How to Desuperheat a Vapor

Calculate the pressure and temperature of saturated steam and the number of degrees it has been heated above the saturation temperature. Select a temperature of steam and determine the corresponding pressure from the steam tables found in the eFunda reference and then add a value of superheat, such as 50 degrees F.

Remove the superheat from the superheated steam by using a heat exchanger desuperheating method. To do this, determine the method for which to desuperheat the steam. For instance, one efficient method is the use of a tube bundle desuperheater. This unit is simply a heat exchanger with superheated vapor on one side and a cooling medium on the other. As superheated steam enters the unit, it gives up some of the heat to the cooling medium (usually cooling or tempered water). If enough heat is liberated from the superheated vapor, it becomes saturated steam once again. If 50 degrees F has been added to the steam, then the desuperheater must have the capacity to remove at least 50 degrees of heat.

Remove the superheat by using a direct contact method. This is the simplest form of desuperheating. For instance, a direct contact water bath is simply a vessel with water. The superheated vapor is injected into the water, which will cause some of the water to evaporate. Pressure controllers maintain a desired pressure and the superheated steam is desuperheated back to a saturated vapor.