Flow distributed buffered/educted gas seal

A system, in certain embodiments, includes a seal assembly having a seal body. The seal body includes an inlet buffer port and an outlet eduction port. The inlet buffer port is configured to receive a compressed buffer gas, such as shop air, which is injected into the inlet buffer port. The compressed buffer gas blocks the flow of a compressed process gas, such as land fill gas, by opposing the flow of the compressed process gas through the seal assembly. Both the compressed buffer gas and the compressed process gas may be expelled through the outlet eduction port.

BACKGROUND

Gas compressors are used in a wide variety of industries including aerospace, automotive, oil and gas, power generation, food and beverage, pharmaceuticals, water treatment, and the like. The compressed gas may include air, nitrogen, oxygen, natural gas, or any other type of gas. Gas compressor systems generally include devices that increase the pressure of a gas by decreasing (e.g., compressing) its volume. Certain types of gas compressors employ one or more mechanisms that employ a rotational torque to compress an incoming gas. For instance, in a centrifugal gas compressor system, a gas is drawn into a housing through an inlet, the gas is compressed by a rotating impeller, and the gas is expelled from the housing. Often, the impeller or other rotating mechanism is driven by a rotating drive shaft that extends into the housing. In such a system, one or more seals are typically disposed around the drive shaft to minimize the amount of compressed gas that leaks around the drive shaft. However, certain gases (e.g., land fill gas) are extremely corrosive and harmful to typical seals used in centrifugal gas compressor systems. As such, centrifugal compressors tend to be used less frequently in certain applications (e.g., land fill gas applications).

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

As discussed above, in certain gas compressor systems, a gas is drawn into a housing through an inlet, the gas is compressed by a rotating impeller, and the gas is expelled from the housing. The impeller or other rotating mechanism is driven by a rotating drive shaft that extends into the housing. In such a system, one or more seals are disposed around the drive shaft to reduce the amount of compressed gas that leaks around the drive shaft. The gas compressor system may employ a wet seal and/or a dry-face seal for this purpose. Wet seals may be simple, but allow more gas to pass than a dry-face seal employed in the same environment. Dry-face seals may be complex in design and employ an equally complex control system. However, even a dry-face seal is susceptible to gas leaks and creates an additional cost relating to installation, operation, and maintenance of the seal.

Unfortunately, compressed gas, sometimes referred to as “process gas,” that leaks past the seal and into the housing is generally undesirable for several reasons. For instance, process gas leaking past the seal may not be recovered, resulting in a net decrease in the gas product output from the compressor. In other words, process gas that leaks by the seal may be unrecoverable or cost a great deal to recover. In addition, the process gas may contain corrosive elements (e.g., carbonic acid, sulfuric acid, carbon dioxide, and so forth) which may adversely affect the functioning of lubrication oil in the gearing of the gas compressor system, among other things. Further, process gas that leaks past the seal may produce other safety concerns that lead to additional procedures and devices in the compression process. For example, the gas compressor system may employ additional seals and/or control systems to capture the process gas, scrub (e.g., clean) the gas, flash (burn off) the process gas, or the like. This can also add to the cost of installing, operating, and maintaining the gas compressor system.

Certain embodiments described herein include a system and method that addresses one or more of the above-mentioned inadequacies of a conventional gas compressor system. In certain embodiments described herein, a gas compressor system includes a buffered/educted gas seal. The buffered/educted gas seal may address the above-mentioned inadequacies by injecting a buffer gas into a body of the buffered/educted gas seal through an inlet buffer port. The buffer gas may oppose the flow of the process gas along an axis of a drive shaft of the gas compressor system, thereby blocking leakage of the process gas into a gearbox of the gas compressor system. In particular, the buffer gas may be injected into the body of the buffered/educted gas seal at a higher pressure than the compressed process gas. Since the pressure of the buffer gas is greater than the pressure of the process gas, the buffer gas opposes further leakage of the process gas along the axis of the drive shaft. Both the buffer gas and the process gas may be collected and expelled from the body of the buffered/educted gas seal through an outlet eduction port.

FIG. 1is a perspective view of an exemplary embodiment of a compressor system10employing a seal assembly50(e.g., a buffered/educted gas seal). The compressor system10is generally configured to compress gas in various applications. For example, the compressor system10may be employed in applications relating to the automotive industries, electronics industries, aerospace industries, oil and gas industries, power generation industries, petrochemical industries, and the like. In addition, the compressor system10may be employed to compress land fill gas, which may contain certain corrosive elements. For example, the land fill gas may contain carbonic acid, sulfuric acid, carbon dioxide, and so forth.

In general, the compressor system10includes one or more of a reciprocating, rotary, axial, and/or a centrifugal gas compressor that is configured to increase the pressure of (e.g., compress) incoming gas. In the illustrated embodiment, the compressor system10includes a centrifugal compressor. More specifically, the depicted embodiment includes a Turbo-Air 9000 manufactured by Cameron of Houston, Tex. In some embodiments, the compressor system10includes a power rating of approximately 150 to approximately 3,000 horsepower (hp), discharge pressures of approximately 80 to 150 pounds per square inch (psig) and an output capacity of approximately 600 to 15,000 cubic feet per minute (cfm). Although the illustrated embodiment includes only one of many compressor arrangements that can employ a buffered/educted gas seal50, other embodiments of the compressor system10may include various compressor arrangements and operational parameters. For example, the compressor system10may include a different type of compressor, a lower horsepower rating suitable for applications having a lower output capacity and/or lower pressure differentials, a higher horsepower rating suitable for applications having a higher output capacity and/or higher pressure differentials, and so forth.

In the illustrated embodiment, the compressor system10includes a control panel12, a drive unit14, a compressor unit16, an intercooler18, a lubrication system20, and a common base22. The common base22generally provides for simplified assembly and installation of the compressor system10. For example, the control panel12, the drive unit14, the compressor unit16, intercooler18, and the lubrication system20are coupled to the common base22. This enables installation and assembly of the compressor system10as modular components that are pre-assembled and/or assembled on site.

The control panel12includes various devices and controls configured to monitor and regulate operation of the compressor system10. For example, in one embodiment, the control panel12includes a switch to control system power, and/or numerous devices (e.g., liquid crystal displays and/or light emitting diodes) indicative of operating parameters of the compressor system10. In other embodiments, the control panel12includes advanced functionality, such as a programmable logic controller (PLC) or the like.

The drive unit14generally includes a device configured to provide motive power to the compressor system10. The drive unit14is employed to provide energy, typically in the form of a rotating drive unit shaft, which is used to compress the incoming gas. Generally, the rotating drive unit shaft is coupled to the inner workings of the compressor unit16, and rotation of the drive unit shaft is translated into rotation of an impeller that compresses the incoming gas. In the illustrated embodiment, the drive unit14includes an electric motor that is configured to provide rotational torque to the drive unit shaft. In other embodiments, the drive unit14may include other motive devices, such as a compression ignition (e.g., diesel) engine, a spark ignition (e.g., internal gas combustion) engine, a gas turbine engine, or the like.

The compressor unit16typically includes a gearbox24that is coupled to the drive unit shaft. The gearbox24generally includes various mechanisms that are employed to distribute the motive power from the drive unit14(e.g., rotation of the drive unit shaft) to impellers of the compressor stages. For instance, in operation of the system10, rotation of the drive unit shaft is delivered via internal gearing to the various impellers of a first compressor stage26, a second compressor stage28, and a third compressor stage30. In the illustrated embodiment, the internal gearing of the gearbox24typically includes a bull gear coupled to a drive shaft that delivers rotational torque to the impeller.

It will be appreciated that such a system (e.g., where a drive unit14that is indirectly coupled to the drive shaft that delivers rotational torque to the impeller) is generally referred to as an indirect drive system. In certain embodiments, the indirect drive system may include one or more gears (e.g., gearbox24), a clutch, a transmission, a belt drive (e.g., belt and pulleys), or any other indirect coupling technique. However, another embodiment of the compressor system10may include a direct drive system. In an embodiment employing the direct drive system, the gearbox24and the drive unit14may be essentially integrated into the compressor unit16to provide torque directly to the drive shaft. For example, in a direct drive system, a motive device (e.g., an electric motor) surrounds the drive shaft, thereby directly (e.g., without intermediate gearing) imparting a torque on the drive shaft. Accordingly, in an embodiment employing the direct drive system, multiple electric motors can be employed to drive one or more drive shafts and impellers in each stage of the compressor unit16. However, any type of indirect drive or direct drive system may be used with the buffered/educted gas seal50in certain embodiments.

The gearbox24includes features that provide for increased reliability and simplified maintenance of the system10. For example, the gearbox24may include an integrally cast multi-stage design for enhanced performance. In other words, the gearbox24may include a singe casting including all three scrolls helping to reduce the assembly and maintenance concerns typically associated with systems10. Further, the gearbox24may include a horizontally split cover for easy removal and inspection of components disposed internal to the gearbox24.

As discussed briefly above, the compressor unit16generally includes one or more stages that compress the incoming gas in series. For example, in the illustrated embodiment, the compressor unit16includes three compression stages (e.g., a three stage compressor), including the first stage compressor26, the second stage compressor28, and the third stage compressor30. Each of the compressor stages26,28, and30includes a centrifugal scroll that includes a housing encompassing one or more gas impellers. In operation, incoming gas is sequentially passed into each of the compressor stages26,28, and30before being discharged at an elevated pressure.

Operation of the system10includes drawing a gas into the first stage compressor26via a compressor inlet32and in the direction of arrow34. As illustrated, the compressor unit16also includes a guide vane36. The guide vane36includes vanes and other mechanisms to direct the flow of the gas as it enters the first compressor stage26. For example, the guide vane36may impart a swirling motion to the inlet air flow in the same direction as the impeller of the first compressor stage26, thereby helping to reduce the work input at the impeller to compress the incoming gas.

After the gas is drawn into the system10via the compressor inlet32, the first stage compressor26compresses and discharges the compressed gas via a first duct38. The first duct38routes the compressed gas into a first stage40of the intercooler18. The compressed gas expelled from the first compressor stage26is directed through the first stage intercooler40and is discharged from the intercooler18via a second duct42.

Generally, each stage of the intercooler18includes a heat exchange system to cool the compressed gas. In one embodiment, the intercooler18includes a water-in-tube design that effectively removes heat from the compressed gas as it passes over heat exchanging elements internal to the intercooler18. An intercooler stage is provided after each compressor stage to reduce the gas temperature and to improve the efficiency of each subsequent compression stage. For example, in the illustrated embodiment, the second duct42routes the compressed gas into the second compressor stage28and a second stage44of the intercooler18before routing the gas to the third compressor stage30.

After the third stage30compresses the gas, the compressed gas is discharged via a compressor discharge46in the direction of arrow48. In the illustrated embodiment, the compressed gas is routed from the third stage compressor30to the discharge46without an intermediate cooling step (e.g., passing through a third intercooler stage). However, other embodiments of the compressor system10may include a third intercooler stage or similar device configured to cool the compressed gas as it exits the third compressor stage30. Further, additional ducts may be coupled to the discharge46to effectively route the compressed gas for use in a desired application (e.g., drying applications).

Each of the compressor stages26,28, and30includes one or more impellers that are located in a housing and are driven by rotation of a pinion. In certain applications, the pinion may extend though a pinion bore in the housing. Unfortunately, in a system that employs a pinion that extends through the housing, gas may leak from the impeller into the gearbox24. This is generally attributed to seals that do not provide a complete seal between the pinion and the pinion bore. Gas that leaks past the seal and into the gearbox24is generally undesirable for several reasons. In particular, the gas may contain corrosive elements (e.g., carbonic acid, sulfuric acid, carbon dioxide, and so forth) which may adversely affect the functioning of lubrication oil in the gearing of the gearbox24, among other things. Further, gas that leaks past the seal may produce other concerns that lead to additional procedures and devices in the compression process. Disclosed below are embodiments of the compressor system10that employ a buffered/educted gas seal50, which may be used to minimize the amount of gas allowed to leak from the impeller into the gearbox24.

FIG. 2is a cross-section view of an exemplary embodiment of the first compressor stage26within the compressor system10ofFIG. 1. However, the components of the first compressor stage26are merely illustrative of any of the compressor stages26,28, and30and may, in fact, be indicative of the components in a single stage compressor system10. As illustrated inFIG. 1, the first compressor stage26may include an impeller48, a seal assembly50(e.g., a buffered/educted gas seal), a bearing assembly52, two bearings54within the bearing assembly52, and a pinion shaft56, among other things. In general, the seal assembly50and the bearing assembly52reside within the gearbox24. The two bearings54provide support for the pinion shaft56, which drives rotation of the impeller48.

In certain embodiments, a drive shaft58, which is driven by the drive unit14ofFIG. 1, may be used to rotate a bull gear60about a central axis62. The bull gear60may mesh with the pinion shaft56of the first compressor stage26via a pinion mesh64. In fact, the bull gear60may also mesh with another pinion shaft associated with the second and third compressor stages28,30via the pinion mesh64. Rotation of the bull gear60about the central axis62may cause the pinion shaft56to rotate about a first stage axis66, causing the impeller48to rotate about the first stage axis66. As discussed above, gas may enter the compressor inlet32, as illustrated by arrow34. The rotation of the impeller48causes the gas to be compressed and directed radially, as illustrated by arrows68. Unfortunately, as the gas is compressed, a certain amount of the compressed gas may leak behind the impeller48. As discussed in greater detail below, the seal assembly50includes a gas seal portion and an oil seal portion, which collectively comprise a buffered/educted gas seal, which helps minimize the amount of gas allowed to leak into the gearbox24. By minimizing the amount of gas into the gearbox24, oil used to lubricate the bearings54may not be subjected to the corrosive effects of certain elements within the gas, such as carbonic acid, sulfuric acid, carbon dioxide, and so forth.

For reference purposes, the impeller48, seal assembly50, bearing assembly52, bearings54, and pinion shaft56of the first compressor stage26may be referred to collectively as a compression stage rotor assembly70. As discussed above, these components may be illustrative of components of any of the stages of the compressor system10ofFIG. 1.FIGS. 3A and 3Bare perspective views of an exemplary embodiment of the compression stage rotor assembly70. In addition,FIGS. 4A and 4Bare cross-section top and side views, respectively, of an exemplary embodiment of the compression stage rotor assembly70. Furthermore,FIG. 5is an exploded view of an exemplary embodiment of the compression stage rotor assembly70.

As illustrated inFIGS. 3A and 3B, the impeller48includes a plurality of blades72extending radially from its center. In certain embodiments, as illustrated inFIGS. 4A and 4B, the impeller48may be attached to an axial impeller end74of the pinion shaft56by a rotor balance washer76. In particular, in certain embodiments, a capscrew78may screw axially into the axial impeller end74of the pinion shaft56, thereby holding the impeller48in place about the axial impeller end74of the pinion shaft56. In particular, a notch80extending radially from the pinion shaft56may limit axial movement of the impeller48when the capscrew78is engaged, with the rotor balance washer76biased axially against the impeller48. In certain embodiments, as illustrated inFIG. 4B, at least one alignment pin82may be used to ensure that the impeller48does not rotate about the axial impeller end74of the pinion shaft56.

Returning toFIGS. 3A and 3B, the seal assembly50may include at least one eduction port outlet84and at least one buffer port inlet86. The operation of the eduction port outlet(s)84and the buffer port inlet(s)86will be discussed in greater detail below with respect toFIGS. 6 through 8. In general, pressurized buffer gas, such as shop air, may be injected into the buffer port inlet(s)86to help prevent leakage of compressed process gas (e.g., land fill gas) around the impeller48into the gearing of the gearbox24ofFIG. 2. In addition, in certain embodiments, the process gas which has leaked into the seal assembly50from the impeller48may be directed back to the compressor inlet32via the eductor port outlet(s)84. In particular, as illustrated inFIGS. 4A and 4B, at least one buffer port88within the seal assembly50may be used to introduce the compressed buffer gas and at least one eduction port90may be used to collect and expel compressed process gas which has leaked into the seal assembly50.

As illustrated inFIGS. 4A,4B,5A, and5B, in certain embodiments, the seal assembly50may be associated with a seal insert92. The seal insert92may fit within an inner annular region of the seal assembly50. In general, the seal insert92may be configured to create a seal on a back face94of the impeller48. In particular, as illustrated inFIGS. 4A and 4B, in certain embodiments, an annular lip96protruding axially from the back face94of the impeller48may be configured to mate with an annular groove98extending axially into a surface of the seal insert92such that a certain amount of process gas may be blocked from leaking further into the seal assembly50. In certain embodiments, a first o-ring100may be used to create a seal between the seal assembly50and the seal insert92. As illustrated inFIG. 5, a second o-ring102may be used to further the seal between the back face94of the impeller48and the seal insert92. In addition, a plurality of bolts104may be used to attach the seal insert92within the seal assembly50.

The two bearings54support the pinion shaft56within the bearing assembly52. As illustrated inFIG. 4A, the bearings54may be coupled to the bearing assembly52using a plurality of screws106. In addition, as illustrated inFIG. 4B, lubrication conduits108within the bearings54may be used to introduce lubrication oil into the bearings54. More specifically, the lubrication conduits108may be supplied with lubrication oil from a lubrication manifold110which extends axially within a wall of the bearing assembly52. The lubrication manifold110fluidically couples to the lubrication conduits108of the bearings54via the lubrication orifices112of the bearings54, as illustrated inFIG. 3A. Leakage of the lubrication oil may be minimized by using a plurality of o-rings114, as illustrated inFIG. 4B.

In certain embodiments, as illustrated inFIGS. 4A and 4B, the pinion shaft56may include thrust collars116on either side of the pinion mesh64, axially between the bearings54and the pinion mesh64. In general, the thrust collars116may cancel out a substantial amount of axial thrust loads, which may improve the efficiency of the compressor system10(e.g., by reducing power losses of the gearbox24). In addition, the thrust collars116may transfer the remaining net thrust load to the bull gear60ofFIG. 2, where it may be absorbed by a low-speed thrust bearing.

As illustrated inFIGS. 4A and 4B, in certain embodiments, the compression stage rotor assembly70may include a bearing retainer118, which may be held in place by a plug120. The bearing retainer118may help protect the components of the compression stage rotor assembly70from the environment (e.g., dust, dirt, and so forth). The bearing retainer118may also protect users from the rotating components of the compression stage rotor assembly70(e.g., protecting against users getting their fingers caught in the rotating components). In addition, the bearing retainer118may help the bearings54retain lubrication oil within the gearbox24. In certain embodiments, the plug120may be threaded and configured to screw axially into the bearing retainer118. The plug120may be used as an access point to the compression stage rotor assembly70for measurement purposes, among other things.

FIG. 6is a cross-section view of an exemplary embodiment of the impeller48, pinion shaft56, seal assembly50and associated seal insert92of the compression stage rotor assembly70ofFIGS. 3 through 5, as indicated by arcuate line6-6inFIG. 4A. In particular, the embodiment illustrated inFIG. 6illustrates how the eduction port90and the buffer port88may be used to minimize leakage of the compressed process gas into a gearbox cavity122, which includes the bearings54, pinion mesh64, and so forth. As discussed above, the compressed process gas may enter the compressor inlet32, as illustrated by arrow34. After being compressed, a certain amount of the compressed process gas may leak behind the back face94of the impeller48, as illustrated by arrow124. Since the process gas has been compressed, it may typically be at an elevated pressure when traversing along the back face94of the impeller48. Conversely, the gearbox cavity122may typically be under vacuum. As such, the compressed process gas may generally tend to leak from a high-pressure region126near the impeller48to the low-pressure gearbox cavity122. In particular, the compressed process gas may gradually leak from the back face94of the impeller48between the seal insert92and the pinion shaft56, as illustrated by arrow128.

A gas seal portion130of the seal assembly50and associated seal insert92may substantially reduce the amount of process gas allowed to leak into the eduction port90, as illustrated by arrow132. In certain embodiments, the gas seal portion130of the seal assembly50and associated seal insert92may include a babbitted surface134on a radially inner surface of the seal insert92. As the name suggests, the babbitted surface134may be comprised of a soft metal composition. The babbitted surface134may interface with annular teeth136which extend radially outward from the pinion shaft56. The pinion shaft56and, therefore, the annular teeth136may be comprised of a harder metal composition than that of the babbitted surface134. Over time, the annular teeth136of the pinion shaft56may cut into the babbitted surface134, creating a close fit between the two and allowing for decreased leakage of the compressed process gas into the eduction port90, as illustrated by arrow132. As discussed above, whatever process gas does leak into the eduction port90may be directed out of the eduction port90, as illustrated by arrow138. Furthermore, in certain embodiments, the process gas may be directed back to the compressor inlet32as indicated by arrow139(e.g., connection line), where it may be compressed again, thereby reducing the total amount of leakage from the compressor system10. In addition, by directing this process gas back to the compressor inlet32, the overall efficiency of the of the compressor system10may be increased since the process gas, which might otherwise be lost, is compressed for further use.

An oil seal portion140of the seal assembly50may further reduce the amount of process gas which is allowed to leak along the pinion shaft56into the gearbox cavity122. In particular, in certain embodiments, the buffer port88may be used to inject buffer gas (e.g., shop air or other relatively non-corrosive gases) into the oil seal portion140, as illustrated by arrow142. Upon reaching the pinion shaft56, the buffer gas may be split between an axial upstream flow path144and an axial downstream flow path146adjacent the pinion shaft56. In certain embodiments, the oil seal portion140may include aluminum labyrinth teeth148which extend from a radially inner surface of the seal assembly50. These teeth148may, to a certain degree, minimize the amount of buffer gas allowed to flow from the buffer port88to both the eduction port90and the gearbox cavity122, as illustrated by arrows150and152, respectively.

In general, the buffer gas may be sufficiently pressurized to counteract the pressure of the process gas leaking into the eduction port90. More specifically, the pressure of the process gas may be adjusted by an operator or a system controller such that the pressure of the process gas is greater than the pressure of the process gas. As such, the pressure of the buffer gas flowing from the buffer port88to the eduction port90, as illustrated by arrow150, may overcome the pressure of the process gas leaking into the eduction port90, as illustrated by arrow132. In particular, the flow of buffer gas may oppose and even block the flow of the process gas. Accordingly, the remaining process gas leaking from the impeller48through the gas seal portion130of the seal assembly50may be directed out through the eduction port90instead of being allowed to further leak through the oil seal portion140of the seal assembly50. As such, only buffer gas will be allowed to flow into the gearbox cavity122, as illustrated by arrow152. As opposed to the process gas, the buffer gas used will generally not be corrosive to the bearings54, lubrication oil, and other gearbox24components. For instance, in certain embodiments, the buffer gas used may simply be compressed air. Therefore, using the buffer port88to inject buffer gas into the seal assembly50may help prevent leakage of the compressed process gas past the seal assembly50into the gearbox cavity122, which includes the bearings54, pinion mesh64, and so forth.

FIG. 7is a cross-section view of an exemplary embodiment of the pinion shaft56, seal assembly50, and associated seal insert92ofFIG. 6, as indicated by arcuate line7-7inFIG. 4B. In the illustrated embodiment, an eduction collection region154may separate the seal insert92and the seal assembly50. The eduction collection region154may act as a collection region into which process gas, which has leaked past the babbitted surface134and the annular teeth136of the pinion shaft56, may be collected before being directed into the eduction port90. For example, the eduction collection region154may, in certain embodiments, include a first annular space156cut out of the seal insert92which is configured to mate with a second annular space158cut out of the seal assembly50.

In the illustrated embodiment, the eduction port90may be located within the seal assembly50at generally the same axial location along the axis66as the buffer port88. Such alignment may facilitate the internal machining of the seal assembly50. For instance,FIG. 8is a cross-section view of an exemplary embodiment of the seal assembly50, as indicated by arcuate line8-8inFIG. 7. As illustrated inFIG. 8, the buffer port88and the eduction port90may be generally located along a common axial plane of the seal assembly50. As discussed above, the buffer gas may be injected through the buffer port inlet86into the buffer port88, as illustrated by arrow142, and the buffer gas and process gas may be expelled out of the eduction port90through the eduction port outlet84, as illustrated by arrow138. However, as illustrated inFIG. 7, the buffer port88and the eduction port90are not in direct fluidic communication with each other. Rather, the eduction collection region154may collect and direct the process gas and buffer gas into the eduction port90. Returning toFIG. 8, the buffer port88may, in certain embodiments, be in direct fluidic communication with buffer cross-drilled ports160, which may be associated with cross-drilled port outlets162. In general, the cross-drilled port outlets162may be plugged during operation of the seal assembly50. As such, the buffer gas entering the buffer port88may also enter the buffer cross-drilled ports160, as illustrated by arrows164. The flow of the buffer gas into the buffer cross-drilled ports160as well as the buffer port88enables the buffer gas to spread across the pinion shaft56more evenly.