Issue 19 - No.1/2009
| Stora Enso

The best chips in the world?

When the time came to modernize the woodyard at the Varkaus mill,  it was not a moment too soon. The old equipment was replaced with ANDRITZ's newest technology and the results have been extraordinary. “We just might have the best chips in the world now,” says the pulp mill production superintendent.

“We received a big efficiency improvement with a one-time investment.”
Ville Varis, Pulp Mill Production Director at Stora Enso's Varkaus mill

Jouni Hiltunen, Producton Superintendent, Pekka Kokko, Chief Woodyard Engineer for ANDRITZ, and Ville Varis, Pulp Mill Production Director, oversee one of the debarking lines (left to right).

The ANDRITZ woodyard at Varkaus consists of a two-line debarking, chipping, and screening operation.  Softwood capacity is 350 m3 sob/h, while hardwood capacity is 250 m3 sob/h.

The Varkaus mill in Finland can trace its roots to 1830.  Pulp production includes ECF at about 225,000 t/a, TMP at about 250,000 t/a, and recycled fiber at about 100,000 t/a.  Up until recently, it had been a struggle for the woodyard to keep up with chip production for the TMP and kraft lines, plus processing bark for the power boiler.  

“The oldest part of our woodyard was installed in the 1950's,” says Ville Varis, Production Director for the pulp mill.  “While we were able to make some small investments to rebuild part of the plant to 1970-1980's technology, basically the equipment was totally worn out.”

top High risk

“We were taking downtime for repairs,” Varis explains, “and there was a risk that paper production would be impaired.”  Varkaus was also the last mill in the Group to operate without a log de-icing system. “Frozen logs do not debark properly,” says Jouni Hiltunen , Production Superintendent for the pulp mill. “We would find dark spots in the paper during the winter time due to poor debarking.”

Chip size distribution was quite variable, to put it mildly. “There was a lot of variability in size, which impacted our fiberline,” Hiltunen says. “And we were experiencing up to three percent wood losses in the chip screening process alone.”    

In short, the woodyard had become high risk potential.  “We were hanging on as best we could,” Varis says, “but we knew that very large investments would be required within the next two years just to repair the old equipment in the woodyard.”

Stora Enso's Board approved the investment for a new woodyard in March 2006.  The main equipment was purchased from ANDRITZ in June of that year.  

“We have been through many innovations together with ANDRITZ,” Varis says.  The Varkaus mill is the site of their first friction-driven debarking drum, the first rotary screen, development of the de-icing system, testing of the first chipper, the first displacement bleaching system, and the first Zedivap® effluent evaporation system.

top Small is the trend

Why ANDRITZ?  “They guaranteed the lowest wood losses,” Varis says.  “We visited a reference installation at Joutseno that was quite convincing.  They demonstrated that they could precisely control the chip quality as conditions changed.  We really wanted that level of flexibility here in Varkaus.”

This flexibility is especially important due to recent trends in wood harvesting.  “With a heavy export duty pending for raw logs from Russia,” Varis says, “we are seeing a dramatic swing to smaller log sizes in Finland.  “There is a high proportion of first thinnings, younger wood, and smaller diameter logs in general.  More logs are required - and more debarking - just to achieve the same production volume.”

top From worn to wonderful

Construction work began at the site on July 31, 2006.  “We worked through a cold winter in Finland,” Varis says.  “You can imagine the challenges of doing the civil construction in frozen ground!”  ANDRITZ began installing the main machinery in March 2007. Commissioning began in August, and start-up began September 7, 2007 as per the agreed schedule.

The Varkaus woodyard represents the most modern and efficient wood processing technologies for cold climates, according to Pekka Kokko, Chief Engineer for ANDRITZ Wood Processing.  There is a two-line debarking plant with de-icing (PowerFeed), two large HHQ-Chippers, JetScreen chip separation and screening systems, and ChipScan chip quality analyzers.  Softwood capacity is 350 m3 sob/h (solid over bark per hour), while hardwood capacity is 250 m3 sob/h.

Spruce logs go directly to the adjoining sawmill.  Chips from the sawmill go to the TMP line, along with chips from spruce pulpwood that is processed in the ANDRITZ system.  Bark from the sawmill is mixed with bark from the woodyard to go to the power boiler.  Pulpwood goes to the ANDRITZ system for the kraft line.  The 800 t/d digester swings quite frequently between hardwood (birch) and softwood (80/20 pine to spruce), with a campaign lasting from one-half to two days.

“One worry I had before the project was that we would improve chip quality, but that the chip size would be too large,” Varis says.  That has not been the case.  “We have gradually controlled the chip size from 28 to 30 to 32 mm in one year.  We are getting better cooks in the digester with less rejects.”

“A side benefit of the dry debarking technology from ANDRITZ is that the fuel quality (bark) to the power boiler has improved significantly,” Hiltunen says.  “Weve seen a 60% reduction in wastewater from the woodyard and a huge reduction in phosphorous and COD.”

top Huge efficiency improvements

With the woodyard fully operational in November 2007, the Varkaus mill immediately began to see results.  “We received a big efficiency improvement with a one-time investment,” Varis says.  “When I came to this mill in 1999, there were 55 people working in wood handling.  Today, there are 13.  Secondly, we have witnessed a dramatic reduction in maintenance costs.  Third, the savings as a result of material efficiency improvements (reduced wood losses, higher chemical pulping yield, etc.) are substantial.”

“We use the ChipScan  analyzer online to get accurate data on chip length, thickness, and variability,” Hiltunen says.  “Before we put in the ANDRITZ system, our distribution was 50 to 62% in the optimum accept chip size, and about 20% in the smaller accept size.  Now we're seeing optimum chip size over 80% of the time and only 10% small accepts.  Meanwhile, we have reduced pins and fines from 9% down to 1.8% and our screening losses are about 1/10th of what we had with the old system.  These are quite extraordinary results.”

Hiltunen was extremely positive about the technologies in the woodyard.  “The PowerFeed  infeed conveys log bundles to the debarking drum without bridging in any weather condition,” he says,  “There is efficient de-icing and the low filling degree in the drum results in lower mass forces and reduces our wood losses. Bark and sand are efficiently removed. The JetScreen  makes it easy to optimize chip quality for the digester.  Chip quality is adjusted simply by adjusting the air pressure.  You cant flood the screen during peak loading periods.  The HQ-Sizer converts about 80% of the overthick and oversized into accepts.”

top Better chips, better pulp

“There is a very clear improvement in the fiberline operation after start-up of the new woodyard,” Varis says.  “It took us a while to adjust the process to the large chip size and the higher proportion of optimum chips -
and were still improving it each week.”

The bottleneck in the fiberline was the chip feeding system , especially with softwood.  So, during a two-week shutdown in November 2007, ANDRITZ installed a Diamondback® chip bin and TurboFeed® chip feeding system on the Varkaus digester.    

“After the restart of the fiberline in December, we were very happy because we no longer have a bottleneck in chip feeding,” Varis says.  “It is difficult to say how much benefit is coming from the chip quality and how much is coming from the pre-steaming and feeding.  But I can tell you that January and February of 2008 were two of our best months for production since I have been at this mill.  Normally, the winter months are very difficult for us, but the improved chip quality and the new feeding system have been excellent.”

top From pulp to caviar

Sturgeon  have been under heavy fishing pressure for their caviar (the roe of the female fish) and their meat.  Carelian Caviar Oy raises Siberian and Beluga sturgeon using environmentally sustainable techniques, which help to protect wild sturgeon to some degree.  The fish farm in Varkaus recirculates heat from the Stora Enso Varkaus mill, maintaining year-round optimal conditions for the sturgeon.  The largest Belugas can weigh over 1500 kg and can live to be over 100 years old.  Caviar from this species is the most delicate and expensive in the world.

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