Valmet supplied pulp mill rebuild at Mercer's Stendal mill started up

Dr. Martin Zenker, plant manager at Mercer Stendal, and Jan-Peter Daum (head of major projects) in front of the three new heat exchangers in the cooking plant at the Arneburg pulp mill. Photo: Stefan Rühling

This is an important part in Mercer’s plans to continuously improve environmental performance and increase the pulp production to 740,000 tons per year at the mill.

Rebuilds were done during planned shutdowns in the spring and summer 2021 and included rebuilds in the batch cooking plant, brown stock washing plant, pulp dryer, lime kiln and in the bark boiler.

“For Mercer Stendal it was of importance to combine capacity and efficiency increase with an increase of environmental performance”,  says Dr. Martin Zenker. “The cooking plant expansion also included the newest developments for batch cooking. This gives added value also to our customers, since pulp quality is even more stable and can be further improved”, the mill manager continues.

Accordingly, Zenker is positive about the future:  “The lime kiln cooler exchange enables us to ensure compliance with the newest tough German environmental regulations. Also the basis was set for future decarbonization projects with a first step of being more energy efficient with the new cooler.” 

Bernhard Trunk, Senior Sales Manager at Valmet, adds: “This project has been interesting in several ways. It will increase efficiency and production capacity in the batch cooking plant and in the pulp drying line. Further, it is the first of its kind in the pulp industry where a traditional lime cooler has been replaced with a stationary cooler. This demonstrates the opportunities to upgrade coolers in existing mid-size to large lime kilns with a stationary cooler that reduces the fuel consumption, increases availability and improves operational flexibility.”

The project was implemented mainly under corona conditions. “This brought with a lot of restrictions normally no project manager could imagine”, says Jan-Peter Daum, Head of Major Projects at Mercer Stendal. “However the project crews of Valmet and Mercer managed to keep the planned timelines and equipment start ups have been performed according to the original plan.”

The measures have not yet been fully completed.  “For this year the remaining rather smaller projects will be implemented. The focus will be on our baling lines to balance sprint capacity and reliability of the equipment”, Daum continues.

Technical information about the delivery

Batch cooking plant capacity was increased by adding two more digesters to have a total of 12 digesters. Liquor feeding system to digesters, black liquor heat recovery and chips feeding to cooking plant were upgraded to match the higher production. The new production rate is approx. 2500 air dried tonnes per day as unbleached pulp. The project included in addition to adding new equipment also finding new and innovative ways of using the existing equipment in a more efficient way.

In September the rebuilt dryer was running so well it exceeded the set guarantees with a good margin during normal operation. The new design of the corner towers enables the end tower area to be used as an effective drying area. It also increases evaporation capacity in the same dryer length and gives better runnability, which improves the sheet support. When upgrading the heat recovery, the speed of the fans was increased and by that increasing the capacity of the line further. The drying capacity is now allowing 2300 air dried tonnes per day.

The original 600tpd burnt lime cooler supplied in 2002 was replaced in 2021 with a new and more effective stationary cooler designed for 680tpd burnt lime. The new stationary cooler was successfully started up in May 2021 and passed performance guaranty test in summer 2021 within one year of receiving the contract. In general, compared to normal lime coolers the stationary cooler has a higher cooling efficiency with lime product temperature of less than 100°C. This reduces the kiln fuel consumption by more than 2%. In addition, the stationary cooler has a very high availability with little wear and provides more operational flexibility compared to traditional coolers.

Information about the customer Mercer Stendal

The Stendal mill was completed in 2004 and it was, for nearly the next decade, the most modern northern bleached softwood kraft (NBSK) pulp mill in the world, originally designed for 520,000 tonnes of NBSK and about 100 MW of green electricity. Today, after a tradition of continuous development of the mill, including the project “Blue Mill” completed in 2014, the mill has now approx. 740.000 tonnes of NBSK capacity, 148 MW of green electricity, and a modern turpentine and tall oil extraction plant. Mercer Stendal produces enough green energy to meet internal needs as well as provide green energy to the electricity grid.

For further information, please contact:

Bernhard Trunk, Senior Sales Manager, Pulp Solutions in EMEA Region, Valmet, tel. +49 173 3080 559