Abstract:
A gas turbine engine for generating electricity having low NOx emissions that includes a turbine system linearly and axially connected by a power shaft to a compressor section and having a combustion section mounted vertically relative to the turbine section and the compressor section. The combustion system includes a plurality of individual combustors mounted in a circular or annular array around the upper cap or dome of the combustion system, each of said combustors being a dual mode, two-stage, emitting low levels of NOx. Each combustor exhausts its combustion gases into a common central plenum chamber that is vertically oriented relative to the turbine engine centerline. The plenum provides the hot gases to the turbine blades through an annular chamber 360 degrees around the shaft. The gas turbine engine vertical combustion system provides for a highly efficient, low nitric oxide emissions while allowing for uniform mixing of the combusting gases powering the turbine system.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a silo type combustor for a gas turbine engine used to provide rotational power to an electrical generator, and specifically to a gas turbine engine with a silo combustor that operates at very reduced levels of nitric oxide (NOx) emissions. 
     2. Description of Related Art 
     In recent years, emissions regulations with the Federal Government has become of great concern to manufacturers and operators of gas turbine engines used to generate electricity, and, in particular, of pollutants produced by the gas turbine combustor. Of specific concern are nitric oxides (NOx) because of their large contribution to air pollution. Depending upon the gas turbine installation site, emission requirements vary, in terms of parts per million (ppm) of NOx that can be emitted each year. Therefore if a particular gas turbine engine is used very little in a year, a higher emissions combustor can be used. However if a gas turbine engine is run on a regular basis, a lower emission combustor system is required to meet emission regulations. In the past, NOx emissions have been reduced by the injection of water or steam in to the combustion process. Although this is an acceptable process, it has many disadvantages including system complexity, the cost of water treatment and increased heat rates. In order to meet pollution emission requirements without using one of the previously mentioned options, operators of gas turbines are required to upgrade older, higher pollutant emitting engines to include a combustion system that emits a lower level of NOx than their existing systems. Each engine manufacturer has taken steps to provide a combustion system capable of reducing NOx emissions to acceptable levels. Most common low emission combustors use natural gas instead of liquid fuel and have improved airflow, cooling, and mixing conditions. 
     Gas turbine engines have certain essential components such as a combustor, a compressor section, a turbine section and the power shaft. Gas turbine combustors vary in geometric configuration, fuel nozzle arrangement, fuel utilized and emission results. For example, one particular gas turbine engine utilizes a “silo” combustor which is stacked vertically above the engine centerline. Older, higher emitting combustor arrangements can use one liquid fuel nozzle for mixing liquid fuel and compressor discharge air. This combustor arrangement typically produces emissions in excess of new environmental regulations. The present invention provides an improved combustor system using the silo configuration to produce low emissions for a natural gas turbine engine. U.S. Pat. No. 4,292,801 describes a gas turbine engine that employs a horizontal combustor mounted in line with the turbine section and the compressor section. 
     The use of a silo combustor can result in a more compact turbine engine, saving space, and providing for operational improvements due to its mounting and location relative to the turbine and compressor sections of the engine. In addition the silo plenum allows for improved fuel/air mixture and a uniform pattern prior to the turbine section. 
     U.S. Pat. No. 5,611,197 issued to Bunker Mar. 18, 1997 shows a closed circuit air cooled turbine. Each combustor  20  is mounted offset from the power shaft such that the output of each of the combustors is directed to a small area of the turbine blades. A plurality of combustors are utilized, each having an output at a different area of the turbine blades. Utilizing the silo orientation of the present invention, a 360 degree output covering the entire turbine blade section can be achieved using a plurality of individual combustors as described further herein. 
     BRIEF SUMMARY OF THE INVENTION 
     A gas turbine engine used for providing power to operate an electrical generator typically for a utility grid comprising a silo combustion system that includes a plurality of two-stage, two-mode combustors for producing low NOx emissions, a turbine system driven by the exhaust gases from said combustion system for providing rotational energy, and a compressor system providing compressed air to said combustion system, said turbine system including an output shaft used to drive a generator as well as the compressor system. 
     The turbine system and the compressor system are joined by the operating shaft mounted horizontally and linearly in the overall turbine engine housing. 
     The combustion system is mounted vertically between said turbine system and said compressor system and includes a combustion gas output channel that communicates directly with the turbine blades providing high velocity exhaust gases that are used to drive the turbine blades. 
     The vertically mounted combustion system includes a plurality of individual combustors mounted on a top cap through annular openings in the top cap of the combustion system. In the embodiment disclosed herein, a plurality of twelve individual combustors are mounted in a ring (annularly) around the combustion top cap. 
     Each combustor is comprised of a two-stage, two-mode combustor that includes six primary fuel nozzles and one secondary, centrally-located fuel nozzle to provide two-stage operation. 
     The exhaust gases from each combustor enters a common plenum chamber. The combusted gases under high pressure are directed through a transition channel into an annular chamber that is in 360 degree communication with the turbine blades. Thus the combustion gases which drive the turbine blades interact around a 360 degree area rather than having individual combustion gas feed chambers from each individual combustor as shown in the prior art. A common plenum chamber provides a more uniform exhaust pattern to the turbine, where as in prior art, individual exhaust ducts to sections of the turbine may differ in pressure, temperature and affect turbine performance. 
     The use of two-stage individual combustors results in very low NOx polluting emissions because of high efficiency of each combustor. 
     Each combustor also includes a venturi section within the combustion liner that utilizes an improved cooling air transfer system. This system cools the entire liner, including the venturi. While cooling the venturi, the air is preheated by radiation from the secondary combustion chamber, and is then directed into the upstream/premix combustion chamber for use in the combustion process. This additional air lowers the fuel/air ratio, which in turn lowers combustion flame temperature and emissions. The improved use of cooling air for a combustion liner for lowering emissions is disclosed in applicant&#39;s current pending U.S. patent application Ser. No. 09/605,765 which is hereby incorporated by reference into this application. The use of the improved device described above in applicant&#39;s patent application is used in all twelve combustors utilized in the present invention. 
     It is an object of this invention to provide an improved gas turbine engine used for generating electrical power that has low NOx pollutants and emissions while utilizing a combustion system that is vertically oriented and uses a common plenum exhaust gas chamber in fluid communication with the turbine blades. 
     It is another object of this invention to use a plurality of two-stage, two-mode combustors in a vertically oriented combustion system for use in a gas turbine engine to reduce NOx emissions while providing exhaust gases in a 360-degree fed chamber through the turbine blades. 
     Yet still another object of this invention is to provide an improved silo type combustor for a gas turbine engine that has a common plenum using a plurality of individual combustors of high efficiency. 
     But yet still another object of this invention is to provide a vertically oriented combustion chamber that includes two-stage, two-mode combustors with a vertically oriented combustion system to improve gas flow distribution throughout the combustion process. 
     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 SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 shows a side elevational view, partially in cross section of a gas turbine engine that includes a conventional silo combustion system, the turbine engine being used for generating electricity. 
     FIG. 2 shows a side elevational view, in cross section of an improved lower emissions can-annular configuration utilized in the present invention. 
     FIG. 3 is a top plan view of the can-annular vertical combustion system utilized in the present invention. 
     FIG. 4 shows a perspective view of the upper silo case showing only one combustor and the fuel manifold used in the present invention. 
     FIG. 5 shows a side elevational view in cross section of the silo combustor system including one individual combustor that is utilized in the present invention. 
     FIG. 6 shows a side elevation view, partially in cross section of a dual stage, dual mode combustor of the type utilized in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a conventional “silo” combustion system that is used in a gas turbine engine is shown. The gas turbine engine  10  will typically be used for generating electricity. The compressor system shown generally at  12  takes in air through the air inlet  11 . The compressor then forces air under pressure into the combustion system  13 . The compressor  12  is a multi-stage axial compressor of conventional design. The combustor system  13  provides combustion gases to turbine  14  which rotates shaft  12   a , rotating the compressor blades in compressor  12  and the output shaft which provides rotational energy to an electrical generator (not shown) which is attached to said output shaft  12   a . The compressor  12  is comprised of rotating and stationary airfoils in an alternating pattern and is conventional in design. The combustion system  13  includes an outer cylindrical wall  17 , a middle liner  20  and a ribbed inner combustion liner  19 . The outer walls of the combustion system  13  are joined by flanges  21  and  24 . The combustion system  13  includes a combustion system cap  16  which is bolted to flange  21 . Compressor  12  discharge air, which is used within the combustion system  13  during the combustion process, exits compressor  12  and travels upwardly along combustion system  13 , between the inner liner  19  and middle liner  20  and between middle liner  20  and outer cylindrical wall  17 . The high pressure compressor air then reverses direction at cap  16  where the air passes through a nozzle swirler arrangement (not shown) within the vertical silo area. Combustion occurs within the inner liner  19  based on a single one-stage, one-mode combustor and hot gases exit the combustor through area  23 . These hot gases travel into the turbine  14  where the exhaust gases turn the rotor which is connected to shaft  12   a  used to generate power. The hot gases, after passing through the turbine, are exhausted through area  15 . The single-stage, single nozzle combustor and combustion system  13  shown in the prior art were characterized by high NOx emissions which are not suitable for current government regulations on the total emissions allowable from gas turbines when generating electrical power. The present invention provides a solution for the emissions problem by including an improved combustion system with a vertical or silo orientation that greatly reduces NOx emissions while at the same time improving the overall efficiency of the gas turbine engine. 
     Referring now to FIG. 2 an individual combustor as utilized in the present invention is shown. The can-annular combustor  40  includes an outer cylindrical case  41  with flanges  48  on each end. These flanges are to be used for mounting and sealing the combustor  40  to mating components described herein. Flow sleeve  42  is used for regulating the amount of compressor discharge air admitted from the compressor to the combustor and retaining the combustor liner  43 . The two-stage, two-mode combustion chamber  400  includes and encompasses the first and second stage combustion chambers, cowl cap and the venturi for improved emissions. The combustion chamber  400  is enclosed by cover  44  which includes six primary fuel nozzles (not shown) used for the primary or first stage combustion and second stage fuel supply. Attached to the cover is a central fuel nozzle  45  which is the secondary fuel nozzle for the combustor. This fuel nozzle is used for transition and flame adjustment purposes and is described in applicant&#39;s pending patent application for the secondary fuel nozzle. Fuel is supplied to cover  44  through an inlet pipe  47 . The can-annular combustors communicate with each other through cross over tubes (not shown) that engage the combustion liner  43  through apertures  46 . The bottom portion of combustion liner  43  has a spring seal  49  that is used for sealing, engaging and aligning with the mating inner dome liner attached at the combustor as shown in FIG.  5 . 
     Referring now to FIG. 3, a top plan view of the entire combustion system is shown. As is readily observable, instead of having a single fuel nozzle in a single chamber, the improved silo combustion system includes twelve individual combustors  40  annularly mounted around the top cap  81  of the combustor system. Each individual combustor  40  is a dual stage, dual mode combustor that has reduced NOx emissions. All twelve of the combustors  40  have their outputs into a single plenum. The combustors  40  are mounted essentially vertical on the top cap  81  such that the exhaust gases from each individual combustor  40  are directed downwardly into the plenum chamber which results in a large single exhaust chamber. Cross communication between the combustors are required in order to propagate flame and maintain flame in each individual system. Each individual combustor  40  is in communication with each other via inner and outer tube sections  60  defining the flame crossovers  401 . The inner tube carries the flame between combustion liners  43  (FIG. 2) while the outer tube or spool piece, bolts directly to the adjacent combustors  40  by mounting pad  61 , shown in FIG.  4 . The inner and outer tubes assembly maybe of a fixed or flexible type. A dome lid  83  covers the cap opening used for internal access. 
     Referring to FIG. 4, the combustion system is shown with one combustor  40  for clarity purposes. Each of the combustor mounting bosses (annual rings  82 ) of which there are  12  disposed around the dome  80  receives its own independent combustor  40 . Each can-annular combustor  40  is mounted to the silo dome  80  by an integral mounting boss  82  that is pre-drilled with a matching bolt pattern to the aft flange  48  of combustor  40 . Spool pieces for connecting individual combustors  40  are mounted to bosses  61 . The silo dome  80  bolts to the upper silo case  92  at flange  81 . The upper silo case  92  also contains a lower mounting flange  85 , which is annular and which mounts to the silo housing (not shown). The silo housing is mounted vertically and contains the plenum chamber into which all  12  combustors output their combustion gases. The upper dome piece  80  forms a cap for the vertical combustion system. 
     The fuel manifold system  86  is shown in FIG.  4 . In this embodiment a single fuel system is utilized without additional additives such as water, steam or alternate fuels. If additional additives are required, additional manifold plumbing system is necessary. The fuel manifold system is comprised of multiple manifolds  87 , 88 , and  89  each of which carry fuel to different locations of the combustor  40 . Natural gas fuel is introduced to the manifolds from ground fed piping (not shown) which would typically arrive from a natural gas pipeline. The natural gas fuel is transferred to the combustor  40  through flexible houses  94  and  95  that are attached to the manifolds  87 , 88 , and  89  and to the cover  44  and central fuel nozzle base  45 . The flexible hoses  94  and  95  are attached to the manifold and combustor by flanges. The fuel manifold system  86  is supported over the combustion system cap by rigid beam assembly  90  which can be mounted to the dome  80  by mounting flanges  91  or to a surrounding maintenance catwalk. Access to the combustor  40  for maintenance and inspection is achieved through an opening  83  that is covered by a dome lid  83   a  which would normally cover opening  83  and which is mounted directly to an annular flange  84  connected to the combustion system dome  80 . 
     Referring now to FIG. 5, the vertical combustion system is shown containing one combustor  40  with the other combustors removed for clarity. The embodiment shown in FIG. 5 also does not include the fuel manifold system as shown in FIG.  4 . The combustion system  13  as shown operates in a vertical position relative to the turbine shaft that operates horizontally relative to the ground. In operation the combusted gases that power the turbine are directed in a downward direction. As described above, with respect to FIG.  1  and the turbine section and the compressor section, the vertical silo combustion system  13  is perpendicular to the linear axis and power shaft  12   a  that connects the turbine system with the compressor system. Because the flow of the combustion gases is downward and the overall height of the silo is increased, it is believed that the vertical orientation that includes having multiple individual combustors  40  provide a uniform gas mixing process for lower Nox emissions. Each of the individual combustors  40  are dual stage, dual mode combustors having very low pollutant emissions of nitric oxides. As shown in FIG. 5, each of the openings at mount  82  receive an individual combustor  40 , with a total of  12  individual combustors  40 . Combustion gas from each individual combustor  40  is forced under pressure downwardly and into the plenum chamber  130 . The combustion system  13  is comprised of a lower case  17  that is vertically oriented and attached to the turbine and compressor sections of the engine. The combustor system  13  includes a middle flow sleeve  20  and a ribbed inner liner  19 . The can-annular combustion assembly  40  is mounted to the silo combustion system case  17  at flange  18 . The upper silo case  92  is mounted to the lower silo case  17  using flanges  18  and  85 . The silo dome  80  is mounted to the upper silo case  92  at flange  81 . The inner dome liner  122  is positioned inside the upper silo case  92  for the purpose of receiving the hot gases from the individual combustors  40  and directing these gases into the plenum chamber  130 . 
     The inner dome liner  122  is held in place and positioned within the upper silo case  92  by four positioning members  123 . These positioning members  123  are adjustable to compensate for tolerances, assembly and operational variations. The inner dome liner openings  124  allow for receipt of the combustor liner  43 . The interface is completely sealed by a spring seal  49  which is integral to the combustion liner  43 . Hot gases exit individual combustion liners  43  into the inner dome liner  122  which transfers the flow of hot gases to the silo combustion system inner liner  19 . The inner dome liner  122  and the dome  80  each have lids  121  and  120  respectively that can be removed for maintenance, inspection and assembly purposes. 
     Referring now to FIG. 6, an improved combustor that is used in the present invention is shown at  310  including a combustor chamber  313  that has a venturi  311   a . This combustors described in Applicant&#39;s pending U.S. patent application Ser. No. 09/605,765 entitled “Combustor Chamber/Venturi Cooling For A Low NOx Emission Combustor”, filed Jun. 28, 2000 incorporated by reference herein. 
     The combustor chamber wall  311  includes a cylindrical portion which forms the combustor chamber  113  and unitary formed venturi walls which converge and diverge in the downstream direction forming an annular or circular restricted throat  311   a . The purpose of the venturi and the restricted throat  311   a  is to prevent back flash of the flame from the combustion chamber  313 . 
     Chamber  312  is the premix chamber where air and fuel are mixed and forced under pressure downstream through the venturi throat  311   a  into the combustion chamber  313 . 
     Concentric, partial cylindrical wall  311   b  surrounds the combustor chamber wall  311  including the converging and diverging venturi wall to form an air passage  314  between the combustor chamber wall  311  and the concentric wall  311   b  that allows the cooling air to pass along the outer surface of the combustion chamber walls  311  to cool the walls  311 ,  311   b.    
     The outside of the combustor  310  is surrounded by a housing (not shown) and contains air under pressure that moves upstream towards the premix zone  312 , the air being received from the compressor of the turbine. This is very high pressure air. The air-cooling passage  314  has air inlet apertures  327  which permits the high-pressure air surrounding the combustor to enter through the apertures  327  and to be received in the entire annular passage  314  that surrounds the combustion chamber wall  311 . The cooling air passes along the combustion chamber wall  311  passing the venturi converging and diverging wall in venturi throat  311   a . Preheated cooling air exits through outlet  328  which exits into an annular belly band chamber  316 . The combustor utilizes the cooling air that has been heated and allowed to enter into premix chamber  312  through apertures  329  and  322 . Note that this is heated air that has been used for cooling that is now being introduced into the premix chamber, upstream of the convergent wall of the venturi and the upstream of venturi throat  311   a . Using preheated air drives the f/a ratio to a lean limit to reduce NOx while maintaining a stable flame. The combustor shown in FIG. 6 herein can be utilized as each of the twelve individual combustors  40  shown in FIG.  3 . These combustors are found to increase the efficiency and reduce emissions of NOx in the vertical silo combustor system described herein. Each combustor  40  provides combustion gases into a central plenum. 
     With the use of a vertical combustion system in a gas turbine engine having the turbine section and the compressor section horizontal in a linear axial alignment and employing individual combustors that are two-stage, provides for a highly efficient gas turbine engine with very low NOx emissions. The combustion gases from each individual combustor  40  is directed into a single plenum chamber which itself empties into an annular chamber providing a 360 degree area of impinging gases for rotating the turbine blades. 
     The instant invention has been shown and described herein in what is considered to be the most practical and preferred embodiment. It is recognized, however, that departures may be made there from within the scope of the invention and that obvious modifications will occur to a person skilled in the art.