Frequency-based characterization of liquid–solid fluidized bed hydrodynamics using the analysis of vibration signature and pressure fluctuations

Abstract

This work is mainly focused on the frequency-based analyses of non-invasive vibration and pressure fluctuations signals to characterize main hydrodynamic events inside a liquid–solid fluidized bed. The power spectra of bed shell vibration and local pressure fluctuations in a frequency domain were calculated over a wide range of liquid velocities to cover the pathway of bed behavior in between three main hydrodynamic events, namely: minimum fluidization, cluster-circulating-to-individual particle motion (termed as the solid regime transition), and solid entrainment points. First rise in the mean power spectral density function (PSDF m ) of vibration fluctuations predicted the minimum fluidization accurately while a sharp level off in pressure signals showed the minimum fluidization velocity. Global maxima in the PSDF m of vibrations as well as second minima in the PSDF m of pressure fluctuations corresponded to the solid regime transition points. Finally, a plateau in the PSDF m of vibration signatures indicated a complete solid entrainment. Moreover, energy-based wavelet transform coupled with Hurst exponent analysis provided a detailed pathway of bed structure evolution, which led to the successful and accurate predictions of minimum fluidization as well as the solid regime transition inside the bed. The frequency-based analysis of non-invasive vibration and pressure fluctuations signals allows the main hydrodynamic parameters inside a liquid–solid fluidized bed (i.e., minimum U mf , solid regime transition velocity U c , and solid entrainment velocity U t ) to be determined. ► Hydrodynamic parameters of a liquid-solid two-phase fluidized bed are determined using non-intrusive vibration and pressure fluctuations. ► Wavelet transform furnishes minimum fluidization and regime transition points. ► The results can be used in the operation of multiphase reactors at severe conditions.