LAUSR

ABSTRACT The crushed and sieved high ash coal samples are treated hydrothermally in a 15 l (liters) lab scale autoclave at a temperature of 394 K and residence times of 30, 45, 75 and 120 minutes. The hydrothermal treatment (HTT) of the coal samples leads to the increase in the carbon and fixed carbon fractions whereas a decrease in the oxygen and volatile fractions. A significant decrease in the maximum settled concentration is observed upon HTT and settling time increases by ~48%. All the suspensions behave like a Newtonian fluid up to a solid concentration of 30% (10–30%) and for the concentrations >40% (40–60%), the suspensions behave like a pseudoplastic or shear thinning fluid. The HTT leads to a significant improvement in the rheological characteristics of the CWS. The apparent viscosity shows an increase with solid concentration for raw as well as HTT coals. Whereas a decreasing trend is observed with treatment time and shear rate. The apparent viscosity shows a maximum improvement by 60.1, 50.71, 39.9, 50.55, 65.69 and 75.41% at 10, 20, 30, 40, 50 and 60% solid concentration, respectively. As similar characteristics are observed at residence times of 75 and 120 minutes, the optimum treatment time is observed to be 75 minutes.