Inter-stage attemperation system and method

A controller, comprising:

• a processor containing an outer control loop comprising a feed-forward controller configured to utilize a predicted value for an outlet temperature of steam from a finishing superheater, the feed-forward controller comprising a first input for receiving an inlet temperature of exhaust gas from a gas turbine and a second input for receiving a set point temperature for the outlet steam from the finishing superheater, wherein the outer control loop comprises a predictive model configured to predict the outlet temperature of steam based on the inlet temperature of exhaust gas from the gas turbine, the set point temperature for the outlet steam from the finishing superheater, and variables corresponding to inlet conditions into the finishing superheater, and wherein the predictive model is further configured to establish a profile for the set point temperature based on the inlet temperature of exhaust gas from the gas turbine such that the set point steam temperature may be reached only at or after the exhaust gas temperature reaches an isotherm;
• and an inner control loop comprising a first proportional-integral controller configured to control attemperation upstream of an inlet into the finishing superheater based on the predicted value.

A controller for controlling exhaust steam temperatures from a finishing superheater, comprising:

• a processor containing model-based predictive temperature control logic configured to predict an exhaust steam temperature from a finishing superheater, wherein the model-based predictive temperature control logic is at least partially based on input variables comprising an inlet temperature of exhaust gas from a gas turbine into the finishing superheater and a set point temperature for the exhaust steam from the finishing superheater, and further wherein the model-based predictive temperature control logic is further configured to establish a profile for the set point temperature based on the inlet temperature of exhaust gas from the gas turbine such that the set point steam temperature may be reached only at or after the exhaust gas temperature reaches an isotherm;
• and attemperation control logic configured to control attemperation upstream of the finishing superheater with feed-forward control logic and the exhaust steam temperature predicted by the model-based predictive temperature control logic.