Latent heat, sensible heat and heat of condensation / Sludge drying, Slurry drying, Recycling drying

Even heat keeps being added to saturated water, water temperature will not rise and water keeps boiling. Steam generated here is called saturated steam though, heat energy which make saturated water into saturated steam is called latent heat. Latent heat depends on pressure and it becomes lower as pressure becomes higher. Latent heat becomes zero when pressure reaches 22.06Mpa.
Also, heat kept in saturated steam and saturated water is called specific enthalpy. There is a table called a steam table and specific enthalpy can be found there. Please refer to the following table.
On the other hand, heat which changes temperature of a substance without changing its state is called sensible heat.
Situation is different from the above like liquid transfers to gas state by adding heat though, temperature raised while liquid stays in its original state is called sensible heat and the temperature is measurable. It is the same for gas and change of temperature while it is staying its original state as gas is sensible heat. It can be said that heat which is measurable is sensible heat and one which is not measurable is latent heat.

Although water evaporate and becomes vapor, the vapor becomes water when it is cooled. Heat which is released during vapor becomes water is called heat of condensation. The heat of condensation is a heat of state change. It is the same amount of energy as latent heat and two to five times larger compered with sensible heat.
 

KENKI DRYER uses saturated steam as its heat source and it is a dryer using heat of condensation. It hits steam indirectly to materials to be dried. Steam is cooled when it hit the material and it change its state into liquid. Heat of condensation generated here is added to materials and used for drying.
There are other methods for indirect type drying such as drying with hot water or oils. They are always in liquid state and there is no state change when it hits to materials to be dried. Only sensible heat exists in the liquid can be added to materials during their drying process. There is a large difference in drying condition compared with steam drying.

Saturated steam has both sensible heat and latent heat, and their ratio depends on pressure. As pressure increased, latent heat will be less and sensible heat will be more. As pressure decreased on the other hand, latent heat will be more and sensible heat will be less.Total heat energy that sensible heat and latent heat are added together becomes larger as pressure increased.
Please refer to the table below.

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