CA1116417A

CA1116417A - Cooled air inlet tube for a gas turbine combustor

Info

Publication number: CA1116417A
Application number: CA000309776A
Authority: CA
Inventors: Shou S. Lin; Li-Chieh Szema; Paul W. Pillsbury
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1977-09-09
Filing date: 1978-08-22
Publication date: 1982-01-19
Also published as: BE870333A; IT7827400A0; AR213702A1; JPS5450717A; IT1098811B; GB2003989A

Abstract

COOLED AIR INLET TUBE FOR A
GAS TURBINE COMBUSTOR

ABSTRACT OF THE DISCLOSURE
An air inlet tube for directing combustion air to the primary zone of a gas turbine combustion chamber is shown. The tube has a stepped configuration defined by a shortened wall spaced outwardly from the downstream facing wall of the main air inlet tube to provide a slot for directing a layer of air over the inwardly projecting downstream wall of the tube to protect this portion and the vulnerable downstream edge of the tube from contact with the hot gases in the combustor.

Description

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Field Or the Invention:
This invention relates to the air inlet tubes for the combustion chamber o~ a gas turbine engine and more particularly to a film-cooled air inlet tube.
Description of the Prior Art:
Air inlet tubes for the combustion chamber o~ a gas turbine engine are well known in the prior art with ref-erence being specifically made to U.S. Patent No. 3,'899,882, of common assignee as the present invention, showing such , structure. The inlets are normally disposed in annular arrays through the c'ombustion chamber wall to in~ect combus-tion air into the fuel spray pattern for mixing therewith to promote complete combustion of the' fuel. The result .of this projected length into the .combusti.on chamber results in the hot combustion gases, having a temperature on the order of

2,000.+F,,flowing over the exterior surface of.the' tubes~
and inducing wakes ad~acent the downstream ~acing wa'll of .~

6~

each tube. These wakes are generally referred to as "hot wakes" and result in a region of high ternperature gases intimately contacting this downstream facing wall of the tube. Further, radiation from the combustion flame is re-ceived directly on this downstream facing wall of the tu~e to add to the temperature thereof. Due to these conditions, the air inlet tube quite often becomes overheated and, gen-erally starting ak the inlet edge of the downstream wall, which is the most vulnerable area to the heat, becomes burned out.
Thus, heretofore, the inlet tubes were made suffi-ciently short so as to keep the most vulnerable portion, i.e. the downstream edge, as far removed from the flame front as possible and still obtain a good intermixing between the fuel and khe air introduced through the tube. ~owever, recent developments in a gas turbine combustor partlcularly directed to adapting it to burn coal gas have resulted in larger diameter combustion chambers (necessitated by an increase in volume of the combustors to obtain similar operating results. In such larger combustor chambers, the short air inlet tubes do not provide sufficient penetration of the air into the fuel such that there are pockets of unburned fuel resulting in smoke. To prevent this smoke, the ~nlet tubes by ~ecessity are required to extend further into the chamber which in turn places the downstream face and particularly the downstream edge closer to the-actual combustion flame, resulting in overheating of the tubes so that burnout occurs quite often.
The previously identified co-owned patent, although directed to cooling the internal walls of the combustion ~116~ ~J~

chamber in generally the same zone o~ the chamber as the inlet tubes, did so by permitting a portlon of the air to enter through a gap in the mounting arrangement of the tubes to ultimately form a film o~ cooling alr along the internal combustor walls. It .Ls therein also stated that this cooling air, entering ad~acent the tubes would also prevent the combustion flame from attaching itself to the downstream side of the inlet tube and thereby reduce the incidence of burnout. However, the structure therein described does not direct the air to penetrate inwardly far enough to protect the downstream edge of the tube, which in the coal gas com--bustor is even further from this wall cooling air and closer to the actual combustion flame.
SUMMARY OF THE INVENTION
The present invention provldes an air inlet tube extending generall.y radially into a gas turbine combustor and an ad~acent radially elongated slot, one boundary of which is the downstream wall of the air inlet tube to provide a layer of air flowing over the downstream surface of the tube with the radlal extent of the sl.ot providing sufficient penetration of the air exiting therefrom to continue to flow across the exposed downstream surface of the tube to prevent the downstream edge of the tube from overheating.
BRIEF V RIPTION OF THE DRAWINGS
Figure 1 is a schematic view of a gas turbine combustion chamber having air in]et tubes projecti.ng there-through, Fi.gure 2 is an enlarged sectiorlal view of a.n a.ir30 inlet tube of the present invention; and 1~16A:17 ~ igure 3 is a view looking down on the inlet tube of Figure 2.
DESCRIPTION OF THE PRE~E~RED_E~BODIME~T
Referring to Figure 1, a gas turbine combustion chamber 10 is schematically shown which comprises a stepped cylindrical configuration, as is well known in the art, with each successive cylindrical portion 12, 14, being larger and connected to the ad~acent upstream cylindrical portion in spaced relation as through a wiggle strip 16 to permit cooling air entry along the walls of the chamber. Fuel is introduced at the upstream end 18 of the chamber through a fuel nozzle 20 providing an atomized fuel spray pattern.
~ombustion air is in~ected into the fuel spray through an annular array of air scoops or air inlet tubes 22 pro~ecting into the combustion chamber transverse to the flow of fuel and the combustion gases through the chamber to provide sufficient penetration of the air into the fuel spray for complete combustion of the fuel in the primary or flame zone of the chamber.
The resulting combustion, once ignited by a spark igniter (not shown) is continuous, resulting ln a flow of hot gases across the surface of the air inlet tubes 22.
This flow results in "hot wakes" or relatively slowly moving hot gases ad~acent the downstream facing portion of the tubes 22. These hot gases come in intimate heat transfer contact with the downstream surfaces of the tubes to cause this portion to become hotter than the upstream surface of the tube. ~urther~ this downstream facing wall, in addition to being the portion of the tube closest to the actual

3 combustion flame and thus contacted by the hot combustion 1~6~

gases, also directly recelves radiation from the flame, with the resulting heat absorbed by this portion o~ the tube causing the tube to overheat and burn out. ~his burnout starts at the vulnerable downstream innermost edge of the tube and generally proceeds until the tube requires replace-ment.
As previously stated, the overheating is parti-cularly critical as the tube length increases to obtain sufficient air penetration in enlarged diameter combustion chambers particularly suited for low BTU fuels such as coal gas~ To prevent the burnout of the air inlet tubes, a film cooling slot is provided adjacent the downstream face of the tube to direct a layer of air to flow over the downstream surface and prevent the hot gases in the combustion chamber from intimately contacting such surface. With such lntlmate heat transfer contact prevented, the tube is able to normally withstand the temperature increase caused by the heat absorbed from the other sources without any burnout.
Thus, referring to Figures 2 and 3, the inlet tube 22 according to the present invention comprises an annular flange 26 for attachment, as by welding, to the wall 28 of the combustion chamber, with the main air flow tube 30 pro-~ecting radially inwardly through an aperture 32 in the wall.
The inlet opening through the flange 26 is larger than the outside diameter of the main tube 30 to provide a gap or slot 36 between the downstream facing wall 38 of the main air tube 30 and the shortened wall 4C~ A radially inwardly extending shortened wall 40, having an arcuate 0 configuration conforming to the outer periphery of ~:116~17 the opening 34 ~ith the opposed terminal ends thereofattached to the side of the main air flow tube 30, de~ines the inwardly extending cooling air inlet 36 that directs a layer or film of cooling alr to flow over the downstream face 38 of the tube 30 with sufficient radial penetration to flow along the complete length of the tube 30 to the inner-most end 42 thereof and thereby minimize heat transfer from the hot gases within the chamber to the downstream wall of the air inlet tube. It is seen from Fig. 3 that the opening 34 and tube 30 are generally elliptical with the ma~or axis in alignment with the direction of hot gas flow through the chamber to minimize the downstream surface 38; however, any configuration would also be enhanced by the cooling air slot 36.
It is apparent that the gap opening 36 and the radial length of the shortened wall 40 are dimensions whlch may vary according to the various parameters such as differ-ential in pressures between inner and outer wall-, the length of the main air flow tube 30, the temperature within the combustion chamber, and the desired maximum temperature of the downstream face 38 of the tube 30, along with other considerations which may vary for each particular engine or application. However, for the most part, the desired effect is a layer of cooling air directed over the downstream facing wall of the inwardly pro~ecting air tube to prevent burnout which generally starts at the downstream terminal edge of the tube. It is also apparent that a cooled air inlet tube as above described could be disposed at any of various positions within the combustion chamber when air penetration is required (i.e. as downstream dilution air) and where burnout of the tube ends may be a potential problem due to increased temperatures wlthin the chamber.

Claims

CLAIMS:

1. In a gas turbine combustion chamber defining an upstream primary combustion zone, a plurality of air inlet tubes extending generally radially into said combustion chamber transverse to the flow of combustion products, and thereby defining a downstream facing portion on the inlet tube; and means for directing a layer of air over said downstream facing portion of each tube for film cooling thereof said means comprising:
an air slot adjacent to and conforming in shape to the downstream facing portion of said tube;
said slot defined by a further downstream radially inwardly extending wall segment terminating radially sub-stantially prior to the innermost end of said tube but sufficiently close to said end to direct a film of cooling air from the outlet of' said slot to said inner end of said air tube.

2. Structure according to claim 1 wherein said inlet tubes are disposed in an annular array about said combustion chamber and disposed to direct air into the primary combustion zone therein, and wherein the radial extent to said tubes causes the innermost end thereof to be closely adjacent the combustion flame.

3. Structure according to claim 1 wherein said tube and said wall extend radially inwardly from a common flange member for mounting said tube and wall defining said slot to said combustion chamber.

4. Structure according to claim 3 wherein said wall segment is integrally attached to said tube on generally opposite sides of the tube.

47,151

5. An air inlet tube for a combustion chamber of a gas turbine engine for directing combustion air into said chamber in a direction generally transverse to the flow of combustion products through said chamber, said tube com-prising:
a tubular member extending generally radially into said chamber from an aperture therein and having a downstream facing wall with respect to the flow of said combustion products;
a short wall member spaced from but adjacent to said downstream facing wall of said tube and extending from said aperture radially inwardly a distance substantially shorter than said member to define a slot between the down-stream facing wall of said tube and said wall member; to direct a film of air over said downsteam facing wall of said tube to reduce contact between said wall and hot gases in said chamber and thereby prevent burnout of said member.

6. Structure according to claim 5 wherein the length of said tube is sufficient to dispose the inner end thereof closely adjacent the combustion flame within the combustion chamber.

7. Structure according to claim 5 wherein said tube and said wall member extend inwardly from a common flange encircling said tube and wall member for mounting to said combustion chamber.

8. Structure according to claim 7 wherein said wall member is integrally attached to said tube on generally opposite sides of the tube.