Alumina Bed Research Articles

Heat transfer between a vertical tube and an air fluidized bed at moderate temperatures (335–528 K)

Heat transfer coefficient is measured between a 25.4 mm outer diameter smooth vertical tube immersed in 0.254 m internal diameter fluidized beds of sand (d p = 265, 507 and 787 μm), glass beds (239, 357 and 412 μm), silicon (368 μm) and alumina (267 μm) as a function of bed temperature (335 – 528 K) and fluidizing velocity. The solids movement and mixing in the bed is investigated by measuring the heat transfer coefficient at two radial positions in the bed for various values of fluidization velocity and bed temperature. The minimum fluidization velocity, bed voidage and maximum heat transfer coefficient are also reported for different experimental conditions. The qualitative variation of h o with different operating and system parameters is found consistent with the known mechanisms of heat transfer for an immersed surface in a fluidized bed. Quantitative correlation of h o and h omax will be reported in a future publication.

A generalized correlation for heat transfer between a gas—solid fluidized bed of small particles and an immersed staggered array of horizontal tubes

A generalized correlation for heat transfer coefficient between a horizontal staggered tube bundle and a gas—solid fluidized bed is proposed. The correlation is based on the experimental data for heat transfer coefficient between electrically heated horizontal tube bundles (12.7 and 28.6 mm diam.) and square fluidized beds (30.5 × 30.5 cm) of alumina ( d p = 259 μm) and silica sand ( d p = 167 and 504 μm). The tubes in the bundle are located at the vertices of equilateral triangles with pitch varying between 1.75 and 9 times the tube diameter. The proposed correlation is examined on the basis of existing data in the literature. The predicted values of heat transfer coefficient from the proposed correlation are, in general, in good agreement with experimental data in the literature.

Microbial and pyrogenic contamination of molybdenum 99/Technetium 99m radionuclide generators

Radionuclide generators employed for the production of short-lived radionuclides may be contaminated with microorganisms during use, although this may not result in significant microbial contamination of the eluate. The mechanism by which this reduction was achieved was examined, using technetium 99m generators deliberately contaminated with known numbers of Escherichia coli. Results indicated that a small proportion of the inoculum was eluted from loaded (‘active’) or unloaded columns suggesting that organisms were entrapped in the alumina bed. Cell death occurred and could be caused by significant exposure to radiation, and the toxicity of aluminium and molybdate ions. Loss of viability led to an increased release of pyrogenic material into the eluate.

ChemInform Abstract: A KINETIC STUDY OF THE SIMULTANEOUS DEALKYLATION AND DISPROPORTIONATION OF CUMENE OVER SILICA‐ALUMINA

AbstractDas Verhältnis von Disproportionierungs‐ zu Desalkylierungsprodukten steigt mit abnehmender Temperatur (210‐254°C) und/oder mit zunehmendem Cumolpartialdruck (0.01‐0.02 at ) an.

A Kinetic Study of the Simultaneous Dealkylation and Disproportionation of Cumene over Silica–Alumina

Abstract Cumene has been passed over a silica–alumina bed at low temperature (210 to 254 °C) and at cumene pressures of 0.003 to 0.023 atm. Both dealkylation and disproportionation occurred simultaneously and independently of each other. The disproportionation/dealkylation ratio increased with decrease in temperature and/or an increase in cumene pressure. The dealkylation and disproportionation reactions followed a Langmuir-Hinshelwood model with inhibition by the reactant. The dealkylation has been interpreted in terms of a unimolecular surface reaction, while the disproportionation reaction in terms of a bimolecular surface reaction. The heat of adsorption of cumene and the entropy loss of cumene on adsorption were much larger for the dealkylation sites than for the disproportionation sites. These results indicated that dealkylation was catalyzed by strong acid sites, while disproportionation by weak acid sites. The dealkylation had a much higher activation energy than the disproportionation reaction. The activation energy for dealkylation (33.5 kcal mol−1) was in good agreement with that predicted on the assumption that the previously reported LFER (linear free-energy relationship) in the alcohol dehydration holds for alkylbenzene dealkylation.

Analysis of the horizontal effective thermal conductivity of a fluidized alumina bed under steady-state conditions

A critical relation is derived for calculating the thermal conductivity of a fluidized alumina bed. Based on the solution to the equation, formulas are then derived for evaluting the nonuniformity factor of the temperature field in a fluidization chamber which is heated around its walls.

Fluidized-Bed Fluorination of UO2-PuO2-Fission Product Pellets with Brf5and Fluorine. Part I: The Fluorination of Uranium, Neptunium, and Plutonium

Fluorination of simulated thermal reactor fuel containing UO2, PuO2, and oxides of elements formed in fission has been studied in a 2-in.-diam reactor containing a fluidized bed of alumina. After o...

Production of Plutonium Hexafluoride by Fluorination in a Fluidized Bed

A total of 2.3 kg of PuF4 was fluorinated to PuF6 with elemental fluorine in a fluidized bed of alumina in three campaigns, each consisting of three separate fluorination runs followed by a fluorin...

Adsorption of Benzene from Nitrogen by Fixed Beds of Alumina.

Adsorption of Benzene from Nitrogen by Fixed Beds of Alumina.

Kinetics of carbon deposition in a fluidized bed

AbstractRate data have been obtained for the deposition of carbon films from methane and acetylene in fluidized beds of alumina, uranium dioxide, uranium monocarbide, uranium dicarbide, and a solid solution of uranium‐thorium dicarbide powders. These carbon films have been shown to provide excellent protection for the powdered fertile material against attack by hot concentrated nitric‐acid solutions. The coated uranium‐thorium dicarbide particles were also shown to be stable in humid air.