| abstract |
A control system for automatically achieving and maintaining a desired sodium/phosphate ratio and phosphate concentration of the boiler water in an industrial boiler for minimizing corrosion. The system uses an adaptive controller that models the boiler which enables the system to predict boiler pH and phosphate concentrations at any future time given the feed rates, feed concentrations of high and low sodium/phosphate stocks, blowdown rate, mass of the boiler water, initial boiler phosphate concentration and initial pH. Once these future concentrations are determined, the controller then determines which feed rates will return the current boiler water state to, and then maintain the boiler water at, the desired sodium/phosphate congruency ratio in the least amount of time. Where the controller determines that it is not possible to move the current boiler water state to the desired congruency setpoint, the controller determines a feed rate program that will move the current boiler water state to the attainable steady state point closest to the desired setpoint. An alternative embodiment fixes the phosphate concentration by ratioing the phosphate feed with the blowdown rate while continuously monitoring blowdown pH. This arrangement allows for the control of sodium by switching between the high and low ratio sodium/phosphate stocks based on the measured pH with respect to the pH setpoint. |