Thermal Analysis of Steam Turbine Casing

Abstract

Energy is the driving force of civilization. Energy can be created from many sources. Among the various energy converting devices steam turbines are used extensively. The steam turbine is among the most important prime movers for generating elec- tricity as well as for process industries. Hence it is important that the turbine should work on the optimum power output and e ciency. Practically it is di cult, due to the losses from the turbine casing. Hence it is necessary to reduce the losses from the turbine casing for utilizing the available energy for work. In order to minimize the heat losses from the turbine casing, it is necessary to provide an optimum thermal insulation thickness on the turbine casing so as to minimize the cost involved for the thermal insulation. In order to arrive at the optimum thickness of insulation, a 3-D model of the turbine casing (SST-300, Siemens make) was prepared using the software Autodesk Inventor. The prepared 3-D model was imported to ANSYS software for evaluating the tem- perature pro le on turbine casing as well as to evaluate the temperature and heat loss after applying the optimum insulation thickness. The analysis was carried out in two parts: Individual component analysis and complete assembly analysis. In the rst analysis, each individual component was divided into di erent parts with in it and the temperature as well as heat loss was evaluated for all the individual parts of in- dividual components. In the later analysis all the individual parts are assembled and analyzed as a complete assembly. Thus after implementing the optimum thickness of insulation, the heat loss was recalculated (and hence the energy saved) as compared with the existing insulation thickness. The overall turbine casing assembly without insulation was further analyzed to check the e ect of the higher inlet steam parameter using ANSYS software. In the case of higher inlet parameter from the preliminary analysis, the stress values are close to the permissible values for the CASE-I [Pressure-105 bar and Temperature-535oC], whereas in CASE-II [Pressure-120 bar and Temperature-550oC], the stress values ex- ceed the permissible limit set by SIEMENS Ltd. The analysis concludes that for the existing turbine SST 300, the Guide Blade Carrier (GBC) front face undergoes a maximum stress, and the maximum permissible steam inlet conditions for the turbine are at 105 bar pressure and 535oC.