Influence of coke particle characteristics on the compaction properties of carbon paste material

• Particle shape aspects had significant effect on packing and compaction behavior.
• Sphericity and convexity were the most important shape factors to particle packing.
• More spherical particles enhanced the final density of compacted anodes.
• Measuring particle apparent density made it possible to study the packing ability.
• VBD was not a reliable method to determine the packing ability of coke particles.

The anode electrodes in electrolytic production of aluminum are composed of coke particles and binder pitch. A paste consisting of the particles and pitch is made and compacted to form the green anode. The influence of coke particle properties including shape factors and density on the particle packing, compaction behavior of the paste and the final density of green anode was studied. Five sponge cokes and one shot coke from different industrial sources were used in this study. The shape factors and apparent density for different size fractions of particles were measured and the volume fraction of open and closed pores within the particles was determined. The bulk density of the particle bed was measured with and without applying vibration. Inter-particle void fraction was then calculated to determine the packing behavior of the particles. The pastes were made and compacted to make laboratory-scale anodes. It has been revealed that particle shape is an important factor determining the packing properties and compacted density.

The influence of shape factors and apparent density of coke on the packing properties of particles and compaction behavior of anode paste (coke + binder) was studied. Shape factors were measured for different sources of coke (figure a). Multivariate analysis showed that apparent density, convexity and sphericity were the most important particle characteristics to achieve high vibrated bulk density (figure b). Anode pastes were made with different sources of coke and compacted (figure c). Results showed that more spherical and regular shape particles resulted in a better packing behavior and higher density after compaction (figure d).Figure optionsDownload as PowerPoint slide