Rheology of coal-water slurries prepared by the HP roll mill grinding of coal. Quarterly technical progress report No. 6, December 1, 1993--February 28, 1994

Abstract

The effect of the addition of nonionic surfactants on the aggregative stability of coal-water slurries was investigated through determination of sedimentation volumes and floc size distributions. Sedimentation volume measurements for nonionic surfactants show that for Triton X-165, Triton X-305 and Triton X-405, the sedimentation volume decreases slightly with added reagent up to 0.5 wt % addition, decreasing sharply for reagent additions between 0.5 to 0.75 wt %. However, at higher additions, the sedimentation volume levels off for Triton X-165, but increases for both Triton X-305 and Triton X-405. These results are in agreement with the viscosity measurements. Because of its plastic nature, bituminous coal is readily briquetted or agglomerated by the intense localized stresses encountered during comminution in the high-pressure roll mill. The degree of briquetting depends on the nature of the coal and the compressive stresses. We have found that the briquettes can readily be deagglomerated by stirring the comminuted products in a in methanol suspension. Our results show that the amount of minus 200-mesh coal produced depends mainly on the energy invested in the high-pressure roll grinding. The percentage of fines generated increases more or less linearly with the specific grinding energy consumed in the initial stages and tends to level off at the high energy inputs higher than 3 kwh/t. Even at 3.74 kWh/t of energy input, the ground product contained only 30 percent of minus 200-mesh particles, which is much lower than 80 percent of minus 200-mesh particles required in the coalwater slurries for direct combustion in power plants. Therefore, future work will encompass grinding of the high-pressure roll milled product in ball mill or rod mill, using hygrid HP roll mill/ball mill circuit for feed preparation.