The latest investment on PM 3 at Enso's Varkaus mill has provided a welcome improvement to both quality and operating rates

by Jim Kenny

Varkaus sets automatic pilot for efficiency gains

Developing and integrating new automation systems has long been recognized as one way for a mill to boost its efficiency and stay competitive. But with so many measurement and control packages available, the tricky part has always been to identify where an automation investment will provide what the Americans might call "the biggest bang for your buck" - ie maximizing the return on your investment.

Enso's Varkaus mill in Finland is one operation that took a long, hard look at exactly what it wanted to get in return for its recent expenditure in a new automation system for PM 3, and overall the company appears to be well-satisfied with its latest investment.

Enso's Varkaus mill attempts to save money and increase quality through the installation of a new control system

As the Varkaus PM 3 production manager, Jarkko Tehomaa, explained, "We can't consolidate everything straight away, so it takes time to really evaluate how much better we are with this system, but we are talking about several percentage points of waste reduction per year. Even if we only manage to reduce the total broke from 7-8% of the yearly production down to 6-7% with the help of the new controls, we are still talking about quite big numbers. We're certainly talking about millions of Finnish markka per year and this is the only way of improving and staying competitive for us."

Old hands

Part of the reason that new automation was considered so appropriate for Varkaus, rather than simply investing in new equipment, was that PM 3 is subject to a large number of bottlenecks. The PM is comparatively old, dating back to 1961, and even with a number of large-scale upgrades over the years, the sheer number of bottleneck sections on the machine meant that the best way to improve efficiency was to concentrate on the automation rather than upgrading the heavy-duty hardware.

PM 3 is an 8.47 m wide Voith unit that has been extensively rebuilt by Valmet over the course of three major projects in 1985, 1987 and 1992. Furnish for the uncoated woodfree PM is a mixture of hardwood and softwood pulp, with GCC (ground calcium carbonate) filler. Today, the PM has a nominal design speed of 1,200 m/min, although it normally runs at around 960 m/min, giving the machine a production capacity of 210,000 tons/yr. Output from the PM is a mixture of constat, writing/educational and offset paper grades, while the basis weights vary from 60-100 g/m.

The wire section of the PM comprises a Valmet Sym-Flo headbox with Jetmatic lip profiling control and a fourdrinier table with a Valmet Sym-Former R top wire unit. Valmet also supplied the Sym-Press II three-nip press section, which includes a granite center roll and a 68-zone control steam box. The press section is followed by two single-tier drying groups with four two-wire units and 55 drying cans. From here the web is taken through a Valmet Sym-Sizer film press before it reaches the two-roll hard nip calender, incorporating a 68-zone Calcoil caliper control system. The PM section finally ends with winding on the pope reel at a web width of 7.82 m.

From here, the first stage of the finishing section involves the slitting/rewinding operation on a Valmet KL 1000 two-drum winder. The slitter/rewinder runs at 2,200 m/min with a maximum trim width of 7.7 m and produces reels of up to 1.5 m in diameter. Automatic slitter-knife positioning in 24 knife pairs allows the unit to produce reels in a width range
of 0.18-2.50 m. There is also a Valmet KL 500 salvage winder in operation with the same width range. It can run at a maximum speed of 1,500 m/min and also produces reels of up to 1.5 m in diameter. Finally, the Valmet Streamline packaging line boasts a 120 reel/hour capacity with fully automatic wrapping.

Hard or soft

That then is PM 3. But from the point of view of the supplier handling the automation upgrade, Honeywell-Measurex, the more interesting aspects of the machine were to be found in the control and measurement systems. As both Honeywell and Measurex had been separately involved in developing the automation systems at the mill over the years (see box), this project was particularly interesting as it represents the first example of truly integrated Honeywell-Measurex technology since the two suppliers merged.

According to the Honeywell-Measurex project manager for automation at Varkaus, Tero Lumpo, "We only started looking at how we were going to construct the two systems into one after the merger went through, and the real work started in May/June last year. This PM here at Varkaus started up after the rebuild on the 23rd of October. So as you can see, we've had to move pretty fast, but the openness that already existed in the two systems helped a lot."

The Varkaus delivery consisted of a fully-integrated TotalPlant Alcont MXOpen quality control system using Alcont's new NT-based GUS workstations. Quality control is implemented through two measuring frames. The first is a reel scanner that measures basis weight, moisture, ash, caliper, color, brightness and fluorescence, while another scanner on the Sym-Sizer measures basis weight and moisture.

The new automation system on Enso's PM 3 could have a payback time of one year

The MD (machine direction) controls are based on a predictive multivariable logarithm (HMPC) and there are two multivariable controls. One of the controls has five inputs and five outputs for basis weight, ash, speed and two moisture values, while the other has three inputs and three outputs for brightness and a* and b* fluorescence values. The saturation point of the optical brighteners is identified using fuzzy logic.

The CD (cross direction) controls cover basis weight and caliper, which are controlled via the Jetmatic and the Calcoil systems on the PM. At the same time, a fiber orientation optimization algorithm adjusts the basis weight target profile based on the results of laboratory analyzes. Added to all that, historic data is gathered on an Alcont HIC (Honeywell info center) unit, which as well as producing the reports, also replaced the conventional plotters previously used at the mill. Fault detection is via an Ulma optical system.

No more news

According to Tehomaa, "In 1985 when PM 3 was first switched to producing woodfrees things were very different. The machine efficiency was only about 60%. The Sym-Sizer was added in 1992 and things improved greatly, but even so our best year was 1995 when we averaged 86% efficiency. But since we've had the new automation systems, the last three months of last year showed an efficiency of about 90% and we expect the improvements to continue throughout this year."

Although more improvement is anticipated, the mill team is already well pleased by the results seen to date. Just weeks after the startup of the new automation system, the mill reported not only better efficiency, but much improved quality as well. Among the results noted:

• CD caliper two-sigma fell by a massive 78%
• CD basis weight two-sigma dropped by some 41%
• MD moisture two-sigma dipped 9%
• MD basis weight two-sigma fell by 13%.

Even so, Tehomaa attributes the bulk of the improvements seen so far to the new automation unit. The mill has been very careful to make sure that it is clearly identifying where efficiency improvements have occurred when calculating the effectiveness of its investment and the results show that the automation system have been even more effective than anticipated.

"In our industry, we're normally looking at payback times of three years or less, with the exception of something like a new machine of course," says Tehomaa. "For this project we established a payback time of approximately two years, but as the initial results have been so promising we think that even that two-year payback time could be halved."

Quick change

The automation system has already helped halve grade change times. Altering basis weight by 10 g/m prior to the rebuild took 10 minutes, but that has now been reduced to just five minutes, drastically improving the overall efficiency of the
mill. Enso is still far from completing
the optimization process for the new automation system, but already the mill is looking at other ways in which it can develop the on-line controls. Although fuzzy logic is already being applied to the brightness controls, the Alcont system has an elaborate fuzzy logic "toolbox" that allows
a huge number of additional control loops to be introduced into the overall operating system. "There are still plenty of opportunities to develop new applications using the toolboxes as well as the positive responses that have already been gained," says Tehomaa.

According to Lumpo, the new Alcont system is so easy to integrate and expand that the mill could be making continuous improvements to the control loops for years to come. As he points out, "One possible thing for the future at Varkaus is to look at controlling the chemistry of the wet end more. We have some ideas in this area and even though some of the PMs are very well organized, they definitely could do with more measurement control."

PM 3's TotalPlant Alcont NT-based operator interface

Tehomaa certainly agrees. "That's right. We really don't have enough on-line measurements for analyzing what is happening in the wet end. We only have pH, temperature and conductivity at the moment, and you obviously can't control things well with just that, so a lot more measurement needs to be done," he says.

The new system is not the only connection between the Varkaus mill and Honeywell-Measurex though. At the end of last year, five staff from Enso's information services group became employees of the supplier. The switch came after the mill signed a deal giving the supplier responsibility for the operation and maintenance of information services at Varkaus, as well as the development of the reporting functions of the process control system.

Marketing more

The quality and efficiency gains made through the automation investment will be invaluable to Varkaus in helping the Enso mill to stay profitable in the future. And for the moment, Enso must be fairly happy with the way the uncoated woodfree market is bearing up. Rumors of extra uncoated woodfree volumes arriving in Europe from the troubled southeast Asian region do not appear to have much basis in reality, and the supply/demand balance in the market is relatively healthy.

Enso has drafted plans for upgrades at Varkaus, but there is no firm commitment to what projects will be undertaken or when. What is clear, however, is that the mill has squeezed practically all the extra possible capacity from its present machines. Any significant production increase, therefore, would rely on either the construction of a new PM or a major rebuild to one of its existing machines. A long involvement with PM 3 at Varkaus

The Varkaus mill has long been close to the hearts of what was formerly the US-based automation supplier, Measurex, as well as Honeywell. PM 3 was the site of the company's first European project in May 1970. At the time, PM 3 was a standard newsprint machine and the supplier installed its Measurex 1000 system, taking basis weight and moisture measurements at the reel and press section. The CPU was an HP 2116B with a "massive" 16k of core memory - less than a lot of pocket calculators these days.

In 1972, caliper measurement was added to the system, but the press scanner was removed as its moisture gauge was a straight-through IR (infrared) sensor, which had endless calibration problems as a result of the furnish variations. The reel moisture gauge was upgraded though, and in 1973, PM 3 became the site of Measurex's first data-link to a mill computer. The unit transferred MIS (management information system) data on a 16-bit parallel link to Enso's IBM 1800.

The mill upgraded the Measurex 1000 unit on PM 3 to a 2000 system in 1976, while at the same time, Honeywell was installing one of the first TDC 2000 DCS (distributed control system) orders on PM 4 and the TMP (thermomechanical pulp) plant. Almost 10 years later in 1985, the Measurex system was replaced by a Lippke 3 scanner controlled by a Honeywell Alcont unit.

Finally, in October last year PM 3 became the first paper machine in the world to be controlled by a totally integrated Alcont/MXOpen solution. Since then though, two similar systems have been sold to Stromsdahl and UPM-Kymmene's Wistaforest mill in Finland.

Working across the divisions at Varkaus

PM 3 is just one of five machines at Varkaus, and this site is one of the few facilities in the company that crosses over all of Enso's five operating divisions - the fine papers division, the publication papers division, Pakenso, Corenso (a UPM-Kymmene/Enso joint venture) and Enso Timber. This diversity means that Varkaus can utilize practically all the raw materials within easy access of the mill. The sawmill takes spruce logs, while spruce, birch and pine go to the stone groundwood, TMP (thermomechanical) and woodfree pulp lines. Long and short fibers are separated for use according to grade and the mill uses a mix of recovered paper and a little chemi-mechanical pulp for its coreboard unit.

Varkaus has the capacity to produce 210,000 tons/yr of ECF (elemental chlorine-free) kraft pulp, 170,000 tons/yr of TMP, 75,000 tons/yr of recycled pulp, 70,000 tons/yr of stone groundwood and 40,000 tons/yr of chemi-mechanical pulp. The timber unit processes 280,000 tons/yr of pine, while the mill also has a capacity of 280,000 tons/yr of fine paper, 270,000 tons/yr of publication papers, 75,000 tons/yr of coreboard and 3,800 tons/yr of packaging (mainly egg trays processed from waste materials).

The mill's history dates back to the first sawmill on the site, which was set up in 1830. Pulp production was added in 1919 and the first newsprint capacity was introduced in 1921. Enso bought Varkaus from Ahlstrom in 1987.

The PMs at Enso's Varkaus Mill

PM 1

Grade Coated fine papers

Basis weight 70-150 g/m (mainly 70 g/m, 80 g/m and 90 g/m)

Capacity 80,000 tons/yr

Width 4.1 m

Startup 1921

PM 2

Grade Publication papers (Newsprint and lightweight directory grades)

Basis weight 28-45 g/m

Capacity 70,000 tons/yr

Width 5.5 m

Startup 1926

PM 3

Grade Uncoated woodfrees (Constat 65%, 25% writing/educational and 5% offset)

Basis weight 60-100 g/m (mainly 60 g/m, 70 g/m and 80 g/m)

Capacity 210,000 tons/yr

Width 7.7 m

Startup 1961

PM 4

Grade Publication papers (Newsprint and a range of uncoated mechanical grades)

Basis weight 34-48.8 g/m

Capacity 200,000 tons/yr

Width 8.7 m

Startup 1977

Note: The mill also has a small coreboard machine and packaging plant.