Characterization of Multi-Scale Structures in Gas-Solids Circulating Fluidized Beds By Recurrence Quantification Analysis

Circulating fluidized bed (CFB) is one of the most complicated hydrodynamic systems. Typical particle-fluid two-phase flow patterns of CFBs exhibit nonlinear and nonequilibrium dynamic characteristics with multiscale flow structures. Power spectrum and recurrence quantification analysis can be used as an effective approach to characterize multi-scale flow behavior in CFB systems. Pressure fluctuations were measured in a circulating fluidized bed of 0.15 m in diameter and 18 m in height under a wide operating conditions with superficial gas velocity from 7 to 9 m/s and solids circulation rates from 100-800 kg/m²s. The measured signals were analyzed using power spectrum and recurrence quantification analysis. The results shows that the complex dynamics of CFB system can be presented as macro, meso and micro structures. It was found that a minimum in wide band energy with an increase in the velocity from 7 to 9 m/s corresponds to the transition between macro structures and finer structures. Based on the PS and RQA methods, three different structures can be determined with frequency range of 0−5 Hz for macro, 5−50 Hz for meso, and 50−200 Hz for micro structures. The results of RQA showed that the micro structures of the CFB systems have the least periodicity.