Successful start-up of Valmet Exergy Pre-Evaporator at Mercer Rosenthal
In early November 2025, the first installation of Valmet Exergy Pre-Evaporator was successfully commissioned and started up at the Mercer Rosenthal mill in Germany.
The Exergy Pre-Evaporator is elegantly integrated into the digester area to reduce the pulp mill’s operating costs (OPEX). This achievement is the result of close collaboration between Valmet’s continuous cooking and evaporation teams throughout the entire project — from concept development to sales, engineering, procurement, site, HSE, commissioning, and start-up, working together with Rosenthal’s mill project team.
Successful project execution with good collaboration
“We wanted to find a solution to improve the energy efficiency of our continuous cooking plant. By installing this pre-evaporation system, we can improve both energy and water efficiency. By more efficient steam consumption we can use more steam for electricity production in our existing steam turbine,” says Tobias Albert, Mill Manager for Mercer Rosenthal.
“The project execution has been very successful thanks to the strong cooperation between Valmet teams and the customer in Rosenthal. Take-over was achieved in less than three days from start-up,” says Maria Arvidsson, Project Manager at Valmet.
New technology for new and existing cooking plants
Installed inside the digester area and operated by the mill’s digester operators, the Exergy Pre-Evaporator is driven by the medium-pressure steam (MP steam) normally consumed by the digester. Black liquor from the digester is evaporated in the pre-evaporator, and the vapor produced is fed back to the digester, replacing MP steam.
“This product can be included in new digester deliveries, but the greatest potential lies in upgrade projects like Rosenthal. If linked to a production increase, or utilizing the reduced load on evaporation to strengthen washing in the fiber line and thereby reducing bleaching chemical costs, the payback for the customer will be excellent. What was really positive to see in Rosenthal is that the system can be seamlessly taken in or out of operation without interfering with the digester,” says Magnus Wilhelmsson, Senior Product Manager, Cooking at Valmet.
Energy efficiency and water savings in focus
The name Exergy Pre-Evaporator reflects its purpose: making more efficient use of the energy quality available in medium pressure steam.
“The mill’s energy efficiency improves in two ways. Firstly, the vapor removed from the liquor in the pre-evaporator making the dry solids content of the weak liquor higher and reduces the load on the evaporation plant, lowering low-pressure steam demand. Secondly, live steam condensate recovered from the pre-evaporator is returned to the boiler, reducing the need for make-up feedwater. This saves energy for heating boiler feedwater and reduces chemical usage. Overall, these savings correspond to about 40% of the steam cost for the digester,” says Mathias Gourdon, Senior Product Manager, Evaporation at Valmet.
The project for Mercer Rosenthal GmbH was delivered by Valmet Technologies Oy, which is a subsidiary of Valmet Oyj, headquartered in Espoo Finland.
Related articles
