US3927521A

US3927521A - Multicone exhaust diffuser system for a gas turbine

Info

Publication number: US3927521A
Application number: US433960A
Authority: US
Inventors: Birger O Hugoson; Carl A Rohr
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1974-01-16
Filing date: 1974-01-16
Publication date: 1975-12-23
Anticipated expiration: 1992-12-23
Also published as: JPS5323445B2; CA1008676A; JPS50101712A

Abstract

An exhaust system for hot motive fluid gases expelled from a gas turbine wherein the hot gases pass into an annular chamber, thereafter the gases are directed through a circumferential array of transition members. Each transition member directs the exhaust gases through generally axially directed diffuser cones. The downstream bearing, the bearing support members and the last row of blades in the gas turbine, are easily accessible because the exhaust cones direct the hot exhaust gases away from those areas.

Description

United States Patent 1 Hugoson et al.

MULTICONE EXHAUST DIFFUSER SYSTEM FOR A GAS TURBINE Inventors: Birger O. Hugoson, Wallingford;

Carl A. Rohr, Springfield, both of Pa.

Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

Filed: Jan. 16, 1974 Appl. No.: 433,960

US. Cl 60/3931; 60/3932; 415/219 R Int. Cl. F02C 7/20; F01D 25/24 Field of Search 60/3932, 39.5, 39.31;

415/201, 209, 219 R, 139; 181/33 H, 33 HB, 33 HD, 41, 46; 239/265.25, 265.27

References Cited UNITED STATES PATENTS Buckland et a1 416/171 Dec. 23, 1975 2,922,278 1/1960 Szydlowski 60/3936 2,933,893 4/1960 Blyth et al.... 3,448,825 6/1969 Booth 181/33 HB Primary Examiner-G. J. Husar Assistant Examiner-Thomas 1. Ross Attorney, Agent, or Firm--F. A. Winans [57] ABSTRACT 5 Claims, 3 Drawing Figures US. Patent Dec. 23, 1975 Sheet 1 of2 3,927,521

US. Patent Dec. 23, 1975 Sheet 2 0f 2 BACKGROUND OF THE INVENTION 1. Field of the Invention:

This invention relates generally to gas turbines and more particularly to exhaust systems for gas turbines.

2. Description of the Prior Art:

As is well known in the art, low pressure ends of axial flow elastic fluid turbines are usually provided with a diffuser for directing fluid discharged from the last stage turbine blades along a smooth aerodynamic path to the ambient atmosphere, as in the case of gas turbines. Diffusers for large stationary gas turbines are often formed from radially spaced inner and outer fairing members forming an annularshaped exhaust outlet for the discharged fluid. The downstream axis support bearing is disposed within the inner fairing member, and aerodynamically-shaped bearing support struts are disposed acrossthe hot exhaust gas annular flow path between the two fairing members. The hearing support struts also, however, create a turbulent flow of exhaust gas, thereby reducing the efficiency of the diffuser in its ability to convert the kinetic energy of the moving fluid into pressure. The discharged fluid does not move smoothly into the exhaust section of the turbine, with major consequences being a decrease in overall turbine efficiency. The downstream support bearings, within the inner fairing memberis disposed within an area that is difficult to reach and hence difficult to inspect without major dismantling of the exhaust system.

In addition to hampering serviceability, present design calls for the use of bearing support strut members being disposed across the hot gas flow path and through site of the purchaser. This places restrictions on the allowable shippable dimensions of the turbine member itself.

An object of the present invention is to overcome the problems presented above in the prior art.

Anotherobject of the present invention is to permit the shipping of as large a gas turbine as practically possible with minimum field assembly.

A still further object of the present invention is to provide an exhaust system for a gas turbine that will permit access to the downstream support bearing.

Yet another object of the present invention is to provide an exhaust system for a gas turbine having a minimum decrease in turbine efficiency due to the turbine exhaust gas diffuser.

SUMMARY OF THE INVENTION A system for ducting hot exhaust gases from a gas turbine is provided wherein the downstream bearing, shaft and last stage blades are accessible for service. In this system, the exhaust gases, after passing through the last stage blades, enter an annular chamber. From this chamber, the exhaust gases pass through transition members into conically-shaped ducts or diffusers which are in registration with the transition members and the annular chamber. The conical diffusers have their in creasing diameters in the generally axially rearward direction.

Bearing support struts are disposed between the diffusers. This avoids the need for the support struts being disposed through the hot exhaust fluid flow area, which would decrease the overall turbine efficiency. The arrangement also reduces the allowable transport or shipping size of the turbine, and reduce the downstream bearing, shaft and last stage blade accessibility.

Other details and advantages of this invention will become'apparent as the following description of a present preferred embodiment proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the exhaust end of a gas turbine with half of the exhaust system cut away;

FIG. 2 is a side view of an exhaust diffuser arrangement showing the different zones therein; and

FIG. 3 shows an arrangement of a pair of exhaust hoods that connect to the exit end of the diffuser cones.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, particularly to FIG. 1, there is shown a portion of an axial flow gas turbine 10 including a rotatable shaft 12, a last stage rotor disc 14 mounted on said shaft 12, a plurality of radially directed blades 16 mounted on said disc 14, a bearing 18 supporting the downstream end of said shaft 12, a plurality of elongated bearing support struts 20, and an exhaust diffuser arrangement 22. As is well known in the art, hot motive gas fluid is supplied through the motive fluid flow passageway, comprised of the rotating and stationary blades, only the rotating blades 16 of the last stage are shown. During flow past the blades, the hot motive gaseous fluid is expanded to impart rotational energy to the rotor.

The gas turbine 10 in the illustration shown, is of the axial flow type, having a shell structure 24 and turbine support member 26. The hot motive fluid is directed from the last row of blades 16 to an exhaust annulus 28, which is defined by a generally toroidal-shaped ring 30 on the downstream end of the gas turbine 10. The toroidal-shaped ring 30 has a plurality of transition members 31 attached adjacent orifices, not shown, in the toroidal-shaped ring 30. g

A plurality of diffuser cones 32, eight in this example, but only four shown, are attached to the transition members 31 and hence in registration with the toroidalshaped ring 30, which comprise the exhaust diffuser arrangement 22. A dotted outline shown in FIG. 1 represents an exhaust hood member 37 which is part of the exhaust system. A cross-section of the toroidalshaped ring 30 and a side view of the transition member 31 and diffuser cone 32, that comprises an additional portion of the exhaust fluid diffuser arrangement 22, is shown in FIG. 2. Several zones are indicated therein. Zone A is called the annular diffuser zone. The walls of zone A are curved so as to act to suppress separation of the hot fluid exhaust gases. A portion of the energy conversion from kinetic energy into static pressure can be made in the hot exhaust gases before entering the next zone, called the transition zone, and indicated by the letter B. A slight reduction in cross-sectional area in the direction of the exhaust gas flow is introduced on the toroidal ring 30 adjacent the transition member 31, to keep the exhaust gas flow aligned. The velocity distribution of the hot exhaust gas flow is kept as uniform as possible as it enters the third zone called the conical diffuser zone, and indicated by the letter C. The transition member 31 and the exhaust diffuser cone 32 each have a flange, 33 and 34, at their juncture, to permit assembly thereby.

An exhaust hood arrangement 36 is shown in FIG. 3. The exhaust hood arrangement 36 is comprised of at least two

exhaust hood members

37 and 37 The exit ends of the conical diffuser cones 32 mate with orifices 38 in each

exhaust hood member

37 and 37 The

exhaust hoods

37 and 37, deflect and duct the hot fluid exhaust gases away from the turbine 10., Tie bars 39 connect the

exhaust hood members

37 and 37 to take the lateral forces generated therein by the turning of the hot gaseous exhaust fluid flow. Axial forces within the

exhaust hood members

37 and 37 are transmitted by other tie rods 41 back to the gas turbine support members 26. Expansion joints 38 are provided at the junction of the diffuser cones 32 with the

exhaust hood members

37 and 37. The exhaust hood members 37 and 37' are each separate shippable members themselves, permitting simple field assembly.

Utilizing this exhaust arrangement, the exhaust diffuser cones are easily removable for inspection and repair of the downstream bearing 18, the shaft 12 and the last stage blades 16. The turbine itself may be shipped to the field without the exhaust diffuser arrangement 22 attached thereto. Prior art arrangements require complete assembly before shipment because the bearing support struts extend through the exhaust annulus. That is, it must be assembled prior to shipment for support of the bearing and shaft. This reduces the maximum size of the turbine shippable because of the overall dimensional limitation imposed by the shipping envelope.

While we have shown and described a present preferred embodiment of this invention, it is to be distinctly understood that the invention is not limited thereto, thatthe invention may be otherwise variously embodied within the scope of the following claims.

We claim:

1. In a gas turbine installation including: a housing, a shaft rotatably mounted in said housing by means including a downstream bearing, alternating annular arrays of stationary and rotatable blades, said rotatable blades being attached to said shaft, a hot motive fluid flow path within said housing, the hot motive fluids driving said rotatable blades, an inlet in said turbine for the hot motive fluid, and a hot motive fluid exhaust outlet arrangement for the hot motive fluid, said hot motive fluid exhaust outlet arrangement comprising:

an annular chamber downstream of the last array of said rotatable blades,

a plurality of generally axially disposed transition members in registration with said annular chamber,

an annular array of a plurality of tubular-shaped generally axially directed hot motive fluid exhaust ducts, each in fluid communication with one of said transition members, said ducts being generally comprised of truncated diffuser cones, the smaller diameter of said truncated cones mating with said transition members,

a plurality of downstream bearing support members disposed between adjacent exhaust ducts, said bearing support members extending between said bearing and said housing,

said hot motive fluid exhaust ducts being detachable from said transition members, to permit access to the bearing and blade assemblies, said bearing support members being free from contact with the hot motive fluid exhaust to limit any thermal effects therein,

a pair of exhaust hoods attached to the downstream ends of said diffuser cones with an expansion joint therebetween, each of said exhaust hoods directing the flow of the hot motive fluid exhaust away from the gas turbine, each of said exhaust hoods having an array of half of said plurality of diffuser cones attached thereto.

2. A gas turbine installation as recited in claim 1, wherein said downstream bearing is disposed axially beyond said annular chamber, said downstreambearing being generally in contact with the ambient air.

3. A gas turbine installation as recited in claim 1, wherein said truncated diffuser cones have flange portions which attach to flange portions of said transition members.

4. A gas turbine arrangement as recited in claim 1, wherein tie bars connect the two exhaust hoods together to restrain the lateral forces generated by the turning of the flow of exhaust gases.

5. A gas turbine installation as recited in claim 1, wherein a plurality of tie bars transmit axial forces generated within the exhaust hoods to the gas turbine housing.

Claims

1. In a gas turbine installation including: a housing, a shaft rotatably mounted in said housing by means including a downstream bearing, alternating annular arrays of stationary and rotatable blades, said rotatable blades being attached to said shaft, a hot motive fluid flow path within said housing, the hot motive fluids driving said rotatable blades, an inlet in said turbine for the hot motive fluid, and a hot motive fluid exhaust outlet arrangement for the hot motive fluid, said hot motive fluid exhaust outlet arrangement comprising: an annular chamber downstream of the last array of said rotatable blades, a plurality of generally axially disposed transition members in registration with said annular chamber, an annular array of a plurality of tubular-shaped generally axially directed hot motive fluid exhaust ducts, each in fluid communication with one of said transition members, said ducts being generally comprised of truncated diffuser cones, the smaller diameter of said truncated cones mating with said transition members, a plurality of downstream bearing support members disposed between adjacent exhaust ducts, said bearing support members extending between said bearing and said housing, said hot motive fluid exhaust ducts being detachable from said transition members, to permit access to the bearing and blade assemblies, said bearing support members being free from contact with the hot motive fluid exhaust to limit any thermal effects therein, a pair of exhaust hoods attached to the downstream ends of said diffuser cones with an expansion joint therebetween, each of said exhaust hoods directing the flow of the hot motive fluid exhaust away from the gas turbine, each of said exhaust hoods having an array of half of said plurality of diffuser cones attached thereto.

2. A gas turbine installation as recited in claim 1, wherein said downstream bearing is disposed axially beyond said annular chamber, said downstream bearing being generally in contact with the ambient air.