What distinguishes a radiant superheater from a convection superheater?

A radiant superheater is distinguished by its exposure to the radiant heat of the furnace. In a radiant superheater, the heating surfaces are positioned in such a way that they receive direct infrared radiation from the flames or the hot combustion gases within the furnace. This design allows for effective heat transfer, as the superheater absorbs energy directly, enhancing the efficiency of steam generation.

This is in contrast to a convection superheater, which primarily relies on the movement of the hot gases to transfer heat to the superheating surfaces. In a convection superheater, the heat transfer occurs as a result of the gas flow around the tube surfaces, usually in a more indirect manner compared to the radiant method.

The other options do not correctly define the unique feature of a radiant superheater. For instance, being placed entirely within the water tank is not characteristic of a radiant superheater and would actually suggest a different configuration. Utilizing hot air from the burners refers more to combustion processes rather than the heat source specific to radiant superheating. Lastly, being installed in a separate structure describes a potential layout but does not pertain specifically to the mechanisms of heat transfer that differentiate radiant and convection superheaters.