Bed inventory balance and stability of dual circulating fluidized bed systems

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 un-balanced 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 recom-mended to keep similar total pressure drops or gas velocities in both reactors.

Fluidization of micro-interconnected fluidized beds for chemical looping

The micro-interconnected fluidized bed(MIFB)was designed to improve the evaluation condition of oxygen carrier,which is difficult to perform in a lab-scale interconnected fluidized bed because of the large demand for bed inventory.The reduction of bed inventory in the MIFB was mainly achieved by the appropriate miniaturization of the reactor size,in which the wall effect and operating flexibility should be taken into consideration.With hematite serving as the oxygen carrier,stable and flexible fluidization could be realized with 342.9 g of bed inventory.Internal perforated plates were arranged in the middle of the reactor to improve gas-solid distribution,which also could restrain the slugging formation and increase the particle residence time by 28.9%.A different fluidization phenomenon was observed in this two-stage reactor in which the particle fluidization was reconstructed in the upper chamber.Throughout 48 h of cold operation,the hematite oxygen carrier attrition rate was evaluated as 0.151 wt.%/h corresponding to 660 h lifetime,where 12.5%of particle attrition was contributed by internal perforated plates.An excellent fitting performance was found between the pressure difference in the risers and the upward particle flow,but the correction factor should be adjusted according to the fluidization flow.

Simulation of mass balance behavior in a large-scale circulating fluidized bed reactor

We determine using a compound model the influence of the mass of granular matter on the behavior of a supercritical circulating fluidized bed （CFB） reactor. Population balance enables a stationary-regime modeling of the mass flow of granular matter inside a CFB unit in a large-scale. The simulation includes some important dynamic processes of gas-particle flows in fluidized bed such as attrition, fragmenta- tion, elutriation, and fuel combustion. Numerical calculations with full boiler loading were performed of operational parameters such as furnace temperature, furnace pressure, feeding materials mass flows, and excess air ratio. Furthermore, three bed inventory masses were adopted as experimental variables in the simulation model of mass balance. This approach enables a sensitivity study of mass flows of granular matter inside a CFB facility. Some computational results from this population balance model obtained for a supercritical CFB reactor are presented that show consistency with the operational data for large-scale CFB units.