Mitigation of segregation and stratification in bulk granular mixtures by the electroclamping method

Granular mixtures with uniform bulk distribution of chemical components are highly desirable in many processes in the chemical industries. A uniform mixture is very important for product consistency and quality. However, it is often very difficult to control the resulting mixtureʹs make-up or segregation tendency reliably. In this paper, the application of a novel technique, utilising high electric fields, is described for minimising segregation and stratification within a granular heap formed by slow filling in a two-dimensional container. This is achieved by creating multi-pour points or a snowstorm effect instead of a single pour point, thereby preventing the formation of a heap. A quantitative analysis of the degree of segregation and stratification is performed using Fast Fourier Transformation (FFT) and Inverse Fast Fourier Transformation (IFFT), together with an image processing and analysis software. In an electric field, a small current flows through the bed of particles, causing electrical adhesion, which can reduce the mobility or even hold the particles between the electrodes. The moisture content plays a significant role here as it controls the surface conductivity of the particles. When the electric field is switched off, the layer of particles falls as a uniform plug flow, preventing the particles from rolling freely down along the inclined surfaces to form a heap. This effectively reduces segregation and stratification within the granular formation. Quantification of the effects of pulsed d.c. fields on reducing segregation shows that there exist an optimum electric field strength and pulsation frequency.