RECYCLING

At Green Bay Packaging's Green Bay, Wis., mill, a new cleaning system enhances a rebuild to produce 100% recycled linerboard

BY MONICA SHAW, Associate Editor

Cleaning Up Grade Improves Sheet Quality at Green Bay Packaging

One of the first totally effluent-free paper mills in the world, Green Bay Packaging's Green Bay, Wis., mill has a history of implementing advanced technologies to achieve its business and papermaking goals. In the late 1940s, the Green Bay mill was the first to use neutral sulfite semichemical pulping in its production of corrugating medium.

Over time, the mill continued its migration toward more environmentally sensitive papermaking, recycling old corrugated containers (OCC) in the late 1950s and achieving 100% mill closure in 1974 while producing 50% recycled corrugating medium. Since 1991, however, Green Bay has focused on the challenging production of 100% recycled linerboard at its totally effluent-free mill. And a series of recent modernization projects, with a concentration on the recycled fiberline, has focused on improving the mill's furnish quality.

In the late 1980s, Green Bay noted the growing demand for recycled corrugated packaging and decided that technology had evolved enough to produce a high-quality, 100% recycled linerboard grade for the corporation's northern box plants. Insistent that this new grade be of comparable quality to its virgin kraft counterpart, Green Bay committed to a $40 million capital expenditure program in 1988 to rebuild the mill and completely close the water system. By 1991, the mill had successfully produced the industry's first high-performance linerboard made from recycled furnish. In 1992, Green Bay became the world's first totally effluent-free mill.

As customer requirements for improved linerboard quality increase at the same time as raw materials quality decreases, Green Bay continues to implement new technologies. Most recently, Green Bay has focused on improving its linerboard quality by becoming the first mill in the world to incorporate modified reverse cleaning technology. In March of this year, the new cleaning technology was completely integrated at the mill with immediate positive results.

Customers, including Green Bay's internal box customers as well as external ones, have been impressed with the appearance improvements in the product. In addition, process improvements, such as the elimination of plugging in the new cleaners and an improved coefficient of friction (COF) that requires less anti-skid coating, have also been noted.

REBUILDING THE MILL. In 1988, the decision was made to rebuild the Green Bay mill and convert it from a producer of 50% recycled corrugating medium to 100% recycled linerboard. According to Jeff Walch, vice president and general manager of Green Bay Packaging's mill division, the decision was based on business, as well as technological, considerations.

"The rebuild project was somewhat driven by the fact that we are still a privately owned, integrated producer of linerboard and corrugated containers," explains Walch. "Our owners have always had a vision of making linerboard in the north for our box plants. If you go back to the 1980s, the only linerboard made in the north was a recycled grade that was inferior to virgin kraft. In the late 1980s, Green Bay Packaging decided that the technology had come far enough to make a grade of recycled linerboard that would compete head-to-head with virgin kraft."

The $40 million rebuild took place in three phases between 1989 and 1991 that corresponded with three mill shutdowns. The first two phases involved the replacement of old equipment as well as the addition of new equipment required for 100% recycled linerboard production; the third phase involved closing the NSSC pulp mill.

Phase One. The longest and most complicated phase of the mill rebuild took place in 1989 during a 34-day shutdown. As part of this phase, Green Bay installed several pieces of equipment, including a new primary headbox and Extended Nip Press (ENP) from Beloit. The fourdrinier table was also modified by AES. In addition, the mill reconfigured the first press section-a Black Clawson model-from a bi-nip press into a straight-through press.

Phase One also involved the rebuild of the paper machine dryer section using equipment from such companies as Valmet, Beloit, Sandy Hill, and Black Clawson. An entirely new ABS machine drive system was installed, as well as a new reel and rewinder from Beloit and a new Bailey distributed control system (DCS). The project marked the first use of AC variable felt roll driven dryers in the paper industry. In addition, the project included the first ever use of an AC variable winder drive that had an AC backstand on it.

As part of Phase One, Green Bay made several upgrades to its wastepaper cleaning system in preparation for the mixture of post-consumer OCC and double-lined kraft (DLK) clippings from its box plants. The upgrades included installation of Black Clawson X-Clone and reconfiguration of existing Contra-Clone cleaners.

Phase Two. In 1991, the Green Bay mill completely changed over to 100% recycled linerboard production. In the fiberline, dispersers were installed for cleaning the linerboard's top stock. On the paper machine, this changeover required a new secondary headbox from Beloit to take advantage of two-ply sheet forming technology. In addition, a Beloit BelBond top wire unit was installed to improve dewatering. By the time the machine rebuild was completed, the original 162-in.-reel trim Beloit machine was the operational equal of a new paper machine.

"This machine would compete very, very effectively with the newest machines in the marketplace right now," explains Walch. "It's not quite the show piece, because we don't have the brand new building, but I think we have made the conversion quite effectively."

The first linerboard was produced in February 1991 and was introduced to the market in March of that year. The mill began producing 550 tpd of the 100% recycled linerboard-a production rate that was maintained until cleaning system improvements allowed an increase. From the start, Green Bay was pleased with the linerboard's quality.

"The results we saw right from the beginning were exceptional, with strength numbers better than we expected," states Walch. "We have run continual comparisons between recycled linerboards, recycled corrugating mediums, and recycled corrugated shipping containers. Test results indicate excellent performance, particularly when using edge crush tests (ECT)."

Green Bay Packaging's box plants that use the Green Bay mill's linerboard are located throughout the North and Midwest, including Green Bay, De Pere, and Wausau, Wis.; Minneapolis/St. Paul, Minn.; Kalamazoo, Mich.; Fremont and Cincinnati, Ohio; and Tulsa, Okla. Through these box plants, Green Bay Packaging's 100% recycled linerboard is used by such external customers as Procter & Gamble, Fort James, Kimberly-Clark, and Whirlpool.

RECLOSURE OF THE WATER SYSTEM. The Green Bay mill operates with a completely closed water system. No process water is discharged from the mill, there is no connection to a municipal treatment plant, and there is no onsite treatment facility. This technology was first developed by Green Bay Packaging in the early 1970s while manufacturing 50% recycled corrugating medium. When the decision was made to rebuild the mill to manufacture 100% recycled linerboard, maintaining this technology was one of the primary design criteria. Reclosure of the process water system was accomplished in September 1992.

The original closure. In 1966, Green Bay started up a fluidized bed reactor to burn spent pulping liquor. With this step alone, the mill's biological oxygen demand (BOD) loading to discharge was reduced by 60%. However, closure took another eight years of work.

To close the mill, Green Bay had to determine exactly where every water source originated and where it discharged. To accomplish this, Green Bay measured the flow of its discharge as well as its city water usage. Next, the mill divided the process into subsections to determine the contribution of each area. Fortunately, the paper mill, pulp mill, wood room, secondary fiber plant, boiler room, chemical makeup building, and the new recovery plant all discharged into a common discharge line. However, tracing their individual points of entry to this common line provided yet another challenge.

Using dye tracers, Styrofoam beads, and visual observation downstream, Green Bay traced all discharge piping, much of which did not appear on its latest engineering drawings. The next step involved a rather unique application of an atomic absorption spectrophotometer purchased for byproduct analysis. All newly mapped discharge streams were injected with a tracer element. Sampling was done downstream, and, by determining the difference in concentration-knowing the original concentration, tracer flow, and the background level-flow was accurately determined.

The next step involved eliminating all river water from contact with the process water system. The machine basement trench was divided, and the vacuum pump cooling water (river water) was discharged separately. River water fire hoses were converted to city water, as were all river water flushing lines, and river water hoses for washup were abandoned. Next, all freshwater inputs to the process had to be discovered, documented, and measured.

Although closing the mill was difficult, the theory behind closure was simple. In Walch's words, "Water in had to equal water out." The sum of all the freshwater sources had to be equal or less than the evaporation in the dryer section. Even the smallest leak of high solids process water would seriously raise the BOD load. In 1982, much of the mill had to be converted to stainless steel construction to prevent corrosion.

With the further addition of vacuum separators, the mill had a recovery rate of 98% to 99.5% of all pollutants by 1979. The process water system leveled out with soluble solids between 6% and 8%, the temperature at about 165F, and suspended solids between 18 and 25 lb/1,000 gal. The sheet ash-the only outlet for system solids-leveled out at about 12.5%.

Reclosing after the rebuild. The process water system remained closed until February 1991, when process changes resulting from Green Bay's conversion to 100% recycled linerboard totally disrupted the balance between freshwater input and evaporation. In anticipation of these early problems, the mill negotiated a short-term solution with the Green Bay, Wis., municipal treatment plant. When the mill's inventory of water was too high, it could call the city and request permission to discharge.

From the beginning, chemical suppliers did not believe that Green Bay could make 100% recycled linerboard without freshwater. It was a recognized fact that starch required at least 49 lb of water for every 1 lb of starch, and that water had to be fresh to ensure that the cationic charge was not stripped. This equated to a requirement of 60 gpm of freshwater to make 500 tpd of linerboard. Retention aids-also cationic-required additional freshwater dilution of up to 10 gpm. Once again, Green Bay surveyed the mill to further restrict freshwater input.

However, Green Bay managed to find solutions to these challenges. Chemical suppliers brought in retention aids that either used no freshwater make down or could use process water. A process water seal system was installed, additional showers were eliminated in the press section, and all large freshwater wash-up hoses were converted to process water.

Since September 1992, Green Bay's process system has been totally closed. According to Walch, the mill personnel are responsible for this accomplishment.

"The people out in the mill are acutely aware of what it takes to remain closed," explains Walch. "They are the ones willing to put up with the challenges associated with this system, and they are the ones who understand why all freshwater is discretionary."

A NEW CLEANING SYSTEM. Despite the success of the mill rebuild and reclosure projects, Green Bay did not become complacent about its linerboard accomplishments. Instead, the mill continued to closely monitor the quality of its linerboard for appearance, strength, and other characteristics.

In 1994, when it felt that its linerboard had fallen behind the industry's appearance standards, Green Bay began examining how a new cleaning system might improve the appearance of its top stock. For Green Bay, however, the constant improvements required to stay competitive are a positive force.

"Everybody is working to make performance grades and the standard is being raised," states Walch, "People used to look at performance board as being board that had a cross-direction ring crush value of 2.0 times basis weight. Now, those numbers keep going up from 2.0 to 2.1 to 2.2. Overall, I think these higher standards are healthy for the industry in that it makes us better at competing with alternative packaging sources. So, a new cleaning system was just one segment of trying to make the highest-quality packaging materials that we can."

To reach its appearance goals, Green Bay began examining the latest cleaning equipment and techniques available in 1994. After conducting detailed trials, the mill chose to install a modified reverse cleaner, becoming the first mill to do so-and with excellent results.

Furnish. Green Bay's current raw material mix is 80% to 85% post-consumer OCC, with the balance in DLK, primarily from its own container plants. Since the installation of the cleaning system, the mill is phasing out its use of DLK, though whether it completely phases it out has not been decided. This is mainly because three of Green Bay Packaging's box plants are located near the mill. Depending upon supply and demand of each grade and the pricing involved, it may or may not be cost-effective to eliminate all of the DLK, according to Walch.

In 1994, Green Bay established its own brokerage division. Known as Bay Fibers, this division has been working to change the mill's raw material supply mix, selling off some of the material that it no longer requires.

"We are basically procuring post-consumer OCC," explains Walch. "We are not running any mixed waste at this point, but I think realistically the time may come that all mills utilizing wastepaper may find it necessary to use some percentage of a lower-quality grade than OCC, which would probably be a mixed waste grade."

The flexibility to handle variations in fiber supply was yet another concern for Green Bay as it sought a new cleaning system.

Selecting the new system. According to Doug Vandenberg, assistant production coordinator at the Green Bay mill, selection of the new cleaning system centered around two goals as the mill began examining systems in 1994.

"We were pulping DLK clippings for our top stock. First, we wanted to improve our sheet's appearance. Secondly, we wanted to realize some cost benefits by reducing raw material costs. Anything else that we improved-whether smoothness, strength, or coefficient of friction-would just be a bonus," Vandenberg says.

With appearance and cost savings as the two major goals, Green Bay identified four cleaning technologies for examination. The first was a cleaner based on the centrifuge principle-the Gyroclean by Fiberprep. The mill also wanted to take a closer look at dispersion cleaning, since the mill was successfully doing a small amount after the coarse screening and fine screening of the DLK. The third technology for consideration was fine slotted screening, while the fourth was other cleaning alternatives.

For throughput and mechanical reasons, Green Bay eliminated the centrifugal cleaner early on. Dispersion was also eliminated early in the selection process.

"Because we have a closed water system, we were very concerned about technology that might not totally remove contaminants from the stock, causing us to have to deal with them when we reuse process water for repulping the OCC," explains Vandenberg. "Dispersion breaks down contaminants and hides them, but runs the risk of leaving those contaminants in the system. Dispersion is also a high-cost technology."

At that point, Green Bay was basically left with a choice between fine screening and cleaning equipment. The mill tested one vendor's screening baskets with 0.004-in. slots. Though they performed well, Green Bay decided, after three months of trials, that the equipment did not fully meet its requirements.

"We were very pleased with the handsheets from the fine screens," says Vandenberg. "But, some hot melts and waxes are going to pass through 0.004-in. slots. We already had a coarse and a fine screening system, so it was going to be hard to justify going to finer slots while still not totally taking care of the problem. This made us somewhat cautious about going to corporate and saying we needed more fine screens."

Green Bay was then left to examine other alternative cleaning equipment to reach its goals. Ironically, the mill had shut down its Thermo Black Clawson X-Clone through-flow cleaners and Contra-Clone reverse cleaners in 1992 due to throughput and stringing and plugging problems. However, upon re-examination, factors other than equipment issues became apparent.

"In retrospect, it probably wasn't an equipment problem," says Walch. " It was probably an application problem having to do with where they were installed in our process and how the process was configured. However, some skepticism existed among our operators concerning this equipment."

Despite past problems, the mill embarked upon a series of detailed cleaner trials. The study involved
getting various cleaner models from different manufacturers and running them on Green Bay's process for 24 hours a day to evaluate cleaning efficiency as well as plugging susceptibility. Above all, Green Bay wanted to validate manufacturer's claims on its own turf.

"We tested one of the X-Clones we had previously used, we tested the Uniflow cleaners from Beloit, and we also tested forward cleaners for the removal of the fine sand and grit that we could see in our sheet," describes Vandenberg.

With the help of three co-op students, Vandenberg compiled handsheet after handsheet indicating linerboard appearance. During a period of five months, six different cleaners were tested. The cleaning systems, at best, proved to be only 90% to 94% effective. However, during this period, Thermo Black Clawson indicated that they would soon have a new cleaning system that might help the mill achieve its goals. In the summer of 1995, Thermo Black Clawson
proposed that Green Bay test the yet unnamed Xtreme reverse cleaner followed by the newly designed X-Clone through-flow cleaner.

Developed by Black Clawson with joint funding from a U.S. Dept. of Energy grant, the Xtreme cleaner was designed to remove lightweight contaminants. When used with the X-Clone cleaner in the tailing position, only two stages are required to minimize fiber loss and maximize removal of small contaminants such as wax, lightweight hot melt adhesives, and stickies. With a 60 psi pressure drop, the Xtreme cleaner uses long residence times in a small diameter cleaner to extract very small contaminants that approach the specific gravity of fiber itself, while the X-Clone, with its 30 psi pressure drop, is operated as a secondary cleaner to collect any residual debris left over from the Xtreme cleaning process.

Through its tests of the new system, Green Bay found that there was a visible difference in handsheet blemishes-even with the fluctuating quality of its incoming recovered fiber. The mill also found that the system had little effect on overall fiber balance, and that it apparently maintained the whitewater quality in its closed water system. Because of these findings, Green Bay committed to a $4 million purchase of the new cleaning equipment.

System design and startup. In January 1997, Green Bay began the installation of its new cleaning system. The new Thermo Black Clawson equipment included a Liqui-Filter reverse screen designed to thicken pulp in-line, three stages of Ultra-Clone forward cleaners, Xtreme reverse cleaners, X-Clone through-flow cleaners, and fine slotted Ultra-V
pressure screens.

As Figure 1 shows, three stages of Thermo Black Clawson Ultra-Clone forward cleaners are installed for the removal of small, heavyweight debris. Rejects from this cleaning sequence are sent to the landfill, while the primary forward cleaner accepts are diluted and sent to the Xtreme reverse cleaners for removal of lightweight debris. Accepts from the reverse cleaners are sent through Ultra-V 0.008-in. fine slotted pressure screens and on to the stock preparation area, while rejects continue through to the X-Clone secondary cleaners. Accepts from the X-Clone cleaner are diluted and sent back through the primary Ultra-Clone cleaner, while rejects, consisting of stickies, adhesives, and wax, are processed by a Krofta dissolved air flotation clarifier and then sent to a compactor.

Green Bay's top stock cleaning system started up in March of this year. In July, the full cleaning system became operational, when the mill "closed the loop" on reject filtrate by bringing the water from thickened and compact rejects back to the Krofta clarifier.

According to Walch, "There was a learning curve in March, and it has only been since July 24th that the whole rejects tailing loop has been closed and the whole cleaning system has been balanced out the way we want it to be. Since then, we have seen some very dramatic changes in what is going on within our system and within our product, such as appearance improvements and a 10% reduction in the use of DLK clippings."

Results. From a product performance standpoint, Green Bay's linerboard quality has seen dramatic improvements in appearance. No problems with stringing and plugging have been noted since the system began operating. Other operation improvements include additional reject thickening, a new compactor, and seal water screening. Yet another improvement has stemmed from the linerboard's improved coefficient of friction, since less wax now enters the final sheet.

"At the end of our paper machine, we spray on a non-skid product with a shower boom across the sheet," explains Walch. "Because of the linerboard's improved coefficient of friction, we have seen a reduction in the amount we have had to use to maintain our degree of slide angle quality specs. And, our box plant in town has been able to reduce the amount of non-stick agent they apply as well."

From an investment perspective, the new cleaning system required about $4 million in capital. Walch describes its results as integral to Green Bay's future direction.

"It was a very small part of a very big project-and a part of it that was totally quality driven. It's just part of our philosophy that you have to produce the best sheet-that you just can't afford not to. By the time we finish the cleaning system improvements and complete a good quantitative study evaluating it, we'll probably need to start looking for that next step," states Walch.

"For right now, we have done as much as possible. But I think we realize that, from an operational, technical, and research perspective, we need to keep monitoring our system not only in terms of quantitative analysis of all the reject streams and the efficiency of all the equipment, but also watching all the new developments. The day will come-whether that is next year or the year after or 5 years from now-where we and everybody else will be taking that next step."

Vandenberg also maintains this "raising the bar" perspective, and specifically mentions further cleaning of the base stock as a potential requirement in the future. "Right now, our top stock cleaning system cleans about 33% of our stock," explains Vandenberg. "Because we have seen such dramatic improvements from cleaning this stock with the new system, we have to consider the impact of additional cleaning for the other two-thirds in the future."