X-ray computer tomography — potential and limitation for the measurement of local solids distribution in circulating fluidized beds

Grassler, T; Wirth, Karl‐Ernst

doi:10.1016/s1385-8947(99)00133-3

Cited by 60 publications

(33 citation statements)

References 13 publications

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“…Results showed various solid concentration distributions from a homogeneous distribution with a parabolic profile to concentrated strands in the center of the bed. Finally, the study also showed that the solids concentration was accurately calculated within 5% error for concentrations up to 20 vol% with a minimum resolution of 0.2 mm (Grassler and Wirth, 2000). Franka and Heindel (2009) studied the effects of side air injection, superficial gas velocity, and bed material on the local time-average gas holdup of a 10.2 cm fluidized bed, using X-ray computed tomography.…”

Section: X-ray Computed Tomographymentioning

confidence: 95%

“…X-rays are produced by accelerated electrons emitted from a heated cathode; the electrons hit an anode producing a deceleration of the electrons and an emission of electromagnetic radiation. The interaction between X-rays and the materials through which they pass cause a decrease in the X-rays intensity (Grassler and Wirth, 2000).…”

Section: Noninvasive X-ray Techniquesmentioning

confidence: 99%

“…Grassler and Wirth (2000) used XCT to determine the solids concentration in a 0.19 m of diameter circulating fluidized bed with 50-70 µm glass beads as the bed material. Tests were carried in two different systems.…”

Section: X-ray Computed Tomographymentioning

confidence: 99%

See 2 more Smart Citations

Bed height and material density effects on fluidized bed hydrodynamics

Escudero

Heindel

2011

Chemical Engineering Science

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Section: X-ray Computed Tomographymentioning

confidence: 95%

Section: Noninvasive X-ray Techniquesmentioning

confidence: 99%

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Bed height and material density effects on fluidized bed hydrodynamics

Escudero

Heindel

2011

Chemical Engineering Science

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“…Concern ing 3 D beds, tomography tracking techniques such as positron emission (Stein et al, 2000), X ray (Grassler and Wirth, 2000) and electrical capacitance (Du et al, 2002) methods are common. Nevertheless non tracking techniques have also been employed to collect data of the motion at a particular position in the bed (Ibsen et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Buoyancy effects on objects moving in a bubbling fluidized bed

Soria-Verdugo

García-Gutiérrez

García-Hernando

et al. 2011

Chemical Engineering Science

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a b s t r a c tThe effect of buoyant forces on the motion of a large object immersed in a bubbling fluidized bed (BFB) was experimentally studied using digital image analysis. The experiments were performed in a 2 D bubbling fluidized bed with glass spheres as bed material and cylindrical objects with different densities and sizes. The object motion was measured using non intrusive tracking techniques. The effect of gas velocity was also analyzed.The circulation of an object in a BFB is defined by several parameters. The object might be able to circulate homogeneously throughout the bed or stay in preferred regions, such as the splash zone or the bottom zone. While circulating, the object moves back and forth between the surface of the bed and the inner regions, performing a series of cycles. Each cycle is composed by sinking and rising paths, which can be one or several, depending on whether a passing bubble is able to lift the object to the surface or the object is detached from it or its drift at an intermediate depth. Therefore, the number of rising paths or number of jumps that the object undergo in a cycle, interleaved with sinking paths, and the maximum attained depth characterize each cycle, together with the mean sinking and rising velocities of the object. In this work, experimental measurements of the probability distributions of the number of jumps and the maximum attained depth, the axial homogeneity of object motion and rising and sinking object velocities are presented for objects with different sizes and densities. The results show a coherent behavior, independent of density and size, for the probability distributions of the number of jumps. This is also true for the maximum attained depth, but only when a proper circulation throughout the bed is ensured. Such a proper circulation and axial homogeneity is, on the other hand, much affected by object density, size and gas velocity. Rising and sinking velocities are highly dependent on gas velocity, as established in well known models of bubble and dense phase velocities. Nevertheless, rising velocities are practically unaffected by object density or size, while sinking velocities show a low dependence on density and a steeper one on size. These results suggest that buoyant forces are relevant during the sinking process, and almost neutral during the rising path.

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“…In some of these studies [1][2][3][4][5][6] the object had a similar density and size to the bed material. These works were intended to characterize the motion of the dense phase.…”

Section: Introductionmentioning

confidence: 99%

Motion of a large object in a bubbling fluidized bed with a rotating distributor

Soria-Verdugo

García-Hernando

Almendros-Ibáñez

et al. 2011

Chemical Engineering and Processing: Process Intensification

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a b s t r a c tThis work studies the effect of a low-frequency rotating distributor on the motion of a large object immersed in a bubbling fluidized bed. The object size and density differ from those of the inert solids that conform the bed. Examples of objects moving in a bubbling fluidized bed include passive particles, catalysts and reactants. The rotation modifies the bed dynamics in the surroundings of the distributor and affects the motion of the object within the bed.A set of experiments was carried out in a lab-scale cylindrical bed, equipped with a perforated plate distributor that can rotate at around 1 Hz, for different bed aspect ratios, gas velocities, and object characteristics. Sizes were far larger than that of the solids of the dense phase and densities ranged from half the bed density to values around it. The experiments were video recorded, capturing the surface of the bed from above.As have often been noted, objects might remain in stagnant regions near the distributor and be "lost" or precluded to circulate. This can be avoided in most practical cases forcing the distributor to rotate. Also, the effect of rotation on the circulation time of the objects is presented, showing a general reduction of large circulation times.

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X-ray computer tomography — potential and limitation for the measurement of local solids distribution in circulating fluidized beds

Cited by 60 publications

References 13 publications

Bed height and material density effects on fluidized bed hydrodynamics

Bed height and material density effects on fluidized bed hydrodynamics

Buoyancy effects on objects moving in a bubbling fluidized bed

Motion of a large object in a bubbling fluidized bed with a rotating distributor

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