Carbon or Stainless steel superheater with shield perfect smooth bending and ovality
1. Superheater tubes are surfaces for heat exchange, with the object of increasing the steam temperature, after it comes from the boiler drum, to a value higher than saturation.
2. This has two basic purposes: to increase the thermodynamic efficiency of the turbine, in which the steam will be expanded; and to make the steam free of humidity. In normal operation, the boiler analyzed in this paper, named REDUC/SG-2001, produces steam that is superheated by approximately 200 °C at the inlet of the turbine.
3. The steam flow has to be intense to permit the heat absorption from the tube, avoiding deformation because of high temperature.
1. The superheater can be divided in two sections, primary and secondary, as in the boiler studied, where the superheater tubes are within the radiation zone.
2. After nineteen years of service, the primary one showed some tube deformation, which had become greater when observed at the last inspection/maintenance shut downs.
3. This residual plastic deformation was observed on the outlet tube, attributed to differential dilatation, because of different temperatures (DT), between the last two tubes, anchored by spacers, and causing buckling.
4. When the boiler had twenty three years of service, a stress and metalographic analysis was made on an assembly removed from the boiler, involving yet dimensional inspection, nondestructive testing, hardness measurement and deposit examination.
Benefits of Superheaters in Boilers
Increase in efficiency of the steam power plant
Minimized erosion of turbine blade
Less steam consumption
Reduction of condensation loss in the boiler steam pipes
Increases the temperature of saturated steam by removing entrained water particles from turbines steam