Abstract:
A nitrogen source supplies a flow of nitrogen to a cooling circuit in the turbine section of a gas turbine. The nitrogen in the cooling circuit absorbs heat from the turbine section and flows to a flow divider where the heated nitrogen is split into a combustor flow and a return flow. The combustor nitrogen flow is injected into the gas turbine combustor. The return nitrogen flow is returned to the flow of nitrogen supplied to the gas turbine cooling circuit.

Description:
TECHNICAL FIELD 
     The present application relates generally to gas turbine engines and more specifically relates to a gas turbine engine with closed circuit nitrogen cooling as well as emissions control. 
     BACKGROUND OF THE INVENTION 
     Known integrated gasification combined cycle (“IGCC”) power generation systems may include a gasification system that is integrated with at least one power producing turbine system. For example, known gasifiers may convert a mixture of a fuel such as coal with air or oxygen, steam, and other additives into an output of a partially combusted gas, typically referred to as a “syngas”. These hot combustion gases may be supplied to a combustor of a gas turbine engine. The gas turbine engine, in turn, powers a generator for the production of electrical power or to drive another type of load. Exhaust from the gas turbine engine may be supplied to a heat recovery steam generator so as to generate steam for a steam turbine. The power generated by the steam turbine also may drive an electrical generator or another type of load. Similar types of power generation systems also may be known. 
     The known gasification processes also may generate flows of nitrogen. For example, an air separation unit may be used to generate a supply of oxygen to the gasifier. The air separation unit may generate oxygen by separating the oxygen from the nitrogen in a supply of air. Some of the nitrogen may be used to control emissions generated by the gas turbine engine or to augment power output of the turbine. For example, nitrogen may be injected into the combustion zone of the gas turbine engine to reduce the combustion temperatures and to reduce nitrous oxide (“NO x ”) emissions. The turbine section of the gas turbine engine is cooled to maintain component temperatures to allowable material limits. The cooling, which is provided by air extracted from the compressor section, penalizes engine power output and heat rate. 
     There is thus a desire for an improved integrated gasification combine cycle power generation system. Such an IGCC system preferably would use all or most of the nitrogen generated therein for productive purposes while improving overall IGCC output and heat rate. 
     SUMMARY OF THE INVENTION 
     The present application thus provides an integrated gasification combined cycle system. The integrated gasification combined cycle system may include a nitrogen source, a combustor, and a turbine. A flow of nitrogen from the nitrogen source passes through and cools the turbine and then flows into the combustor. 
     The present application further provides a method of operating an integrated gasification combined cycle system. The method may include generating a flow of nitrogen, flowing the flow of nitrogen through a gas turbine, heating the flow of nitrogen as it flows through the gas turbine, injecting a portion of the now heated flow of nitrogen into a combustor, and reducing a combustor operating temperature. 
     The present application further provides an integrated gasification combined cycle system. The integrated gasification combined cycle system may include an air separation unit for generating a flow of nitrogen, a compressor for compressing the flow of nitrogen, a combustor, and a turbine. The compressed flow of nitrogen passes through and cools the turbine and then flows into the combustor. 
     These and other features and improvements of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic of a prior art gas turbine engine. 
         FIG. 2  is a schematic view of a number of stages of a gas turbine. 
         FIG. 3  is a schematic view of a portion of an integrated gasification combined cycle system with a nitrogen cooled gas turbine as may be described herein. 
         FIG. 4  is an alternative embodiment of the integrated gasification combined cycle system with a nitrogen cooled gas turbine. 
         FIG. 5  is an alternative embodiment of the integrated gasification combined cycle system with a nitrogen cooled gas turbine. 
         FIG. 6  is an alternative embodiment of the integrated gasification combined cycle system with a nitrogen cooled gas turbine. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows a schematic view of a gas turbine engine  100  as may be described herein. The gas turbine engine  100  may include a compressor  110 . The compressor  110  compresses an incoming flow of air  120 . The compressor  110  delivers the compressed flow of air  120  to a combustor  130 . The combustor  130  mixes the compressed flow of air  120  with a compressed flow of fuel  140  and ignites the mixture to create a flow of combustion gases  150 . Although only a single combustor  130  is shown, the gas turbine engine  100  may include any number of combustors  130 . The flow of combustion gases  150  are in turn delivered to a turbine  160 . The flow of combustion gases  150  drives the turbine  160  so as to produce mechanical work via the turning of a turbine rotor  170 . The mechanical work produced in the turbine  160  drives the compressor  110  and an external load such as an electrical generator  180  and the like via the turbine rotor  170 . 
     The gas turbine engine  100  may use natural gas, various types of syngas, and other types of fuels. The gas turbine engine  100  may be any number of different turbines offered by General Electric Company of Schenectady, N.Y. or otherwise. The gas turbine engine  100  may have other configurations and may use other types of components. Other types of gas turbine engines also may be used herein. Multiple gas turbine engines  100 , other types of turbines, and other types of power generation equipment may be used herein together. 
       FIG. 2  shows a number of stages  190  of the turbine  160 . A first stage  200  may include a number of circumferentially spaced first stage nozzles  210  and buckets  220 . Likewise, a second stage  230  may include a number of circumferentially spaced second stage nozzles  240  and buckets  250 . Further, a third stage  260  may include a number of circumferentially spaced third stage nozzles  270  and buckets  280 . The stages  200 ,  230 ,  260  may be positioned in a hot gas path  290  through the turbine  160 . Any number of stages  190  may be used herein. One or more of the buckets  220 ,  250 ,  280  may have a tip shroud  300  thereon. Other types of turbine configurations also may be used herein. 
     The rotating components, i.e., the buckets  220 ,  250 ,  280 , and the stationary components, i.e., the nozzles  210 ,  240 ,  270 , may have one or more cooling circuits  310  extending therethrough. In this example, the cooling circuit  310  may be a closed circuit. A cooling medium may pass therethrough so as to cool the components of the turbine  160  within the hot gas path  290 . Other types of cooling configurations may be used herein. 
       FIG. 3  shows portions of an integrated gasification combined cycle system  350  as may be described herein. The IGCC system  350  may includes the gas turbine engine  100  and the components thereof as is described above and also in similar configurations. The IGCC system  350  also may include an air separation unit  360 . As is described above, the air separation unit  360  may be in communication with a gasifier (not shown) and the like. The air separation unit  360  may produce a flow of oxygen as well as a flow of nitrogen  370 . Other sources of nitrogen and/or other gases also may be used herein. 
     In this example, the air separation unit  360  may be in communication with the turbine  160  of the gas turbine engine  100  via one or more nitrogen compressors  380 ,  385 . The nitrogen compressors  380 ,  385  may be of conventional design. The nitrogen compressors  380 ,  385  compress the flow of nitrogen  370  to a sufficient pressure, i.e., a pressure sufficient to meet compressor diluent injection requirements plus all losses due to piping, equipment, turbine component coolant circuitry, and the like. A pressure control valve  390  also may be used. The pressure control valve  390  protects against over pressure via, for example, balloon stress mitigation and other techniques. 
     The flow of nitrogen  370  may be directed to the cooling circuit  310 . The flow of nitrogen  370  may be divided into a stationary component cooling flow  400  to cool the stationary components therein and a rotating component cooling flow  410  to cool the rotating components therein. The cooling flows  400 ,  410  then may merge downstream of the turbine  160 . 
     At a three-way valve  420  or at a similar type of flow device, the flow of nitrogen  370  again may be split, this time into a combustor flow  430  and a return flow  440 . The combustor flow  430  may be delivered to the combustor  130  as a diluent injection for NO x  emissions and/or gas turbine power augmentation. The return flow  440  may be cooled in a nitrogen cooler  450  via boiler feed water or another flow source to a temperature suitable for compression via the compressor  385 . The return flow  440  may then be recirculated into the cooling circuit  310  or used for other purposes. The nitrogen cooler  450  may be any type of heat exchanger and the like. Other configurations may be used herein. Other types of flows also may be used herein. 
       FIG. 4  shows an alternative embodiment of portions of an integrated gasification combined cycle system  460 . The IGCC system  460  may be similar to the IGCC system  350  described above and with the addition of a fuel heater  470 . The fuel heater  470  may be in communication with the combustor flow  430  downstream from the turbine  160  and the flow of fuel  140 . The combustor flow  430  may be cooled to an allowable maximum temperature based on combustion system design requirements by heat exchange with the incoming flow of fuel  140  either directly or via an intermediate heat exchange loop. Alternatively, the combustor flow  430  also may exchange heat with boiler feed water or other type of suitable cooling source. Other configurations may be used herein. 
       FIG. 5  shows an alternative embodiment of an integrated gasification combined cycle system  480 . The IGCC system  480  may be similar to the IGCC system  350  described above. In this example, the return flow  440  downstream of the heat exchanger  450  may include a mixing flow  490 . The hot combustor flow  430  may be mixed with the cooled mixing flow  490  to an allowable maximum temperature before being injected into the combustor  130 . A temperature control valve  500  also may be used herein. Other configurations may be used herein. 
     In use, the IGCC&#39;s  350 ,  460 ,  480  described herein utilize the flow of nitrogen  370  for hot gas path cooling and combustion diluent injection in a sequential arrangement so as to provide significant operational improvements in both power output and heat rate. Specifically, the IGCC&#39;s  350 ,  460 ,  480  may reduce the total amount of turbine component cooling air extracted from the compressor  110 , may transfer high level energy from the hot gas path cooling directly to the combustion system, and may allow for optimization of turbine cooling flows and firing temperatures as a function of nitrogen cooling flow and temperature. The IGCC&#39;s  350 ,  460 ,  480  also may utilize the nitrogen coolers  450  to heat the boiler feed water or another source to produce steam for import into the bottoming cycle so as to increase steam turbine power output. The IGCC&#39;s  350 ,  460 ,  480  thus use all or most of the flow of nitrogen  370  produced via the air separation unit  360  or otherwise and/or recirculates the flow for further use. 
     The lower temperature of the nitrogen flow supplied to the turbine  160 , as compared to a conventional compressor extraction flow, allows for a reduction in the required cooling flow so as to enable optimization of component cooling passages and overall gas turbine performance. The recovery of heat from the component cooling scheme to the combustor  130  via the hot combustor flow  430  thus should reduce the overall flow of fuel  140  and hence improve overall equipment heat rate. The lower temperature of the flow of nitrogen  370  also may result in a reduction in the total required cooling flow herein. 
       FIG. 6  shows a further alternate embodiment of an integrated gasification combined cycle system  510 . The IGCC system  510  may be similar to the IGCC system  350  described above. In this example, the flow of nitrogen  370 , after passing through the turbine cooling passages  400 ,  410 , mixes with an additional nitrogen flow  520  from the nitrogen compressor  380 . A mixed nitrogen flow  530  then may be delivered to the combustor  130 . A mixing valve  540  may be provided to control the flow split between the two mixing nitrogen streams  370 ,  520 . Other configurations may be used herein. 
     It should be apparent that the foregoing relates only to certain embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.