Publication: Pulp & Paper Magazine
Green Bay Packaging Begins Third Year with Closed Water SystemBY JIM YOUNG, Executive Editor
Successful operation depends upon keeping things simple, meticulous monitoring, correct chemicals, dedicated staff
UP IN GREEN BAY, WIS., A pioneering tradition extends to papermaking as well as to professional football. When Green Bay Packaging Inc. brought its greenfield mill on line in 1949--30 years after the Packers' initial season--it claimed the first commercial application of the neutral sulfite semichemical (NSSC) pulping process.
The mill began recycling postconsumer old corrugated containers (OCC) in 1957, sending its own truck out for collection. Producing corrugated medium, the mill first closed its process water system in 1974. This achievement was honored with the Izaak Walton League National Award, thought to be the only time that this award has been presented to the paper industry.
In 1991, the mill converted to 100% recycled linerboard, requiring the addition of a secondary headbox and a top dewatering unit. Following this conversion and subsequent learning curve was the reclosing of the mill's process water system. Begun in February 1991 and completed September 1992, the system has been running continuously since then.
"This technology does work," affirms Jeff Walch, Mill Div. vice president/general manager. "We have successfully adapted it to both 50% recycled corrugating medium production with an onsite pulp mill, then to 100% recycled linerboard production."
Equipment does not play a major role with this technology. Rather, it begins with what Walch describes as an elemental Engineering 101 approach to material balance around the mill, judiciously monitoring water usage within the entire facility. It's a matter of how many gallons per minute of freshwater need to be added, where the most critical uses are, and what alternative water sources can replace freshwater.
Freshwater required by the paper machine and the rest of the process is calculated, as is the amount of moisture that is evaporated and the approximately 7% that goes out with the product. Careful attention is also given to seal water in the pumps and motors. Success demands that literally every mill employee be involved--utility people washing up stock spills as well as machine tenders.
REDUCING FRESHWATER USAGE.
A mill survey found the following ways to further reduce freshwater demand:
* The 2-in.-dia paper machine wash-up hoses use recycled water only. Where a freshwater rinse may be called for, a 0.5-in.-dia garden hose is used, complete with hand-operated gun-type nozzles.
* Mechanical seals and a process water seal system were installed.
* Shower nozzle sizes on the paper machine were adapted for minimal water use and carefully monitored for wear. In the press section, some of the normal flooding showers were replaced with either high-pressure showers or single-nozzle traversing showers.
* Chemical aids were selected that are adaptable to recycled process water or that require no water at all.
* Wet-strength resins were eliminated because they were incompatible with the system, attaching themselves to small particles in the water rather than to the fiber. The mill primarily uses mechanical strength enhancements as an option.
Extra storage capacity is required for times when the machine is down and water cannot be evaporated or sent out with the sheet. The mill has about a million-gal capacity, preferring to run at 600,000 gal or a little less.
CHEMICAL ADDITIVES PROGRAM.
Adapting to a closed process-water system for 100% recycled linerboard was a learning experience for chemical suppliers as well as for the mill. Walch recalls that the suppliers all presented themselves as having the most experience in working with closed systems. But after 30 or 60 days, they admitted they didn't realize the mill was this closed.
Dave Meverden, production coordinator, says the mill went full circle by trial and error, including four or five stages of sizing, retention and drainage aids, and defoamers--all with totally different chemistries--before finding a combination that could stabilize the closed water system. Kathy Nelson, environmental manager, relates that a lot of the additives normally used with freshwater will interfere with the contaminants in process water and become nonfunctional or perhaps cause foaming problems. She recalls one occasion where foam bubbled all the way to the ceiling, forcing an operator to scurry down a ladder to join others in getting out of the way.
BUCKING THE CONVENTIONAL WISDOM.
Walch says his closed system is doing almost all of the things that the conventional wisdom of the larger engineering firms argues won't work. "I guess it's a matter of perception," he reasons.
Nelson notes the mill was cautioned that 2,000 micromoles of conductivity in the water system was the maximum for effective papermaking, but the system has been carrying 10 times that amount--20,000 micromoles--with no ill effect. Also, the quantity of some chemicals required will be greater, not less, as previous additives no longer react.
Meverden adds that another current theory holds that solids have to be bled out of the system, maintaining a very low parts-per-million figure. "We've _proven that you don't have to do that," he says. Retention aids ensure that solids particles adhere to the fiber and go out with the sheet. According to Nelson, the mill's reject system is probably one of the best in the world regarding minimal disposal. Only about 3% of everything coming into the mill goes to landfill--mostly plastic, styrofoam, and wire.
KEEPING IT SIMPLE.
The mill philosophy is to keep everything as simple as possible, avoiding the more sophisticated technology such as reverse osmosis. Walch cautions that the process is not easy, it is "just not as complicated as people think it is." Like operating a treatment plant, the closed system requires constant monitoring. Every drop of freshwater is accounted for.
Says Meverden, "We have to be realistic in understanding that our product line is part of this water system, so we've had to compromise to some extent." Beginning with the initial closure, certain products could no longer be produced, and colored paper runs were eliminated. Still, the second closure had to meet the added quality and cleanliness demands of linerboard and permit production of a high-performance, recycled board that could compete with a virgin kraft product. According to Walch, similar closed water systems for other grades and other colors are at least another generation of technology away.
RETROFITTING VS GREENFIELD.
Meverden states that a greenfield mill would have a major advantage in optimizing equipment placement. Sorting out different water supplies was an extensive undertaking in the reclosure. "We actually had to run pipes in opposite directions to keep the clean water sent back to the river separated from the process water," he says.
Walch adds that a new workforce in a greenfield mill would not need to change old habits, although Green Bay mill employees have been conditioned since the initial closure in 1974. Another greenfield advantage, he says, is psychological. In a greenfield mill designed with a closed effluent system, there is less option to give up on the process after possible initial failures. Conversely, he continues, a greenfield mill faces the problem of what to do before designed paper capacity is reached and the water balance is accomplished.
THE NEXT STEPS.
Walch notes that by installing a cooling tower for the liquid ring vacuum pumps, or replacing these pumps with a centrifugal vacuum exhauster, Green Bay Packaging can also eliminate its noncontact river water stream. This is currently available technology. "At this point," he concludes, "recycled containerboard mills could be totally independent of our nation's waterways."
Copyright 2000 Paperloop Inc. All rights reserved.