RHEOLOGICAL BEHAVIOR OF COAL-WATER MIXTURES .1. EFFECTS OF COAL TYPE, LOADING AND PARTICLE-SIZE

Factors affecting the rheological characteristics of coal-water mixture (CWM) were investigated, including the properties of the coal, the volume fraction of solids and the mean size and size distribution of the coal particles. The apparent viscosity was measured with a Brookfield viscometer, and the non-Newtonian properties based on the power-law model were investigated using a Haake rotational viscometer at shear rates up to 512 s(-1). The results showed that the slurry exhibited shear thinning, i.e. pseudoplastic behaviour, and that it became more viscous as the mean particle size decreased, but less viscous with decreasing equilibrium moisture content. The degree of pseudoplasticity increased with increasing coal content and with decreasing mean size of particles. The mixing of coarse and fine coal particles was found to be very effective in obtaining mixtures characterized by high solids content and low viscosity. CWM viscosity was lowest when the blending ratio of fines was similar to 0.35, irrespective of the mean-size ratio. The particle size distribution which gives high fluidity also appears to enhance the stability of the suspension.