Investigation of performances of a multishaft disk (MSD) system with overlapping ceramic membranes in microfiltration of mineral suspensions

This paper investigates a new design of dynamic filtration system which has become recently available. The pilot unit tested contains 12 ceramic membrane disks with 0.2 μm pores, 9.0 cm in diameter, mounted on two parallel shafts rotating in the same direction at the same speed and surrounded by a steel housing. The fluid is sheared between overlapping disks. The differential speed (DVn) between two adjacent disks has been shown to be uniform in the overlapping region and 51% higher than the azimuthal rim speed of a disk. Test fluids were CaCO3 suspensions at various concentrations ranging from 100 to 280 g L−1 and 24 °C. Permeate fluxes obtained at 1930 rpm (DVn = 13.47 m s−1) and 200 kPa were very high, ranging from 880 L h−1 m−2 at 100 g L−1 to 720 L h−1 m−2 at 280 g L−1. At 738 rpm (DVn = 5.25 m s−1), these fluxes were respectively, 690 and 430 L h−1 m−2. When a system with rotating membranes is operated at a fixed inlet pressure, its permeate flux rises with increasing speed until it reaches a maximum and decreases at higher speed, due to build-up of permeate pressure caused by centrifugal forces, which reduces the transmembrane pressure. In our pilot, this phenomenon was only observed at low inlet pressures. Rotation speeds at which a maximum flux occurred were 800 rpm at 40 kPa and 1600 rpm at 75 kPa.