Method for a continuous dry milling operation of a vertical grinding mill and vertical grinding mill

A method for a continuous dry milling operation using a vertical grinding machine having

• a vertical, closed milling container (1);
• a screw conveyor (2) which is arranged centrally in the milling container (1), the screw conveyor (2) including:
• a drive shaft (4) with a central axis (3) and
• at least one screw flight (5) which is arranged on the drive shaft (4), extends along a height hs up to an upper end (6) and covers the cross-section of the milling container (1) only partially;
• a package of grinding bodies (17), the package having an upper surface (39);
• a grinding stock inlet (19) which projects into the milling container (1) above the package of grinding bodies (17);
• a gas inlet (24, 24′, 24″) which projects into the milling container (1) for introducing gas;
• a grinding stock outlet (11) which projects out of the milling container (1) and has a lower edge (18) and a height h13 for discharging grinding stock (22) and gas;
• and
• a motor (7) for driving the screw conveyor (2) in a direction of rotation (8) where the at least one screw flight (5) conveys grinding bodies (17) upwards,
• said method comprising the steps of:
• adjusting the surface (39) of the package of grinding bodies (17) such that when the screw conveyor (2) is driven for rotation, the surface (39) obtains an approximately frustoconical shape which slopes radially outwards and ends radially outside in the region of the lower edge (18) of the grinding stock outlet (11);
• introducing the gas into the milling container (1) above the package of grinding bodies (17);
• and
• discharging the gas and grinding stock (22) from the milling container (1) in the region of the surface (39) of the package of grinding bodies (17) through the grinding stock outlet (11).