Optimization of ultrafine particles filtration in granular beds

Ultrafine particles are generated by many manufacturing processes: surface processing and coating (thermal spraying ...), machining (drilling, rectification ...), combustion welding, and cutting of metals etc...
The development of suitable protection systems therefore appears crucial in order to protect persons and the environment. The most efficient and widely used de-dusting methods for separating the particles from the carrier fluid are currently fibrous media. These pleated fiber filters are initially very efficient but generate a strong increase in pressure drop because of a quick and sometimes irreversible clogging.
Granular beds also exhibit interesting performance, in terms of ultrafine particle collection efficiency, and a higher resistance to mechanical and thermal stresses comparatively to fibrous filters.
Our optimization approach consists in increasing the time between two unclogging operations of the granular bed, i.e. in reducing the pressure drop increase. Experiments were achieved using a three-stage column, each composed of a given diameter stainless steel beads. Performances of an optimized 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 are compared to those of a conventional granular bed (with beads diameter of 0.5 mm in the 3 stages). Results show that the optimization of the granular bed filtration by means of a collector diameter gradient seems quite promising.