Patent Description:
Turbomachines, such as but not limited to centrifugal and axial compressors require rotary seals to prevent or limit fluid leakages towards the bearings or towards the environment.

A variety of shaft sealing devices have been developed for this purpose, among which labyrinth seals, oil fill seals, mechanical contact seals, and dry gas seals. <CIT> discloses a shaft seal assembly. <CIT> discloses an annular seal apparatus. <CIT> discloses a seal for a pump shaft.

Dry gas seals comprise a stationary ring and a rotating ring adapted to rotate integrally with the shaft. Dry seal gas, which is typically the same process gas flowing through the rotary equipment, is injected in the seal to provide a barrier against gas leakage. Most of the dry seal gas flows across an inboard labyrinth seal back into the machine, and a minor part of the dry seal gas flows as a primary or secondary vent from the dry gas seal and is either recovered or flared.

While providing excellent sealing properties, dry gas seals are not free of drawbacks, such as, for example, the need to provide seal gas also while the rotary equipment is at stillstand. Moreover, the flowrate of the vented seal gas is relatively high, which may result in severe environmental impact or loss of valuable gaseous components, if the vented seal gas is not recovered.

Attempts to overcome the drawbacks have been made, using stationary porous sealing members co-acting with rotary sealing members. Pressurized seal gas is fed to the porous sealing member and migrates thereacross towards an interface between the stationary porous sealing member and the rotating sealing member. These sealing assemblies using porous sealing members suffer from some drawbacks. In particular the small length of the flow path of the leak causes relatively high leak rate.

It would therefore be desirable to provide sealing assemblies using porous sealing members, which overcome or alleviate at least some of the drawbacks and limitations of the seal assemblies of the prior art.

A shaft seal assembly is disclosed, which is configured to sealingly separate a high-pressure region and a low-pressure region in a rotary equipment, such as a compressor or another turbomachine. As used herein, the term rotary equipment may include any machinery having an outer casing and a shaft supported for rotation in the casing. The shaft seal assembly includes a rotary seal member adapted to be drivingly coupled to a rotary shaft for co-rotation therewith, and a stationary porous seal member adapted to be coupled to a stationary housing of the rotary equipment and extending around the rotary seal member. The shaft seal assembly further includes at least one seal gas inlet port adapted to deliver pressurized seal gas to the stationary porous seal member. The rotary seal member has a conical outer sealing surface (i.e. a convex conical sealing surface) and the stationary porous seal member has a conical inner sealing surface (i.e. a concave conical sealing surface). The conical inner sealing surface faces the conical outer sealing surface.

In currently preferred embodiments disclosed herein, each of the above mentioned conical outer sealing surface and conical inner sealing surface has a respective first end adapted to face the high-pressure region and a second end adapted to face the low-pressure region, when the shaft seal assembly is mounted in the rotary equipment. Each said first end has a diameter larger than the corresponding second end.

Further features and embodiments of the seal assembly will be described below and are set forth in the attached claims.

According to a further aspect, disclosed herein is a rotary equipment, such as for example a turbomachine, wherein a high-pressure region and a low-pressure region shall are sealingly separated from one another. At least one or more shaft seal assemblies as outlined above can be arranged along the rotary shaft between the high-pressure region and the low-pressure region.

Reference is now made briefly to the accompanying drawings, in which:.

The following description refers specifically to turbomachines and more specifically to dynamic compressors, such as axial or centrifugal compressors, and pumps. It shall however be understood that novel features of the present disclosure can be used with advantage to provide efficient shaft sealing in other kinds of rotary equipment, such as turbines, expanders, and other rotating machinery where a high-pressure side or region and a low-pressure side or region shall be sealingly separated from one another.

To provide efficient sealing along a rotary shaft in a turbomachine, a new seal assembly for use in rotary equipment has a rotary conical surface that co-acts with a stationary conical surface, i.e. a non-rotating conical surface. The stationary conical surface surrounds the rotary conical surface. The stationary conical surface is formed in a porous body, through which pressurized seal gas can flow. A gap or space between the stationary conical surface and the rotary conical surface forms under the combined action of the pressurized seal gas and a resilient axial force applied on the stationary conical surface.

With "axial force" a force is understood, which is oriented in the direction of a geometrical axis of the stationary conical surface and of the rotary conical surface. Said axis is substantially coincident with the rotation axis of the shaft, on which the seal assembly is mounted.

The resilient axial force is oriented to push the stationary conical surface against the rotary conical surface in a direction of the rotation axis of the rotary shaft of the turbomachine. This achieves an efficient separation between the high-pressure region and the low-pressure region with a minimum flowrate of seal gas.

Turning now to the drawings, <FIG> schematically illustrates a turbomachine <NUM>, for instance a centrifugal compressor, comprising a casing <NUM> and a rotary shaft <NUM> supported for rotation in the casing <NUM>. Impellers <NUM> rotate with the rotary shaft <NUM> around a rotation axis A-A of the rotary shaft <NUM>. Process gas flows to the compressor <NUM> through a suction side <NUM> fluidly coupled to an inlet line <NUM>. Pressurized process gas is delivered by the compressor <NUM> at a delivery side <NUM> and flows in an outlet line <NUM>.

The rotary shaft <NUM> is supported by bearings, schematically shown at <NUM> and <NUM>. Seal assemblies <NUM> and <NUM> are arranged along the rotary shaft <NUM>, inboard the bearings <NUM> and <NUM>, to prevent process gas from leaking along the rotary shaft <NUM> through the bearings <NUM>, <NUM> and towards the environment. In further embodiments, not shown, additional seal assemblies can be arranged between adjacent compressor stages inside the casing <NUM>.

<FIG> illustrates an embodiment of the seal assembly <NUM> of the present disclosure. The seal assembly <NUM> can be configured in substantially the same way as the seal assembly <NUM>.

In general terms, the seal assembly <NUM> is arranged between a high-pressure region HP and a low pressure region LP, for instance between the most upstream compressor stage and the bearing <NUM>, or between the most downstream compressor stage and the bearing <NUM>.

In embodiments, the seal assembly <NUM> comprises a rotary seal member <NUM> constrained, i.e., connected to the rotary shaft <NUM> for rotation therewith and to avoid axial displacements of the rotary seal member <NUM> along the rotary shaft <NUM>. As understood herein, "constrained to the rotary shaft" means that the rotary seal member <NUM> rotates with the shaft <NUM> as a single body. Connection, i.e., fastening of the rotary seal member <NUM> to the rotary shaft <NUM> can be obtained in any suitable manner, for instance by welding, slip fitting, friction fitting, adhesive, or the like. In other embodiments, connection of the rotary seal member <NUM> to the rotary shaft <NUM> can also be obtained with screws, pins, clamps, keys, tabs, splined profiles, or the like. By way of non-limiting example, in <FIG> the mechanical connection between rotary shaft <NUM> and rotary seal member <NUM> is schematically represented by screws <NUM>.

The rotary seal member <NUM> includes a shaft sleeve, having a cylindrical through hole for the rotary shaft <NUM>, and a conical outer surface <NUM>, i.e. a conical male surface. The conical outer surface <NUM> is coaxial to shaft <NUM>, i.e. the axis whereof coincides with the rotation axis A-A of the rotary shaft <NUM> and of the compressor rotor. The conical outer surface <NUM> surrounds an inner cylindrical surface <NUM> of the rotary seal member <NUM>. One or more stationary seal members, such as O-rings <NUM>, can be positioned between the inner cylindrical surface <NUM> and the rotary shaft <NUM>.

The conical outer surface <NUM> of the rotary seal member <NUM> extends from a first end facing the high-pressure region HP to a second end facing the low-pressure region LP. The conical outer surface <NUM> has a circular cross-section with a variable diameter. The first end which faces the high-pressure region HP has a diameter larger than the second end, i.e., the ideal vertex of the conical outer surface <NUM> is located opposite the high-pressure region HP. In other, currently less preferred embodiments the position of the conical outer surface <NUM> with respect to the high-pressure region and the low pressure region can be reversed; i.e. the large-diameter end of the conical outer surface <NUM> can face the low-pressure region and the small-diameter end of the conical outer surface <NUM> can face the high-pressure region.

The seal assembly <NUM> further includes a stationary porous seal member <NUM>, which is substantially co-axial to the rotary seal member <NUM>. As understood herein, "substantially coaxial" means that the stationary porous seal member <NUM> and the rotary seal member <NUM> are coaxial within acceptable mechanical tolerances. These may vary depending upon the specific application. In general terms, the mutual position of the geometrical axes of the conical surfaces of the rotary seal member <NUM> and of the stationary porous seal member <NUM> may depart from a strict coaxial condition both in terms of eccentricity, as well as in terms of mutual inclination. The eccentricity of the two axes may be within a range from <NUM>% to <NUM>% of the maximum diameter of the mutually facing conical surfaces. The parallelism error, i.e., the angular offset may be between <NUM>° and <NUM>°, preferably between <NUM>° and <NUM>° or less, for instance.

The term "stationary" as used herein means that the stationary porous seal member <NUM> is not rotating with the rotary shaft <NUM> around the rotation axis A-A. The stationary porous seal member <NUM> may, however, vibrate or oscillate around a stationary position. For instance, the stationary porous seal member <NUM> may perform limited angular displacements within a range of <NUM>°-<NUM>° or less, due to mechanical tolerances.

Moreover, the stationary porous seal member <NUM> may perform limited displacements in the axial direction, i.e., in a direction parallel to the rotation axis A-A of the rotary shaft <NUM>. The axial displacement may be caused by thermal expansion of the turbomachinery. The displacement may range from <NUM> to <NUM>, for instance, and generally depends upon the length of the axis of the turbomachine.

Additionally, as will be described in greater detail later on, the stationary porous seal member <NUM> is adapted to perform small movements with respect to the rotatory seal member <NUM> in the direction of the rotation axis A-A of the rotary shaft <NUM>, to form a gap between the conical inner surface of the stationary porous seal member <NUM> and the conical outer surface <NUM> of the rotary seal member <NUM>, to prevent mutual contact therebetween when the rotary shaft <NUM> is rotating. This mutual displacement between opposite facing conical surfaces may be in the range between <NUM> micrometer and <NUM> micrometers or less, for instance between <NUM> micrometer and <NUM> micrometers or less, preferably less than <NUM> micrometers, even more preferably less than <NUM> micrometers.

The stationary porous seal member <NUM> can include a body of porous material, for instance made of a sintered material. In embodiments, the sintered material can be selected among carbon, graphite, alumina, tungsten carbide, or the like. In other embodiments, the body of porous material can be manufactured by additive manufacturing, with a suitable porous structure.

In the embodiment of <FIG>, the stationary porous seal member <NUM> is entirely formed of porous material, but in other embodiments, not shown, for instance if the stationary porous seal member <NUM> is manufactured by additive manufacturing, the stationary porous seal member <NUM> may include porous and non-porous regions.

In the present description and in the attached claims, the term "porous" referred to the stationary porous seal member <NUM> means that seal gas which is injected in the seal will migrate through the stationary seal member <NUM> under a pressure differential.

In the embodiment of <FIG>, the stationary porous seal member <NUM> includes a conical female surface <NUM>, i.e., a conical inner surface <NUM>. The conical inner surface <NUM> surrounds the conical outer surface <NUM> of the rotary seal member <NUM>, i.e. extends around the rotary seal member <NUM>, and is substantially coaxial therewith, in the sense defined above. In use, a gap <NUM> forms between the conical inner surface <NUM> and the conical outer surface <NUM> as will be explained here below.

The conical inner surface <NUM> of the stationary porous seal member <NUM> extends from a first end facing the high-pressure region HP to a second end facing the low-pressure region LP. The conical inner surface <NUM> has a circular cross-section with a variable diameter, the first end having a diameter larger than the second end, i.e. the ideal vertex of the conical inner surface <NUM> is located opposite the high-pressure region HP. In other, currently less preferred embodiments, the large-diameter end of the conical inner surface <NUM> faces the low-pressure region and the small-diameter end of the conical inner surface <NUM> faces the high-pressure region.

In the embodiment of <FIG> the stationary porous seal member <NUM> is housed in an annular housing <NUM> which surrounds the stationary porous seal member <NUM> and the rotary seal member <NUM>. The stationary porous seal member <NUM> has an external surface in sealing contact with the annular housing <NUM>. In the embodiment of <FIG> the external surface of the stationary porous seal member <NUM> includes a main cylindrical outer surface <NUM> coaxial with the conical inner surface <NUM>, and two end planar surfaces <NUM>, <NUM>. The main cylindrical outer surface <NUM> and the end planar surfaces <NUM>, <NUM> are in sealing contact with the inner surface of the annular housing <NUM>. In this way pressurized seal gas delivered to the stationary porous seal member <NUM> will be prevented from leaking through the side surfaces <NUM>, <NUM>, <NUM>.

The annular housing <NUM> comprises at least one seal gas inlet port <NUM>. In preferred embodiments, a plurality of seal gas inlet ports <NUM> are distributed annularly around the rotation axis A-A of the rotary shaft <NUM>. In preferred embodiments, the seal gas inlet ports <NUM> are distributed with a constant angular pitch around the rotation axis A-A. The seal gas inlet ports <NUM> are arranged adjacent or near the end of the stationary porous seal member <NUM> that faces the high-pressure side, and opposite the end of the conical inner surface <NUM> that faces the low-pressure side.

In the embodiment shown, the stationary porous seal member <NUM> is resiliently biased in an axial direction, i.e., in the direction of the geometrical axis of the conical surfaces <NUM>, <NUM>, such that the conical inner surface <NUM> is forced against the conical outer surface <NUM>.

In some embodiments, an elastic member pushes the stationary porous seal member <NUM> against the rotary seal member <NUM>. In embodiments, the elastic member may include one or more resilient elements, such as compression springs. In <FIG> the elastic member includes a plurality of compression springs <NUM> arranged around the axis A-A. In the embodiment of <FIG> the springs <NUM> are arranged between the annular housing <NUM> and a ring casing <NUM>, in which the annular housing <NUM> is arranged. The ring casing <NUM> can be fixedly mounted in the casing <NUM> of the compressor <NUM>.

As shown in <FIG>, the axial extension of the annular housing <NUM> is less than the axial extension of an inner seat <NUM> formed in the ring casing <NUM>, in which the annular housing <NUM> is slidingly housed. In this way, sufficient axial clearance exists between the annular housing <NUM> and the ring casing <NUM>, allowing the annular housing <NUM> to move in an axial direction, i.e. in the direction of the rotation axis A-A of the rotary shaft <NUM>. In inoperative conditions, when no pressurized seal gas is delivered to the seal assembly <NUM>, the springs <NUM> push the stationary porous seal member <NUM> in a rest position in abutment against the rotary seal member <NUM>. In the rest position the conical inner surface <NUM> contacts the conical outer surface <NUM>.

The radial dimension of the ring casing <NUM> is such that a radial clearance is available between the annular housing <NUM> and the ring casing <NUM>, as shown in <NUM>.

Balancing gaskets <NUM>, <NUM> are arranged between the annular housing <NUM> and the ring casing <NUM>. The gaskets <NUM>, <NUM> allow some degree of axial and radial displacements of the annular housing <NUM> inside the seat <NUM> of the ring casing <NUM>.

At least one aperture <NUM> in the ring casing <NUM> is fluidly coupled directly or indirectly to a source of pressurized seal gas and is adapted to deliver pressurized seal gas towards the seal gas inlet ports <NUM>. The source of pressurized seal gas can be any source of sufficiently clean gas at a pressure higher than the pressure in the high-pressure region HP. In some embodiments, the pressurized seal gas can be process gas diverted from the delivery side of the compressor <NUM> and suitably pre-treated in a pretreatment unit <NUM>, as schematically shown in <FIG>, for instance. In other embodiments, a dedicated seal gas source can be foreseen for this purpose, for instance, a nitrogen source.

In use, pressurized seal gas is delivered through aperture <NUM> in the ring casing <NUM> and is forced to enter the seal gas inlet ports <NUM>. The porous structure of the stationary porous seal member <NUM> causes pressurized seal gas to migrate therethrough and leak from the conical inner surface <NUM>. The pressure of the seal gas generates a hydrostatic lift with an axial component that counter-acts the elastic force of the elastic member <NUM> (springs <NUM>). The hydrostatic lift is sufficient to displace the stationary porous sealing member <NUM> in the direction of the rotation axis A-A with respect to the rotary sealing member <NUM>. Due to said axial displacement the gap <NUM> is formed between the conical inner surface <NUM> and the conical outer surface <NUM>. The dimension of the conical gap <NUM> is determined by the balance between the hydrostatic force generated by the pressurized seal gas, the axial thrust applied by the elastic member <NUM>, as well as the force acting on the axially displaceable stationary porous seal member <NUM> and resulting from the differential pressure between the high-pressure region HP and the low-pressure region LP.

The axial clearance in the ring casing <NUM> allows the axial housing <NUM> to move in the axial direction against the elastic thrust of the elastic member <NUM>. The gaskets <NUM> and <NUM> prevent gas leakages between the ring casing <NUM> and the annular housing <NUM>, and the stationary porous seal member <NUM> can thus "float" on the rotary seal member <NUM> due to the hydrostatic thrust generated by the pressurized seal gas migrating through the porous structure of the stationary porous seal member <NUM>.

The porous structure of the stationary porous seal member <NUM> causes a gradual loss of pressure of the pressurized seal gas migrating through the porous structure from the seal gas inlet ports <NUM> towards the conical inner surface <NUM>. <FIG> illustrates isobaric lines, representing the seal gas pressure variation inside the porous structure of the stationary porous seal member <NUM>. The pressure decreases from the first end (facing the high-pressure region HP) towards the second end (facing the low-pressure region LP) of the conical inner surface <NUM> and the conical outer surface <NUM>. A part of the seal gas escaping the gap <NUM> leaks towards the high-pressure region HP, i.e., inside the compressor <NUM>, and the remaining part of the seal gas flows towards the low pressure side. A vent, not shown, can be provided to collect the seal gas escaping towards the low-pressure region, preventing dispersion of the de-pressurized seal gas towards the environment. In some embodiments, a further seal can be positioned between the sealing assembly <NUM> and the outboard bearing <NUM> and a separation gas can be delivered between the sealing assembly <NUM> and the outboard bearing <NUM>, to prevent seal gas from contacting the bearing <NUM>.

During stillstand of the compressor <NUM> no pressurized seal gas through the seal assembly <NUM>, <NUM> is required, which avoids the need for a continuous seal gas delivery, as conversely required by dry gas seals of the current art. This is achieved by the multiplying effect of the contact pressure between the two mating members <NUM> and <NUM> due to the slope of the conical inner surface <NUM> and conical outer surface <NUM>.

The axial and radial clearance around the annular housing <NUM> compensates for the wear of the porous material forming the stationary porous seal member <NUM>. Moreover, the axial and radial clearance allows axial and radial displacements of the seal assembly, which may be caused by radial and axial displacements of rotary shaft <NUM>, for instance due to thermal expansion.

In the embodiment of <FIG> the axial and radial displacements of the annular housing <NUM> and of the stationary porous seal member <NUM> housed therein are allowed by the capability of gaskets <NUM>, <NUM> to deform. However, if larger radial and axial displacements of the stationary porous seal member <NUM> are required or desirable, separate gaskets adapted to allow radial and axial movements can be used. An embodiment of a seal assembly, which is capable of allowing larger radial and axial displacements is shown in <FIG>. The same reference numbers designate parts corresponding to those of <FIG>. These parts will not be described again in detail.

In the embodiment of <FIG>, the stationary porous seal member <NUM> is rigidly constrained in the annular housing <NUM> in a way similar to <FIG>. Differently from the embodiment of <FIG>, in <FIG> an intermediate annular component <NUM> is provided between the ring casing <NUM> and the annular housing <NUM>, with the stationary porous seal member <NUM> housed therein. The annular housing <NUM> is arranged in the intermediate annular component <NUM> with a radial clearance. Annular balancing gaskets <NUM>, <NUM> seal the gap between the annular housing <NUM> and the intermediate annular component <NUM>, allowing a radial displacement of the former inside the latter, to compensate for radial movements of the rotary shaft <NUM>.

The intermediate annular component <NUM> is housed in the seat <NUM> formed by the ring casing <NUM> with an axial clearance, i.e., a space allowing displacements of the unit including the stationary porous seal member <NUM>, the annular housing <NUM> and the intermediate annular component <NUM> in the direction of the rotation axis A-A of the rotary shaft <NUM>. Annular balancing gaskets <NUM>, <NUM> seal the gap between the intermediate annular component <NUM> and the ring casing <NUM>, allowing axial displacements therebetween. Therefore, the stationary porous seal member <NUM> can lift from the rotary seal member <NUM> due to the hydrostatic thrust generated by the pressurized seal gas injected in the seal assembly through apertures 67A and 67B, said gas migrating through the porous structure of the stationary porous seal member <NUM>.

The apertures 67A and 67B in the ring casing <NUM> and in the intermediate annular component <NUM> feed pressurized seal gas to the seal gas inlet ports <NUM>. As mentioned above, the seal gas can be pressurized process gas diverted from the deliver side of the compressor <NUM>. Alternatively or in addition, a separate source of pressurized seal gas can be foreseen.

The seal gas migrating through the porous structure of the stationary porous seal member <NUM> generates a hydrostatic thrust, which is sufficient to displace the stationary porous seal member <NUM> and the rotary seal member <NUM> one with respect to the other in the direction of rotation axis A-A of the shaft <NUM>, thus forming the gap <NUM>. As in the embodiment of <FIG> described above, the value of the thrust required to lift the stationary porous seal member <NUM> from the rotary seal member <NUM> depends upon the differential pressure across the seal assembly and upon the total biasing force applied by the elastic member <NUM> (e.g. spings <NUM>).

By providing separate sets of gaskets <NUM>, <NUM> and <NUM>, <NUM>, larger axial and radial displacements of the stationary porous seal member <NUM> with respect to the rotary seal member <NUM> are possible.

Some or all the surfaces of the above-described seal assembly can be provided with a hardened coating, to reduce wear of surfaces in mechanical contact. In some embodiments, hardening can be provided on the conical outer surface <NUM> of the rotary seal member <NUM> and/or on the conical inner surface <NUM> of the stationary porous seal member <NUM>. In addition or alternatively, some surfaces or surface portions of the members of the seal assembly which are in mutual sliding contact can be hardened, such as in the areas labeled <NUM> and <NUM> in <FIG>. In some embodiments hardness above <NUM> HRC, preferably above <NUM> HRC or higher can be envisaged. Any known hardening technique adapted to achieve the desired hardness value can be used. For instance, suitable hardening techniques include nitriding, tungsten/chromium carbide coatings or the like.

In some embodiments an anelastic feature can be positioned between adjacent components which may perform mutual displacements in radial direction, e.g. due to vibrations induced by rotation of the compressor <NUM>. For instance, an anelastic feature, such as an anelastic coating <NUM>, can be arranged between the outer surface of the annular housing <NUM> and the intermediate annular component <NUM>. The anelastic feature <NUM> is adapted to damp vibrations arising during rotation of the rotary shaft <NUM>, and thus reduce noise and wear.

Claim 1:
A shaft seal assembly (<NUM>,<NUM>) configured to sealingly separate a high-pressure region and a low-pressure region in a rotary equipment (<NUM>), the shaft seal assembly comprising:
a rotary seal member (<NUM>) adapted to be drivingly coupled to a rotary shaft (<NUM>) of the rotary equipment for co-rotation therewith;
a stationary porous seal member (<NUM>) adapted to be coupled to a stationary housing of the rotary equipment and extending around the rotary seal member (<NUM>); and
at least a seal gas inlet port (<NUM>) adapted to communicate a pressurized seal gas to the stationary porous seal member (<NUM>);
characterised in that
the rotary seal member (<NUM>) has a conical outer sealing surface (<NUM>) and the stationary porous seal member (<NUM>) has a conical inner sealing surface (<NUM>), wherein the conical inner sealing surface (<NUM>) faces the conical outer sealing surface (<NUM>).