Exhaust Noise Suppressor For Gas Turbine

Abstract

An exhaust noise suppressor is provided for a gas turbine. The turbine has an upwardly opening exhaust discharge port, and the suppressor is mounted thereabove, with its exhaust intake port receiving the turbine exhaust. The suppressor comprises an elongated exterior shell, leading from the intake port to a stack, and inside thereof is a perforated interior wall structure or liner, spaced inside the shell walls to provide a space for a packing of high heat resistant sound insulation material. The interior perforated liner attains a high temperature, e.g., of the order of 1,100.degree. F., and is subject to substantial thermal expansion. The invention features an arrangement by which the interior liner is free for thermal expansion within the longitudinal direction of the shell, as well as transversely thereof. The turbine exhaust gas entering the intake port of the turbine casing opens inside a perforated conical diffuser, which reduces back pressure on the turbine to an important degree. Running down the center of the longitudinal gas passage in the casing is a sound absorbing structure comprised of perforated side walls containing high heat resistant sound absorbing material. The perforated walls are covered with fiber glass cloth.

Description

FIELD OF THE INVENTION

This invention relates generally to suppressors for the exhaust discharge noise of stationary gas turbine installations for use as the prime mover for electric generators, for example. A typical turbine installation may drive a 750 watt electrical generator, for example, and the exhaust noise from such a turbine may be very loud, and, at a distance of 50 feet, may exceed levels of tolerance for workmen or other personnel having business in the vicinity.

Accordingly, efforts are now commonly made to reduce the intensity of the noise at the gas discharge outlet of a gas turbine. These efforts have not heretofore been sufficiently successful, and it is a purpose of the invention to provide a practical gas turbine exhaust noise suppressor which is capable of reducing the noise level in the vicinity of the turbine to a degree materially below the best heretofore available, and which will permit personnel to remain indefinitely as close as approximately 50 feet to the turbine, without use of ear protectors, and without liability of ear damage.

BRIEF DESCRIPTION OF THE INVENTION

The invention provides an exterior shell, and a perforated liner positioned therein, with an intervening spacing therebetween for a packing of high heat resistant sound insulation therebetween. The liner receives combustion gases through an intake port opening inside the shell, and preferably through a divergent perforated diffuser, and the heated gases then flow through the liner to a combustion gas discharge stack, and on its way pass over the perforated liner surfaces over the mineral wool sound insulation material. The invention has special provisions for minimized heat transfer from the liner to the shell, and also for thermal expansion of the liner inside the shell. It features also a configuration of sound absorbers inside the liner leading to a surprising extent of acoustic attenuation.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view through a present preferred embodiment of the invention;

FIG. 2 is a transverse section on line 2--2 of FIG. 1;

FIG. 2A is an enlarged fragmentary view of the area encircled by the arrow 2A of FIG. 1;

FIG. 3 is a plan view of the gas intake end of the suppressor;

FIG. 4 is an exploded view of the suppressor of FIGS. 1, 2, and 3;

FIG. 5 is a cross-sectional view of a modified embodiment of the invention; and

FIG. 6 is a graph showing sound intensity in decibels vs. sound frequency.

DESCRIPTION OF A PREFERRED EMBODIMENT

In the drawings, an elongated, horizontally disposed sheet steel shell or conduit is designated at 10, with a gas intake fitting 11 opening into its bottom near one end, and a stack 12 leading upwardly from the top near its other end. The stack may, if desired, be increased in height, as suggested at 12a, but normally uses just the short stack 12.

The shell 10 comprises side walls 13, and top and bottom walls 14 and 15. The shell has in addition opposite end walls 16 and 17. In the present illustrative embodiment, the design concept of the conduit has in view a minimized vertical dimension to permit hauling on a truck on the streets without exceeding height limits. Accordingly, the shell is box shaped, relatively flat, short and wide in cross-section. In other situations, where minimization of vertical height is not a factor, a more economical shape is round (see FIG. 5 ), i.e., cylindrical, and such a shape is an optional alternative. However, the flat shape of the presently described embodiment maximizes the area of later described sound absorption walls for a given gas flow, and is an important improvement when maximized sound suppression is paramount.

Spaced inside the exterior shell 10, for reception of an intervening layer of heat resistant sound insulation material, is a perforated sheet steel liner 18, comprised of perforated side walls 20, a perforated bottom wall 21, perforated end walls 22 and 23, and a perforated top wall 24. The perforations are preferably one-eighth to three thirty-seconds inch holes, on three-sixteenths inch staggered centers. The liner walls may be one-eighth inch in thickness.

Bent inwardly from the upper edge of end wall 16 of shell 10 is a top flange 25, which forms an end portion of the top of the shell. The edge of this flange 25 is abutted by the ends of legs 26 of the top wall 14 of the shell, formed by notching into the end of wall 14 to receive the stack 12. The stack 12 is rectangular in cross section, and to its lower end are affixed the vertical flanges of supporting angle irons 29, the horizontal flanges of which extend horizontally outward, and rest down on top wall 14 and the top flange 25 for support. The perforated liner has a rectangular opening 30 at the stack end of the suppressor which is defined by portions of side and end walls 20 and 22, respectively, extending upwardly above the level of liner top wall 24, and by an upwardly slanting extension 31 from wall 24, and a short vertical wall 32 at the top of the latter. These wall members are snugly received at the top inside the lower end of the stack. The edge of flange 25 is normally (when the apparatus is cool) spaced about three-fourths inch from the perforated end wall 22, as at 33, and the stack support angle members 29 rest slidably on the top 14, 25 of the shell. The gap at 33 closes as the apparatus heats up. The stack thus gradually moves toward the left with the heated perforated liner, and this is permitted by the initial expansion gap 33. The opposite end of the liner remains somewhat loosely anchored in position, by constructions hereinafter described.

The liner 18 is provided on all sides with Z-supports 40 which slidably engage tracks or runners 41 inside the exterior shell 10, which is intended to heat only to a moderate temperature, such as 150.degree. F. In order to minimize heat transfer from the hot running liner to the exterior shell, the tracks 41 at the bottom, as well as similar tracks on the sides and top, are in the form of narrow longitudinally extending flanges, having minimized heat transfer contact with the Z-shaped supports 40. The flanges 42 of these Z-supports 40 are welded to the perforated side, bottom and top walls of the liner, and the opposite flanges 43 thereof thus engage and can slide or shift along longitudinal support tracks 41 in the shell. The webs 44 of the supports 40 are at an angle of approximately 60.degree. to the liner walls and tracks, and accordingly can bend to accommodate lateral thermal expansion of the heated liner. In the particular embodiment shown, the bottom of the shell is so fabricated as to afford a pair of the longitudinal tracks 41, engaged by a plurality, here five in number, of the Z-supports 40.

Each side wall of the shell is equipped with one longitudinally extending angle iron guide or track 41, one flange of which is engaged by three of the Z-shaped suppports on the side of the perforated liner. And finally, the underside of the shell is equipped with two longitudinal angle irons 50, whose depending flanges 41 serve as the tracks or guides engages by four of the Z-shaped supports 40 mounted on the top of the liner.

In the spaces between the shell and the perforated walls of the liner are placed packings 54 of high heat resistant mineral wool, capable of withstanding a temperature of 1,500.degree. - 1,600.degree. F., and chosen for its high noise absorption characteristics. A layer of fiber glass cloth is used between the perforated wall and mineral wool to guard the latter against disruption by the high velocity gases flowing through the liner. The glass cloth is flexible, and therefore acoustically "invisible" to the sound waves in the gases. These waves accordingly are transmitted through the perforations and the glass cloth to the fibrous sound insulation material 54.

The aforementioned gas intake fitting 11 comprises a frusto-conical, upwardly divergent member 55, with a flange 56 at its lower end for attachment to the flange 57 of the combustion gas discharge outlet of the gas turbine. The inlet member 55 projects downwardly somewhat between the bottom of the suppressor shell 10. A frusto-conical wall 58, at a greater inclination than that of the member 55, extends from the lower end of member 55 to the level of the bottom of the shell, being closely received in an opening in the bottom wall of the shell, and being welded to the shell at the junction, as at 59. A vertical cylindrical wall 60 rises from the junction, where it is welded to the top edge of the wall 58, and extends upwardly to and just through an opening 64 in the bottom wall of the perforated liner 18. A ring plate 66 is welded inside the top end of wall 60, and extends radially inward substantially to the member 58. The space defined between the members 55, 58, 60 and 66 is packed with high heat resistant sound insulation or absorbent material, preferably a mineral wool material capable of withstanding the high heat of the turbine discharge gases. A packing 67 of fiber glass cloth is placed between the perforated member 58 and the packing 67.

The top of the frusto-conical member 55 has a cover plate 66, spaced just below the top wall of the liner.

The hot turbine gases rise through the perforated frusto-conical member 58, and pass through the perforations therein into the space inside the perforated liner 18 for travel along the latter and eventual discharge up the stack. The divergence of the frusto-conical member expands the intaken gases, and so affords a diffuser action which importantly reduces the back pressure on the turbine during running.

Spaced outside the rearward half of the frusto-conical diffuser 55 is a half-cylindric perforated wall 72, which acts as a deflector for gases escaping through the perforations in the rearward half of the diffuser 55. Thus, such gases impinge on the deflector wall, and are deflected thereby in a uniform flow pattern around the sides of the diffuser wall, to join with the gases emerging through the perforations in the front half of the diffuser for relatively uniform non-turbulent flow downstream of the liner.

In accordance with the invention, the gas flow space down the liner has a large perimeter for its cross-sectional area, because of its flat cross-section, and there is therefore a relatively large area of sound absorber treatment provided by the mineral wool packing in back of the perforated liner walls, in relation to the gas flow along the liner. It is desirable to further increase this area of sound absorber treatment, and to this end the liner, in the illustrative embodiment, is subdivided into two upper and lower flow channels by longitudinally running additional sound absorbers 78, constructed in this case in the unique form of a medially positioned longitudinal panel 79, with two absorbers 78 unified in a back to back position, and together making up a sound absorber assembly 80 with two opposed sound absorber sides.

In detailed make up, the assembly 80 comprises parallel upper and lower perforated sheet metal walls 82, whose longitudinal edges are received in channels 83 secured to the side walls of the liner 18. At the front and rear ends, these walls converge on a gradual angle to a solid mid-plate or septum 84, which is parallel to the two outside plates or walls 82 and is midway therebetween. The septum 84 is fastened to the flanges at the ends of the convergent portions of the walls 82, and the assembly fastened properly together. Thus, the end portions of the absorber are of a streamlined contour, and avoid turbulence where the gas stream divides and recombines. It is, of course, evident that the gas flow should be as non-turbulent as possible, not only in reducing back pressure on the turbine, but in gaining maximized uniformity of gas impingement throughout the perforated regions of the liner where the sound absorber fibrous material is accessible.

High heat resistant mineral wool is packed in between each of the perforated walls 82 and the septum 84, as indicated at 90, and fiber glass cloth is placed between this sound absorbent material 90 and the perforated walls 82.

A preferred feature of the invention is a curved shield 94 used in the gas discharge outlet, close to the angle between the stack and the top of the shell. A deflector 95 mounted in the stack over this shield 94 shields it from falling snow, leaving open, in all weather, a throat 96 through which the turbine can exhaust to atmosphere. In the event that the stack and the liner cavity therebelow become choked with snow, the back pressure on the turbine becomes so great that the turbine cannot be started. The shield 94 and throat 96 thus constitute an important feature of the invention.

Used with a gas turbine driving a 750 Watt electric generator, and with a shell of 24' in overall length, with other dimensions in proportion, the performance of the noise suppressor of the invention is in accordance with the chart shown in the drawings. Curve A shows the sound intensity of the turbine discharge, without a suppressor, in Decibels (dynes per square centimeter), at a distance of 50 feet, curve B shows the noise level on a typical quiet city street, and curve C shows the sound intensity level at 50 feet from the stack of the suppressor of the invention. The very marked attenuation should be noted, as well as the fact that the noise level at 50' is, with the attenuater, is less than that on a quiet city street.

In operation, the liner structure attains a running temperature of the order of 1,100.degree. F., while the exterior shell remains at about 150.degree. F. The liner expands thermally both transversely and longitudinally. The angular webs of the Z-supports allow bending of the supports to accommodate to the transverse expansion. The liner is somewhat loosely anchored at one end to the shell at and by the perforated frusto-conical diffuser shell. As the temperature rises, the longitudinal thermal expansion is accommodated by shifting of the Z-supports along the longitudinal tracks 41 in the shell. The low running temperature of the shell is owing to the minimized heat conduction path from the liner walls to the shell, which is substantially limited to the U-shaped supports on the liner and the narrow support flanges 41 on the shell.

The favorable aerodynamic flow characteristics provided by the invention minimize back pressure on the turbine, and at the same time minimize noise attenuation. The frusto-conical intake diffuser for example reduces back pressure by expansion of the intaken exhaust gases. These gases are at the same time distributed uniformly through the walls of the diffuser into the gas passage in the liner. The deflector gathers the gases thus emitted into the liner from the diffuser around the back or far side of the diffuser and directs these to the longitudinal liner passage leading to the stack.

FIG. 5 shows in transverse section a more economical construction within the scope of the invention wherein the shell 100, perforated liner 102, and interior sound absorber 104 are circular and concentric. This modification in geometric configuration will be understood withour further description.

The invention has been disclosed by way of drawings showing, and a specification describing, a certain present illustrative construction. It will, of course, be understood that various changes in design, structure and arrangement may be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

I claim:

1. In a noise suppressor, the combination of:

a stationary elongated exterior sheet metal shell;

an elongated perforated interior liner conduit inside said shell and extending longitudinally thereof;

said liner being spaced inside said shell;

packing of high heat resistant, noise-absorbent material in the space between said shell and said liner;

flexible resilient support means supporting said liner from said shell in its spaced position inside the shell, said support being attached to one of said shell and liner, and being in slidable engagement with the other of said shell and liner, accommodation to transverse thermal expansion of the liner, and to permit longitudinal shifting of the liner relative to the shell with longitudinal thermal expansion of the liner.

2. The subject matter of claim 1, wherein said supports are attached to said liner and are in slidable engagement with said shell.

3. The subject matter of claim 1, including also a gas intake fitting opening into said liner through said shell in the region of one end portion of said shell, and

a stack opening from said liner through said shell in the region of the other end portion of said shell.

4. The subject matter of claim 3, wherein said gas intake embodies a frusto-conical perforated diffuser.

5. The subject matter of claim 3, including also sound absorber means inside said liner and extending longitudinally thereof, said absorber means being between said gas intake and said stack.

6. The subject matter of claim 5, wherein said sound absorber means embodies a panel dividing said liner into two longitudinal gas passage ways, said panel comprising a pair of parallel perforated, sheet metal side plates on opposite sides thereof, and high heat resistant, noise-absorbent material packed between said plates.

7. The subject matter of claim 6, wherein said side plates converge smoothly at opposite ends of the absorber to a relatively thin edge.

8. The subject matter of claim 7, wherein said absorber includes a solid sheet metal plate between said perforated side plates.

9. The subject matter of claim 3, wherein said gas intake extends laterally through the sides of said liner and shell and is fixed to said shell and loosely connected to said liner, and

said stack is fixed to said liner and extends laterally therefrom through a side of said shell,

there being a thermal expansion gap in said shell for said stack.

10. In a noise suppressor, the combination of:

a stationary, elongated exterior sheet metal shell, of rectangular cross-section, of greater horizontal width than vertical height,

an elongated, perforated interior liner conduit spaced inside said shell and extending parallel to and longitudinally of said shell;

packing of high heat resistant noise-absorbent material in the space between said perforated liner and said shell,

flexural and slidable supports between said liner and said shell supporting said liner for thermal expansion in transverse directions and for longitudinal thermal expansion by longitudinal shifting of the liner relative to the shell,

a gas intake fitting extending upwardly through adjacent bottom walls of said shell and said liner near one end of said shell for discharging exhaust gas inside said liner, said intake fitting being affixed to said shell, and

a stack extending upwardly from the end of said liner and through the top of said shell near the opposite end of said shell, said stack being affixed to said shell.

11. The subject matter of claim 10, including an expansion joint in said top of said shell for said stack.

12. The subject matter of claim 10, wherein said gas intake fitting embodies a perforated frusto-conical diffuser, with a closure at its upper end, disposed in said liner.

13. The subject matter of claim 10, wherein the walls of said shell mounts rails slidably engaged by said flexural supports, and said supports are fixed to said liner.

14. In a noise suppressor, the combination of:

a stationary, elongated interior sheet metal shell, of rectangular cross-section, of greater horizontal width than vertical height;

an elongated, perforated interior liner conduit spaced inside said shell and extending parallel to and longitudinally of said shell;

packing of high heat resistant noise-absorbent material in the space between said perforated liner and said shell;

a gas intake fitting extending upwardly through adjacent bottom walls of said shell and said liner near one end of said shell for discharging exhaust gas inside said liner;

a stack extending upwardly from the end of said liner and through the top of said shell near the opposite end of said shell, and

a horizontal sound absorber panel mounted in said liner between said gas intake fitting and said stack, and dividing the space inside said liner into two parallel upper and lower gas passages.

15. The subject matter of claim 10, including also deflector means in and below said stack and within said liner for preserving a gas passage from the liner into the stack in event of snow accumulated in said liner received therein through said stack.