Method and system for grinding fragmentary starting material

1. A method for grinding fragmentary starting material, in particular ores, with a dry grinding system, the method comprising:

determining the moisture of starting material for a certain period of time;

preparing at least one screening stage, the cut point of which is selected depending on the determined moisture in such a manner that the moisture of a screen oversize does not exceed a predetermined moisture limit value (ψ G ) when starting material having the determined moisture is fed to the screening stage;

feeding starting material to the screening stages;

transferring a screen oversize arising in the screening stage to the dry grinding system; and

grinding the screen oversize in the dry grinding system.

2. The method of claim 1 , wherein a screen undersize arising in the screening stage is supplied to a wet grinding system.

3. The method of claim 1 , wherein a screen undersize arising in the screening stage is supplied to a drying device and subsequently to the dry grinding system.

4. The method of claim 1 , wherein the moisture of the feedstock to be ground is measured online and the starting material is supplied to the screening stage if the moisture of the starting material exceeds the predetermined moisture limit value (ψ G ), and the starting material is supplied directly to the dry grinding system if the predetermined moisture limit value (ψ G ) is not exceeded.

5. The method of claim 1 , wherein a plurality of screening stages having different cut points are provided and the moisture of the feedstock is measured online, wherein the starting material is supplied depending on the determined moisture thereof is supplied to that screening stage having the smallest cut point, the screen oversize of which has a moisture which does not exceed the predetermined moisture limit value (ψ G ).

6. The method of claim 1 , wherein the predetermined moisture limit value (ψ G ) is between about 2% to about 8% by weight.

7. The method of claim 1 , wherein a ball mill, roller mill or roll press, in which that portion of the starting material which does not exceed the predetermined moisture limit value (ψ G ) is ground, is provided as the dry grinding system.

8. The method of claim 1 , wherein the starting material is ground to a grain size of ≦600 μm.

9. The method of claim 1 , wherein the at least one screening stage is operated dry or wet.

10. A system for grinding fragmentary starting material, comprising:

a dry grinding systems;

a wet grinding systems; and

at least one screening stage which has a screen oversize outlet connected to the dry grinding system and a screen undersize outlet connected to the wet grinding system, wherein the screening stage has a cut point which is defined depending on a determined moisture of a starting material in such a manner that the moisture of a screen oversize does not exceed a predetermined moisture limit value (ψ G ) when starting material having the determined moisture is fed to the screening stage.

11. The system of claim 10 , further comprising a moisture measuring device and at least one material gate, which material gate is arranged downstream of the moisture measuring device and is switchable between at least one first and one second output, wherein the first output is connected directly to the dry grinding system and the second output is connected to the at least one screening stage.

12. The system of claim 11 , wherein said at least one screening stage comprises a plurality of screening stages having different cut points, and the material gate has such a multiplicity of switchable outputs that said material gate can be coupled either directly to the dry grinding system or to one of the screening stages.

13. A system for grinding fragmentary starting material, comprising:

a dry grinding system;

a drying device; and

at least one screening stage which has a screen oversize outlet connected to the dry grinding system and a screen undersize outlet connected to the drying device, wherein the screening stage has a cut point which is defined depending on a determined moisture of a starting material in such a manner that the moisture of a screen oversize does not exceed a predetermined moisture limit value (ψ G ) when starting material having the determined moisture is fed to the screening stage.