Arnaud Delebarre

Removal of mercury in aqueous solution by fluidized bed plant fly ash

Abstract Coal combustion in power plant produces fly ash. Fly ash may be used in water treatment to remove mercury (Hg2+) from water or to immobilize mercury mobile forms in silts and soils. Experiments were carried out on two kinds of fly ashes produced by two circulating fluidized bed plants with different chemical composition: silico-aluminous fly ashes and sulfo-calcic fly ashes. For the two kinds of fly ashes, adsorption equilibrium were reached in 3 days. Furthermore, removal of mercury was increased with increasing pH. Sulfo-calcic fly ashes allow us to remove mercury more efficiently and more steady. The chemical analysis of fly ash surface was carried out by electron spectroscopy. The results show that mercury is bound to ash surface thanks to several chemical reactions between mercury and various oxides (silicon, aluminium and calcium silicate) of the surface of the ashes.

Influence of the bed mass on its fluidization characteristics

Two series of fluidization tests were carried out on two test models with catalyst, alumina and sand particles to determine the bed mass influence on the characteristics at the minimum of fluidization. The main conclusions of the present study are: (i) the measured minimum fluidization velocities increased with the inventory whatever were the solid and the test rig used; (ii) the measured bed porosity at minimum fluidization decreased with the increase of the bed inventory; (iii) the definition of the minimum fluidization velocity by the balance between weight and drag forces and some usual mathematical modeling attempts were not able to describe the minimum fluidization increase with the bed inventory; (iv) the addition of a complementary consolidation effect in the force balance was able to match the obtained experimental results; (v) the consolidation effect sorted out the solids in the same order than the one given by their flowability as measured in shearing test.

Characterization and Selection of Materials for Air Biofiltration in Fluidized Beds

A methodology is described for the selection of the best material to employ in a fluidized biofilter applied to volatil organic compounds (VOC) treatment. Two different supports were considered: one natural, scrap wood, and one synthetic, polyurethane foam. In a first part, the main objective was to establish the fluidizability of the selected solids. Particles of increasing moisture content were tested in rigs equipped with different air distribution technologies. Maps of flow regimes were drawn by varying air velocity and bed height. In the second part, the sorption capacities of the selected materials were evaluated at different humidity levels for a soluble organic compound (ethanol) and an insoluble one (toluene). Their ability for supporting viable microorganisms was then measured. Fine particles with 45% moisture content fluidized with the tuyere distributor in channeling and slugging regimes, whereas the conical distributor generated a spouted bed regime. Coarse wood particles with 45% moisture commonly used in fixed bed biofilters were considered as less suitable due to limitations borne by their fluidization regimes. Finally polyurethane foam filled with Agar gel could not endure the mechanical stress to which particles are subjected in fluidized beds. It was shown that a 45% moisture content was optimum to ensure transfer for both soluble and hydrophobic compounds. Considering the biological criterion, it appeared that a 45% humidity level was sufficient to ensure biomass growth and biodegradation of pollutants on fine scrap wood particles.