Coal Based Thermal Power Plants Superheater Mechanical and Electrical High quality
Description of Boiler Superheaters
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.
Boiler Superheater in details
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. 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. 2. This residual plastic deformation was observed on the outlet tube, attributed to differential dilatation, because of different temperatures, between the last two tubes, anchored by spacers, and causing buckling. 3. After that, in December 2001, 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.
Construction and Working Principle
1. There are many types of superheaters. A combination type of radiant and convective superheater is shown in figure. 2. Both these superheaters are arranged in series in the path of flue gases. Radiant superheater receives heat from the burning fuel by radiation process. Convective superheater is placed adjacent to the furnace wall in the path of flue gases. It receives heat by convection. 3. Steam stop valve is opened. The steam (wet or dry) from the evaporator drum is passed through the superheater tubes. First the steam is passed through the radiant superheater and then to the convective superheater. 4. The steam is heated when it passes through these superheaters and converted into superheated steam. This superheated steam is supplied to the turbine through a valve.