Rheological and Transport Analysis of Micronized Coal-Water Suspensions Prepared in Conventional and High-Speed Stirred Ball Mills

Abstract

The purpose of this paper is to compare the rheological properties of micronized coal-water suspensions (CWS) prepared in different grinding devices. This hypothesis is based on the theory that the interaction between particulate phase and the nature of forces prevailing in the mill affects the particle size distribution and shape of particles. The grinding devices used were conventional tumbling ball mill and high speed stirred ball mill having pin and disc option. Flow properties of the suspensions were found to differ appreciably at desired fineness of grind (d80). This was explained on the basis of packing density and morphology of particulate phase. Typically, the high-speed stirred ball mill produced broader particle size distribution yielding distribution modulus (DM) of 0.213 as opposed to 0.384 for the conventional mill. Rheological data collected on a typical distribution constructed based on the Farris analysis revealed that suspensions were most viscous for particles ground in the pin device followed by the disc device and the conventional mill. A simple theoritical analysis has been presented to estimate the shear rate in the vicinity of the tips for the stirred ball mill under typical operating condition for this type of application. This resulted in an estimate of 680 sec−1.