Patent Application
20110052109
In turbomachine systems, if a primary bearing (such as a magnetic bearing) fails, the shaft of the turbomachine will generally fall or drop onto the adjacent mechanical surfaces. This drop often causes substantial damage to the shaft and/or the surrounding components. In turbomachine systems that include an auxiliary bearing, the shaft may drop onto the auxiliary bearing without damaging the shaft or surrounding components.
There are two common designs for a traditional auxiliary bearing: (a) a dry-lubricated bushing, and (b) one or more rolling element bearing(s) with a clearance between the bearing inner ring(s) and the shaft.
The bushing design consists of one or more segments of a material containing a dry lubricant. When a shaft drops onto this bearing, it slides within the bearing as it coasts down from speed. Considerable heat is generated in this process, which limits the time the rotor can spin on the auxiliary bearing. Furthermore, the bearing surface is subject to wear, and the friction forces on the rotor have the potential for sending it into destructive backward whirl.
With the rolling element bearing design, the shaft drops onto the inside of the bearing inner ring. In this configuration, the auxiliary bearing is accelerated almost instantaneously to match the shaft speed when a drop occurs. The auxiliary bearing may then be used to allow the shaft to coast down on the auxiliary bearing (maintaining normal operating speed is generally not possible). However, this configuration may cause amplitude backward whirl of the shaft, brinelling of the races from the impact of the shaft, skidding between rolling elements and races due to the high acceleration rate of the bearing to match the shaft speed, high stresses in the cage or separator (if employed), and overheating of the auxiliary bearing. Further, the life of auxiliary bearings in this configuration is often only a few drops of the shaft, and as such, the longevity and reliability are challenges.
The lack of a reliable, long-lasting auxiliary bearing technology, also known as “coastdown bearing” or “catcher bearing” technology, has been a barrier to the implementation of magnetic bearings into turbomachines. Magnetic bearings are now being considered for applications where the auxiliary bearing may be required to support the shaft at operating speed for sustained operation when a primary bearing fails (e.g., minutes to days). Thus, there is a need for an auxiliary bearing system or configuration that provides for continued operation of a turbomachine for longer periods of time when a primary bearing fails.
Embodiments of the disclosure may provide a system for supporting a rotating shaft, including a primary bearing configured to maintain the shaft within a predetermined range of operational shaft positions; a process fluid source; and a hydrostatic auxiliary bearing having an inner surface manufactured from a self lubricating composite material. The hydrostatic auxiliary bearing is fluidically coupled to the process fluid source and configured to use a pressurized process fluid provided by the process fluid source to maintain the shaft within the predetermined range of operational shaft positions when the primary bearing fails to maintain the shaft within the predetermined range of operational shaft positions when the primary bearing fails.
Embodiments of the disclosure may further provide a method for supporting a rotating shaft, including maintaining the shaft within a predetermined range of operational shaft positions using a primary active magnetic bearing. The method may further include maintaining the shaft within the predetermined range of operational shaft positions using a hydrostatic auxiliary bearing when the primary active magnetic bearing fails to maintain the shaft within the predetermined range of operational shaft positions. The hydrostatic auxiliary bearing is configured to support the shaft using a pressurized process fluid from a process fluid source, and an inner surface of the hydrostatic auxiliary bearing comprises a self lubricating composite material.
Embodiments of the disclosure may further provide a system for supporting a rotating shaft, including first means for maintaining the shaft within a predetermined range of operational shaft positions. The system may further include a second means for maintaining the shaft within a predetermined range of operational shaft positions when the first means fails to maintain the shaft within the predetermined range of operational shaft positions, wherein the second means uses a pressurized process fluid from a means for storing process fluid. An inner surface of the second means comprises a self lubricating composite material.
The present disclosure is best understood from the following detailed description when read with the accompanying Figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.
It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure, however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure may repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the various Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed interposing the first and second features, such that the first and second features may not be in direct contact. Finally, the exemplary embodiments presented below may be combined in any combination of ways, i.e., any element from one exemplary embodiment may be used in any other exemplary embodiment, without departing from the scope of the disclosure.
Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities may refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function. Further, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.” All numerical values in this disclosure may be exact or approximate values unless otherwise specifically stated. Accordingly, various embodiments of the disclosure may deviate from the numbers, values, and ranges disclosed herein without departing from the intended scope.
Primary bearings 106a and 106b are coupled to respective interior surfaces of the casing 102 at opposing end portions of the shaft 104, and provide support for the shaft 104. Each of the primary bearings 106a and 106b is an active magnetic bearing that has one or more electromagnets controlled by a magnet control 107. The magnet control 107 may also be equipped with one or more sensors configured to monitor operating conditions of the primary bearings 106a and 106b. In an exemplary embodiment, each of the primary bearings 106a and 106b may be a passive magnetic bearing that only includes permanent magnets. In yet another exemplary embodiment, each of the primary bearings 106a and 106b may be a suspension bearing. In other exemplary embodiments, each of the primary bearings 106a and 106b may be any kind of conventional bearing that may fail and cause the shaft to drop or otherwise become positioned out of the normal operation position (axially within the turbomachine). Means for maintaining the shaft within a predetermined range of operational shaft positions may include any of the foregoing embodiments of the primary bearing 106 and any equivalents thereof.
A plurality of labyrinth seal assemblies 108a-i circumferentially surround the shaft 104. In an exemplary embodiment, the labyrinth seal assemblies 108a-i may include one or more labyrinth seal segments that form one or more labyrinth packing rings. The labyrinth seal segments may be segmented cylindrical-toothed rings. Other designs for labyrinth seal assemblies 108a-i that are known in the art are also within the scope of the present disclosure. A leakage recycler 112 is fluidically coupled to a leakage recycler pipe 114. The leakage recycler pipe 114 is also be fluidically coupled to openings 115a-c formed in the casing 102. In other exemplary embodiments, other configurations for positioning the leakage recycler pipe 114 may also be used without departing from the scope of the present disclosure.
The turbomachine 100 also includes auxiliary or catcher bearings 116a and 116b that circumferentially surround the shaft 104. The auxiliary bearing 116a is located between the labyrinth seal assemblies 108c and 108d. The auxiliary bearing 116b is located between labyrinth seal assemblies 108h and 108i. In an exemplary embodiment, the auxiliary bearings 116a and 116b may include a hydrostatic bearing. A hydrostatic bearing is also sometimes referred to as a fluid film bearing. In an exemplary embodiment, a clearance 118a may be formed between an inner surface 119a of the auxiliary bearing 116a and the shaft 104, and a clearance 118b may be formed between an inner surface 119b of the auxiliary bearing 116b and the shaft 104.
In an exemplary embodiment, the inner surface 119 may include material that consists of a durable surface, such as NASA PS300. As disclosed in U.S. Pat. No. 5,866,518, NASA PS300 is a self lubricating, friction-reducing, and wear-reducing composite material. U.S. Pat. No. 5,866,518 is herein incorporated in its entirety to the extent it does not contradict the present disclosure. In another exemplary embodiment, the inner surface 119a or 119b may include a hard coating such as chrome oxide or titanium nitride, and may include materials such as clutch material, brake material, and sintered material.
In an exemplary embodiment, the auxiliary bearings 116a and 116b include inlets 120a and 120b, respectively, which are fluidically coupled to a process fluid source 122 via a process fluid pipe 124. The fluid source 122 may provide boiler feedwater to the inlets 120a and 120b via the process fluid pipe 124. Further, the leakage recycler 112 is fluidically coupled to the process fluid source 122 via a recirculation pipe 126. In other exemplary embodiments, multiple recirculation pipes 126 may fluidically couple the leakage recycler 112 to the process fluid source 122. Also, a system recycle pipe (not shown) may fluidically couple the leakage recycler 112 to other components of the turbomachine 100 that are not shown in
The process fluid pipe 124 is configured to operate with valves 128a and 128b. The valves 128a and 128b have valve controls 129a and 129b, respectively, which are configured to control the valves 128a and 128b. A master control system (not shown) may be communicably coupled to the valve controls 129a and 129b and the magnet control 107. One or more wires may facilitate communication between the master control system, the valve controls 129a and 129b, and the magnet control 107.
Turning now to the operation of the turbomachine 100, in an exemplary embodiment, the primary bearings 106a and 106b maintain the shaft 104 within a predetermined range of operational shaft positions. When the magnet control 107 detects that the primary bearing 106a or 106b is failing to maintain the shaft 104 within the predetermined range of operational shaft positions, the magnet control 107 sends a signal to the valve controls 129a-b to open the valves 128a-b.
In another exemplary embodiment, one or more sensors (not shown) may be used to monitor the operation conditions of the turbomachine 100. The valve controls 129-b may be configured to communicate with the sensors, and open the valves 128a-b when a predetermined set of operating conditions is detected by the sensors. For example, in one embodiment, the valve controls 129a-b cause the valves 128a-b to open when a sensor detects that the temperatures of the inner surfaces 119a-b of the auxiliary bearings 116a-b have reached a predetermined temperature that indicates that the shaft 104 is outside of a predetermined range of operational shaft positions, i.e., that a drop is about to occur or is occurring.
In yet another exemplary embodiment, one or more sensors may track the center of the shaft 104, and may instruct the valve controls 129a-b to open the valves 128a-b when the sensors detect that the center of the shaft 104 is outside a predetermined range of operational shaft positions. In another exemplary embodiment, the auxiliary bearings 116a-b may be configured to idle at a predetermined hydrostatic pressure that may be lower than an operating pressure of the bearings, so that the auxiliary bearings 116a-b may become fully operational (brought up to operating pressure) more quickly when the valves 128a-b are opened. Other methods for determining when to open the valves 128a-b are also within the scope of the present disclosure.
In an exemplary embodiment, when the valves 128a-b are open, high-pressure process fluid may be provided from the process fluid source 122 to the inlets 120a-b via the process fluid pipe 124. Upon entering the inlets 120a-b, the process fluid may form a fluid film between the shaft 104 and the inner surfaces 119a-b. The hydrostatic pressure of the fluid film may maintain the shaft 104 within a predetermined range of operational shaft positions.
In an exemplary embodiment, the pressure of the process fluid may be less than about 1000 psi. In another exemplary embodiment, the pressure of the process fluid may range from about 500 psi to about 900 psi, and may preferably be about 750 psi. Other process fluid pressure ranges are also within the scope of the present disclosure. The process fluid may be maintained at a temperature that will not flash with a pressure drop that exists outside of the auxiliary bearings 116a-b.
In an exemplary embodiment, the process fluid may be water. A high pressure feed pump or an emergency high-pressure pump may provide the water to the auxiliary bearings 116a-b in liquid form. The water may also be made available to the auxiliary bearings 116a-b in gaseous form as high-pressure steam. According to an exemplary embodiment, the water may be feedwater from a Rankine cycle turbomachine. In yet another exemplary embodiment, the process fluid may be ethylene glycol. It should be understood that a gas, such as air or an inert gas, may also be used as a process gas instead of using a process fluid.
According to an exemplary embodiment, process fluid leakage may pass through the auxiliary bearings 116a-b via the clearances 118a-b. The leakage may be restricted by the labyrinth seal assemblies 108a-i and may be directed via the leakage recycler pipe 114 to the leakage recycler 112. The leakage recycler 112 may recycle the leakage. Recycling the leakage may include cooling the leakage, as well as performing other operations on the leakage so that it may be reused as process fluid. Upon recycling the leakage, a portion of the recycled leakage may be directed to the process fluid source 122 via the recirculation pipe 126. Further, the recycled leakage may be directed to other components of the turbomachine 100 via a system recycle pipe. In an exemplary embodiment, the leakage recycler 112 may include a condenser configured to cool the leakage. However, other means for recycling leakage are also within the scope of the present disclosure.
In several exemplary embodiments, auxiliary bearings that are substantially similar to the bearing 106a or 106b may circumferentially surround other portions of the shaft 104.
Referring now to
A clearance 203 is formed between the inner surface 202 of the pocketed auxiliary bearing 200 and the shaft 104. Various clearance 203 widths may be used. A decreased clearance 203 width may result in decreased fluid flow between the outer surface of the shaft 104 and the inner surface 202 of the pocketed auxiliary bearing 200. In another exemplary embodiment, an increased clearance 203 width may result in increased fluid flow between the shaft 104 and the inner surface 202. In one exemplary embodiment, the size of the clearance 203 may vary depending on the weight of the shaft 104. The pocketed auxiliary bearing 200 includes one or more pockets 204a-d formed along the inner surface 202. Each of the pockets 204a-d are formed across two adjacent bearing segments 201a-d.
One or more inlets 206 are formed between circumferentially adjacent bearing segments 201a-d. The inlet 206 may correspond to either inlet 120a or inlet 120b in
Each pocket 204a-d may be fed with a high-pressure process fluid via the inlet 206. Each orifice 208a-c may regulate process fluid flow and prevent the effects of pressure changes in one pocket 204a-d from affecting another pocket 204a-d, as described below. In another exemplary embodiment, other means may also be used to regulate the flow of process fluid and prevent the effects of pressure changes within a pocket 204a-d from affecting another pocket 204a-d.
In an exemplary embodiment, when the pocketed auxiliary bearing 200 receives process fluid, the resulting fluid film may cause the shaft 104 to adjust its position within a predetermined range of operational shaft positions. During operation of the pocketed auxiliary bearing 200, radial and/or axial forces may cause the shaft 104 to move out of a predetermined range of operational shaft positions. For example, if the shaft 104 moves toward the pocket 204c, such movement may cause a reduction in process fluid leakage out of the pocket 204c via the orifice 208b. Such reduction in leakage may cause the pressure within the pocket 204c to rise. As a result, the clearance 203 between the pocket 204a and shaft 104 may increase. A balancing reaction may cause leakage out of the pocket 204a via the orifice 208a to increase. This increase in leakage out of the pocket 204a may counteract the increased pressure in pocket the 204c. Similar balancing reactions occurring at each of the pockets 204a-d may maintain the shaft 104 within the predetermined range of operational shaft positions.
Referring now to
The operation of the pocketed auxiliary bearing 250 may be similar to the operation of the pocketed auxiliary bearing 200, except that the tilting pads 252 may adjust its position within the clearance 254 to help maintain the shaft 104 within a predetermined range of operational shaft positions.
Referring now to
In an exemplary embodiment, each of the bushings 302 may define a pattern of small apertures on its inner surface 304. The small holes may either be circular, honeycomb-shaped, or any other shape. Such bushings 302 may be referred to as “damper seals.”
In an exemplary embodiment, the bushings 302 circumferentially surround the shaft 104. The bushings 302 may be installed in a back-to-back arrangement between, for example, the labyrinth seal assemblies 108c and 108d, and between the labyrinth seal assemblies 108h and 108i, as illustrated in
With continuing reference to
When the process liquid has entered the inlets 310a-b, the process fluid axially flows across the bushings 302 towards regions of lower pressure. Leakage may be restricted by the labyrinth seal assemblies 108a-i, and may be directed to the leakage recycler 112 via the leakage recycler pipe 114. When leakage reaches the leakage recycler 112, the leakage recycler 112 recycles the leakage and directs the recycled leakage to the process fluid source 122 via the recirculation pipe 126. In an exemplary embodiment, the leakage recycler 112 may include a condenser configured to cool the leakage. Furthermore, a system recycle pipe (not shown) may fluidically couple the leakage recycler 112 to other components of the turbomachine 300 that are not shown in
Embodiments of an axially-fed auxiliary bearing may be less efficient than embodiments of the pocketed bearing 200. However, the use of design tools combined with application experience may increase the efficiency of an embodiment of the axially-fed auxiliary bearing 302.
According to an exemplary embodiment, shaft resonance may determine whether a auxiliary bearing has the radial stiffness and damping required for use in the turbomachine 100 or 300. During the operation shaft on the auxiliary bearings the natural frequencies of the rotor-bearing system, and therefore the critical speeds, may change because both the location and stiffnesses of the rotor supports change. Likewise, the dynamic amplification factors for vibration at a critical speed or resonant frequency also may change due to the changes in support location, stiffness and damping. Due to these factors, it may be desirable or necessary to avoid operating at or near a critical speed while the rotor is supported on the auxiliary bearings. Therefore, during the operation of the turbomachine 100 or 300, the shaft 104 may be maintained at an operational speed that does not either surpass or encompass a critical speed where shaft resonance will exist.
Referring now to
In an exemplary embodiment, the auxiliary bearing 116a and/or 116b of the turbomachine 100 includes a combined auxiliary radial and thrust bearing.
Referring now to
If the primary bearing fails to maintain the shaft within the predetermined range of operational shaft positions, such as when the shaft drops as a result of a failed primary bearing (step 504), a control system may immediately engage a hydrostatic auxiliary bearing before the shaft drops onto the inner surface of the hydrostatic auxiliary bearing, so as to maintain the position of the shaft within the predetermined range of operational shaft positions, as shown in step 506. In one exemplary embodiment, the auxiliary bearing may be configured to idle at a predetermined pressure during the operation of the primary bearing, so that the auxiliary bearing may become fully operational more quickly when the primary bearing fails.
The hydrostatic auxiliary bearing may be configured to support the shaft using a pressurized process fluid, such as water or ethylene glycol, that may be provided by a process fluid source. It should be understood that a gas, such as air or an inert gas, may also be used as a process gas instead of using a process fluid. Means for maintaining the shaft within a predetermined range of operational shaft positions when the primary bearing fails to maintain the shaft within the predetermined range of operational shaft positions, may include the auxiliary bearings 116a and 116b, the pocketed auxiliary bearings 200 and 250, axially-fed auxiliary bearings, such as the bushings 302, and any equivalents of the foregoing.
Any leakage resulting from the pressurized process fluid used to support the shaft may be recycled, as shown at step 508. In an exemplary embodiment, the leakage recycler may include a condenser configured to cool the leakage before directing the leakage to the process fluid source.
Generally, hydrostatic bearings have not been utilized as auxiliary bearings in conventional technology, because the lubrication systems (e.g., oil tank, coolers pumps, etc.) that are necessary to provide lubrication to a hydrostatic auxiliary bearing are usually not included in turbomachinery that uses magnetic bearings. Instead of utilizing traditional lubrication systems, the exemplary embodiments set forth in the present disclosure utilize process fluid that is readily available. Further, in the exemplary embodiments disclosed herein, the process fluid may be recycled for use in other areas of a turbomachine. Taking advantage of a readily available process fluid and recycling the process fluid for other uses may result in substantial cost savings.
Potential advantages of the auxiliary bearing embodiments described above over conventional technology may include simplified integration into established bearing technology. The current availability of design tools is one factor that makes this possible. Another potential advantage of the exemplary embodiments described herein may be longer system operating life. The exemplary embodiments of the present disclosure may also exhibit increased load capacity potential.
Turbomachinery implementing the exemplary embodiments disclosed herein may be more compact than conventional turbomachinery using hydrostatic auxiliary bearings, because a variety of process fluids may be used as bearing lubricant. Exemplary embodiments of the present disclosure may be physically smaller and less complex than conventional technology, because traditional lubricant pumping technology is not necessary when process fluid is used as the bearing lubricant. Further, the exemplary embodiments disclosed in the present disclosure allow for process fluid to be recycled after the process fluid is used as bearing lubricant. Recycling process fluid may improve efficiency and lower turbomachinery operating costs.
Although the present disclosure has described embodiments relating to specific turbomachinery, it is understood that the apparatus, systems and methods described herein could applied to other environments. For example, according to another exemplary embodiment, rotating machinery that is driven by a turbomachine may be configured to use embodiments of the auxiliary bearings described above. However, in such applications, the machinery may have to be modified to ensure that the process fluid leaks do not adversely affect the machine.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the detailed description that follows. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present disclosure.
