RHEOLOGY OF LOW-RANK COAL-WATER SLURRIES AT BOTH HIGH AND LOW SHEAR RATES

Combustibility of coal-water fuel (CWF) slurries in pressurized systems is influenced by the apparent viscosity of the slurry at shear rates range of 10(4) - 10(5) s-1 that are estimated to arise during atomization. Fuel slurries of beneficiated low rank coals and a bituminous coal were tested with a Haake rotational viscometer and a capillary extrusion rheometer at shear rates up to 10(5) s- 1. Real time acquisition of flow rate and pressure data and use of a Coriolis-type mass flow meter contributed to accurate determination of power law flow parameters. Coefficient of variation of the flow behaviour index was less than 0.2% in all cases. Most low-rank-fuel slurries displayed some degree of increased pseudoplasticity with increasing shear rate, especially for slurries of lower average particle size. Fuel slurries of micronized Taggart bituminous coal exhibited increased dilatancy as the rate of shear increased. This difference in flow behaviour at shear rates over 10(4) s-1 helps to explain the reported higher combustion efficiency of beneficiated low-rank CWFs as compared to bituminous CWF.