WEIGHT OPTIMIZATION OF STEAM TURBINE CASING USING OPTISTRUCT TOOL

The Turbine Casing guides the steam from the last stage of the turbine to the condenser and it is designed to minimum pressure losses, which would increase the efficiency of the turbine. After the steam leaves the CASING section, it then enters the exhaust section of the turbine and then to a condenser where it is cooled to its liquid state in vacuum condition. A Steam Turbine Casing was designed earlier for use with the 8MW-12MW impulse steam turbine (ST) newly developed by BHEL. This design of Turbine Casing is complicated in comparison to those used in industrial turbines of comparable ratings. Hence a need was felt by BHEL to optimize the Casing design to reduce its weight. This objective has been achieved in the present work. The Casing is made in four parts, the lower left part, lower right part, upper right and upper left part. The casing has the assembly with a valve chest and exhaust hood from the lower parts. The existing Casing is first analyzed for stresses and deformations and then optimization of the same is carried out. Since the Casing is a large and complicated part it needs a lot of inputs to accurately define the complete geometry. The solid model is created in I-DEAS and finite element model for the casing is created with ten-node tetrahedral elements in HYPERMESH software. Optimization of the casing is done using HYPERMESH. This FE Model is then transferred to ANSYS.8.0 for analysis as it has better FE analysis capabilities. The type of analysis done in the present work is Stress analysis.