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The way in which the disintegration process is influenced by the addition of substances to aid grinding and by pretreatment of material for grinding was investigated using coal of a series of coal ranks. Tests were carried out using a single grain impact apparatus, a laboratory oscillating mill, a plant ball mill, a toothed colloid mill and a technical school ball mill. Methanol, ethanol, ethylene glycol and lignin sulphonate were applied for wet grinding and triethanolamine (TEA) for dry grinding. Pretreatment of the coal consisted of varying periods of storage in methanol and in water. The mode of action of grinding additives in coal grinding is determined by the surface structure, the cavity structure, the degree of cross-linkage of the coal macromolecules, and also the influence of the additives on the flow behaviour of the sludge of ground material. In wet grinding small additions of the grinding aids used bring about wetting of the entire coal surface and a reduction in the viscosity of the suspension of ground material. The resulting improved dispersion of fine material produced during grinding has a positive influence on friction and energy transfer within the grinding chamber and leads to a reduction in the energy needed to achieve disintegration during the grinding process. According to coal type and duration, storage of coal in liquids (methanol and water) causes swelling processes within the coal matrix, which are linked to the formation of new microfissures and a weakening of the bonds between coal and mineral intergrowths. In subsequent grinding this brings about a reduction in the energy requirement and an increase in the proportion of fine material and ash concentration in the coarse grain fractions.

Additional information

Authors: LEONHARDT J, Bergbau-Forschung GmbH, Essen (DE)
Bibliographic Reference: EUR 12076 DE (1990) 91 pp., MF, ECU 4
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