Wet, Saturated and Hot Steam
In closed containers, hot steam is generated by boiling water in a dense steam atmosphere. During vaporization, small water particles are carried along. Wet steam is generated. This process continues until a balance occurs between vaporization pressure of the water and vapor pressure. From this point of time no steam can be generated anymore in the boiler. Once this state has been reached the generated steam is called saturated steam.
As long as saturated steam stays in contact with the water temperature, the amount of steam can only increase by raising pressure of the steam atmosphere. If saturated steam is separated from water, steam can be heated up and become hot steam without the increase of pressure. Hot steam is also called “dry” since in contrast to wet steam it does not contain water particles. However, dry steam contains the same amount of water as wet steam.
For soil steaming in particular hot steam is suitable since thermal losses during transportation are compensated, soil siltation is avoided, energy content is increased and penetration of soil is facilitated by superheating. All these advantages lead to more effective and efficient soil steaming.
To be able to produce dry, superheated steam, steam boilers need to be specially designed and possess a superheater, which guides steam through the flame tube before exiting.