Chip Quality Effects in Mechanical Pulping - A Selected Review, 1996 Pulping Conference Proceedings

John R. Wood

PAPRICAN

Literature and previously available chip classification information have been reviewed to summarize knowledge on the effects of chip quality in mechanical pulping and make recommendations for the future. Since refiner residence time is about a second, uniformity, over short periods, of chip size classification, bulk density and wood source is the most important attribute of a chip furnish. For Northern softwoods there is no clearly demonstrated effect of chip size independent of wood properties. Chip size should be chosen to facilitate similar size chips from all chippers and to prevent size segregation and resultant feed variations. There is, however, a reported advantage in removing a small oversize and undersize fraction. It is recommended that two classification fractions, a small and a large, preferably from a thickness classifier, be used to follow chip properties, rather than an accept fraction between two sizes, which is less precise, and misleading. Results should be used to characterize wood from different sources for separation and proportioning to refiners. Inadequate mixing, chip segregation by size, and chip damage should be minimized in storage and handling. Future work is necessary to distinguish chip size and wood property, including seasonal, effects, and to improve mixing.