Optimizing particle translation and self-rotation by adjusting gravity-driven hydrocyclone inclination angle for separation and activation of granular sludge

Abstract

Hydrocyclone was experimentally confirmed important for the granulation, separation, and activation of granular sludge. However, almost all the existing hydrocyclones are pressure-driven, requiring an intake pump to transport materials. Recent experiments revealed granular sludge breakdown occurred more in intake pumps than hydrocyclones. Therefore, we proposed the gravity-driven hydrocyclone operating like a waterfall to separate and activate the granular sludge, with the benefit of avoiding granular sludge crushing. CFD simulations were carried out to study the effects of inclination angle on the fluid flow and particle motion, and separation performance. Results show that the proposed gravity-driven hydrocyclone without intake pump can successfully activate and separate the 0.5-mm simulated granular sludge. Unlike a widely used pressure-driven hydrocyclone, the new hydrocyclone gives the separation efficiency and split ratio positively correlated with the inclination angle. Generally, the inclination angle does not significantly affect particle translation, particle self-rotation, and particle revolution. The maximum angular and linear velocities of particle self-rotation are mainly obtained in the cylindrical section, especially its upper part. The shear stress of the fluid micro cluster obtains its maximum near the wall, and the maximum wall shear stress is only 252 Pa.