In general, concerning the drying of solids, a difference is made between two processes: convection drying and contact drying. In a contact dryer, also known as mixing reactor, the goods to be dried are led along a heated surface by a dynamic tool and a shifting of the goods is achieved. The mixing reactor requires no complex treatment of the flue gas and a significantly smaller construction volume. Since contact drying is carried out by technically tight machines, toxic and carcinogenic products can be dried as well.
The operation of the contact-drying is as follows: Due to the contact with the indirectly heated walls, the required temperature for drying of the product is achieved. The process in the mixing reactor can take place under atmospheric conditions as well as at gauge pressure or vacuum.
In the vacuum mixing reactors of the vertical type, as amixon® distributes and manufactures them, the mixing good moves upward on the rotating and fully heated screw band mixing tool and slides downward along the shaft, following the rules of gravity. The heated mixing tool in the mixing reactors offers an optimum heat transfer at its contact surface. The result is a highly effective and time saving drying process.
The mixing reactor requires the consideration of various process parameters that should be determined beforehand in laboratory experiments. The maximum temperature at the contact surface is especially crucial for drying. The wall temperature of the mixing reactor is influenced by the thermal stability of the material to be dried. In addition, the tendency to crusting of products in mixing reactors must be observed. Also, the product can undergo different product phases at the mixer reactor, which should be previously determined in the laboratory through the pilot phase.