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

Abstract

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 1Hz 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.