Q: What is superheated steam? Some people in our plant talk about it all the time; they say it is no good and results in poor humidity control in the plant.

A: When we 'make' steam in a boiler, it will have a certain temperature, based on the pressure of the steam. We can look up this temperature in a Saturated Steam table. Often, a boiler runs at fairly high pressure (meaning high temperature steam). Just before we use the steam, we often will lower the pressure to just a few pounds of pressure. However, when we lower the pressure, the heat is still there. The heat does not just disappear. So, even though we have low-pressure steam (which is desired for plant humidification), this steam is much hotter than normal. When we inject this steam into our plant's atmosphere, we get a lot of heat and not much moisture. This very hot steam is called superheated.

Incidentally, to get rid of this extra heat, you can use a desuperheater. This simple device adds water to the steam. The extra heat converts this water to steam, ending up with the correct temperature. The steam is then called saturated, low-pressure steam, which is ideal for humidification in a plant atmosphere, as well as in dry kilns.