Abstract: A method of the present invention separates lightweight grains from raw grains. In a primary separation step, raw grains containing the lightweight grains are whirled upward with primary air along the inner wall of the cylindrical section for allowing raw grains and part of the lightweight grains to stay in a certain flow area by frictional resistance with respect to the wall surface generated by whirl, and to drop into the conical section on the downside by their own weight. In a secondary separation step, secondary air is blown toward the raw grains dropping into the conical section in the primary separation step to blow the contained lightweight substances upward to the space in the cylindrical section. In a discharging step, raw grains with the lightweight grains removed are taken out from the conical section. A tertiary separation step for blowing the tertiary air may be added.

Abstract: A method of the present invention separates lightweight grains from raw grains. In a primary separation step, raw grains containing the lightweight grains is whirled upward with primary air along the inner wall of the cylindrical section for allowing raw grains and part of lightweight grains to stay in a certain flow area by frictional resistance with respect to the wall surface generated by whirl, and to drop into the conical section on the downside by their own weight. In a secondary separation step, secondary air is blown toward the raw grains dropping into the conical section in the primary separation step to blow the contained lightweight substances upward to the space in the cylindrical section. In a discharging step, raw grains with the lightweight grains removed are taken out from the conical section. A tertiary separation step for blowing the tertiary air may be added.