The Application of the Baumann Stage in the Low-Pressure Cylinders of Condensing Turbines

Among the characteristics of the power-generating steam turbines, the specific metal intensity ranks very high. Low-pressure cylinders (LPCs) that use a two-tier Baumann stage have the lowest value of this parameter. The Baumann stage allows a 50% increase in the limit steam passage rate to the condenser without increasing the last-stage blade length and the weight of the turbine. In Russia, such a solution was implemented in the most widely used K-200-12.8 (K-200-130) turbine manufactured by LMZ. However, the experience from operating the turbine and results of investigations into the economic efficiency of the K-200-12.8 turbine have shown that these turbines equipped with the Baumann stage have lower efficiency than similar turbines without the Baumann stage. In the course of subsequent modernization of the K-200-12.8 turbine, the Baumann stage was replaced by a new last stage with longer rotor blades. The design solutions employed by different turbine manufacturers to modernize the K-200-12.8 turbine have been analyzed. It is pointed out that the LPC of this turbine was modernized without analyzing the causes of the low economic efficiency of the basic LPC. An investigation into the real causes of the reduced efficiency of the K-200-12.8 turbine has shown that the LPCs modernized by different companies preserved the drawbacks intrinsic to the basic design. In view of this, a simple variant for modernization of the LPC preserving the Baumann stage is proposed. Its efficiency should not be inferior to the efficiency of modern LPCs whose last stage is equipped with longer blades; a conclusion that is supported by the results of mathematical modeling of the flows in the penultimate- and last-stage nozzle diaphragms of the new LPC.