Hydrophobic modification of Xinjiang lignite to improve its slurryability

The abundant pore structure and large number of oxygen-containing groups cause high water content of lignite, which limit its efficient utilization. In this paper, high concentration, low viscosity and high stability coal water slurry was prepared by hydrophobic modification of low rank coal to make it have the property of high rank coal. Using anionic surfactant sodium stearate and nonionic surfactant OP-10 as emulsifier emulsified alkyl ketene dimer (AKD), anionic AKD modifier and non-ionic AKD modifier were prepared, which were coated on the surface of microwave drying coal to improve the hydrophobic properties of coal particles. The surface properties of coal particles before and after modification such as chemical composition, pore distribution, hydrophobic properties and Zeta potential were studied. Combined with the adsorption results of NSF dispersant on the surface of coal particles before and after modification, the slurryability, rheology and stability of lignite coal water slurry were discussed. It is found that surface of the modified coal particles has higher carbon content and lower oxygen content, while their pore volumes are reduced, the contact angles of coal-water interface are increased, and hydrophobicity of the coal particles is enhanced. The adsorption capacity of NSF dispersant on surface of modified coal increases, which makes the surface electronegativity of coal particles increases, and coal particles have better dispersion effect in water. The maximum concentrations of CWS prepared by anionic AKD modified coal and non-ionic AKD modified coal increase from 56.6% of raw coal to 61.0% and 62.5% respectively, and the water evolution rates of CWS decrease from 13.97% of raw coal to 7.45% and 7.89% respectively. At the same time, the CWS prepared by modified coal particles show shear-thinning pseudoplastic fluid. Overall, the physical and chemical properties of coal particles have significantly changes after modification, and high-quality slurry fuels with high solid concentration, superior pseudo-plastic behavior, and good stability are easier to be prepared.