Process for making paper products

摘要

During the prodn. stages for a paper material, using a fraction of recycled paper pulp, the acidification stage uses an injection of carbon dioxide into the pulp suspension at a point where the fractions are in the process circuit between the outlet of the pulper (15) for the used paper fraction and the mixing point where the pulp is mixed with fresh pulp. The second stage dilutes the pulp in at least two phases, using clean water which has been injected with carbon dioxide. The clean water is recovered from the papermaking machine or from an external supply such as from the pulp preparation stage and/or cleaned water recovered from other stages. The carbon dioxide is injected pref. at two points in the fraction treatment circuit, on leaving the pulper for the fractions and the end point of the treatment process. The second fraction processing stage has at least one phase where lumps are broken down and/or at least one complementary cleaning phase for the pulp delivered by the pulper (15). The first injection of carbon dioxide is to set the pH at an intermediate level for the grinding and/or cleaning phases. The second injection gives the diluted pulp a pH compatible with the pH level in force during the mixing stage (2). The diluted pulp has a pH value of 5.5-8.5 from the fraction treatment, and the intermediate pH value of the pulp during grinding and/or cleaning is 7.5-9.0 and pref. 8.0-8.5. The carbon dioxide is injected into one and/or more of the points of: Into the clean water used to dilute the fractions (18); into the clean water (20) for dilution at the outlet of the fraction pulper (15); into the clean water for final dilution of the fraction mixed with fresh pulp; into the pulp fraction on leaving the pulper (15) and before the following stages; or into the pulp fraction at the end of the processing but before mixing with fresh pulp. The carbon dioxide is fed by an initial dilution water feed on leaving the pulper to give a pH value of 7.5-9.0 and pref. 8.0-8.5 to the level at the grinder, and by a second dilution water feed between the grinder and the final stage to give a pH value for the diluted pulp equal to the level in force at the pulp mixing stage, where the fraction is mixed with the remainder of the cellulose pulp. The carbon dioxide is fed as a gas or a liquid, or partially a gas and partially a liquid.