Improvement of granular bed filtration performances

Some authors highlighted that during the filtration of ultrafine particles, the deposit is essentially located in the first layers of the granular bed. Thus, only a small depth is useful thereby reducing both the operation time between each unclogging and the process yield. Our improvement approach consists in reducing the pressure drop increase while maintaining a high collection efficiency by using a new type of granular bed. The clogging by particles generated by thermal spraying of a three-stage column filled with bead diameters equal to 1 mm in the first stage, 0.8 mm in the second and 0.5 mm in the third and of a conventional granular bed (with beads diameter of 0.5 mm in the 3 stages) were compared. Since the collection efficiency is a decreasing function of the collector size, this improved configuration permits to firstly clog the downstream layers of the granular bed. Although there is a 20% decrease of the initial efficiency for this new type of bed compared to the conventional one, this gap is rapidly reduced during the clogging process. At the same time, the results highlight a lower pressure drop increase of the modified granular bed. A predictive clogging model was also developed in order to find an optimized configuration of bead diameter so that the whole granular bed depth contributes to the filtration.