Title of Invention

"A LOW EMISSION (NOX) COMBUSTOR"

Abstract

The present invention is directed generally to an apparatus for providing air cooling to the venturi (11) and the combustion chamber(13) in a low emission Nox cumbustor (10) as used in the gas turbine engine that includes providing an anular air passage(14) surrounding the combustion chamber / venturi near the aft portion of the combustion chamber (13) passing the air along the combustion chamber (13), past the venturi(l 1) where the air exits near the front portion of the convergent area of the venturi(l l).The cooling air is heated as it passes over the combustion chamber (13) and the venturi(l 1) and then it is directed back into the premix chamber (12) thereby improving the efficiency of the combustor (10) while lowering the Nox emission in the combustion process.

Full Text

COMBUSTION CHAMBER/VENTURI COOLING FOR A LOW NOx EMISSION COMBUSTOR - PCT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to an apparatus and method for cooling the combustion chamber and venturi used in a gas turbine engine for reducing nitric oxide emissions. Specifically an apparatus is disclosed for cooling the combustion chamber/venturi to lower nitric oxide .(NOx) emissions by introducing preheated cooling air into the premix chamber for use in the combustion process. Hi 2 . Description of Related Art The present invention is used in a dry, low NOx gas turbine engine typically used to drive electrical generators. Each combustor includes an upstream premix fuel/air chairfcer and a dov;nstream combustion chambei" separated by a venturi having a narrow throat constriction that acts as a flame retarder. The invention is concerned with improving the cooling of the combustion chamber which includes the venturi walls while at the sam.e time ^reducing niti~ic oxide emissipns. U.S. Patent 4,292,801 describes a gas turbine combustor that includes upstream premix of fuel and air and a downstream combustion chamber. U.S. Patent 5,117,636 and U.S. Patent 5,285,631 deal v;ith cooling the combustion chamber wall and the venturi walls. The patents state that there is a problem vjith allowing the cooling air passage to dump into the combustion chamber it the passage exit is too close to the venturi throat. The venturi creates a separation zone dov;nstream of the divergerit portion which causes a pressure difference thereby attracting cooling air which can cause combustion instabilities. However, it is also essential that the venturi v;alls and combustion chaTiber wall be adequately cooled because of the high temperatures developed in the combustion chamber. The present invention eliminates the problem discussed in ; he prior art because the cooling circuit for the venturi has been adjusted such that the cooling air no longer dumps axially aft and downstream of the venturi throat into the combustion zone. In fact, cooling air flows in the opposite direction so that the air used for cooling the combustion chamber and the venturi is forced into the premix chamber upstream of the venturi, improving the efficiency of the overall combustion ]3rocess while eliminating any type of cooling air recirculation separation zone aft of the venturi as discussed in the U.S. Patent 5,117,636_^ Recent government emission regulations have become of great concern to both manufacturers and operators of gas turbine combustors. Of specific concern is nitric oxide (NOx) due to its contribution to air pollution. It is well known that NOx formation is a function of flame temoerature, residence time, and equivalence ratio. In the past, it has been shown that nitric oxide can be reduced by lowering flame temperature, as well as the time that the flame rerains at the higher temperature. Nitric Oxide has also been found to be a function of equivalence ratio and fuel to air (f/a) stoichiometry. That is, extremely low f/a ratio is required to lov;er NOx emissions. Lowering f/a ra,tios do not come without penalty, primari-ly the possibility of "blow-out". "Elow-Out" is a situation when the flame, due to its instability, can no longer be maintained. This situation is common as fuel-air stoichiometry is decreased just above the lean flammability limit. By preheating the premix air, the 'blov;-out" flame temperature is i'educed, thus allowing stable combustion at lower temperatures and consequently lower iSJOx emissions. Therefore, introducing the preheated air is the ideal situation to drive f/a ratio to an extremely lean limit to reduce NOx, while maintaining 'a stable flame. In a dual-stage, dual-mode gas turbine system, the secondary combustor includes a venturi configuration to stabilise the combustion flame. Fuel (natural gas or liquid) and air are premixed in the combustor premix chamber upstream of the ventviri and the air/fuel mixture is fired or combusted downstream of the venturi throat. The venturi configuration accelerates the air/ fuel flow through the throat and ideally keeps the flame from flashing back into the premix region. The flame holding ,region beyond the throat in the venturi is necessary for continuous and stable fuel burning. The combustion chamber wall and the venturi walls before and after the narrow throat region are heated by the combustion flame and therefore must be cooled. In the past, this has been accomplished with back side impingement cooling v;hich flov;s along the back side of the combustion wall and the venturi walls v;here the cooling air exits and is dumped into combustion chamber downstream of the venturi.The present invention overcomes the problems provided by this type of air cooling passage by completely eliminating the dumping of the cooling air into the conibustion zone do'.vnstream of the venturi. The present invention does not permit any airflow of the venturi cooling air into the downstream combustion chamber whatsoever. At the same time the present invention takes the cooling air, which flows through an air passageway along the combustion chaniber v.-all and the venturi walls and becomes preheated and feeds the. cooling air upstream of the venturi (converging wall) into the premixing chamber. This in turn improves the overall low emission NOx efficiency. -BRIEF SUMMARY OF THE INVENTION An itupr'oved apparatus for cooling a coml)ustion chamber wall having a flame retarding venturi used in low nitric oxide emission gas turbine engines that includes a gas turbine coom,bristor having a premixing chamber and a secondary combustion chamber and a venturi, a cooling air- passagev;ay concentrically surrounding said venturi walls and said combustion chamber wall. A plurality of cooling air inlet openings into said cooling air passageway are disposed near the end of the combustion chamber. The combustion chamber wall itself is substantially cylindrical and includes the plurality of raised ribs on the outside surface which provide additional surface area for interaction with the flow of cooling air over the combustion cylinder liner. The venturi walls are also united with the combustion chamber and include a pair of convergent/divergent walls intricately formed with the combustion chamber liner that includes a restricted throat portion. The cooling air passes round not only the cylindrica'l combuscion chamber wall but both vvalls that form the venturi providing cooling air to the entire combustor chamber and venturi. As the cooling air travels jpstream toward the throat, its temperature rises. The cooling air passageway is formed from an additional cylindrical wall separated from the combustion chamber wall that is concentrically mounted about the combustion chamber wall and a pair of conical walls that are concentrically disposed around the venturi walls in a similar confiqiiiration to form a complete annulai' passageway for air to flov; around the entire combustion chan±)er and the entire venturi. The downstream end of the combustion chamiber and the inlet opening of the cooling air passageway are separated by a ring barrier so that none of the cooling air in the passageway can flow downstream into the combustion chamber, be introduced co-wnstream. of the combustion chamber, or possibly travel into the separated region of the venturi. In fact the cooling air outlet is located upstream of the venturi and the cooling air flows opposite relative to the corubustion gas flow, first passing the combustion chamber wall and then the venturi walls. The preheated cooling air is ultimately introduced into the premix chairiber, adding to the efficiency of the system and reducing nitric oxide emissions with a stable flame. The source of the cooling air is the turbine compressor that forces high pi"essure air around the entire combustor body in a direction that is upstream relative to the combustion ;3rocess. Air under high pressure is forced around the combustor body and through a plurality of air inlet holes in the cooling air passageway near the do'wnstream end of the combustion chamber, forcing the ccolirig air to flow along the combustor outer wall toward the venturi, passing the throat of the ventu2ri, passing the leading edge of the venturi wall where there exists an outlet air passageway and a receiving channel that directs air in througli another series of inlet holes into the premix chatTLber upstream of the venturi throat. With this flow pattern, it is i-inpossible for cooling air to interfere with the combustion process taking place in the secondary combustion chamber since there is no exit or aperture interacting with the secondary couil-nistion chamber itself. Also as the cooling air is heated in the passageway as it flows towards the venturi and is introduced into the inlet premix chamber upstream of the venturi, the heated air aides in combustor efficiency to reduce pollutant emissions. The outer combustor housing includes an annular outer band that receives the cooling air through, outlet apertures upstream of the venturi. The air is then directed further upstx'eam through a plurality of inlet air holes leading into the premix chamber allowing the preheated cooling air to flow from the air passageway at the leading venturi wall into the premix area. The gombustion chamber wall includes a plurality of raised rings to increase the efficiency of heat transfer from the combustion wall to the air, giving ;:h-e wall more surface area for air contact. Although a separate concentric wall is used to form the air cooling passageway around the combustion chamber and the venturi, it is possible in an alternative embodiment that the outer wall of the combustor itself could provide that function. It is an object of the present invention to reduce nitric oxide (Nox) emissions in a gas turbine combustor system while maintaining a stable flame in a desired operating condition while providing air cooling of the combustor chamber and venturi. It is another object of this invention to provide a low emission combustor system that utilizes a venturi for providing multiple uses of cooloing air for the combustor chamber and venturi. And yet another object of this invention is to lower the blow out flame temperature of the combustor by utilizing preheated air in the premixing process that results from cooling the combustion chamber and venturi. In accordance with the present invention it is directed to a low emission (NOx) combustor (10) for use with gas turbine engine having: a liner having a first annular wall and including a premix chamber (12) for mixing fuel and air and a combustion chamber (13) for combusting said fuel and air, said premix chamber (12) in communication with said combustion chamber (13), said first annular wall having at least one first aperture and at least one second aperture, said second aperture being radially outward of said premix chamber (12); a venturi (11) having a second annular wall that have a converging wall and a diverging wall, said converging wall connected to said diverging wall thereby defining a throat (1 la) portion of the venturi (11), said throat (11a) portion being positioned between said premix chamber (12) and said combustion chamber (13), said second annular wall being radially inward from said first generally annular wall and having an aft end adjacent said at least one first aperture; a passageway (14) for flowing cooling air through said venturi (11), said passageway (14) extending from said at least one first aperture to said at least one second aperture, said passageway (14) having a first portion radially inward from said first annular wall and radially outward from said second annular wall, and said passageway (14) having a second portion (46) radially outward from said first portion (45) of said passageway (14), said second portion (46) extending from said passageway (14) first portion (45) to said at least one second aperture, and said first aperture being radially outward from said first portion (45); and, a blocking ring (40) extending from said aft end of said second annular wall to said first annular wall and sealingly connected thereto, said blocking ring (40)preventing cooling air that is in said first portion (45) of said passageway (14) from flowing directly into said combustion chamber (13) without flowing through said second portion (46) of said passageway (14); wherein said passageway (14) is in fluid communication with said at least one first aperture and said at least one second aperture, said passageway (14) communicates with said premix chamber (12) through said at least one second aperture, and cooling air, after being heated by cooling said venturi (11), exits from said passageway (14) into the premix chamber (12) thereby increasing the efficiency of the combustion process and reducing NOx em.issions. In accordance with these and other objects, which will become apparent hereinafter, the instant invention will now be described with particular reference to the accompanying drawings. Brief description of the drawings has been disclosed as follow: Fig. 1 shows a side elevational view in cross-section of a gas turbine combustion systen that emties into and around the combustion chamber. Fig.2 shows a gas turbine combustion system in a respective view in accordance with the present invention. perspective view in accordance with the present invention. Figure 3 shows a side elevational viev; in cross-section of £ gas turbine combustor system in accordance with the present invention. Figure 4 shows a cut avjay version in cross section of the combustion chamber and venturi and portions of the premix chamber as utilized in the present invention. Figure 5 shows a cross-sectional view, partially cut away of the cooling air passageway at the upstream end of the venturi in the annular bellyband chamber for receiving cooling air for introducing the aii~ into the premix chambier. Figure 6 is a cut away and enlarged viev; of the aft end of tlie comh)ustion chamber wall in cross-section. DET/VILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to Figure 1, an existing gas turbine combustor well knovm in the prior art 110 is shown. The combustor 110 includes a venturi 111, a premixing chamber 112 for premixing air and fuel, a combustor chamber 113 and a combustion cap 115, As shown in this parlor art combustor, cooling air represented by arrows flows under pressure along the external wall of the venturi 111. The cooling air enters the system through multiple locations along the liner 110. A portion of the air enters through holes 12 0 while the remainder runs along the outer shell. The cooling air, which is forced under pressure, with the turbine compressor as the source, enters the system through a plurality of holes 121. As seen in Figure 1 the cooling air impinges and cools the conveirgent/divergeni walls 127 of the venturi 111, which are conically shaped and travel dovjnstream through the cylindrical passage 114 cooling the v.-alls of combustion cylinder chamber 113 . The cooling air exits along the combustion chamber wall through annular discharge opening 125. This air is then dumped to the downstream conibustion process. A portion of the cooling air also enters the premixing zone through holes 126. The remaining cooling air proceeds to the front end of the liner where it enters through holes 123 and the combustion cap 115. The portion of the cooling air that does not enter through holes 123 enters and mixes the gas and fuel through area 124. U.S. Patent 5,117,636 discusses the prrior art configuration of the venturi stipwn in Figure 1. Problems are discussed regarding the cooling air exiting adjacent the venturi 111 through passage exit 125 which interferes with the combustion process and mixture based on what tne '636 Patent states as a separation zone. The present invention completely alleviates any of the problems raised in the '635 Patent. Referring now to Figures 2 and 3, the present invention is shown as gas turbine corobustor 10 including a venturi 11. The venturi 11 includes a cylindrical portion which forms the combustor chamber 13 and unitarily formed venturi walls which converge and diverge in the downstream direction forming an annular or circular restricted throat 11a. The purpose of the venturi and the restricted throat l]a is to prevent flash back of the flame from combustion chamber 13. Chamioer 12 is the premix cha-iber v;here air and fuel are mixed and forced under pressure dcv.'nstream through the venturi throat 11a into the combustor chamber 13. A concentric, partial cylindrical wall lib surrounds the /enturi 11 including the converging and diverging venturi walls to form an air passageway 14 between the venturi 11 and the :;oricentric wall lib that allows the cooling air to pass along rJie outer surface of the venturi 11 for cooling. The outside of the conibustor iO is surrounded by a housing (not shown) and contains air under pressure that moves upstream towards the premix zone 12, the air being received from the compressor of the turbine. This is very high pressure air. The cooling air passageway 14 has a:.: inlet apertures 27 which permit the high pressure air surrounding the combustor to enter through the apertures 7.7 and to be received in the first portion 4 5 of passageway 14 that surrounds c;he venturi 11. The cooling air passes along the venturi 11 passing the venturi converging and diverging walls and venturi t::roat 11a. Preheated cooling lir exits through outlet apertures 28 which exit into an annular bellyband chamber 16. The combustor utilizes the cooling air chat has been heated and allowed to enter into premix charrber 12 through apertures 29 and 22. Details are shown in Figures 5 and 6. Note that this is heated air that has been used for cooling that is nov; being introduced in the premix chamber, upstream o£ the convergent v.'all of the venturi a.nd upstream of venturi throat 11a. Using preheated air drives the f/a ratio to a lean limit to reduce NOx while maintaining a stable flame. Referring now to Figure 4, the cooling air passage 14 includes a plurality of spacers 14a that separate venturi 11 from wall lib. The bellyband wall 16 defines a radially outer boundary of the second portion 4 6 of the passageway 14 and provides a substantially annular chamber that allows the outside pressure air and the exiting cooling air to be received into the premix chamber 12. At the downstream end of the combustion chamber 13, defined by the annular aft end of venturi 11, there is disposed an annular air blocking ring 4 0 which prevents any cooling air from leaking downstream into the comibustion chamber. This alleviates any combustion problems .caused by the cooling air as delineated in the prior art iiscussed above. Referring now to Figure 5 the air passageway 14 is shov;n along the venturi section having the convergent and divergent wlls and the throat 11a with cooling air passing through and axiting through apertures 2 8 that go into the air chamber formed by bellyband wall 16, Additional air under a higher pressure enters through apertures 32 and forces air including the now heated cooling air in passageway 14 to be forced thorough apertures 22 and 29 into the premix chamber 12. Figure 6 shows the aft end portion of the combustion chamber 13 and the end of venturi 1]. that includes the blocking ring 4 0 that is annular and disposed and attached in a sealing manner around the entire aft portion of the venturi 11. The ::ooling air that enters into passageway 14 cannot escape or be a]lowed to pass into any portions of the combustion chamber 13 . Note that some air is permitted into the after chamber wall beyond combustion chamber 13 through apertures 3 0 to 31 which are disposed around the outside of the combustor 10 and for cooling the aft end of the combustor. The invention also includes the method of improved cooling of a combustion chamber and venturi v;hich allows the air used for cooling to increase the efficiency of the combustion process itself to reduce NOx emissions. With regards to the air flow, the cooling air enters the venturi outer passageway 14 through multiple apertures 27. A predetermined amount of air is directed into tiie passageway 14 by a element 17. The cooling air is forced upstream by blocking ring 40 which expands to contact the combustor 10 under thermal loading conditions. The cooling air travels upstream through the convergent/divergent sections of the first portion 45 of passageway 14 where it exits into the second portion of passageway 14 through apertures 2E in the venturi 11 and the corabustor 10. The cooling air then fills a chamber careated by a full ring bellyband 16. Due to the pressure drop and increase in temperature that has occurred throughout the cooling path, supply air which is at an increased pressure is introduced into the bellyband chamber 16 through multiple holes 32. The cooling air passes around nultiple elements 18 which are located throughout the bellyband chamber 16 for support of the bellyband under pressure. The cooling air is then introduced to the premix chamber through holes 22 and slots 29 in the combustor 10. Undesired leakage does not occur between the cooling passageway 14 and the premixing chamber 12 because of the forward support 19 which is fixed to the combustor 10 and venturi 11. The remainder of the cooling air not introduced to passagev;ay 14 through apertures 2 7 passes over the element 17 and travels upstream to be introduced into the combustor 10 or cap 15. This air is introduced through multiple locations forward of the bellyband cavj.ty 16. It is through this process, rerouting air that was used for cooling and supplying it for combustion, that lovv'ers the fuel to ail" ratio such that NOx is reduced without creating an unstable flame. While the invention is been described and is known as presently the preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment but, on the contrary, it is intended to cover various moodifications and equivalent arrangemer.ts within the scope of the following claims. We claim; 1. A low emission (NOx) combustor (10) for use with gas turbine engine having: a liner having a first annular wall and including a premix chamber (12) for mixing fuel and air and a combustion chamber (13) for combusting said fuel and air, said premix chamber (12) in communication with said combustion chamber (13), said first annular wall having at least one first aperture and at least one second aperture, said second aperture being radially outward of said premix chamber (12); a venturi (11) having a second annular wall that have a converging wall and a diverging wall, said converging wall connected to said diverging wall thereby defining a throat (11a) portion of the venturi (11), said throat (11a) portion being positioned between said premix chamber (12) and said combustion chamber (13), said second annular wall being radially inward from said first generally annular wall and having an aft end adjacent said at least one first aperture; a passageway (14) for flowing cooling air through said venturi (11), said passageway (14) extending from said at least one first aperture to said at least one second aperture, said passageway (14) having a first portion radially inward from said first annular wall and radially outward from said second annular wall, and said passageway (14) having a second portion (46) radially outward from said first portion (45) of said passageway (14), said second portion (46) extending from said passageway (14) first portion (45) to said at least one second aperture, and said first aperture being radially outward from said first portion (45); and, a blocking ring (40) extending from said aft end of said second annular wall to said first annular wall and sealingly connected thereto, said blocking ring (40)preventing cooling air that is in said first portion (45) of said passageway (14) from flowing directly into said combustion chamber (13) without flowing through said second portion (46) of said passageway (14); wherein said passageway (14) is in fluid communication with said at least one first aperture and said at least one second aperture, said passageway (14) communicates with said premix chamber (12) through said at least one second aperture, and cooling air, after being heated by cooling said venturi (11), exits from said passageway (14) into the premix chamber (12) thereby increasing the efficiency of the combustion process and reducing NOx emissions. 2. A low emission (NOx) combustor (10) as claimed in claim 1, having an annular bellyband wall (16) radially outward from the first annular wall, and at least one-third aperture in said first annular wall, said first portion of said passageway (14) communicating with said second portion (46) of said passageway through said third aperture, wherein said bellyband wall (16) defines a radially outer boundary of the second portion (46) of the passageway (14). A low emission (NOx) combustor (10) as in claim 2 wherein said at least one first aperture a plurality of first apertures spaced circumferentially about the first annular wall, and each of said first apertures is radially outward of the first portion (45) of the passageway (14). 4. A low emission NOx combustor (10) of claim 3 wherein said at least one second aperture a plurality of second apertures spaced circumferentially about the first generally annular wall, and each of said second apertures is radially outward of the premix chamber (12). 5. A low emission NOx combustor (10) as in claim 4 wherein said at least one-third aperture a plurality of third apertures spaced circumferentially about the first annular wall, and each of said third apertures is radially outward of the venturi (11). 5. A low emission (NOx) combustor (10) for use with gas turbine engine as herein described with reference to the foregoing description and the accompanying drawings.

Documents:

1383-delnp-2004-abstract.pdf

1383-delnp-2004-assignment.pdf

1383-delnp-2004-claims.pdf

1383-delnp-2004-complete specification (as file).pdf

1383-delnp-2004-complete specification (granted).pdf

1383-delnp-2004-correspondence-others.pdf

1383-delnp-2004-correspondence-po.pdf

1383-delnp-2004-description (complete).pdf

1383-delnp-2004-drawings.pdf

1383-delnp-2004-form-1.pdf

1383-delnp-2004-form-13.pdf

1383-delnp-2004-form-18.pdf

1383-delnp-2004-form-2.pdf

1383-delnp-2004-form-3.pdf

1383-delnp-2004-form-5.pdf

1383-delnp-2004-gpa.pdf

1383-delnp-2004-pct-101.pdf

1383-delnp-2004-pct-205.pdf

1383-delnp-2004-pct-210.pdf

1383-delnp-2004-pct-220.pdf

1383-delnp-2004-petition-137.pdf