DRY GAS SEAL DEVICE, TURBOMACHINE INCLUDING ARRANGEMENT, STRUCTURE, AND METHODS

Abstract

The turbomachine includes a rotor supported by at least one bearing and including a dry gas seal device on an inboard side of the bearing. The dry gas seal device includes a primary dry gas seal and a secondary dry gas seal. The dry gas seal device further includes a primary seal gas supply fluidly coupled to the process gas path through which gas processed by the turbomachine is supplied to the primary dry gas seal. The secondary seal gas supply is fluidly coupled to the source of inert seal gas and adapted to buffer the secondary dry gas seal with the inert seal gas. The primary vent is fluidly coupled to the primary and secondary dry gas seals and adapted to recover process gas leaking from the primary and secondary dry gas seals at a first vent pressure and return at least the leaking process gas to the process gas path. The secondary vent is fluidly coupled to the secondary dry gas seal, on an outboard side thereof, and adapted to recover inert seal gas leaking from the secondary dry gas seal.

Description

[Technical Field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to turbomachines, and more particularly to improvements in sealing arrangements for turbomachines. [Background technology]

[0002] Turbomachines are machines in which a fluid is compressed (pumps and compressors) or expanded (expanders and turbines), exchanging power with a rotor supported for rotation within a casing.

[0003] Specifically, a dynamic compressor is a turbomachine that accelerates particles of a compressible fluid, such as a gas, by transmitting mechanical power through rotating blades or an impeller that form part of a rotor. The rotor has a shaft rotatably supported by axial and radial bearings within a casing. At least one end of the shaft typically protrudes from the casing for connection to a drive device, such as a turbine or electric motor. A sealing device is provided inside the bearing to prevent fluid processed by the compressor (called the "process fluid") from leaking along the shaft toward the bearing and the external environment.

[0004] Recently, so-called "dry gas seals" have become increasingly popular as sealing systems for centrifugal compressors. A dry gas seal is a non-contact, dry-operating mechanical face seal that includes a mating or rotating ring and a primary or stationary ring. During operation, grooves in the rotating ring generate hydrodynamic forces that separate the stationary rings and create a gap between them. These seals are called "dry" because they do not require lubrication, which has several drawbacks. Dry gas seals have reduced maintenance requirements. For centrifugal compressors, such dry gas seals are available in different configurations, such as tandem and double-opposed configurations, which include two dry gas seals in combination. Tandem and double-opposed dry gas seals are primarily used in compressors processing toxic or flammable gases.

[0005] Current technology dry gas seals are effective at reducing gas leakage from turbomachinery and require little maintenance. However, they still have some drawbacks. In particular, the sealing gas vented from the dry gas seal typically contains pollutants that cannot be discharged directly into the environment. For example, methane or other gaseous hydrocarbons contained in the gas vented from the primary vent of the dry gas seal must be burned in a flare. This has a two-fold negative impact on the environment, as the energy contained in the gas is wasted and the resulting combustion gases are released into the atmosphere.

[0006] Therefore, it is desirable to further reduce emissions from dry gas seals in dynamic compressors and other turbomachines. Summary of the Invention

[0007] According to one aspect, disclosed herein is a turbomachine, such as a centrifugal compressor, comprising a casing and a rotor rotatably supported within the casing, the rotor comprising at least one impeller. The turbomachine further comprises at least one bearing rotatably supporting the rotor within the casing, and a dry gas seal arrangement disposed between the rotor and the bearing. In some embodiments, the rotor is disposed between the bearings and supported for rotation by two end bearings, with two dry gas seal arrangements provided on the inboard side of each bearing.

[0008] The or each dry gas seal apparatus has an inboard side facing the rotor and an outboard side facing the bearing. Each dry gas seal apparatus includes a primary dry gas seal on the inboard side of the dry gas seal apparatus and a primary seal gas supply fluidly coupled to the process gas path, through which gas processed by the turbomachine is supplied to the primary dry gas seal. The dry gas seal apparatus further includes a secondary dry gas seal disposed adjacent to the primary dry gas seal on the outboard side of the primary dry gas seal, and a secondary seal gas supply fluidly coupled to a source of inert seal gas and adapted to buffer the secondary dry gas seal with the inert seal gas. A primary vent is fluidly coupled to the primary and secondary dry gas seals and adapted to recover process gas leaking from the primary and secondary dry gas seals at a first vent pressure and to return at least the leaking process gas toward the process gas path. A secondary vent is fluidly coupled to and outboard of the secondary dry gas seal and adapted to recover inert seal gas that leaks from the secondary dry gas seal.

[0009] According to a further aspect, disclosed herein is a method for sealing a turbomachine comprising: a rotor having at least one impeller; a casing; a bearing rotatably supporting the rotor within the housing; and a dry gas seal arrangement between the rotor and the bearing, the dry gas seal arrangement comprising a primary dry gas seal on an inboard side of the dry gas seal arrangement and a secondary dry gas seal disposed adjacent to the primary dry gas seal on an outboard side of the primary dry gas seal. The method comprises: processing a process gas through a process gas path comprising a turbomachine; supplying a process gas as a primary seal dry gas to a primary dry gas seal; supplying the inert gas as a secondary dry gas to the second dry gas seal and buffering the secondary dry gas seal with the inert gas; collecting process gas leaked from the primary dry gas seal and inert gas leaked from the secondary dry gas seal in a primary vent and recirculating at least the leaked process gas into the process gas path; and collecting inert gas that leaks from the secondary dry gas seal in a secondary vent.

[0010] Further features and embodiments are outlined below and set forth in the accompanying claims. [Brief explanation of the drawings]

[0011] Reference will now be made briefly to the accompanying drawings, in which: [Figure 1] 1 is a schematic cross-sectional view of a turbomachine, in particular a centrifugal compressor, according to the present disclosure; [Figure 2] FIG. 2 is a detailed cross-sectional view of a dry gas seal device according to one embodiment. [Figure 3] FIG. 10 is a detailed cross-sectional view of a dry gas seal device according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1 is a schematic diagram illustrating a turbomachine 1 equipped with a dry gas seal device according to the present disclosure. The exemplary turbomachine of FIG. 1 is a centrifugal compressor.

[0013] Centrifugal compressor 1 includes a casing 3 having a process gas inlet 5 on the suction side of compressor 1 and a process gas outlet 7 on the delivery side. Inlet 5 is fluidly coupled to a suction line 9 through which lower pressure gas is supplied to the compressor. Outlet 7 is fluidly coupled to a delivery line 11 through which higher pressure compressed gas is delivered by centrifugal compressor 1.

[0014] The centrifugal compressor 1 includes a rotor 13 that is rotatably supported at its ends within the casing 3 by axial and radial bearings, indicated generally at 15 and 17. In the exemplary embodiment of Fig. 1, the rotor 13 includes a plurality of impellers 21 that are attached to and rotate with a shaft 19. The shaft 19 is supported at a first end by a bearing or bearing arrangement 15 and extends outside the casing 3 at an opposite end where the shaft 19 is supported by a bearing or bearing arrangement 17. Each bearing, i.e., each bearing arrangement 15 and 17, includes a radial bearing, and at least one of the bearing arrangements 15, 17 includes an axial or thrust bearing.

[0015] The impellers may be press-fit onto the shaft. In other embodiments, the impellers may be stacked in a so-called stacked impeller arrangement and connected to each other by tie rods. In such cases, the shaft is formed in part by the inner portions of the stacked impellers. The specific configuration of the impellers and shaft is not relevant to this disclosure. What is important is that the rotor includes impellers and end shaft portions that rotatably engage the respective bearings.

[0016] This disclosure and the accompanying drawings refer to a so-called mid-bearing configuration in which the impeller is disposed between two end bearings. In such a configuration, a sealing device is provided on the inboard side of each bearing. In some embodiments, not shown, one or more impellers may be fitted onto a rotating shaft supported by a single bearing in a so-called overhang configuration. In such cases, a single sealing device may be provided on the inboard side of the single bearing.

[0017] Dry gas seal devices 23 and 25 are coupled to bearings 15 and 17, respectively, and are located on the inboard side of bearings 15, 17. "Inboard" means the side of the bearing facing the inside of casing 3. The two dry gas seal devices 23A and 23B may be similar to each other; only one of them will be described in detail below and is designated by the reference numeral 23.

[0018] Continuing to refer to Figure 1, a cross-sectional view of a first embodiment of the dry gas seal apparatus 23 is shown in Figure 2. Because the dry gas seal apparatus 23 is substantially axisymmetric, the cross-sectional view shows only half of the dry gas seal apparatus 23. AA indicates the axis of rotation of the shaft 19 around which the dry gas seal apparatus 23 is disposed. The left side of the dry gas seal apparatus 23 in Figure 2 is the inboard side, i.e., the side facing the interior of the casing 3, and the right side of the dry gas seal apparatus 23 is the outboard side, i.e., the side facing the associated bearing or bearing assembly with which the dry gas seal apparatus 23 is combined.

[0019] The dry gas seal apparatus includes a primary dry gas seal 33, also known as an inboard gas seal, a secondary dry gas seal 35, also known as an outboard gas seal, a separation seal 37, also known as a barrier seal, and a process-side seal 39, e.g., an inner labyrinth seal. The primary dry gas seal 33 is disposed between the process-side seal 39 and the secondary dry gas seal, i.e., on the inboard side of the secondary dry gas seal 35. The separation seal or barrier seal is disposed on the outboard side of the secondary dry gas seal 35. An intermediate labyrinth 41 is disposed between the primary dry gas seal 33 and the secondary dry gas seal 35.

[0020] The primary dry gas seal 33 includes a rotating ring 43 that fits over the shaft 19 and rotates with it, and a stationary ring 45 that is fixedly housed within the housing 31. As understood herein, stationary means that the ring 45 does not rotate with the shaft but is capable of small axial displacement, i.e., displacement parallel to the shaft's rotational axis AA. The resilient member 47 and thrust ring 49 urge the stationary ring 45 against and into contact with the rotating ring 43 when the shaft 19 is not rotating. The rotating ring 43 includes grooves that create a dry gas seal flow gap between the rotating ring 43 and the stationary ring 45 when the shaft 19 and the rotating ring 43 rotate about the rotational axis AA. Primary seal gas is supplied to the primary dry gas seal 33 through port 51. Most of the primary seal gas cushions the process-side seal 39 and leaks through it toward the interior of the compressor casing. A smaller portion of the primary seal gas leaks between the stationary ring 45 and the rotating ring 43 and is collected in the primary vent 52.

[0021] The secondary dry gas seal 35 includes a rotatable ring 53 that fits onto the shaft 19 and rotates with it, and a fixed ring 55 that is fixedly accommodated within the housing 31. A resilient member 57 and a thrust ring 59 press the fixed ring 55 into contact with the rotatable ring 53 when the shaft 19 is not rotating. The rotatable ring 53 includes grooves that generate a flow of secondary sealing gas that creates a gap between the rotatable ring 53 and the fixed ring 55 when the shaft 19 and the rotatable ring 53 rotate about the rotation axis AA. The secondary sealing gas is supplied to the primary dry gas seal 33 via a port 61.

[0022] A portion of the secondary seal gas buffers the intermediate labyrinth seal 41 and leaks through it towards the primary vent 52. The remaining flow of secondary seal gas leaks between the stationary ring 55 and the rotating ring 53 and is collected in the secondary vent 62.

[0023] The separation gas supply port 71 is positioned to provide a flow of separation gas that cushions the separation seal 37. The separation gas leaks partially toward the secondary vent 62 and partially toward the outboard side of the bearing of the dry gas seal device 23.

[0024] According to embodiments disclosed herein, the primary seal gas supplied to the primary dry gas seal 33 is process gas from the process gas path, which includes the suction line 9, the interior of the compressor 1, and the delivery line 11. The pressure at which the process gas is delivered to the seal gas supply port 51 is such that the seal gas flows through the process-side seal 39 and through the primary dry gas seal 33. The secondary seal gas is typically nitrogen or another inert gas. The purpose of the secondary seal gas is to prevent the process gas from leaking toward the secondary seal 35.

[0025] Process gas leaking past the primary dry gas seal 33 and secondary seal gas leaking past the intermediate labyrinth seal 41 are collected in the primary vent 52, recompressed, and reinjected into the process gas path.

[0026] In some embodiments, the process gas may be natural gas, such as methane, hi other embodiments, the process gas may be a refrigerant for a natural gas liquefaction plant, ammonia, hydrogen, or other gases that should not be leaked into the environment.

[0027] In Figure 1, a process gas supply line 73 is shown schematically supplying process gas to both dry gas seal apparatuses 23A, 23B. The process gas used as the primary seal gas supply may be pretreated before delivery to the dry gas seal apparatuses 23A, 23B. Pretreatment may be aimed at removing contaminants, moisture, and other impurities from the process gas. A seal gas pretreatment unit for that purpose is shown schematically in Figure 1 at 75.

[0028] The primary and secondary seal gases discharged through the primary vent 52 can be recovered from both dry gas seal devices 23A, 23B in a vent line 77 and processed in a separator 79 (see FIGS. 1 and 2). The separator 79 is adapted to separate the process gas, such as natural gas, from the secondary seal gas, such as nitrogen. The latter is discharged to the environment as indicated at 81, while the process gas is recycled into the process gas path as indicated at 83. A process gas compressor 85 can be provided to increase the pressure of the vented process gas at the correct pressure and reinject it into the process gas path.

[0029] The secondary seal gas supplied through port 61 is an inert gas, i.e., a gas that can be released into the environment and / or mixed with the process gas. In the embodiment disclosed herein, the secondary seal gas is nitrogen (N2). Inert gases other than nitrogen, such as helium, can be used as the secondary seal gas. However, nitrogen is much less expensive and is therefore preferred for this application.

[0030] Similarly, the separation gas supplied from the separation gas supply port 71 may be an inert gas such as nitrogen that can be released into the atmosphere.

[0031] Thus, the gases vented through the second vent 62 contain only environmentally friendly inert gases, which can be released into the atmosphere.

[0032] The dry gas seal apparatus described above therefore provides a zero leakage system in that the process gas is not released into the atmosphere or flared, but is completely recovered and recycled. Only inert gases such as nitrogen are dispersed into the environment, with zero environmental impact.

[0033] Continuing with reference to FIGS. 1 and 2, a further embodiment of the dry gas seal apparatus 23 is shown in FIG. 3. Like reference numerals in FIG. 3 refer to the same components, parts, or elements shown in FIG. 2 and described above. These elements will not be described again. The primary difference between the embodiment of FIG. 2 and the embodiment of FIG. 3 is that the embodiment of FIG. 3 does not include a separator 79. The gas vented from the primary vent consists of process gas and an inert gas (e.g., nitrogen). The small amount of inert gas exhausted from the dry gas seal can be added harmlessly to the main process gas flow, allowing the mixture to be returned to the process gas path without separation.

[0034] Exemplary embodiments are disclosed above and shown in the accompanying drawings. Those skilled in the art will understand that various modifications, omissions, and additions may be made to what is specifically disclosed herein without departing from the scope of the invention as defined in the claims that follow.

Claims

1. 1. A turbomachine, comprising: a casing, a rotor rotatably supported within said casing and comprising at least one impeller; at least one bearing for rotatably supporting said rotor within said casing; a dry gas seal device arranged between the rotor and the bearing; the dry gas seal device has an inboard side facing the rotor and an outboard side facing the bearing, The dry gas seal device is a primary dry gas seal on the inboard side of the dry gas seal device; a primary seal gas supply fluidly coupled to the process gas path through which gas processed by the turbomachine is supplied to the primary dry gas seal; a secondary dry gas seal disposed adjacent to the primary dry gas seal on the outboard side of the primary dry gas seal; a secondary seal gas source fluidly coupled to a source of inert seal gas and adapted to buffer the secondary dry gas seal with the inert seal gas; a primary vent fluidly coupled to the primary dry gas seal and the secondary dry gas seal and adapted to recover process gas leaking from the primary dry gas seal and inert seal gas leaking from the secondary dry gas seal at a first vent pressure and to direct at least the leaking process gas back toward the process gas path; a secondary vent fluidly coupled to the secondary dry gas seal, the secondary vent being on an outboard side of the secondary dry gas seal and adapted to recover inert seal gas leaking from the secondary dry gas seal.

2. The turbomachine of claim 1 , further comprising a labyrinth seal between the primary dry gas seal and the secondary dry gas seal, the labyrinth seal being buffered by the inert gas.

3. The turbomachine of claim 1 , wherein the inert seal gas is nitrogen.

4. 4. The turbomachine according to claim 1, further comprising: a separation seal disposed outboard of the secondary dry gas seal and between the secondary dry gas seal and the bearing; and a separation gas supply port adapted to supply separation gas to the separation seal, wherein the secondary vent is disposed between the secondary dry gas seal and the separation seal.

5. 5. The turbomachine of claim 1, further comprising a gas separator fluidly coupled to the primary vent and adapted to separate a process gas and an inert gas from one another, the separator fluidly coupled to the process gas path and configured to return the separated process gas that leaks past the primary dry gas seal to the process gas path.

6. 5. The turbomachine of claim 1, wherein the primary vent is fluidly coupled to the process gas path to return a mixture of process gas leaking past the primary dry gas seal and inert gas leaking from the secondary dry gas seal toward the process gas path.

7. The turbomachine of any preceding claim, further comprising an inner labyrinth seal on the inboard side of the primary dry gas seal.

8. 1. A method of sealing a turbomachine comprising: a rotor having at least one impeller; a casing; a bearing rotatably supporting the rotor within the housing; and a dry gas seal arrangement between the rotor and the bearing, the dry gas seal arrangement comprising a primary dry gas seal on the inboard side of the dry gas seal arrangement and a secondary dry gas seal disposed adjacent to the primary dry gas seal on the outboard side of the primary dry gas seal, the method comprising: processing a process gas through a process gas path comprising the turbomachine; supplying a process gas as a primary dry gas seal to the primary dry gas seal; supplying an inert gas as a secondary dry gas to the second dry gas seal and buffering the secondary dry gas seal with the inert gas; collecting process gas leaked from the primary dry gas seal and inert gas leaked from the secondary dry gas seal in a primary vent and recirculating at least the leaked process gas back into the process gas path; and collecting inert gas leaking from the secondary dry gas seal in a secondary vent.

9. 9. The method of claim 8, wherein a labyrinth seal is disposed between the primary dry gas seal and the secondary dry gas seal, and wherein inert gas flows from the secondary dry gas seal through the labyrinth seal toward the primary vent.

10. 10. The method of claim 8 or 9, wherein a separator seal is disposed between the secondary dry gas seal and the bearing, the method further comprising buffering the separator seal with an inert gas.

11. The method of any one of claims 8 to 10, further comprising separating an inert gas from the process gas vented through the primary vent and reintroducing the process gas into the process gas path.

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