Optimal Use of Hydrogen Peroxide to Design Low AOX ECF Sequences, 1995 Pulping Conference Proceedings

J. Devenyns, A. Renders, J. Carlier

P. Walsh

Solvay Interox

In order to meet standards set by ecolabelling and environmental legislation, the formation of AOX, COD, TSS and Color must be limited during pulp bleaching. D100 bleaching with C1O2 for the production of ECF pulp has become well accepted practice, but will face difficulties in meeting the proposed AOX limits. AOX formation during ECF bleaching can be progressively reduced by designing sequences that can evolve to increasingly substitute hydrogen peroxide for chlorine dioxide. Basic features of such hydrogen peroxide stages, such as metals control and the effect of consistency, temperature and pressure have been examined. A five stage D E D E D sequence for fully bleached softwood has been selected as the base case in the mill development scenario; reduced AOX ECF sequences that will be discussed in detail include Q (PO) D E D and D E D Q (PO), evaluating H2O2’s potential to substitute for C1O2 in prebleaching and final brightening. When applying H2 O2 in both prebleaching and final brightening areas according to Q (PO) D (PO), the amount of chloride ions introduced is low enough to be supported by conventional recovery technology, hence facilitating ECF mill closure.