An attemporator controls steam temperature while a de-superheater removes whatever superheat there is in steam and reduces the temperature to a point at or nearly at saturation temperature. Attemporators are generally found in and/or associated with boiler steam, in zones where too high of a temperature affects something down stream of that point. An attemporator might be used between super-heater zones in a multi-zone super-heater boiler or in a re-heater zone to control re-heater outlet temperature.
Attemperation is the process in which water is prayed to control the temperature. In this case feed water from the boiler feed pump is sprayed directly to the steam coming out from the primary super heater through the nozzle. Here the temperature of steam reduces, This steam then passes through the secondary super heater. If outlet temperature of the super heater is high than the control valve allow more spray water through the nozzle to reduce temperature. The Temperature control valve is put in auto mode so that the spray water quantity can be adjusted automatically.