METHOD OF COMMINUTING FERTILIZER SLUGS IN A TWO-ROLL MILL

Abstract

The invention relates to a method for comminuting fertiliser slugs or slug pieces in a two-roll mill (3) in the course of producing granular fertiliser material, wherein the two-roll mill (3) has two rotatingly driven grinding rolls, the roll surfaces of which are provided with a profiling, wherein the slug or slug pieces is/are placed on the two-roll mill (3) and comminuted into granular material in the roll nip formed between the grinding rolls, wherein the grinding rolls rotate at a circumferential speed of more than 5 m/s. This e method is characterised in that the surfaces of the grinding rolls are cooled during operation.

Claims

1. A method of comminuting fertilizer flake or flake particles in a two-roller mill when making fertilizer granules, where the two-roller mill comprises two rotationally driven grinding rollers having respective outer surfaces provided with profilings, the flake or flake particles are fed to the two-roller mill and granules are comminuted in the nip formed between the grinding rollers, the grinding rollers rotate at a peripheral speed or with peripheral speeds of more than 5 m/s, and the outer surfaces of the grinding rollers are cooled during operation.

2. The method according to claim 1, wherein the roller surfaces are cooled with an internal cooling of the rollers by cooling systems integrated in the rollers.

3. The method according to claim 2, wherein the cooling systems are designed as liquid cooling systems that have one or more cooling passages for a liquid cooling medium.

4. The method according to claim 1, wherein the grinding rollers rotate at a peripheral speed or with peripheral speeds of 5 to 25 m/sec.

5. The method according to claim 1, wherein the grinding rollers have diameters of 200 mm to 1000 mm, and/or rotate at a rotational speed or rotational speeds of 80 to 2400 rpm.

6. The method according to claim 1, wherein the flake or the flake particles are fed to the two-roller mill at a temperature of at least 100° C.

7. The method according to claim 1, wherein the cooling of the grinding rollers is carried out such that the temperatures of the roller surfaces do not exceed 100° C.

8. The method according to claim 1, wherein the roller gap has a gap width of 0.5 to 10 mm or is set to such a gap width in the case of a variable gap setting.

9. The method according to claim 1, wherein the surfaces of the grinding rollers have corrugations formed by a multiplicity of grooves and ridges that extend over the roller width and are oriented parallel or obliquely to the roller axis or spirally or arcuately.

10. The method according to claim 1, wherein the flake or the flake particles are scattered into the nip as a curtain of loose material.

11. A two-roller mill for comminuting fertilizer flake or flake particles, for carrying out the method according to claim 1, wherein the rollers are equipped with cooling systems for cooling the roller surfaces.

12. A method of making fertilizer granules from inorganic substances, wherein inorganic substances in a roller press are first compacted to form flake as starting material, and the flake particles produced from the flake are then comminuted or comminuted in a two-roller mill using a method according to claim 1.

13. The method according to claim 12, wherein the flake are precomminuted with at least one precomminutor, for example a roller crusher and/or a hammer mill, to form flake particles that are fed to the two-roller mill.

14. The method according to claim 13, wherein between the precomminutor and the two-roller mill and/or downstream of the two-roller mill the flake particles are classified, for example with one or more sieves.

15. The method according to claim 12, wherein the material is circulated in that material emerging from the two-roller mill preferably fed back to the screening device.

16. The method according to claim 12, wherein the starting material is fed to the roller press at a temperature of at least 100° C. or the flake or the flake particles are fed to the two-roller mill at a temperature of at least 100° C.

17. A system for making fertilizer granules from fertilizer salt with a method according to claim 12, with at least one roller press and at least one two-roller mill, wherein the rollers of the two roller mill are equipped with cooling systems for cooling the roller surfaces.

18. The system according to claim 17 in the embodiment as a circulating compacting and granulating plant.

Description

[0031] The invention will be described in the following with reference to drawings illustrating a single embodiment. In the drawing:

[0032] FIG. 1 is a greatly simplified flow diagram for a plant or process for making fertilizer granules from inorganic substances,

[0033] FIG. 2 is a view of a two-roller mill for the comminution of fertilizer flake according to the method, and

[0034] FIG. 3 is a section through the two-roller mill according to FIG. 2.

[0035] FIG. 1 shows schematically greatly simplified a plant for making fertilizer granules from inorganic substances at a temperature of, for example, at least 100° C. The plant has a high-pressure roller press 1. In this roller press 1, the starting material A, namely inorganic substances, is pressed and thereby compacted to form flake S. Subsequently, these flake S are granulated in that a precomminution is first optionally carried out in at least one precomminutor 2a, 2b. This precomminutor can be designed, for example, as a roller crusher 2a. Alternatively or additionally, it can also be a hammer mill 2b or a plurality of such devices can also be combined with one another for precomminution. In any case, granules or flake particles P are produced from the flake S in this way that are then comminuted in a next process step and consequently granulated. For this purpose, the flake particles P that have, for example, a temperature of at least 100° C. are fed to a two-roller mill 3 and comminuted in the two-roller mill to form granules G.

[0036] In the embodiment shown in FIG. 1, a classification takes place between the precomminution and the comminution and a screening device 4 with a plurality of sieve stages 4a, 4b, 4c is provided between the precomminutor 2 and the two-roller mill 3.

[0037] The flake particles P are fed to the screening device and very coarse granules having a size of more than 10 mm are screened off as the coarse fraction by the first sieve stage 4a. This coarse fraction a can be supplied, for example, to a further comminutor 2c, for example a hammer mill, and from there the comminuted granules are fed again to the screening device 4. In the second screening stage 4b, an average-size fraction b having a grain size of, for example greater than 4 mm to 10 mm, is supplied as a feed material to the two-roller mill 3 and is comminuted there in the manner described. The comminuted material is circulated and consequently fed again to the screening device 4. In the third screening stage 4c, a material having a fine grain size of 2 mm to 4 mm and consequently the desired granulate G is sieved off and discharged as product G. The finest material F passing through all the sieve passages is fed back to the compacting granulation process again and consequently the roller press 1 is reloaded for compaction.

[0038] The design and operation of the two-roller mill 3 are of particular importance in the context of the invention. In order to prevent the flake particles or granules from sticking to the roller surfaces or profiling, the roller surface is cooled. For this purpose, reference is made to FIG. 2.

[0039] FIG. 2 schematically shows a two-roller mill 3 with two counter-rotating grinding rollers 7 having respective outer surfaces provided with profilings 8 formed, for example, as complementary arrays of ridges and grooves that mesh together. These arrays axially cover the rollers and the grooves and ridges extend at an angle obliquely to the roller axis. In the illustrated embodiment, each of the rollers 7 consists of a rotatably driven roller core 9 and an annular jacket 10 mounted on the roller core and in turn provided with the profiling 8.

[0040] The rollers 7 are each equipped with a cooling system that chills the respective roller surface. For this purpose, cooling passages 11 are integrated in the rollers. In this embodiment shown, these cooling passages 11 are each designed as spiral-shaped cooling passages 11. ?Structurally, these can be realized in that the roller core 9 is provided on the outside circumferentially with an annularly circumferential spiral groove that is closed by the mounted jacket 10, so that a spiral-shaped cooling passage 11 forms between the roller core 9 and the jacket 10. In this embodiment, the cooling medium is supplied via a central feed passage 12 along the axis of the roll core. The cooling medium can be fed to and outputted from the cooling passage 11 via radial passages 13.

[0041] In addition, the drawing shows that the two-roller mill 3 is surrounded by a housing 14. Furthermore, a feed chute 15 is provided through which the material is supplied, and this chute 15 can be part of the housing or housing 14.

[0042] The material is loosely scattered into the nip like a curtain without pressure. For this purpose, a vibration feeder or vibration platform (not shown) can be provided, via which the material passes into the chute 15 above the roller gap and is guided from there into the roller gap.

[0043] According to the invention, the cooling of the described two-roller mill is of particular importance, since the cooling in this method surprisingly makes it possible to avoid clogging of the profiling or fluting. This is of essential importance, since clogging the profiling results in shearing action being reduced in the gap and thus the material is broken into finer pieces. Furthermore, the open, middle roller gap is reduced and this also results in more fine material being produced. Both are fed back again to the roller press after the next sieve passage and passes through the process again. As a result of this undesired fine material, the circulating load in the system increases and thus loss of product is reduced. Overall, clogging of the profiling consequently leads to a reduction in the efficiency and thus to a reduction in the economic efficiency of the plant. According to the invention, these disadvantages are avoided in a surprisingly simple manner by the described cooling of the rollers, specifically explicitly in a two-roller mill with the described method.