A critical review of the complex pressure fluctuation phenomenon in gas–solids fluidized beds

Bi, Hsiaotao T.

doi:10.1016/j.ces.2006.12.092

Cited by 202 publications

(114 citation statements)

References 54 publications

(145 reference statements)

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“…An alternative is to measure the differential pressure between a position in the bed and the freeboard. Compared to the single-point method, this method can eliminate the potential effect of the pressure variations in the freeboard (Bi, 2007). However, pressure variations in the freeboard are normally small, and a disadvantage of this method is that it leads to an "off-set" in the signal (i.e., the average pressure difference between the position in the bed and the freeboard) which decreases the obtainable resolution.…”

Section: Time-resolved Pressure Measurementsmentioning

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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Section: Time-resolved Pressure Measurementsmentioning

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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“…It has been reported in literature that pressure fluctuations within the bed can be due to local and global contributions (Bi et al, 1995;Sasic et al, 2007;Bi, 2007). That fact leads to the use of different techniques focused on identifying and distin guishing those contributions from the measured signal.…”

Section: Frequency Domainmentioning

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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“…Figure 8 shows the standard deviation profiles of pressure fluctuations along the dipleg under different particle mass fluxes. The pressure fluctuations are attributed to many factors in the operation of diplegs, including particle clusters, gas bubbles, wall friction, and instability of feed and discharge, which enable the pressure fluctuations to be multi-scale and complex in nature (Bi 2007;Jing and Li 1999). When G s was small (such as G s \ 50.0 kg m -2 s -1 ), the fluidization pattern in the dipleg was featured by the coexistence of dilute falling flow and dense flow.…”

Section: Standard Deviation Of the Pressure Fluctuationsmentioning

confidence: 99%

Experimental analysis of pressure characteristics of catalyst powder flowing down a cyclone dipleg

et al. 2016

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An experiment was carried out for investigating pressure behavior of catalyst powders, with a Sauter mean diameter of 63.6 lm, flowing downward in a cyclone dipleg with 150 mm inner diameter and 9000 mm high. Time mean pressure and time series of pressure fluctuations were measured at different axial positions in the dipleg with particle mass fluxes ranging from 50.0 to 385.0 kg m -2 s -1 . The experimental results showed that the time mean pressure in the dipleg increased progressively from the top section to the bottom section. The experimental phenomena displayed that the fluidization patterns in the dipleg can be divided into two types on the whole, namely the dilute-dense coexisting falling flow and the dense conveying flow along the dipleg. In the dilutedense coexisting falling flow, the dilute phase region was composed of a length of swirling flow below the inlet of dipleg and a dilute falling flow above the dense bed level. With increasing particle mass flux, the dilute-dense coexisting falling flow was gradually transformed to be the dense conveying flow, and the exit pressure of the dipleg increased considerably. The pressure fluctuations were closely related to the fluidization patterns inside the dipleg. In the dilute-dense coexisting falling flow, the pressure fluctuations in the dilute flow region originated from particle clusters, propagating downward as a pressure wave; however, the pressure fluctuations in the dense flow region originated from rising gas bubbles, propagating upward. When the dense conveying flow was formed in the dipleg, the pressure fluctuations originated mainly from instability of the feed and the compressed gas, propagating downward. The standard deviation of the pressure fluctuations indicated that the intensity of pressure fluctuations first increased and then decreased with increasing particle flux.

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A critical review of the complex pressure fluctuation phenomenon in gas–solids fluidized beds

Cited by 202 publications

References 54 publications

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

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

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

Experimental analysis of pressure characteristics of catalyst powder flowing down a cyclone dipleg

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