Improved decanter operation by reduced particle fragmentation

M.Kuhn*, M. Reichenbach, S. Weis, A. Siebelitz, Andritz Separation GmbH, Germany; J. Grossalber, Andritz AG, Austria

Particle attrition, i.e., a reduction of solid particle size due to breakage, fracture or abrasion, is a phenomenon that is often encountered in decanters used for solid liquid separation. Here particle fragmentation is highly undesired as smaller particles are difficult to separate and a cake consisting of fine grained solids exhibits higher capillary forces and consequently results in higher residual moisture of the solid product. Moreover centrate quality deteriorates due to higher particle concentration. Downstream process units will also be affected negatively.

Grain breakage occurs especially when high shear forces are present and the flow is disturbed. In decanters particularly critical locations represent the feed ports where the slurry gets into contact with the rotating machinery after leaving the fixed feed pipe. The standard feed port design is a radial straight channel with circular or oval profile. These ports accelerate the flow in rotational as well as radial direction. Locally high shear and impact forces act on the flow and the feed ports are exposed to high wear and tear. The radial accelerated feed flows straight into the pond which results in a significant particle load and breakage.

With special focus on preventing particle fragmentation the inlet design has been altered. Particularly the feed ports have been optimized resulting in a more gentle flow redirection, acceleration and pond immersion. Experimental tests with coal slurry confirmed....

Session: L4 - Decanter and Tube Centrifuges
Day: 11 October 2016
Time: 14:45 - 16:00 h