Enhancing the load ramp-up capability of the subcritical CFB power unit by considering the evolution of internal stored energy

The substantial inertia of the boiler restricts the flexibility of circulating fluidized bed (CFB) power units. To enhance the load ramp-up capability of the CFB power unit, we proposed a novel control strategy considering the spatial-temporal evolution of its internal stored energy. A dynamic model of the subcritical CFB power unit with a capacity of 300 MW was developed, incorporating the mechanism and control modules. By analyzing the spatial-temporal evolution of the stored energy in bed material, flue gases, refractory materials, economizer, evaporation subsystem, superheater subsystem, reheater subsystem, and turbine subsystem, we identified that the over-utilization of chemical and thermal stored energy in the bed materials is the primary factor restricting load ramp-up, while the thermal stored energy of the economizer is suitable for further utilization. Under the optimized control strategy that utilizes deviations of stored energy per mass of bed materials as a feedforward mechanism, the deviations of the key operating parameters during the load ramp-up process are significantly reduced, and the load ramp-up rate of the subcritical CFB power unit can be improved from 2.0 % Pe/min to 3.0 % Pe/min.