Geothermal Turbine

The present invention relates to turbines and pertains particularly to an improved two-phase fluid turbine for geothermal fluids.

The end of the era of low cost fossil fuels has created a substantial interest in alternate sources of energy. Among these sources of energy yet to be fully developed is that of geothermal energy. Enormous amounts of energy are stored beneath the earth surface in the form of high temperature rocks, molten lava, and other materials including water and steam.

Attempts to develop this source of energy by means of turbines utilizing subterranean sources of steam have met with numerous difficulties. The principal problems with geothermal fluids are the typical multiphase character thereof and the entrapped minerals and particles within the fluids. Conventional steam turbines are impractical as a means of extracting the energy from such geothermal sources.

Attempts to separate the phases of the fluid to utilize only the steam and to remove entrapped particles and dissolved minerals prior to use has been impractical because of the high cost thereof.

It is therefore desirable that a turbine be available which is capable of utilizing two-phase geothermal fluids directly without the necessity of filtering, separating and the like.

It is therefore the primary object of the present invention to provide an improved two-phase geothermal turbine.

In accordance with the primary aspect of the present invention, a geothermal turbine includes a housing defining a generally cylindrical turbine or rotor chamber having a curved end and peripheral nozzle inlets with a central axial outlet and containing a rotor having a plurality of radial scroll segment overlapping blades positioned and configured to provide maximum surface contact with multiphase geothermal fluid for utilizing boundary layer drag for extracting the kinetic energy of the fluid and converting it to a rotary power.

The above and other objects and advantages of the present invention will become apparent from the following description when read in conjunction with the drawings wherein:

FIG. 1 illustrates schematically a typical geothermal turbine installation;

FIG. 2 is an enlarged top plan view of the turbine unit with portions cut away;

FIG. 3 is an underside view of the turbine unit with the lower housing removed;

FIG. 4 is an enlarge sectional view taken on line 4--4 of FIG. 2; and

FIG. 5 is a sectional view taken on line 5--5 of FIG. 4.

Turning to the drawings, FIG. 1 schematically illustrates a typical geothermal turbine installation designated generally by the numeral 10. The installation includes a geothermal well including piping or casing 12 tapping or communicating with a geothermal collection dome 14 for conveying geothermal fluids which typically include a two-phase combination of steam and water to the surface for utilization in a turbine as illustrated. The pipe or conduit 12 includes a suitable control valve 16 and communicates to a turbine 18 for driving an electrical generator 20 by a shaft 22. The fluids pass through the turbine and the energy is extracted therefrom by way of the turbine and converted to rotary power which is utilized to drive the generator 20. The spent fluid is collected and an effluent collector 24 where it is by means of a discharge tube or pipe 26 back to the earth formation by means of a second or return well. A valve 28 in the line 26 is utilized to control the flow therein. A booster pump 30 driven by motor 32 and connected to the pipe 26 by means of bypass or booster conduits 34 and 36 may be used to apply sufficient pressure to the effluent to return it to the earth formation. A bypass line 38 controlled by valve 40 may be utilized to bypass the turbine when necessary or partially bleed off the fluids as desired.

The formation itself may supply sufficient water and/or steam to satisfy the requirements requiring only a drilling of a well and tapping into the source of the water or steam. In other instances it may be necessary to pump a source of water to the formation to be heated and returned to the turbine generating system. In any event, the present invention contemplates the utilization of two-phase fluids, such as would be obtained primarily from geothermal sources wherein the fluids also may contain dissolved mineral salts and/or other solid particles.

Turning to FIGS. 2 through 5, a preferred embodiment of a turbine embodying the principals of the present invention is illustrated in substantial detail. The turbine includes a housing 42 having a somewhat, or generally flat circular configuration, however with the upper end 44 viewed in FIG. 4 having a curved configuration extending outwardly and curving from the outer diameter radially inward toward the axis and then extending a curving back axially, inwardly to the central axis. A substantially flat circular lower wall 46 connected to the substantially cylindrical side walls 48 complete the basic housing structure.

The housing forms a central rotor chamber 50 having a configuration substantially identical to that described for the housing. This chamber has a substantially flat bottom wall and an axially downwardly curved upper wall to the center axis.

A manifold 52 of a circular configuration surrounds the circumference or outer diameter of the housing and includes an inlet line 54 and a plurality of nozzles 56 communicating from the manifold 52 into the vane chamber, preferably at an angle somewhere on the order of about 35.degree.. This angle can vary within limits not yet established. However, the angle of about 35.degree. is found to be preferred angle for the illustrated embodiment.

It will be appreciated that both steam and/or water may be injected through the nozzles 56 which for purposes herein are schematically illustrated. It will be understood that specific configurations for the nozzles may be developed and may have critical significance.

Referring to FIG. 4, a rotor is mounted within the chamber and supported therein on a drive shaft 55 which, in turn, is mounted for rotation within conventional bearings 57 and 59 within the turbine housing. The rotor includes a central cylindrical core structure 58 secured in a suitable manner directly to the drive shaft 55. The central core 58 defines a central annular fluid outlet or exit passage including inlet ports 60 communicating fluid from the vane chamber along the passage to outlet ports 62 which in turn communication with an outlet port or conduit 64. A radial flange 66 extends outward from the axial center of the central core 58 for mounting and supporting one side of a plurality of identical turbine blades 68. The turbine blades are identical in construction and in the illustrated embodiment consists of six in number, each forming a segment of substantially 90.degree. thereby overlapping each adjacent blade as best seen in FIGS. 3 and 5. These blades may be variously described as a segment of a spiral evolute or a scroll as these terms may be broadly defined. Each blade comprises a segment of a geometric figure which is hollow forming an internal channel and progressively and continuously without steps decreases in radius and in axial width with the direction of rotation about the axis.

Referring first to FIG. 4, it will be seen that each blade includes a generally flat bottom wall 70 with a curved upper wall 72 joined at their outer peripheries with a generally straight peripheral wall 74 that progressively decreases in radial position from the central axis from a trailing edge or tip 76 thereof to a leading edge or tip 78. The bottom side 70 as seen in FIGS. 3 and 5 terminates in a straight forward edge 80 with a similarly shaped trailing edge 82.

As will also be appreciated from FIGS. 3 and 5, each blade has an enlarged front end converging downward both in radius and width to a small trailing end that is viewed from the nozzle intercepting end of the blade with the small front edge extending into the enlarged trailing end of a preceding or adjacent blade forming a peripheral flow channel from the exterior of the rotor to the interior thereof. As will be also appreciated from viewing, particularly FIGS. 2 and 5, the angle of the blades at the outer end and along the surface is such that only a small frontal area is presented to the respective nozzles resulting in flow from the nozzles passing along the exterior and interior surfaces of the respective vanes. This, as will be appreciated from the following discussions results in a transfer of energy from the fluid to the fluid and then to the rotor vanes by way of boundary layer drag or friction between the fluid and the adjacent blade.

Turning to FIG. 2, the curved edge or end 72 of each respective blade is formed with a curved forward edge spiralling downward from the outer rear tip 76 inward to the central or rotary axis of the rotor. This together with the upper wall curvature directs the fluid inward and slightly axially downward along the axis of the rotor.

While the rotor has been illustrated, described with the axis being vertically oriented with certain walls being upper and certain being lower, it should be understood that the turbine will function in a horizontal axis position with the axis positioned horizontally. The particular configuration, however, has been designed to provide a preferential flow of the discharge fluids downward through the passage in the rotor along the axis to the discharge port 64.

In operation, a pressurized fluid such as a geothermal fluid having a mixture of water and steam, is introduced into the turbine via the inlet port 54 into the manifold 52 passing from the manifold by way of nozzles 56 into the rotor chamber engaging the trailing tip or edge of the rotor blades as it passes into the rotor chamber. Some of the liquid in the fluid will flash to steam as it passes from the nozzles increasing the steam and expanding gasses in the chamber. A certain amount of the fluid (i.e., water) will accumulate in and swirl around as a body within the chamber. The body of fluid will form a vortex, contacting and engaging the vanes and carrying them along within the chamber. The combination of the rotor chamber and the blades together with the flowing fluid, creates a vortex with the fluid flowing inward to the center low pressure vortex area of the rotating fluid. The fluid flowing along, or attempting to pass along, the surfaces of the blades of the turbine transfers the kinetic energy thereof directly to the blades by means of a boundary layer drag and as its energy is dissipated it moves downward and toward the low pressure center or vortex in the chamber. The fluid as its energy dissipates flows into the central passageway in the rotor by way of ports 60 and out port 62 through the discharge port 64 and returns to the reinjection well.

Thus, while we have illustrated and described our invention by means of specific embodiments, it is to be understood that numerous changes and modification may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.