Method to integrate regenerative rankine cycle into combined cycle applications using an integrated heat recovery steam generator

Abstract

A system is disclosed that incorporates a regenerative Rankine cycle integrated with a conventional combined cycle. This novelty requires minimal changes to a conventionally designed Heat Recovery Steam Generator and uses an added duct firing array(s) to boost the enthalpy of combustion turbine exhaust. The higher enthalpy in said exhaust is then extracted with the co-shared heating elements of the conventionally designed combined cycle to produce high pressure main and reheat steam. In practice, the condensate stream from the condenser is bifurcated such that a separate and dedicated feedwater flow, used for regeneration, is directed to feedwater heaters and then converted to steam with the provided additional enthalpy at the same pressure and temperature as the main steam in the conventional combined cycle. The fractional amount of condensate that is not sent through the feedwater heaters is directed to the HRSG to be heated in conventional fashion.

What is claimed is: 
     
         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 one or more common heating elements that is co-shared with the first stream first being preheated by a one or more feedwater heaters utilizing extraction steam from an extraction turbine;   generating steam in a parallel cycle using a regenerative Rankine cycle and co-mixing said steam with the steam produced in a traditional non-regenerative combined cycle 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 common heating elements 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 duct burner is placed inside the combustion turbine exhaust ducting and before the heat recovery steam generator. 
     
     
         4 . The method of  claim 1 , wherein the commonly fired heating elements of the heat recovery steam generator 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 co-shared 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 co-shared 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 co-shared 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 co-shared heating element is supplied through the use of one or more duct burners placed in the combustion turbine exhaust ducting and before the commonly fired heating element. 
     
     
         10 . The method of  claim 2 , wherein the low temperature enthalpy supplied by the duct burner is used for steam dearation or low pressure steam for power production. 
     
     
         11 . The method of  claim 2  where additional enthalpy is added by conventional duct firing and there is a proportional increase in the low temperature feedwater flow to provide additional capacity and energy through a straight through non-regenerative Rankine cycle in the conventional manner of duct firing. 
     
     
         12 . The method of  claim 2  where a combination of increase of the low temperature feedwater flow in conjunction with an increase of the high temperature regenerative feedwater is used in parallel to optimize both capacity and energy output. 
     
     
         13 . A method to generate reheated steam utilizing a co-shared 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 a co-shared 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 from the high pressure turbine exhaust is located upstream of the heat recovery steam generator.   
     
     
         14 . 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 co-shared 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 co-shared 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.