Since steam formation process in boiler depends on pressure, so steam formation process is performed at constant pressure. If 1 kg of water at 20C is heated in a closed vessel with constant pressure (1 atm), then during the first heating process, temperature of boiling reach 100C, steam begins to be formed. In this case, this steam is called wet steam (saturated liquid), because the steam still mix with grains of water.
If all steam including grains of water which is mixed in wet steam is heated again, it will get saturated steam (saturated vapor). Saturated steam is condition where the steam form is entirely pure steam, there is not mixture. The amount of heat that required converting 1 kg of boiling water into saturated steam at constant pressure is called latent heat. When the heating is continued so the temperature of saturated steam will rises and this steam is called as superheated steam / superheated vapor.
At steam formation process in boiler, air and fuel are distributed into furnace to perform combustion process. Combustion gases will pass through evaporator, superheater, air heater, and finally to be discharged into atmosphere through chimney / stack. While the feedwater, after doing heating process in deaerator, then to be distributed into evaporator and then saturated steam is heated further in a pressure part which is called superheater and finally heat superheated steam can be obtained.
|Figure 1: Graphic T-S on Steam Formation in Boiler|