Patent ID: 7229527

Claim:
A method for controllably thickening a pulp comprised of a low consistency fiber suspension, said method comprising the steps of: introducing a pulp comprised of a low consistency fiber suspension into a pre-thickener apparatus at a feeding pressure, the pre-thickener apparatus having a perforated filter surface, a shaft and a cleaning member attached to the shaft so as to define a space between the shaft and the cleaning member, removing liquid from a portion of the pulp through the perforated filter surface in said pre-thickener apparatus by means of the feeding pressure of the pulp into the pre-thickener apparatus to form a thickened pulp, a filtrate, and an unthickened pulp, allowing a layer of the thickened pulp to be formed on the perforated filter surface of the pre-thickener apparatus, wiping the layer of the thickened pulp off the perforated filter surface of the pre-thickener apparatus with the cleaning member to prevent a permanent precoat pulp layer from forming on the perforated filter surface by pushing the layer of the thickened pulp by the cleaning member in an essentially axial direction along the perforated filter surface to the discharge end of the pre-thickener apparatus to thereby provide an open portion of the perforated filter surface behind the cleaning member onto which unthickened pulp may be deposited, simultaneously while wiping the layer of the thickened pulp off the perforated filter surface allowing the non-thickened pulp to flow through the apparatus from the feeding end to the discharge end via the space defined between the shaft and the cleaning member, discharging from the pre-thickener apparatus the filtrate and the thickened pulp wiped from the perforated filter surface by the cleaning member, guiding a part of the non-thickened pulp to the open portion of the perforated filter surface behind the cleaning member that was provided during wiping of the perforated filter surface; regulating the flow speed of the pulp in the pre-thickener apparatus by means of valves for the filtrate and the thickened pulp; and controlling the thickening of the pulp in response to input power or input torque of the cleaning member or in response to a pressure difference prevailing over the filter surface.