WO2000001488A1

WO2000001488A1 - Multi-pass grain grinding method with intermediate separation, and apparatus for implementing the method

Info

Publication number: WO2000001488A1
Application number: PCT/EP1999/004547
Authority: WO
Inventors: Giorgio Duchi
Original assignee: Braibanti Golfetto S.P.A.
Priority date: 1998-07-03
Filing date: 1999-07-01
Publication date: 2000-01-13
Also published as: IT1305243B1; AU5155999A; ITVE980031A1

Abstract

A multi-pass grain grinding method with intermediate separation, characterized in that the product is subjected to at least one stage of air-operated separation between passes.

Description

WO 00/01488 _ ι _ PCT/EP99/04547

MULTI-PASS GRAIN GRINDING METHOD WITH INTERMEDIATE SEPARATION, AND APPARATUS FOR IMPLEMENTING THE METHOD

This invention relates to a multi-pass grain grinding method with intermediate separation, and an apparatus for implementing the method. The methods known in the high-grinding industry are the following:

- grinding in successive passes alternating with separation by sifting to feed to the next pass only that product still to be ground. After each pass, and in particular after the initial passes, the ground product is divided into coarse, fine and flour or finished product. The coarse and fine have to be subjected to further passes, namely break-down (or type B) for the coarse and regrinding (or type C) for the fine. The successive break-down passes

(coarse or fine) vary normally from four to five and are known as B-i, B₂, B₃

...., whereas the successive regrinding passes (coarse, medium and fine) vary normally from seven to eleven and are known as Cι, C2, C₃ ..... - grinding in successive passes alternating with separation by sifting, which however does not each grinding pass, but two or more grinding passes.

Again in this case the passes are known as break-down or type B passes and regrinding of type C passes.

An object of the invention is to propose a method and apparatus which, although based on the known principle of subjecting the product to be ground to a separation stage between two finishing stages, is more advantageous than the conventional art both in terms of method, enabling a better quality product to be obtained, and in terms of apparatus, enabling this better quality to be obtained with a more simple and reliable apparatus. This and further objects which will be more apparent from the ensuing description are attained, according to the invention, by a multi-pass grain grinding method with intermediate separation as claimed in claim 1.

An apparatus for implementing the method is used as claimed in claim 8.

A preferred embodiment of the invention is described hereinafter with reference to the accompanying drawings, on which:

Figure 1 is a vertical section through a quadruple rolling mill according to the invention; Figure 2 shows in the same view an enlarged detail of the grinding rolls and the air-operated separator positioned between the roll pairs, and Figure 3 is an enlarged detailed view of the sampling device.

As can be seen from the figures the apparatus of the invention can be considered a double rolling mill or a mill with pairs of superposed rolls, ie comprising two superposed pairs of grinding rolls 2 and 4, mounted within a single structure, which can also comprise a further two superposed pairs of grinding rolls, to hence from a quadruple rolling mill.

Between the two pairs of grinding rolls 2 and 4 there is provided an air-operated separator, comprising essentially a transverse channel 6 of width equal to the axial length of the rolls 2 and 4 and bounded on one side by a fixed wall 8 and on the other side lowerly by an adjustable wall 10 and upperiy by another adjustable wall 12 separate from the preceding.

More specifically, the fixed wall 8 and movable wall 12 substantially face each other and hence the channel defined between them is substantially narrow. At the same time the wall 12 lies substantially at an angle to the wall

10, to form a sort of hopper able to receive the ground product leaving the upper rolls 2 and to convey it, through a lower aperture existing between the walls 10 and 12, into the lower end part of the channel 6.

From the continuous upper aperture of the channel 6 there extend a plurality of substantially frusto-conical diffusers 14 opening upperly into two vertical suction ducts 16, for transferring the product by suction into a sampling device or to the pneumatic conveying line 20. The line 20 can be that for conveying the product leaving the lower roll 4 and hence be the only line for the two products, or can be an independent conveying line.

The sampling device 18 consists essentially of a closed parallelepiped container 22 to which an entry conduit 24 is connected originating from the two vertical ducts 16 into which the multiple diffuser formed from the frusto- conical elements 14 opens. The container 22 also receives a second conduit 26 of greater diameter than the conduit 24 and shaped such that its end faces the end of the conduit 24. That portion of the conduit 26 situated inside the container 22 can rotate about the external portion and is associated with a crank-type operating member operable from the outside to move said external portion between a position facing the end of the conduit 24 and a position not facing it.

A withdrawal member for the ground product is also applied to the container 22. This withdrawal member, indicated overall by 30, comprises a cylindrical portion which can rotate axially while remaining inside the container 22 and is provided with an aperture 32 in its side surface and a closure plug 34 with handgrip 36, for sealing the container.

The described apparatus operates as follows: the ground product leaving the rolls 2 falls into the hopper defined by the walls 10 and 12, passes through the bottom aperture defined between these and into the lower terminal part of the channel 6, through which there flows in an ascending direction an air stream originating from the pneumatic conveying line via the exit conduit 26 from the sampler 18, the sampler 18 itself, its entry conduit 24, the vertical ducts 16 and the frusto-conical diffusers 14. When setting-up and adjusting the apparatus the walls 10 and 12 will already have been adjusted to ensure that the apparatus operates correctly for that particular product, for that air flow and for the particular system operating parameters.

This air stream consequently strikes the stream of ground product leaving the rolls 2 and separates from said stream those lighter parts which are not to be subjected to further grinding through the rolls 4. Consequently within the channel 6 the light fraction of the product is separated from the heavier fractions, which are subjected to further grinding. The ground product leaving the rolls 4 is combined within the conveying line 20 with the previously separated light fraction, which reaches the said line after passing through the sampler 18.

When the two ends of the conduits 24 and 26 face each other within the sampler 18 there is continuous passage of the separated product fraction from one conduit to the other, whereas when the operator wishes to withdraw sample to check it, he operates the crank operating member 28 to rotate the end of the conduit 26 about the end of the conduit 24 into a non-aligned position.

In this manner the hermetically sealed construction of the container 22 ensures that the vacuum in the conveying line is maintained, while at the same time the difference in cross-section between the two conduits 24 and 26 means that the product which enters the container 22 through the conduit 24 falls onto the container bottom, from which it can be removed to the outside by pulling out and rotating the withdrawal member, which also ensures that the pneumatic circuit remains under vacuum.

It is apparent from the aforegoing that the method of the invention is particularly advantageous compared with the traditional separation method of sifting between two grinding passes, in that separation by means of an air stream not only separates the light product but also cools it, this being particularly important in that the product leaving a grinding stage, and in particular regrinding, has generally undergone heating. In addition, separation by means of an air stream is also advantageous in that it can be effected by an apparatus which has in any case to be provided for conveying the ground product.

Consequently the product separation involves no substantial additional plant or operating cost. The apparatus of the invention is also particularly advantageous compared with traditional apparatus, in that separating the fine product without subjecting it to further grinding eliminates a processing stage which not only appears superfluous, but indeed appears inadvisable in that it mistreats already finished flour and results in crumbling of any bran, making its subsequent separation by sifting after the next grinding pass more difficult. If bran is not completely separated from the flour, the final product obtained is commercially less valid because of its possible high ash content.

Finally the apparatus of the invention also has the advantages of subjecting to the second finishing pass only that product which effectively needs it, so increasing the overall process yield and the apparatus efficiency, by reducing the transformation energy consumption.

Claims

C L A I M S 1. A multi-pass grain grinding method with intermediate separation, characterised in that the product is subjected to at least one stage of air- operated separation between passes.

2. A method as claimed in claim 1 , characterised in that the air-operated separation is effected by means of an air stream in countercurrent with the product stream originating from the grinding pass.

3. A method as claimed in claim 2, characterised by regulating the flow rate of the air stream on the basis of the characteristics of the product stream to be treated.

4. A method as claimed in claim 1 , characterised by effecting an air- operated separation after at least two successive grinding passes.

5. A method as claimed in claim 1 , characterised by combining the product separated prior to the grinding pass with the product subjected to grinding.

6. A method as claimed in claim 1 , characterised by using for the separation the actual air used for pneumatically conveying the product.

7. A method as claimed in claim 5, characterised by using two separate air lines for the separation and for the pneumatic product conveying.

8. An apparatus for implementing the method claimed in one or more of claims 1 to 7, characterised by comprising within the same rolling mill at least one pair of grinding rolls (2) and an air-operated separation device positioned downstream of said pair.

9. An apparatus as claimed in claim 8, characterised in that the air- oeprated separator device comprises a hopper (10,12) for collecting the ground product originating from the overlying pair of grinding rolls (2), said hopper communicating lowerly with a separation air circulation channel (6) extending in a substantially vertical direction and having a lower aperture through which the heavy separated product fraction passes, and at least one upper aperture through which the light separated product fraction is drawn in or pneumatically conveyed.

10. An apparatus as claimed in claim 9, characterised in that one of the hopper walls (12) also forms one wail of the separation and conveying channel (6) for the light ground product fraction.

11. An apparatus as claimed in claim 10, characterised in that at least one of the two walls (10,12) of the hopper is adjustable in position relative to the other.

12. An apparatus as claimed in claim 9, characterised in that at least one of the two walls (8,12) of the channel (6) is adjustable in position relative to the other.

13. An apparatus as claimed in claim 9, characterised in that the channel (6) communicates upperly with the separated product conveying channel via diffuser elements (14).

14. An apparatus as claimed in claim 9, characterised in that one wall (10) of the hopper is bent at an angle, with its upper part forming a wall of the hopper and its lower part forming the lower part of the wall of the channel (6).

15. An apparatus as claimed in claim 8, characterised in that a sampler device (18) is inserted into the ground product exit conduit.

16. An apparatus as claimed in claim 15, characterised in that the sampler device (18) comprises a container (22) receiving an entry conduit (24) and an exit conduit (26) for the treated product, said conduits being mutually dissociable while ensuring that the container (22) still remains under vacuum, and also comprises a product extraction member (30).

17. An apparatus as claimed in claim 16, characterised in that the entry conduit (24) has a smaller diameter that the exit conduit (26), said conduits being movable relative to each other in such a manner as to pass from a facing position to a non-facing position.

18. An apparatus as claimed in claim 17, characterised in that the entry conduit (24) is fixed relative to the container (22), the exit conduit (26) being associated with an external handle (28) for controlling its movements.

19. An apparatus as claimed in claim 16, characterised in that the product extraction member comprises a cylindrical element axially slidable in the manner of a drawer relative to the container (22) between a position of total insertion, in which the container is hermetically sealed, and a position of partial withdrawal in which an aperture provided in the cylindrical element faces the outside for removal of the product collected within said cylindrical element.