Characteristics of coal sludge slurry prepared by a wet-grinding process

Coal sludge slurry (CSS) is an alternative fuel and a potential competitive method for sludge reduction. Based on the researches of coal water slurry, we studied CSSs by using a wet-grinding process with different types of regional municipal sludge (sludge) in an orthogonal experiment. The sludge type, sludge mixing proportion, dosage of dispersant, and grinding time were tested in this study. The results show that water content and its occurrence characteristics in the sludge have primary hindering influences on slurry ability. The range of fixed-viscosity concentrations with raw wet sludge is from 50.78% to 44.40% (by weight), while the range is from 53.35% to 51.51% (by weight) with dry sludge. All of the CSSs exhibit shear-thinning behaviors with different variation trends, especially the CSSs with more than 15% (by weight) raw wet sludge in it. Adding the same proportion of raw wet sludge increases the thixotropic properties of CSSs and the highest area of thixotropy loop is 3065 Pa/s, while the highest value of dry sludge is 1798 Pa/s. Hydrophilic group plays an important role in adsorbing water and building three-dimension networks with other particles, which is the main reason for CSS properties. Therefore, the mechanism can be used to find the way for making high quality CSS.