Particles,particle aggregates and the wall of a reactor complicate the dynamic microstructure in circulating fluidized beds(CFB).Based on the local solids concentration data from a riser of 10m high and 76.2mm i.d.with FCC particles (d(η)7 μ m,p(η) 1500kg/m3),this paper presents an improved denoising process before nonlinear chaos analysis.The analysis shows that for the local solids concentration time series,high frequency fluctuation may be one of the properties of the system,and meanwhile,interference of noise can also have some low frequency ingredient.An exact denoising method is needed in such cases.Correlation dimension and Kolmogorov entropy were calculated with denoised data and the results show that the behavior of particles in the circulating fluidized bed is very complicated.Generally,two correlation dimensions coexist in low flux CFB.The first correlation dimension is low,corresponding to small scale fluctuations that reveals a high frequency pseudo-period movement,but the second correlation dimension is high,corresponding to large scale fluctuations that indicate multi-frequency movements including particles aggregate and breakage.At same axial level the first correlation dimensions change a little with radial position,and the main tendency is high in the center and a bit lower near the wall.However,the second correlation dimensions have a big change along the radial direction,again high in the core region,and after r/R≥0.6 the dimension dropped down clearly.This indicates that the behavior of particles is more complicated and has higher degrees of freedom in the center,but near the wall clusters were restrained to some degree because of wall effect.