Patent Application
20180328210
Heat engines are used to convert heat or thermal energy into useful mechanical work and are often used in power generation plants. One example of a heat engine is an expander (e.g., a turbine) which is often rotatably coupled to a generator or other power converting device. As working fluids are expanded in the expander, the shaft connecting the expander and generator rotates and generates electricity in the generator.
Most power plant expanders are based on the Rankine or Brayton cycle and obtain high temperature/pressure working fluids through the combustion of coal, natural gas, oil, and/or nuclear fission. Typical working fluids for Brayton cycles include steam and organic fluids. Recently, however, due to perceived benefits in terms of hardware compactness, efficiency, heat transfer characteristics, etc., there has been considerable interest in using super-critical carbon dioxide (ScC02) as a working fluid for certain heat engine applications. Notable among such applications are nuclear, solar, and waste heat energy conversion cycles.
Many waste heat recovery schemes utilizing ScC02 as the working fluid have relatively high process temperatures/pressures. For example, in some applications the temperatures can approach or exceed 600° C. and the operating pressures can range from between about 1000 psia and about 4500 psia. Elevated operating pressures can potentially impose large axial thrusts on equipment rotors, which may damage accompanying bearing systems if not properly managed. In addition, elevated operating temperatures may also damage the rotating equipment and bearing systems of the expander via unmanaged thermal growth of one or more components of the expander.
What is needed, therefore, is a compact expander capable of processing working fluids, such as supercritical carbon dioxide, at elevated pressures and temperatures.
Embodiments of the present disclosure may provide an expander. The expander may include a longitudinal axis, an inner casing, an outer casing, a plurality of inlets, a plurality of transfer tubes, a plurality of nozzles, a plurality of expansion stages, and a plurality of seals. The inner casing may extend along the longitudinal axis and may define at least in part an axial flow passage. The outer casing may extend along the longitudinal axis and may be spaced radially outward from and may encompass the inner casing. Each axial end of the outer casing may form a respective gland seal housing, and the outer casing and inner casing may define an exhaust chamber therebetween. The plurality of inlets may extend radially outward from the outer casing and may be configured to receive a working fluid from a working fluid source. The plurality of transfer tubes may extend radially between the inner casing and the outer casing. Each transfer tube fluidly may be coupled to a respective inlet. Each nozzle may fluidly couple a respective transfer tube with the axial flow passage. The plurality of expansion stages may include a rotor shaft disposed within the axial flow passage. The plurality of expansion stages may be configured to expand the working fluid received from the working fluid source. The plurality of seals may be disposed within each of the gland seal housings. The plurality of seals may include an annular seal mounted circumferentially about the rotor shaft, a first plurality of self-adjustable seals mounted circumferentially about the rotor shaft and disposed outboard of the annular seal, and at least one dry gas seal mounted circumferentially about the rotor shaft and disposed outboard of the first plurality of self-adjustable seals.
Embodiments of the present disclosure may further provide a method for operating an expander. The method may include receiving a working fluid in a plurality of inlets equally spaced and circumferentially disposed about a longitudinal axis of the expander. The method may also include expanding a working fluid in a plurality of expansion stages fluidly coupled to the plurality of inlets and disposed within an inner casing of the expander. The method may further include discharging an expanded working fluid through an outlet extending radially from an outer casing of the expander. The outer casing may be spaced radially outward from and may encompass the inner casing. Each axial end of the outer casing may form a respective gland seal housing, and the outer casing and inner casing may define an exhaust chamber therebetween. The method may also include preventing or substantially preventing the working fluid from leaking across the outer casing to an external environment. Preventing or substantially preventing the working fluid from leaking across the outer casing to the external environment may include disposing in series in each of the gland seal housings each of an annular seal, a first plurality of self-adjustable seals, and at least one dry gas seal circumferentially about a rotor shaft of the expander. Preventing or substantially preventing the working fluid from leaking across the outer casing to the external environment may also include injecting a process fluid into each of the gland seal housings via a first conduit disposed between the annular seal and the first plurality of self-adjustable seals, the process fluid being injected at a higher pressure than a pressure within the respective gland seal housing. Preventing or substantially preventing the working fluid from leaking across the outer casing to the external environment may further include removing at least a portion of the process fluid from the respective gland seal housing via a second conduit disposed between the first plurality of self-adjustable seals and the at least one dry gas seal.
Embodiments of the present disclosure may further provide an expander. The expander may include a longitudinal axis, an inner casing, an outer casing, a plurality of inlets, a plurality of transfer tubes, a plurality of nozzles, a plurality of expansion stages, a first plurality of seals, and a second plurality of seals. The inner casing may be split horizontally along the longitudinal axis and may define at least in part an axial flow passage. The outer casing may be split horizontally along the longitudinal axis and may be spaced radially outward from and may encompass the inner casing. Each axial end of the outer casing may form a respective gland seal housing, and the outer casing and inner casing may define an exhaust chamber therebetween. The plurality of inlets may be equally spaced and circumferentially disposed about the longitudinal axis of the expander and configured to receive a working fluid including carbon dioxide from a working fluid source. The plurality of transfer tubes may extend radially between the inner casing and the outer casing. Each transfer tube fluidly may be coupled to a respective inlet. Each nozzle may fluidly couple a respective transfer tube with the axial flow passage. The plurality of expansion stages may be disposed within the axial flow passage. The plurality of expansion stages may be configured to expand the working fluid received from the working fluid source. Each expansion stage may include a plurality of rotor blades mounted circumferentially about a rotor shaft. The first plurality of seals may be disposed within each of the gland seal housings. The first plurality of seals may include an annular seal mounted circumferentially about the rotor shaft, a first plurality of self-adjustable seals mounted circumferentially about the rotor shaft and disposed outboard of the annular seal, and at least one dry gas seal mounted circumferentially about the rotor shaft and disposed outboard of the first plurality of self-adjustable seals. The second plurality of seals may be disposed at an end portion of the inner casing and configured to prevent or substantially prevent a leakage of working fluid from the inner casing to the exhaust chamber. The second plurality of seals may include a second plurality of self-adjusting seals aligned in series and disposed circumferentially about the rotor shaft.
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. 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 disclosure. 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 disclosure, 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. Additionally, 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. Furthermore, as it is used in the claims or specification, the term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein.
As used herein, the terms “fore” and “upstream,” on the one hand, and the terms “aft” and “downstream,” on the other hand, are used interchangeably and are intended to indicate positions and directions relative to the principal direction of gas flow over a turbomachine rotor blade airfoil. Thus as will be appreciated by those skilled in the art, in an expander the fore and upstream positions of a rotor and a rotor blade will be at a higher static pressure than the aft and downstream positions. In either case, however, there is a possibility for leakage flow to occur between adjacent blade platforms or between a cavity and flow path, and it is the minimization of such leakage flow to which one or more embodiments of the present disclosure is directed.
As used herein, the terms “upstream” and “downstream” are intended to indicate positions and directions relative to the principal direction of gas flow over an expander rotor blade airfoil. Thus as will be appreciated by those skilled in the art, in the expander the upstream positions of a rotor and a rotor blade will be at a higher static pressure than the downstream positions. Further, the terms “upper” and “lower” are intended to indicate positions and directions relative to the horizontal orientation of the expander.
As used herein, the term “substantially prevent” means to prevent to a measurable extent, but not necessarily to completely prevent.
Turning now to the Figures,
Referring now to
Each of the inner casing 104 and the outer casing 110 may be cast from a high nickel alloy and horizontally split along the longitudinal axis 102 of the expander 100 to allow for more facile access to and maintenance of the expander 100. Accordingly, the inner casing 104 may be formed from an inner casing upper portion 104a and an inner casing lower portion 104b coupled with one another via a plurality of fasteners (one indicated 118). Likewise, the outer casing 110 may be formed from an outer casing upper portion 110a and an outer casing lower portion 110b coupled with one another via a plurality of fasteners (one indicated 120). As shown most clearly in
As illustrated in
In other embodiments, the working fluid may be a binary, ternary, or other combination working fluid blend. The working fluid combination can be selected for the unique attributes possessed by the fluid combination within heat recovery systems. For instance, one such fluid combination includes a liquid absorbent and C02. In another embodiment, the working fluid may be a combination of C02 and one or more other miscible fluids or chemical compounds. In yet other embodiments, the working fluid may be a combination of C02 and propane, or C02 and ammonia, without departing from the scope of the disclosure.
Referring now to
Each of the transfer tubes 128 may be coupled to a respective nozzle 126 extending though respective openings defined in the inner casing inlet end portion 106 of the inner casing 104. Each nozzle 126 may fluidly couple a respective inlet 122 with an axial flow passage 132 defined by the inner casing 104 and extending axially to the outlet 124 of the expander 100 at the inner casing outlet end portion 108. By positioning the plurality of inlets 122 circumferentially and equally spaced about the longitudinal axis 102 of the expander 100, a symmetric delivery of the working fluid may be provided to the axial flow passage 132, thereby minimizing gradients during thermal transients and maintaining alignment of the internal components of the expander 100.
As further illustrated in
As shown most clearly in
Each of the radial bearings 156 may be oil-lubricated, hydrodynamic journal bearings. In some embodiments, the radial bearings 156 may be magnetic bearings, such as active or passive magnetic bearings. In other embodiments, however, other types of radial bearings 156, such as gas bearings, may be used without departing from the scope of the disclosure. For example, the radial bearings 156 may be gas bearings utilizing a portion of the working fluid including carbon dioxide provided from a storage tank, a portion of the expander 100, or another process component. In addition, at least one axial thrust bearing 162 may be provided at or near the end of the rotor 150 adjacent the non-drive end 146 of the expander 100 in the bearing case 158. The axial thrust bearing 162 may be a magnetic bearing configured to bear at least a portion of the axial thrust generated by the expander 100. It will be appreciated, however, that the axial thrust bearing 162 may be arranged in other locations along the rotor 150, or omitted altogether, without departing from the scope of the disclosure. Each of the radial bearings 156 and the bearing case 158 may be axially split to facilitate assembly and maintenance thereof.
The expander 100, as shown in
In one or more embodiments, one or more of the rotating blades 168 may be constructed from vacuum cast Inconel 738. In one or more embodiments, one or more of the wheels 170 may be constructed from a high nickel alloy (e.g., Inconel 901). In one or more embodiments, one or more of the diaphragm discs 172 may be constructed from precision investment casting FSX-414.
In operation, the working fluid enters the expander 100 via the plurality of inlets 122 and proceeds to the axial flow passage 132 via the plurality of nozzles 126 fluidly coupled to the plurality of inlets 122 via the transfer tubes 128. Each of the plurality of nozzles 126 may be configured to direct the working fluid to the first expansions stage 164a. The working fluid enters the first expansion stage 164a where the stator vanes 166 direct the working fluid into the axially-succeeding blades 168. As the working fluid contacts the blades 168, a rotating force is imparted, causing the rotor 150 to rotate. The partially-expanded working fluid in the first expansion stage 164a is then directed to the second through eight expansion stages 164b-h, successively, and the foregoing process is repeated in each expansion stage 164b-h. As the working fluid progresses through the expansion stages 164a-h from right to left, more rotational force is imparted to the rotor 150 and the pressure and temperature of the working fluid progressively decreases.
In at least one embodiment, one or more of the internal components of the expander 100 may be cooled with a portion of the working fluid directed circulating through or provided from another portion of the power plant. For example, the inner casing 104 or components of one or more of the expansion stages 164a-h (e.g., vanes 166 and/or blades 168) may be cooled from a portion of the working fluid stored in a storage tank (not shown). In another example, the inner casing 104 or components of one or more of the expansion stages 164a-h (e.g., vanes 166 and/or blades 168) may be cooled from a portion of the working fluid discharged from another process component (e.g., compressor, pump, or heat exchanger).
Referring now to
Referring now to
Without limiting disclosed embodiments to any theoretical principle of operation, a non-contacting seal, self-adjusting dynamic seal, such as the foregoing HALO™ seal, takes advantage of variation in hydrostatic pressures with seal tooth clearance (e.g., forming a hydrodynamic wedge separating seal from rotor (thus, non-contacting)) to develop a force balanced operational clearance as tight as a few thousandth of an inch (hundredths of a millimeter) over the rotor. The acceleration of fluid between the seal and the rotor creates a low-pressure region that draws the seal towards the rotor. As the seal approaches the rotor surface, the velocity of the fluid decreases, resulting in a pressure rise that increases the outward force on the seal. The operational clearance is achieved when this outward force is balanced with the inward force from the upstream and downstream pressures acting on the backside of the seal. Seal dimensions may be appropriately tuned to achieve the desired operational clearance for a given application. This seal can be effectively set for any desired clearance gap, and can further effectively accommodate both rotor off-set and run-out variation in real-time during operation.
As seem most clearly in
Each of the seals 188, 190, 192, 194 may be mounted in the expander 100 via a seal carrier or other means known in the art. In one or more embodiments, the plurality of self-adjusting seals 192 may be disposed outboard of the outboard casing annular seal 190 and adjacent a balance piston configured to counter the axial thrust generated by the plurality of expansion stages 164a-h. The gland seal housing may further include an inlet process fluid conduit 196 and an outlet process fluid conduit 198 configured to cool the bearings 156, 162 and rotor shaft 152 and to purge any working fluid leaking from the inner casing 104.
In one embodiment, the inlet process fluid conduit 196 may extend between the outer casing annular seal 190 and the plurality of self-adjusting seals 192 and may be fluidly coupled to a process fluid source (not shown). In one or more embodiments, the process fluid source may be a storage tank, an expansion stage 164a-h of the expander 100, or another process component. The process fluid may be supercritical carbon dioxide, according to one or more embodiments of the disclosure.
The inlet process fluid conduit 196 may be injected at a higher pressure than the leakage flow of the working fluid from the inner casing 104 such that the process fluid seals against the flow of leakage flow across the outer casing annular seal 190. Further, the injected process fluid may travel outboard across the self-adjusting seals 192, thereby preventing any lubricant (e.g., oil) for the radial bearings 156 from entering the inner casing 104. The outlet process fluid conduit 198, in one or more embodiments, may be disposed between the self-adjusting seals 192 and the dry gas seal(s) 194. Accordingly, the process fluid flowing across the self-adjusting seals 192 is directed through the outlet process fluid conduit 198 in addition to any lubricant from the bearing case 158 and may be redirected to the process fluid source and filtered as needed before being further processed. In addition to the location of the seals 190, 192, 194 within the gland seal housing, one of ordinary skill in the art will appreciate that one or more of the seals 190, 192, 194 may be disposed within the expander 100 at other locations along the rotor 150 typically known in the art to benefit from the prevention of working fluid leakage therefrom.
Referring now to
The method may also include preventing or substantially preventing the working fluid from leaking across the outer casing to an external environment, as at 208. Preventing or substantially preventing the working fluid from leaking across the outer casing to an external environment may include disposing in series in each of the gland seal housings each of an annular seal, a first plurality of self-adjustable seals, and at least one dry gas seal circumferentially about a rotor shaft of the expander. Preventing or substantially preventing the working fluid from leaking across the outer casing to an external environment may also include injecting a process fluid into each of the gland seal housings via a first conduit disposed between the annular seal and the first plurality of self-adjustable seals. The process fluid may be injected at a higher pressure than a pressure within the respective gland seal housing. Preventing or substantially preventing the working fluid from leaking across the outer casing to an external environment may further include removing at least a portion of the process fluid from the respective gland seal housing via a second conduit disposed between the first plurality of self-adjustable seals and the at least one dry gas seal.
In the method 200, the annular seal may be a labyrinth seal, and the first plurality of self-adjustable seals may be HALO™ seals. In another embodiment, each of the annular seal and the first plurality of self-adjustable seals may be HALO™ seals. In the method 200, the working fluid may include supercritical carbon dioxide.
It should be appreciated that all numerical values and ranges disclosed herein are approximate valves and ranges, whether “about” is used in conjunction therewith. It should also be appreciated that the term “about,” as used herein, in conjunction with a numeral refers to a value that is +/−5% (inclusive) of that numeral, +/−10% (inclusive) of that numeral, or +/−15% (inclusive) of that numeral. It should further be appreciated that when a numerical range is disclosed herein, any numerical value falling within the range is also specifically disclosed.
The foregoing has outlined features of several embodiments so that those skilled in the art may better understand the present disclosure. 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 scope of the present disclosure, and that they may make various changes, substitutions and alterations herein without departing from the scope of the present disclosure.
This application claims benefit of the May 15, 2017 filing date of U.S. provisional application 62/506,337, which is incorporated by reference herein.
This invention was made with government support under Government Contract No. DE-FE0025959 awarded by the U.S. Department of Energy. The government may have certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 62506337 | May 2017 | US |
