Pressure fluctuations in a fluidized bed

Fan, Liang‐Shih; Ho, Tho-Ching; Hiraoka, S.; Walawender, Walter P.

doi:10.1002/aic.690270308

Cited by 196 publications

(79 citation statements)

References 8 publications

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“…This shows that, even in the multiple bubble regime, one frequency component always stands out from the others. Keeping in mind that pressure fluctuations are caused by the occurrence of air bubbles in the solids bed (Fan et al, 1981), the power spectra suggest that of the bubbles of different sizes, especially in the bubble fluidized bed, one in particular is found in larger numbers, thus standing out in relation to the others.…”

Section: Resultsmentioning

confidence: 99%

“…Measurements are easy to make, requiring a single pressure transducer connected by a small tube to a measurement point in the bed usually a hole in the wall of the column (Brown and Brue, 2001). Fluidization regimes described above, which are closely related to bubble size, bubble rising velocity and the motion of the bed surface with time, strongly influence in fluctuation pressures (Fan et al, 1981). Therefore, the pressure fluctuations in a fluidized bed provide potential information about what is happening inside the fluidization column, because of its approximate relationship with the fluidization state (Kage et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

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Time series analysis of pressure fluctuation in gas-solid fluidized beds

Felipe

Rocha

2004

Braz. J. Chem. Eng.

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-The purpose of the present work was to study the differentiation of states of typical fluidization (single bubble, multiple bubble and slugging) in a gas-solid fluidized bed, using spectral analysis of pressure fluctuation time series. The effects of the method of measuring (differential and absolute) pressure fluctuations and the axial position of the probes in the fluidization column on the identification of each of the regimes studied were evaluated. Fast Fourier Transform (FFT) was the mathematic tool used to analysing the data of pressure fluctuations, which expresses the behavior of a time series in the frequency domain. Results indicated that the plenum chamber was a place for reliable measurement and that care should be taken in measurement in the dense phase. The method allowed fluid dynamic regimes to be differentiated by their dominant frequency characteristics.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Time series analysis of pressure fluctuation in gas-solid fluidized beds

Felipe

Rocha

2004

Braz. J. Chem. Eng.

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“…In fact, there has been much debate about the origin of pressure fluctuations measured in fluidized beds (e.g., Fan et al, 1981, Musmarra et al, 1995, Bi et al, 1995, M"chirgui et al, 1997, van der Schaaf et al, 1997 with most of the attention aimed at bubbling beds. It appears that the measured pressure signal is a combination of (1) local bubble passages and (2) non-local compression waves; the latter resulting from a number of hydrodynamic phenomena.…”

Section: Origin Of Pressure Fluctuationsmentioning

confidence: 99%

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

Ommen¹,

Mudde²

2008

International Journal of Chemical Reactor Engineering

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In gas-solid fluidized beds, the distribution of the particles typically varies both in time and space. Since the gas-solids distribution and its variation have a strong influence on the performance of a fluidized bed for a given process, it is very important to accurately measure the gas-solids or voidage distribution. This paper reviews techniques for measuring the voidage distribution in gas-solid fluidized beds, with a focus on the developments during the last ten years. We will treat subsequently direct visualisation, tomography, optical probes, capacitance probes, and pressure measurements.Dense gas-solids flows are typically opaque to visible light. This makes optical techniques only of limited use in dense gas-solids flow. However, direct visualization can be useful for very dilute systems, pseudo 2-D beds, and the outer layer of dense, 3-D systems. Tomography is frequently used to obtain the voidage distribution in a horizontal cross-section of the bed. Electric capacitance tomography is fast, but its spatial resolution is limited and image reconstruction is still troublesome. Although some steps forward have been made, research is continuing at this point. For nuclear (X-ray and gamma-ray) tomography, the image reconstruction is much easier and the spatial resolution better, but its temporal resolution is typically much lower. Therefore, research efforts for nuclear tomography are mainly aimed at increasing the measurement frequency. Optical probes determine the voidage as a function of time in a small measurement volume, either by the degree of reflection or by the degree of transmission of a light bundle. Capacitance probes determine the voidage as a function of time in a small measurement volume by measuring the dielectric permittivity of the gas-solids suspension in the measurement volume. Both optical and capacitance probe techniques are reasonably well-developed; the current research effort spent at improving them seems * We would like to thank M.O. Coppens, J. Nijenhuis, R.W.S Bohlken, and M.A. Wormsbecker for useful suggestions during preparation of this manuscript. limited, especially for capacitance probes. Time-averaged pressure measurements are commonly used to determine the average bed density and bed height. By sampling the local pressure at a sufficiently high frequency (typically in the order of 200 Hz), much more information can be obtained about the fluidized bed hydrodynamics. However, obtaining quantitative voidage data from pressure fluctuations measurement remains a difficult task; in-bed pressure fluctuation (and acoustic) measurements are mostly used to determine changes in the voidage dynamics and distribution.

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“…They used the time lag from the cross-correlation function and the distance between probes to calculate the propagation velocity of the pressure wave. Fan et al 16 used these two functions in a similar manner. Clark et al 17 also discussed the autocorrelation function, power spectral density, and fast Fourier transform techniques and provided examples of each with a slugging fluidized bed.…”

Section: Pressure Fluctuation Analysis Techniquesmentioning

confidence: 99%

“…Other researchers have experimentally confirmed this relationship for bed depths extending to over 1000 particle diameters. 16,18,19 Sun et al 20,21 developed a relationship in which the frequency was inversely proportional to the bed diameter, but subsequent work by Bi and Grace 22 showed that the appropriate independent variable was the bed height.…”

Section: Pressure Fluctuation Characteristics In the Frequency Domainmentioning

confidence: 99%

Analysis of Pressure Fluctuations in Fluidized Beds

Falkowski

Brown

2004

Ind. Eng. Chem. Res.

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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.

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Pressure fluctuations in a fluidized bed

Cited by 196 publications

References 8 publications

Time series analysis of pressure fluctuation in gas-solid fluidized beds

Time series analysis of pressure fluctuation in gas-solid fluidized beds

Measuring the Gas-Solids Distribution in Fluidized Beds -- A Review

Analysis of Pressure Fluctuations in Fluidized Beds

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