De-superheater

Another boiler internal fitting is the de-superheater. It maybe located either in the steam drum or in the water drum. All the steam generated in a single-furnace boiler is led through the superheater.

In High Pressure Boilers the superheater is the first section where the flue gasses contact the metal tubes are subject to hot section fireside deposits. This means that starting from maintenance, as deposits accumulate, its efficiency drops.

As to keep the turbines efficiency constant, superheaters are oversized as to provide sufficient heat, even when fouled. So the steam is over-superheated at the superheater during normal operation, and is lowered the heat load.

Also,   since   some   auxiliary machinery is not designed for superheated steam, the steam must be cooled down. This is done with a de-superheater. 

The de-superheater gets steam from the superheater outlet, and decreases its temperature to the desired level.

The most common type of desuperheater in power plants is to inject pure water into the superheated steam, through automatic quill. Such water has to be in extremely pure quality, otherwise deposition into desuperheater will occur, because this water is totally evaporated.

Another desuperheater design is to pass a flow of a superheated steam through a coil, submerged in water either in the steam drum or in the water drum.

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