Superheated steam and saturated steam / Sludge drying, Slurry drying, Recycling drying

Temperature of water does not rise for a while after the water is boiled and starts generating saturated steam. However, the temperature starts rising at some point. Condition of saturated steam can be distinguished as “wet saturated steam” and “dry saturated steam” more specifically. When steam contains water in it even just a little, it is wet saturated steam, and called “wet steam” in general. Water in the steam will be gone completely when this wet saturated steam keeps being heated and the steam at this point is defined as dry saturated steam. Under this condition of saturated steam, temperature stays the same even more heat is added.
Temperature starts rising when the steam in saturated steam condition is heated more. In other words, temperature goes up when dry saturated steam is heated more, and this steam is called “superheated steam”. Superheated steam is a steam whose temperature is more than 100℃ under atmospheric pressure.
When the conditions of steam are put in order, they are changed as “saturated water” -> “wet saturated steam” -> “dry saturated steam” -> “superheated steam” according to addition of heat onto the water, and in terms of their definition.

KENKI DRYER uses saturated steam as its heat source and it is a dryer which uses heat of condensation. Steam is hit indirectly on materials to be dried. Steam is cooled when it hit the materials and turns into liquid. Condensing heat (latent heat) generated here is added to the materials and used for drying.

• Since latent heat is used, heat can be added quickly and evenly.

• It is stable as a heat source. Amount of supply and its temperature is stable and seldom fluctuate.

• Temperature can be controlled more easily than by changing steam pressure.
  

• It is safe and hygienic since direct fire and hot blast are not used as heat source. 

• Since it is low temperature drying, number of consumable and replacement parts is small. 

Superheated steam is often used as driving power of turbine, etc., however, application for drying and direct heating in anaerobic condition as high temperature gas is being investigated recently.
Normally, condensing heat of saturated steam is used for heating though, saturated steam will not be condensed when amount of reduced temperature is small. It is because heat energy which heated the saturated steam of superheated steam is sensible heat.
One of the reasons that superheated steam is used for turbine is, since steam is supplied in a state of superheated steam and discharged in a state of superheated steam as well, that drain will not be generated under small amount of temperature change and erosion caused by collision of high speed fluid rarely happen.

Difference in running cost is mostly depends on fuel cost. Also, the low-temperature drying makes less damages on the dryer’s body.

Comparison between heat pump type KENKI DRYER and the previous type which uses steam generated by boiler (saturated steam) is the following. Values are not actually proofed values but estimated values.

Heat pump dryers

Even KENKI DRYER uses only saturated steam as its heat source, it is outstanding in safety and hygiene point of view with its unique drying mechanism based on combined use of conductive heat transfer method and heated air method. Since steam is a stable heat source, quality of discharged material after drying is also stable and equable. Maximum allowed steam pressure is 0.7Mpa and adjustment of steam pressure, adjustment of drying temperature in other words, can be easily done. Saturated steam is commonly used in many factories so that it can be said as a familiar and handy heat source. In comparison with drying methods using burner or hot blasts, saturated steam method is an indirect drying applying heat exchange via pipes that steam is passing through, therefore, it hardly burns the materials and is outstanding in safety and hygiene point of view.

Why low-temperature is used for drying? / KENKI DRYER / sludge drying, slurry drying, feed drying

Heat source, Steam