Experimental study of granular bed filtration of ultrafine particles emitted by a thermal spraying process

• Granular beds can offer an alternative solution to media filters for ultrafine particles collection.
• Variation of granular bed efficiency and pressure drop during filtration was studied.
• Clogging occurred primarily in the first centimeter of the surface layer.
• Shocks applied to the granular bed enable the pressure drop to be maintained within acceptable limits.

Ultrafine particles (UFP) emitted by metal thermal spraying processes are responsible for rapid and partially irreversible clogging of filters. Granular filter beds could offer an alternative solution to media filters based on their capacity for efficient UFP collection and surface collection layer renewal. The influence of the electric charges carried by particle and grains on filtration efficiency was revealed and there was a close agreement between the model and measured values without electric charges. Variation in the efficiency and pressure drop during filtration, hence gradual clogging of the bed, was studied using two types of column. The influence in filtration rate on clogging kinetics was also investigated. The column composed on three distinct one centimetre stages showed that clogging occurred primarily in the bed surface layer. The regular elimination of cake during filtration would enable the pressure drop to be maintained within acceptable limits.