Analysis of the effect of wash water reduction on bleached pulp characteristics

Abstract

The main objective of this study was to analyse cost reduction by reducing the use of fresh water in the cellulose bleaching process and to make it easier to obtain water in a closed circuit. Eucalyptus oxygen delignified industrial pulp was used. The pulp was bleached 10 times in the D(E+P)DP sequence in the same conditions. Counter current washing was used in the bleaching stages, and each sequence was carried out with different wash factors: 9, 6, 3, and 0 m³ of distilled water/ton of oven dry pulp. The goal was to reach brightness of 92 ± 0.5% ISO. The results showed that there was a chemical oxygen demand (COD) increase and brightness reversion, but the kappa number and viscosity did not change. The apparent colour was increased by increasing COD in the effluent during the cycles and by decreasing the wash water. Up to 3 m³/t of water was tolerable and even recommended to wash pulp. Nine cubic metre per tonne of fresh water is most commonly used in the industry, so water savings make the implementation of the process possible.

Keywords:

• cellulose
• bleaching
• water reduction
• cost

Acknowledgements

The authors are grateful for the support of CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico – Brazil).