Paper Machine Rebuild, New Controls Offer Competitive Edge for Green Bay

AN INCREASINGLY COMPETITIVE mottled white linerboard market, along with growing customer expectations for graphics-friendly packaging, have led Green Bay Packaging's Arkansas Kraft Div. in Morrilton, Ark., to respond with paper machine improvements focused strongly on quality. In 1998, the mill completed a rebuild of its No. 2 paper machine that incorporated advanced technology in the areas of forming, pressing, and process control. In addition, the mill also rebuilt an aging bark boiler, showing a long-term commitment to the mill and its products.

Since it began producing mottled white linerboard at Morrilton in the early 1980s, Green Bay has demonstrated a willingness to adopt the latest technologies for producing a linerboard with excellent appearance and strength characteristics. In 1991, the mill installed top wire formers on both its paper machines, but continued examining new technologies that might apply to linerboard production.

To allow independent formation of the mottled white linerboard's top sheet, the Morrilton, Ark., mill chose to install a mini-fourdrinier with a hydraulic headbox.

Green Bay's 1997-1998 upgrade of its No. 2 paper machine included the installation of a new mini-fourdrinier that would allow separate formation of the linerboard's top white sheet. The $28 million upgrade also included a new shoe press, and another $6 million was spent for a new DCS on the No. 1 and No. 2 paper machines. In addition, a $20 million rebuild of an older bark boiler was performed to ensure an adequate supply of steam for the future.

To H. Marion Swindell, vice president and general manager for the Arkansas Kraft Div., these upgrades show Green Bay's strong commitment to the mottled white linerboard market.

"To stay competitive for the long term, the top management at Green Bay is willing to risk the money for upgrades that improve the quality of the paper," states Swindell. "Certainly, when the brown market gets weak, other mills start looking to change their product line to mottled white. But we are in this business for the long haul."

Green Bay's commitment to the mottled white linerboard market has paid off, with profits rising significantly in the past 10 years due to the change. In addition, Green Bay currently holds 18% of the mottled white linerboard market.

NO. 3 BARK BOILER REBUILD. In 1997, the Morrilton mill began looking for ways to ensure that it had an adequate, long-term supply of steam. At that time, the mill was operating with one recovery boiler, one natural gas-fired package boiler, and three bark boilers. The total steam produced by all five boilers was 610,000 lb/hr, of which the three bark boilers produced 210,000 lb/hr.

In September of 1996, Green Bay decided to rebuild its No. 3 bark boiler to increase steam capacity. This boiler was chosen because it was the only bark boiler that had the potential capacity to make a rebuild economically feasible.

No. 3 bark boiler history. Installed in 1965 when the mill opened, the No. 3 bark boiler was actually the mill's original recovery boiler. In 1975, it was replaced by a new recovery boiler. After being decommissioned for three years, the mill discovered a way to burn bark in it without a true bark boiler conversion by burning dryer fines in suspension, with a gas gun burning under the bark for safety.

However, because it did not have a true bark boiler design, the No. 3's capacity was only 90,000 lb/hr to 120,000 lb/hr, depending on the season. In 1992, the Morrilton mill had the No. 3 bark boiler closely inspected by an outside agency. The results showed that its pressure parts were in good condition and that it could support major repairs. By 1996, Green Bay targeted the boiler for a major rebuild.

Modifications to the boiler. In late 1996, the mill contracted with Babcock & Wilcox for the pressure part equipment fabrication and erection on the No. 3 bark boiler. In addition, BMH Technology was chosen to provide a new bark feed and ash removal system, while Foxboro would supply DCS computerized instrumentation and control room revisions. The entire boiler rebuild project was managed by the Morrilton mill's own engineering and expansion group.

The mill's contract with its rebuild contractor stipulated that the rebuilt boiler would have a capacity of 250,000 lb/hr at 600 psi and 710F. In addition, it would run with an efficiency of 71% on bark and 85% on gas. Also, air emissions would meet state and federal requirements.

To accomplish the major pressure part revision, the No. 3 bark boiler was taken offline in May 1997. While it was offline, the mill purchased another package boiler to cover the vacancy.

Modifications to the No. 3 bark boiler included cutting off the bottom one-third of the furnace to install a hydrograte bottom for automated ash removal and a separate new reactor, referred to as a controlled combustion zone (CCZ). The CCZ's hourglass-shaped side walls improve burning efficiency by employing wood gasification technology that produces volatile gases which are transferred into the boiler furnace where they are burned.

The generating section of the boiler was also opened up and the baffle was removed to accommodate lower flue gas velocities. In addition, there was a retrofit of the economizer, and a new superheater section with alloy tubes was installed along with gas burners for full loads, air heaters for providing 550 F undergrate air, and an induced draft (ID) fan located on the ground. Figure 1 shows a design similar to the one adopted at the Morrilton mill.

Although the project was originally scheduled to take 16 months, engineering and design complications associated with wood gasification during the project pushed startup back to March 1998. These changes were related to how air is introduced into the boiler, with the mill requesting changes that supported firing of the boiler with new gasification technology. This type of firing allowed burning of methane and other gases in the bark higher in the boiler rather than the bottom, which was more environmentally and economically sound. To help fund this expansion, Green Bay was able to obtain third party financing, so that the limited capital of the small company could be used elsewhere.

The Morrilton mill's boiler had a successful startup in March 1998 and is currently functioning under the parameters specified in its contract. The boiler consumes 349,000 tons of bark/wood residue on an annual basis, which displaces 2,760,000 MMbtu of natural gas.

FIGURE 1: Modifications to the No. 3 bark boiler included cutting off the bottom of the furnace to install a hydrograte bottom for automated ash removal and a separate new reactor, known as a controlled combustion zone (CCZ).

NEW DCS FOR NO. 1 PM & NO. 2 PM. Although a DCS had been installed in the pulp mill in 1992 to provide better cooking consistency, both of Green Bay's paper machines were still using older PLCs complemented by scanner systems. Pleased with the success of the pulp mill DCS, which had improved cooking kappa number consistency from 10% to 15%, Green Bay decided to upgrade the control systems on its two paper machines in 1997. As with the decision for the machine rebuild, the purchase was based on quality.

"While the DCS had the potential to provide incremental production increases, its installation was fundamentally a matter of being able to watch the process much closer and control it better," states Swindell. "If you do that, then you wind up with a better quality product than the competition."

DCS customization and operator training. To avoid a complicated startup after the rebuild, which was scheduled for June 1998, Green Bay decided to phase in the DCS implementation starting in January of that year.

"We didn't want to start up the rebuilt machine with brand new controls," describes Swindell. "So, we started using the new DCS in January to familiarize the operators with how the process operated with the new control scheme. That greatly helped the learning curve associated with starting up the paper machine."

Based on the success of the Foxboro AI DCS in its pulp mill, Green Bay decided to implement another such system for its two paper machines. The ABB Accuray 1190 scanner systems would remain as input to the new system, while the old Moore PLCs would be replaced by the DCS. Prior to this January implementation were months of training and customization of the new control system by Foxboro's software customization company, Feedforward.

Beginning in June 1997, the software company worked closely with Green Bay to define and implement the various screens required to operate the paper machines, and paper machine operators were closely involved in this process. In January 1998, the software company brought in six employees and set up a trailer with simulators for training. Hardware was also installed at this time, requiring no unscheduled downtime.

"To help us start up the new DCS on the paper machines, the software guys literally lived here from January until we started up No. 2 after the rebuild," describes Swindell. "The guys constantly interfaced with our operators, implementing control loops and talking with them about the process. The operators were able to define the screens that they needed to operate the machines."

Getting the operators involved from the outset of the DCS project was crucial in the project's eventual success, according to Swindell.

"We got our operators involved in the very front end so that they could see how this would make everyone's job easier in the long run," states Swindell. "They had to go from using dials and knobs to using a keyboard and mouse, but they have accepted the system 100%. This had a great deal to do with its success."

Startup. The new controls for both machines were a success from the beginning of their use in January. However, the true success for the new DCS came with the startup of the rebuilt No. 2 paper machine in June. In addition, Swindell has been pleased with the discipline provided by the new system.

"It certainly takes a lot of the human element out of it, with set procedures for startups and constant monitoring of the process to inform you of problems," says Swindell. "This means that things are not forgotten and that you can change things faster if there is a problem. The system just gives so much more detail and a lot more time for feedback on what the process is actually doing."

Swindell also appreciates the volume of information provided by the new system, as well as the easy access to its information. "I could run it from the computer in my office if I needed to. I can also look at it from my home computer if there is a problem."

NO. 2 PAPER MACHINE IMPROVEMENTS. Installed in 1979, Green Bay's No. 2 paper machine is a Beloit machine with a 184 in. width and 166 in. trim width. The No. 2 machine first produced unbleached kraft linerboard. However, as demand for boxes and displays with enhanced graphics grew in the early 1980s, the mill started manufacturing mottled white linerboard on the No. 2 machine in 1983. The No. 2 paper machine currently operates at speeds of up to 2,000 fpm and produces 220,000 tpy of mottled white linerboard.

Green Bay's mottled white linerboard products consist of an unbleached kraft base sheet that contains 8% to 10% recycled fiber, with the balance in virgin yellow pine that is harvested from nearby forestland. The top sheet is 100% recycled fiber that is either pre-consumer or post-consumer, depending on the product. To handle the recycled fiber that comes from printers, paper stock brokers, and greeting card manufacturers within a 650 mile radius, the mill has three secondary fiberlines.

The Morrilton mill produces Ark-Brite, which contains more than 40% pre-consumer wastepaper, and Eco-White, which has a total secondary fiber content of more than 50% post-consumer wastepaper. Since introduction of these products, Green Bay's share of the mottled white market has risen to 18%.

Committed to staying a major supplier of mottled white linerboard by producing a high quality product, Green Bay added a Beloit Bel Bond top wire former to the No. 2 machine in 1990 to improve sheet whiteness. Although the 1990 upgrade produced the desired results by limiting the mixing of white water from the top and bottom sheets during formation, the growing U.S. production rate for mottled white linerboard led Green Bay to look for further ways to differentiate itself from competitors. Mottled white production in the U.S. had increased an average of 6%/yr from 1990 to 1995, and though it had actually decreased in 1996 and 1997, Green Bay felt the need to respond to the growing quality demands of its customers.

"Each time we have raised the bar as far as quality, our competition has reacted in a similar way with improvements," explains Swindell. "The rebuild we instigated in 1997 was all quality driven - every bit of it. None of the justification was around an increase in production."

In 1997, Green Bay began examining ways to improve cross direction (CD) strength, ring crush values, and brightness while reducing fiber costs, which had risen for recycled grades. After reviewing the latest in technology from major suppliers, the Morrilton mill chose to adopt Valmet's mini-fourdrinier concept and its associated Sym-Flo T hydraulic headbox, which would allow independent formation of the mottled white's top sheet. To further improve strength properties, the mill also chose to purchase a Sym-Belt shoe press for placement in the third position following its bi-nip press. A purchase order for the Valmet equipment was placed in February 1997, and plans began for the rebuild.

In addition to forming and pressing equipment, Green Bay decided to purchase new top stock screening equipment to improve sheet quality. This included a Beloit primary top stock screen with 0.062 in. holes and a Thermo Black Clawson secondary top stock screen with 0.012 in. slots, as well as a new top stock silo and associated piping. The mill planned to continue screening its base stock using the existing Bird primary screen with 0.079 in. holes and Black Clawson secondary screen with 0.078 in. holes. Also, rejects from both top and base stocks would go to a new Voith Sulzer tertiary C-Bar screen with 0.012 in. slots.

Construction. Green Bay's new equipment was installed during a 27-day period starting May 26, 1998. However, at least 14 months of preparation were involved in the rebuild, which was accomplished in less than the scheduled time by several days. S.J. Baisch, who had provided the original designs for the No. 2 paper machine, was in charge of engineering for the rebuild, including the design of the electrical, structural, piping, and stock preparation systems. C.R. Meyer & Sons served as the construction contractor, with IHP Industrial Contractors providing the piping labor and Koontz Electric performing all instrument and electrical work. The Morrilton mill's own engineering and expansion group provided onsite project management services.

Starting in January 1998, the mill and its construction contractors took advantage of each monthly outage to prepare for the rebuild by installing as much equipment as possible. This early work involved installation of piping for the new machine and top stock preparation equipment, including screens and pumps. According to Doug Latimer, Green Bay project engineer for the rebuild, these early installations reduced the time required for the actual rebuild from 60 days to less than 27 days.

On May 26, the rebuild began with the demolition of existing equipment, including removal of the existing former and its piping. The new machine design required moving the existing Voith headbox back 13 ft. to provide additional capacity on the base ply table. In addition, to make room for the shoe press, five dryer cans that immediately followed the press section were removed. A breaker stack section was also removed and four of the dryers were reinstalled in place of the breaker stack. Fortunately, the No. 2 machine room was designed to structurally support an expansion. However, the biggest challenge associated with the project involved the mini-fourdrinier.

"Constructing the mini-fourdrinier was challenging, because the top stock headbox weighs 64,000 lb and is elevated 15 ft.," describes Latimer. "Also, its superstructure had to support clothing changes which require the headbox to be cantilevered backwards."

At the height of the rebuild outage, the Green Bay mill had 350 additional personnel onsite. The equipment was shipped to the mill on 27 trucks, nine of which were held at the mill to store the largest pieces of equipment. Although pre-assembly of the equipment in the aisle had been considered, Latimer says that it was decided that this might hinder production on the No. 1 paper machine.

During the rebuild, the mill's construction contractor controlled the master schedule. However, this required a great deal of interaction between mill personnel, the engineering contractor, and the equipment supplier. In addition, schedules-especially for the crane-were further complicated by the one-week annual outage on the No. 1 paper machine during the second week of construction.

"We started with the master schedule from our construction contractor and then adjusted it based on input from the other contractors to identify 'domino effect' items that would impact the sequence of activities," explains Latimer. "We worked hard to focus both pipe fitting and electrical within the schedule created by their software."

Due to the advance preparation, the mill completed the rebuild in 26 days, 21 hours. Latimer notes that the total number and magnitude of unexpected modifications that had to be made during the project were very small because of this preparation, and especially points to the benefits from Valmet's preassembly of the equipment in Charlotte prior to shipping.

Training. Training for the No. 2 paper machine operators consisted of a nine-day course that began two weeks before the May outage. This training content was organized by the mill, and it involved the participation of all the major suppliers, including Valmet, clothing providers, and Foxboro.

Although operators had been using the No. 2 machine's new Foxboro DCS since January 1998 and were familiar with its operation, the May training focused on the new control schemes required for the rebuilt machine. As with the original DCS training, operators were strongly encouraged to provide input into the design of this control scheme.

Startup. Green Bay's startup of the rebuilt No. 2 paper machine was successful, with paper being produced within two hours. According to Swindell, the machine threaded on the first attempt, which was not expected for another two or three shifts. However, some problems did arise as the mill learned more about operation of the rebuilt machine. Despite these problems, though, the mill's production rate in the first month of operations was the same as it had been before the outage.

"We had some issues associated with startup, but with that much complexity and hardware, you are just going to have some things to work through," says Swindell. "All in all, it was very, very successful."

While the biggest challenge associated with installing the equipment was the mini-fourdrinier, the biggest issues associated with starting it up were with the shoe press. One problem that was easily corrected was the installation of a larger hydraulic pump and motors so that the press could operate at loads of up 6,000 pli if needed, since the old pumps were limiting operation to 4,300 pli.

Another issue involving the new press was wadding. At operating speeds, wads were carrying through the previous press and feeding into the new press, severely damaging or breaking the felts and causing the sleeve to rupture on the bottom roll. To correct this problem, the mill devised a wad deflector to deflect wads downward and installed it at a point just before the sheet enters the shoe press. This was successful in correcting the problem, and Valmet later designed another deflector to replace the mill's in-house version.

In addition, since five dryer cans were moved to make room for the new shoe press, a longer draw was created going into the first dryer section. However, according to Chung-Haw (Tiger) Teng, production manager at the Morrilton mill, any problems associated with this were compensated by the performance of the shoe press.

"Downtime issues associated with the longer draw going into the dryer section were somewhat offset by the dryness of the sheet, which is now 46% coming out of the press," states Teng. "The sheet is tougher now and less prone to breaks."

Current operations and results. The Morrilton mill is still adjusting to the many changes from the new machine and is constantly tweaking factors such as machine chemistry, press loading, and press fabrics to achieve its quality goals.

From both an operational and quality standpoint, Green Bay has been pleased with the multi-ply forming allowed by the mini-fourdrinier, especially when compared with the old system.

Machine tender Charlie Crowder (left) and backtender Jerry York (right) were among the operators that worked with the software supplier to define new DCS control screens.

"Before, we started out with the base stock and then just poured the top stock on," describes Swindell. "With that method, you don't have good control of how the sheet is formed, because you are trying to form the top sheet through the base sheet. With Canadian standard freeness running from 650 to 700 for the longer kraft fiber in the base stock and 150 to 200 for the short hardwood fiber in the top stock, there were difficulties in removing the water at the correct rate to produce the desired appearance."

Teng agrees that formation with the new machine is a great improvement and describes the new machine as "very forgiving on how you control the look of the sheet."

"By forming the sheets separately, it is much easier to control appearance," says Teng. "We are still learning about the correct moisture levels required for each sheet to laminate together to provide the best results, but we are already seeing better moisture consistency from reel to reel."

Consistency out of both the primary and secondary headboxes is running around 0.35% to 0.45%. After the two sheets are brought together, consistency numbers are at 10% to 12%, and sheet dryness off the couch is 30%. Going into the third (shoe) press, sheet dryness is at 40%, and increases to 46% as the sheet goes in to the first dryer section.

Green Bay has been very pleased with the results of the rebuild. So far, the mill has seen a 16% improvement in mullen test numbers, a 24% in ring crush test numbers, a 30 point improvement in smoothness, and a 15% savings in fiber. Moisture variation across the sheet is still somewhat of a problem, but has improved since the rebuild. And, according to Swindell, the mill has also seen nominal increases in speed for the No. 2 paper machine - an added benefit since the rebuild was driven by quality issues.

Future plans. In the near future, Green Bay would like to change the sheet path going into the shoe press from uphill to downhill to alleviate stress on the sheet. In addition, to raise the competitive bar a bit further, Green Bay is also examining on-machine coating for its linerboard.

"To remain competitive, we have looked at coating applications as an advancement for the sheet," says Swindell. "If you look at the top of the linerboard rung, it's bleached board, but we would never want to produce that because of environmental concerns. So, the one thing that we could do is to apply a coating to the quality sheet we are currently producing."

Monica Shaw is Technical Editor for Pulp & Paper.