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

Bubbling fluidized bed combustion (BFBC) plants for combined heat and power (CHP) production have traditionally been dispatched under slow load changes. As the amount of variable renewable electricity increases in energy systems worldwide, knowledge regarding the transient capabilities of the gas and water-steam sides of BFBC plants is required. The aim of this work is to investigate the dynamic performance of large-scale BFBC plants when accounting for both the gas and water-steam sides. To do so, this paper presents a dynamic model of BFB-CHP plants that result from connecting a model of the gas side to a process model of the water-steam side. The plant model output is validated by comparisons with operational data measured in a 130-MWth BFBC plant that produces electricity, district heating (DH) water and steam for industrial clients. The validation shows that the model can satisfactorily describe both multi-load steady-state operation and load transients. The simulation results highlight the fact that the water-steam cycle achieves stabilization more rapidly after changes in the DH line and steam delivered to customers, as compared to changes in the combustor load. The timescales of the plant outputs for different changes have been calculated, with stabilization times ranging from 2 to 15 min for the power production versus 2-25 min characterizing the DH production. Compared to the stabilization times of the gas side, the water-steam side is an order of magnitude slower, thereby limiting the transient operation capabilities of BFB-CHP plants.