Flow characteristics in a bubbling fluidized bed at elevated temperature

Abstract A bubbling fluidized bed with 0.082 m in diameter and 1.5 m in height was employed to investigate the minimum fluidization velocity and flow dynamics at bed temperature up to 1000 °C. Ashes of three sizes (Geldart B) from pressurized fluidized bed boiler were used as fluidization materials. Experiments show that the minimum fluidization velocity decreases with increasing bed temperature. Pressure fluctuation signals were analyzed by using power spectral density function (PSDF), chaos, and wavelet analysis. The major frequency of pressure fluctuation signals is in the range from 1 to 4 Hz in the fluidized state. It demonstrates that a bubbling fluidized bed at high temperature is a deterministic chaos system since all the largest Lyapunov exponents are positive. The correlation dimension and Kolmogorov entropy increase with an increase in the fluidization number, and then they vary little with increasing fluidization gas velocity. By the wavelet transform, the fluctuating pressure signals in the bed can be decomposed into its approximations and details at different resolutions. The number of peaks in the scale six detail signal represents the number of bubbles passing through pressure probe measurement region over the sampling time, which agrees with the major frequency obtained from PSDF analysis of pressure fluctuation signals.