After six years of smooth operation, the two-casing 135 MW condensation steam turbine, which is the heart of the Kladno heating plant, was opened for the first time for an overhaul to ensure safe and reliable operation in coming years.
Regular technical inspections are a must for extensive machinery units like steam turbines and turbine auxiliaries however, 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.
“Part of the general overhaul was the exchange of the high-pressure inner casing. All scheduled and unscheduled work ascertained after the machine was opened were done in accordance with the agreed schedule and the turbine was put in operation by the required deadline,” says Stanislav Klanduch, operations and maintenance director at Teplárna Kladno.