NON-NEWTONIAN BEHAVIOR OF KRAFT BLACK LIQUORS

Kraft black liquor exhibits complex rheological behaviour at high soli ds concentration. A single point determination of viscosity at a refer ence shear rate and temperature using conventional rotational viscomet ers is not always sufficient to describe the flow behaviour in process ing equipment that may be operating over a wide range of shear rate an d temperature. In this study, the rheological characteristics of a mix ture of 9% NSSC, 47% pine kraft and 44% eucalypt kraft black liquors a t different solids concentrations and temperatures are presented. The viscosity-shear rate relations of these liquors fit the Power Law and the Quemada models well. The apparant viscosities are temperature depe ndent and conform to the Arrhenius equation. The use of the rheologica l properties in the calculation of pipe flow pressure drop is also ill ustrated.