Patent Description:
Dry gas seals are typically used to seal centrifugal compressors that are often used in transportation and distribution of gasses such as natural gas. For instance, in a natural gas pipeline, compressors may be located at set intervals to boost the gas pressure for processing, to counter the effect of flow losses along the transmission pipelines, and to generally keep the gas moving towards its destination.

In general, dry gas seals operate by providing a seal between a rotating ring and a stationary ring. The rotating ring is sometimes referred to as a "mating ring" as it is mated to the rotating shaft/rotor. The rotating ring can be mated to the rotor via a shaft sleeve. The stationary ring can sometimes be referred to as the primary ring and does not rotate during operation. In operation, a layer of gas is developed between the two rings that forms a seal while allowing the rings to move relative to one another without contacting each other. The gas layer is formed from process or sealing gas injected into the dry gas seal.

When installed into a compressor, such dry gas seals may be located next to or near a bearing or bearing cavity of the compressor or other machinery. These bearings can be lubricated by and operate with, for example, oil or another liquid lubricant.

A separation seal can serve to prevent or reduce oil or other lubricants of the bearing from entering the dry gas seal. In the typical separation seal, a separation gas is injected between two bushings to create a pressure barrier between the bearing and the dry gas seal. In more detail, a typical separation seal includes an inlet into which the separation or buffer gas is provided. The separation gas escapes axially outward in both the in-board and outboard directions. The gas is provided between two bushings that can either contact the shaft (or a sleeve placed thereon) in a contact separation seal or be slightly separated from the shaft in a non-contacting separation seal.

<CIT> discloses a porous media ventless thrust bearing seal that may include a primary porous media thrust bearing also serving as a seal ring including porous media positioned over a plenum and a port connected to the plenum, and conductive passages for communicating pressurized fluid to the plenums through the ports of the primary ring. The porous media ventless thrust bearing may also include a treated process gas supplied to a port which is closest to the untreated process gas, at a pressure which is higher than the untreated process gas. An inert gas (or fluid in a liquid state) may be supplied to the remaining port, at a pressure which is the same as the untreated process gas. A certain amount of treated process gas may flow into the untreated process gas, and may prevent the untreated gas from entering the porous media seal.

Disclosed is a separation seal for preventing fluid from entering a dry gas seal surrounding a shaft of a rotating machine. The separation seal includes a stator configured to be mounted around the shaft and configured to be fixedly attached to the rotating machine, the stator including primary ring control chamber formed therein, a porous primary ring formed of a porous material and having a back, and a first thrust ring at least partially within the primary ring control chamber and coupled to the porous primary ring. The seal also includes a mating ring coupled to the shaft that rotates with the shaft and relative to the porous primary ring and one or more biasing members that urges the porous primary ring toward the mating ring to form a seal interface between porous primary ring and the mating ring. In this seal, the wherein the stator includes a passageway constructed and arranged to convey pressurized buffer gas to the primary ring control chamber such that gas passes from the back of the porous primary ring, through the porous primary ring and to the seal interface and buffer gas that reaches the seal interface passes, in normal operation, both radially inward and radially outward along the seal interface. The mating ring includes grooves formed on a face thereof. In the event of a buffer gas delivery reduction the grooves pumps gas from an inner diameter of the seal interface to an outer diameter of the seal interface.

In any embodiment disclosed herein, the porous primary ring can be formed of porous carbon.

In any embodiment disclosed herein, the seal can include one or more sealing elements disposed between the first thrust ring and the back of the porous primary ring and within the primary ring control chamber. The sealing elements are spaced apart from the back of the porous carbon seal by a separating member.

In one embodiment, the sealing elements are spaced apart from the back of the porous carbon seal by a separating member. In one embodiment, the separating member is a ring and in another it is a second thrust ring.

Also disclosed is an assembly for sealing a fluid in a rotating machine that includes a primary dry gas seal adapted and configured to surround a shaft of the rotating machine and prevent the fluid from exiting the rotating machine; and a secondary seal connected to the primary dry gas seal adapted and configured to prevent a liquid from entering the dry gas seal.

The secondary seal can comprise any seal mentioned or otherwise disclosed herein.

In one embodiment according to the invention, the secondary seal of the assembly includes a stator configured to be mounted around the shaft and configured to be fixedly attached to the rotating machine, the stator including a primary ring control chamber formed therein; a porous primary ring formed of a porous material and having a back; and a split thrust ring at least partially within the primary ring control chamber and coupled to the porous primary ring, the split thrust ring including an inner ring and outer ring, wherein the inner ring is configured to move axially inboard relative to the outer ring in the event of an increase in the flow of the fluid through the primary dry gas seal. The secondary seal also includes a mating ring coupled to the shaft that rotates with the shaft and relative to the porous primary ring; an outer ring biasing members that urges the outer ring and the porous primary ring toward the mating ring to form a seal interface between porous primary ring and the mating ring; an inner ring biasing members that urges the inner ring and the porous primary ring toward the mating ring; and one or more sealing elements disposed between the split thrust ring and the back of the porous primary ring and within the primary ring control chamber. In this embodiment, the stator includes a passageway constructed and arranged to convey pressurized buffer gas to the primary ring control chamber such that gas passes from the back of the porous primary ring, through the porous primary ring and to the seal interface.

In one embodiment, in the assembly, buffer gas that reaches the seal interface passes, in normal operation, both radially inward and radially outward along the seal interface.

In one embodiment, in the assembly, a vent is provided that receives gas that passes through the primary dry gas seal and the buffer gat that travels radially inward along the seal interface.

In one embodiment, in the assembly, the stator defines a dry gas seal side passage way that allows buffer gas that passes radially inward to reach the vent during normal operation.

In one embodiment, in the assembly, the fluid is process gas and, in the event that the flow process gas through primary gas seal increases pressure in the vent above a threshold, the process gas that passes through the primary gas seal travels along the dry gas seal side passage to an inner diameter of the seal interface.

In one embodiment, in the assembly, the process gas at the inner diameter causes the inner ring to move axially with respect to the outer ring when the gas in the vent exceeds the threshold.

In one embodiment, in the assembly, axial movement of the inner ring allows the process gas to enter the primary ring control chamber.

In one embodiment, in the assembly, the mating ring includes grooves formed on a face therein, wherein the grooves pumps process gas from the inner diameter of the seal interface to an outer diameter of the seal interface.

In one embodiment, in the assembly, the porous primary ring is formed of porous carbon.

In one embodiment, in the assembly, the sealing elements are spaced apart from the back of the porous carbon seal by a separating member that can be, for example, a ring.

In any embodiment of the seal or assembly herein, the back of the primary ring can include one or more grooves to receive a sealing element.

In any embodiment of the seal or assembly herein, the front surface of either of the inner and outer thrust ring can be flat or can include grooves to receive a sealing element.

In any embodiment of the seal or assembly herein, the sealing members can be o-rings with different cross-sectional diameters.

The diagrams depicted herein are illustrative. There can be many variations to the diagram or the operations described therein without departing from the scope of the invention as defined by the claims. For instance, the actions can be performed in a differing order or actions can be added, deleted or modified. Also, the terms "connected," "coupled" and the like and variations thereof describes having a communications path between two elements and does not imply a direct connection between the elements with no intervening elements/connections between them. All of these variations are considered a part of the specification.

Disclosed herein is a seal that includes a porous carbon primary ring. The seal can be a standalone seal that operates, for example, as a separation seal. Alternatively, the seal can be operated as a containment or back-up seal to a primary dry gas seal. In both cases, the carbon primary ring is either directly or indirectly coupled to a thrust ring. In normal operation, a buffer or separation gas is provided to the seal, the gas passes through the thrust ring and through the porous carbon primary ring, and the gas creates a thin film between the faces of the carbon primary ring and a rotating mating ring. To address situations where the gas flow may be reduced (e.g., below a threshold that will independently keep the rings from contacting each or that can support the thin film), the mating ring may have grooves formed thereon that pump gas between the faces to prevent them from contacting. In the separation seal usage case, the thrust ring can be a single or a split thrust ring.

In cases where the seal is used as a containment seal, in normal operation the seal operates generally as above. This allows for long running, non-contacting back-up seal. The mating ring may have (but does not have to have) the above described grooves.

In such a case, while both single and split thrust rings may be utilized, in one embodiment, the thrust ring is a split thrust ring that includes two portions that are typically mated but can be separated. If the primary dry gas seal has in increase in gas passing between the rings (e.g., above a pressure that can typically vented out through, for example a choke in the vent), the pressure of the gas escaping from the primary seal will cause the portions of the thrust ring to separate (e.g., the lower/inner thrust ring described below moves away from the porous carbon primary ring). The upper/outer thrust ring takes over and creates a new balance diameter. The grooves on the mating ring will take over and draws high pressure gas from the dry gas seal side and pump it through the sealing interface (e.g., between the face of the primary and mating rings) to create a level of flow towards the bearing side. The result is the maintenance of a positive restriction to prevent or reduce leakage of pressurised gas. While describe as a "back-up" seal, it shall be understood that such a seal may serve a dual purpose as a back-up seal and a separation seal. This can allow for a single seal unit to be provided that does not need an additional separation seal.

<FIG> is a cross section of a seal <NUM> according to one embodiment. This embodiment shows the seal <NUM> as a separation seal but the teachings related to can also be applied to a back-up seal or containment seal of dry gas seal assembly. For simplicity, the discussion of <FIG> will refer to the seal <NUM> simply as a seal but it can be used in either context. In addition, <FIG> will be used to describe the general operation of the seal.

In one use, the seal <NUM> is intended to be located between a dry gas seal <NUM> and a bearing cavity <NUM>. Herein, the seal <NUM> shall be referred to as having an inboard (or seal) side <NUM> and an outboard (or bearing) side <NUM>. The inboard side <NUM> is typically disposed proximate a dry gas seal <NUM> and the outboard side <NUM> is typically disposed proximate a bearing or bearing cavity <NUM> containing a bearing. This is, however, not a required orientation of elements. As will be understood, the seal <NUM> and the dry gas seal <NUM> can be included as part of a cartridge that can include one or more separation and dry gas seal elements. Examples of dry gas seals can be found in the prior art and the dry gas seal <NUM> can be any type of dry gas seal. The same is true of the bearings in the bearing housing.

Both the seal <NUM> and the dry gas seal <NUM> are arranged and designed to be attached to shaft <NUM>. Herein, the term shaft will generally be used to refer to a shaft of a turbocompressor. The teachings herein can be applied, however, to any rotating machine and the shaft may or may not include a sleeve thereon. In the case where a sleeve is provided, the term "shaft" shall include the combination of the shaft and the sleeve.

From time to time certain directions will be used herein. An outboard direction is the direction extending in the direction of arrow A and the inboard direction (e.g., towards the dry gas seal <NUM> or the process chamber <NUM> described below) is in the opposite direction as indicated by arrow A'. The radially inward direction is in the direction of arrow B which is directed toward a center of the shaft <NUM> and the radially outward direction is in the opposite direction as indicated by arrow B'.

At least a portion of the seal <NUM> is positioned between a rotating compressor shaft <NUM> and a compressor housing <NUM>. The seal <NUM> is also positioned between the bearing cavity <NUM> and the gas seal <NUM> to keep bearing oil from impinging in the gas seal <NUM>.

The rotating compressor shaft <NUM> is generally part of a compressor and is operably coupled to a compressor impeller (not shown) disposed in a process cavity <NUM> of the compressor, and is supported by the housing <NUM> via a bearing (not shown) disposed in a bearing cavity <NUM> of the housing <NUM>. The rotating compressor shaft <NUM> is the rotor of the compressor in most instances and may be referred to simply as a rotating shaft from time to time herein. It shall be understood that the rotating shaft need not be the rotor of the compressor itself but could be any shaft connected to the rotor that rotates with it around which a seal should be provided.

The compressor housing <NUM> includes a bore <NUM> formed in it that extends between a process cavity <NUM> and a bearing cavity <NUM> and defines an annular seal chamber <NUM> into which the seal <NUM> and the dry gas seal <NUM> may be inserted. The process cavity <NUM> includes the gas (typically a hydrocarbon) being compressed by the compressor. That gas is referred to as process gas herein.

The seal <NUM> includes a stator <NUM> that can be formed of one or more components and joined in a fixed relationship to one another as well as with the compressor housing <NUM> when installed. As shown, the stator <NUM> is formed as a retainer ring that can be sealed to the compressor housing <NUM> by any sealing element such as a radial seal <NUM>.

The seal <NUM> can also include a sleeve ring <NUM> that can be formed of one or more components and that is attached to the rotating shaft <NUM> such that it rotates with the rotating shaft <NUM>. The illustrated separation seal sleeve ring <NUM> includes two portions 115a, 115b in <FIG>. In particular, the separation seal sleeve ring <NUM> includes a rotating ring 115a that is configured to contact and rotate with the rotating shaft <NUM>. In the illustrated embodiment, a spacer or locking sleeve 115b is included as part of the sleeve ring <NUM>. Of course, the sleeve ring <NUM> could be formed as a unitary piece or could include any number of pieces that are either joined together or otherwise held stationary relative to each other during operation (e.g., all pieces rotate together as one).

Assuming that the process gas in the process cavity <NUM> is under pressure, all components of the seal <NUM> and the dry gas seal <NUM> are urged in the outboard direction A toward thrust/retaining rings <NUM>/<NUM> during operation. Axial movement of the sleeve ring <NUM> relative to the rotating shaft <NUM> is limited by a shaft thrust ring <NUM> received in a groove in the rotating shaft <NUM>. Axial movement of the stator <NUM> is limited by stator thrust ring <NUM> received in a groove in the housing <NUM>.

In the above example, it should be understood that the shaft thrust ring <NUM> can be fixed relative to the sleeve ring <NUM> so that the two elements rotate together. Also, for sake of completeness, it shall be understood that other elements can be attached to the sleeve ring <NUM> to provide support or other functions but are not specifically described herein.

The sleeve ring <NUM> carries and otherwise mates rotating or mating ring <NUM> to the rotating shaft <NUM>. That is, the sleeve ring <NUM> being mated to the rotating shaft <NUM> allows the mating ring <NUM> to also rotate with the shaft <NUM>. The mating ring <NUM> can include one or more grooves <NUM> formed on a face thereof.

During operation, gas <NUM> in the process cavity <NUM> that passes through the seal interface formed by mating/primary rings in the dry gas seal can exit a vent <NUM> in the compressor housing <NUM>.

The seal <NUM> impedes oil from the bearing cavity <NUM> from reaching the gas seal <NUM> in a manner that is similar to how a dry gas seal works. In particular, as with a typical separation seal, the seal <NUM> keeps the oil from traveling inboard due to the interaction of the mating ring <NUM> and a primary ring <NUM>. The primary ring <NUM> can also be referred as stationary ring as it does not rotate with the shaft and is thus, generally or completely, rotationally stationary relative to the housing <NUM> during operation. Reference numeral <NUM> identifies the location of the seal interface formed between the mating ring <NUM> and the primary ring <NUM>.

As will be understood by the skilled artisan, the primary ring <NUM> is axially movable relative to the housing <NUM> during operation such that a controlled distance may be maintained between the mating ring <NUM> and the primary ring <NUM> at the rotating seal interface <NUM>. In the illustrated embodiment, a force is applied to the primary ring <NUM> by one or more biasing members <NUM>.

During operation, a flow of a gas sometimes referred to as "buffer gas" is provided to a back side <NUM> of the primary ring <NUM> via a buffer gas passage <NUM>. The buffer gas passage <NUM> can receive the gas from a buffer gas inlet <NUM> formed in the compressor housing <NUM>.

As generally shown by arrows <NUM>, this gas passes through the primary ring <NUM> and exits it at or near the seal interface <NUM> at primary ring face 116a. This gas, in normal operation as shown in <FIG>, can travel both radially inward (direction B) and radially outward. Gas that travels readily outward can generally pass into the bearing cavity <NUM>. Gas travels radially inward passes between the stator <NUM> and the sleeve ring <NUM> (in this case, between the spacer or locking sleeve 115b and the stator <NUM>) and exits the seal chamber <NUM> via vent <NUM>. The buffer gas is shown generally by arrows <NUM> that identify the path taken by the gas through the seal <NUM>. The buffer gas can be provided into the buffer gas passage <NUM> at a buffer gas pressure. Gas that passes through the seal interface <NUM> in the radially inward direction (direction B) and gas <NUM> that escapes from the dry gas seal <NUM> can exit via a vent <NUM>.

With reference now to both <FIG> and <FIG>, the gas from the buffer gas passage <NUM> is provided into a primary ring control chamber <NUM>. This chamber is formed in the stator <NUM>. This gas, in combination with the biasing members <NUM> can bias the primary ring <NUM> towards the mating ring <NUM>.

As shown, a thrust ring <NUM> is disposed in the primary ring control chamber <NUM>. The thrust ring <NUM> includes a passage <NUM> formed therein that allows the buffer gas <NUM> to pass through it allowing it to reach the back side <NUM> of the primary ring <NUM>. The passage <NUM> can be sized such that gas in buffer gas passage <NUM> passes through and equalizes pressure on both sides of the thrust ring <NUM> over time. Based on this pressure balance, both the biasing members <NUM> and the gas in the primary ring control chamber <NUM> serve to resist motion of the mating ring in the inboard direction (e.g., opposite of direction A).

In one embodiment, the primary ring <NUM> is formed of a porous material that allows the buffer gas to pass through it from the back side <NUM> thereof to its mating ring (or sealing) face 116a. The porous material can be carbon in one embodiment. The primary ring <NUM> can be configured such that the buffer gas travels from the back side <NUM> to the primary ring face 116a.

Rotation of the mating ring <NUM> due to its connection to the rotating shaft <NUM> will cause some of the buffer gas at the seal interface <NUM> to be drawn toward the OD. However, due to the pressure of the buffer gas, the gas can travel between the faces towards both the inner and outer diameters of the mating ring <NUM>/primary ring <NUM> such that it travels in the manner described above. The presence and pressure of the buffer gas <NUM> at the seal interface <NUM> and the relative motion of the mating/primary rings <NUM>, <NUM> results in a so-called "lift off" resulting in physical separation of the rings.

During normal operation, as described above, pressure in the process cavity <NUM> as well as heat can cause the rotating shaft <NUM> to move or expand axially. The biasing members <NUM> can allow for the primary ring <NUM> to keep a constant distance during operation between itself and the mating ring <NUM> even as the mating ring <NUM> moves axially due to such movement of the rotating shaft <NUM>.

One or more radial seals <NUM> may be provided to direct the buffer gas <NUM> so that gas leaving the primary ring control chamber <NUM> travels through the seal interface <NUM> (e.g., between the primary ring <NUM> and the stator <NUM>). The seals may be formed of a polymer or an elastomer and one example of such a seal is a lip seal. In <FIG> the seal is illustrated as first and second o-rings 205a, 205b but that is by way of example only and not meant to be limiting. The o-rings 205a, 205b also serve to seal the thrust ring <NUM> and the primary ring <NUM>. Thus, as shown, as the primary ring <NUM> moves (either due to lift off or shaft movement) the thrust ring <NUM> will move relative to the stator <NUM>. This motion can result damage to the o-rings <NUM> in some instances.

With reference now to <FIG>, an example of the primary ring <NUM> is shown. The illustrated primary ring <NUM> can be formed of a porous material such as carbon in one embodiment. The primary ring <NUM> includes a primary ring face 116a and a back side <NUM>. The primary ring <NUM> can be configured to promote motion of the buffer gas <NUM> from the back side to the mating ring face as shown by the arrows in <FIG>.

In the embodiment shown in <FIG> the primary ring <NUM> includes a front or face portion <NUM> that includes the primary ring face 116a. The primary ring <NUM> also includes back section <NUM>. The back section <NUM> can be narrower than the face portion <NUM> in one embodiment. As illustrated in <FIG> and <FIG> some or all of the back section <NUM> can be disposed within the primary ring control chamber <NUM>. Thus, in one embodiment, the primary ring control chamber <NUM> is sized and arranged to receive a portion of the primary ring <NUM> and, in particular, a portion of the back section <NUM> of the primary ring <NUM>. Further, the primary ring control chamber <NUM> can also be sized so that it receives at least one sealing member (e.g., radial seal <NUM>) and one thrust ring <NUM>.

The mating ring <NUM> can include grooves <NUM> formed therein that draw gas from the inner diameter into the seal interface <NUM>. As more fully described below, these grooves <NUM> may help to prevent the mating and primary rings <NUM>, <NUM> from contacting one another in the event that gas flow of the buffer gas ceases or becomes otherwise ineffectual at forming a gas film between the mating and primary rings <NUM>, <NUM>.

The shape of the grooves <NUM> is optimized to enhance seal performance. As is known in the art, the grooves <NUM> typically are machined or etched only to the radial midpoint of the face of the mating ring <NUM> and have a very shallow depth of only a few microns. The grooves are shaped to have a tip such that gas enters the grooves is compressed because of the volume reduction at the tips.

In the above examples, it shall be understood that in normal operation high pressure buffer gas <NUM> flows through the primary ring <NUM> to its face 116a at the seal interface <NUM>. In such operation, the buffer gas <NUM> leaves the interface towards both the bearing and dry gas seal sides (e.g., radially inwardly and radially outwardly). Due to the presence of the grooves <NUM>, potentially, greater flow of the buffer gas <NUM> is directed radially outward towards the bearing cavity <NUM> which provides a greater restriction against the bearing oil.

Regardless of particular flow, the pressure from the buffer gas <NUM> present at the seal interface <NUM> after passing the porous material of the primary ring <NUM> creates a thin film (and separation/gap) between the mating and primary rings <NUM>, <NUM>. Such separation can create a non-contacting regime of operation. Further, the pressure of the buffer gas <NUM> as provided from the inlet <NUM> can allow for a much greater film stiffness that in a typical non-contacting seal and may provide greater back pressure to resist against oil ingress from the bearing side.

Embodiments of the present invention may also effectively operate in situations wherein supply of buffer gas <NUM> is diminished. With reference now to <FIG>, in the event of diminished buffer gas flow, less gas flows through inlet <NUM>, passage <NUM>, or primary ring <NUM>. In such a case, the grooves <NUM> will serve to ensure that the mating and primary rings do not contact in manner that they are destroyed or otherwise significantly damaged. As discussed above, the grooves <NUM> draw in low pressure gas <NUM> from the dry gas seal side (e.g., at the ID) and pump it through the rotating seal interface <NUM> to create a radially outward flow <NUM> towards the OD and the bearing cavity <NUM>. In more detail, as the grooves <NUM> compress air as the is drawn (or pumped) from the ID towards the OD. As it compresses, the air at the tips of the grooves is compressed and has a higher pressure. The area of slightly higher gas pressure creates a pressure dam and results in the above described "lift off" resulting in physical separation of the mating and primary rings <NUM>, <NUM>. As above, when operating, the grooves <NUM> will create a thin film (and separation/ gap) between the mating ring <NUM> and primary ring <NUM>. In operation, this gap will be sufficient to prevent premature seal wear by ensuring a non-contacting regime. The grooves <NUM> can be either uni-directional or bi-directional grooves.

In all of the prior examples the thrust ring <NUM> has been shown as being formed of two separate pieces (e.g.,, outer and inner thrust rings 202a/202b). However, the ring can be formed as a single piece. An example of such a single piece ring <NUM> is shown in <FIG>. In such a case, the above description is generally applicable. It should be noted that such a single ring can be used in any embodiment disclosed herein.

<FIG> shows cut-away perspective view of the seal <NUM> of the prior embodiments that includes a two-piece thrust ring <NUM>. This cross section is shown without shaft and is used to show relative spacing and to identify the gas outlet passages in more detail. In particular, gas that exits the seal interface <NUM> as the ID of the primary ring <NUM> can traverse the inboard or dry gas seal side passage way <NUM> in the inboard direction (direction A'). This gas can be released via vent <NUM> (<FIG>) to atmosphere in one embodiment. The thrust ring <NUM> can either be formed as a single ring with one or more passages <NUM> (e.g., holes) formed therein or it can be formed of two different elements where spaces between the elements define the passageway (see, e.g., elements 202a/202b in <FIG> below). For reference, a single ring thrust ring is also shown in <FIG> and <FIG> below and such a ring can be used in all embodiments.

Similarly, gas that exits the seal interface <NUM> as the OD of the primary ring <NUM> can traverse the outboard passageway <NUM> in the outboard direction A. This gas can be released via vent <NUM> (<FIG>) to atmosphere in one embodiment.

In <FIG> certain aspects of the prior embodiments are illustrated for further clarity. The illustrated seal <NUM> includes, as above, a stator <NUM>. The stator <NUM> can be formed as a ring. The stator <NUM> can define primary ring control chamber <NUM> into which the thrust ring <NUM> is disposed. The thrust ring <NUM> can be single ring with passageways (holes) formed therein as discussed above.

The rings 202a, 202b are preferably shaped and arranged such that, when mated, one or more passageways exist between them through which buffer gas <NUM> described above can pass. The rings 202a, 202b shown in <FIG> include mating elements such as mating tabs <NUM> (on ring 202a) and receiving regions <NUM> (on ring 202b) to allow the rings to separate in operation. Other types of mating elements could be utilized. In one embodiment, the tabs <NUM> can house the biasing elements. As discussed further below, in some instances, the rings 202a, 202b can separate in certain circumstance with relative movement between the two in the inboard direction A'. In the example discussed below, the inner ring 202a can move axially inward relative to the outer thrust ring 202b. Motion in the other direction will be stopped by the back <NUM> of the primary ring <NUM> (or another element such as ring <NUM> of <FIG> or another thrust ring as shown below).

Inner and outer seals (o-rings 205a, 205b), are disposed between the respective inner and outer rings 202a, 202b and the back <NUM> of the mating rings. These seals can serve to seal the back section <NUM> of the primary ring <NUM> in the primary ring control chamber <NUM> in this embodiment.

With reference to <FIG> and <FIG>, one or more retaining elements <NUM> can be provided that mates with a ring extensions 116b of the primary ring <NUM> to align the ring during assembly. Such retaining elements <NUM> are optional and can be omitted in certain instances.

As above and with reference now to <FIG>, generally, in operation buffer gas <NUM> is introduced from a gas supply. The buffer gas <NUM> can be an inert gas such as nitrogen, helium, neon, or argon. The gas <NUM> is provided into the primary ring control chamber <NUM> and generally urges the primary ring <NUM> (and the first and second thrust rings <NUM>, <NUM>) in the outboard direction A. It shall be understood the biasing members <NUM> discussed above also urge the primary ring <NUM> towards the mating ring <NUM>.

The buffer gas <NUM> travels through the porous material of the primary ring <NUM> from its back <NUM> and exits at the primary ring <NUM> at its face 116a (e.g., at the seal interface <NUM> formed between the mating and primary rings <NUM>/<NUM>).

As discussed in the above examples, the embodiments herein include primary ring control chamber <NUM> that includes at least one thrust ring <NUM> disposed at least partially therein. Further, as shown in <FIG> and <FIG>, portions of a second thrust ring <NUM> can also be disposed in the in primary ring control chamber <NUM>. Additionally or alternatively, in some cases another ring, such as ring <NUM> shown in <FIG> can be disposed between the thrust ring <NUM> and the back <NUM> of the porous primary ring <NUM>. Thus, the embodiment of <FIG> can be said to include a first thrust ring <NUM> and a second thrust ring <NUM> (of course, the ring <NUM> of any prior embodiment can be referred to as first thrust ring in some instances).

The seal shown in <FIG> is illustrated without a shaft and is used to show relative spacing of the first and second thrust rings <NUM>, <NUM> and to identify the gas outlet passages. In particular, gas that exits the seal interface <NUM> as the ID of the primary ring <NUM> can traverse the inboard or dry gas seal side passage way <NUM> in the inboard direction (direction A'). This gas can be released via vent <NUM> (<FIG>) to atmosphere in one embodiment. Similarly, gas that exits the seal interface <NUM> as the OD of the primary ring <NUM> can traverse the outboard passage way <NUM> in the outboard direction A. This gas can be released via vent <NUM> (<FIG>) to atmosphere in one embodiment.

With reference to both <FIG> and <FIG>, and as in the prior embodiments, the primary ring control chamber <NUM> can include one or more biasing members <NUM> that urge the first thrust ring <NUM> towards the mating ring <NUM> (e.g., in the outboard direction A). The buffer gas enters the primary ring control chamber <NUM> via inlet <NUM> as above also serves to urge the first thrust ring <NUM> in the outboard direction.

The first thrust ring <NUM> can either be formed as a single ring with one or more passages <NUM> (e.g., holes) formed therein. Of course, it could be formed as a split ring as described above. As illustrated, all of the first thrust ring <NUM> is disposed in the primary ring control chamber <NUM>. The seal <NUM> includes first and second sealing elements 205a, 205b. These can be any type of sealing elements and, as illustrated, are formed as o-rings. The first and second sealing elements 205a, 205b direct the gas in primary ring control chamber <NUM> through the passage <NUM> formed in the first thrust ring <NUM>. The first and second sealing elements 205a, 205b also form a seal between the first thrust ring <NUM> and the second thrust ring <NUM> so that barrier gas in primary ring control chamber <NUM> is directed through the back <NUM> of the porous primary ring <NUM> and then through the primary ring <NUM> to the face 116a.

As shown best in <FIG>, one or more sealing elements 740a, 740b are disposed between the second thrust ring <NUM> and the back of the porous primary ring <NUM>. The second thrust ring <NUM> can be shaped and arranged such that it maintains the sealing elements 740a, 740b between it and the primary ring <NUM>. Further, the second thrust ring <NUM> can be shaped and arranged such that it and the first thrust ring <NUM> move, the sealing elements 740a, 740b do not contact any stationary surface (e.g., the walls 201a of the primary ring control chamber <NUM>). This can avoid possible damage to sealing elements 740a, 740b in some embodiments.

In general, the embodiment shown in <FIG> and <FIG> operates in generally the same manner as described above. It should be noted that the porous primary ring <NUM> can be the same or similar to that as described above. However, in aspects of this embodiment, the back section <NUM> (<FIG>) of the porous primary ring <NUM> may not be disposed within the primary ring control chamber <NUM>. In one particular, embodiment, none of the back section <NUM> of the porous primary ring <NUM> is disposed within the primary ring control chamber <NUM>. In another, some of the back section <NUM> (<FIG>) of the porous primary ring <NUM> can be disposed within the primary ring control chamber <NUM> but in such a case it may be preferable to ensure that neither of the sealing elements 740a, 740b can contact the walls 201a of the primary ring control chamber <NUM>.

As above and with reference now to <FIG>, generally, in operation buffer gas <NUM> is introduced from a gas supply. The buffer gas <NUM> can be an inert gas such as nitrogen, helium, neon, or argon or any other type of gas (e.g., air). The gas <NUM> is provided into the primary ring control chamber <NUM> and generally urges the primary ring <NUM> (and the thrust ring <NUM>) in the outboard direction A. The biasing members <NUM> discussed above also urge the primary ring <NUM> towards the mating ring <NUM>.

The buffer gas <NUM> passes through the first and second thrust rings <NUM>, <NUM> and then travels through the porous material of the primary ring <NUM> from its back <NUM> and exits at the primary ring <NUM> at its face 116a (e.g., at the seal interface <NUM> formed between the mating and primary rings <NUM>/<NUM>).

In the case a reduction in buffer gas supply, the seal will operate as described above with respect to <FIG>. In the event of buffer gas reduction, gas may not longer appreciably flow through inlet <NUM>, passage <NUM>, or primary ring <NUM>. In such a case, the grooves <NUM> will serve to ensure that the mating and primary rings do not contact in a manner that they are destroyed or otherwise significantly damaged. As discussed above, the grooves <NUM> draw in low pressure gas from the dry gas seal side (e.g., at the ID) and pump it through the rotating seal interface <NUM> to create a radially outward flow towards the OD and the bearing cavity <NUM>. In operation, this gap will be sufficient to prevent premature seal wear by ensuring a non-contacting regime.

In the prior description the seal including a porous primary ring was illustrated as a separation seal that was separate from the dry gas seal. In another embodiment, and a shown in <FIG>, such a seal can also be utilized as a back-up or containment seal of dry gas seal that includes two seals (e.g., a tandem seal). In particular, the dry gas seal assembly <NUM> includes in first or primary seal <NUM> and a secondary, back-up or containment seal <NUM> (secondary seal hereinafter). The secondary seal <NUM> includes primary ring <NUM> formed of a porous material is in the above.

At least a portion of the dry gas seal assembly <NUM> is positioned between a rotating compressor shaft <NUM> and a compressor housing <NUM>. The rotating compressor shaft <NUM> is generally part of a compressor and is operably coupled to a compressor impeller (not shown) disposed in a process cavity <NUM> of the compressor, and is supported by the housing <NUM> via a bearing (not shown) disposed in a bearing cavity <NUM> of the housing <NUM>. The rotating compressor shaft <NUM> is the rotor of the compressor in most instances and may be referred to simply as a rotating shaft from time to time herein. It shall be understood that the rotating shaft need not be the rotor of the compressor itself but could be any shaft connected to the rotor that rotates with it around which a seal needs to be provided.

The compressor housing <NUM> includes a bore <NUM> formed in it that extends between the process cavity <NUM> and the bearing cavity <NUM> and defines an annular seal chamber <NUM> into which the dry gas seal assembly <NUM> may be inserted. The process cavity <NUM> includes the gas (typically a hydrocarbon) being compressed by the compressor. That gas is referred to as process gas herein.

An optional shroud not shown that may include a labyrinth seal and which extends over a radially extending opening formed between the rotating shaft <NUM> and the compressor housing <NUM> may be provided to inhibit the free flow of process gas from the process cavity <NUM> into the bore <NUM>. The shroud <NUM> is disposed in the bore <NUM> and, as illustrated carries a labyrinth seal <NUM> that serves to totally or partially prevent the free flow of process gas from the process cavity <NUM> into the bore <NUM>. The combination of the shroud <NUM> and the labyrinth seal <NUM> extends over a radially extending opening formed between the rotating shaft <NUM> and the compressor housing <NUM>. As illustrated, the shroud <NUM> and the labyrinth seal <NUM> are shown as two separate items but they could be formed as an integrated unit in one embodiment. The dry gas seal assembly <NUM> illustrated in <FIG> includes the first seal <NUM> and the secondary seal <NUM>. Typically the components of the first and second seals <NUM>/<NUM> are preassembled into a cartridge and then disposed in the seal chamber <NUM>. The cartridge <NUM> includes a first stator <NUM> that can be formed of one or more components and joined in a fixed relationship to one another as well as with the compressor housing <NUM> when installed.

The cartridge can also include a sleeve ring <NUM> that can be formed of one or more components and that that is attached to the rotating shaft <NUM> such that it rotates with the rotating shaft <NUM>. The illustrated sleeve ring <NUM> includes four portions <NUM>, <NUM>, <NUM>, <NUM>. The first portion <NUM> carries rotating portions of the first seal <NUM> and the fourth portion <NUM> carries rotating portions of the secondary seal <NUM>. As shown, two spacer rings <NUM>, <NUM> are located between the first and second portions of the sleeve ring. The portions can be formed as rotating rings configured to contact and rotate with the rotating shaft <NUM>. Of course, the sleeve ring could be formed as a unitary piece or could include any number of pieces that are either joined together or otherwise held stationary relative to each other during operation (e.g., all pieces rotate together as one).

Assuming that the process gas in the process cavity <NUM> is under pressure, all components of the dry gas seal assembly <NUM> are urged in the direction toward thrust rings <NUM> and <NUM> (direction A) during operation. Axial movement of the primary dry gas seal <NUM> relative to the rotating shaft <NUM> is limited by a shaft thrust ring <NUM> received in a groove in the rotating shaft <NUM>.

In the above example, it should be understood that the shaft thrust ring <NUM> can be fixed relative to the sleeve rings so that the two elements rotate together. Also, for sake of completeness, it shall be understood that other elements can be attached to the sleeves to provide support or other functions but are not specifically described herein.

The portion <NUM> carries and otherwise mates first seal rotating or mating ring <NUM> to the rotating shaft <NUM>. That is, the portion <NUM> is mated to the rotating shaft <NUM> allows the first seal mating ring <NUM> to also rotate with the shaft <NUM>. First mating ring <NUM> can include one or more grooves (not shown) formed on a face thereof.

It shall be understood that during normal operation the secondary seal <NUM> operates in the same manner as described above with respect to <FIG> with the gas <NUM> traveling in the manner shown in <FIG>. That is, buffer gas <NUM> enters the primary ring control chamber <NUM> via the buffer gas passage <NUM>. As above, this gas passes through the primary ring <NUM> and exits it at or near the seal interface <NUM> at primary ring face 116a. This gas, in normal operation, can travel along the seal interface <NUM> both radially inward (direction B) and radially outward (direction B'). Gas that travels radially outward can generally pass into the bearing cavity <NUM>. Gas travels radially inward passes between the stator <NUM> and the sleeve ring <NUM> (in this case, between the third portion <NUM> and the stator <NUM>) exits the seal chamber <NUM> via vent <NUM> after passing vent chamber 974a. The buffer gas can be provided into the buffer gas passage <NUM> at a buffer gas pressure. In the event of a reduction of the buffer gas flow, the secondary seal <NUM> will draw gas from the vent chamber 974a due to grooves <NUM> as described above. Further operation of the secondary seal <NUM> is described below.

During operation, gas present in the process cavity <NUM>, which can reach pressures of <NUM>,<NUM> PSI-G (<NUM> BAR-G) or above, is sealed from the bearing cavity <NUM> and from the environment by the interaction of the first seal mating ring <NUM> and a first seal primary ring <NUM>. The first seal primary ring <NUM> can also be referred as a stationary ring as it does not rotate with the shaft and is thus, generally or completely, rotationally stationary relative to the housing during operation. Reference numeral <NUM> identifies the location of the seal interface formed between the first seal mating ring <NUM> and the first seal primary ring <NUM>.

As will be understood by the skilled artisan, the first seal primary ring <NUM> is axially movable relative to the housing <NUM> during operation such that a controlled distance may be maintained between the first seal mating ring <NUM> and the first seal primary ring <NUM> at the seal interface <NUM>. In the illustrated embodiment, a spring force is applied to the first seal primary ring <NUM> by one or more biasing members <NUM> disposed between a retainer ring 917a and the first seal primary ring <NUM>. As shown, the biasing members <NUM> are disposed between the stator <NUM> and a carrier ring <NUM> that is attached to or otherwise contacts the first seal primary ring <NUM>. The skill artisan will realize that in different types of seals, the primary/first seal design and geometry may be varied from that shown in <FIG> and embodiments herein are not limited to particular primary/first seal design and geometry shown here.

During operation, some of the process gas travels between the seal interface <NUM> of the first seal mating and primary rings <NUM>, <NUM>. The process gas that so travels is identified by arrow <NUM>.

In more detail, of rotation of the first seal mating ring <NUM> due to its connection to the rotating shaft <NUM> and/or pressure of the process gas in the process chamber <NUM> will cause some of the process gas to be drawn from an outer diameter of the first seal mating ring <NUM> into the groves formed therein. The shape of the grooves is optimized to enhance seal performance. As is known in the art, the grooves typically are machined only to the radial midpoint of the face of the first seal mating ring <NUM> and have a very shallow depth of only a few microns. The grooves can be shaped to have a tip such that gas enters the grooves is compressed because of the volume reduction at the tips. The area of slightly higher gas pressure creates a pressure dam and results in a so-called "lift off" resulting in physical separation of the primary and mating rings <NUM>, <NUM>. As such, in operation, gas flows over the dam area (between the primary and mating rings <NUM>, <NUM>) to a low pressure side <NUM> of the first seal seal interface <NUM>. Gas that passes through the seal interface can exit the dry gas seal assembly <NUM> via a vent <NUM> in the compressor housing <NUM>.

To allow for the above described lift off, the carrier ring <NUM> is provided as a means for allowing the required movement. The carrier ring <NUM> is coupled to the stator <NUM> by the biasing members <NUM>. The biasing members <NUM> can be a singular element or composed of a plurality elements. The biasing members <NUM> are comprised of one or more springs in one embodiment. Of course, the shape and design of the carrier ring in the first seal can be varied.

During operation, as described above, pressure in the process cavity <NUM> as well as heat can cause the rotating shaft <NUM> to move or expand axially. The biasing members <NUM> can allow for the first seal primary ring <NUM> to keep a constant distance during operation between itself and the first seal mating ring <NUM> even as the mating ring <NUM> moves axially due to such movement of the rotating shaft <NUM>.

As mentioned above, the secondary seal <NUM> receives a flow a buffer gas. It shall be understood that the secondary seal can be formed in the same or similar to any prior disclosed embodiment of <FIG>. Thus, the discussion related there is incorporated as if fully restated here.

The gas, after passing through the seal interface <NUM> travels both radially and axially outward to the bearing cavity <NUM> and radially and axially inward (direction A') towards the process cavity <NUM>. In <FIG>, a vent <NUM> (including a vent passage 974a) is provided that allows for the controlled release of both axially inward traveling buffer gas and process gas <NUM> that has passed through first seal seal interface <NUM> to escape during normal operation. Such vents are known in the art and can typically include a choke that limits gas flow to a level at or below about <NUM>-<NUM> barg.

In normal operation, the pressure in the vent <NUM> is roughly atmospheric or slightly higher. In the event that the buffer gas flow is reduced, the secondary seal <NUM> will operate in the manner as described above with respect to <FIG> and draw gas from the vent <NUM> though the dry gas seal side passage way <NUM> in the axially outward direction A.

In the event that the primary seal <NUM> is leaking, and now with reference to <FIG> which shows the secondary seal <NUM> operating in such a condition, gas will escape from the primary seal <NUM> and reach the vent passage 974a. As discussed above, the vent <NUM> includes a choke that will generally prevent the gas from escaping. In some cases, gas leaking through the first seal will raise the pressure of gas supplied to the vent chamber passage 974a above what the choke will allow to escape. As shown in <FIG>, this may result in the process gas <NUM> traveling from the vent chamber 974a in the axially outward (direction A) through the dry gas seal side passage way <NUM> to the ID of the primary ring <NUM> at a higher pressure than in normal operation (e.g., above the pressure allowed to escape via the choke).

The high pressure process gas <NUM> can also cause the the inner thrust ring 202a and inner seal 205a to be pushed axially inward as illustrated in <FIG>. When this happens, the pressure behind the porous primary ring <NUM> will become approximately equal to the pressure of the process gas <NUM> leaking through the first seal and the pressure at the seal interface <NUM> will generally be lower and will decay in the gap from the ID to the OD. It shall be understood that the process gas <NUM> will be kept from fully escaping from the primary ring control chamber <NUM> due a choke in the vent <NUM>.

After the pressure has stabilized in the primary ring control chamber <NUM>, the outer thrust ring <NUM> defines a new balance diameter of the secondary seal <NUM> and grooves <NUM> in the mating ring <NUM> will draw the high pressure process gas <NUM> from the ID and through the sealing interface <NUM> to create level flow towards the bearing chamber <NUM>. In this manner, the secondary seal <NUM> can maintain a positive restriction in this catastrophic event and prevent extreme leakage of pressurised gas into the atmosphere.

There are several variations that can applied to the teachings herein. For example, and a shown in <FIG>, the radial seals <NUM> of any prior embodiment can be implemented as o-rings. These o-rings can have different diameters. As shown in <FIG>, the first o-ring 110ba has a smaller cross-sectional diameter than the second o-ring 1105b. In another embodiment, this relationship could be reversed with the first o-ring 1105a having a larger diameter than the second o-ring 1105b.

In <FIG> and the figures that follow, gas flow paths are shown in the normal operating state. It shall be understood that the embodiments in these figures can all operate in all of the various conditions discussed above.

In another embodiment, and as shown in <FIG>, the back <NUM> of the primary ring <NUM> can be configured such that it defines uneven sealing planes. For example, the outer sealing plane 1280b at the back of the primary ring116 can be axially inboard relative to the inner sealing plane 1280a at the back of the primary ring. This will result in a slight adjustment in alignment of the front (outboard) faces of the inner and outer thrust rings 202a/202b.

It shall be understood that additional variations in the back of the primary ring are contemplated. For instance, grooves 1302a/1302b can be formed in the back <NUM> of the primary ring <NUM> as shown in <FIG>. This concept of grooves can be extended or otherwise combined with variation of sealing planes of <FIG> to provide an grooved planes where an outer sealing plane 1380b at the back of the primary ring can be axially inboard relative to the inner sealing plane 1380a at the back of the primary ring.

In the prior embodiments having grooves in the back of the primary ring <NUM>, it should be understood that one of the grooves could be omitted. Further, in such cases, while not required, one of more of the outboard faces of the thrust ring could be adjusted so that it does not include a receiving area for an o-ring (<FIG>/<FIG>). In more detail, the outer thrust ring 202b in <FIG> includes a receiving area 1402b to receive the outer o-ring 1405b. The front face 1402a of the inner thrust ring 202a in <FIG> is shown as being substantially planar. This variation will result in changes in the sealing planes and could be used with primary ring <NUM> that includes the groove 1280a shown in <FIG> or with any primary ring <NUM> shown herein (e.g., without or without grooves in it back).

In <FIG>/<FIG> different sized o-rings 1405a/1405b are illustrated but that is not required and they could be of the same diameter.

For sake of completeness, <FIG> shows the reverse situation of <FIG>. In particular, In more detail, the outer thrust ring 202b in <FIG> is substantially flat and has front face 1404b. The inner thrust ring 202a includes a receiving area 1404a to receive the inner o-ring 1405a. The front face 1402a of the inner thrust ring 202a in <FIG> is shown as being substantially planar. This variation will result in changes in the sealing planes and could be used with primary ring <NUM> that includes the groove 1280b shown in <FIG> or with any primary ring <NUM> shown herein (e.g., without or without grooves in it back).

Various embodiments of the invention have been described herein with reference to the related drawings. Alternative embodiments of the invention can be devised without departing from the scope of this invention. Various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. Thus, any coupling or connection herein may later be called direct in the claims below even if not specifically recited in that manner above. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein.

Claim 1:
An assembly for sealing a fluid in a rotating machine, the assembly comprising:
a primary dry gas seal (<NUM>) adapted and configured to surround a shaft (<NUM>) of the rotating machine and prevent the fluid from exiting the rotating machine; and
a secondary seal (<NUM>) connected to the primary dry gas seal (<NUM>) adapted and configured to prevent a liquid from entering the dry gas seal (<NUM>), the secondary seal comprising:
a stator (<NUM>) configured to be mounted around the shaft (<NUM>) and configured to be fixedly attached to the rotating machine, the stator (<NUM>) including primary ring control chamber (<NUM>) formed therein;
a porous primary ring (<NUM>) formed of a porous material and having a back (<NUM>);
a split thrust ring (<NUM>) at least partially within the primary ring control chamber (<NUM>) and coupled to the porous primary ring (<NUM>), the split thrust ring (<NUM>) including an inner ring (202a) and outer ring (202b), wherein the inner ring (202a) is configured to move axially inboard relative to the outer ring (202b) in the event of an increase in the flow of the fluid through the primary dry gas seal (<NUM>);
a mating ring (<NUM>) coupled to the shaft (<NUM>) that rotates with the shaft and relative to the porous primary ring (<NUM>);
an outer ring biasing member (<NUM>) that urges the outer ring (202b) and the porous primary ring (<NUM>) toward the mating ring (<NUM>) to form a seal interface (<NUM>) between porous primary ring (<NUM>) and the mating ring (<NUM>);
an inner ring biasing member (<NUM>) that urges the inner ring (202a) and the porous primary ring (<NUM>) toward the mating ring (<NUM>); and
one or more sealing elements (205a/205b) disposed between the split thrust ring (<NUM>) and the back of the porous primary ring (<NUM>) and within the primary ring control chamber (<NUM>);
wherein the stator (<NUM>) includes a passageway (<NUM>) constructed and arranged to convey pressurized buffer gas at a buffer gas pressure during normal operation to the primary ring control chamber (<NUM>) such that gas passes from the back (<NUM>) of the porous primary ring (<NUM>), through the porous primary ring (<NUM>) and to the seal interface (<NUM>).