Patent Application
20090087334
The present invention relates in general to cryogenic refrigeration cycles useful in commercial and industrial applications including the liquefaction of gases, and more particularly to a sliding vane compression/expansion device that can operate in extreme conditions of pressure and temperature differentials and incorporate a very high expansion/compression ratio to deliver high operating efficiencies.
Typical sliding vane expanders/compressors are designed as low cost, medium efficiency pieces of equipment. Materials of construction are normally limited to very basic materials and uses to very benign types of fluid media. There are of course some exceptions in special applications. Most common uses are for low-pressure air motors/compressors and low-pressure liquid (hydraulic) pumps and motors. There are also some applications in medium pressure aircraft hydraulic pumps and motors. These devices are considered a “Positive Displacement Machine,” much like a piston style compressor.
Sliding vane rotary devices generally comprise straight vanes slidably received within respective slots radially formed in a rotor. As the rotor spins, vanes are driven outward by centrifugal forces to an extent constrained by the wall contour, so as to execute radially reciprocating motion as the rotor spins. In an effort to reduce vane tip loading and increase outward radial movement response, a variety of vane actuation methods have been developed, such as including a biasing spring disposed at the base of each vane, employing a pair of controlling sidewall cam grooves engaged by sub-shafts fixed to lower side portions of a vane, or using a transfer passage connecting a pressurized fluid to the base of the vanes. Although the functionality of such means of vane actuation have been proven, they are characterized in some respects with increased friction, fluid slip, and leakage.
Typically the rotor assembly of a sliding vane rotary device is set off center the maximum allowable amount from the centerline of the round chamber. This permits a nominal maximum offsetting mechanical inlet/discharge expansion/compression ratio (expansion/compression ratio) of approximately 7.5 to 1. More common ratios are in the 6.5 to 1 range. These machines are recognized to be generally “leaky” in most instances, and by-pass slippage of the fluid media involved is controlled only by fit and finish. In many instances these fits and finishes are deliberately designed to be on the “loose side” to facilitate ease of manufacture and assembly. This creates a device that performs generally poorly, efficiency wise, but sufficiently well enough to accomplish its function.
Many industrial gases such as propane, butane and carbon dioxide can be liquefied by placing them under very high pressure. However, producing liquid from methane may not be achieved with high pressure alone. To this extent, methane, a cryogenic gas, is different from other industrial gases. To liquefy methane it is typically necessary to reduce the temperature of the gaseous phase to below about −160° C., depending upon the pressure at which the process is operated.
Therefore, when employing such a sliding vane expander/compressor for the production of liquefied natural gas, it would be desirable to augment the general design of these devices to specifically create a unit that can operate in extreme conditions of pressure and temperature. It would also be advantageous to incorporate a very high expansion/compression ratio into a sliding vane device.
Accordingly, the present invention relates to a sliding vane expander/compressor for both cryogenic and normal refrigeration cycles, including the production of liquefied natural gas, which can operate in extreme conditions of pressure and temperature. The device incorporates replaceable wear elements as well as functional design elements into a sliding vane device to permit processing of a wide variety of gases (for example, but not limited to, methane, nitrogen, oxygen, argon, etc.), liquids and other media under very extreme conditions, including, but not limited to, super-heated steam, cryogenic liquids, bi-phase gas/liquids (wherein both gaseous and liquid media co-exist or are created in the same area), plasma media, semi-solids and powders.
One aspect of the invention provides a sliding vane expander/compressor device for receiving a cooled, compressed natural gas feed stream and expanding the stream to form a bi-phase stream with a vapor component and a liquid component, the device comprising: (a) a stator comprising an inner polydynamic ellipse profile, an inlet port and at least one discharge port; (b) a rotor rotatably supported in the stator for rotation about a main shaft, the rotor comprising a plurality of vane slots for receiving sliding vanes; and (c) a plurality of sliding vanes, each vane adapted to be slidably mounted within one of the plurality of vane slots in the rotor.
Another aspect of the invention provides a sliding vane expander/compressor device for receiving a cooled, compressed natural gas feed stream and expanding the stream to form a bi-phase stream with a vapor component and a liquid component, the device comprising: (a) a stator comprising an inner polydynamic ellipse profile, an inlet port and at least one discharge port; (b) a rotor rotatably supported in the stator for rotation about a main shaft, the rotor comprising a plurality of vane slots for receiving sliding vanes; and (c) a plurality of sliding vanes, each vane adapted to be slidably mounted within one of the plurality of vane slots in the rotor, wherein each sliding vane comprises: (i) a vane vent operable to provide an escape path for fluid; (ii) a vane tip insert configured to be retained at the top of the vane, wherein the vane tip insert is made of a low friction material; (iii) a pair of vane bearing inserts configured to be retained within each bottom face of the vane; (iv) a pair of vane side seal inserts operable to seal the side ends of the vane against the rotor housing, wherein each of the vane side seal inserts are preloaded from behind by a waffle spring; and (v) a plurality of vane load springs adapted to stabilize the vane tip within the stator.
Another aspect of the invention provides a positive displacement sliding vane expander/compressor device, comprising: (a) a stator comprising an inner polydynamic ellipse profile, an inlet port and at least one discharge port; (b) a rotor rotatably supported in the stator for rotation about a main shaft, the rotor comprising: (i) a plurality of vane slots for receiving sliding vanes, each of the plurality of vane slots comprising an end support and a pair of rotor bearing inserts; (ii) outer rotor end seals; and (iii) inner rotor end seals; and (c) a plurality of sliding vanes, each vane adapted to be slidably mounted within one of the plurality of vane slots in the rotor, wherein each sliding vane comprises: (i) a vane vent operable to provide an escape path for fluid; (ii) a replaceable vane tip insert configured to be retained at the top of the vane, wherein the vane tip insert is made of a low friction material; (iii) at least one replaceable vane bearing insert configured to be retained within the bottom face of the vane; (iv) a pair of vane side seal inserts operable to seal the side ends of the vane against the rotor housing, wherein each of the vane side seal inserts are preloaded from behind with a waffle spring; and (v) a plurality of vane load springs adapted to stabilize the vane tip within the stator.
A further understanding of the nature and advantages of the present invention will be more fully appreciated with respect to the following drawings and detailed description.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
As used herein, the term “ambient temperature” refers to the temperature of the air surrounding an object. Typically the outdoor ambient temperature is generally between about 0 to 110 degrees Fahrenheit (° F.) (−18 to 43 degrees Celsius (° C.)).
The term “cryogenic gas” refers to a substance which is normally a gas at ambient temperature that can be converted to a liquid by pressure and/or cooling. A cryogenic gas typically has a boiling point of equal to or less than about −130° F. (−90° C.) at atmospheric pressure.
The term “hydraulic lock” refers to a condition where a vane would be prevented from receding into its rotor groove, thus preventing rotor rotation and perhaps causing structural damage to the machine.
The terms “liquefied natural gas” or “LNG” refers to natural gas that is reduced to a liquefied state at or near atmospheric pressure.
The term “natural gas” refers to raw natural gas or treated natural gas. Raw natural gas is primarily comprised of light hydrocarbons such as methane, ethane, propane, butanes, pentanes, hexanes and impurities like benzene, but may also contain small amounts of non-hydrocarbon impurities, such as nitrogen, hydrogen sulfide, carbon dioxide, and traces of helium, carbonyl sulfide, various mercaptans or water. Treated natural gas is primarily comprised of methane and ethane, but may also contain small percentages of heavier hydrocarbons, such as propane, butanes and pentanes, as well as small percentages of nitrogen and carbon dioxide.
The term “pressure” refers to a force acting on a unit area. Pressure is usually shown as pounds per square inch (psi). “Atmospheric pressure” refers to the local pressure of the air. Local atmospheric pressure is assumed to be 14.7 psia, the standard atmospheric pressure at sea level. “Absolute pressure” (psia) refers to the sum of the atmospheric pressure plus the gage pressure (psig). “Gage pressure” (psig) refers to the pressure (pounds per square inch) measured by a gage, and indicates the pressure exceeding the local atmospheric pressure. Kilopascals (kPa) is the International measure of pressure.
The sliding vane compression and expansion device of the invention is a bi-phase turboexpander capable of forming a bi-phase stream of gas and liquid, namely a refrigerated vapor component and a liquid component. It generally includes radially sliding vanes that convert pressure, velocity and heat energy in the feed gas stream into power, thereby converting potential, kinetic and thermal energy from the gas stream into power. In one embodiment, a portion of a natural gas feed stream can be condensed as liquefied natural gas (LNG) as the compressed and cooled feed gas is directed through and expands within the turboexpander. The device is typically capable of operation in pressure and temperature ranges that permit the condensation of a portion of the feed gas to liquid within its internal flow channels and passages, and is thus able to operate with quantities of condensed liquid that normally can cause hydraulic lock or otherwise stifle the function of current turboexpanders. Additionally, this machine is tolerant of this internal liquid formation without experiencing damage, excessive wear or loss of efficiency.
In general, the invention uses sliding vane positive displacement technology, rather than piston positive displacement or flow-through technology, and includes a polydynamic expansion chamber profile design. As illustrated in
The following design features can augment the general design of the device described above to specifically permit utilization of the device in what would be considered non-standard uses. The device can thus operate in extreme conditions of pressure and temperature, incorporate a very high expansion/compression ratio, and deliver operating efficiencies well beyond what would be considered normal. These features can be applied to both compression and expansion machinery. In many instances the following design features can serve multiple purposes or provide multiple benefits.
Polydynamic Ellipse Profile: the “polydynamic ellipse profile” incorporates an expansion area that is composed of a series of blended, connected radii that appear in the machinery as an ellipse (see
The rate of expansion/compression can be controlled by the rate of opening of the ellipse profile relative to the rotation of the rotor and the number of vanes employed in the rotor. This profile configuration greatly enhances the available expansion/compression area available for the fluid media to be “worked.” In conventional designs the available radial angle of workable area is only about 70 degrees of rotor rotation. With the polydynamic profile this can increased to as much as (or more than in some instances) 210 degrees—three (3) times as much.
Because this profile is infinitely variable, a timeline can be established that can be adjusted for best efficiency of expansion or compression as determined by the media being expanded or compressed. Computer modeling has shown mechanical expansion/compression ratios of 30 to 1, and as high as 55 to 1, are achievable and practical. In practice, an ideal polydynamic profile can be developed using data available regarding the characteristics of expanding gases from The National Institute of Standards and Technology (NIST).
EXAMPLE: A polydynamic ellipse chamber profile of 10.0 to 1 was utilized with operating conditions including a very high inlet pressure of 2,600 psig, a very low discharge pressure of 100 psig, and an operational temperature range of 295 F (+80 F to −215 F). This expander was specifically designed for a media that changes to a bi-phase condition (changes from a gas to a liquid) during its expansion phase.
Vane Vent: A typical vane 30 of the invention is shown in
The venting mechanism is typically a timed event, with the vent holes 34, closing off as the vane slides in its rotor slot under full vane compression, and opening to equalize the pressure on extension. This timing can shut off the flow paths to reduce back flow and leakage to other areas of the machine during operation, thus improving its efficiency of operation. Proper venting also permits “bi-phase” operation of the machinery (i.e. the formation of liquids within the expansion chamber during the expansion process), if used as an expander. The vents provide a lubrication path for the fluid media to reach the bearing surfaces of the vane bearings. Finally, these vents also provide a reverse flow at early exposure to provide a rapid pressure balance between the bottom of the vane and the tip, thereby reducing the possibility of “vane bounce” and bearing overload at the stator profile surface.
Vane Tip Inserts: A vane tip insert 42 is illustrated in
Typically the inserts disclosed herein, including the vane tips 42, are made of a low friction material, such as (but not limited to) straight bronze, polytetrafluoroethylene (PTFE, also known as Teflon) impregnated bronze (available from INA-Schaeffler KG (Germany) under the trade name Permaglide®), bronze impregnated with graphite and/or lead, pure Teflon, reinforced Teflon, ceramics, ceramic based composites, polymers, reinforced polymers, composite polymers, and virtually any bearing quality materials that resists wear under heavy loads and at the same time conforms to distortions in the outer stator housing due to thermal or pressure influences.
The use of an insert in this area also permits an ease of tip profile adjustment to maintain optimal bearing contact area. This permits a profile change in the polydynamic ellipse profile, should conditions require, without replacing the entire vane.
Vane Bearing Inserts: Looking again at
These inserts 44, 46 are designed primarily as replaceable wear component and antifriction element, but also serve other purposes. A design consideration is the high loading of the vane sliding face produced by very high change in pressure between each vane segment of the rotor. By supporting the vane with a specifically designed bearing material, this sliding friction can be reduced to acceptable levels. Properly placed, they can also serve as sealing strips to reduce leak paths in the machine. The fit between the insert and rotor slot can be easily controlled to produce a very precise fit, which reduces “media slippage” and thus improves overall efficiency of the machinery. Common prior art sliding vane compressor/expanders depend on a relatively loose fit between the insert and rotor slot to permit venting of the vanes and low resistance to sliding. Sliding friction is nominally not an issue due to the modest pressure conditions normally encountered. However, this “loose fit” has historically permitted a great deal of media bypass, thus reducing efficiency.
Vane End Seals:
The vane end seals, including the inserts 48, 50 and the waffle springs 52, 54, are employed to seal a leak path at the vane side ends. Due to the extreme temperature differentials this machinery is subjected to, it is necessary to greatly increase the “running clearance” between the vane ends and the end housings of the machine to compensate for dimensional changes of all the interrelated components over the course of operation. These elements both take up this gap and act as bearings to facilitate keeping the vane centrally located in its slot while running and lowering the friction forces at the ends of the vanes, against the end housing.
Vane Load Springs:
Rotor Vane Slot End Support:
Rotor Bearing Inserts:
Outer Rotor End Seals: The primary design function of the outer rotor end seals 66 is to provide a first stage seal at the ends of the rotor in relation to the end housing. The rotor end seals 66 (
Inner Rotor End Seals: The primary design function of the inner rotor end seals 68 (
Floating Thrust Bearing:
Lateral movement of the main shaft 84 is permitted by the bearings within the housings 82, 83. The shaft 84 is thus able to float in a bore 88 of the end seal housing 86 due to sufficient radial and lateral clearances. The bearings within housing 82 and 83 are fixed to the shaft and heavily spring loaded against a locating shoulder provided in the end housing. This spring preload allows the main shaft 84 sufficient lateral flexibility to keep the internal components of the machinery centered and from engaging the end housing faces 86, 87 in a fashion that would create enough interference to interrupt the operation of the machinery or damage the internal components. Though other means could be employed, the self-adjusting, floating bearing feature is typically employed to prevent overloading of end thrust bearing in the machinery and engagement of the rotor end face against the end housings during this shaft growth/contraction.
The sliding vane compressor/expander device of the invention can be incorporated into existing cryogenic refrigeration cycles or natural gas liquefaction systems which are useful in many commercial and industrial applications. For example, U.S. Patent publication No. 2006/0213222 by this inventor, entitled “Compact, Modular Method and Apparatus for Liquefying Natural Gas” can incorporate the sliding vane turboexpander of the present invention, and this application is hereby incorporated herein in its entirety. As part of such a system, the device can receive a cooled, compressed natural gas feed stream and expand the stream to form a bi-phase stream with a vapor component and a liquid component. Typically the sliding vane expander device can receive a cooled feed stream having a temperature of between about −10° F. to about −100° F. The cooled feed stream enters the inlet of the device and is then expanded to lower the pressure, cool it further, and convert the previously gaseous feed stream into a bi-phase stream consisting of a refrigerated vapor component and a liquid component, which exit via the discharge outlets at a pressure of between about 15 to about 135 psig, typically between about 80 to about 105 psig, and more typically between about 90 to about 95 psig. Both the exiting refrigerated vapor and liquid components can typically have a temperature of between about −155° F. to about −240° F., typically about −190° F. to about −215° F., and more typically about −200° F. to about −205° F.
Several features of the sliding vane device of the invention include the following: (1) a vane design which permits high pressure/very low temperature operation; (2) a chamber profile design (polydynamic ellipse) permitting high pressure operation and high efficiency expansion characteristics from high pressure to much lower pressure in a single pass; and (3) a bearing and lubrication design which will permit high pressure, heavy load operation in extreme conditions. The invention can extend the life of wear surfaces and provide better flexibility and durability as compared to conventional turboexpander designs, and increase the range of parameters of operation in regard to temperature, pressure and expansion ratio extremes. The use of the sliding vane turboexpander described above is not limited to use with methane. Indeed, all cryogenic gases, including but not limited to nitrogen, oxygen, argon, etc., and bi-phase gases such as steam can be used with the sliding vane turboexpander.
While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will be readily apparent to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrated examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the invention.
This application claims the benefit of U.S. Provisional Application No. 60/976,048, filed Sep. 28, 2007.
| Number | Date | Country | |
|---|---|---|---|
| 60976048 | Sep 2007 | US |
