Model-based once-through boiler start-up water wall steam temperature control

The paper concerns the furnace wall outlet steam temperature control for once-through boilers during start-up. As part of the boiler start-up process, water wall outlet water/steam temperature ramps from ambient temperature up to about 785°F. At 550°F and above, temperature change exhibits strong nonlinear behavior with respect to energy input. Long time delay (especially for a coal-fired unit) and other operating constraints bring additional difficulties for automatic control. To better improve the start-up water wall steam temperature control, a dynamic model-based control approach is proposed. A feedforward control profile is computed first based on an optimization criterion subject to model dynamics and operating constraints. A feedback controller is then designed separately to correct any uncertainties (e.g., fuel type variation). A simulation study demonstrates the model-based and systematically designed control scheme reduces temperature ramp-up time and avoids undesirable temperature overshoot during the entire process