Cooling of gas turbine at varying loads

Abstract

Embodiments of the present disclosure relate to cooling a gas turbine which operates at varying loads. An apparatus according to embodiments of the present disclosure may include: an outlet heat exchanger positioned within a transition duct of a turbine outlet of a gas turbine, wherein the transition duct is positioned upstream from a heat recovery steam generator (HRSG); an extraction line fluidly connecting the outlet heat exchanger to the HRSG, such that a heat exchange fluid flows from the HRSG to the outlet heat exchanger through the extraction line; and a return line fluidly connecting the outlet heat exchanger to the HRSG, such that the heat exchange fluid returns to the HRSG through the return line after passing through the outlet heat exchanger.

What is claimed is: 
     
         1 . An apparatus comprising:
 an outlet heat exchanger positioned within a transition duct of a turbine outlet of a gas turbine, wherein the transition duct is positioned upstream from a heat recovery steam generator (HRSG);   an extraction line fluidly connecting the outlet heat exchanger to the HRSG, such that a heat exchange fluid flows from the HRSG to the outlet heat exchanger through the extraction line; and   a return line fluidly connecting the outlet heat exchanger to the HRSG, such that the heat exchange fluid returns to the HRSG through the return line after passing through the outlet heat exchanger.   
     
     
         2 . The apparatus of  claim 1 , further comprising an inlet heat exchanger positioned within an inlet to the compressor of the gas turbine and fluidly coupled to the extraction line through an inlet line, such that the heat exchange fluid passes through the inlet line and the inlet heat exchanger before entering the outlet heat exchanger. 
     
     
         3 . The apparatus of  claim 1 , wherein the transition duct receives a flue gas from a diffusor component of the turbine outlet, such that the outlet heat exchanger is in thermal communication with the flue gas. 
     
     
         4 . The apparatus of  claim 1 , further comprising a drain line fluidly coupled between the outlet heat exchanger and a drain, wherein the drain line includes a drain valve for controlling a flow of the heat exchange fluid from the outlet heat exchanger into the drain. 
     
     
         5 . The apparatus of  claim 1 , further comprising a bypass line fluidly coupling the extraction line to the return line, wherein the bypass line includes a bypass valve for controlling a flow of the heat exchange fluid from the extraction line into the return line to bypass the outlet heat exchanger. 
     
     
         6 . The apparatus of  claim 1 , wherein the outlet heat exchanger includes a plurality of tubes each extending between the extraction line and the return line. 
     
     
         7 . The apparatus of  claim 1 , wherein a material composition of the outlet heat exchanger includes one of a steel or a nickel-based alloy. 
     
     
         8 . An apparatus comprising:
 an inlet heat exchanger positioned within a compressor inlet of a gas turbine;   an outlet heat exchanger positioned within a transition duct of a turbine outlet of the gas turbine, wherein the transition duct is positioned upstream from a recovery steam generator (HRSG);   an extraction line fluidly coupling the inlet heat exchanger to the heat recovery steam generator (HRSG);   an inlet return line fluidly coupling the inlet heat exchanger to the outlet heat exchanger; and   a return line fluidly coupling the outlet heat exchanger to the HRSG.   
     
     
         9 . The apparatus of  claim 8 , further comprising a pre-filter heat exchanger fluidly coupled between the extraction line and the inlet heat exchanger, the pre-filter heat exchanger being positioned within the compressor inlet upstream from each of a silencer and a filter of the gas turbine, wherein the inlet heat exchanger is positioned downstream from the silencer and the filter of the gas turbine. 
     
     
         10 . The apparatus of  claim 9 , further comprising a condensate line fluidly coupling the pre-filter heat exchanger to the return line, wherein the condensate line transmits a condensed heat exchange fluid in the pre-filter heat exchanger directly to the return line. 
     
     
         11 . The apparatus of  claim 10 , wherein the pre-filter heat exchanger includes a plurality of heating pipes each extending between the extraction line and the condensate line. 
     
     
         12 . The apparatus of  claim 8 , further comprising a drain line fluidly coupled between the outlet heat exchanger and a drain, wherein the drain line includes a drain valve for controlling a flow of the heat exchange fluid from the outlet heat exchanger into the drain. 
     
     
         13 . The apparatus of  claim 8 , further comprising a bypass line fluidly coupling the extraction line to the inlet return line, wherein the bypass line includes a bypass valve for controlling a flow of the heat exchange fluid from the extraction line into the inlet return line to bypass the inlet heat exchanger. 
     
     
         14 . The apparatus of  claim 8 , wherein a material composition of the inlet and outlet heat exchangers includes one of a steel or a nickel-based alloy. 
     
     
         15 . A method for cooling a gas turbine at varying loads, the gas turbine including a compressor inlet and a turbine outlet, wherein the turbine outlet further includes a transition duct positioned upstream from a heat recovery steam generator (HRSG), the method comprising:
 operating the gas turbine at one of a startup load and a reduced load, the startup load and the reduced load having a reduced power output relative to a base load of the gas turbine;   extracting a heat exchange fluid from the HRSG through an extraction line;   transmitting the extracted heat exchange fluid through the extraction line to an outlet heat exchanger positioned within the transition duct of the turbine outlet to yield a heated fluid; and   transmitting the heated fluid through a return line to the HRSG.   
     
     
         16 . The method of  claim 15 , further comprising draining the heat exchange fluid from the outlet heat exchanger during operation of the gas turbine at the base load. 
     
     
         17 . The method of  claim 15 , further comprising, in response to operating the gas turbine at the reduced load, transmitting the extracted heat exchange fluid to at least one inlet heat exchanger positioned within the compressor inlet of the gas turbine through an inlet line, before transmitting the extracted heat exchange fluid to the outlet heat exchanger through the extraction line. 
     
     
         18 . The method of  claim 17 , wherein the at least one inlet heat exchanger includes a pre-filter heat exchanger in thermal communication with the compressor inlet, and positioned within the inlet to the compressor upstream from a filter and a silencer of the gas turbine. 
     
     
         19 . The method of  claim 17 , further comprising transmitting a condensed portion of the extracted heat exchange fluid from the pre-filter heat exchanger directly to the outlet heat exchanger through a condensate line. 
     
     
         20 . The method of  claim 15 , wherein the transition duct receives a flue gas from a diffusor component of the turbine outlet, such that the outlet heat exchanger is in thermal communication with the flue gas.