Effect of hydrophobicity on viscosity of carbonaceous solid–water slurry

Carbonaceous solid–water slurry rheology is greatly affected by the surface properties of the carbonaceous solids used. Slurriability studies showed that, for the same solids loading, viscosities of highly hydrophobic petcoke and bitumen–water slurries were approximately one order of magnitude higher than the viscosity of non-hydrophobic Illinois #6 (bituminous) coal–water slurry. Apart from slurriability, the hydrophobicity of the carbonaceous solids was found to influence the type of additives used to reduce the viscosity. Selected to reduce viscosity, the addition of non-ionic additive Triton X-405 caused a drastic reduction in petcoke and bitumen–water slurry viscosities, whereas anionic additive ammonium lignosulfonate reduced Illinois #6 coal–water mixture viscosity more effectively. Optimum particle-size distribution was also found to be dependent on the surface properties of the solids. Experimentally determined optimum particle-size distributions were observed to deviate from the theoretical predictions. A deviation of 8% was noted in the case of Illinois #6 coal–water slurry, whereas deviations of 30% were observed in the case of hydrophobic bitumen and petcoke–water slurries. Viscosity predictions of semi-empirical models were compared to experimentally measured viscosities. The predicted viscosities did not match the experimental results, especially at higher solids loading. A thixotropic model taking into account particle aggregation was found to predict viscosity more accurately in the case of these hydrophobic carbonaceous solid–water slurries.