Study on flow microstructure and scale‐up effect in circulating fluidized bed riser using solids concentration signals

Abstract

The dynamic microstructure in circulating fluidized beds (CFBs) is complex due to particle aggregation and particle-wall interactions. Based on the local solids concentration time series from a twin-riser CFB system of 10 m high and 76.2 mm (3 in.) and 203 mm (8 in.) id with FCC particles (d p = 67 μm, ρ p = 1,500 kg/m 3 ), the dynamic microstructure and scale-up effect were studied using nonlinear chaos analysis after an improved denoising signal process. The analysis shows that for the local solids concentration time series in the whole riser, the solids concentrations in the larger (8 in.) riser are higher and have higher fluctuation frequency than those in the 3-in. riser. The pressure drops at the various axial levels of the 8-in. riser are higher than the 3-in. riser.Correlation dimension and Kolmogorov entropy in the 8-in. riser are also higher than those in the 3-in. riser under the identical condition. The microstructure of the gas-particle flow in the 8-in. riser appears to be more complex than that in the 3-in. riser at identical axial levels and under the same solids flux and superficial gas velocity. In the larger riser, the energy distribution in wavelet domain is also stronger than that in the 3-in. riser. Clearly, the scaleup effect is very notable in CFB reactors, not only on the macroscale level but also on the microscale level. Such effect should be considered during designing and operating commercial size CFB reactors. KEYWORDS chaotic analysis, circulating fluidized beds, dynamic microstructure, scale-up effect, wavelet transform