MILL EXPERIENCE USING A HOT ACID STAGE FOR EUCALYPTUS KRAFT PULP BLEACHING

摘要

Votorantim Celulose e Papel (VCP) has been running a hot acid stage (A) in Line B of its Jacarei mill, which used to operate with the O/OZ(DQ)(PO) sequence, since September 2000. The A-stage was placed right before the Z-stage and led to a decrease in pulp hexenuronic acids (HexA's) content from an average of 66 meq/kg to 27 meq/kg of pulp, a reduction of approximately 59%. The kappa drop across the A-stage was about 4.3 units, indicating a ratio of roughly 9 meq/kg HexA's per kappa unit. The implementation of the A-stage had a significant negative impact on Z-stage efficiency, but it has still been cost effective to run both stages. The active chlorine consumption in the bleach plant was reduced by about 13 kg/adt after the A-stage implementation. The incidence of oxalate scaling in the bleach plant and brightness reversion decreased significantly after the A-stage start-up. However, pulp refinability increased while tear/tensile strength were unaffected when measured at 36°SR. Closure of the A-stage significantly increased the level of metals in the digester washing zone while closure of the (PO)-stage increased the level of chloride in the bleach plant filtrate that returns to recovery, but not to a point that disturbed recovery boiler performance.