Open access publications in the SLU publication database

Abstract

In general there is an understanding that geometrical consistency of chips is desirable in the pulping processes (both for mechanical and chemical pulping). Scandinavian pulp mills normally communicate requirements for chip geometry to the producers through quality regulations and bonus penalty systems. To optimize their deliveries sawmills try to produce chips of optimal size and screen out undesired fractions, and as a standard procedure they re-chip oversized chips into acceptable sizes. This thesis evaluates the level of consistency of market chips and the possibilities to increase consistency. Studies were conducted in the value chain from the point of chip production in sawmills to the point of delivery at the pulp mill gate. The geometry of chips from a single sawmill is almost as uniform as that of chips made by a pulp mill and the geometry is relatively consistent over time. However the geometry differs among sawmills and the resulting mix can be expected to have low consistency. There are possibilities to increase total consistency by steering chips from different sawmills toward common geometrical targets. In 2001 an additional (fifth) screen was introduced in the SCAN-standard for measuring chip fractions, with the aim to increase possibilities to promote consistency. When constructing bonus penalty systems for the new standard it is important to take into consideration the effects the additional screen has on the classification result. Oversized chips that are re-chipped were found to differ from ordinary market chips in geometry, in addition to having high content of bark and defects.