Non-spherical carbon composite agglomerates: Lab-scale manufacture and quality assessment

Abstract

For recycling steel work dust and improving blast furnace (BF) performance, a few types of non-spherical carbon-iron oxide agglomerates were manufactured in laboratory scale and their strength and reducibility were evaluated using a shatter and a tumbler tester, a simulator for lumpy zone in BF and a softening/melting tester. The flat or ragged shape was expected to enhance reducibility and to prevent the agglomerate from unwilling rolling down to the center of BF. Agglomerate in the shape of column with concave triangle cross-section (Tetra) showed the highest yield during extruding and almost same strength compared with a commercial spherical cold-bond pellet. In reducibility Tetra excelled sinter but spherical carbon composite pellet, which denied shape effect. Reduction disintegration of Tetra initiated at 600°C and reached to the maximum of 60% at 860°C, the entrance of thermal reserve zone, meaning the issue of cement bonding on disintegration remained unsolved. In case of single use, Tetra did not melt down up to the upper limit temperature of the softening/melting tester, causing S-value enlarged. Using Tetra mixed with sinter was recommended as a trial of admixing 50% Tetra to sinter accelerate reduction rate of sinter, improving BF efficiency by 45kg/t decreases in RAR; moreover, the mixture remarkably reduced the pressure loss of cohesive zone.