Depending upon the way heat is transferred, super-heaters are classified into three types:

1. Radiant superheaters
2. Convective superheaters
3. Combined radiative and convective superheaters

Radiant Superheater

• Radiant superheaters receive energy primarily from thermal radiation from the furnace with little energy from convective heat transfer.
• Radiant superheaters are located at the furnace exit or turning section.
• The radiant superheater absorbs more enthalpy at partial loads when compared to the convective type.
• At lower loads, the flow distribution inside the superheater tubes is less uniform. The radiant superheater outlet temperature decreases with increasing boiler output.
• At higher loads the mass flow rate of the combustion gas is high, because of the increased amount of fuel and air for combustion.
• The convective heat transfer coefficient increases both inside and outside the tubes. Thus the steam re- receives more heat transfer per unit mass flow rate, and its temperature increases with load.
• The surface area required to transfer a given amount of energy will be lower due to the higher log mean temperature difference and higher heat transfer coefficient.