Determination of plastic viscosity for brown coal pastes using an instrumented mixer

Abstract

Flow curves are generated for lignite pastes using an instrumented measuring kneader, converting the torque and rpm to shear stress and shear rate data, respectively. Contrary to previous findings obtained when instrumentation of this kind was unavailable for these applications, the pastes are yield pseudoplastic in nature, with significant differences between actual and Bingham yield stresses. Flow curves were generated over for 14, 17 and 22 °C for as-mined lignite paste, 54% moisture, wet basis (w.b.), and increased moisture concentrations, through moisture addition, of 56 and 58%, w.b. Flow curves for the latter were generated at 14 and 22 °C. The flow properties presented are the plastic viscosities and, using Hershel Bulkley and Bingham fits, yield stresses. In general, the pastes exhibited high yield stresses (2–5.3 kPa, depending on the moisture content and process temperature), high Bingham yield stresses (2–8 kPa), and low plastic viscosities (0.5–29.4 Pa s). Increasing temperature and/or moisture content resulted in reductions in the magnitudes of these properties.