Pressure fluctuation analysis of solid exchange in a dual-leg fluidized bed

The differential pressure fluctuation frequency characteristics were studied in a bench-scale dual-leg fluidized bed with dimensions of 0.24 m width, 0.02 m depth, 0.8 m height and 0.16 m height for the legs. The differential pressure monitoring system was established to measure pressure fluctuations in two half beds and processed by power spectrum density (PSD) to get the dominant frequency and its energy. In addition, the analysis of PSD was combined with digital images of solid distribution to study the bubbling actions and the behaviors of solid exchange between two half beds with fluidization velocities at 1.88, 2.71, 3.42, 4.16 and 5.06 m/s for static bed material heights 40, 60,80 and 100 mm respectively. The PSD results show two dominant frequencies with less than 1 Hz for the first dominant frequency and bigger than 3 Hz for the second dominant frequency. Analytical results by combining with the digital images indicate that the first dominant frequency represents solid exchange between two half beds in the form of clusters and the second dominant frequency stands for both bubbling actions and solid exchange behaviors in the form of single particles. Furthermore, with the increase of fluidization velocity, the second dominant frequency and its energy both decrease representing that the difference of bubbling actions is weaker gradually, while the first dominant frequency and its energy vary complexly. Higher static bed material height contributes the second dominant frequency to decrease, and the effect of static bed material height on the first dominant frequency is complex at different fluidization velocities. Energy of the dominant frequency increases firstly and then levels off with increasing static bed material height. The dominant frequency can be used to describe the bubbling actions and solid exchange behaviors between two half beds. Power spectrum density analysis is verified a useful way to study the bed material overturn in the dual-leg fluidized bed. (C) 2012 Elsevier B.V. All rights reserved.