Bed inventory balance and stability of dual circulating fluidized bed systems

Abstract

Experiments and modelling are conducted for general understanding on the imbalance phenomenon and for discussion on the strategies to improve the bed inventory balance and stability of a dual circulating fluidized bed (DCFB) system. The experiments are carried out in a 15.5 m high pilot-scale DCFB cold test system. A fluid-dynamic DCFB model is developed based on a 1.5-dimensional semi-empirical model of an industrial CFB boiler, validated by experimental data. The effects of control methods and operation conditions on the bed inventory balance and on the stability of the pilot- and large-scale DCFB systems are discussed. A “stable-unbalanced” state, where the system reaches a steady state, consisting of unbalanced bed inventories, is observed in both experiments and model simulation. To maintain a balanced state and similar bed inventory in the DCFB systems with similar cross-sectional areas, it is recommended to keep similar total pressure drops or gas velocities in both reactors.