Patent Application
20070132193
The invention relates generally to rotary machines, and in particular to a compliant abradable sealing system for a rotary compressor, and method for a operating a compliant abradable sealing system for facilitating a minimum dynamic clearance during steady state and transient operating conditions of a rotary compressor.
Efficiency of rotary devices utilized for pumping a fluid or compressing a vapor (e.g. gas) depends upon the internal tolerances of the components comprising the device. A loosely-toleranced rotary pump or compressor may have a relatively poor fit between internal components and may therefore exhibit poor efficiency, with relatively high leakage occurring within the device from regions of high pressure to regions of lower pressure. The traditional approach to this situation is to decrease the amount of clearance on these critical interfaces.
Sealing systems are used in rotary machines such as turbines, compressors, or the like to reduce leakage of fluid flowing through the rotary machines. Fluid leakage through the rotary machines is generally undesirable for various reasons. For example, fluid leakage between the rotor and a circumferentially surrounding casing of a compressor may lower the efficiency of the compressor leading to increased fuel costs.
To reduce the leakage of fluid in rotary compressors, labyrinth seals or honeycomb seals are sometimes used. Sealing strips in such arrangements are typically disposed between the rotor and the stationary casing. The effectiveness of the seal depends on maintaining a desired clearance between the sealing strips and the rotor. If the clearance exceeds a desired amount, efficiency of the compressor is lowered. Running clearances may deviate from design intent due to misalignment between rotor and casing, and during transients such as start-up, the rotor may expand relative to the casing or sweep through orbits, causing the rotor and stationary components to interfere (i.e., contact one another). As a result, seal components, which are provided on the rotor as well as the stator, may be damaged.
Accordingly, there is a need for a technique that reduces leakage of fluid in a rotary machine, and that maintains minimum clearance without impairing the performance of a seal during steady state and transient operating conditions. In addition, a system for reducing leakage of fluid in a rotary machine during steady state and transient operating conditions is also desirable.
In accordance with one aspect of the present invention, a method for operating a compliant abradable sealing system includes biasing a radially movable sealing element to contact a mating radially fixed sealing element. The radially fixed sealing element is rotated relative to the radially movable sealing element. A plurality of permanent sealing grooves are formed in the radially movable sealing element to form a zero-clearance labyrinth seal between the radially movable sealing element and the radially fixed sealing element.
In accordance with another aspect of the present invention, a compliant abradable sealing system includes at least one biasing member. A radially movable sealing element is coupled to at least one biasing member and configured to contact a mating radially fixed sealing element. The radially fixed sealing element is rotatable relative to the radially movable sealing element to form a plurality of permanent sealing grooves in the radially movable sealing element to form a zero-clearance labyrinth seal therebetween.
In accordance with another aspect of the present invention, a rotary compressor includes a rotor disposed in a stator housing. A compliant abradable sealing system is disposed between the rotor and the stator housing and configured to control leakage of a fluid flowing through the compressor. The sealing system includes at least one biasing member. A radially movable sealing element is coupled to at least one biasing member and configured to contact a mating radially fixed sealing element. The radially fixed sealing element is rotatable relative to the radially movable sealing element to form a plurality of permanent sealing grooves in the radially movable sealing element to form a zero-clearance labyrinth seal therebetween.
In accordance with another aspect of the present invention, a method for improving performance of a rotary compressor includes disposing a rotor in a stator housing. A compliant abradable sealing system is disposed between the rotor and the stator housing and configured to control leakage of a fluid flowing through the compressor. A radially movable sealing element is coupled to at least one biasing member within the stator housing. A mating radially fixed sealing element is coupled to the rotor. The radially fixed sealing element is rotated relative to the radially movable sealing element to form a plurality of permanent sealing grooves in the radially movable sealing element to form a zero-clearance labyrinth seal therebetween.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
As discussed in detail below, aspects of the present invention provide a compliant abradable sealing system for a rotary machine having a radially movable sealing element configured to contact a mating radially fixed sealing element. The radially fixed sealing element is rotatable relative to the radially movable sealing element to form a plurality of permanent sealing grooves in the radially fixed sealing element or in the radially movable sealing element. During transient operating conditions of the rotary machine, the compliant abradable sealing system facilitates minimum clearance between a rotor and a stator casing. As a result, fluid leakage through the rotary machine is minimized and the overall efficiency is enhanced. Also disclosed is a method of operating the compliant abradable sealing system. Specific embodiments of the present invention are discussed below referring generally to
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In one embodiment the abradable coating 22 may include an alloy of cobalt, nickel, chromium, aluminum, yttrium, hexagonal boron nitride, and polymers such as polyesters, polyimides, or the like. In another embodiment, the abradable coating typically includes nickel, chromium, aluminum, and clay (bentonite). In yet another embodiment, the abradable coating may include nickel, graphite, and stainless steel. In yet another embodiment, the abradable coating may include nickel, chromium, iron, aluminum, boron and nitrogen. In yet another embodiment, the abradable coating may also include non-metallic materials (e.g. teflon applied by electrostatic powder coating process or teflon filled synthetic mica which may be attached by a mechanical device). Similarly, in the other embodiments, other compositions of the abradable coating 22 as known to those skilled in the art are also envisaged. The abradable coating 22 may be formed on the substrate 24 by brazing or thermal spraying. In one example, the substrate may be composed of carbon steel, although other materials may be suitable, depending upon such factors as the design of the machine, it's operating temperatures and transients, the fluid treated (i.e., compressed), and so forth.
A plurality of biasing members 26 such as springs are disposed between the packing ring 18 and the stator housing 20. Exemplary springs may include leaf springs, coil springs, helical springs, stacked belleville washers provided in a housing or the like. The springs 26 are configured to bias the packing ring 18 against a radially fixed sealing element 28 provided on the rotor 12. The packing ring 18 is radially movable with respect to the housing 14. The arrangement, number, and type of springs may be varied depending on the application. In certain exemplary embodiments, the springs may be used in conjunction with other biasing mechanisms for providing a force to bias the packing ring 18 against the radially fixed sealing element 28. For example, the springs may be used in conjunction with gas pressures for providing a force to bias the packing ring 18 against the radially fixed sealing element 28. In the illustrated embodiment, the radially fixed sealing element 28 includes a plurality of teeth 30 formed integrally on the rotor 12.
During assembly, the sealing system 16 is provided between the rotor 12 and the stator housing 14 in such a way that tip portions 32 of the plurality of teeth 30 contact the abradable coating 22 of the packing ring 18. The height of the teeth corresponds to the maximum radial incursion of teeth 30 into the abradable coating 22 of the packing ring 18. The abradable coating 22 typically protects packing ring 18 against possible wear due to interference between the packing ring 18, itself, and the plurality of teeth 30 during typical operating conditions, such as during start-up, and transient conditions of the rotary compressor.
Referring to
During start up of the rotary compressor, the tip portions 32 of the plurality of teeth 30 slide over the surface of the abradable coating 22 due to the interference between the packing ring 18 and the teeth 30. The combined effect of centrifugal forces and the forces resulting from biasing the packing ring 18 against the teeth 30 dislodges the particles in the abradable coating 22, causing an incursion of the teeth 30 in the abradable coating 22. As a result, a plurality of permanent sealing grooves 34 are formed in the abradable coating 22. In one example, during start-up operation of the rotary compressor, the sealing grooves 34 have a profile matching as that of the teeth 30. As a result, close clearance is maintained between the sealing elements. The location, number and height of the teeth 30 may be varied as appreciated by those skilled in the art. The abradable coating 22 has a porosity and hardness that prevents rupture, delamination, and damage to the rotor 12 during rubbing. In the illustrated embodiment, the sealing system 16 may include a stopping device 36 provided in the slot 20 of the stator housing 14 and configured to control the radial movement of the packing ring 18 so as to adjust the depth of the grooves 34 formed in the abradable coating 22 of the packing ring 18.
Referring to
It should be noted that, as used herein, the term “zero clearance” denotes the overlap in the maximum outer perimeter of inner elements of the sealing system, and the maximum inner perimeter of the outer elements. That is, in the embodiment described above, during operation of the compressor, the teeth 30 have an outer diameter that is greater than the inner diameter of the coating 22. It is this zero clearance that initially forms the grooves 34, and that locates the teeth back in the grooves for sealing thereafter.
Referring to
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The plurality of biasing members 26 such as springs are disposed between the packing ring 18 and the stator housing 20. The springs 26 are configured to bias the packing ring 18 against the radially fixed sealing element 28 provided on the rotor 12. In the illustrated embodiment, the radially fixed sealing element 28 includes the abradable coating 22 provided on the rotor 12. During assembly, the sealing system 16 is provided between the rotor 12 and the stator housing 14 in such a way that tip portions 32 of the plurality of teeth 30 contact the abradable coating 22 provided on the rotor 12. As discussed previously, during start up of the rotary compressor, the tip portions 32 of the plurality of teeth 30 slide over the surface of the abradable coating 22 due to the interference between the packing ring 18 and the coating 22. The combined effect of centrifugal forces and the forces resulting from biasing the packing ring 18 against the coating 22 dislodges the particles in the abradable coating 22, causing an incursion of the teeth 30 in the abradable coating 22. As a result, a plurality of permanent sealing grooves are formed in the abradable coating 22.
Referring to
In yet another embodiment, a plurality of teeth may be detachably fitted to slots formed in the packing ring 18. The plurality of teeth protrudes downwards to a bumped surface of the rotor 12. Flow of fluid is throttled at locations where the teeths are provided on the rotor 12. The bumped surface of the rotor facilitates to divert fluid flow along a radial direction providing a more tortuous path.
Referring to
When the rotary compressor operation is started, the radially fixed sealing element is rotated relative to the packing ring as represented by step 46. The tip portions of the plurality of teeth slide over the surface of an abradable coating of the packing ring due to the interference between the packing ring and the teeth as represented by step 46. The combined effect of centrifugal forces and the biasing forces dislodge the particles in the abradable coating, causing an incursion in the abradable coating as represented by step 48. As a result, a plurality of permanent sealing grooves 34 are formed in the abradable coating as represented by step 50. The depth of the grooves formed in the packing ring may be adjusted by controlling the radial movement of the packing ring via a stopping device. The height of the teeth also serve to limit their incursion into the coating material.
During transient operating conditions of the rotary compressor, expansion of the rotor, or more generally, changes in the clearance of the rotor and stator occur, causing the rotor to be pushed against the stator housing. As a result, the teeths are engaged to the grooves to form a zero-clearance labyrinth seal as represented by step 52. During steady state operating conditions of the rotary compressor, the rotor is maintained at the predetermined original position relative to the stator housing. As a result, the teeth are engaged to the grooves formed in the abradable coating 22 so as to maintain a minimal clearance between the rotor and the stator housing.
Referring to
Thereafter, as described previously, when the rotary compressor operation is started, the radially fixed sealing element is rotated relative to the packing ring as represented by step 62. The tip portions of the plurality of teeth slides over the surface of an abradable coating of the packing ring due to the interference between the packing ring and the teeth. As a result, a plurality of permanent sealing grooves are formed in the abradable coating as represented by step 64. During transient operating conditions of the rotary compressor, changes in radial dimensions occur between the rotor and the stator housing, causing the rotor to be pushed against the stator housing. As a result, the teeths are engaged to the grooves to form a zero-clearance labyrinth seal. Leakage of fluid through the rotary compressor is thereby reduced and the overall efficiency and performance of the rotary compressor is improved.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.
