Stress Analysis and Optimization of Low Pressure Turbine Outer Casing for Supercritical Fossil Power Plant

Abstract

Supercritical Steam Turbine is an important element in any power plant using fossil fuel. The present dissertation work focuses on designing and optimization of casing of low pressure stage of a super-critical turbine of 660 MW capacity as to reduce the fabrication cost and save material. Modeling of the outer casing has been performed using Siemens NX 9.0 taking standard outer casing drawings. For any FE solutions, the sensitivity of solution output if getting a ected by mesh density can lead to error. To eliminate the same in the present case, grid independency has been checked using benchmark model of seal oil test bed. The same is applied to the model of outer casing of low pressure turbine. Finite element analysis of the component has been carried out using Ansys 16.0. Equivalent stresses of each trials are compared with the allowable limit. Allowable stress limit is being decided based upon the calculated factor of safety. FE based size optimization has been done in which the thickness of horizontal ange has been varied and compared to limits as discussed above. In the same, thickness of end wall plate and side wall plate of the upper casing have been varied and observations were compared to give the best e ective results. Also, end wall plate of the lower casing is being modi ed and the results were noted down. In order to avoid resonance, modal analysis is being performed along with har- monic analysis at excitation frequency of 50Hz to see whether the optimized model is safe or not. Stresses are being compared with the stress limits as discussed above. Re-optimization has been performed in order to satisfy the requirements posed by Harmonic analysis. Moreover, the shape of the casing is also checked using topology optimization to ensure proper distribution of material within continuum.