Abstract
The general tendency in the pulp industry towards reduced fresh water consumption and minimum effluent causes major deposit problems in mills. Chemical pulp bleach plants are affected by several types of mineral deposits, the most frequent being calcite, calcium oxalate and barite. We present a coupled chemical process simulation of kraft pulp bleaching line, which handles chemical equilibria, together with dissolution and precipitation effects. The simulation could adequately predict formation of mineral deposits throughout a D0(EP)D1D2 bleaching line. Strategies to help reduce formation of calcium oxalate and barite scales could be evaluated. Partial substitution of sodium hydroxide by a magnesium source at extraction stage is anticipated to inhibit formation of calcium oxalate throughout the line. Also, using sulfuric acid instead of spent acid for pH regulation at D0 would reduce but not suppress barite deposits.
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