Holdup correlations in slurry-solid fluidized beds

The use of slurry-solids fluid beds plays an important role in the development of synthetic fuels and the hydrogen processing of petroleum resids. In the H-Coal process in particular, coal oil slurries are processed over extrudates of hydrodesulfurization catalyst. The objective of this note is to present a model which describes the volume fraction occupied by the slurry phase. The accurate prediction of the liquid holdup is important not only for the calculation of the bed height in liquid solid fluidized beds, but also is required for the development of a model predicting the holdup in three-phase fluidized beds. In the present publication, the application of two different correlations is considered: (1) the Richardson and Zaki; and (2) Ramamurthy and Sabbaraju

Deposition of H_2-permselective SiO_2 films

Films of amorphous SiO_2 were deposited within the walls of porous Vycor tubes by SiH_4 oxidation in an opposing-reactants geometry: SiH_4 was passed inside the tube while O_2 was passed outside the tube. The two reactants diffused opposite to each other and reacted within a narrow front inside the tube wall to form a thin SiO_2 film. Once the pores were plugged the reactants could not reach each other and the reaction stopped. At 450°C and 0.1 and 0.33 atm of SiH_4 and O_2, the reaction was complete within 15 min. The thickness of the SiO_2 film was estimated to be about 0.1 μ. Measurements of H_2 and N_2 permeation rates showed that the SiO_2 film was highly selective to H_2 permeation. The H_2: N_2 flux at 450°C varied between 2000 and 3000. Thermal annealing at 600°C reduced somewhat that selectivity. Thermal annealing in the presence of H_2O vapor decreased further the flux of H_2 and increased the flux of H_2. Permeation of H_2 is believed to occur through an activated diffusion mechanism. Applications of such H_2-permeable films to membrane reactors for equilibrium-limited reactions are discussed