Multistage hrsg control in a combined cycle unit

Abstract

A system and method include receiving waste heat from a gas turbine, adding heat via duct firing, using the received waste heat and added heat via duct firing to create steam at multiple stages of a heat recovery steam generator, and controlling the multiple stages of the heat recovery steam generator utilizing parameters representative of heat input to each stage.

1 . A method comprising:
 receiving waste heat from a gas turbine;   adding heat via duct firing;   using the received waste heat and added heat via duct firing to create steam at multiple stages of a heat recovery steam generator; and   controlling the multiple stages of the heat recovery steam generator utilizing parameters representative of heat input to each stage.   
     
     
         2 . The method of  claim 1  wherein a first stage of the heat recovery steam generator is a high pressure stage, HP, and a second stage is a medium pressure stage, MP. 
     
     
         3 . The method of  claim 2  wherein the HP and MP stages are cascaded and represented by parallel models. 
     
     
         4 . The method of  claim 3  wherein the parallel models comprise:
     Q   steam,HP =α HP ( Q   in   , O   2 )· Q   in   =: F   α,HP ( Q   in   , O   2 )
 
     Q   steam,MP =α MP ( Q   in   , O   2 )· Q   in   =: F   α,MP ( Q   in   , O   2 )
 
 where O 2  is oxygen concentration, α HP  and α MP  are efficiency coefficients, and Q in  is input heat, and Q steam,HP , Q steam,MP  correspond to heat in steam for respective stages. 
 
     
     
         5 . The method of  claim 4  and further comprising adapting the parallel models by including multiplicative factors to account for environmental changes. 
     
     
         6 . The method of  claim 5  wherein the multiplicative factors account for heat exchanger fouling and variations in feed-water temperature. 
     
     
         7 . The method of  claim 4  and further comprising modeling environmental changes as multiplicative perturbations in accordance with:
     {circumflex over (F)}   α,HP ( Q   in   , O   2 , θ HP )=θ HP   ·F   α,HP ( Q   in   , O   2 )
 
     {circumflex over (F)}   α,MP ( Q   in   , O   2 , θ MP )=θ MP   ·F   α,MP ( Q   in   , O   2 ).
 
 
       where F α,HP  and F α,MP  are functions and θ HP  and θ mP  are perturbation parameters estimated from process data. 
     
     
         8 . The method of  claim 7  wherein θ HP  and θ mP  are estimated using a recursive estimator with inequality bounds. 
     
     
         9 . A system comprising:
 a duct to receive waste heat;   a heat recovery steam generator having multiple stages to receive the waste heat and add heat via duct firing to create steam;   sensors to sense heat parameters at an input to each of the multiple stages; and   a controller to control the multiple stages of the heat recovery steam generator using the parameters representative of heat input to each stage.   
     
     
         10 . The system of  claim 9  wherein a first stage of the heat recovery steam generator is a high pressure stage, HP, and a second stage is a medium pressure stage, MP, wherein the HP and MP stages are cascaded and represented in the controller by parallel models comprising:
     Q   steam,HP =α HP ( Q   in   , O   2 )· Q   in   =: F   α,HP ( Q   in   , O   2 )
 
     Q   steam,MP =α MP ( Q   in   , O   2 )· Q   in   =: F   α,MP ( Q   in   , O   2 )
 
 where O 2  is oxygen concentration, α HP  and α MP  are efficiency coefficients, and Q in  is input heat, and Q steam,HP , Q steam,MP  correspond to heat in steam for respective stages. 
 
     
     
         11 . The system of  claim 10  wherein the controller models environmental changes as multiplicative perturbations in accordance with:
     {circumflex over (F)}   α,HP ( Q   in   , O   2 , θ HP )=θ HP   ·F   α,HP ( Q   in   , O   2 )
 
     {circumflex over (F)}   α,MP ( Q   in   , O   2 , θ MP )=θ MP   ·F   α,MP ( Q   in   , O   2 ).
 
 
       where F α,HP  and F α,MP  are functions and θ HP  and θ mP  are perturbation parameters estimated from process data. 
     
     
         12 . The system of  claim 11  wherein θ HP  and θ mP  are estimated using a recursive estimator with inequality bounds. 
     
     
         13 . The system of  claim 11  wherein the multiplicative perturbations account for heat exchanger fouling and variations in feed-water temperature. 
     
     
         14 . A computer readable storage device having code to cause a computer to perform a method, the method comprising:
 receiving waste heat from a gas turbine;   adding heat via duct firing;   using the received waste heat and added heat via duct firing to create steam at multiple stages of a heat recovery steam generator; and   controlling the multiple stages of the heat recovery steam generator utilizing parameters representative of heat input to each stage.   
     
     
         15 . The computer readable storage device of  claim 14  wherein a first stage of the heat recovery steam generator is a high pressure stage, HP, and a second stage is a medium pressure stage, MP, wherein the HP and MP stages are cascaded and represented by parallel models, and wherein the parallel models comprise:
     Q   steam,HP =α HP ( Q   in   , O   2 )· Q   in   =: F   α,HP ( Q   in   , O   2 )
 
     Q   steam,MP =α MP ( Q   in   , O   2 )· Q   In   =: F   α,MP ( Q   in   , O   2 )
 
 where O 2  is oxygen concentration, α HP  and α MP  are efficiency coefficients, and Q in  is input heat, and Q steam,HP , Q steam,MP  correspond to heat in steam for respective stages.