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

This paper concerns the furnace wall outlet steam temperature control for once-through boilers during startup. As part of the boiler start-up process, water wall outlet water/steam temperature ramps from ambient temperature up to about 785 degrees CF). At 550 degrees (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 feed-forward 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). 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.