DZ STATE-OF-THE-ART ECF BLEACHING .1.

In the part, ozone has been considered to be a chemical that is used o nly for TCF bleaching. Today that is not the case, as a number of mill s are producing fully bleached, high strength pulps in ozone based ECF sequences. A particularly attractive solution consists of combining c hlorine dioxide and ozone in a single stage - (ZD) or (DZ). Several mi lls are operating with such ozone ''enriched'' chlorine dioxide stages . This paper reviews the history and economics of (DZ) or (ZD) sequenc es in a natural evolution from: (CD) (EOP) D E D D100 (EOP) D E D O D1 00 (EOP) D E D O (DZ) (EOP) D E D or O (ZD) (EOP) D E D O Z E D or O Z (EOP) D D The application of oxygen and ozone is such cases as these may allow for an unique use of the oxygen-rich vent gas from the ozone system. Application of this vent gas in the production of polysulphid e liquor for application in the digestor may provide further benefits to the mill as wood yield is improved.