Predicting the Future - Metris Digital Twin in Action at Äänekoski

We have heard a lot about the possibility of “foreseeing digitally” when it comes to processes in the pulp and paper industry, but now it’s actually happening. Metsä Fibre’s Äänekoski bioproduct mill in Finland is predicting the future utilizing the latest digital technology from ANDRITZ for its white liquor plant.

Metsä Fibre’s, part of Metsä Group, Äänekoski bioproduct mill is no stranger to the implementation of new technology. In fact, the mill is world-renowned as a leader in the new era of pulp mills as they revolutionize production processes, and become dynamic hubs for the production of bioproducts.

© vetre - stock.adobe.com

In 2019, the mill was looking to solve issues with its recausticizing plant that was causing variation in white liquor quality. In particular, the mill was looking to install an advisory platform for its recausticizing process to provide enhanced visibility for operators in the white liquor plant.

Matti Toivonen, Metsä Fibre’s Vice President of Technology says, “At the outset and start-up of the mill the decision was taken not to have any advanced tools to help the operators so that they learned how to run the process themselves. In the beginning, apart from a few basic controls, the white liquor plant was essentially run manually.

“However, we soon noticed that we were getting a lot of variation in burnt lime and white liquor quality, so it was decided to implement a system to help us solve these issues, as well as give us a good overview of what was happening across the white liquor plant. We turned to ANDRITZ as they delivered the plant and had deep knowledge of the processes, as well as working references using the Digital Twin solution.”


Metris Digital Twin is a spearhead online tool, powered by IDEAS technology, that provides comprehensive process performance insights for process improvement, operational visibility, and proactive decision-making. The Digital Twin technology can be applied across the mill and in all process islands.

The Digital Twin works in the white liquor plant by directing the automatic process control, a task usually carried out by a human operator. The technology has the ability to look around and decide on smart setpoints, optimizing the process to the full. The technology also has the ability to look ahead and decide on the next setpoints according to the data gathered from the process.

Jani Honga, Manager, ANDRITZ Automation explains, “With the Digital Twin implemented in the white liquor plant, we can predict the behavior of the process in real time by using a combination of virtual transmitters and soft sensors.

“The ultimate goal of the Digital Twin is to stabilize the process and maintain the optimal level of production. The most important factor here is monitoring and managing the causticizing efficiency (CE%), taking out the manual part of the action, and automating the process. Other advantages that the Digital Twin brings are providing visibility of the process, and advising on factors such as production levels and lime mud quality.”

The contract for implementing Digital Twin in the white liquor plant at Äänekoski was signed in March 2019 and work began on building the model offline. This was a first not only for the mill, but also for ANDRITZ. By August 2019 live communication with the Digital Twin application was set up and starting to advise the operators by providing predictions and process information. By March 2021 the mill had optimal closed loop control of the white liquor plant, allowing full visibility, monitoring, and maintenance of the process.

The ANDRITZ scope of supply to the mill included a Digital Twin of the recausticizing plant to optimize white liquor quality, along with virtual transmitters.

The outputs now being obtained from the Digital Twin include:

  • Early (3 hours) predictions for lime, lime milk, and white liquor quality
  • Under and over liming predictions for scheduling white liquor filter washing
  • Optimum delta temperature and lime/GL ratio RSP for slaker Digital Twin control (DCS control logic)
  • Calculator for production and inventory planning
  • Virtual densitometer (GL, lime mud) and white liquor flowmeters for white liquor and lime mud

Recausticizing plant at Metsä Fibre bioproduct mill at Äänekoski, Finland

© Chris Rausch

Toivonen says, “In close collaboration with ANDRITZ’s experts we built the system up and to begin with in phase I the Digital Twin was only advising our operators what to do, giving continuous advice and optimum setpoints for the white liquor process operation. We saw straight away the difference it was making to levelling the operation.

“We quickly moved onto phase II and decided to enable the Digital Twin to give the setpoints automatically with only minor operator interaction. Again we noticed that the process was becoming more stable and uniform, automatically adjusting parameters more often and keeping to the set targets much more accurately than was done manually.”


The Digital Twin at Äänekoski has now been running constantly at the mill since April 2021 with excellent results. The closed loop control for causticizing efficiency (CE) (1% increase in CE and a 15% reduction in standard deviation for CE% and efficient alkaline (EA). Operators are regularly using the production calculators for operations planning, and Metsä Fibre is delighted with the metrics and predictions made possible by the Digital Twin.

“We are successfully using the Digital Twin to control the recausticizing in the white liquor plant,” says Toivonen. “It is predicting what will happen in the process three hours ahead of time, so the end result is known for the set point of the calcium to be added to the slaker in the recausticizing process.

“We are using the Digital Twin to achieve certain target values, in particular CE% for the end product after the recausticizing process where setpoints are automatically added so we reach the targets in all cases.”

Ultimately the Digital Twin has created major improvements across the whole white liquor plant and process, including increasing capacity. Toivonen continues, “The variation in the process is now a lot lower than before the system was in place, which means we can control the level of carbonate in the white liquor. Also, the white liquor used in the cooking process is now more uniform, lowering the risks of impurities in the fiberline. One of the surprises we had with the Digital Twin is how accurate the output is. We estimated that it would be good, maybe 95%, but actually its closer to 99% and often 100% accurate.

“Overall, the Digital Twin is helping us to have a more consistent product at the same time as opening up the bottlenecks in the white liquor plant. This means more capacity in the white liquor plant due to lower variation.”

An extra hidden bonus for Äänekoski is the feature of the Digital Twin that will also calculate the quality of the lime mud coming out of the process. This ability has greatly assisted when it comes to washing the white liquor filter. “Traditionally we did a wash, and then there was still an hour of waiting when there was low quality lime mud still coming from the process, which meant another wash. Now the Digital Twin lets us know immediately when the lime mud quality is good, and has eliminated the need for another wash. This again helps us to increase capacity of the white liquor plant.

“We didn’t know about this feature when we first implemented the Digital Twin, so we were delighted with the extra bonus.”


“We are successfully using the Digital Twin to control the recausticizing in the white liquor plant. It is predicting what will happen in the process three hours ahead of time, so the end result is known for the set point of the calcium to be added to the slaker in the recausticizing process.”

Matti Toivonen,
Vice President of Technology,
Metsä Fibre


The implementation of the Digital Twin at Äänekoski is part of the ANDRITZ SYNERGY concept at the mill that offers a combination of the latest in technology with in-depth process knowledge.

“The Digital Twin is a good tool to have in the SYNERGY agreement,” Toivonen concludes. “It is designed to enable us to have access to deep process knowledge from ANDRITZ, at the same time as implementing the latest digital tools, all in one package.”

Hannu Pyykönen, Product Manager, SYNERGY, says, “The implementation of the Digital Twin at Äänekoski is a prime example of how SYNERGY agreements benefit our customers. They are never left alone, our experts are always on hand to provide the very best in process expertise at the same time as implementing the very latest technology.

“We are very pleased with the fruitful and continuous cooperation we have with Metsä Fibre at Äänekoski.”

Other SYNERGY agreements in place at the Äänekoski mill include Digital Twin for the cooking process, DD-Washers and Smart Woodyard.

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    Metris Digital Twin in action at Äänekoski

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