Patent Description:
Turbomachinery is used extensively in the oil and gas industry, such as for performing compression of a process fluid, conversion of thermal energy into mechanical energy, fluid liquefaction, etc. One example of such turbomachinery is a compressor, such as a centrifugal compressor.

<CIT> describes an axial flow machine, particularly an axial turbine or axial compressor, having a stator which has a housing defining a flow channel for a working medium to be expanded or a working medium to be compressed, and guide vanes projecting into the flow channel, and having a rotor which has at least one stage, each stage of the rotor having a radially inner rotor disc and radially outer rotor blades. The rotor is pressed in the axial direction via a tie rod which extends in a radially inner recess of the rotor. A barrier pressure channel is formed between the tie rod and each rotor disc and in that a compensating pressure channel is formed between the flow channel and the blocking pressure channel. The pressure in the blocking pressure channel is greater than the pressure in the compensating pressure channel and the pressure in the flow channel is likewise greater than in the compensating pressure channel.

<CIT> describes a multi-stage compressor wherein heat developed by compressing the fluid processed by the compressor is used to heat the tie rod, which holds the stacked impellers of the compressor rotor. The multi-stage compressor comprises a return flow path, along which a fraction of the compressed process gas flows back from a downstream location to an upstream location of the gas compression path. The return flow path flows along the tie rod, so that heat generated by compression in the compressed or partly compressed processed gas is transferred to the tie -rod by forced convection. The tie rod is thus heated faster than in current art compressors.

<CIT> describes a spool of a compressor on a gas turbine which allow increased surface speed of the rotors and improved efficiency to reduce fuel burn per pound of trust. A spacer disk with an outer portion and a web portion is disposed between adjacent rotor disks. The outer portion has a catenary shape that extends between the peripheral rims of the adjacent rotor disks.

As would be appreciated by those skilled in the art, turbomachinery, such as centrifugal compressors, may involve rotors of tie bolt construction (also referred to in the art as thru bolt or tie rod construction), where the tie bolt supports a plurality of impeller bodies and where adjacent impeller bodies may be interconnected to one another by way of elastically averaged coupling techniques, such as involving hirth couplings or curvic couplings. These coupling types use different forms of face gear teeth (straight and curved, respectively) to form a robust coupling between two components.

These couplings and associated structures may be subject to greatly varying forces (e.g., centrifugal forces), such as from an initial rotor speed of zero revolutions per minute (RPM) to a maximum rotor speed, (e.g., as may involve tens of thousands of RPM). Additionally, these couplings and associated structures may be exposed to contaminants and/or byproducts that may be present in process fluids processed by the compressor. If so exposed, such couplings and associated structures could be potentially affected in ways that could impact their long-term durability. By way of example, a combination of carbon dioxide (CO2), liquid water and high-pressure levels can lead to the formation of carbonic acid (H2CO3), which is a chemical compound that can corrode, rust or pit certain steel components. Physical debris may also be present in the process fluids that if allowed to reach the hirth couplings and associated structures could potentially affect their functionality and durability.

In view of the foregoing considerations, to attain consistent high performance and long-term durability in a centrifugal compressor, an aspect of the invention involves seal elements arranged to cover respective hirth couplings to inhibit passage onto the respective hirth coupling of process fluid being processed by the compressor, and thus ameliorate the issues discussed above.

The present inventor has recognized that --notwithstanding of utilization of seal elements-- some residual leakage of process fluid may still occur into one or more cavities that may be disposed about the tie bolt. Leakage of process fluid into such cavities, for example, could detrimentally affect aerodynamic and/or rotordynamics performance of the rotor structure. For example, condensate or moisture that could be trapped in such cavities could potentially lead to increased levels of rotor vibration. For example, high pressure gas could leak from an area of high potential pressure to an area of low potential pressure and possibly lead to increased gas recycle and reduced aerodynamic performance. Accordingly, disclosed embodiments involve a flow loop that provides fluid communication through the tie bolt and is appropriately pressurized to keep any such residual leakage from travelling onto the hirth couplings. Another aspect of the invention involves a venting arrangement for venting such cavities, such as by way of a venting outlet.

In the following detailed description, various specific details are set forth in order to provide a thorough understanding of such embodiments. However, those skilled in the art will understand that disclosed embodiments may be practiced without these specific details that the aspects of the present invention are not limited to the disclosed embodiments, and that aspects of the present invention may be practiced in a variety of alternative embodiments.

Furthermore, various operations may be described as multiple discrete steps performed in a manner that is helpful for understanding embodiments of the present invention. However, the order of description should not be construed as to imply that these operations need be performed in the order they are presented, nor that they are even order dependent, unless otherwise indicated. Moreover, repeated usage of the phrase "in one embodiment" does not necessarily refer to the same embodiment, although it may.

It is noted that disclosed embodiments need not be construed as mutually exclusive embodiments, since aspects of such disclosed embodiments may be appropriately combined by one skilled in the art depending on the needs of a given application.

<FIG> illustrates a fragmentary cross-sectional view of one non-limiting embodiment of a disclosed rotor structure <NUM> used in compressors (e.g., centrifugal compressors, etc.).

In one disclosed embodiment, a tie bolt <NUM> extends along a rotor axis <NUM> between a first end and a second end of the tie bolt <NUM>. A first rotor shaft 104i is fixed to the first end of tie bolt <NUM>. A second rotor shaft <NUM><NUM> is fixed to the second end of tie bolt <NUM>. Rotor shafts <NUM><NUM>, <NUM><NUM> may be referred to in the art as stubs shafts. It will be appreciated that in certain embodiments more than two rotor shafts may be involved.

A plurality of impeller bodies <NUM>, such as impeller bodies 106i through <NUM>n, are disposed between rotor shafts <NUM><NUM>, <NUM><NUM>. In the illustrated embodiment, the number of impeller bodies is six and thus n=<NUM>; it will be appreciated that this is just one example and should not be construed in a limiting sense regarding the number of impeller bodies that may be used in disclosed embodiments.

A first impeller body 106i of the plurality of impeller bodies is arranged to provide a first stage of compression to a process fluid, and each subsequent impeller body provides a subsequent stage of compression to the process fluid. The embodiments respectively illustrated in <FIG> and <FIG> involve a center-hung configuration of back-to-back impeller compression stages; it will be appreciated that this configuration is just one example compressor configuration and should not be construed in a limiting sense regarding the applicability of disclosed embodiments.

In a back-to-back configuration, a given compressor may, for example, comprise a first compressor section including a portion of the plurality of impeller bodies. Each respective impeller body in the first compressor section having a respective inlet arranged to receive a flow of the process fluid in a first direction. The respective inlet of a respective impeller body is disposed opposite to a back of the respective impeller body. The compressor further comprises a second compressor section including the remainder of the plurality of impeller bodies. Each respective impeller body in the second compressor section having a respective inlet arranged to receive the flow of the process fluid in a second direction opposite the first direction. That is, the compression stages of the first compressor section are oriented opposite to the compression stages of the second compressor section. One advantage of the back-to-back configuration is its innate characteristic to reduce and substantially balance the axial thrust forces generated in the impellers of each compressor section. Since the two compressor sections are oriented in an opposite direction, the generated axial thrust forces in each section are acting in opposite directions. This may be particularly beneficial in high pressure, high density compression applications such as gas injection services where unbalanced thrust forces can be substantial.

Returning to <FIG>, the plurality of impeller bodies <NUM> is supported by tie bolt <NUM> and is mechanically coupled to one another along rotor axis <NUM> by way of a plurality of hirth couplings, such as hirth couplings <NUM><NUM> through <NUM>n-<NUM>. In the illustrated embodiment, since as noted above, the number of impeller bodies is six, then the number of hirth couplings between adjoining impeller bodies <NUM> would be five. It will be appreciated that two additional hirth couplings <NUM><NUM> and <NUM><NUM> may be used to respectively mechanically couple the impeller bodies <NUM>n, 106i with respectively abutting rotor shafts <NUM><NUM>, <NUM><NUM>. It will be appreciated that the foregoing arrangement of impeller bodies and hirth couplings is just one example and should not be construed in a limiting sense.

A plurality of respective seal elements <NUM> is arranged to respectively span (e.g., along <NUM> degrees) a circumferentially extending junction between adjoining impeller bodies to inhibit passage onto respective hirth couplings <NUM> of process fluid being processed by the compressor. Further seal elements <NUM> may be used to provide a sealing functionality between a respective abutting impeller body (e. g, impeller body <NUM><NUM>; impeller body <NUM>n) and a respective rotor shaft (e.g., rotor shaft <NUM><NUM>; rotor shaft <NUM><NUM>) of the two rotor shafts <NUM><NUM>, <NUM><NUM>. The respective impeller body 106i is mechanically coupled by hirth coupling <NUM><NUM> to the respective rotor shaft <NUM><NUM> and respective impeller body <NUM>n is mechanically coupled by hirth coupling 109i to respective rotor shaft <NUM><NUM>.

<FIG> illustrates a fragmentary cross-sectional view of one non-limiting embodiment of a disclosed rotor structure <NUM>, where the compression stages are arranged in a straight-through configuration aligned along a common direction, such as indicated by arrow <NUM>. As schematically shown in <FIG>, disclosed rotor structure <NUM> includes a respective flow loop <NUM> that is defined by an input flow section <NUM> (schematically represented by dashed lines) extending at least in part along a flow channel <NUM> formed between respective impeller bodies of the plurality of impeller bodies and a radially outward surface <NUM> of tie bolt <NUM>.

Flow loop <NUM> is further defined by a return flow section <NUM> (schematically represented by dashed and dotted lines), where at least a portion of return flow section <NUM> is defined by a flow channel <NUM> extending within tie bolt <NUM>. Flow channel <NUM> extends through an inner space defined by a bore <NUM> (<FIG>) that extends along rotor axis <NUM> within the center line of tie bolt <NUM>. Tie bolt <NUM> further defines a thru hole <NUM> (also seen in <FIG>) through the solid core of tie bolt <NUM> to establish fluid communication between input flow section <NUM> and return flow section <NUM>. In one non-limiting embodiment, thru hole <NUM> may be located between an upstream point and a downstream point of the first stage of compression (labelled <NUM>st stage in <FIG>).

In one non-limiting embodiment, input flow section <NUM> of flow loop <NUM> is fluidly coupled with a first location exposed to the process fluid and return flow section <NUM> is fluidly coupled with a second location outside any of the stages of compression. A pressure differential (Δp) between the first location and the second location establishes a flow of fluid in the flow loop.

In the disclosed rotor structure <NUM> shown in <FIG>, the first location may be disposed at the outlet of the last stage of compression (labelled <NUM>th stage in <FIG>) and the second location may be disposed in a balance piston <NUM> disposed downstream from the last stage of compression. As would be readily appreciated by one skilled in the art, a balance piston seal --in connection with balance piston <NUM>-- is commonly used to seal the high-pressure area (e.g., first location) with respect to the relatively lower-pressure area (e.g., second location) to prevent or at least reduce leakage about the tie bolt from the high-pressure area to the relatively lower-pressure area. The balance piston seal may be a labyrinth seal axially extending between a rotating portion and a stationary portion of balance piston <NUM>.

It will be appreciated that the pressure differential formed between such first location and second location is effective to have low impact on the efficiency of the compressor since the pressure differential between such locations is relatively lower compared to implementations where the pressure differential may, for example, be arranged between the first stage of compression and the last stage of compression, where a relatively larger pressure differential would be formed and in turn this would lead to a relatively larger mass flow in the flow channel/s and thus to decreased compressor efficiency.

It is noted that input flow section <NUM> is at a location that experiences the highest pressure level compared to the respective pressure levels experienced by hirth coupling locations disposed upstream from input flow section <NUM>, and thus the pressure level in flow loop <NUM> would be relatively higher compared to the respective pressure levels experienced by such upstream hirth coupling locations. Consequently, in the event of any residual leakage through any of seal elements <NUM>, the pressurized flow loop <NUM> would be effective to keep such residual leakage from entering into a respective hirth coupling, such as otherwise would enter through the outer diameter (OD) and travel onto the inner diameter (ID) of the hirth coupling. Moreover, process fluid received at input flow section <NUM>, being substantially pressurized and warm, does not contain any liquid condensate, as would likely be the case in the first stage, for example; thus avoiding trapping of condensate or moisture in internal cavities, such as internal cavities about the tie bolt.

It is further noted that the balance piston seal axially extending in piston seal <NUM> would experience a certain delta p drop along its axial length. Accordingly, the outlet of return flow section <NUM>, based on the needs of a given application, can be selectively positioned at an axial location on balance piston <NUM>, such that just sufficient pressure differential (Δp) is generated between the first location and the second location to fluidly actuate the flow loop but not so much (Δp) is generated that would result in excessive mass flow through the flow loop and in turn lead to potentially excessive internal recycle losses and lower efficiency in the given application.

<FIG> illustrates a fragmentary cross-sectional view of one non-limiting embodiment of a disclosed rotor structure <NUM>', where the plurality of impeller bodies is arranged along rotor axis <NUM> in a back-to-back configuration of a first compressor section <NUM> comprising, for example, two compression stages (labeled <NUM>st stage and <NUM>nd stage) and a second compressor section <NUM> comprising, for example, two additional compression stages (labeled 3rd stage and <NUM>th stage) that in combination form the compressor. In this example, the impellers of first compressor section <NUM> are oriented opposite to the compression stages of second compressor section <NUM>, as schematically represented by arrows <NUM> and <NUM>.

As schematically shown in <FIG>, disclosed rotor structure <NUM>' includes a respective flow loop <NUM>', conceptually analogous to flow loop <NUM> as described above in the context of <FIG>. Flow loop <NUM>' is defined by an input flow section <NUM>' (schematically represented by dashed lines) extending at least in part along a flow channel <NUM>' formed between respective impeller bodies of second compressor section <NUM> and radially outward surface <NUM> of tie bolt <NUM>.

Flow loop <NUM>' is further defined by a return flow section <NUM>' (schematically represented by dashed and dotted lines), where at least a portion of return flow section <NUM>' is defined by a flow channel <NUM>' extending within tie bolt <NUM>. That is, flow channel <NUM>' extends through the inner space of tie bolt <NUM>. In this embodiment, another portion of return flow section <NUM>' is defined by a further flow channel <NUM> defined between respective impeller bodies of first compressor section <NUM> and radially outward surface <NUM> of tie bolt <NUM>.

Without limitation, input flow section <NUM>' of flow loop <NUM>' is fluidly coupled with a first location exposed to the process fluid and return flow section <NUM>' is fluidly coupled with a second location outside any of the stages of compression. A pressure differential (ΔP) between the first location and the second location establishes a flow of fluid in the flow loop.

In this embodiment, the first location may be disposed at the outlet of the last stage of compression (labeled <NUM>th stage) of second compressor section <NUM> and the second location may be disposed in a centrally located balance piston <NUM> (also known in the art as a division wall spacer) disposed between first compressor section <NUM> and second compressor section <NUM>. As would be appreciated by one skilled in the art, a division wall seal--in connection with division wall spacer <NUM>-- is commonly used to seal the high-pressure area (e.g., first location) with respect to the relatively lower-pressure area (e.g., second location) to prevent or at least reduce leakage from the <NUM>th stage to the <NUM>nd stage and also leakage about the tie bolt from the high-pressure area <NUM>'to the relatively lower-pressure area <NUM>'.

It will be appreciated that the division wall spacer in a back-to-back compressor configuration functions conceptually analogous to the balance piston in a straight-through compressor configuration. The division wall is a non-rotating component that in part holds the division wall seal that provides sealing functionality with respect to a corresponding rotating component, which is the division wall spacer. Once again, it will be appreciated that the pressure differential formed between such first location and second location is effective to have low impact on the efficiency of the compressor since the pressure differential between such locations is relatively low compared to flow implementations where the pressure differential may, for example, be arranged between the first and the last stage of compressions, where a relatively larger pressure differential would be formed and in turn this would lead to a relatively larger mass flow in the flow channel/s and thus to decreased compressor efficiency.

This embodiment also provides at least the following advantages. As discussed above in the context of <FIG>, for example, input flow section <NUM>' is at a location that experiences the highest pressure level compared to the respective pressure levels experienced by the remaining hirth coupling locations, and thus the pressure level in flow loop <NUM>' would be relatively higher compared to the respective pressure levels experienced by such remaining hirth coupling locations. Consequently, in the event of any residual leakage through any of seal elements <NUM>, the pressurized flow loop <NUM>' would be effective to keep such residual leakage from entering into a respective hirth coupling, such as otherwise would enter through the OD and travel onto the ID of the hirth coupling. Once again, process fluid received at input flow section <NUM>', being substantially pressurized and warm, does not contain any liquid condensate. Thus, avoiding trapping of condensate or moisture in internal cavities, such as internal cavities about the tie bolt.

In this embodiment a location of thru hole <NUM> to establish fluid communication between input flow section <NUM>' and return flow section <NUM>' may be between an upstream point and a downstream point of the first stage of compression (labeled <NUM>rd stage) of second compressor section <NUM>.

Tie bolt <NUM> may define a second thru hole <NUM> disposed at a further location of tie bolt <NUM> arranged to establish fluid communication between flow channel <NUM>' extending within the tie bolt and further flow channel <NUM>. The location of second thru hole <NUM> may be between an upstream point and a downstream point of the first stage of compression (labeled <NUM>st stage) of first compressor section <NUM>.

<FIG> illustrates a zoomed-in, fragmentary cross-sectional view of one embodiment of a disclosed rotor structure <NUM>", where a respective impeller body (e.g., impeller body 106i) of the plurality of impeller bodies is in abutting relationship with rotor shaft <NUM><NUM>. In this embodiment, impeller body <NUM><NUM> includes at least one axially-extending conduit <NUM> in fluid communication with one or more cavities <NUM> disposed about the tie bolt <NUM> along rotor axis <NUM>.

At least one radially-extending conduit <NUM> is constructed through rotor shaft <NUM><NUM>. Radially-extending conduit <NUM> defines an opening <NUM> at a radially-inward surface <NUM> of rotor shaft <NUM><NUM> permitting fluid communication through a gap <NUM> about tie bolt <NUM> with axially-extending conduit <NUM>. Radially-extending conduit <NUM> defines another opening <NUM> at a radially-outward surface <NUM> of rotor shaft <NUM><NUM> that, for example, may be used to vent process fluid that may have leaked into the one or more cavities <NUM> disposed about the tie bolt along the rotor axis. The foregoing arrangement disclosed in the context of impeller body 106i and abutting rotor shaft <NUM><NUM> could alternatively be implemented in connection with impeller body <NUM>n and abutting rotor shaft 104i (<FIG>).

<FIG> illustrates a fragmentary view of one embodiment of tie bolt <NUM> including bore <NUM> (conceptually analogous to a gun bore hole) and thru hole <NUM>, which are arranged to provide fluid communication through the solid core of tie bolt <NUM>. A plug <NUM> may be used to plug bore <NUM> downstream of thru hole <NUM>.

In operation, disclosed embodiments can make use of seal elements appropriately arranged to cover the hirth couplings and effective to inhibit passage onto the respective hirth coupling of process fluid being processed by the compressor, and thus inhibiting potential exposure of the hirth couplings and associated structures to contaminants, chemical byproducts, and/or physical debris.

In operation, disclosed embodiments can make use of a flow loop that at least in part flows through the interior of the tie bolt, as described in the context of <FIG> and <FIG>. In operation the flow loop may be appropriately pressurized to keep any such residual seal leakage from travelling onto the hirth couplings.

In operation, certain disclosed embodiments can use a venting arrangement that at least in part extends through one of the rotor shafts of the rotor structure, as described in the context of <FIG>.

Claim 1:
A rotor structure (<NUM>, <NUM>) in a compressor, the rotor structure (<NUM>, <NUM>) comprising:
a tie bolt (<NUM>) ;
a plurality of impeller bodies (<NUM>) supported by the tie bolt (<NUM>);
wherein a first impeller body (<NUM>) of the plurality of impeller bodies (<NUM>) is arranged to provide a first stage of compression to a process fluid, and each subsequent impeller body (<NUM>) provides a subsequent stage of compression to the process fluid; and
a flow loop (<NUM>) being defined by an input flow section (<NUM>) extending at least in part along a flow channel (<NUM>) between respective impeller bodies (<NUM>) of the plurality of impeller bodies (<NUM>) and a radially outward surface (<NUM>) of the tie bolt (<NUM>), the flow loop (<NUM>) being further defined by a return flow section (<NUM>) (<NUM>);
characterized in that,
the tie bolt (<NUM>) having a bore (<NUM>) that extends along a rotor axis (<NUM>) and defines an inner space in fluid communication with a thru hole (<NUM>) in the tie bolt (<NUM>);
at least a portion of the return flow section (<NUM>) is defined by a flow channel (<NUM>) extending within the inner space of the tie bolt (<NUM>),
the thru hole (<NUM>) establishes fluid communication between the input flow section (<NUM>) and the return flow section (<NUM>).