Optimization of ECF Bleaching, 1998 Pulping Conference Proceedings

Optimizing bleaching chemical consumption in an ECF sequence should consider the following key factors:

- what species of wood is being bleached (hardwood or softwood);
- has the pulp been delignified with oxygen prior to ECF bleaching;
- the amount of black liquor carryover to the first stage;
- the number of bleaching stages and applications of oxidizing chemicals;
- the final brightness required.

A good tool for comparing mill performance to literature or laboratory references is the kappa factor in the first stage of bleaching and the development of kappa factor throughout the sequence. The kappa factor can point out where in the bleach plant less than optimum performance is being achieved.

When comparing mill performance to reference values, the data should be normalized to the unbleached kappa no. and the final brightness.

Non-optimum performance is often characterized by:

- high kappa factor in the first stage of bleaching;
- high residual in the first stage of bleaching
- low extracted kappa no.;
- high D1 brightness in a 5-stage bleach plant

Mill case examples show bleaching costs can be decreased by ~ 10-15% by optimizing performance.