Port Hawkesbury Paper implemented a comprehensive energy savings initiative when Stern Partners took ownership of the mill in 2012. Examples included pushing mainline refiner production for energy efficiency, deactivating the refined rejects screening unit operation and using bleaching chemistry to enhance brightness and strength. The team soon recognized that the deactivated rejects screens could be re-purposed by modernizing the screen room.
The screen room modernization project kickoff meeting occurred in early 2018 and the team included PHPaper, FPInnovations, and KSH (now Afry). Key elements for the project included:
- Deactivate the primary and secondary Radiclone fractionating hydro-cyclones for a minimum energy reduction of 1 MW. This energy reduction was based on deactivating the large centrifugal pumps required to pump the dilute feed pulp suspension (~ 0.8% Cs).
- Repurpose the reject screens as front screens, enabling the existing primary and secondary screens to operate effectively with narrow slot baskets.
- Enable a capacity increase of approximately 10%.
- Execute the project with minimal Capex investment.
- Maintain or increase both shive and coarse long fiber removal efficiencies, and maintain the overall mass reject rate within the range of 50% to 55%. This requirement ensures that the mill’s series rejects refining system will supply well developed long fibers to add both tensile and tear strength to the formed sheet.
- Mitigate risk by utilizing a phased approach, implementing the new technology on Line 1 screens and proceed with Line 2 screens once Line 1 is proven.
Following supplier meetings, it was concluded that the front screens followed by primary and secondary screens was a viable configuration, and the team recognized that the U-Twist technology opened the door to utilizing very narrow 0.12 mm slots in both primary and secondary positions (Figure 1). The supplier of this technology, Andritz, as well as FPInnovations screen fractionation experts agreed that when the front screens are fitted with 1.6 mm perforated baskets, the subsequent screening stages can operate successfully with the narrowest slots running in Canada on 100% softwood furnish!
Phase I was implemented in the fall of 2018 (Figure 2) and success was rewarded with a “go” decision for Phase II. The second phase allowed the mill team to deactivate all primary and secondary Radiclone fractionators and run with the completed modernized screen configuration.
Additional efforts have included the evaluation of more aggressive profiles on the 0.12 mm U-Twist slotted baskets and the installation of slightly larger 1.8 mm hole baskets on the front screens. This recent change has resulted in the full realization of all goals, including the stretch goals for production and energy reduction. Operating experience, together with numerous rigorous audits conducted jointly by PHPaper and FPInnovations, has demonstrated that energy savings of ~4% have been achieved while maintaining all quality parameters including tensile, tear, shive levels, drainage and fiber length distribution.
Authors: Jeff Woolsey1, Meaghan Woolsey1, Quanqing Zha2, Mark Frith1
1: Port Hawkesbury Paper, 2: FPInnovations
