Cost- Effective Retrofit of Existing Bleach Plants to ECF and TCF Bleached Pulp Production Using a Novel Peroxide Bleaching Process, 1995 Pulping Conference Proceedings

Debra Breed, Lewis D. Shackford

Ingersoll-Rand Company

Elenice R. Pereira, Jorge L. Colodette

Universidade Federal de Viçosa

With current known technology, the investment required to modify existing bleach plants to suit them for application of “chlorine-free” bleaching sequences is quite high. It is thus desirable to develop techniques that permit the use of existing bleach plant equipment for new bleaching sequences. A new peroxide bleaching process has been developed which is designed to use existing equipment in the mill with minor additions of pumps, mixers, and small reaction tubes. The process denoted as high temperature peroxide (PHT ) consists of two steps: first, applying peroxide under conditions of high temperature (105°C - 130°C) and moderate pressure for a short period of time (10-30 minutes) followed by atmospheric retention in an existing bleach tower. This technology results in minimal use of peroxide to achieve significant delignification and brightening at the beginning of a sequence or high brightness gain at the end of a sequence, to produce high quality ECF and TCF pulp at minimal investment. Metals removal is key prior to the PHT stage, with chelant dosage, retention time, temperature and consistency being important variables in this treatment. Simple evaluation of the pulp metal profile after chelation is shown not to be a complete tool for predicting bleaching results. The PHT process is evaluated as an attractive retrofit or additional stage in both ECF and TCF bleaching sequences, with and without ozone. In ECF sequences, the application of PHT technology provides a supplemental oxidizing power for mills with limited ClO2 generation capacity. In TCF bleaching the PHT stage helps to produce an 88% ISO TCF eucalyptus pulp without ozone at a minimal capital investment. With a reasonable capital...