Patent Description:
<CIT> discloses a rotor structure that has a first stub shaft that is connected through a flange-like interface to a first impeller. The rotor structure comprises further impellers stacked in an axial direction on the first impeller. Each impeller has a central passage through that a tie rod is guided. At its end neighboring the first stub shaft a nut is affixed to a threaded region of the tie rod, wherein the nut axially tensions the plurality of impellers. An axial end of the tie rod is received in a cavity of the first impeller. The stub shaft is a massive part and the tie rod does not penetrate there through. A similar rotor structure is disclosed in document <CIT>.

<CIT> discloses a gas recovery system of a turbocompressor having a seal portion between a stator and a rotor. The seal comprises a multi-labyrinth-seal arrangement with first, second, third and fourth labyrinth seals. Between the first labyrinth seal and a neighboring first dry gas seal a first space is formed that is fluidically connected to a channel that supplies pressurized process gas to the first space so that a leakage of process gas through the first labyrinth seal is avoided or at least reduced. Axially neighboring to the first space a second space is formed that at one axial end is sealed by said first dry gas seal and at the other axial end is sealed by a second labyrinth seal. The second space is fluidically connected to a channel that feeds process gas leaking through the first dry gas seal to a gas recovery system. Consequently, the sealing system disclosed therein is arranged between a stationary part and a rotating part, i.e. relates to dynamic seals.

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.

As would be appreciated by those skilled in the art, turbomachinery involving rotors of tie bolt construction (also known in the art as thru bolt or tie rod construction) need to be sealed so that a process fluid (which could be flammable or otherwise hazardous) and which is pressurized by a turbomachine (e.g., a compressor) is inhibited from escaping to the atmosphere. In certain known rotor structures, this sealing is typically done using one or more seals (e.g., O-rings) disposed between the tie-bolt and the bore of a shaft section of the rotor. A respective O-ring may thus be subject to the process fluid internal pressure on one side and to atmospheric pressure on the other side. The present inventors have recognized that such known rotor structures lack features that would allow monitoring an incipient leakage of the process fluid about the tie bolt. Additionally, such known rotor structures lack features that would allow conveying a sealing fluid (such as a dry sealing fluid) about the tie bolt.

Disclosed embodiments make use of an innovative venting/sealing arrangement providing reliable and cost-effective venting/sealing backups and/or venting/sealing redundancies, such as with features that may be effective for venting about the tie bolt so that, for example, an incipient leakage of the process fluid can be monitored and in turn malfunctioning seals can be appropriately and timely replaced before escalating to an undesirable condition. The venting may be carried out by way of a conduit --drilled or otherwise constructed through a stub shaft-- that under certain operational conditions effectively functions as a vent. Additionally, such features may be effective for conveying an appropriately pressurized sealing fluid about the tie bolt effective for reducing the likelihood of the process fluid escaping to the atmosphere. The conveying of the sealing fluid to the tie bolt may be carried out by way of another conduit -- similarly drilled or otherwise constructed through the stub shaft-- that under certain operational conditions effectively permits conveying the sealing fluid to the tie bolt.

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>, as may be used in industrial applications involving turbomachinery, such as without limitation, compressors (e.g., centrifugal compressors, etc.).

According to the invention, a tie bolt <NUM> extends axially between a pressurized (e.g., relatively high pressure) process side and an atmospheric pressure side of the turbomachine. As would be readily appreciated by one skilled in the art, a stub shaft <NUM><NUM> is fixed to a first end of tie bolt <NUM>. A second stub shaft <NUM><NUM> is fixed to a second end of tie bolt <NUM>. Second end of tie bolt <NUM> is axially opposite the first end of tie bolt <NUM>.

The description will proceed in connection with a first venting/sealing arrangement arranged proximate the first end of tie bolt <NUM>, as illustrated in <FIG>. As would be appreciated by one skilled in the art, a second venting/sealing arrangement is arranged proximate the second end of tie bolt <NUM>. Since the first and second venting/sealing arrangements comprise identical structural and/or operational relationships in order to avoid pedantic and burdensome repetition the description will proceed in connection with just the first venting/sealing arrangement arranged proximate the first end of tie bolt <NUM>, as illustrated in <FIG>. Essentially, the first and second venting/sealing arrangements would exhibit structural symmetry with respect to one another about a radial plane <NUM> that cuts the longitudinal axis of the turbomachine.

According to the invention, a plurality of axially spaced apart annular seals <NUM>, such as annular seals <NUM><NUM>, <NUM><NUM> through <NUM>n (e.g., O-rings) may be arranged about a segment of tie bolt <NUM> in correspondence with a radially-inward segment <NUM> of respective stub shaft <NUM>. In <FIG>, the number of illustrated annular seals is equal to <NUM> and so in this example n=<NUM>. It will be appreciated that the foregoing should be construed as one non-limiting example.

It will be further appreciated that each respective neighboring seal pair of the plurality of axially spaced apart annular seals <NUM> defines sealing sides of a respective chamber <NUM> of a plurality of axially sequential chambers, such as chambers <NUM><NUM>, <NUM><NUM>, as seen in <FIG>, disposed between the process side and the atmospheric pressure side of the turbomachine. In the foregoing example, four axially sequential chambers would be defined by annular seals <NUM><NUM>, <NUM><NUM> through <NUM><NUM>. For the sake of simplicity of illustration just two of such chambers are shown in <FIG>.

In the general case, the relationship that defines the number of chambers formed by an n number of annular seals is n-<NUM>. Accordingly, if the number of annular seals is <NUM>, then the number of chambers is n - <NUM> = <NUM>.

A plurality of conduits <NUM>, such as conduits <NUM><NUM>, <NUM><NUM> through <NUM>n-<NUM> (e.g., drilled or otherwise constructed through the tie bolt) extend from a radially-outward segment <NUM> of the respective stub shaft <NUM> through the stub shaft to communicate with the plurality of axially sequential chambers <NUM> disposed between the process side and the atmospheric side of the turbomachine. In the foregoing example, four conduits would communicate with the four chambers defined by annular seals <NUM><NUM>, <NUM><NUM> through <NUM><NUM>.

According to the invention, the plurality of conduits <NUM> alternates between a first conduit <NUM><NUM> fluidly coupled at the radially-outward segment of the respective stub shaft <NUM> to receive a sealing fluid and a second conduit <NUM><NUM> fluidly connected at the radially-outward segment of the respective stub shaft to a venting outlet. It will be appreciated that the source of the sealing fluid and the venting outlet may be obtained by way of a dry fluid seal system <NUM>, such as is commonly used in process gas centrifugal compressors. Without limitation, dry fluid seal system <NUM> may involve a tandem seal configuration involving stationary and rotatable sealing elements. As would be appreciated by one skilled in the art, dry fluid seal system <NUM> may be disposed about the radially-outward segment <NUM> of the respective stub shaft <NUM> and, as noted above, may be used as the source of the sealing fluid and may be further used to provide a venting mechanism to a flow that may comprise the incipient leakage of the process fluid.

In one non-limiting embodiment, a plurality of impeller stages <NUM> (just one is illustrated in <FIG>) may be disposed between stub shafts <NUM><NUM> and <NUM><NUM>. The plurality of impeller stages being supported by tie bolt <NUM> using any affixing technique appropriate for a given application. In one non-limiting embodiment, respective joint structures <NUM> may be arranged to couple contiguous impeller stages to one another. In one non-limiting embodiment, the respective joint structures <NUM> may, without limitation, comprise joining/stacking rotating elements, such as Hirth joint structures, Gleason curvic joints, and piloted rabbet or spigot-fit joints, each of which, as would be appreciated by one skilled in the art may center parts and transmit load but may also leak gas through the joint area.

In one non-limiting embodiment, a computerized leakage monitor <NUM> may be coupled to second conduit/s (e.g., venting conduits <NUM><NUM>,<NUM><NUM>, etc.) to monitor a presence of any incipient leakage of process fluid in any of such venting conduits.

<FIG> respectively illustrate zoomed-in views of a portion of the cross-sectional view shown in <FIG> that may be used for illustrating and describing certain non-limiting structural and/or operational relationships of features in the disclosed rotor structure.

<FIG> illustrates an example where annular seals <NUM><NUM>, <NUM><NUM> and <NUM><NUM> are intact. That is, no seal malfunction is present in any of the annular seals. In this case, no fluid flow would develop in conduits <NUM><NUM> and <NUM><NUM>. This is essentially a static condition.

illustrates an example where annular seal <NUM><NUM> is broken and annular seals <NUM><NUM> and <NUM><NUM> are intact. That is, a seal malfunction is present in annular seal <NUM><NUM>. In this case, pressurized process fluid would pass through malfunctioning annular seal <NUM><NUM> into chamber <NUM><NUM>; pressurized sealing fluid would flow into chamber <NUM><NUM> and this would be effective to inhibit further progress of the pressurized process fluid in chamber <NUM><NUM>, provided the internal pressure of the sealing fluid is relatively larger compared to the internal pressure of the process fluid passing into chamber <NUM><NUM>.

illustrates an example where annular seal <NUM><NUM> is broken and annular seals <NUM><NUM> and <NUM><NUM> are intact. That is, a seal malfunction is present in annular seal <NUM><NUM>. In this case, sealing fluid would pass through malfunctioning annular seal <NUM><NUM> and into chamber <NUM><NUM>, effectively forming a fluid buffer zone overlapping chambers <NUM><NUM> and <NUM><NUM> with venting through conduit <NUM><NUM>.

illustrates an example where annular seals <NUM><NUM> and <NUM><NUM> are broken and annular seal <NUM><NUM> is intact. That is, seal malfunctions are present in annular seals <NUM><NUM> and <NUM><NUM>. In this case, sealing fluid mixed with pressurized process fluid would pass through malfunctioning annular seal <NUM><NUM> and this mixture would be vented through conduit <NUM><NUM>. In this example, this mixture would not advance beyond chamber <NUM><NUM>.

In one non-limiting embodiment, the alternating chambers <NUM><NUM>, <NUM><NUM> through <NUM>n-<NUM> include at least one backup first chamber (e.g., the chamber connected to first conduit <NUM><NUM> fluidly coupled to receive the sealing fluid) relative to the first chamber <NUM><NUM>, which is disposed downstream of the backup chamber connected to first conduit <NUM><NUM>. (The term downstream is indicative of the direction of process fluid flow between the pressurized process side and the atmospheric pressure side of the turbomachine). Similarly, the alternating chambers <NUM><NUM>, <NUM><NUM> through <NUM>n-<NUM> includes at least one backup second chamber (e.g., the chamber connected to second conduit <NUM><NUM> fluidly coupled for venting) relative to a second chamber <NUM><NUM> disposed downstream of the chamber connected to second conduit <NUM><NUM>. It will be appreciated that the first chamber (e.g., chamber <NUM><NUM>) and the backup first chamber (e.g., chamber <NUM><NUM>) is each independently arranged to receive sealing fluid, and the second chamber (e.g., chamber <NUM><NUM>) and the backup chamber (e.g., chamber <NUM><NUM>) is each independently arranged to permit venting, such as discussed in the context of the foregoing examples.

In operation, for example, when one or more annular seals malfunctions in a respective neighboring seal pair of the plurality of annular seals <NUM><NUM>, <NUM><NUM> through <NUM>n, and the malfunction of the one or more annular seals leads to incipient leakage of process fluid, a first fluid flow may be established through the first conduit/s (e.g., conduits <NUM><NUM>,<NUM><NUM>) to convey sealing fluid into the respective chamber in communication with the first conduit/s, and/or a second fluid flow is established through the second conduit/s (e.g., conduits <NUM><NUM>,<NUM><NUM>) to permit venting of the respective chamber in communication with the second conduit/s.

In operation, disclosed embodiments make use of innovative venting/sealing arrangements effective for venting the tie bolt rotor so that, for example, an incipient leakage of the process fluid can be monitored. Additionally, in operation disclosed embodiments are effective to, for example, convey to the tie bolt rotor a pressurized sealing fluid effective for reducing the likelihood of process fluid escaping to the atmosphere.

Claim 1:
A rotor structure (<NUM>) for a turbomachine, the rotor structure comprising:
a tie bolt (<NUM>) that extends axially between a pressurized process side and an atmospheric pressure side of the turbomachine;
a respective stub shaft (<NUM><NUM>) fixed to a first end of the tie bolt;
the rotor structure being characterised by
a first venting/sealing arrangement comprising:
a plurality of axially spaced apart annular seals (<NUM>) arranged about a segment of the tie bolt in correspondence with a radially-inward segment (<NUM>) of the respective stub shaft (<NUM><NUM>), wherein each respective neighboring seal pair of the plurality of axially spaced apart annular seals (<NUM>) defines sealing sides of a respective chamber (<NUM>) of a plurality of axially sequential chambers (<NUM>) disposed between the process side and the atmospheric pressure side of the turbomachine; and
a plurality of conduits (<NUM>) extending from a radially-outward segment (<NUM>) of the respective stub shaft (<NUM><NUM>) through the stub shaft to communicate with the plurality of axially sequential chambers (<NUM>) disposed between the process side and the atmospheric pressure side of the turbomachine, the plurality of conduits (<NUM>) alternating between a first conduit (<NUM><NUM>) fluidly coupled at the radially-outward segment of the respective stub shaft to receive a sealing fluid and a second conduit (<NUM><NUM>) fluidly connected at the radially-outward segment of the respective stub shaft (<NUM><NUM>) for venting,
wherein, in response to flow of an incipient leakage of a process fluid through one or more of the plurality of axially spaced apart annular seals (<NUM>), a first fluid flow is established through the first conduit (<NUM><NUM>) to convey sealing fluid into the respective chamber (<NUM>) in communication with the first conduit (<NUM><NUM>), and/or a second fluid flow is established through the second conduit (<NUM><NUM>) to permit venting of the respective chamber (<NUM>) in communication with the second conduit (<NUM><NUM>).