this purpose, the differential pressure-measuring device  42  has a measuring instrument  44  and a signal generator  46  of a predefined upper measurement threshold, and also a signal generator  48  of a predefined lower measurement threshold. If the pressure difference between the first piston chamber  32  and the second piston chamber  34  drops below the value of the lower measurement threshold, the signal generator  48  generates an electrical signal which is directed to a control device  50  of a replenishment-pump drive  52 . The replenishment-pump drive  52  is part of a replenishment pump  54  by means of which cooling medium can be admitted from a storage tank  56  of the replenishment and storage device  40 , past a safety valve  58 , through a check valve  60  and a shut-off element component  62 , into the cooling circuit line  20 . 
     The safety valve  58  protects the replenishment and storage device  40 , and essentially the extending line downstream of the pump  54 , against overpressure in this case, for example in the case of the check valve  60  being closed or shut-off component being closed, whereas the check valve  60  prevents a return flow of cooling medium from the cooling medium circuit line  20  back into the storage tank  56  while the replenishment pump  54  is inoperative. 
     The cooling medium is introduced by means of the replenishment pump  54  into the cooling circuit line  20  between the cooling chamber  16  and the cooling pump  22  so that as a result the pressure in the cooling chamber  16  and also in the first piston chamber  32  is increased. This increase of pressure is carried out until the upper measurement threshold for the pressure difference between the first piston chamber  32  and the second piston chamber  34  is determined by the signal generator  46 . 
     In this way, the differential pressure control device  28  with its valve  38 , the differential pressure measuring device  42 , and also the replenishment and storage device  40  with its replenishment pump  54 , together form a compensating device  64  by means of which it is ensured that during operation of the compressor device  10  the pressure of the cooling medium in the cooling chamber  16  is held above the pressure of the compressor medium in the compressor chamber  12 . 
     Finally, a control valve  66  is additionally provided on the replenishment and storage device  40  for admitting nitrogen into the storage tank  56 , which takes place in the case of cooling media which react sensitively to air moisture or air oxygen, or which are to be shielded against an external atmosphere. An overpressure valve  68 , which is furthermore provided on the storage tank  56 , protects the storage tank  56  against overpressure in this case. 
     Furthermore, two differential pressure protectors  70  and  72  are additionally interposed between the cooling chamber  16  and the compressor chamber  12  and in the case of an excessive pressure difference between the compressor chamber  12  and the cooling chamber  16  on both sides (i.e. once in the direction of the compressor chamber  12  and once in the direction of the cooling chamber  16 ) can form a pressure balance after a predefined pressure threshold.