Superheater

• It is used to remove the moisture from saturated steam coming out of boiler to increase its temperature above saturation point
• It avoids condensation of steam and avoids the erosion of blades in turbine
• The metal used for super heat tubes must have high temperature strength, creep strength and resistance to oxidation
• Normally carbon steel and chromium Molybdenum alloys are used they withstand temperature of 510ºC and 650 ºC
• Temperature of combustion is approaching the fusing temperature of ash in the coal and therefore there is tendency of the ash to collect in the fluid form on superheat tubes. This is called as slagging.
• Methods to avoid slagging

• Locate close to the furnace to develop required steam temperature
• A bank of screen tubes before superheater to limit slag accumulation
• Limiting constant temperature of 60 to 65% of load rating
• Use of combined convection-radiation superheater
• It effects improvement and economy in the following ways

• The super heater increases the capacity of the plant.
• Eliminates corrosion of the steam turbine.
• Reduces steam consumption of the steam turbine.

Types of Super Heater

• Plate Super heaters
• Pendant Super heaters
• Radiant Super heaters
• Final Super heaters