No stranger to change

Pulp & Paper, Feb 2005 by Shaw, Monica

The No. 97 paper machine at Stora Enso's Kimberly, Wis., mill, ups the pace with its 2004 rebuild, optimized for grade and speed performance like the recently rebuilt No. 96 machine

Stora Enso's Kimberly, Wis., mill is no stranger to change. From ownership transitions to changes on its three paper machines, the mill continues to adjust its approach to papermaking for competitive domestic and international markets.

The Kimberly, Wis., mill is another important stop on Stora Enso's fast-moving investment plan-known as PEP (Profit Enhancement Program)-that is geared toward optimizing paper machines to produce specific grades, as Pulp & Paper described in the July 2004 issue. As the table on p. 31 of that issue showed, the mill's No. 95 paper machine transitioned its grade structure from coated groundwood to coated specialties, while a $13-million rebuild has positioned the No. 96 paper machine to enter the coated free-sheet (CFS) market (see sidebar, p. 29).

With the No. 96 paper machine focused on a narrower basis weight segment, there was an opening for the No. 97 paper machine to be moved into heavier-weight, higher-contribution CFS grades. As part of PEP, a $23-million pulp conversion project-including a wet lap pulp machine at Stora Enso's Wisconsin Rapids, Wis., mill-would provide hardwood pulp for the free-sheet capacity at Kimberly, where new wet lap pulp makedown equipment would support its use. Also, a rebuild of Wisconsin Rapids' No. 16 paper machine allowed that machine to optimally produce the heaviest-weight CFS for Stora Enso.

With two off-machine coalers, three supercalenders, and two winders, the No. 97 paper machine line had more than enough finishing capacity, so the focus became the paper machine. Built in 1988, the 223-in. trim width Voith machine was speed limited, and its equipment was not tailored to efficiently produce heavier grades.

"One of the goals of the PEP project is to maximize the production capability of key assets so that we can do more with fewer paper machines," describes Paul Wochinski, engineering manager for the No. 97 paper machine rebuild. "We had a significant amount of grade duplication between the No. 16 and the No. 97 paper machine that needed eliminating so we wouldn't require so many grade changes each day on both machines."

To tailor the No. 97 paper machine to make medium-weight CFS at higher speeds, a $24-million upgrade was planned as part of PEE Taking place in May 2004, the upgrade included a new headbox, shoe press, and size press, as well as changes in the dryer section.

Maximizing the machine

For the rebuild, Stora Enso purchased a package from Metso, with a drives and PLC upgrade from GE. The choice of Metso was predicated upon the practicality of dealing with one supplier, plus the flexibility of that supplier's equipment.

"We spoke with three vendors, but Metso brought an offering that was a complete package as opposed to segmented parts, and we saw single source supply as very positive," describes Wochinski.

To correct hydraulic limitations on the No. 97 paper machine's headbox, a new dilution control headbox was installed with an Andritz low-consistency system as the second recirculation loop. The headbox would provide improved, flatter sheet profiles to achieve quality requirements and would support a speed increase from 3,700 fpm to 4,200 fpm.

According to John Ryan, No. 97 paper machine rebuild project manager, changes made to the former were "very, very minimal but geared at better performance at higher speeds." The changes included replacement of old "art foils" with conventional gravity foils and modification of the vacuum deflector in the S-wrap section of the Voith former.

The No. 97 paper machine press section was comprised of four presses, the fourth of which did not provide "very much in terms of water removal, as is typical of that position," according to Jim Purchatzke, process manager for the rebuild. He also notes that the fourth position was where the majority of breaks were occurring. To support better water removal at the targeted speeds and improve efficiency by eliminating breaks, a new SymBelt shoe press was installed as part of the rebuild. "We're not really doing anything unique in terms of the shoe press," Purchatzke notes.

Modifications were also made in the dryer section to help support the higher I speeds and basis weights. No. 97 paper I machine has five dryer sections. After the main dryer section is the size press. The mill installed Metso's new coating color circulation system to supply the size press. As mentioned, flexibility was key in the equipment choice. Following the size press is the IR dryer, an air dryer, and another conventional double felted section.

During the rebuild, drying changes were focused on runnability and avoiding bottlenecks. The ventilation system was improved to increase exhaust capabilities of the hood, and the air systems technology in the unirun sections was upgraded. Also, the No. 97 paper machine is now ropeless through the main dryer section, although ropes are required through the size press. ;