Patent Application
20060233647
Not applicable
Not Applicable.
Not applicable
1. Field of the Invention
This invention relates to turbine discs used in rotary mechanisms, such as in steam turbines, gas turbines and jet engines, hydroelectric plants, and in bladed wind turbines. Slotted bladeless discs provide less costly rotor and stator discs than bladed discs or wheels historically used in such turbines. The slotted disc is fabricated from a single blank disk by stamping and forging instead of fabricating and assembling a multitude of individual turbine blades requiring attachments to a central hub
2. Description of Prior Art
Steam turbines were invented during the late 1800s and early 1900s. One of the first patents for bladed steam turbines is found in U.S. Pat. No. 639,608, dated Dec. 19, 1899, by Sir Charles A. Parsons of Newcastle-Upon-Tyne, England and assigned to the Westinghouse Machine Company of Pittsburgh, Pa. Parsons' first steam engine patent was issued in 1884. Additional related patents were issued to C. A. Parsons on Jan. 29, 1924 (U.S. Pat. No. 1,482,031) and on Jun. 14, 1932 (U.S. Pat. No. 1,862,827). Many other patents have been issued relating to the shape of the blades and to the attachment of the blades to the hub of the turbine wheel and thus to the turbine shaft. While many more patents have been issued to improve the seal between the bladed turbine wheel and the turbine housing, seals are not within the scope of this invention.
There is a longstanding need for relatively inexpensive steam driven power generators capable of using renewable sustainable sources of energy. Slotted disc steam turbines are ideally suited for such machines. Wood and other bio-mass burning stoves and boilers are commonly used to generate steam. Other suitable sources of energy include but are not limited to solar energy, geothermal energy and energy from flammable oils, gases and chemicals. There is a further need for small distributed electrical power generating units in remote areas where power distribution lines do not exist. Mainly there is a need for an inexpensive steam or gas turbine to satisfy these requirements. Although small steam and gas turbines do exist, the widespread use of these machines has been greatly prohibited by the cost of bladed turbine discs. My invention will enable the building of small inexpensive power plants to satisfy these needs using stamped, welded and widely available off-the-shelf parts. This invention is not limited to energy derived from steam or gas but can also be applied to hydroelectric power plants, where energy is derived from flowing water or other incompressible fluids, and to wind driven turbine generators.
Nearly all steam and gas turbines use a bladed turbine disc or wheel constructed of individual flat or twisted blades mounted radially on a hub to form a wheel or disc arrangement. The purpose of the bladed turbine wheel is to transform energy contained in high-pressure steam or other fluid media flowing through the blades into rotational energy. Steam does this by harnessing the energy released when gas under pressure flows from a higher temperature and pressure through a turbine stage, wheel or set of wheels to a lower temperature and pressure. High-pressure steam is allowed to expand, resulting in an acceleration of the axial flow of material through the turbine blades. When the high pressure is on one side of the turbine blades and the low pressure is on the opposite side of the turbine blades the flow of steam attains a relatively high rate of speed through the flat, twisted or curved turbine blades. As the material passes through the turbine blades, the direction of the fluid is changed and the resulting reaction creates an equal and opposite force on the turbine blades and thus a torque on the hub and shaft of the rotating wheel.
Structure of the turbine. In a 1911 speech Parsons said:
Turbine blades are generally made of high temperature hardened steel or other alloy capable of withstanding heat and centrifugal forces associated with high speed rotating machinery. Failures in turbine blades can be catastrophic. If one blade fails the resulting imbalance causes the whole machine to become unbalanced and must be shut down to avoid more serious damage. In more serious failures, a blade breaking at high speed results in other blades being shattered as well as the casing containing the high-pressure steam or gas. This condition sometimes results in catastrophic explosions.
The slotted disc
A longstanding need has existed for a simpler, less expensive and easier to fabricate turbine disc, especially for use in rotating mechanism applications. My invention operates using the same properties of steam and hot gases that the well-known bladed turbine discs or wheels use in steam and gas turbines. Unlike bladed turbine wheels, the slotted turbine disc can be stamped from a single piece of material. The slotted disc comprises a disk with a multitude of slots through which steam, gas or other fluid passes at high speed, and through which the direction and speed of the moving media is changed as it passes through the plane of the disc. The action of the change in speed and direction through the slots causes a force to be imposed upon the slot tabs according to the law of action and reaction resulting in a rotational force or torque upon a rotor disc and therefore upon the shaft to which the disc is rigidly attached.
The slotted disc is fabricated from a flat circular steel plate, or disk, by forming slots in the plate through which, in the preferred embodiment, steam is allowed to pass; each slot comprising a dimensioned hole, also called an aperture or orifice, plus an associated shaped tab. The shape of the slot is important and is formed by pressing, hammering, forging, casting or otherwise creating an open orifice or passageway through which steam or other fluid passes, and in the same operation forming the associated tab comprising the same material that was forced out of the plate to form the orifice. The direction of the flow of steam or fluid changes as it passes through a slot. As it passes through a slot from a higher pressure side to a lower pressure side, steam velocity increases, while the temperature and pressure drop, and some of the energy is imparted to the slanted or curved portion of the tab, according to the law of action and reaction. When the disc is connected to a rotating shaft, the force vector applied to the slanted portion of the slot's tab imposes a rotational force, or torque, upon the disc and therefore on the shaft to which it is attached.
A slotted disc illustrated in
The tabs on the downstream side of each slot act in a manner similar to the blades in a bladed turbine. Turbine blades or vanes are alternatively known as buckets. The tabs associated with the slotted disc are functionally similar to the blades in a bladed turbine wheel and hereafter may also be referred to as buckets. Altering the opening of the slots and the shape and angle of the tabs in the slotted disc is equivalent to altering the angle and openings between the blades of a bladed disc. The length of each slot in a slotted disc roughly corresponds to the length of each blade in a bladed wheel, therefore the diameter of the discs do not have to be increased for subsequent turbine stages. Instead of increasing the diameter of the disc, it is only necessary to vary the length and the width of the slots in subsequent stages of the turbine assembly as illustrated in
The same general materials used to fabricate a bladed wheel are used to fabricate a slotted disc, thus maintaining similar thermal and mechanical characteristics of the materials. Seals are attached to turbine discs to reduce leakage between stages. Seals and stuffing boxes as used in turbines are not within the scope of this invention.
With compressible fluids the slots in each consecutive disc increase in size and shape to compensate for the expected drop in temperature and pressure of the fluid through the assembly, as illustrated in
Accordingly, several objects and advantages of my invention are as follows.
An object of my invention is to provide turbine rotor and stator discs for a rotary mechanism, comprising one or a multitude of slotted discs. The rotor disc is the working part of a turbine that converts some of the energy in moving water, steam or gas into mechanical energy, expressed as torque and velocity of a rotating shaft.
An advantage of my invention is the simplicity of manufacturing a turbine disc with a single stamping operation rather than with an expensive bladed disc made from many machined blades requiring complicated blade-to-hub attachments.
It is also an object of my invention to provide simple methods for attaching a slotted bladeless disc to a shaft, such as by welding or by other means generally well known to persons versed in the art and engineering of rotating machinery.
A further advantage of the slotted disc is that it has mechanical strength where the bladed turbine is weak, namely in the blades themselves and in their attachment to the hub and thus the attachment to the shaft.
Furthermore, the slotted disc can be fabricated from much thicker material than common turbine blades, thus providing more strength and more weight to a single turbine stage whereby the added weight tends to act as a flywheel, which tends to reduce certain vibrations unavoidable or difficult to control with thinner lighter material.
Another advantage is that the cost of manufacturing the slotted disc is much less than the cost of machining and fabricating the multi bladed disc. Blades and other parts in bladed turbine wheels must be separately machined. A slotted disc is stamped out of appropriate material in a single stamping operation, thus eliminating many steps in the manufacturing process.
Another advantage is a more uniform distribution of temperature across the surface of the bucket than that of a blade in a bladed turbine. This results in less thermodynamic stress across the surface of the bucket in the slotted disc.
Another advantage is reduced testing and balancing requirements of the assembled wheel.
A further advantage is the smooth surface of the bucket in the slotted disc upon which the moving material impinges compared to the sharp edge of the blade in a bladed turbine wheel. In a bladed turbine, the edges of the blades are worn down by the impact and eroded by the material moving through the circular array of blades. The path of the moving material through the slots in a slotted disc does not encounter sharp edges and the disc is subject to much less erosion from the moving media.
A disadvantage of the slotted disc is that it can not accommodate as many buckets of the same size and the same width as a bladed wheel. A rotor and a stator, if a rotor is used, comprise a single stage. However, an increase in the number of slotted disc stages can be added to compensate for the difference.
Further objects and advantages of my invention will become apparent from a consideration of the drawings and ensuing description.
Preferred and Other Embodiments. The preferred embodiment of this invention comprises a disc with a multitude of evenly spaced slots surrounding a center hole through which a rotatable shaft is inserted; for use in steam turbines and other rotating mechanisms. The cost advantage of stamping out turbine discs over the cost of present methods of fabricating bladed turbine wheels means that stamped discs can be used to build relatively inexpensive turbines. Conversely, the high cost of fabricating bladed wheels means they can only be used in relatively high-powered expensive turbines. Using my invention small steam turbines can be fabricated primarily with stamped and welded parts that require a minimum of machining operations compared to the bladed turbine. The ability to obtain small inexpensive turbines suggests that such turbines connected to suitable electric generators may be used to power households and other facilities where electric power is not presently available or where it is cheaper to produce electricity than to purchase it. It is suggested that such small turbines can be adapted to power vehicles by using direct drives or by using the output to drive a generator and an electric motor or a combination of both.
Another embodiment of this invention is for use in low-pressure steam turbines. Bladed steam turbines are generally used with high pressure and high temperature steam where high power electrical generation is required, such as in electric power plants. The cost advantage of fabricating and operating a small steam turbine using slotted turbine discs suggests that such distributed power sources can be installed in remote places where power lines from central power plants are not available.
Another embodiment of this invention is for use as an impeller in a compressor or pump.
Another embodiment of this invention is for use as a rotor in a hydroelectric plant turbine where hydro turbines are used to turn generators.
Another embodiment of this invention is for use in a wind turbine.
Another embodiment of this invention is for use as a toy, similar to a pinwheel.
Another embodiment of this invention is for use as a lawn and garden ornament, commonly known as a whirligig.
Another embodiment of this invention is for use as a rotor for a helicopter or other lifting machine.
A further embodiment of this invention is for use as a fan to move air in the same manner as any bladed fan.
In the preferred embodiment the shape of the slot is oblong or eye-shaped, but it could be round, square or triangular or have other geometrical shapes. In the preferred method, one side of the slot, or bucket protrudes from the rear or downstream surface of the flat plate, away from the direction of the flow of steam through the slot. It is possible for the other side of the slot to protrude toward the front of the disc in such a way as to open the pocket to allow more steam to pass through it. Control of the amount of steam passing through the slots is attained by varying the size and shape of the openings in the slots and by controlling the temperature, pressure and volume of the supply steam.
A complete turbine can have a single disc, forming a single stage turbine, or a multitude of discs, forming a multi-stage turbine. An important difference between a conventional bladed turbine and a slotted disc turbine, is that all the slotted discs can be made with the same outer diameter. The first stage has smaller slots than the last stage and each intermediate disc in the turbine has sequentially larger slots. This allows more steam to pass through each successive disc in a way that is similar to the flow of steam through a conventional bladed turbine, without the need to have each disc increase in diameter.
The shape of the slots in the disc can be varied to accommodate a wide range of requirements to control the flow of steam. A narrower slot will generally result in less steam passing through but at a higher speed than that of a wider slot. A wider slot will allow more steam to pass through at a slower speed. The length of the slot can also be varied to control the amount of steam passing through it. The longer the slot, the more steam will pass through it. It is noted here that if the slot is too wide or too long, steam can pass through the slot without changing direction. If this occurs some rotational forces on the disc are lost and the efficiency of the turbine is reduced.
The tab in the back of the slot, or lower pressure side of the disc, can be varied in shape and angle from the plane of the disc to control the direction of the steam leaving the tab. The angle of the tab relative to the plane of the disc must always be an acute angle of less than ninety degrees. The shape and position of the tab can vary along the radial of the disc on which it resides in such a manner as to emulate the bent shape of a turbine blade. The strength of the tab can be increased by adding more material to the back of the tab by welding or by other fabrication methods well known to those skilled in the arts of sheet metal fabrication. Tabs can be fabricated separately from the disc and attached to the back of the disc by any means known to those skilled in the art. The preferred embodiment is to fabricate the tabs as part of the original round plate by means of first cutting slits in the disk and then pressing the tab in such a way that it does not tear or otherwise significantly weaken the plate. After forming the slots, the entire disc can be heat treated as is commonly done for bladed turbines.
Two types of solid plates can be used in the fabrication of the bladeless disc, either thin plates or thick plates. Other types of plates can be fabricated from laminated, sandwiched or honeycomb materials. The description above is related to the fabrication of bladeless discs made from thin plates. Thick plates can also be used as described above, or the slots can be formed in a thick plate without the need for a tab, or with the use of a smaller tab. If the slot in the thick plate is cut along a radial of the disc, but the direction of the slot is other than perpendicular to the plane of the disc, then the direction of the flow of steam through the plate will be altered in such a manner as to result in a component force vector perpendicular to the radial and along the plane of the disc. Redirecting the steam in this manner is the same as redirecting the steam using the tabs on the back of the thin plate. One reason for using a thick or honeycombed plate rather than a thin plate is to increase the strength of the disc, which allows higher steam pressure and greater flow of material through the slots. For high-pressure turbines, the edges of the slot can be processed and shaped to further reduce wear and erosion. The same processes used to increase the strength of blades in a bladed turbine can be used to strengthen the slots in a bladeless disc. Tabs can be added to the back of the thick plate or honeycombed disc to enhance the redirection of the steam flowing through the disc.
The embodiments of the invention illustrated in the following drawings are disclosed in greater detail in the Description:
b illustrates an embodiment of a steam turbine comprising only slotted rotor discs.
Preferably the slots in the disc are geometrically located along radials and equally spaced to assure a balanced disc.
As illustrated in
The shape and thickness of the slots vary depending on the strength and stiffness required for disc operation under thermal and mechanical stresses encountered in operation of the turbine. In
In
It is noted that the increase in the size of the slots from the first through the last stages in a slotted disc turbine emulates the increase in the length of the turbine blades in a bladed turbine without requiring a conical shaped casing.
It can further be seen that the direction of the flow of steam, in the case of a steam turbine, through the disc slots changes as the steam passes through each disc. The purpose of the slots and buckets in the stationary disc [320] is to redirect the flow of material in such a manner as to increase the force of the impinging fluid on the buckets of the next rotating disc [200]. As the steam or fluid moves through a bucket in the rotating disc, it changes direction resulting in a reaction that produces a component of a force vector in a direction parallel to the plane of the disc and perpendicular to a radial, thereby producing torque on the rotating shaft. The sum of all the torque components from all the buckets in all the rotating discs in the complete turbine assembly equals the total torque on the rotatable shaft.
In
The inner ring [460] may be attached to the disc in the same manner as the outer ring. The primary purpose of the inner ring is to strengthen the area of the disc where large forces may build up around the center portion of the disc in the area of the shaft attachment [450]. The inner hub ring may also be used as a means of spacing the adjacent discs and to provide a means of attaching the disc to the shaft. In
Designing a slotted disc or template. In accordance with the spirit of complete disclosure, the following detailed step-by-step method of creating a slot pattern is hereby included in this description. A single template illustrated in
Suggested tools are as follows:
Endcaps or endplates [882] and [884] are attached to the ends of the cylindrical casing [310] to provide a means of holding the entire rotor assembly in place during operation of the turbine. The shaft is precisely located by positioning end bearing assemblies comprising bearings or bushings [862] and [872], washers [860] and [870], seals [864] and [874], and retaining nuts [866] and [876]. The bearing assemblies are inserted within spaces provided in the endcaps and secured to the shaft [328] by the threaded retaining nuts [866] and 867].
In this illustrated preferred embodiment of a small slotted disc steam turbine, steam enters the assembly through the input ports [810] [812] and passes through a multitude of nozzles [842] [843] which increase the velocity of the steam. As steam passes through the slots in the multitude of turbine stages, torque is applied to the rotatable shaft as previously described. While there are many ways to transfer mechanical energy from a rotating shaft, one of the easiest means is by use of a belt and pulley system, whereby a belt pulley [850] is attached to the shaft as illustrated in
A multitude of exhaust ports are arranged as a means of removing exhaust materials from the turbine casing. Two such ports [820] and [822] are illustrated in
b illustrates a turbine without stationary nozzle discs. This embodiment includes several stages of rotating slotted discs. The first slotted disc [803] has small slots and the last disc [896] has the largest slots. The discs in between have slots that gradually increase in direct proportion to their distance from the first disc. The intent here is to increase the active area of the disc or the slots so as to compensate for the reduction in pressure as a compressible fluid passes from one stage to the next. For a multi-stage turbine, the slots in each successive disc increase in proportion to the number of stages. In a ten-stage turbine, the smallest slots in the first disc are approximately one tenth the size of the slots in the largest disc and the size of each successive disc increases by one tenth the size of the largest slots in the final stage. This gradation in slot size allows a similar force on each disc to be realized from the steam as it passes through the disc, since the pressure of the steam drops as it passes through each disc. In
In the case of incompressible fluids, it is not necessary to vary the size of the slots.
In
An advantage of this arrangement is that it can be made to fit in irregular or narrow spaces where needed and where suitable steam, gas or other liquid is already available.
Another advantage is that the more stages a turbine has, the slower it runs. However, there is an inherent theoretical limit to achievable efficiency, called the Betz limit of approximately 59% for bladed turbines, which also applies to slotted disc turbines.
Another advantage related to the lower speed is the reduction of high-speed gears required in the power train of the bladed turbine. Lower gear ratios result in less expensive gearing in the power train.
| Number | Date | Country | |
|---|---|---|---|
| 60672196 | Apr 2005 | US |
