N. American Mill Experience With High Temperature Peroxide Bleaching of MOW, 1997 Pulping Conference Proceedings

In bleaching mixed office waste the main challenge is the large variations in the quality of the incoming raw material. The raw material can contain from almost none to more than 15 % mechanical pulp and also some per cent un-bleached kraft fibers like OCC. The unbleached brightness can vary between 60 and 78 % ISO and the color number (b* value) between 5 and 15. The target is to obtain brightness levels of +82 % ISO and a low color shade (b*<3) in="" the="" final="" pulp="" and="" no="" unbleached="" kraft="" fibers="" should="" be="">

Our bleaching system is based on a high temperature peroxide stage followed by a reductive stage has proven to very well level out variations in the quality of incoming material. The process can constantly deliver a product with a final brightness over 82 % ISO, no visible unbleached kraft fibers and a low color shade. After several years of development work in the laboratory we have now been able to confirm the results in two US MOW mills. The mills are utilizing the high temperature peroxide process (PHT) in combination with either FAS or hydrosulfite.