ROEZ, s.r.o. has successfully finished Slovenské elektrárne, a.s. job ref. no.: IPR M18007 – Modification of moisture separators before TG on the 2nd Unit of NPP Mochovce. Works on unit 1 are currently in progress.

Scope of Works included design, supply of materials, manufacture, NDT, packaging, transportation, erection and trial run tests of new DN500 carbon steel dynamic moisture separators without mechanical screens as replacement for existing nonconforming, out of lifetime and technically obsolete ball separators along with adjoining systems and equipment customisation (pipe supports, drains, insulation etc..).Separators are installed in steam lines before steam entrance to steam turbine as a critical component protecting the steam turbine from bigger water particles and other possible contamination entry.

Existing ball separators equipped with mechanical screens were no table to fully separate the water phase and mechanical particles as their construction caused swirling without the possibility of proper separation. Also their pressure loss was significant. Complicated design was a potential risk of leakage and defects occurance.

New designed dynamic separators have a different internal arrangement than the old ones, which for separation of water phase (bigger water droplets) and mechanical contaminant utilises only the dynamic effect, where by sudden direction change of steam flow these are catched in socalled „blind catcher“. Considering the difficult internals absence and reinforced walls, mainly in excentric reduction areas their life time is significantly increased (to min. 40 years). The „blind catcher“ is used to hold the catched mechanical contamination and regulary cleaned during planned outage or shut down. Catched condensate is leaded from the bottom part of the catcher via standard steam trap.

During the engineering phase the separators were calculated acc. to EN13480-3 requirements using Visual Vessel Design by Hexagon AB software, so the sufficient strength could be proven. Strength-dilatation calculations of adjoining pipeline were also made for correct spring supports design. One of the main goals was to decrease of the current separators pressure loss by maintaining the high efficiency of separation. To secure this, optimalisation of the rip-off edge radius was made with reflection to find such a geometry where the ability to separate is high, pressure loss low and the extreme steam velocity causing unwanted side effects on rip-off edge are not present (noise, vibration etc...). Separators were also CFD hydrocalculated for different types of rip-off edge pressure loss determination and optimal solution selection.

Calculation methodology for numerical CFD solution is based on finite volume method implemented in OpenFOAM software. SimpleFoam solver for laminar and turbulent sustained flow of liquids was used. Medium – saturated steam was thought as non compressable medium with related properties depending of temperature. Turbulent flow was simulated via RANS model (Reynolds Average Navier Stokes equations) close to walls common used function to omega SST („wall function“).

During planned outage the newly designed dynamic separators were installed to fixed place. During start-up and operation complex trial run tests were performed, proofing achievement of guaranteed parameters, mainly the pressure loss below 23kPa compliant to our calculations.

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