Multi-tier steam turbines. Prospects and particularities. Part 2: Two-tier stages for new two-tier low-pressure cylinders with elevated capacity

Abstract

There are reviewed possible options of a structure of two-tier stages being basis for creation of elevated capacity low pressure (LP) cylinders with two-tier steam path. Two tier steam path is created by a number of stages of which the most loaded and consequently highly engineered is the last two-tier stage, namely the moving blade. That is exactly why this work is focused on search of optimal structure of moving blade of the last two-tier stage of the LP cylinders. Based on strength and aerodynamics calculations we were able to create a construction of fork blade combining high values of stage aerodynamic efficiency in which the internal efficiency ratio is 87.6% for upper and 77% for lower tier with respect to all losses including turbine exit losses, that allows us to reach LP cylinder efficiency ratio of 87.1%; at that the proposed construction provides high reliability – strength factor of two-tier last stage rotor blade is over 2.8, that reaches the level of present norms.