PM2 - 1st stage cleaners behind the papermachine headbox

A New Approach – With Significant Environmental and Financial Returns. The Huge Benefits of an Approach System Rebuild

Graphic paper demand has taken a big hit over the last decade, which, along with volatile energy prices and increasing environmental regulations, has meant paper producers need to look at every area of production to improve efficiency and save energy. For a second time, Stora Enso chose ANDRITZ to rebuild a paper machine approach system at its Anjalankoski mill in Finland, a project that has obtained extraordinary results.

1^st stage cleaners behind the papermachine headbox

PM2 - 4th trough 6th stages TC 133MIVC and SC 133FR cleaners

4^th through 6^th stages TC 133MIVC and SC 133FR cleaners

It’s not often that a major system or process upgrade at a paper mill has an ROI of less than a year. However, in the case of the latest approach system rebuild on PM2 at Stora Enso’s Anjalankoski mill in south east Finland, the investment payback time was just eight months.

“We already had success with a rebuild of the approach system on PM3 at the Anjalankoski mill which was carried out in 2015,” explains Jouni Parviainen, Global Director, Technology & Sales, Cleaners at ANDRITZ. “In that case we managed to save the mill over 5,000 MW in electricity annually after the system rebuild.

“Five years later in 2021, we were asked to carry out the same project on PM2 due to the energy and operational savings achieved.

Again, we have achieved major savings on energy, raw materials and water, as well as dramatically reducing the carbon footprint at the mill.”

Jouni Parviainen

Global Director, Technology & Sales, Cleaners at ANDRITZ

ANDRITZ has a lot of experience in approach system rebuilds around the world with some 20 successful projects already completed in Europe and Asia. In 2013 ANDRITZ carried out audits for 13 out of 50 of Stora Enso’s paper machines located at various mills around the world which could benefit from a rebuild of the approach systems. Parviainen says, “We trained Stora Enso mill personnel to gather data that would tell us whether a rebuild would be beneficial, and from that data we produced a detailed report that covered recommendations on the 13 machines for short and long-term benefits possible.

After analyzing the recommendations, in 2014 Stora Enso decided to go ahead with a rebuild on its PM3 which was carried out in 2015. In 2020 ANDRITZ was contacted again by Stora Enso to carry out the same project on PM2 due to the energy and operational savings achieved on the PM3 machine.

A COMPLETE RETHINK – OUT WITH THE OLD, IN WITH THE NEW

The PM2 at Anjalankoski produces 780 t/d of both coated and uncoated book paper at basis weights ranging from 52 to 100 g/m². The machine runs at a speed of 1,340 m/min with a trim width of 5.4 m. In May 2020 ANDRITZ was contracted by Stora Enso to carry out the approach system rebuild which then took place in 2021.

The rebuild initially involves having an expert audit to define exactly where and how the energy savings can be made. The audit also defines what existing equipment in the approach system can be retained or upgraded to ensure capital cost is kept to a minimum. Parviainen says, “In the case of PM2, we simply replaced all the cleaners which were obsolete TC 132s with new TC 133s. We also replaced all the old-style banks with modern TC 133s.”

“We also looked at all the pumps,” continues Parviainen. “We found that some were in good condition and just needed upgrading with changes such as frequency converters and new motors. We took out the second stage large pump completely and replaced it with the existing third stage pump and changed the impeller to enable further energy savings.”

On a paper machine approximately 30% of electrical energy consumed comes from pumping, and pump-based systems represent the largest energy consuming area where potential savings can be made. In fact the largest pump in a paper machine is contained in the approach system.

Changes to pumps included:

1st stage fan pump 800 kW motor and gearbox replaced with 355 kW motor and coupling
2nd stage feed pump and 400 kW motor replaced with the existing 3rd stage pump, new impeller, 160 kW motor and a new common base for pump and motor
A new 5th stage feed pump with 18.5 kW motor replaced the existing 6th stage pump with 37 kW motor

New 1st stage cleaner feed pump motor

New 5th stage cleaner feed pump and motor

ANDRITZ reconfigured the various stages of the approach system, reusing existing equipment wherever possible as well as adding its new MIVC chamber cleaning solution which has molded section chamber with dilution holes for better performance.

The initial design of the rebuild was carried out using the latest in 3D modeling where each working area of the machine room floor and basement were laser scanned. The full scope of the approach system rebuild from ANDRITZ included:

Mechanical engineering, layout and piping engineering, basic control engineering
Process pipes, fittings and pipe supports
Complete erection for cleaners, dilution manifolds, piping changes, valves, instrumentation, pumps, and impeller change
Erection supervision, commissioning and start-up
Performance test run

OVER 50% REDUCTION IN ENERGY, AND A DRAMATIC REDUCTION IN CO₂EMISSIONS

Before the rebuild, PM2 was consuming 1032 kW and ANDRITZ had given a guarantee that after the project consumption would not exceed 503 kW. After the rebuild was started up in October 2021 the installed power was 650 kW and the power consumption had come down to 492 kW – representing a remarkable 54% saving in energy. This means an annual saving in power consumption of 4,536 MW.

“We found we were able to save power at every stage of the existing approach system with this rebuild,” adds Parviainen.

However, the savings were not limited to power and energy. Stora Enso was also losing a lot of fiber due to rejects – some 7 bdmt per day in 2020. After the rebuild the good fiber loss on PM2 reduced by 931 bdmt/a, or 2.7 bdmt per day, and a further reduction in power consumption of 2,379 MW/a was achieved due to the lowering of fiber loss. The amount of white water loss rejected has also reduced by 54% to 46,200 t/a.

“We calculated all the savings made after the rebuild on energy, fiber loss and water usage, and the savings were substantial,” says Parviainen. “The customer is very happy with this result.”

The success of the PM2 approach system rebuild at Anjalankoski was the subject of a special masters thesis at Aalto University in Finland which was carried out in 2022. The thesis calculated that the total energy savings over a year as a result of the rebuild added up to 6,915 MWh/a, which is equivalent to a CO₂emission reduction of 2,891 tons per year.

“Our customers are now almost always asking us about the CO₂ emissions they can save when embarking on specific projects,” concludes Parviainen. “This rebuild on PM2 is a prime example of major financial savings and environmental improvements going hand-in-hand for a new approach to paper machine efficiency.”

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