Method and device for cleaning paper raw materials containing impurities

摘要

The cleaning of paper pulp suspensions contaminated by heavy components for the production of paper raw material, comprises supplying the suspension into a closed screening apparatus (2) by a feed pump (11) without further purification or deflaking from a repulping apparatus in a primary or secondary hydropulper (1). A process stream is allowed to pass through a cylindrical or conical sieve (3) with slit-shaped screening apertures and discharged as accepted stock stream while the substances retained at the sieve are discharged as rejected stream from the screening apparatus. The cleaning of paper pulp suspensions contaminated by heavy components for the production of paper raw material, comprises supplying the suspension into a closed screening apparatus (2) by a feed pump (11) without further purification or deflaking from a repulping apparatus in a primary or secondary hydropulper (1). A process stream is allowed to pass through a cylindrical or conical sieve (3) with slit-shaped screening apertures and discharged as accepted stock stream while the substances retained at the sieve are discharged as rejected stream from the screening apparatus. The suspension is fed in from the outside of the sieve in a radially inward manner. A drum pulper is used in combination with an immediately downstream drum screen as the repulping apparatus. The rejected stream is continuously discharged from the screening apparatus and is set in such a manner that its volumetric portion in the suspension flowed through the screening apparatus amounts to 20%. The rejected stream is partly supplied to a separation device (5). The heavy components are discharged from the separation device by a heavy component sluice. The accepted stock stream is refluxed into the screening apparatus. The rejected stream is diluted by the addition of purified reflux water in such a way that the consistency in the separation device reduces to 1.5% or less. The quantity of the rejected stream is measured before the addition of the liquid diluents and the quantity of the liquid diluents is set in such a manner that the size of the rejected stream corresponds to a specified value. In the separation device, the heavy components are mainly separated under the influence of gravity. Centrifugal forces are produced in the separation device and are lower than 5-times of gravity. The heavy components are discharged by the centrifugal forces. The residence time of the rejected stream is 5-20 sec. The diameter of the screening apertures is 1.5-3 mm. The slit width of the aperture is not greater than the diameter of the cord pieces to be removed. An independent claim is included for a device for cleaning of paper pulp suspensions contaminated by heavy components.