Calcination of Lime
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In lime calcining in the vertical kiln, practical manufacture have been depended on the empirical technique, while much of the technical directions were abstractive.<BR>The economical lime manufacture requires fundamental research of the calcining process in kiln. Then, author offered the data that theoretically analysed the heat balance and the heat conduction in the hypothetical kiln has a strong resemblance to the practical lime kiln. Data that Azbe reported about time-temperature-size relationship ofs tone in simplified condition of the experimental kiln, seems that most of the reported condition are different from the practical state.<BR>Four ordinary processes of heat transfer in kiln are given so under : <BR>(1) Radiation from inner hot wall of the kiln.<BR>(2) Radiation from the hot gas around the stone.<BR>(3) Convection from the hot gas around the stone.<BR>(4) Conduction from surface to inner part of stone.<BR>Radiation heat transfer coefficient and convection heat transfer coefficient were calculated assuming the conditions of hypothetical kiln, and was tabulated.<BR>The smaller the size of stone, the smaller the void of stone packing in kiln and the larger velocity of gas by forced draft ; the larger the convection heat transfer coefficient in preheating and cooling zone.<BR>And besides, since the dissociated carbon dioxide increases the gas emissivity and the gas beam length, consequently radiation heat transfer coefficient is large in zones mentioned above. Radiation heat transfer is absent in cooling zone, because the gas emissivity is zero.<BR>The relations of capacity-stone size-calcining time, capacity-calcining time-calcining height and stone size-surface temperature in every zone were calculated by the equation, that was derived from the heat transmission in stone as stationary heat conduciion because for the dissociation of stone requires long time, and was illustrated. These figure gives the packing height in every zone, and it makes possible to estimate the kiln scale, kiln capacity by summation of these values.<BR>Example : Given the conditions, capacity 5t/m<SUP>2</SUP>, radius of ston 0.1 m, average temperature in kiln 950°C.<BR>Using the illustrated figures, height in calcining zone 5.1 m (Fig 3), height in preheating zone 0.9 m, hieght in cooling zone 2.5 m, 8.5 m corresponds to the total height of kiln.<BR>It may be concluded that the raising the calcining temperature, reducing the stone size and growing the kiln height are essential for increasing the lime production.
- 無機マテリアル学会の論文
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