Comparison of ECF short-sequence bleaching processes for bagasse pulp

In this paper, first, three typical element chlorine-free (ECF) short-sequence bleaching processes, namely D0EpD, OpDEp and OpD, were comparatively investigated. Then, the difference in delignification rate between the chlorine dioxide delignification (D0) and the peroxide-reinforced oxygen delignification (Op) was revealed, and the effect of pre-delignification on the subsequent bleaching was analyzed. Finally, the AOX (Absor-bable Organic Halides) emission and the direct chemical cost during the bleaching were discussed. The results indicate that (1) D0 possesses high delignification selectivity; for instance, the delignification rate reaches 40% at a ClO2 dosage of only 0. 8% and continuously increases with ClO2 dosage; (2) Op can not only delignify the residual lignin in pulp but also remarkably improve the pulp brightness to a value much higher than that of D0 pulp; (3) OpDEp bleaching is more effective than D0EpD bleaching at the same chemical dosage in the subsequent bleaching because it may result in higher pulp brightness; (4) the final brightness of OpDEp bleached pulp is about 12 percentage points higher than that of OpD bleached pulp; and (5) at the same pulp brightness, the AOX emitted du-ring the OpDEp bleaching is only about half of that emitted during the D0EpD bleaching, and the direct chemical cost of OpDEp bleached pulp is 40.00 Yuan/t lower than that of D0EpD bleached pulp, which means that OpDEp bleaching is of higher environmental and economic benefits.