Method for operating cooling mixer for bulk material in powder and granular form

A method for operating a cooling mixer for bulk material in powder and granular form, said cooling mixer comprising:

• a) a cylindrical container with a bottom portion, a container double wall with an intermediate space between an inner and an outer wall of said container double wall, at least one outlet opening at said bottom portion, and a cover with at least one feed opening and a cover double wall with an intermediate space within said cover double wall;
• b) a rotating mixing device having a hub and mixing paddles fixedly connected to said hub, said mixing device concentrically connected to said container such that a vertical rotating axis of said mixing device coincides with an axis of said container;
• c) a coolant circuit containing a coolant that is circulated during operation of said cooling mixer within said intermediate spaces of said container double wall and said cover double wall, said coolant circuit comprising connectors for connecting said coolant circuit to said container double wall and said cover double wall;
• said method comprising the steps of:
• selecting a diameter to height ratio of 4:1 to 8:1 for said container such that said cover is positioned close to said bottom portion;
• arranging said mixing paddles so as to form an obtuse angle with said bottom portion in a direction of rotation of said mixing device;
• vertically upwardly deflecting the bulk material to be cooled with said mixing paddles so as to bring the bulk material into contact with said cover, positioned close to said bottom portion, for increasing the cooling effect on the bulk material;
• and
• rotating said mixing device at a low circumferential speed of 1-3 m/sec that generates a low, neglectable centrifugal force within the bulk material and reduces frictional heat within said container and the bulk material to be mixed without reducing the cooling effect of the cooling surfaces on the bulk material to be mixed.