Fiber pulp bleaching method for bleaching fiber pulp from recycled used paper materials

摘要

To increase the whiteness of paper fiber pulp(P), the watery mixture (S) passes through a process stage (2) before bleaching (3), where a gas (G) is introduced which has an oxygen content significantly above the oxygen level in air. The gas treatment stage (2) has a duration of at least 5 secs. The gas (G) has an oxygen content of max. as high as the oxygen gas (G') used in the bleaching stage (3). The watery mixture (S) is eddied in the preparation stage (2), with the mixture (S) and gas (G) flowing against or across each other. The watery mixture (S) has a solid matter content of at least 20% during the preparation (2) and bleaching (3) stages. The mixture (S) is heated before or during the preparation stage (2) by the introduction of a hot gas (G), which is composed of steam and more than 20% oxygen. Oxidized chemicals are used in the bleaching stage (3) with pref. peroxide. The bleaching stage (3) operates at an absolute pressure of at least 1.5 bar.