Patent ID: 7655097

Claim:
A process for continuously washing solid particles comprising: (1) feeding solid particles into a washing tank from an upper portion thereof and allowing the solid particles to gravitationally sediment, and forming a high-concentration zone of the solid particles in the washing tank, wherein a concentration of the solid particles in the high-concentration zone is 15-50% by volume, wherein the high-concentration zone is stirred by a stirrer, the stirrer having a disc-form stirring blade, wherein a rotation speed of the stirrer is controlled to a speed in a range of 0.84 to 5 m/s, in terms of a peripheral speed of its tip end, and wherein the stirring is made so as to form circular flows in the high-concentration zone by the stirrer, the stirrer comprising a stirring shaft extending, in a vertical direction and a plurality of stirring blades fitted to the stirring shaft along the vertical direction; (2) feeding a washing liquid into the washing tank from a bottom portion of the washing tank so that a part of the washing liquid fed forms an upward flow; (3) bringing the solid particles into counter-current contact with the upward flow of the washing liquid to wash the solid particles; (4) discharging the washed solid particles as a slurry together with a part of a remainder of the washing liquid; and (5) separating the washed solid particles from the slurry, wherein a height of the high-concentration zone, from a bottom of the washing tank, is 0.5 to 0.95 times a height, from the bottom of the washing tank, of an outlet of the washing liquid from the washing tank, after the washing liquid has been used to wash the solid particles.