湿式選別法を用いた石炭燃焼灰からの中空球形粒子の回収

抄録

Fly ash is a by-product in coal power plants and a rich source of hollow and spherical particles. Hollow and spherical particles having density less than 1 g/cm³ are known as cenospheres. Their concentration in coal fly ash is around 1%. Particles are widely used as fillers and insulators with high performances in rubber, plastics, oil industry, space industry, glass steels, etc. due to their shape, specific surface, excellent physical and chemical properties; as a consequence, their value is relatively high. However, hollow and spherical particles are filled up with N₂ and/or CO₂ gas bubbles so their densities can vary from 0.6g/cm³ to near or greater than 2.0 g/cm³. Fly ash can consist of more than 80% hollow and spherical particles having particle diameter less than several hundred μm and density less than 2.0 g/cm³, but there is no efficient and economic way to selectively recover them.
The authors study on the recovery of cenospheres and hollow and spherical particles having density more than 1 g/cm³ from coal fly ash using a two-inch hydrocyclone and laboratory/pilot scale Mozley multi-gravity separator(MGS). A two-inch hydrocylone having 6.4 mm of spigot diameter was used to effectively concentrate cenospheres in overflow product. A very small amount of cenospheres having density less than 1 g/cm³ were recovered as a float of overflow product. Underflow product and overflow product without cenospheres were supplied to MGS and the influence of MGS parameter such as drum rotation speed and wash water rate was studied. As a result, 54% of hollow and sphercal particles having 2.08 g/cm³ of density and 61.6 μm of median diameter in underflow product was recovered as MGS lighter product and 17% of hollow and sphercal particles having 2.19 g/cm³ of density and 8.4 μm of median diameter in overflow product was recovered as MGS lighter product. These results show that hollow and spherical particles having median diameter less than one hundred μm with middle density can be recoverd.