Improved Pitch Management with a New Washing System and TMP Upgrade at Norske Skog Albury

In August 2005 the Norske Skog Albury mill, (located in New South Wales, Australia), rebuilt its Thermo Mechanical Pulp (TMP) system to improve the quality of pulp made from Pinus radiata. The main targets for the project were an increase of strength properties and reduction of shive content by a rebuild of the screening system and the installation of an additional low consistency refining stage. To solve the mill's pitch problem and reduce the pulp's extractive content, a pulp washing system consisting of two screw presses, run in parallel, was installed after secondary refining. Suspended solids and fibre from the screw press filtrates are recovered in a separate fibre recovery system, using a pressure screen. Filtrate from the pressure screen is sent to a dissolved air flotation (DAF) unit where bentonite and polymer are added to assist in flotation. The extractive rich DAF solids are combined with other mill solids that go to solid waste disposal, whilst the treated filtrate is returned to the process water system. Fibre recovered using the pressure screen is returned to the process. The new washing system has reduced the COD and extractives content in the pulp and thus led to a significant improvement of availability and runnabil ty through reduced deposits on the newsprint paper machine. Mill operating data strongly suggest that when the extractives content is reduced to below a particular threshold, calender stack deposits on the paper machine are almost eliminated. The mill is further optimizing the fibre recovery system with the objective to selectively remove the detrimental extractives and keep the valuable fibres and fines in the system. This shall further improve pulp quality and reduce operating costs.