METHOD AND ARRANGEMENT FOR TREATING FILTRATE AFTER OXYGEN DELIGNIFICATION OF CHEMICAL PULP COOKED TO A HIGH KAPPA NUMBER

摘要

A method to pulp cellulosic fibrous material including: alkaline cooking cellulosic fibrous material in a continuous digester vessel to produce a pulp having a kappa number in a range of 50 to 120; washing the pulp discharged from the digester vessel; treating the washed pulp in the presence of oxygen and alkali to remove lignin; washing the oxygen-treated pulp such that the kappa number is recued by at least at least 30; separating lignin from wash filtrate generated by the washing of the oxygen-treated pulp, and using the separated wash filtrate as a washing liquid in the washing of the pulp from the digester vessel.