High density combined cycle power plant process

Abstract

A process for increasing the specific output of a combined cycle power plant and providing flexibility in the power plant rating, both without a commensurate increase in the plant heat rate, is disclosed. The present invention demonstrates that the process of upgrading thermal efficiencies of combined cycles can often be accomplished through the strategic use of additional fuel and/or heat input. In particular, gas turbines that exhaust into HRSGs, can be supplementally fired to obtain much higher steam turbine outputs and greater overall plant ratings, but without a penalty on efficiency. This method by and large defines a high efficiency combined cycle power plant that is predominantly a Rankine (bottoming) cycle. Exemplary embodiments of the present invention include a load driven by a topping cycle engine, powered by a topping cycle fluid which exhausts into a heat recovery device.

1 - 15 . (canceled)  
   
   
       16 . A method of operating a combined cycle power plant comprising at least one gas turbine, at least one heat recovery steam generator associated with said gas turbine, and at least one steam turbine, said method comprising: 
 operating said gas turbine to produce shaft work and exhaust gas;    passing said exhaust gas through said heat recovery steam generator;    adding supplemental heat to said heat recovery steam generator;    generating steam at predominantly a single pressure level at said heat recovery steam generator using heat from said exhaust gas and said supplemental heat;    passing said steam to said steam turbine;    operating said steam turbine to produce shaft work;    converting said steam to feedwater;    passing said feedwater to said heat recovery steam generator; and    controlling at least one of said supplemental heat added to said heat recovery steam generator and said flow of said feedwater through at least a portion of said heat recovery steam generator to maintain a balance between exhaust gas flow and feedwater flow, thereby controlling heat recovery in said heat recovery steam generator.    
   
   
       17 . The method of  claim 16  wherein said steam generated at said heat recovery steam generators is high pressure steam predominantly at supercritical pressure at rated combined cycle plant output.  
   
   
       18 . The method of  claim 16  wherein said flow of feedwater through at least a portion of said heat recovery steam generator is controlled by diverting at least some of said feedwater from said heat recovery steam generator to a parallel feedwater loop and supplying said diverted feedwater back to said heat recovery steam generator.  
   
   
       19 . The method of  claim 18  further including preheating said feedwater in said parallel feedwater loop using steam turbine extraction steam.  
   
   
       20 . The method of  claim 18  further including preheating said feedwater in said parallel feedwater loop using energy from at least one of generator losses and other auxiliaries.  
   
   
       21 . The method of  claim 16  wherein adding supplemental heat to said heat recovery steam generator includes substantially continuously supplemental firing said heat recovery steam generator.  
   
   
       22 . The method of  claim 16  wherein said balance between said exhaust gas flow and said feedwater flow is controlled such that said feedwater flow is nominally about four times said exhaust gas flow downstream from a high pressure evaporator in said heat recover steam generator.  
   
   
       23 . The method of  claim 16  wherein said flow of feedwater through at least a portion of said heat recovery steam generator is controlled by diverting at least some of said feedwater away from said heat recovery steam generator.  
   
   
       24 . The method of  claim 23  further comprising modulating power plant load by at least one of controlling addition of said supplemental heat to said heat recovery steam generator and controlling operation of said gas turbine.  
   
   
       25 . The method of  claim 16  further comprising modulating the rate of adding said supplemental heat when said gas turbine associated with said heat recovery steam generator is at or below about 100% of its nominal gas turbine power output capacity, and diverting at least some of said feedwater away from said heat recovery steam generator when said gas turbine associated with said heat recovery steam generator is above about 100% of its nominal gas turbine power output capacity.  
   
   
       26 . The method of  claim 16  wherein said combined cycle power plant is a single 2-on-1 arrangement comprising two gas turbines, two heat recovery steam generators associated with respective said gas turbines, and a single steam turbine.  
   
   
       27 . The method of  claim 16  wherein the operational ratio of the rated output of said steam turbine to said gas turbines is at least about 0.75.  
   
   
       28 . The method of  claim 16  wherein heat recovery in said heat recovery steam generators is controlled such that a ratio of mass flow through said heat recovery steam generators of said feedwater to mass flow through said heat recovery steam generators of said exhaust gas is substantially equal to a ratio of heat capacity of said exhaust gas to heat capacity of said feedwater.