Patent Publication Number: US-8974205-B2

Title: Progressing cavity gas pump and progressing cavity gas pumping method

Description:
FIELD OF THE INVENTION 
     The present invention relates to a progressing cavity gas pump and a progressing cavity gas pumping method. 
     BACKGROUND OF THE INVENTION 
     From DE 10 2004 050 412 A1, a gas compressor is known which comprises a compression device for compressing gas by operating two helical rotors which are in engagement with each other. Within its housing, this gas compressor comprises, among other things, a lubricant chamber and a rotor chamber, wherein the latter is sealed by seals against penetrating lubricant such as, e.g. oil and lubricating grease. 
     From DE 19849098 A1, the use of a progressing cavity gas pump as displacement machine for delivering and compressing gas, preferably as vacuum pump, is known. It is also proposed therein that said inner screw pump is configured in a completely dry-running manner so that no supply of the known operating fluids such as water or oil is required in the working space or in the other areas of the machine. In this case, only a one-time lifetime grease lubrication for bearing and gearing is to be carried out in the factory, wherein the bearings can be configured as hybrid bearings, thus ceramic balls in steel rings, and the stationary internally toothed gear wheel can optionally be configured as plastic gear wheel. 
     SUMMARY OF THE INVENTION 
     Apart from that it is known from practice that progressing cavity pumps with a rotor and a stator are widely used for delivering such media which are composed of liquids, solids and liquids, as well as liquids and gases in many different concentrations. Here, the liquids or liquid parts serve for lubricating and also cooling the pump. In the case that only gas is to be delivered, no lubricating or cooling effect is available in this known uses, and dry running between rotor and stator takes place. In absence of lubrication, the pump rotor rotating within the stator generates frictional heat which results in a local overheating of the elastomer from which at least the inside of the stator is made. Thereby, this elastomer loses first its elastic properties and is subsequently subjected to carbonization if oxygen is present because the material-related temperature limits for the elastomere are exceeded. Associated with this are not only downtimes for repair and maintenance but also losses with regards to the pumped quantities so that progressing cavity gas pumps of this type cannot be used in an optimal manner for delivering or compressing gas. 
     Thus, it is the object of the present invention to improve progressing cavity gas pumps. 
     The invention achieves this object by provision of a progressing cavity gas pump and a progressing cavity gas pumping method as described herein. 
     Accordingly, the invention provides a progressing cavity gas pump with a stator which has a stator interior with an elastomeric inner surface as well as a gas outlet and a gas inlet, whereby from the gas inlet to the gas outlet, a pump delivery direction is defined, and with a rotor which engages with stator interior and is rotatably drivable, wherein upstream of the stator, a lubricant reservoir is arranged which is connected via lubricant conduit devices with the stator interior. 
     Preferably, the lubricant conduit devices comprise a lubricant feed line from the lubricant reservoir to the stator interior and a lubricant return line from the stator interior to the lubricant reservoir. It is further preferred to integrate a throttle nozzle into the lubricant feed line. 
     A further preferred configuration is that an anterior pump chamber is provided which, with respect to the pump delivery direction, is connected on the inlet side to the stator interior and that the gas inlet opens out into the anterior pump chamber. In particular, it can further be provided that the rotor or a rotor drive device is guided through the anterior pump chamber. Alternatively or additionally, the lubricant feed line can open out into the anterior pump chamber, wherein it is further preferred that the opening of the lubricant feed line into the anterior pump chamber is upstream of the gas inlet so that gas to be pumped or to be compressed only gets into the anterior pump chamber if lubricant has already been fed. 
     Suitable previously explained configurations can be further developed in that in the pump delivery direction, a distributor having a gas branch-off extending upward to the gas outlet and having a lubricant branch-off extending downward to the lubricant return line is connected to an outlet of the stator interior so that due to gravity, lubricant reaches the lubricant return line and gets into the lubricant reservoir. 
     Yet another preferred configuration provides that the lubricant reservoir is designed for cooling the lubricant contained therein and in particular the lubricant recycled from the stator interior. 
     Furthermore, it can preferably be provided that the lubricant reservoir is a lubricating oil reservoir or lubricating oil tank and/or that a gear motor is contained for rotationally driving the rotor. 
     The object of the invention is also achieved with a progressing cavity gas pumping method, wherein in a progressing cavity gas pump, gas coming from a gas inlet is delivered with a rotationally driven rotor within a stator and through a stator interior having an elastomeric inner surface to a gas outlet and is compressed, whereby from the gas inlet to the gas outlet, a pump delivery direction is defined, and wherein from a lubricant reservoir below the stator, a lubricant supply to the stator interior takes place via lubricant conduit devices, and lubricant from the stator interior is recycled via the lubricant conduit devices into the lubricant reservoir. 
     Further preferred configurations are provided in
         that due to the arrangement of the lubricant reservoir below the stator, at or downstream of an outlet of the stator interior, a gravitational separation of lubricant and gas takes place, and/or   that lubricant cools or is cooled in the lubricant reservoir, and/or   that lubricant is conveyed through the lubricant conduit devices which comprise a lubricant feed line from the lubricant reservoir to the stator interior and a lubricant return line from the stator interior to the lubricant reservoir, and that the lubricant flow in the lubricant feed line is throttled by a throttle nozzle, and/or   that gas from the gas inlet is directed into an anterior pump chamber from where it gets into the stator interior, wherein it is further preferred that lubricant is fed through the lubricant feed line at one position into the anterior pump chamber before the gas is conveyed from the gas inlet into the anterior pump chamber so that gas to be pumped or to be compressed only gets into the anterior pump chamber if the lubricant has already been fed, and/or wherein, in particular, the gas is conveyed in the pump delivery direction from an outlet of the stator interior and in a distributor with an upwardly extending gas branch-off to the gas outlet and with a downwardly extending branch-off to the lubricant return line so that due to gravity, lubricant reaches the lubricant return line and gets into the lubricant reservoir which can preferably be further developed in that by the pressure acting on a lubricant column in the lubricant return line and in the lubricant reservoir, lubricant is pressed from the lubricant reservoir via the lubricant feed line via the anterior pump chamber into the stator interior located above the lubricant reservoir, and/or   that the rotor is rotatably driven by means of a gear motor.       

     The procedural solution can preferably be further developed through the different configurations according to and analog to the above device variants and vice versa. Further preferred and/or advantageous configurations of the invention arise from the claims and their combinations as well as the complete present filing documents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is illustrated in more detail hereinafter only exemplary by means of exemplary embodiments with reference to the drawing, wherein 
         FIG. 1  shows in a perspective schematic illustration a first exemplary embodiment of a progressing cavity gas pump, and 
         FIG. 2  shows a schematic partial longitudinal section for clarifying further details of the first exemplary embodiment of the progressing cavity gas pump of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention is illustrated in more detail only exemplary by means of the exemplary embodiment and example of use described below and illustrated in the drawings, i.e., it is not limited to said exemplary embodiment and example of use or the complete feature combination within said exemplary embodiment and example of use. 
     Also, device and method features arise in each case analog from the pictorial and written descriptions of methods and devices. 
     Individual features described and/or illustrated in connection with the concrete exemplary embodiment are not limited to this exemplary embodiment or the combinations of remaining features but can be combined within the technical possibilities with any other variants, even if they are not treated separately in the present documents, and in particular with features and configurations of other implementation forms. 
     Identical reference numbers in the individual figures and pictures of the drawing designate identical or similar or identically or similarly acting components. Due to the illustrations in the drawing, also such features become apparent which are not provided with reference numbers regardless of whether such features are described hereinafter or not. On the other hand, features which are included in the present description but are not visible or illustrated in the drawing are readily understandable for a person skilled in the art. Further, the reference number list at the end of this description is explicitly part of this description. 
     In the  FIGS. 1 and 2 , an exemplary embodiment of a progressing cavity gas pump  1  is shown in each case schematically in a perspective view and a partial longitudinal section, respectively. Such progressing cavity gas pumps  1  can be used, for example, for compressing natural gas which occurs during crude oil production so that the natural gas can be obtained, distributed and used as independent energy source. 
     As is clearly shown in detail in  FIG. 2 , said progressing cavity gas pump  1  comprises a stator  2  which, within a housing  3 , has a stator interior  4  with an elastomeric inner surface  5  as well as a gas inlet  6  and a gas outlet  7 , whereby from gas inlet  6  to gas outlet  7 , a pump delivery direction (arrow  8 ) is defined. The housing  3  of the stator  2  comprises a rigid outer casing  9  in which an elastic screw pipe  10 , for example made from an elastomer, is seated and forms or provides the elastomeric inner surface  5 . The progressing cavity gas pump  1  comprises further a rotor  11  which engages with the stator interior  4  and is rotatably drivable. For rotatably driving the rotor  11 , a gear motor  12  is included. Such designs are commonly used and are well known to the person skilled in the art so that it is not necessary here to further discuss the structural and design-related possibilities of stator  2  and rotor  11 , but reference is made to the relevant literature. In any case, all currently known versions can be used within the context of the present invention and are hereby incorporated by reference in this description. 
     Furthermore, below the stator  2 , a lubricant reservoir  13  is arranged which is connected via lubricant conduit devices  14  to the stator interior  4 . Due to the fact that the lubricant reservoir  13  is arranged on the lower side  15  of the stator  4  of the progressing cavity gas pump  1  and is connected via the lubricant conduit devices  14  to the stator interior  4 , the delivery and/or compression of a medium (not shown) which consists 100% of gas is made possible. By arranging the lubricant reservoir  13  below the stator  4 , a simple gravitational separation of lubricant (not shown) and gas (not shown) takes place. The actual pump component consisting of stator interior  4  with elastomeric inner surface  5  and the rotor  11  as well as the lubricant conduit devices  14  and the lubricant reservoir  13  form a lubricant circuit which also carries out a cooling and thus is also to be considered as cooling circuit. In any case, the lubricant circuit provides that the dry running mentioned above with respect to the prior art is prevented. 
     The lubricant conduit devices  14  comprise a lubricant feed line  16  (see  FIG. 1 ) from the lubricant reservoir  13  to the stator interior  4  and a lubricant return line  17  from the stator interior  4  to the lubricant reservoir  13 . In the lubricant feed line  16 , a throttle nozzle or a throttle valve  18  is integrated. Furthermore, an anterior pump chamber  19  is provided which, with respect to the pump delivery direction (arrow  8 ), is connected on the inlet side or feed side to the stator interior  4 . The gas inlet  6  opens out into the anterior chamber  19  which therefore is arranged upstream of the stator interior  4 . A rotor drive shaft device  20  in the form of a shaft which is coupled via connecting devices  21  to the rotor  11  is guided through the anterior pump chamber  19 . The lubricant feed line  16  opens out into the anterior pump chamber  19  in such a manner that the opening  22  of the lubricant feed line  16  into the anterior pump chamber  19  lies upstream of the opening  23  into the gas inlet  6  so that gas (not shown) to be pumped or to be compressed during normal operation gets only into the anterior pump chamber  19  if lubricant has already been fed, whereby a lubrication of the rotor  11  or the rotor drive shaft device  20  in the anterior pump chamber  19  is ensured from the beginning and no region through which gas (not shown) flows is without lubrication. 
     Viewed in pump delivery direction (arrow  8 ) or gas flow direction within the stator interior  4 , a distributor  25  with a gas branch-off  26  extending upward to the gas outlet  7  and a lubricant branch-off  27  extending downward to the lubricant return line  17  is connected to an outlet  24  of the stator interior  4  so that due to gravitation, lubricant (not shown) reaches the lubricant return line  17  and gets into the lubricant reservoir  13 . Thus, a simple and reliable separation of gas and lubricant takes place (both not shown). The gas (not shown) flowing into the anterior pump chamber  19  is mixed with the injected lubricant (not shown) such as, e.g. oil, from the lubricant reservoir  13  arranged below the stator interior  4 , and the gas and the lubricant (both not shown) are fed together through the stator interior  4  to the pressure side towards the distributor  25 . The mixture of gas and lubricant (both not shown) arriving at the distributor  25  separates automatically due to gravity: The gas (not shown) is discharged upwardly through the distributor  25  via the gas branch-off  26  to the gas outlet  7  and the lubricant (not shown) flows downward in the distributor  25  via the lubricant branch-off  27  and the lubricant return line  17  into the lubricant reservoir  13  where the lubricant (not shown) can additionally cool down in order to be able to absorb later in the circuit the heat again generated by friction and gas compression during the operation of the progressing cavity gas pump  1 . In trials, a maximum lubricant or oil temperature of 80° was detected. 
     When gas with a concentration of 100% flows into the progressing cavity gas pump  1  and is fed with the rotor  11  in the stator interior  4  towards the outlet  24 , which also defines the pressure side, and is compressed, then, an increased pressure is also available in the lubricant return line  17 , which can also be designated as pressure port, wherein the pressure acts on the lubricant (not shown) in the lubricant return line  17  and in the lubricant reservoir  13 . Thus, the pressure acting on the lubricant column in the lubricant return line  17  and in the lubricant reservoir  13  causes that lubricant (not shown) from the lubricant reservoir  13  such as, for example, a lubricant tank, is pressed via the lubricant feed line  16  via the anterior pump chamber  19  into the stator interior  4  located above the lubricant reservoir  13 . The aforementioned throttle nozzle  18  in the circuit in the lubricant feed line  16  then ensures that the pressure at the gas outlet  7  does not drop or not too much because of the lubricant circuit. 
     The invention is illustrated in an exemplary manner only by means of the exemplary embodiments in the description and in the drawing and is not limited thereto but comprises all variations, modifications, substitutions and combinations which the person skilled in the art can derive from the present documents in particular within the context of the claims and the general descriptions in the introductory part of the description as well as the description of the exemplary embodiments and their illustrations in the drawing and can combine with his/her specialized knowledge as well as the prior art, in particular the disclosures of the aforementioned own prior publications. In particular, all individual features and configuration possibilities of the invention and its embodiment variants can be combined.