SUPERHEATER AND REHEATERS
• The function of the super heater is to remove the last trash of moisture from the saturated steam leaving the boiler tubes and also increases its temperature above the saturation temperature.
• For this purpose the heat of the combustion gases from the furnace is utilized.
• Super heated steam is that steam which contains more heat than the saturated steam at the same pressure. The additional heat provide more energy to the turbine hence power out put is more.
• Superheated steam causes lesser erosion of the turbine blades and can be transmitted for longer distance with little heat loss
• A superheater may be convention type, radiant type or combination. However ,convention superheaters are more commonly used.
|Functions of superheater
• In addition to super heater modern boiler has reheater also. The function of the reaheater is to superheat the partly expanded steam from the turbine, this ensure that the steam remain dry through the last stage of the turbine.
• A reheater may be convention type, radiant type or combination.
Feed Water Heaters:
These heaters are used to heat the feed water by means of blend steam before it is supplied to the boiler.
Necessity of heating feed water before feeding it back to the boiler arises due to the following reasons.
• Feed Water heating improve overall efficiency.
• The dissolved oxygen which would otherwise cause boiler corrosion are removed in the feed water heater.
• Thermal stresses due to cold water entering the boiler drum are avoided.
• Quantity of steam produced by the boiler is increased.
• Some other impurities carried by steam and condensate, due to corrosion in boiler and condenser, are precipitated outside the boiler.
|Water steam flow diagram