Comparison of Various Hardwood Kraft Pulp Pre-Beaching Techniques, 2007 Engineering, Pulping & Environmental Conference

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In an effort to reduce bleaching costs, five distinct pre-bleaching methods were examined with the same starting hardwood Kraft brownstock pulp. Each of these pretreated pulps was subjected to a D(EP)D bleaching sequence. A D1 brightness curve as a function of the percent applied chlorine dioxide was obtained for each of these pre-bleaching methods and for a baseline pulp sample. The amount of chlorine dioxide required to obtain a D1 stage brightness of 79.1% ISO was calculated for each of these pre-bleaching methods and the net cost savings for each sequence was determined. Pre-bleaching methods that produced a net savings in the D1 stage were also subjected to a four stage bleaching sequence of D(EP)DD to an 89%ISO brightness. Net cost savings resulting from pretreatment of the fully bleached pulps was also determined. These pre-bleaching methods have either been reported in the literature separately or are combinations of two different methods reported separately. The methods examined included mild acid pretreatment, xylanase enzyme pre-bleaching, brownstock peroxide pretreatment, acidic brownstock peroxide treatment, and xylanase enzyme followed by acidic peroxide pretreatment. Enzyme pretreatment and small applications of acidic peroxide pretreatment were found to result in net D1 stage cost savings at 79.1% ISO brightness. Only enzyme pretreatment resulted in a net savings at 89% ISO.