Big savings in pumping energy with new synchronous reluctance motor at Stora Enso

2014-04-16 - Stora Enso’s pulp and paper mill in Nymölla, Sweden recently replaced a pulp pump motor and drive with ABB’s IE4 synchronous reluctance (SynRM) motor and ACS850 drive package to test out the energy savings. The measured reduction in energy consumption, in the range of 15 to 25%, seems almost too good to be true. But based on numerous tests, and a fair bit of skepticism, the results have been reconfirmed via thousands of data points.

ABB’s new synchronous reluctance motor and drive technology offers super-premium IE4 efficiency. The main benefits are seen in big energy savings, with a reduced carbon emissions and a cooler running motor.

Stora Enso was very interested in the energy saving potential with ABB’s SynRM motor and drive technology.
Sendy Zigon is an Automation Engineer in the Electrical Department in the Nymölla mill. He explains why the company was keen to test the new technology.

“Energy saving is a very high priority for our mill, which presently uses about 60 MW and the plan is to reduce that by half a megawatt per year. Of course the big savings comes in steam used in the pulp and paper mill, but we have hundreds of motors in this plant and if we can gain efficiencies it makes a big total impact on energy consumption too.”

“Therefore we were interested in the new SynRM motor and drive technology due to the promised energy savings of 5-10%. To make a valid test comparison, we chose a position in the pulp mill where there are two motors and pumps sitting side-by-side pumping the same thick pulp solution.”

Side-by-side for valid comparison
In February 2013 the new SynRM motor and drive package was installed on one of the pumps, while the other kept the old motor and drive. Typically, the pumps are alternated where one runs 24/7 for one week, then they switch to the other pump and repeat the process. Only one pump is normally needed for mill operation with the other on standby. The motors both run at about 40-50% of maximum capacity. Because the process has changed over the years they don’t need to run at 80 to 90% as they did in the past.

Sendy continues the story: “So we measured the new motor and drive versus the old motor and the old drive, using a standard Dranetz PX5 power monitor to measure the power consumption. We can easily change from using one of the pumps to the other, so we worked to make sure the process conditions were similar as far as the pressure head and the tank levels, as well as the pulp consistency. In our mind the process conditions are very similar. I’m not saying this is rocket science but we made a pretty valid comparison.”

“Energy saving is a very high priority for our mill, which presently uses about 60 MW and the plan is to reduce that by half a megawatt per year."

The new SynRM motor (left) and the existing induction motor, right.

25% less energy consumption
The results have been almost too good to believe, but there is no logical explanation for why they should not be valid. The highest mean value measured was 32.0 kW for the new SynRM motor, while for the old motor the lowest mean value was 43.6 kW. This gives a saving of more than 25% in energy consumption, measured at the switchgear to give complete consumption of the combined motor and drive.

Thousands of data points
Sendy admits that the results seem very high. “We as automation engineers were very skeptical about this result in the beginning as well. And when we spoke with our process engineer colleagues they were very blunt and said that it was impossible to save so much. Therefore we went through the exercise numerous times, with a very long series of data collection, and got essentially the same result. I have an Excel document with thousands of measurement points and the fact is these are the numbers we have for comparing the two motors.”

The only thing that is not exactly the same for the side-by-side pumps is the slightly different pipe geometry. The old pump feeds into a T-joint, while the new one feeds into a more rounded pipe elbow. Otherwise the testing conditions were extremely similar, with the same pulp and tank levels, at the same temperature and consistency. So the process condition differences are very small, and it’s hard to believe that T-joint pipe geometry could cause such energy losses.

ABB engineers think that a SynRM motor could perhaps save 6% in energy consumption, and perhaps the new drive another 2 or 3%, meaning about 10%. Mattias Meijer, sales engineer for ABB Sweden, says that they are looking into what the possible explanations could be for such incredible energy savings.

Sendy Zigon (right) discusses the data collection with ABB’s Mattias Meijer.
“The synchronous reluctance motor is still a very new product, and we are continuing to gain knowledge about just how efficient it is and what energy savings it can give.

When I asked the Stora Enso automation people how the motor was running, they said the results were much better than we had indicated they would be. I couldn’t restrain myself from saying, jokingly: We at ABB don’t keep our promises. We do much better than that.”

100% certain
Concluding the discussion, Sendy Zigon from Stora Enso smiles and says: “We don’t know for sure how much energy saving we are getting from the new motor technology. Maybe it’s 25%. Even if it is 10 or 15% it is big. But I am 100% certain that we can conclude that it is much better than the old one!”

ABB ( is a leader in power and automation technologies that enable utility and industry customers to improve their performance while lowering environmental impact. The ABB Group of companies operates in around 100 countries and employs about 150,000 people.

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