Rheology of coal-water slurries prepared by the HP roll mill grinding of coal. Quarterly technical progress report No. 2, December 1, 1992--February 28, 1993

The rheological behavior of coal-water slurries made with Pittsburgh No. 8 coal at four solids contents was investigated with the Haake viscometer after conditioning for 16 hours at 200C. The results show that the viscosity of the slurries increases as the solids content is increased. Slurries at high solid-liquid ratios not only exhibit significant yield stresses but also viscosities which decrease with increasing in the shear rate. It was found that the empirical Heschel-Buckley equation fits the measured shear stress of slurries at different shear rates quite well. The standard deviation of the shear stress of coal-water slurries measured with the Haake viscometer was found to be less than 10%. The apparent viscosities measured with the Brookfield Synchro-Lectric LVT viscometer were comparable with values obtained with the Haake Rotovisco RV12 viscometer for slurries having solids contents of 50 and 55 wt%. In studying the effect of conditioning time on the measured viscosity of coal-water slurries (at 60 wt% solids content), it was observed that the viscosity of a slurry increases when the conditioning time is increased from 0.25 to 0.75 hour and then decreases when the conditioning time is increased further. The initial increase in viscosity with conditioning time is probably related to the penetration of water into the pores of the coal, and the decrease in the viscosity at longer conditioning times over 0.75 hour may be due to the development of a hydration layer and the electrical double layer on coal surfaces