Cement, Energy and Environment July-Sep 2002

I A SUPERIOR VERTIC~L-ROLLER PRE-GRINDING MILL I S.C. Jain, Vice-President (Engg. Business) ACC Machinery Company Limited, Butibori, Nagpur In the drive for energy conservation in size reduction operations, pre-grinding mills are finding favour with Indian cement industry. The article describes a vertical-rolle/ pre-grinding mill (VRPM) which has proved its superior performance in grinding clinker. The mill, originally designed and developed in Japan, is current(v being manufactured indigenously. While three of them are successfully operating in the country in the last four years, three more are in the pipeline....Ed Introduction Pre-grinding involves use of a suitab le equipment before the conventional ball mill/tube mill to carry out size reduction in a more efficient way at larger particle-size range. In other words, while the input material size for the ball mill/ tube mill is less than 25 mm, it will become less than 3 mm after introduction of a pre-grinding system. After detailed research and development, combined with their own extensive experience, Nihon Cement Co Ltd, Japan, developed a superior Vertical-roller pre-grinding Figure 1 Vertical roller pregrinding mill mill. With transfer of the techno logy, ACC Machinery Company Limited, a wholly owned subsid iary ofthe Associated Cement Compani es Ltd (ACC) is in a position to offer this vertical-roller pre-grinding mill (VRPM). A deta il ed study has established the superiority qf this verti cal-roller pre-grinding mill' s e ffic iency in comparison to other ava il able technologies , and its suitability as a solution, both for exis ting plants to increase their grinding capacity and reduce power consumption , and for new plants seeking lower investments. Principle of the VRPM Clinker is fed through a central chute in th e VRPM where centri fugal force, combined with the rotation of the table, distributes the product over the table surface. The m table and the rollers then grind the material , which is then extracted from the VRPM by grav ity and a little he lp from a scraper. The grindi ng force is transmitted to a set of three rollers through a hydraulic system. Advantages • Non-airswept grinding and hence energy efficient. • Conside rabl e increase in g rinding capac ity as clinker grinding can be increased by more than 50 per cent and even up to I00 per cent. • More th an 15 per cent reducti on in power consumption qf the clinker grinding system. • Requires little maintenance. • Longer table-liner and roller li fe, > IOOOOhrfortab le liners and > 20000 hr for rollers. Salient features High- efficiency spherical roller grinding mechanism - The spherical rollers used in the VRPM provide highgrindi ng efficiency and a more stable operation. Spherical rollers also offer high compressive force as sliding contact between table and roller is increased and the shearing fo~cc that is generated is greater. Thus by the simultaneous compressive and shear forces, high efficiency grinding results. Grooved spherical roller - The centrifugal force generated by the rotation of the table spreads the material across the entire table surface in a uniform layer, where it is caught between the roll er and the tabl e Iiner segme nt s, and gets crushed before being carried to the outer circumference of the table. At ,..