デカンタ型遠心分離機による土壌微細粒分の分級  [in Japanese] SEPARATION OF A FINE-GRAINED FRACTION FROM SOIL SLURRY BY DECANTER CENTRIFUGE  [in Japanese]

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Abstract

本研究は,デカンタ型遠心分離機による微細粒分の分級の実態と操作因子(RCF, feedのDS, feed体積流量)が分級性能,特に50%分級径とUFへの質量回収率に与える影響を詳細に把握することを目的とした.<i>Q</i><sub>feed</sub>/Σ, すなわちfeed流量を遠心沈降分離面積Σで割った値に対して質量回収率<i>E</i><sub>UF</sub>の値は直線的に減少すること,<i>Q</i><sub>feed</sub>/Σに対して50%分級径<i>D</i><sub>50C</sub>の値は直線的に増加すること,<i>E</i><sub>UF</sub>値は<i>D</i><sub>50C</sub>に対して直線的に減少することが判明した.<i>D</i><sub>50C</sub>近傍の細粒分を多く含む土壌では,<i>E</i><sub>UF</sub>値のバラツキが大きかった.実験から得られた<i>D</i><sub>50C</sub>の値は自由沈降を仮定した遠心沈降の理論値と大きく異なった.土壌微細粒分の遠心沈降では,(a)干渉沈降の影響を大きく受けること,(b)微細な粒子が球形と異なる形状であること等が推察された.

 The objective of this study was to develop a better understanding of the effects of operational parameters of decanter centrifugation, such as dry solid ratio (DS), sigma value (Σ), and volumetric flow rate of feed (<i>Q</i><sub>feed</sub>), on separation performance, especially corrected cut size (<i>D</i><sub>50C</sub>) and particle recovery to underflow (<i>E</i><sub>UF</sub>), with regard to separating a fine-grained fraction from soil slurry. The sigma value (Σ) represented the area of a settling tank capable of the same separation performance in the gravitational field.<br> As a result of this study, following observations were made; 1) the values of <i>E</i><sub>UF</sub> declined in a linear fashion with <i>Q</i><sub>feed</sub>/Σ, 2) the corrected cut sizes (<i>D</i><sub>50C</sub>) increased in proportion to <i>Q</i><sub>feed</sub>/Σ, 3) the value of <i>E</i><sub>UF</sub> declined in a linear fashion with <i>D</i><sub>50C</sub>, 4) <i>D</i><sub>50C</sub> obtained through this experimental study differed significantly from the theoretical values calculated on the basis of the sigma values by assuming free settling. It was inferred that (a) centrifugal separation performance was strongly influenced by hindered settling even if feed slurry was relatively low concentration (11-20%DS), and (b) the smaller the grain size, the larger its percentage of platy and cylindrical particles.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research)

    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 74(3), 142-151, 2018

    Japan Society of Civil Engineers

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