Interparticle Interactions in Highly Concentrated Coal-Water Slurries and Their Effect on Slurry Viscosity

Coal/petcoke-water slurry viscosity is affected by interparticle interactions of the solids in water, which, in turn, is governed by the surface chemistry of the solids. To determine interparticle interactions of these carbonaceous solids in water, interfacial energies were determined on the basis of surface chemistries characterized by contact angle and zeta potential measurements. Hydrophobic/hydrophilic interaction energies, observed to be 2-3 orders of magnitude higher than the electrostatic interaction energies and the van der Waals interaction energies, were clearly the dominant interaction energies for such a system. Hydrophobic interactions lead to the formation Of aggregation networks of solids in the suspensions with entrapped water, whereas hydrophilic interactions result in the formation of hydration layers around the carbonaceous solid particles, causing loss of free water from the slurry. This results in an increase in the effective solid volume fraction, leading to an increase in viscosity. The increase in the effective solid volume fraction was observed to be a function of surface chemistry of the solid. A relationship between the effective solid volume fraction and the oxygen/carbon ratio of the carbonaceous solid was developed using both experimental measurements and the Krieger-Dougherty (K-D) equation. This modification improved the predictive capabilities of the K-D equation. Therefore, to accurately predict slurry viscosity of any carbonaceous solid, the increased effective solid volume fraction predicted on the basis of its oxygen/carbon ratio should be used in the K-D equation to account for its surface chemistry. This modified model was validated using three concentrated carbonaceous solid-water slurries and was observed to accurately predict viscosity.