Improving the gas-solids contact efficiency in a fluidized bed of CO2 adsorbent fine particles.

A modified CO(2) adsorbent is obtained by dry mixing of a Ca(OH)(2) fine powder as received with a commercial silica nanopowder. Silica nanoparticles form light agglomerates of size of the order of tens of microns, which are uniformly fluidizable. These agglomerates act as dispersants of the Ca(OH)(2) fine particles, which coat the nanoparticle agglomerates likely due to contact charging. Ca(OH)(2) particles (CO(2) adsorbent) are thus provided with a vehicle for uniform fluidization. In this way, the contact efficiency between the CO(2) adsorbent and CO(2) in the fluidized bed is greatly enhanced. Experimental results show that the improvement of Ca(OH)(2) fluidizability serves to enhance the carbonation reaction in the fluidized bed.

Novel instrument to characterize dry granular materials at low consolidations.

The performance of traditional instruments for measuring the flow properties of dry granular materials at small consolidation stresses is not fully satisfactory. Generally, commercial quick tests, as, for example, the angle repose method, do not yield intrinsic material properties. This difficulty is solved in currently available ring shear testers, in which the externally applied torque necessary for shearing the sample is measured as a function of the normal stress previously applied through an annular lid. In this article we show a novel device in which the shear stress is caused by the action of a centrifugal force on a vertical layer of unconsolidated material, which is rotated around its vertical axis. At a critical point the shear stress is large enough to drive material avalanches. From a theoretical analysis of these avalanches based on Coulomb's method of wedges, we derive the angle of internal friction and cohesion of the granular material. To illustrate the functioning of the instrument, measurements on steel, ferrite, and magnetite beads of different particle size are presented. The data obtained are used to analyze the gravity-driven avalanches of these materials in a slowly rotated drum.