Method and apparatus for treating waste paper

Claim 1

Apparatus for sorting dissolvable fibrous material from non-dissolvable material in waste paper, the apparatus comprising: an elongated cylindrical steeping drum mounted for rotation about its longitudinal axis, said axis being oriented substantially horizontally, the steeping drum having a circumferentially closed wall with an axial inlet at one end for receiving waste paper and an axial outlet at the other end from which the steeped material discharges, the interior of the steeping drum having a plurality of circumferentially spaced, substantially longitudinal ledges for lifting and dropping the waste paper as the drum rotates during the steeping; means for feeding waste paper into the axial inlet of the steeping drum; means for adding water to the waste paper to be steeped; means for rotating the steeping drum about its longitudinal axis, the rate of waste paper feed into the drum, the specific orientation of the longitudinal axis of the steeping drum, the rate of addition of water to the waste paper, the specific orientation of the ledges within the drum, the configuration of the outlet and the speed of rotation being coordinated to yield a steeping time of between 10 and 120 minutes at a substance density of between 10% and 40%; a mixing chamber for receiving the steeped material after it is discharged from the outlet of the steeping drum; means for adding diluting water to the steeped material in the mixing chamber, the mixing chamber comprising a rotor for rapidly mixing and circulating the steeped material and diluting water in order to obtain a fibrous suspension, the rate of addition of diluting water to the steeped material in the mixing chamber being coordinated with the rate of steeped material feed into the mixing chamber to achieve a substance density of between 2% and 6%; and pressureless screening means for sorting the fibrous suspension from the non-dissolvable material, the screening means being located at a level lower than the mixing chamber whereby the material may be transferred by gravity alone from the mixing chamber to the screening means.