Modular compressor with gas bearings and system for raising the pressure in production gas

Abstract

A system and modular compressor for raising the pressure in production gas is disclosed, wherein in a set of compressor modules each second module is a rotor module carrying an impeller driven in rotation relative to an adjacent stationary module, a rotor module and a stationary module in combination providing a compressor stage in which production gas is accelerated through a flow duct that passes an interface between the rotor module and the stationary module, wherein at the interface at least one bearing for axial and/or radial load is provided for journaling the rotor module on the stationary module. The at least one bearing is a gas bearing, wherein a passage is arranged in the stationary module to lead an extracted portion of production gas at raised pressure from the compressor to the gas bearing(s).

Claims

1. A modular compressor for raising the pressure in production gas, comprising: a plurality of compressor modules arranged in a stacked configuration, each module of the plurality of compressor modules comprising a rotor module and a stationary module in combination; a diffuser section; and an internal gas tap located in the diffuser section, wherein the rotor module carries an impeller driven in rotation adjacent to the stationary module, and the compressor module accelerates a production gas through a flow duct that passes an interface between the rotor module and the stationary module, wherein at the interface at least one gas bearing for taking up axial and/or radial load is provided for journaling the rotor module on the stationary module, and wherein a gas feed passage is arranged in the stationary module to lead production gas, extracted from the diffuser at raised pressure, from the internal gas tap directly to the at least one gas bearing.

2. The compressor of claim 1, wherein a gas feed passage is arranged through a stationary vane in the stationary module.

3. The compressor of claim 1, further comprising a production gas tap line connected to the compressor discharge and arranged with a valve for extraction of production gas which is supplied to at least one of the at least one gas bearing via an accumulator and/or a separator.

4. The compressor of claim 3, wherein the at least one gas bearing comprises multiple gas bearings that receive a supply of the production gas from the accumulator/separator from a manifold pipe in fluid commination with the accumulator/separator.

5. The compressor of claim 1, wherein a feed gas passes through the at least one of the at least one gas bearing into an interface between rotating parts of the rotor module and the stationary module, and wherein the interface is isolated from the production gas duct and outer environment by means of labyrinth seals.

6. The compressor of claim 1, wherein between the stationary module and the rotor module there is arranged a thrust bearing which is not a gas bearing.

7. The compressor of claim 6, wherein the thrust bearing is a contact bearing.

8. The compressor of claim 7, wherein the contact bearing comprises polycrystalline diamond pads.

9. The compressor of claim 7, further comprising a passage in the stationary module for supply of lubricant and/or cooling fluid to the contact bearing via a hollow, shaft-less center of the compressor.

10. The compressor of claim 1, wherein the rotor module comprises a ring motor including a permanent magnet rotor and an electromagnet stator.

11. The compressor of claim 10, wherein the permanent magnet is supported on the rotor module whereas the electromagnet stator comprises a magnet that is secured between the stationary module and an adjacent stationary module of an adjacently stacked compressor module of the plurality of compressor modules, in concentric relation with the permanent magnet rotor.

12. The compressor of claim 10, wherein every other rotor module in the set of compressor modules is driven in the opposite direction of rotation relative to the adjacent one.

13. The compressor of claim 10, wherein each rotor module is individually controlled via a separate variable speed drive.

14. A system for raising the pressure in production gas comprising the modular compressor of claim 1.

15. The system of claim 14, comprising: a gas tap line connected to a discharge of the compressor; an accumulator and/or separator arranged to receive production gas extracted from the discharge via the gas tap line; and a manifold arranged to supply production gas from the accumulator/separator to the at least one gas bearing of the stationary compressor module.

16. The system of claim 15, wherein a distributor pipe is located in a shaft-less, hollow center of the modular compressor.

17. A modular compressor for raising the pressure in production gas, comprising: a plurality of compressor modules arranged in a stacked configuration, each module of the plurality of compressor modules comprising a rotor module and a stationary module in combination; and an external infeed port on an exterior of the stationary module, wherein the rotor module carries an impeller driven in rotation adjacent to the stationary module, and the compressor module accelerates a production gas through a flow duct that passes an interface between the rotor module and the stationary module, wherein at the interface at least one gas bearing for taking up axial and/or radial load is provided for journaling the rotor module on the stationary module, and wherein a gas feed passage is arranged in the stationary module to directly lead production gas, extracted from the compressor at raised pressure, from the external infeed port to the least one gas bearing.

18. The compressor of claim 17, further comprising: a diffuser section; an internal gas tap located in the diffuser section; and an internal feed port in a hollow center of the modular compressor, wherein the at least one gas bearing comprises multiple gas bearings, and an amount of the production gas is fed respectively from the internal feed tap and the internal feed port via corresponding passages to at least one respective gas bearing of the multiple gas bearings.

19. A system for raising the pressure in production gas comprising the modular compressor according to claim 17.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the invention will be explained in more detail below with references made to the accompanying drawings. In the drawings

(2) FIG. 1 is a partially sectioned schematic view showing the general setup in an embodiment,

(3) FIG. 2 is a corresponding view to FIG. 1 showing the general setup in an embodiment,

(4) FIG. 3 is a sectioned, cut out detail of a modular, stackable compressor arranged in accordance with several embodiments,

(5) FIGS. 4 and 5 are sectioned views corresponding to FIG. 3, showing alternative embodiments of the modular, stackable compressor with gas bearings, and

(6) FIGS. 6 and 7 are diagrams showing alternative pathways for gas to be supplied to gas bearings in the modular, stackable compressor.

DETAILED DESCRIPTION

(7) With reference to FIGS. 1 and 2, the components of a system for raising the pressure in production gas comprises a compressor 1 with a compressor inlet 2 and a compressor discharge 3. The compressor 1 is of modular design comprising rotating compressor modules 4 and stationary compressor modules 5 arranged in a stacked configuration. To be more specific, in a set of compressor modules each second module is a rotor module 4 carrying an impeller 5 and driven in rotation relative to an adjacent stationary module 6, a rotor module and a stationary module in combination providing a compressor stage in which production gas is accelerated through a flow duct 7 that passes an interface 8 between the rotor module and the stationary module.

(8) An accumulator 9 is arranged to receive and hold a portion of production gas at raised pressure, which can be extracted from the compressor discharge 3 via a gas tap line 10. A valve 11 can be arranged on the gas tap line to regulate the amount of gas to be extracted. A drain pipe 12 is arranged on the accumulator for discharge of liquid that may have precipitated on the inside walls of the accumulator. In that sense the accumulator 9 may also be seen as a separator which is effective for separation of phases in the production gas.

(9) A gas outlet 13 on the accumulator 9 is connected to a manifold pipe 14 which is arranged for supply of production gas to the compressor. More precisely, the manifold 14 is arranged for distribution of production gas, extracted from the compressor discharge, to radial gas bearings 15 and thrust gas bearings 15′ arranged at the interfaces 8 between the rotating and stationary modules 4,6.

(10) FIG. 2 illustrates a modified embodiment wherein a distributor pipe 16 is arranged, instead of or in addition to the manifold pipe 14, for supply of production gas via a hollow centre 17 of a shaft-less compressor 1.

(11) As will be explained in further detail below, the gas for operation of the gas bearings is supplied via feed passages that are formed in the stationary modules 6 of the modular compressor.

(12) With reference to FIG. 3, a cut out detail of the modular and stackable compressor 1 is shown on a larger scale. More precisely, FIG. 3 shows the sectional views of a rotor module 4 arranged between two stationary modules 6 included in the left hand compressor half in the drawings of FIGS. 1 and 2. In this connection it should be pointed out that the illustrated compressor 1 can be modified for operation in either horizontal or vertical orientation.

(13) The modular compressor 1 is a multistage centrifugal compressor wherein each stage comprises a rotor module 4 and a stationary module 6. The rotor module 4 is driven in rotation by means of a ring motor comprising an electromagnet stator 18 including an iron core 19 and stator windings 20. The stator 18 is stationary housed between two stationary compressor modules 6 and fixated in concentric relation about the rotor module 4. Permanent magnets 21 are supported in the periphery of the rotor module, the magnets 21 causing the rotor module 4 to rotate about a rotor centre C (see FIG. 1) as the magnets 21 are subjected to an alternating magnetic field which is generated as alternating current is fed to the stator windings 20. The rotational speed and direction of rotation can be individually controlled for each rotary module 4 by means of separate, dedicated variable speed drives (VSD).

(14) The rotor module 4 carries an impeller 5 arranged in a flow duct section of radial-axial extension through the rotor module 4. More precisely, the impeller 5 comprises a set of curved impeller blades arranged in a ring about the rotor centre C. The impeller 5 accelerates the production gas through the flow duct in flow direction F, towards a diffusor section 22 and return channel 23 in a flow duct section of radial-axial extension formed through the adjacent downstream stationary compressor module 6.

(15) In transition from the rotary module to the stationary module, the gas flow crosses the interface 8 between the compressor modules. The interface 8 is a gap of sufficient width to accommodate for rotor movements caused by unavoidable variations in the radial load and thrust load applied to the rotor module from the production gas. The changing axial and radial loads acting on the rotor are essentially absorbed in radial bearings and thrust bearings arranged at the interface between the compressor modules. In embodiments of the present invention the bearings are realized in the form of gas bearings 15 or 15′, each including tilting bearing pads 15″. The radial and thrust gas bearings 15 and 15′ are seated in the stationary modules 6.

(16) The gas bearings 15, 15′ can be of traditional design as those known by persons skilled in the art. For proper operation they require air/gas of sufficient pressure to create a film and cushion of gas between a gas permeable pad in the bearing and a counter surface on a rotating member that is supported by the bearing.

(17) In embodiments of the present invention, gas for producing the gas film is extracted from the production gas flow and supplied to the bearings via feed passages arranged through the stationary modules 6.

(18) More precisely, in one embodiment, a feed passage 24 is arranged to feed an extracted portion of production gas to the gas bearings 15, 15′ from an internal gas tap 25 arranged in the diffusor section 22 of the flow duct 7. The internal gas tap 25 may be located at the downstream end of the diffusor section (where pressure recovery is maximized), or at any other position in the duct through the stationary module depending on the gas bearing's pressure needs.

(19) In another embodiment the feed passage 24 may be arranged to receive production gas from an internal infeed port 26 that is available for supply of gas from the compressor discharge, via a hollow centre of a shaft-less compressor.

(20) In yet an embodiment a gas feed passage 27 is arranged in the stationary module for feeding production gas to gas bearings from an external infeed port 28 which is available on the exterior of the stationary module for supply of gas from the compressor discharge, via the manifold pipe 14.

(21) Still another embodiment foresees supply of production gas to gas bearings via passages machined in the inlet or outlet stator guide vanes which extend through the duct passage in the stationary module.

(22) It will be understood that these embodiments can all be used in different combinations.

(23) The gas bearings 15, 15′ are arranged within a length of the interface 8 between the rotary and stationary modules which can be isolated from the external environment by means of labyrinth seals 29, which can be radial and/or axial.

(24) In the embodiment illustrated in FIG. 3, non-gas bearings 30 may be installed as landing or back-up bearings and active for suspending the rotor module 4 in transient modes when gas supply to the gas bearings is insufficient for their proper operation. The non-gas bearing 30 is a contact bearing which can be supplied with lubricant and/or cooling fluid from a lubricant fluid supply 31, as indicated schematically in FIG. 2. The lubricant fluid may advantageously also be production gas that is supplied to infeed ports 32 to a lubricant fluid passage 33 in the stationary module, via the hollow centre of a shaft-less compressor as illustrated in FIGS. 2 and 3. The lubricant may alternatively be glycol.

(25) Alternatives to the previous embodiment are illustrated in FIGS. 4 and 5, where like elements are identified by the same reference numbers. A difference between the embodiment of FIG. 3 and the embodiments of FIGS. 4 and 5 is that where the previous embodiment comprises convex radial bearings 15, having bearing pads facing outwards towards the periphery of the compressor, the latter embodiments comprise concave radial bearings 34, i.e. with bearings pads facing inwards towards the centre of the compressor.

(26) Although not illustrated in the embodiments of FIGS. 4 and 5 it will be understood that back-up bearings may be installed for operation in transition modes, substantially as explained with reference to the embodiment of FIG. 3.

(27) A passage 35 through the material of the rotating module 4 is advantageously arranged for balancing the pressures in the gas bearing circuits on either upstream and downstream sides of the rotating module 4, whereby these circuits are connected, over labyrinth seals 29, to the suction pressure PS generated by the impeller 5.

(28) The principle circuits which feed production gas to gas bearings of the modular, stackable compressor is illustrated diagrammatically in FIGS. 6 and 7. FIG. 6 shows extraction of gas from the production gas flow F in the flow duct 7 in order to feed, via gas supply lines 24, the gas bearings 15, 15′ or 34 in which the rotors 4 are journaled.

(29) FIG. 7 shows the extraction of production gas from the compressor discharge 3 to feed gas bearings 15, 15′ or 34 via the tank 9 and control valves 36, the valves being controllable to set a proper pressure differential between the pressure in the gas supplied to the gas bearings and the pressure of the production gas in the compressor.

(30) This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.