Fluidization characteristics of fine particles in the AUC(ammonium uranyl carbonate)process

Abstract

The basic date used in analyzing the fluidization characteristics such as mean particle size, size distribution, repose angle, internal friction angle, sphericity, true density, enveloped particle density, bulk density, tap density and fluidized bed density of $UO_2$ powders have been determined. The particle characteristics (the pore structure and the apparent particle density) within $UO_2$ particles were examined quantitatively by using mercury porosimetry and observed by SEM according to the following equation: $D_c/L_{min}= \sqrt{2}\alpha/\sqrt{\alpha^2+1}$ In order to measure interparticle forces, break-off and glass plate tests were performed and the obtained values are $3.64\times 10^{-8}$, $1.75\times 10^{-9}$ and $5.99\times 10^{-9}$ N for AUC, $UO_3$ and $UO_2$, respectively. In the bubble-free expansion region, the bed structure has been investigated in a two-dimensional bed (200 mm-width ×10mm-depth×500 mm-height) through a stereo-microscope(Nicon, SMZ2T). In the freely bubbling state, the fluidization characteristics such as bed expansion, dense and bubble phases and the characteristic velocities have been measured in a 0.07m I.D ×2.5 m high Plexiglas column. The microcavity size distribution of $UO_2$ powder follows the logarithmic-normal distribution and cavity fraction can be represented by the following equation: $a_{ca}=4.825\times 10^{-10}U_0/U_{mf}+0.325$, $(1 \le U_0/U_{mf} ≤ 4)$ The variation of bed height of fine powders can be well explained by the microcavity structure. It is confirmed that the bed expansion in the non-bubbling region is well represented by the Richardson and Zaki``s equation. The fluidization characteristic velocities [minimum fluidizing velocity ($U_{mf}$), minimum bubbling velocity ($U_{mb}$) and free bubbling velocity ($U_{fb}$)] of AUC, $UO_3$ and $UO_2$ powders have been determined. The voidage and velocity in the dense phase have been determined by the proposed ``optimum dual drainage`` (ODD) bed collapsing me...