A successful boiler conversion enables fossil-free production
The conversion of a coal-fired district heating boiler to bubbling fluidized bed (BFB) unit enabling wood-pellet firing at the Salmisaari district heating plant in Helsinki, Finland, was a key milestone in Helen’s transition away from coal.
Helen Ltd provides electricity, heating and cooling for approximately 600,000 customers in Finland. The company’s district heating network covers over 90 percent of heating needs of Helsinki’s residents. Helen aims to achieve net-zero emissions by 2040.
The recent conversion of K7 boiler at the Salmisaari district heating plant supported Helen’s goal of phasing out coal and at the same time strengthens the development of a sustainable energy system.
The conversion of the Salmisaari K7 boiler was the final major step enabling the shutdown of our last coal-fired unit.
“Helen has been on a long, carefully phased journey to abandon coal, and the conversion of the Salmisaari K7 boiler was the final major step enabling the shutdown of our last coal-fired unit. The conversion played a crucial role in ensuring security of supply during our transition towards cleaner energy,” explains Aleksi Nurmi, Project Manager at Helen.
Extensive market dialogue enabled the selection of the optimal solution
Helen’s initial pre-studies suggested choosing a pulverized pellet boiler similar to Helen’s K6 unit.
“However, the extensive market dialogue we had with several suppliers, together with our own operational experience, made us reconsider. In the end, BFB (Bubbling Fluidized Bed) firing of wood pellets emerged as the most reliable option. With that choice, we were also able to centralize pellet logistics to our Salmisaari plant,” Nurmi says.
During the public procurement process, Valmet stood out due to its strong technical expertise in both boiler conversions and flue gas condensing systems, its deep understanding of the project scope – including the constraints of a protected 1950s building – and its ability to reuse existing equipment, structures and piping, reducing cost and complexity.
“Valmet demonstrated strong procurement and project management competence, which is essential in public tendering. They presented a technically convincing overall solution that integrated the boiler, flue gas condenser, district-heating heat recovery and even district-cooling heat recovery – a rare configuration in Finland – along with the automation systems.
From well-managed project execution to successful handover
One of the success factors during the project was the close cooperation between Helen and Valmet. Frequent coordination meetings ensured alignment on technical solutions, and any concerns were addressed immediately.
Helen’s Production Manager Sami Pesonen says that the installation window was very tight, which required work to be carried out in two shifts, and at times around the clock. The building itself is listed, meaning no new openings could be made. As a result, all large components had to be brought in through existing doors and assembled inside.
“The installation phase was demanding, but Valmet reacted quickly and decisively whenever challenges arose. Their response showed commitment to keeping the tight schedule on track. Valmet also allocated a well-resourced project team, which meant the right expertise was always available,” Sami Pesonen says.
Commissioning of the new boiler began in late 2024, and commercial operation started in March 2025. Thanks to thorough training and documentation, the handover was smooth, with operational responsibility gradually transferred to Helen.
“During its first operational year, the plant has performed well in base load operation. When issues have come up, Valmet has taken an active, solution-oriented role in investigating them and proposing fixes,” Pesonen says.
Aleksi Nurmi, Project Manager, and Sami Pesonen, Production Manager, at Helen’s Salmisaari district heating plant in Helsinki, Finland, where the converted K7 boiler now supports fossil-free heat production.
Service agreement ensures long-term performance
To ensure optimal performance of the newly commissioned boiler through its entire lifecycle, Helen and Valmet signed a four-year service agreement. The agreement covers process disturbance support, on-site inspections, operational review meetings, remote troubleshooting, and reporting and fault-analysis support.
The agreement helps us maintain high availability and supports continuous improvement.
“The agreement helps us to maintain high availability and supports continuous improvement. Valmet has been quick to respond and proactive in helping us optimize the plant,” Pesonen says.
As Helen moves toward its long-term decarbonization targets, the combination of modern technology and ongoing lifecycle support ensures that the K7 boiler will continue to operate efficiently and reliably throughout its service life.
Text: Marianne Valta
