Dynamics of large-scale bubbling fluidized bed combustion plants for heat and power production

Paper in proceeding, 2022

This paper presents a dynamic model of bubbling fluidized bed (BFB) units for combined heat and power (CHP) production that results from connecting a model of the gas side with a process model of the water-steam side. The model output is validated by comparison with operational data measured in a 130-MWth BFB plant that produces electricity, district heating (DH) water and steam to industrial clients. The validation shows that the model can satisfactorily describe both multi-load steady-state operation as well as load transients. The validated model is here used to compute the inherent process dynamics of the reference plant. The simulation results highlight the fact that the water-steam cycle reaches stabilization faster after changes in the DH line and steam delivered to clients than to changes in the combustor load. The timescales of the plant outputs for different changes have been computed, with stabilization times ranging between 2 and 15 min for the power production versus 2-25 min characterizing the DH production. When comparing these results with the characteristic times of the gas side, it is concluded that the water-steam side is an order of magnitude slower, i.e., limiting the transient operation capabilities of BFB-CHP plants. This in in contrast to earlier findings for circulating fluidized bed plants, where the characteristic times of both sides are in the same order of magnitude.