The steam vapor picks up energy and its temperature is now superheated above the saturation temperature.
Most boilers produce steam to be used at saturation temperature; that is, saturated steam.
It is a liquid at a temperature lower than the saturation temperature at a given pressure.
The steam is then described as superheated by the number of degrees it has been heated above saturation temperature.
Similarly, a liquid at saturation temperature and pressure will boil into its vapor phase as additional thermal energy is applied.
This article in Wikipedia discusses the saturation temperature of a liquid.
This is because the vapor will be at a temperature higher than the saturation temperature (212F for water) for a given pressure.
The water is kept below the saturation temperature to prevent film boiling and the associated drop in heat transfer rate.
This economizer heats up the water to its saturation temperature.
At this saturation temperature, further cooling results in condensation of water.
