Optimizing birch chips for kraft pulp cooking

This study investigates the possible benefits of treating Scandinavian birch chips for kraft pulp cooking with one commercially available destructuring device, namely BMH Wood Technology's Chip Optimizer. Effects on cooking and penetration characteristics as well as on bleaching response and physical properties were studied under laboratory and pilot conditions. Treating chips with the Chip Optimizer resulted in better cooking liquor penetration, easier and faster cooking, improved screened yield, much less reject and slightly improved bleaching response. Reject dropped by 60-75% and screened pulp yield increased by 1-1.5% points. Savings of 5-10% of active chlorine are possible in bleaching. The effects become greater when a greater proportion of the total chip flow is treated. Not only the overthick chips but also "accept" sized chips clearly benefit from the treatment. Up to 55% of the total sample was treated with no effect on physical properties, but treating the total sample simultaneously seemed to impair the physical properties of the fibers. Treating the whole chip flow together with single Optimizer settings is not, however, the optimum way to carry out the treatment. No attempt was made in this study to optimize treatments of different fractions.