METHOD AND INSTALLATION FOR CRYOGENIC CRUSHING OF PRODUCTS

Abstract

A plant for grinding a product, which includes a grinder in which the product is ground, which plant also includes a hopper for supplying the grinder with product to be ground, configured to be supplied with product to be ground; a means for bringing a cryogenic fluid into the hopper; and a means for discharging product from the hopper into the grinder. Wherein the hopper is provided in a lower part with a hollow screw provided with turns allowing the product to be discharged out of the hopper, into the grinder; and the means for bringing a cryogenic fluid into the hopper comprise an injection lance which is positioned inside the turns of the hollow screw, extending in a direction substantially parallel to the axis of the screw.

Claims

1.-4. (canceled)

5. A plant for grinding a product, which comprises a grinder in which the product is ground, which plant also includes the following elements: a hopper for supplying the grinder with product to be ground, configured to be supplied with product to be ground; a means for bringing a cryogenic fluid into the hopper; a means for discharging product from the hopper into the grinder; wherein: the hopper is provided in a lower part with a hollow screw provided with turns allowing the product to be discharged out of the hopper, into the grinder; the means for bringing a cryogenic fluid into the hopper comprise an injection lance which is positioned inside the turns of the hollow screw, extending in a direction substantially parallel to the axis of the screw.

6. A method for grinding a product in a grinder, comprising: supplying the grinder with product to be ground by a feed hopper, which is itself supplied with product to be ground; cooling the product to be ground to a controlled temperature or to the embrittlement temperature of the product, in the hopper, before being discharged into the grinder, by admission of a cryogen into the hopper; wherein: the hopper is provided in a lower part with a hollow screw provided with turns allowing the product to be discharged out of the hopper into the grinder; and the cryogen is supplied to the hopper via an injection lance that is positioned inside the turns of the screw, extending in a direction substantially parallel to the axis of the screw.

7. The method as claimed in claim 6, wherein the gas resulting from the vaporization of the cryogen, which is extracted from the hopper, is reinjected into the grinder to recover energy.

8. The method as claimed in claim 6, wherein the injection of cryogen into the lance is regulated by a measurement of the temperature of the product, performed at the outlet of the screw, in the zone in which the product drops from the screw toward the grinder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein:

[0030] FIG. 1 illustrates a schematic representation of one embodiment of the present invention.

[0031] FIG. 2 illustrates a schematic representation of another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] The appended FIG. 1 gives a partial schematic view of a plant in accordance with the prior art, in which the following elements can be recognized: [0033] the grinder 1 is supplied with product to be ground by a transfer screw 2 (screw with a central shaft); [0034] the screw is itself supplied with product to be ground by a hopper 3, provided with a rotary valve 5 that was mentioned above; [0035] the product is pre-cooled in the screw by the fact that the screw is supplied with liquid nitrogen, for example by virtue of a spraying rail, the product then being delivered by the screw into the grinder 1.

[0036] The appended FIG. 2 provides a partial schematic view of the lower part of a hopper in accordance with the invention, provided with a hollow transfer screw and with a cryogen injection lance situated within the hollow screw, i.e. within the rings of the hollow screw.

[0037] The results of the experiments carried out by the applicant under these conditions showed the following points: [0038] a substantial saving in nitrogen consumption compared with a conventional technology such as mentioned above implementing a transfer screw with a central shaft (for example an Archimedes screw): a saving of the order of 20%. [0039] a substantial improvement in the cleanability of the plant (it will be understood that such a hollow screw is much easier to dean than the screws of the prior art without the need for further elaboration). [0040] it was possible to confirm that the hollow screw makes it possible to achieve a much more stable product flow rate than a rotary valve of the prior art (no blockages, no jolts), and therefore a much better stability of the conditions of flow rate/temperature of the product that enters the grinder, leading to a much more targeted final particle size.

[0041] It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.