FRACTAL ASSESSMENT OF FINELY GROUND LIMESTONE FOR FLUE-GAS DESULFURIZATION

Industrial minerals, those utilised for their physical properties and chemical content, e.g., limestone, often employ comminution during the ir preparation. A study was performed to investigate if the type of pu lveriser used to comminute limestone, a grade suitable for flue gas de sulphurisation, influenced its morphology and subsequent behaviour. Sa mples of the limestone were pulverised by three different devices a ha mmer mill, rolls crusher and ball mill. A narrow size fraction was rem oved from each of the products by elutriation. These fractions were th en subjected to sulphuric acid digestion tests, to simulate the desulp hurisation process. The tests revealed that the amount of acid consume d, i.e., limestone utilisation, varied with the pulveriser under study , with the hammer mill having the highest limestone utilisation. From SEM micrographs of the limestone fragments their overall geometric sha pe and fractal dimension were determined, using image analysis procedu res. The fractal dimension is a useful descriptive parameter for chara cterising boundaries that take on a randomly rugged appearance. Using the classical geometric shape factors, aspect ratio and circularity, o ne could not distinguish between the three comminution products. Howev er, fractal analysis was sensitive enough to differentiate between the fragments produced by the different pulverisers. Hammer milling produ ced the most rugged particles followed by rolls crushing and ball mill ing respectively.