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The helical flow promoter (HFP), inserted in the downcomer of an airlift reactor (ALR), generates a helical flow pattern in the circulating gasliquid (solid) mixture. Data on the fluidization capacity, gas holdup, liquid velocity and mass transfer rate for two-and three-phase systems with two different carboxymethylcellulose solutions collected in a 58 L ALR-HFP are presented and compared with those of common pneumatic reactors. Generally, an increasing solid concentration led to a slight decrease in gas holdup and liquid velocity but to a considerable decrease in mass transfer rates. Insertion of HFPs produced a significantly enhanced fluidization capacity of solid particles compared to the common systems.L'activateur d'ecoulement helicoidal (Helical Flow Promoter (HFP)) insere dans la colonne descendante d'un reacteur a air ascendant (ALR) donne un mode d'ecoulement helicoi'dal dans le melange circulant gaz-liquide (solide). Les donnees sur la capacite de fluidisation, la retention de gaz, la vitesse du liquide et la vitesse du transfert de matiere pour des systemes biphasiques et triphasiques avec deux solutions de carboxymethylcellulose differentes recueillies dans un ALR-HFP de 58 L, sont presentees et comparees aux donnees de reacteurs pneumatiques courants. En generale, une concentration accrue de solides entraine une Iegere baisse de la retention de gaz et de la vitesse du liquide mais une forte diminution des vitesses de transfert de matiere. L'insertion d'un HFP donne une capacite de fluidisation des particules solides nettement amelioree. comparativement aux systemes habituels.

The growth of the red microalga it Porphyridium sp was studied in three bench-scale bioreactors of 13 dm 3 volume: a bubble column, an airlift reactor and a modi®ed airlift reactor with helical¯ow promoters in the top of the downcomer. Most of the experiments reported were run with a photon¯ux density of 250 mE m À2 s À1 , but other illuminances were studied as well. Super®cial gas velocities were in the range of 5.4 Â 10 À4 to 82 Â 10 À4 m s À1 (0.033±0.5 vvm). Algal growth in the airlift reactor with helical¯ow promoters had lower gas requirements than in the other reactor con-®gurations. This implies lower costs in air compression and in air and CO 2 requirements. It was concluded that the advantages found are related to the particular¯uid dynamic characteristics of the reactor.

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