97/03715 Rheological properties of coal-water highly concentrated suspensions

Abstract

High solid concentrated suspensions are more and more used , like coal- water slurries . They are generally stabilized according to an electrostatic repulsion. The measurements of the zeta or electrokinetic potential constitute a means to gain an idea of the stability of such suspensions. Thus, a suspension is stable if the surface charge of the particles is high. In principle, the zeta potential must be higher in absolute value than 60 mV. With concentrated suspensions (50 % of solid), zeta potential can be determined using a mass transfer apparatus which eliminates sedimentation effects by continuous rotation of the measurement cell (30 cycles per minute) during the determination of electrophoretic mobility. But this technique also becomes inadequate if the solid concentration exceeds 60 %. Even sedimentation measurements (sediment height) lead to erroneous results. Indeed, the study of highly concentrated suspensions shows that the sedimentation speed becomes very much smaller than that of corresponding diluted suspensions (Stokes equation). In fact, stability measurements of concentrated suspensions do not exist. Some authors apply the drawing off technique which consists of introducing the concentrated suspension in a test-tube and drawing off a part of the suspension at two different levels after a given sedimentationmore » time. The inconvenience of the technique is that it cannot be used with suspension concentrations exceeding 60%. We intend in this paper to apply penetrometry in order to obtain information both on the stability and the fluidity of highly concentrated coal in water slurries.« less