Cryogenic grinding apparatus and process

A cryogenic grinding apparatus for producing fine material from a material to be ground comprising:

• a material charge for charging the material to be ground;
• a low-temperature embrittling device connected to said material charge and configured for embrittling the charged material to be ground at a low temperature by supplying a low-temperature gas;
• a whirlwind mill connected to said low-temperature embrittling device and configured for grinding the embrittled material to be ground in an atmosphere containing the supplied low-temperature gas;
• a separating device configured for separating the fine material from a mill-output volumetric flow leaving the whirlwind mill;
• said mill-output volumetric flow containing the low-temperature gas and ground material;
• said whirlwind mill comprising:
• a plurality of metal plates,
• a stator,
• a rotor with a vertical axis of rotation bearing the plurality of metal plates,
• the plurality of metal plates being surrounded at an outer circumference by a grinding path to form a grinding gap between the rotor and the stator bearing the grinding path, and
• a temperature control device configured to variably control an amount of the low-temperature gas taken up per unit of time to thereby keep a temperature during milling below a setpoint value which is in a range of −40° Celsius to −70° Celsius;
• said separating device including a wind classifier configured to separate off a classifier-output volumetric flow containing the fine material from a classifier-input volumetric flow containing the ground material;
• the classifier-input volumetric flow including pulsations induced by the temperature control device of the whirlwind mill when the temperature control device variably controls the amount of the low-temperature gas taken up per unit of time;
• the wind classifier including:
• a classifier wheel, which defines an upper grain limit by rotating at a constant rotational speed,
• a classifier chamber from where such particles of the ground material contained in the classifier-input volumetric flow rise, which are sucked up by the classifier wheel, and
• a coarse material discharge, into which such particles of the ground material sink downward from the classifier chamber, which are too heavy to be sucked up;
• a removal device connected to the mill and configured to remove the ground material from said mill-output volumetric flow;
• and,
• a directing device comprising a line network, detection device, at least one throttle damper, and a controller in communication with the detection device and the at least one throttle damper, the directing device being configured to feed the ground material removed by the removal device into said classifier-input volumetric flow and to discharge excess mill-output gas of said mill-output volumetric flow, and
• the controller being configured to smoothen said classifier-input volumetric flow over time by removing from said mill-output volumetric flow the pulsations induced by the temperature control device of the whirlwind mill by controlling the at least one throttle damper based on an output of the detection device.