Rheological characteristics of coal–water slurry using microwave pretreatment – A statistical approach

The present study addresses the treatment of microwave energy for rheological characteristics of coal–water slurries (CWS) performed in an online Bohlin viscometer. Detailed experimental investigations were carried out for high ash Indian coal (Jamadoba washery, 38% ash). Experiments were conducted at high power level (900 W) for all the test samples in microwave oven. The exposure times were fixed at 30, 60, 90 and 120 s. Before and after treatment, the test samples were ground and sieved into different fractions for chemical and physical analysis. Central composite design (CCD) was applied to study the influence of particle diameter, solid concentration, microwave (MW) exposure time and shear rate on apparent viscosity for rheology characteristics of coal–water slurry. A quadratic model was developed for apparent viscosity using Design-Expert software. The model was used to calculate the optimum operating conditions for minimization of apparent viscosity. The apparent viscosity (22.83 mPa s) produced at these operating conditions showed an excellent agreement with the amounts predicted by the models.