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Hiroshima-shi, Japan

Nomura S.,Hiro Ohshingai 2 15 26 | Tanaka T.,Hokkaido University
Powder Technology | Year: 2011

A theoretical energy-size reduction relationship is derived for tumbling ball mills based on a solution of the integro-differential equation of comminution kinetics, in which the proportional relationship is applied between the grinding rate constant and the net mill power. The derived formula is similar to an empirical energy law, dW ∝dxr/xr i, where W is the specific energy input, xr is the particle size of product and the exponent i is shown to be a variable depending upon the ground material, the type of mill and the method to measure energy. Derived results are confirmed with reported data in reasonable agreement. Also, the Bond's energy law is examined and a method for the correction of the Bond work index is discussed. © 2010 Elsevier B.V. Source

Nomura S.,Hiro Ohshingai 2 15 26 | Callcott T.G.,P.O. Box 122
ISIJ International | Year: 2011

A theoretical study is made on the maximum injection rates of pulverized coal in ironmaking blast furnaces.The study takes account of two restrictive conditions which enable stable blast furnace operations to be maintained. One is to burn out the injected coal in the raceway zone and the other is to avoid the coal ash deposition on the blowpipe wall. The predicted maximum injection rates for some operating blast furnaces are about 190-210 kg per ton of pig-iron produced, which seem to be reasonable in comparison with experiences reported. Also, the influences of pulverized coal injection on the coke consumption, the production rate of pig-iron and the bosh gas temperature are examined in relation to some blast gas conditions such as the oxygen enrichment and the moisture addition. © 2011 ISIJ. Source

Nomura S.,Hiro Ohshingai 2 15 26
Powder Technology | Year: 2012

The present paper deals with a theoretical analysis of the dispersion properties, the dispersion coefficient and the Peclet number, of particulate material in a continuous ball mill. In the analysis, a dispersion zone where the brief dispersion of particles occurs, is postulated in the lower portion of an operated mill called the grinding zone. Consequently, the dispersion coefficient is derived to be a function of the size of the dispersion zone and the mobility of balls in the grinding zone and the Peclet number is a function of the dispersion coefficient, the axial mean velocity of material flowing and the mill length. Results derived from the theory are within reasonable agreement with reported data for dry and wet grinding operations, although minor variations are observed between theory and experiment. Additionally, the mill diameter and length are predicted to affect greatly the Peclet number, implying the importance of designing mill sizes for required product size distributions as the residence time distribution is dominated by the Peclet number. Further, a proportional relationship to predict the Peclet number is derived, which appears to be valid as confirmed with data regardless of the mill sizes tested. © 2012 Elsevier B.V. Source

Nomura S.,Hiro Ohshingai 2 15 26
Powder Technology | Year: 2013

A theoretical study is made on holdups of particulate material in continuous ball mills. The analysis is based on a consideration that holdups are influenced by the discharge properties at the mill exit, the existence of media balls interrupting the material to flow towards the mill exit and the dead space generated depending on the exit configuration. As a result, the linear relation between holdup and feed rate obtained experimentally is derived to be valid under specific discharge properties. Further, the effects of other operating variables such as ball filling, ball diameter, mill speed and slurry density on holdups are clarified based on physical backgrounds deduced from the theory. The derived equation to predict holdups includes three constants relating to the discharge properties of mill exit, the resistance of media balls against material flow and the dead space, respectively. These constants are estimated by the least square regression to give a best fit to data of various operating conditions within reasonable convergence between calculated holdups and experimental ones. Also, the effect of material kind on holdup is discussed using existing data. © 2012 Elsevier B.V. Source

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