Method to integrate regenerative rankine cycle into combined cycle applications

Abstract

A system is disclosed that incorporates a regenerative Rankine cycle integrated with a conventional combined cycle. An added duct firing array, typically located after the combustion turbine exhaust and before the conventionally designed Heat Recovery Steam Generator (HRSG), is used to boost enthalpy of said exhaust. An added heating element downstream of the firing array provides sufficient heating for sensible heating, evaporation and superheating of feedwater that has been previously heated by feedwater heaters as part of a regenerative Rankine cycle. In practice, the condensate stream from the condenser is bifurcated such that a dedicated feedwater flow is directed to feedwater heaters. After further heating in the added heating element, the superheated steam, at the same pressure and temperature as the main steam, is now mixed with the main steam prior to turbine entry. The condensate is directed to the HRSG to be heated in conventional fashion.

1 . A method for generating electric power that incorporates the use of a regenerative Rankine cycle with a combined cycle, the method comprising the steps of:
 Bifurcating the condensate from a condenser into two or more separate condensate feed streams whereby the condensate in at least one condensate feed stream is pressurized to feedwater and sent directly to a heat recovery steam generator and the condensate in at least one condensate feed stream is pressurized to feedwater and sent to at least one separately fired heating element first being preheated by a one or more feedwater heaters utilizing extraction steam from an extraction turbine;   generating steam in at least one separately fired heating element and transferring the steam to an extraction steam turbine having one or more extraction ports;   converting the steam into electricity through the use of an extraction steam turbine and generator and extracting some of the steam for heating feedwater.   
     
     
         2 . The method of  claim 1 , wherein additional heat enthalpy is supplied to the separately fired heating element and used to boost the temperature and enthalpy of the combustion turbine exhaust flow such that there is additional enthalpy in said combustion turbine exhaust flow to generate steam for use in a regenerative Rankine cycle. 
     
     
         3 . The method of  claim 1 , wherein the separately fired heating element is placed downstream of the combustion turbine inside the combustion turbine exhaust ducting. 
     
     
         4 . The method of  claim 1 , wherein the separately fired heating element may be configured in a “once through” or drum design. 
     
     
         5 . The method of  claim 1 , wherein the method may be utilized in conjunction with a single pressure or multiple pressure heat recovery steam generator. 
     
     
         6 . The method of  claim 2 , wherein some or all of the additional heat enthalpy supplied to the separately fired heating element is generated from combusting fuel in at least one duct burner. 
     
     
         7 . The method of  claim 2 , wherein the additional heat enthalpy supplied to the separately fired heating element may be generated from fossil fuel or non-fossil fuel or a combination of both. 
     
     
         8 . The method of  claim 2 , wherein substantially all of the additional heat enthalpy supplied to the separately fired heating element is utilized to generate steam. 
     
     
         9 . The method of  claim 2 , wherein some or all of the additional heat enthalpy supplied to the separately fired heating element is supplied through the use of one or more duct burners placed in the combustion turbine exhaust ducting and before the separately, fired heating element. 
     
     
         10 . A method to generate reheated steam utilizing a separately fired heating element in a regenerative Rankine cycle used in conjunction with a combined cycle, the method comprising of:
 Partially expanded steam from the high pressure turbine exhaust is sent to an independent fired heating element to boost said steam to a temperature that is compatible with the hot reheat steam produced by the heat recovery steam generator for mixing with total mix directed to the intermediate pressure turbine inlet;   a duct burner to provide for the necessary enthalpy into the separately fired heating element to reheat the steam is placed downstream of the combustion turbine inside the combustion turbine exhaust ducting.   
     
     
         11 . A method for generating electric power that incorporates the use of a regenerative Rankine cycle with a combined cycle, the method comprising the steps of:
 Bifurcating the condensate from a condenser into two or more separate condensate feed streams whereby the condensate in at least one condensate feed stream is pressurized to feedwater and sent directly to a heat recovery steam generator and the condensate in at least one condensate feed stream is pressurized to feedwater and sent to at least one separately fired heating element first being preheated by a one or more feedwater heaters utilizing cold reheat steam from a non-extraction turbine;   generating steam in at least one separately fired heating element and transferring the steam to a non-extraction steam turbine;   converting the steam into electricity through the use of a non-extraction steam turbine and generator.