(267e) Full-Loop Simulation of Gas-Solids Flow in Circulating Fluidized Beds with Different Sizes

Circulating fluidized beds (CFB) are widely used in petrochemical, coal, metallurgy, and other industrial fields. To obtain detailed information and fully understand gas-solids flow behaviors in CFB, computational fluid dynamics (CFD) had been applied to simulate gas-solid flow behaviors in CFB. Circulating fluidized bed is a complex and integrated process coupling all inter-connected units including the riser, cyclones, downcomer, storage tank and valve. Therefore, the full-loop simulation is a promising way to describe complex gas-solids interaction in CFB under fully consideration of effects of the whole system by treating the whole CFB system as a simulation object. Most studies focused on gas-solid behaviors in a certain CFB device, and there were little comparison between different sizes of different CFB devices such as heights and diameters of riser. In fact, sizes of CFB are the most critical factors in design, which affect the length of region affected by entrance and exit structure, determining length of fully developed region finally. To keep stable operation and ensure the validity of experiment data, enough length of fully developed region is necessary, which closely related to the sizes of CFB. Therefore, effects of sizes of CFB need to be fully discussed.

In this work, effects of CFB sizes including riser heights and riser diameters were investigated by full-loop simulation method. A pilot-scale gas-solid circulating fluidized bed with riser in height of 18 m has already been set up in our group. The simulation condition was chosen according to experiments with different superficial gas velocity, solids inventory, valve opening and fluidizing air flow rates. A reliable model applying to multiple flow regimes was established, and the validity of the model was guaranteed by comparing simulation results and experiment data. Then simulation of different CFB sizes were conducted, and the effects of CFB sizes in different operating conditions on distribution of pressure, solids holdup, velocity and length of fully developed region in system were also investigated. The lengths of fully developed region with different CFB sizes and different operation conditions were analyzed, and optimum ranges of CFB sizes under different operation condition were provided to give a reference to the design.