Non-intrusive determination of bubble and slug length scales in fluidized beds by decomposition of the power spectral density of pressure time series

Schaaf, van der J John; Schouten, JC Jaap; Johnsson, Filip; Bleek, van den Cm

doi:10.1016/s0301-9322(01)00090-8

Cited by 196 publications

(192 citation statements)

References 5 publications

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“…By comparing the time series measured simultaneously in the wind box and in the fluidized bed, a characteristic length scale for the bubble diameter could be derived. This technique, proposed by Van der Schaaf et al (2002), was tested in a 2-D column using video image analysis. It was found that the bubble diameter is proportional to the incoherent standard deviation at the range of fluidization velocities and measuring heights studied, but that the proportionality factor depends on the type of material being fluidized.…”

Section: Discussionmentioning

confidence: 99%

“…A technique proposed by Van der Schaaf et al (2002) was used to decompose the pressure fluctuation time series in its different components. They used the coherence between two time series measured at different heights in the fluidized bed to distinguish between the different components of the pressure signals.…”

Section: Measuring Pressure Fluctuations To Determine Bubble Sizementioning

confidence: 99%

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Bubble Size Reduction in a Fluidized Bed by Electric Fields

Willigen¹,

Turnhout²,

Ommen³

et al. 2003

International Journal of Chemical Reactor Engineering

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The reduction of the size of bubbles can improve both selectivity and conversion in gas-solid fluidized beds. Results are reported of the reduction of bubble size by the application of electric fields to uncharged, polarizable particles in fluidized beds. It is shown how average bubble diameters can be drastically reduced, with little change of the bed expansion. A literature review shows that to maintain smooth fluidization, electric fields in the direction of the gas flow, with a relatively low alternating frequency, are optimal. To measure average bubble diameters, a spectral decomposition technique of pressure fluctuation time series is used. Using this method, based on non-intrusive measurements, a characteristic length scale for bubble diameters can be found. It is shown experimentally, using video analysis, that this length scale is of constant proportionality for a given bed material and bed dimensions. The proportionality of the length scale to bubble diameter is independent of measuring height or gas velocity. With this, we have a tool for measuring bubble diameters in both 2-D and 3-D fluidized beds. Electric fields were applied to fluidized beds using thin wire electrodes placed inside the column. Both 2-D and 3-D columns were tested over a range of frequencies and field strengths. For Geldart A glass beads, an optimal range was determined at 5-20 Hz and 400-1600 V/cm fields. The reduction of bubble diameter was measured to be up to 25% for this system. Larger Geldart B glass particles show a larger reduction of bubble diameters -up to 85%. For these particles, the optimal frequency was at a higher range, 20-70 Hz. At higher frequencies (up to 100 Hz), bubble size reduction is less, but still substantial. Experiments in the 3-D column using Geldart A particles show a similar reduction in bubble diameters.

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Section: Discussionmentioning

confidence: 99%

Section: Measuring Pressure Fluctuations To Determine Bubble Sizementioning

confidence: 99%

Bubble Size Reduction in a Fluidized Bed by Electric Fields

Willigen¹,

Turnhout²,

Ommen³

et al. 2003

International Journal of Chemical Reactor Engineering

View full text Add to dashboard Cite

show abstract

“…It has been reported (van der Schaaf et al, 2002) that some dynamic phenomena such as bubble coalescence, gas flow fluctuation, bubble eruption and bed mass oscillation generate fast pressure waves that propagate in such a way that they can be measured almost instantaneously through the entire bed. Conse quently, pressure measurements taken at different bed positions will show coherence due to those fast travelling waves.…”

Section: Cop/iop Analysismentioning

confidence: 99%

“…The success of the pressure monitoring is explained by its low cost and the direct relation that exists between the property measured and the bed dynamics. Moreover, from pressure measurements sampled at relatively low frequency it is possible to extract useful informa tion about the bulk, bubble and wave dynamics (van der Schaaf et al, 2002). Therefore, both the quality and the quantity of the low frequency information contained in the pressure signal make this technique the most used to monitor the bed dynamics.…”

Section: Introductionmentioning

confidence: 99%

Can low frequency accelerometry replace pressure measurements for monitoring gas-solid fluidized beds?

Martín

Briongos

Aragón

et al. 2010

Chemical Engineering Science

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a b s t r a c tThis paper is addressed to introduce a methodology based on low frequency accelerometry that can be used for gas solid fluidized bed monitoring, and for dynamic diagnosis purposes. The proposed methodology consists on extracting the low frequency information encoded within an accelerometry signal, by means of the Hilbert transform method. The time and the frequency domain analysis show how this low frequency information is directly related to the conventional pressure fluctuation measurements, providing useful information on bulk and bubble dynamics. The cross correlation and the coherence function analysis between the pressure and the envelope process of the measured accelerometer signals ''E'', exhibit values approaching unity for frequencies ranging between 2 and 4 Hz. This reveals that pressure signals and accelerometry envelope are related processes. The results from the Coherent Output Power, COP, and the Incoherent Output Power, IOP, analysis confirms that both pressure and envelope time series exhibit the same global and local features open the possibility of using low frequency accelerometers instead of conventional pressure transducers for monitoring and for dynamic diagnosis purposes.

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“…Whereas deriving the bubble size distribution from pressure signals remains awkward, van der Schaaf et al (2002) proposed a power spectral decomposition method to obtain the time-averaged bubble diameter at a given height using two absolute pressure fluctuation measurements. One probe is placed in the windbox, the other probe in the bed at the position were the average bubble diameter should be determined.…”

Section: Deriving Bubble Sizesmentioning

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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Non-intrusive determination of bubble and slug length scales in fluidized beds by decomposition of the power spectral density of pressure time series

Cited by 196 publications

References 5 publications

Bubble Size Reduction in a Fluidized Bed by Electric Fields

Bubble Size Reduction in a Fluidized Bed by Electric Fields

Can low frequency accelerometry replace pressure measurements for monitoring gas-solid fluidized beds?

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

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