Fluidization of solids with water in supercritical conditions - Characteristics of pressure fluctuations

Three flow pattern evolution processes of fixed-homogeneous, fixed-homogeneous-bubbling and fixed-bubbling have been observed in a water-solid fluidized bed in supercritical conditions. In this paper, pressure fluctuation signals of each fluidization regimes were analyzed by time domain, frequency domain, and time-frequency methods. The characteristics of standard deviation of absolute pressure (AP), power density spectrum (PDS) of differential pressure (DP), multi-resolution decomposed signals and decomposed signals of three scales (macro-scale, meso-scale and micro-scale) were obtained in different flow regimes. The plot of AP standard deviation vs. superficial velocity showed a peak on the transition from fixed bed to homogenous expansion. The dominant frequency of homogenous regime (at ambient, high pressure and sub-critical conditions) was close to zero. In the bubbling regime (some supercritical conditions), a band of frequency between 0 and 1 Hz was observed, which was smaller than the classical gas-solid bubbling fluidized bed. The energy proportion of macro-scale signal component was the highest among the three scales components of signals, which indicated that the macro-scale flow dynamic was dominant.