Brightening the bleaching process

The complexities of bleach plant chemistry sometimes lead to severe bleachability issues and increased costs. To stay competitive against state-of-the-art operations around the world, new bleaching strategies and solutions for aging kraft pulp mills are crucial. The bleaching optimization work by Shree-Prakash Mishra and the Smart Manufacturing – Fibre Production team at FPInnovations focuses on each stage of the bleaching process to help kraft pulp mills maintain a stronghold in the market.

With the recent volatility of bleaching chemical prices combined with an already competitive environment, every dollar counts. “Our team focuses on lowering pulp mills’ bleaching chemical costs by optimizing the bleaching process,” explains FPInnovations’ Scientist, Shree-Prakash. “When bleach plants of kraft pulp mills are not fully optimized, costs rise and pulp quality can be compromised.” FPInnovations is uniquely armed to resolve issues of the very complex, multi-stage bleaching process.

From wood chips to pulping to oxygen delignification and then to the bleach plant, each step has a significant impact on fibreline performance. Shree-Prakash believes that, “To provide an effective solution, we need to know and identify the problem.” The team takes a holistic approach to get at the root of the issue, where the entire fibreline is analyzed to fully understand the downstream processes and their impact on the bleaching operation. Not only do they draw from their own extensive pool of expertise, but they are also interconnected with FPInnovations’ fibreline specialists for research details such as digester variability and kappa, the type and quality of wood chips, and washing effectiveness. In a unique example, the team demonstrated that a chemical additive at the front end of the fibreline had a significant impact on the bleaching chemical consumption. With FPInnovations’ recommendations the mill was able to save approximately one million dollars per year.

Each mill has their own distinctive parameters that vary, particularly their operational strategies and performance. Historical bleaching data analysis in addition to laboratory evaluations determine mills’ optimal operating conditions. Recommended process changes tailored to the mill’s specific bleaching configuration and needs often include the best possible distribution of the bleaching chemicals to achieve the target brightness at the lowest cost.

Solutions might also include using proprietary technologies to decrease bleaching costs. For example, FPInnovations’ patented near-neutral brightening (NNB) technology maximizes the efficiency of bleaching by creating a final pH that is close to neutral; conditions in which chlorine dioxide brightening is most effective. In North America, six mills have successfully implemented NNB to improve final brightness, decrease caustic consumption, and eliminate the need for antichlor. Papricycle is another FPInnovations’ development that utilizes the alkalinity and heat value of the first extraction stage filtrate. Shree-Prakash suggests, “If a mill is capable of arranging a spare washer, Papricycle is worth re-considering, as it can save 25% to 30% of caustic in the first extraction stage.”

Additives can also be applied to further reduce bleaching costs. Enzymatic bleaching is being evaluated in various locations in the bleach plant targeting different aspects of the final pulp quality. FPInnovations’ bleaching team is equipped to help pulp mills screen a variety of xylanase and cellulase enzymes and to provide guidance on mill trials for bleaching chemical cost savings. They can also determine the precise impact of using enzymes on post-bleaching yield.

Over the years, the Smart Manufacturing – Fibre Production team’s expertise, research and technologies have helped kraft pulp mills reduce their bleaching costs typically by $500,000 to $1M per year. Currently, the team is exploring low-cost alkali substitutes in response to the significant rise in caustic soda. Ongoing research, alongside member collaboration, will continue to advance bleaching optimization and help pulp mills adapt to a continuously shifting market.

For more information about this project, please contact Shree-Prakash Mishra.