Process for producing bleached thermomechanical pulp (TMP) or bleached chemithermomechanical pulp (CTMP)

摘要

In the present invention, there is disclosed a process for producing bleached thermomechanical pulp (TMP) or bleached chemithermomechanical pulp (CTMP), including defibrating finely divided lignocellulosic material, such as wood chips, after pretreatment, and bleaching the resultant pulp in the form of a suspension with bleaching agent that enhances the anionic charge of the pulp fibers, whereafter the pulp suspension is subjected to cleaning treatment and then possibly further treated, for instance bleached, prior to delivering the pulp suspension to a paper machine or converting said suspension to storable pulp, characterized in that the defibrating of the lignocellulosic material is carried out with the aid of a) a refiner that has counter-rotating refining discs while using an extra high temperature (HTDD) with or without an immediate following refining stage; or b) a refiner that has a single rotating refining disc (s) with a single refining zone or with two parallel refining zones, while using an extra high temperature and extra high speed of rotation of the refining disc (s) (RTS) with or without an immediate following refining stage; and in that the cleaning treatment comprises first screening the pulp suspension and then hydrocyclone cleaning said suspension, wherewith the reject obtained in respective cleaning processes is treated individually and the treated reject returned to the advancing pulp suspension.