Some segregation effects in packed‐fluidized beds

Sutherland, J. P.; Wong, K. Y.

doi:10.1002/cjce.5450420407

Cited by 13 publications

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“…1952). or the number of line cuts at a fixed pressure level (Sutherland, 1964), or the number of line cuts at 10% maximum pressure fluctuation (Fiocco, 1964). These latter data could have been a combination of the fluctuation intensity and the real frequency.…”

Section: A P J D D Is Plotted Against An Expansion Term (N -Hmf)/hmentioning

confidence: 99%

“…The normalized power spectral density functions were similar for the packed and unpacked fluidized beds, though peak frequencies showed some dependence on packing dimensions. PRESSURE drop fluctu,ations in aggregative fluidized beds have been studied as a basis for defining an index of fluidized bed quality (Fiocco, 1964;Shuster and Kisliak, 1952;Sutherland, 1964). In these studies.…”

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confidence: 98%

“…PRESSURE drop fluctu,ations in aggregative fluidized beds have been studied as a basis for defining an index of fluidized bed quality (Fiocco, 1964;Shuster and Kisliak, 1952;Sutherland, 1964). In these studies.…”

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Pressure Fluctuations in a Fluidized Bed with and without Screen Cylindrical Packings

Kang¹,

Sutherland²,

Osberg³

1967

Ind. Eng. Chem. Fund.

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Pressure fluctuation data were obtained from an air-fluidized sand bed (-48 + 65 Tyler mesh) with openended cylindrical packing. The tests were made in a 5-inch diameter column, and with packings made from steel wire cloth 4-, 6-, or 14-mesh per inch and '/? X '/2, "4 X 3/4, and 1 X 1 inch in size. These data were analyzed to yield r.m.s. values, the probability density, and the normalized power spectral density functions. The r.m.s. values of the pressure fluctuations were lower for the packed fluidized beds than for the same bed fluidized with no packing. For each packing, a maximum was observed on a plot of r.m.s. vs. flow rate or bed expansion. When no packing was used, r.m.s. values increased continuously with gas flow or bed expansion; the distributions were Gaussian at low flow rates, and skewed at high flow rates. The probability distributions of the differential pressure fluctuations were Gaussian for a fluidized bed containing packings over the whole flow range tested. The normalized power spectral density functions were similar for the packed and unpacked fluidized beds, though peak frequencies showed some dependence on packing dimensions. PRESSURE drop fluctu,ations in aggregative fluidized beds have been studied as a basis for defining an index of fluidized bed quality (Fiocco, 1964;Shuster and Kisliak, 1952;Sutherland, 1964). In these studies. strip chart recordings of the pressure changes \vere analyzed in various ways to give peak counts, line-cut counts, average fluctuation, etc. These data are of limited value because of the arbitrary way in which the recordings Lvere analyzed. In the present study, the pressure data were analyzed b;; a current spectral technique, which provides a more detailed examination of the data.The source of the pressure fluctuation is not yet fully understood. In gas-solid fluidized beds, the pressure drop fluctuations correspond directly to the bubble flow, though the pressure drops are really a consequence of changes in gas flow through the dense phase. Reuter (1963Reuter ( , 1966 has reported that the axial pressure gradient in the dense phase near the bubble is larger than in the undisturbed regions of the bed, \vhile the gradient inside the bubble is nil. Though Reuter's kvork provides a partial explanation for the pressure fluctuation in fluidized beds, the data are not yet sufficient for a complete interpretation of a fluctuating pressure signal.In this paper. preliminary experiments are first reported on the correlation of pressure fluctuations \vith bed height fluctuations, and then on the pressure change \vhich occurs when a single artificial bubble ]passes through a bed. Finally, data are given on the effect of screen packing on pressure fluctuations in a fluidized sand bed.Various packings, such as spheres, solid cylinders, Raschig rings, Berl saddles, and screen rings. have been used to improve fluidization. Data have been reported on the effect of packings on gas mixing (Chen and Osberg, 1967;Gabor and Mecham, 1964); solid mixing (Gabor, , 1965(Gabor, , 19...

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Section: A P J D D Is Plotted Against An Expansion Term (N -Hmf)/hmentioning

confidence: 99%

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confidence: 98%

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Pressure Fluctuations in a Fluidized Bed with and without Screen Cylindrical Packings

Kang¹,

Sutherland²,

Osberg³

1967

Ind. Eng. Chem. Fund.

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“…Particles inside batchwise operated bubbling fluidized bed reactors usually are ideally mixed. Con-ditions to be satisfied are small differences in particle size and density (Nienow et al, 1978) and the absence of mechanical barriers like densely packed heat exchanger tubes (Sutherland andWong, 1964, Sitnai, 1981). If these conditions are satisfied, a continuously operated bubbling fluidized bed reactor can be regarded as a Completely Segregated Stirred Tank Reactor (CSSTR) provided that the average residence time of the particles is long in comparison with the time needed for particle mixing (Yagi and Kunii, 1961;Cranfield, 1978).…”

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The influence of particle residence time distribution on the reactivity in fluidized bed reactors

Heesink

Klaus

Swaaij

1994

Chemical Engineering Science

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The influence of particle residence time distribution on the average conversion rate (or reactivity) of particles undergoing a non-catalytic gas-solid reaction inside a continuously operated fluidized bed reactor is evaluated. A so-called &factor is defined as the ratio of the actual reactivity in the reactor and the reactivity of a batch of particles that react under similar circumstances and that all have a conversion extent equal to the average conversion extent in the reactor. The D-factor concept is elaborated for shrinking core conversion behaviour. According to Heesink et a[. (l993), three extreme types of conversion behaviour are distinguished: core reaction limitation, product-layer diffusion limitation and grain reaction limitation. For each type of behaviour a mathematical function is derived that expresses fi as function of average particle conversion, maximum attainable conversion (with regard to pore plugging) and a new-defined expansion factor, which is a measure for the expansion (or shrinking) of the reacting solid during conversion. These functions can be easily incorporated in fluid&d bed reactor models.

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“…In fluidized beds containing particles of different physical properties, segregation which prevents the attainment of a random state of mixing is usually encountered. The forces which promote particle segregation in a fluidized bed have been discussed by Sutherland and Wong (1964), and Pruden and Epstein (1964). Though there has been moderate interest in studying the segregation behaviour of a mechanically homogenized mixture during fluidization (see, e.g., Wen and Yu, 1966;Gelperin et al, 1967;Bena e t al., 1968;Goossens et al, 1971), relatively little has been done in investigating the mixing of segregating particles in a fluidized bed.…”

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Mixing of large particles in two‐dimensional gas fluidized beds

Fan

Chang

1979

Can J Chem Eng

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The fluidization and solids mixing characteristics of very large particles were investigated in a two‐dimensional gas fluidized bed. Bubble or slug induced drift and gross solids circulation appeared to be the predominant solids mixing mechanisms in this large particle bed. The contribution from wake mixing appeared to be negligible and radial mixing was more rapid than axial mixing. Apparently, segregation in the axial direction resulted from preferential transportation of the lighter particles upwards with rising bubbles and from interparticle competition to fill the voidage created by the rising bubbles. No appreciable segregation occurred in the radial direction. A nonstationary random walk model has been developed to characterize mixing and segregation of fluidized large particles.

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Some segregation effects in packed‐fluidized beds

Cited by 13 publications

References 2 publications

Pressure Fluctuations in a Fluidized Bed with and without Screen Cylindrical Packings

Pressure Fluctuations in a Fluidized Bed with and without Screen Cylindrical Packings

The influence of particle residence time distribution on the reactivity in fluidized bed reactors

Mixing of large particles in two‐dimensional gas fluidized beds

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