Eo Pre-Bleaching as an Effective Means to Delignify Pulp Prior to the Bleach Plant, 1995 Pulping Conference Proceedings

Scott E. Johnson

Air Liquide America Corp.

Derek Hornsey

Canadian Liquid Air

Michel Epiney

Canadian Liquid Air

The utilization of oxygen delignification by various techniques such as the conventional high or medium consistency stage or the alternative EO Pre-bleaching stage is evaluated. The potential of the EO Pre-bleaching stage to effectively delignify pulp prior to the bleach plant has been proven on the mill scale with significantly lower initial capital cost requirement. Methods to compensate for the impact of oxygen delignification on associated mill processes such as recovery boiler operation, evaporators, and kiln operation is examined based on techniques proven on mill scale. The EO Pre-bleaching stage is effective in reducing the Kappa# of pulp by as much as 35% depending on the alkali charge, reactor temperature, pressure, and retention time. The conditions in this stage are similar to those currently used in bleach plant alkaline extraction stages. In some cases existing equipment from existing bleach plant stages may be applied in the EO Pre-bleaching stage with overall positive impact on the pulping and bleaching process. The estimated percentage increase in recovery boiler heat and solid loading as a result of oxygen delignification are in the ranges less than 1% and 2 - 4%, respectively. Techniques are presented which are currently utilized on the mill scale and can be applied to compensate for the increases in recovery cycle loading as a result of oxygen delignification.