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Hydrodynamics characterization of a fluidized bed reactor with an internal circulation of solids (fb-ics). Application to anaerobic methanogenic phase.

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Many advantages of the fluidized beds for the anaerobic treatment are widely reported in literature. Heijnen et al. (1989) comments the following main potential advantages: higher purification capacity, no clogging of the reactor, no problems of sludge retention and small volume and area requirements. Malina and Pohland (1992) denote a high biomass concentrations and long SRT achievable, an excellent mass transfer characteristics and biogas evolution and an extensive effluent recycle insure relatively uniform temperature, pH and substrate concentrations in reactor. However, they have hydrodynamic characteristic that reduces its efficiency. The particle movement and its configuration cause bed stratification, which lead to a different biomass concentration and a variation of the trophic groups activity throughout the reactor (Diez Blanco et al., 1995; Buffiere et al., 1998). This behaviour make difficult the control of biomass growth in the start-up period. This growth can bring about that particle density be similar to that in water, causing that little oscillations of the liquid flow, can yield a great variation in bed expansion. To avoid these problems, we propose a Fluidized Bed Reactor with an Internal Circulation of Solids (FB-ICS), to improve solid mixture.

We can get an internal circulation of solids, which improve the mixing behaviour and expansion control, introducing a draft tube inside the column. With an appropriate distributor, all the liquid is introduced in the annular section. Once the superficial liquid velocity (JL) is over the minimum fluidization velocity (Vmf), the expansion in annular zone increase and solids particles in this section get the top of the draft tube dragged by liquid flow. Subsequently, return inside the draft tube because of the drastic reduction of liquid velocity at the top of draft tube. The velocity which provokes solid circulation is denominated JLrec (Figure. 1).

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