Enhanced fine coal dewatering by size enlargement using asphalt emulsion

The dewatering of fine coal represents a great challenge facing the energy industry since the conventional dewatering techniques are unable to produce sufficiently low moisture. A novel hydrophobic agglomeration process based on a domestic asphalt emulsion, commercially known as the cationic coal binder (CCB), has been developed in this study for enhanced fine coal dewatering. The asphalt emulsion was characterized by excellent stability, relatively low viscosity and easy handleability. Vacuum filtration dewatering results have shown that it effectively reduced filter cake moisture from 35% to 26% at a dosage of 0.5% by weight, which is significantly lower than the dosage of the imported "Orimulsion" used in the patented "GranuFlow Process".; The interactions between CCB asphalt droplets and coal particles have been investigated using the extended DLVO theory. The hydrophobic interaction played a predominant role in CCB induced coal agglomeration. Nanobubble bridging extended the hydrophobic interaction distance from about 20 nm up to 80 nm. Oil/asphalt bridging contributed to the stability of coal agglomerates.; The CCB asphalt emulsion has been characterized by zeta potential, size distribution, viscosity and surface tension. Coal agglomeration by CCB was a rapid process, reaching the equilibrium within 15 seconds after the addition of CCB. Two dimensional coal agglomerates were formed at low CCB dosages and three dimensional ones at higher dosages. Larger coal agglomerates were more sensitive to conditioning mode and intensity than smaller ones. The CCB droplets showed preferential adsorption on hydrophobic coal particles as compared to hydrophilic quartz particles.; The vacuum filtration dewatering process was improved by CCB in filtration rate, cake formation time, solids recovery and cake structure. Scanning electronic microscopy (SEM) studies indicated that particle segregation in filter cake was considerably reduced by the addition of CCB. Clay particles had a huge capacity in adsorbing asphalt droplets, thus significantly reducing the efficiency of coal agglomeration by asphalt. No ash rejection effects were observed with the CCB enhanced filtration dewatering process. The thermogravimetrical analysis (TGA) study of the moisture distribution in filter cake showed CCB agglomeration significantly affected the total moisture and interstitial moisture but had little influence on the bound moisture.