MAGNETIC FIELD ENHANCED CAKE FILTRATION

摘要

Cake filtration is a widely used solid/liquid separation process.The design ranges from lab-scale discontinuous Nutsche filters to large-scale continuous rotary drum filters.Another common separation device,especially in the mineral industry,is the magnetic separator which uses magnetic forces to separate magnetic from non-magnetic materials.The combination of the two mechanisms described in this paper is a totally new approach and results in positive synergetic effects and an extension of the field of application for the cake filtration process.The work describes the phenomenology of this new hybrid separation which combines pressure forces with magnetic fields or forces and defines potential areas of applications like pigment separation or bio-separation as well as separation of nanostructured magnetic materials in the electronic industry.The experimental results show that the cake filtration of magnetic particulate products can be improved significantly by superimposing a homogeneous,as well as an inhomogeneous,magnetic field.The reason can be seen in magnetophoretic effects as well as magnetic field enhanced structure changes of the particulate system.These result in less solids breakthrough,a faster cake formation,a higher permeation rate through an already built filter cake and therefore an integral improvement of the overall cake filtration process.However,the experimental results also define a critical magnetic field strength,above which there will no longer be a homogeneous cake formation.The critical field strength is a function of the applied gas pressure as well as a function of the (magnetic) product properties.In addition to the experimental results this work also introduces a theoretical approach to describe magnetic field enhanced cake filtration.An excellent agreement between experimental results and theoretical predictions is shown.