Analysis of Pressure Fluctuations in Fluidized Beds

Abstract

Pressure fluctuations were measured in a fluidized bed and evaluated in the frequency domain. The objective of this research was to determine the effect of bed parameters on the power spectra from the corresponding pressure fluctuations. The motivation for this work is to develop pressure fluctuations as a diagnostic tool for fluidized-bed reactors and combustors. Pressure fluctuation data for a range of bed heights, fluidization velocities, particle sizes, particle densities, and bed temperatures were taken to determine the effect of these parameters on the power spectrum. The dominant frequency was a function of the height of the fluidized bed. Secondary peaks were not influenced by the height of the bed, although they did depend on the position of the probe in the bed. Peaks in power spectra were observed to shift in frequency as the gas superficial velocity through the bed was changed. Powders of different classification had distinctive power spectra. Group A powders behaved like first-order linear systems; group B powders showed similarities to second-order linear systems; and group D powders exhibited harmonic behavior in their power spectra. When pressure fluctuations were measured over a temperature range from ambient to above 500 °C, power spectra varied little when the ratio of the superficial velocity to the minimum fluidization velocity was held relatively constant. Pressure fluctuations were measured in a fluidized bed and evaluated in the frequency domain. The objective of this research was to determine the effect of bed parameters on the power spectra from the corresponding pressure fluctuations. The motivation for this work is to develop pressure fluctuations as a diagnostic tool for fluidized-bed reactors and combustors. Pressure fluctuation data for a range of bed heights, fluidization velocities, particle sizes, particle densities, and bed temperatures were taken to determine the effect of these parameters on the power spectrum. The dominant frequency was a function of the height of the fluidized bed. Secondary peaks were not influenced by the height of the bed, although they did depend on the position of the probe in the bed. Peaks in power spectra were observed to shift in frequency as the gas superficial velocity through the bed was changed. Powders of different classification had distinctive power spectra. Group A powders behaved like first-order linear systems; group B powders showed similarities to second-order linear systems; and group D powders exhibited harmonic behavior in their power spectra. When pressure fluctuations were measured over a temperature range from ambient to above 500°C, power spectra varied little when the ratio of the superficial velocity to the minimum fluidization velocity was held relatively constant.

Experimental study of the nature of gas streaming in deep fluidized beds of Geldart A particles

“…As the figure shows, scale 5 detail presents a dominant frequency of 2 Hz. Since the presence of several bubbling activities with different dominant frequencies has been reported in the previous literature [23], scale 5 detail may be indeed presenting another bubbling activity. After decomposition of scale 4, the dominant frequency of the detail parts shifts towards lower frequencies with lower power in the PSD graph.…”

“…3b and 5b. There is a general agreement on the fact of increasing the dominant frequency with increasing superficial velocity in the literature [21][22][23]. Fan et al [22] measured the bubble rise velocities in several fluidization regimes, including bubbling, slugging, and turbulent fluidization.…”

Characterization of pressure fluctuations from a gas–solid fluidized bed by structure density function analysis

“…There have been previous studies on the effects of temperature on the domain frequency of power spectra, minimum fluidization velocity, amplitude of pressure fluctuations and dense phase properties (e.g. Svoboda et al, 1983;Lettieri et al, 2001;Formisani et al, 2002;Guo et al, 2002Guo et al, , 2003Falkowski and Brown, 2004), but work concerning influences of bed temperature on multi-scale flow behavior are few in number.…”

Hydrodynamics of Gas Solids in a Bubbling Fluidized Bed with Binary Particles

“…The gas bubble characteristics can be investigated with direct methods by measuring the local voidage in fluidized bed such as optical and capacitance, and indirect method by measuring pressure fluctuations. Measuring pressure fluctuations has received more attention due to its advantages such as relatively simple, non-intrusive, and inexpensive, and time-and frequency-domain analysis techniques have been widely used to analyze the pressure time signals [2][3][4]. Bi [5] and Sasic et al [3] reviewed the investigation of the fluid-dynamic behavior of gas-solid fluidized beds using pressure signals and the sources of pressure fluctuations, propagation features and the nature of pressure waves in fluidized beds.…”

“…Bi [5] and Sasic et al [3] reviewed the investigation of the fluid-dynamic behavior of gas-solid fluidized beds using pressure signals and the sources of pressure fluctuations, propagation features and the nature of pressure waves in fluidized beds. Falkowski and Brown [2] investigated the effect of bed parameters on the power spectra from the corresponding pressure fluctuations for developing pressure fluctuations as a diagnostic tool for fluidized-bed reactors and combustors.…”