Method for crushing of grinding material and corresponding mill

Abstract

A method is disclosed for crushing material to be ground with a mill which contains a grinding chamber which is connected to a feed for material to be ground and to an outlet for ground particles, and contains grinding devices for producing particles of the desired fineness from the fed material to be ground, wherein the grinding takes place in a reducing atmosphere which contains a reduction gas. Also disclosed, is a mill having a grinding chamber which is connected to a feed for material to be ground and to an outlet for ground particles, and contains grinding devices for producing particles of the desired fineness from the fed material to be ground, wherein the grinding chamber contains a reducing atmosphere in which the grinding takes place and which contains a reduction gas.

Claims

1. A method for the crushing of grinding material by a mill, which contains a grinding chamber that is connected to a grinding material feed and an outlet for ground particles, and grinding devices for producing particles of a desired fineness from the fed grinding material, said method comprises: grinding the grinding material in the grinding chamber; introducing a reduction gas into the grinding chamber during the grinding step to provide a reducing atmosphere; and adjusting operating parameters of the mill to ensure a reduction reaction between the reduction gas and ground particles which produces ground particles without oxygen contamination or ground particles with an oxygen contamination lower than that achieved by grinding in a protective gas atmosphere; wherein the reduction gas includes carbon monoxide or hydrogen.

2. The method according to claim 1, wherein said grinding is performed with a degree of the fineness equal to d.sub.50<1 μm.

3. The method according to claim 1, wherein the reduction gas comprises a mixture of the carbon monoxide and hydrogen.

4. The method according to claim 1, wherein the grinding occurs in at least one run of grinding material that has already been ground at least once by the mill.

5. The method according to claim 1, further includes a step of air classification.

6. The method according to claim 1, wherein the mill is a continuously operated dry agitator mill.

7. The method according to claim 1, wherein the mill is a jet mill in which the crushing of grinding material occurs by means of jet grinding with the use of grinder gas in the form of grinder gas jets to produce particles of desired fineness, and the grinder gas contains the reduction gas or serves as the reduction gas that is required for the reduction reaction to which the ground particles are to be subjected.

8. The method according to claim 1, wherein the grinding occurs in several runs of grinding material that has already been ground at least once by the mill.

9. A mill comprising: a grinding chamber, which is connected to a feed for grinding material and an outlet for ground particles and contains grinding devices to produce particles of a desired fineness from the fed grinding material, wherein during a grinding process, the grinding chamber receives a reduction gas to provide a reducing atmosphere, wherein the mill comprises a controller that adjusts operating parameters of the mill to ensure a reduction reaction between the reduction gas and ground particles which produces ground particles without oxygen contamination or ground particles with an oxygen contamination lower than that achieved by grinding in a protective gas atmosphere, and wherein the reduction gas includes carbon monoxide or hydrogen.

10. The mill according to claim 9, wherein the degree of the fineness of the grinding is equal to d.sub.50<1 μm.

11. The mill according to claim 9, wherein the reduction gas comprises a mixture of the carbon monoxide and hydrogen.

12. The mill according to claim 9, wherein feedback devices are provided from the outlet for ground particles to the feed for grinding materials, so that particles ground at least once are further grindable.

13. The mill according to claim 9, wherein an air classifier is integrated in the mill.

14. The mill according to claim 9, wherein the mill is a dry agitator mill.

15. The mill according to claim 14, wherein the mill is a continuously-operated dry agitator mill.

16. The mill according to claim 9, wherein said mill is a jet mill that contains nozzles for directing jets of grinding gas into an interior of the grinding chamber to produce particles of the desired fineness by jet grinding the fed grinding material, and the grinding gas is or contains the reduction gas for a reduction reaction to the ground particles.

17. The mill according to claim 9, wherein the particles are ground by the grinding devices in at least one run through the mill.

18. The mill according to claim 9, wherein the particles are ground by the grinding devices in several runs through the mill.

Description

DETAILED DESCRIPTION

(1) Hereinafter, the basic principles and effects of the invention, as well as the particular advantages in using hydrogen as reduction reaction gas, or reduction gas for short, are introduced by presenting physical connections and relevant magnitudes.

(2) By using hydrogen as reduction reaction gas, or in some cases simultaneously as grinding gas, it is possible not only to extract metals from its oxide but also to perform grinding operations at reducing atmosphere. An additional characteristic can be advantageously employed here: On the basis of its thermodynamic properties, hydrogen placed under pressure at identical temperatures and pressures expands at an approximately 3.7—fold speed in comparison with nitrogen, for example. As an advantageous result, greater speed of the gas jets is achieved with the use of a jet mill without additional means, if the reducing atmosphere is produced by H.sub.2.

(3) As a result of the reducing atmosphere in the grinding chamber or, according to this method, as the environment of the grinding, it is possible, for example, to protect purity metals Al, Si and the like from oxidation, in particular. Passivation by oxidation on the surface of particles, particularly in fracture zones, is avoided. Reactivity of the purity metals is unaffected.

(4) The use of specific reduction gases or reduction reaction gases as grinding gas, in the case of the jet mill and jet milling, yields additional favorable impacts on the grinding itself, in addition to the aforementioned advantages of reducing grinding.

(5) The outlet speed of the grinding gas is consequently decisive for the achievable final speed of grinding material and particles for the finest-grade crushing, that is, for a final fineness of ground particles of <5 μm-10 μm and is given by:

(6) $\upsilon =\sqrt{2.Math.\frac{\kappa }{\kappa -1}.Math.R.Math.T_0.Math.\left[1-{\left(\frac{p_e}{p_0}\right)}^{\frac{\kappa -1}{\kappa }}\right]}$

(7) The applied energy, finally, is decisive for the flow rate of grinding material in a machine of a given size, and for the adiabatic expansion the result is:

(8) $E=\frac{m}{2}.Math.{\upsilon }^2$

(9) This leads, for example, for nitrogen: p.sub.0=4 bar(abs); T.sub.0=20° C. water vapor: p.sub.0=40 bar(abs); T.sub.0=320° C. hydrogen: p.sub.0=4 bar(abs); T.sub.0=20° C.

(10) with the corresponding specific magnitudes, to the following results:

(11) TABLE-US-00001 N.sub.2 Water vapor H.sub.2 Isentropic exponent κ 1.4 1.41 Gas constant R [J/kgK] 297 4124 Dynamic viscosity [10.sup.−6 Pas] 16.6 14.2 8.4 Density, unstressed [kg/m.sup.3] 1.25 0.57 0.09 Sound velocity c.sub.0 [m/s] 343 504 1280 Adiabatic sound velocity [m/s] 449 1150 1661

(12) As shown in the table, the jet speed (adiabatic sound velocity) with hydrogen is about 3.7—fold in comparison with nitrogen. Thus the kinetic energy of the particles on collision in comparison with hydrogen and nitrogen is about 13.6 times as great, constituting a significant advantage for the finest degree of crushing.

(13) The invention is presented in the description section only by examples and through embodiments and preferred configurations and is not restricted to them, but rather includes all variations, modifications, substitutions and combinations that a person skilled in the art can obtain from the present documents, in particular in the context of the claims and the general depictions in the introduction to this description as well as in the description of the embodiments and that such a person can combine with their technical knowledge and with the prior art. In particular, all individual features and all possible configuration possibilities of the invention can be combined.