Non-linear Analysis Of Fluctuation Signal Of Circulating Fluidized Bed

The hydrodynamics in circulating fluidized bed (CFB) are complex. In spite of increasing interest in CFB fundamental research in the past decades, the knowledge on the hydrodynamics is still not sufficient for straightforward design control and scale-up of CFB . In this work the non-linear analysis technique (chaos and fractal theory) combining with the new mathematics tool (wavelet transform) is applied to analyze the solid hold-up and pressure fluctuation signals in CFB riser for understanding the complex non-linear dynamic behavior in CFB from a new point of view.Based on the wavelet transform and fractal theory, a new noise-reduction algorithm is put forward and successful used in noise reducing of solid hold-up and pressure fluctuation signal of CFB riser. This method does not require information on the properties of noise and equation of dynamic system and is practicable and effective. The true fluctuation signal can be extracted through this method and used for chaotic analysis .The frequency characteristic of fluctuation signals is dissected through power spectral analysis. The frequency range of signals changes with the operation conditions. Gas movement fluctuation is the predominant source for pressure fluctuation in CFB riser at the low solid circulating rate, and the solid movement is the predominant source for pressure fluctuation at the high solid circulating rate. The main frequency range of pressure fluctuation signal is smaller than 5Hz.Based on the C-C method (correlation integral),the Td(time delay) and rw(time window) used for reconstructing chaotic attractors from experimental time series have been estimated simultaneously. Results show that fixing TW is better than fixing rd in calculating correlation dimension .The correlation dimension and Kolmogorov entropy are first obtained with this method. In addition, the chaotic characteristics of fluctuation signal in both axial and radial direction are also analyzed quantitatively. The change of the chaotic characteristic can be used to characterize the flow dynamic behavior in CFB riser.In order to understand the heterogeneity non-linearity and chaotic behavior of particle-fluid system in CFB, based on wavelet transform modulus maxima(WTMM) method ,we perform multifractal measure analysis on solid hold-up and pressure fluctuation signals of CFB riser and get the multifractal singularity spectrum . The method to calculate intermittent index is also proposed according to the WTMM method. With this method, we propose a new judgement to determine the transition of flow regimes from fast fluidization to dense pneumatic conveying. Results show that the transition of flow regimes in CFB riser does not change at the same time along the axial direction. The transition on the upper region is more early than on the bottom region.