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The properties of the air-water state diagram, representing the liquid holdups according to gas velocities, in a 0.075 m diameter column are restated. After measurement of the interfacial areas and mass-transfer coefficients, the part of the diagram corresponding to high gas velocities and low liquid contents ( I 0 < Uc < 14 m i s and 0.005 < UL < 0.04 d s ) was chosen for the treatment of polluted gas streams. Under these conditions, it was shown that a "droplet column" is very efficient for the treatment of gases polluted by acid vapors (SO2, HCI) and dust (iron oxide, talc, etc.). The cost of energy appeared more favorable than for classical bubble columns.Les proprietes du diagramme d'etat air-eau, representant les retentions du liquide en fonction des vitcsses de gaz, dans une colonne de 0,075 m de diametre ont ete rappelees. Apres mesure des aires interfaciales et des coefficients de transfert de matiere, le domaine utilisant des hautes vitesses de gaz et de faibles teneurs en liquide (10 < U , < 14 m/s et 0,005 < UL < 0,04 d s ) a ete choisi pour le traitement des effluents gazeux. II est montre que dans ces conditions, la "colonne a gouttes" est tres performante pour traiter des gaz pollues par des vapeurs acides (SO,, HCI) ou des poussieres (oxyde de fer, talc...). Les depenses energetiques apparaissent plus favorables que pour les colonnes classiques.

In this paper we wish to propose a new and simple approach to the scaling-up of catalltic fluidized reactors, which leads to an inexpensive development method for making-up small tonnage products. In a fluidized bed reactor, the greater part of gas flows in the form of bubbles practically devoid of catalyst. Such reactors operate by mass transfer between the bubbles and dense phase gases. This transfer is denoted quantitatively by the height of transfer H,,, and is measurable by chemical reaction or a tracer study [l, 21. In practice, backmixing of the dense phase can be neglected. From the results of previous studies, it appears that a 0.5 m diameter pilot plant has up till now been required for an extrapolation to be made with any degree ofconfidence; this approach is very expensive .and only justified for the development of processes for large tonnage products. ,The value of H,, is dependent upon the catalyst particle size and the bed diameter. In order to obtain a low value of H,, (0.7 to 1 m) the industrial catalyst must be finely divided: 50 to 80 pm. Thus,the bubblesize will belimited (0.02 to0.05 m)andremains fixed throughout the whole bed height. Thelaboratory beds (0.02 to 0.05 m in diameter)are always slugging, whatever the catalyst granulometry.A comparative study of the hydrodynamic and transfer characteristics of these two kinds of beds leads to the following results: 1) The incipient fluidization velocity uf, for a fine catalyst under working conditions, and the bed diameter D, are sufficient parameters to correlate all the data required for fluidized reactor design, whatever its diameter; provided that the superficial gas velocity u is high enough. u, is the reference gas velocity in the dense phase given by ujo.3 = (uf/0.2)o.75. In the range of interest 0 < uf < 1.5, 1.3 < ep < 2.84.2) In a 0.02 m diameter bed filled up to a height 0.5 m, the pressure drop can become greater than the theoretical one as follows :. m. This value is a decreasing function of uf, allowing it to be determined in the range 0.1 to 0.8. 4)The velocity of bubbles slugging in small beds is a quasi-linear increasing function of u and the corresponding slope is a decreasing function of uf allowing it to be determined in the range: 0.1 to 0.8.