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Light-ECF Bleaching - Why Implementing Green Bleaching Practices is a Real Plus for Pulp Production.

Authors
Alexis MĂ©tais, Jean-Christophe Hostachy

Introduction
Beginning of 2011, 22 pulp mills worldwide, producing hardwood and/or softwood bleached pulps, use ozone in their bleaching sequence. And Oji Paper just contracted a greenfield kraft pulp mill including an ozone bleaching stage to be built in Nantong (China). Start-up of the pulp mill is scheduled at the end of 2012.

The choice of ozone was either motivated by ecological constraints or by the economic goal to decrease chemicals costs: both targets can be reached simultaneously with ozone bleaching. By choosing ozone, pulp production leaders such as International Paper, Fibria, Nippon Paper, Mondi and Sappi have already improved product quality, environmental and process performances.

Ozone bleaching was first used in 1992 in Lenzing (Austria) and its development was strongly related to the emergence of Total Chlorine Free bleaching (TCF). Until today, some people considered the use of ozone is dedicated only to TCF-bleaching… But the first Light-ECF fiberlines (including both chlorine dioxide and ozone) already appeared during the 90s in order to significantly reduce the operating costs of the bleaching sequence1 and increase effluents quality. Today, the positive environmental impact of ozone bleaching concerning water load and discharge is well established. Compared to conventional ECF bleaching such as DHT-OP-DD, an ozone-based bleaching sequence Ze-DD decreases:

- Total water consumption by 23% and consequently the total effluent flow by 30%2;
- COD discharge by 39%2;
- AOX discharge by 50%2;
- Colour discharge by 60%3.

Explaining why ozone bleaching induces bleaching costs savings is one of the goals of the present paper. But the question of pulp quality should be assessed first.

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