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A hybrid dynamic model for a 600 MW supercritical circulating fluidized bed (CFB) boiler is presented. The combustion system includes combustion chamber, cyclone separator, standpipe, and ash cooler. The steam-water system mainly contains water wall, external heat exchanger, superheater, reheater, and economizer. The ‘core-annulus cell model’ is employed to simulate complex physical and chemical processes in the boiler. A series of classical empirical models have been chosen to model main physical and chemical processes. The water-steam system is modelled by means of modular modelling method, a new user-defined model for external heat exchanger is established and validated. The combustion system is coupled with the water-steam system via heat exchange in water wall tubes. The static state calculation is taken to compare with the design values indicating the model has reached a rather high precision. Dynamic simulations under three typical transient conditions are conducted which are 5% fuel decrease, 5% secondary air decrease and 5% supply water decrease, respectively. The results demonstrate that the hybrid model is capable of performing good characteristics of CFB. The modelling method has important theoretical and engineering values for researchers, and the hyrbid model can be very helpful to optimize operating and design parameters to get a better performance of large-scale commercial CFB.

The rapid expansion of the electricity demand causes the gap between the peak load and valley load increasing in China. Since the coal-fired supercritical power plant needs to be started up frequently, the operations of power plant become more flexible. During the start-up process, the operation parameters are off-designed, the multi-transient phenomenon is inevitable and the intensive emission always appears during varying working condition, it is difficult to ensure the operator of the real power plant to start up the boiler following the design curve. In this work, a new dynamic model for simulating start-up dynamic process of a 600 MW supercritical boiler is introduced in this paper. The six-equation solution of two-phase flow was applied to modeling the evaporator, and the process from ignition to the load at 30% Boiler Maximum Continuous Rating (BMCR) was simulated. The results demonstrate that the model is reasonable and dynamic behavior can be observed clearly. Also, these prove that the control strategy is advisable. Moreover, the fuel consumption of the start-up process can offer a reference to operator of the real power plant. The validated model is of high relevance for further optimizing the boiler start-up process.