Renewing a district heating steam turbine

After six years of smooth operation, the two-casing 135-MW condensation steam turbine, heart of the Kladno heating plant in Czech Republic, was opened for the first time for an overhaul to ensure safe and reliable operation in coming years.

 Overhaul of such a complex machinery unit takes more than a few hours or days. Since more than 30 bars steam at temperatures exceeding 535°C flow into the turbine at full power, the turbine had to be shut down and cooled before the inspection so that it could be stripped of the insulation, steam pipes dismantled, screws in the split plane loosened and the unit “opened”. Only then could all of the internal parts – particularly the casings, guided wheels and the rotors which have more than 25 steel blade stages – be inspected, sandblasted where needed, and tested for further operation.

The most technically challenging step was repairing the turbine’s parting plane. The Doosan Škoda Power engineers used 3D scanning and computer modelling for this job. With this technology, a model of the outer casing parting plane was created that enabled the technicians to assess the deformations, which were subsequently welded, ground down and scraped away. Partially owing to this progressive 3D scanning method, the upgrade was completed one day ahead of schedule.

“Most of the repairs were done right at the Kladno heating plant. Only the rotor from the combined high- and medium-pressure section and the guided wheels from the low-pressure section were hauled to the Pilsen plant to replace the sealing elements," says Jaroslava Soysal, project manager at Doosan Škoda Power.

Teplárna Kladno s.r.o. based in Kladno, a member of the Sev.en Energy Group, operates three heating plant blocks using a fuel mix that includes biomass, and two flexible gas turbines. In Kladno, it currently operates only state-of-the-art machinery gradually commissioned between 2000 and 2013. Therefore, the heating plant meets strict environmental limits applicable in the Czech Republic, as well as new regulations of the European Union valid as of 2021. In the Zlín heating plant, coal is the primary fuel and can be co-combusted with biomass and biogas. The average annual production of Teplárna Kladno s.r.o. operations is 2,100 TJ of heat which is supplied to over 35,000 consumers in Kladno and Zlín. On the average, the total production of energy exceeds 2.3 TWh. With its 250 employees in Kladno and 150 employees in Zlín, Teplárna Kladno s.r.o. is a major local employer.