Behavior of the Dense-Phase Transportation Regime in a Circulating Fluidized Bed

The dense-phase transportation regime is noted as a flow regime in a gas−solid circulating fluidized bed with large solids throughputs, high bed density, and low gas and solids back mixing. The quasi-three-dimensional images obtained by the ECT with the NN-MOIRT reconstruction technique reveal a significantly different solids concentration distribution in the dense-phase transportation regime from that in the dense-phase fluidization regimes, i.e., the bubbling, the turbulent, and the slugging regimes. The transient and time-averaged flow behavior in the dense-phase transportation regime is compared to that in the dense-phase fluidization regimes based on the statistical properties including the standard deviation, power spectra, and intermittency index of the local and cross-sectional averaged solids concentration fluctuations. Examining the statistical properties indicates a less segregated solids concentration distribution over the bed cross section in the dense-phase transportation regime than in the fast fluidization regime. In the dense-phase transportation regime, at a given gas velocity below U tr, choking takes place upward along the CFB riser at a decreasing solids concentration as the solids circulation rate increases.