This paper presents an investigation for wet steam flow through the slit on the last stage hollow stationary blades of a steam turbine. The aim of this investigation is to evaluate the moisture removal performance by measuring the quantity of drain and “Motive steam” from some kinds of slit configurations under the actual turbine operating environment. Motive steam is effective steam sucked from the slit and removed together with drain.

The measurement was carried out on a 105 MW class steam turbine at “T-point”, a verification power plant owned by Mitsubishi Hitachi Power Systems, Ltd. [MHPS]. The measurement system was constructed right under the turbine. Even though both drain and steam were sucked from the slit on the stationary blade, drain was separated by the cyclone separator and measured by detecting the water level accumulated in the water level tank by the optical pulse sensor. For the measurement of the motive steam quantity, the choked flow rate measured by the critical nozzle was used to obtain the slit characteristic data of pressure ratio (ratio of blade surface static pressure to outer ring inner pressure). The critical nozzles were arranged in parallel, and the measurement was carried out by adopting a multi-valve switching system. And CFD slit analysis, in which the drain discharge path inside the last stage hollow stationary blade is modeled, was also carried out. The CFD slit analysis was compared with the measurement result to examine the internal flow. The corresponding CFD was calculated by ANSYS CFX. And the coarse water droplets analysis by the kinetic equation of the discrete droplet model was also carried out.

From the measurement result and the evaluation, it was confirmed that the slit with groove configuration is more effective than the normal slit under the actual turbine operating environment.

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