METHOD FOR THE REFINEMENT OF FERTILIZER SHELLS IN A TWO-ROLLER MILL

Description

[0001] The invention relates to a method for comminuting fertilizer slugs or slug pieces in a two-roller mill during the production of fertilizer granules. The two-roller mill comprises two rotatingly driven grinding rollers whose roller surfaces are provided with a profile. The slug or slug pieces are fed onto the two-roller mill and comminuted into granules in the roller gap formed between the grinding rollers. The grinding rollers rotate at a peripheral speed (at the roller surface) of more than 5 m / s. The roller can be designed as a solid roller or have a roller core and a roller shell or a bandage attached to the roller core, which is provided with the profile.

[0002] Furthermore, the invention relates to a method and a plant for producing fertilizer granules from inorganic substances, wherein inorganic substances, e.g. as fertilizer salt, are compacted into a slurry in a roller press as starting material and wherein the slurry or the slurry pieces produced from the slurry are comminuted into fertilizer granules in a two-roll mill in the manner described above.

[0003] This method of producing fertilizer granules is also known as press granulation or compaction granulation. The starting material (inorganic substances) is pressed under high pressure in the (high-pressure) roller press and compacted, creating what is known as "slugs." This process step is called press agglomeration. This is followed by a further step of granulation by comminuting the slugs and, preferably, classifying them, e.g., using a sieve. The slugs emerging from the roller press are generally not fed directly to the two-roller mill, but are pre-comminuted by first crushing the slugs into slug pieces in a crusher and / or hammer mill. These slugs are then fed to the two-roller mill, possibly with the aid of an intermediate classifier.

[0004] Since the inorganic substances are initially available as relatively fine-grained materials, which in this form are unsuitable for mechanical spreading on the areas to be fertilized, press granulation produces fertilizer granules with defined grain sizes that are easy to handle. The goal is generally to produce fertilizer granules with a grain size between 1 mm and 5 mm.

[0005] The inorganic substances used in the invention for the production of fertilizer granules are, for example, mineral substances or substances obtained from the evaporation of salt water, e.g., chlorides or sulfates. Thus, they can preferably be potassium sulfate or potassium chloride.

[0006] In the processes and systems described, a distinction must therefore be made between a roller press on the one hand and a two-roller mill on the other. In the roller press, the starting material is compacted into the slurry under high pressure and with relatively low peripheral speeds of the rollers. The two-roller mill is used in a further process step to crush the slurry or to crush slurry pieces that are produced from the slurry after compaction, e.g. with the help of a roller crusher or a hammer mill. In contrast to roller presses, two-roller mills operate at a relatively high peripheral speed and the material is scattered loosely as a material curtain into the roller gap. The roller surfaces of the two-roller mill are provided with a profile, i.e. the roller surfaces are usually structured. In contrast to a crusher with a large number of crushing elements (e.g.While the grinding surfaces of a two-roller mill are composed of teeth (e.g., teeth) that act individually or in small numbers on the feed material and crush it, comminution in a two-roller mill takes place between the grinding surfaces, which may well be structured, but without any specific impact of individual comminution elements on the particles to be crushed. The focus of the invention is the design of the two-roller mill, which should therefore not be confused with a roller press or a roller crusher.

[0007] The compaction of inorganic substances in a roller press is known, for example, from DE 28 24 827 B2, DE 38 02 173 C1 and DE 1 758 978.

[0008] According to DE 28 24 827 B1, the material is pressed into the roller gap under pressure using a screw conveyor. The material to be pressed is applied at a temperature greater than 120 °C, and pressing occurs with a high specific pressing force. The rollers rotate at a peripheral speed of 0.55 to 0.75 m / s. The roller surface should be kept at a temperature below 80 °C to prevent the material from melting onto the press surface and thus produce a slug with a bright, hard surface. This prior art explicitly relates to a high-pressure roller press.

[0009] Furthermore, DE 652 349 A describes a device for granulating clod-like products, in particular fertilizers containing ammonium nitrate, consisting of two rollers rotating against each other, with their outer circumferences kept apart from each other, the working surface of which is formed by sharp-edged grooves offset from the grooves of the opposing roller.

[0010] Furthermore, a process for producing granules from potassium chloride is known from document US 4,439,384 A. The salt is compressed into granules in a roller press with a pair of synchronously driven rollers, which are then used as fertilizer. To improve the absorption of the salt onto the roller surface, the rollers used are provided with a profiled surface.

[0011] WO 2006 / 064483 A2 describes a device and method for shredding primarily elastomeric materials using a first and a second roller assembly. The primary application is the processing of scrap tires to ensure adequate shredding of the rubber. The rollers used can be provided with a ridged surface.

[0012] Furthermore, the two-roll mills mentioned at the beginning are known from practice, which are operated at high peripheral speed during the production of fertilizer granules and in which the previously produced flakes are loosely scattered into the gap without pressure.

[0013] The milling of grain on grooved or smooth rollers is also known from DE 21293. To prevent damage to the grain from harmful heating, the rollers are cooled.

[0014] Roller cooling is also described in DE 496543, which deals with the rolling of plastic and soft masses, particularly cocoa and chocolate masses, and alternatively mentions the rolling of rubber, oil paints, and other oil- and fat-containing masses. Cooling also serves to prevent damage to the processed masses. Furthermore, it is intended to prevent impairment of the rolling process, including the burning of the mass onto the rollers. The processing of plastic materials also takes place at relatively low peripheral speeds and comparatively high pressure.

[0015] Furthermore, a device and method for producing fine rubber using two counter-rotating rollers are known from US 2013 / 193245 A1. These are primarily used to process scrap tires into rubber particles with a small particle size. The grinding process depends primarily on the speed of the rollers and the friction conditions between them. The rollers are cooled by a coolant circulating within them.

[0016] DE 635 879 A describes a roller for mills and rolling mills equipped with a cooling system. However, this roller does not have a coolant flow through it. Instead, the roller cavity is filled with a liquid for the purpose of heat distribution within the roller. This liquid is added once, after which the inlet opening is tightly closed.

[0017] Finally, cooled rollers are also used in roller presses for hot briquetting or hot compacting of materials processed at high temperatures, e.g., in the processing of reduced iron ore or sponge iron at temperatures exceeding 900 °C (see, for example, DE 10 2012 106 527 A1). At such temperatures, the roller bandages and especially the press tools attached to them (e.g., mold cavities) are subject to significant wear. To limit this wear, cooling systems, e.g., water cooling, are usually provided.

[0018] These developments had no influence on the design of two-roller mills for the comminution of fertilizer slurries or slurry pieces.

[0019] The invention is based on the technical problem of creating a method for comminuting fertilizer slurries or slurry pieces in a two-roll mill of the type described above, which is characterized by improved functionality and economic efficiency.

[0020] To achieve this object, the invention teaches in a generic method for comminuting fertilizer slugs or slug pieces in a two-roll mill during the production of fertilizer granules that the surfaces of the grinding rollers are cooled during operation and consequently during the comminution of the slugs or slug pieces.

[0021] According to the invention, cooling of the roller surfaces of the two-roll mill is provided during the comminution of granular material, namely fertilizer flakes or flake pieces previously produced using a high-pressure roller press, i.e. the (preferably hot) fertilizer flakes or flake pieces are comminuted in a two-roll mill with cooled roller surfaces. The invention is based on the surprising discovery that in such a two-roll mill when processing fertilizers, clogging of the profiled roller surfaces can be reliably prevented by cooling, despite the low pressures in the roller gap and the high peripheral speeds of the roller surfaces and the associated very short contact times of the material with the roller surface. Despite the very short contact times, the cooling prevents the salts orPieces of slugs on the roll surfaces and consequently in the profiles of the rolls. Of particular importance here is the fact that the granular and preferably hot material, i.e. the slugs or the pre-shredded slugs (e.g. with a size / fraction of 4 to 10 mm) is scattered loosely into the roll gap as a material curtain without compaction, e.g. via a vibrating material chute arranged above the roll gap and a drop chute arranged downstream or below the chute, which extend across the entire width of the roll. The roll width can be, for example, 1000 mm to 3000 mm, e.g. 1500 mm to 2500 mm. A typical roll width is, for example, 1800 mm to 2000 mm. The material is scattered as a material curtain into the chute arranged above the roll gap via the vibrating chute or similar means.

[0022] It is also important that the grinding rollers are operated at high peripheral speeds, whereby the speed of the two rollers can be the same or different, depending on the material to be processed. The speed of the two rollers is more than 5 m / s, preferably more than 6 m / s. If the speeds are different, the slower roller has a speed of more than 5 m / s, preferably more than 6 m / s. The peripheral speeds can thus be 5 to 25 m / s, e.g. 5 to 20 m / s, preferably 7 to 15 m / s. The diameter of the grinding rollers is, in a known manner, approximately 200 mm to 1000 mm, preferably 400 mm to 800 mm, e.g. 500 mm to 700 mm. The rotational speed (for both rollers or for the slower roller) can be 80 to 2400 rpm, e.g., 100 to 1000 rpm, preferably 200 to 600 rpm, e.g., 200 to 500 rpm. The achieved peripheral speed is then determined from the roller diameter and the rotational speed.

[0023] The grinding rollers are driven in opposite directions. The roller gap can be, for example, 0.5 to 10 mm, or 1 to 5 mm. The roller gap can be fixed by design. However, it is preferable that the roller gap can be variably adjusted to a specific value within the specified range. During operation, however, the roller gap is preferably fixed, so that – unlike compacting presses, for example – the roller gap does not change during operation.

[0024] The surface of the grinding rollers is preferably provided with a ribbing (as a profiling), whereby this ribbing can be formed, for example, by a plurality of groove-shaped depressions and projections. These depressions and projections can, for example, extend across the width of the roller and be oriented, for example, straight (parallel) or obliquely to the roller axis, spirally or arcuately. Two rollers with different profiling can also be used in one press, e.g., one with straight and one with non-straight oriented ribbing can be combined. The profiling of the grinding rollers of the two-roller mill must be distinguished from the individual crusher elements used in roller crushers.

[0025] Preferably, the flake (or the flake parts) are introduced into the two-roll mill in dry condition, whereby the flake or the particles preferably have a moisture content of max. 1.5 wt.%.

[0026] The material, i.e., the slug or slug pieces, are generally fed to the two-roll mill in a warm state, e.g., at a temperature of at least 100°C. The temperature is preferably between 100°C and 200°C, e.g., between 120°C and 150°C. The cooling according to the invention generally prevents the (granular and hot) material from adhering to the roll surfaces. For this purpose, the cooling can be implemented with the proviso that the temperature of the roll surfaces does not exceed 100°C, e.g., 90°C, preferably 80°C.

[0027] Cooling the roller surfaces is essential, and for this purpose, the rollers can be equipped with internal cooling, for example, by integrating one or more cooling devices into the rollers. These cooling devices can be designed, for example, as liquid cooling systems with one or more cooling channels arranged within the roller for a cooling medium. Water, for example, can be used as the cooling medium.

[0028] Of particular importance according to the invention is the method for comminuting fertilizer slurries or slurred pieces in such a two-roll mill, specifically during the production of fertilizer granules based on inorganic substances. The method according to the invention can be carried out using a two-roll mill of the type described for comminuting such fertilizer slurries, wherein this two-roll mill is provided with a cooling system. The roller of such a two-roll mill can be designed as a solid roller or, in a generally known manner, can have, on the one hand, a roller core and, on the other hand, a roller shell or an annular bandage arranged on the roller core, wherein this roller shell or the annular bandage is provided with the described profiling.The roll shell, which can also be made up of several segments, or the ring bandage can therefore be replaced as wearing elements and detachably fastened to the roll core. Cooling is preferably achieved by one or more cooling channels which are designed to cool the roll surface. For this purpose, cooling channels can be arranged in the roll core, in the bandage (or the roll shell) and / or between the roll core and bandage / shell. Such channels can be introduced, for example, as bores in the roll core and / or in the bandage. One possible embodiment is characterized in that the cooling channels or an annular or spiral cooling channel is formed between the roll core and bandage. This can be achieved structurally, for example,This can be achieved by creating a spiral annular groove on the outer circumference of the roll core, which is closed by the attached bandage, thus forming a spiral annular channel as a cooling channel on the inside of the bandage. Alternatively, such an annular groove can also be created on the inner circumference of the bandage. It is always advisable to feed the cooling medium into the roll body via a central or axially parallel feed channel. From there, the cooling medium can be guided, for example, via radial feed channels into the surface area, e.g., into the spiral cooling channel.

[0029] The invention also relates to a process for producing fertilizer granules from inorganic substances, wherein the feed material is first compacted into a slurry in a (high-pressure) roller press, and wherein the slurry or the slurry pieces produced from the slurry are then comminuted in a two-roll mill as described, wherein the rollers of the two-roll mill are cooled during comminution. The focus here is on the processing of granular, hot material. The starting material is fed to the roller press as feed material, preferably at a temperature of at least 100°C. Consequently, hot material is processed, so that the slurry or the slurry pieces, as preferably granular material, are also fed to the two-roll mill in a hot state, preferably at a temperature of at least 100°C.

[0030] In a preferred embodiment, the slurry emerging from the high-pressure roller press is not fed directly to the two-roll mill, but is first pre-shredded in a pre-shredding device. The shredding device can be, for example, a roller crusher and / or a hammer mill. Consequently, slurry pieces or particles are first generated from the slurry, which are then fed to the roller mill for granulation.

[0031] For this purpose, it is also advantageous if the slugs are classified between the pre-shredding device and the two-roll mill, e.g., using one or more screening devices. For this purpose, reference is made to the description of the figures.

[0032] Finally, the invention also relates to a plant for producing fertilizer granules using such a process, wherein the plant comprises at least one roller press (high-pressure roller press) and a two-roll mill, wherein the two-roll mill is provided with cooling of the roller surfaces according to the invention. Preferably, at least one pre-shredding device and / or a classifying device are also provided. Reference is also made to the description of the figures for examples.

[0033] The invention is explained below with reference to drawings which represent only one exemplary embodiment. They show: Fig. 1 a highly simplified flow diagram for a plant or a process for the production of fertilizer granules from inorganic substances, Fig. 2 a two-roll mill for the comminution of fertilizer slurries within such a process and Fig. 3 a section of the two-roll mill according to Fig. 2 .

[0034] In Fig. 1 is a schematic representation of a plant for producing fertilizer granulate from inorganic substances, with a temperature of, for example, at least 100 °C. The plant has a roller press 1, which is designed as a high-pressure roller press. In this roller press 1, the starting material A, namely inorganic substances, is pressed and thereby compacted into a slurry S. This slurry S is then granulated, with initial pre-crushing in at least one pre-crushing device 2a, 2b optionally being provided. This pre-crushing device can, for example, be designed as a roller crusher 2a. Alternatively or additionally, it can also be a hammer mill 2b, or several such devices can be combined with one another for pre-crushing. In any case, in this way, slurry pieces orFlake particles P are produced, which are comminuted and subsequently granulated in a subsequent process step. For this purpose, the flake pieces P, which, for example, have a temperature of at least 100 °C, are fed to a two-roll mill 3 and comminuted in the two-roll mill to form granules G.

[0035] In the Fig. 1 In the embodiment shown, classification takes place between the pre-shredding and the shredding, and for this purpose a screening device 4 with several screening stages 4a, 4b, 4c is arranged between the pre-shredding device 2 and the two-roll mill 3.

[0036] The flakes or particles P are fed to the screening device and in the first screening stage 4a, very coarse particles with a size of more than 10 mm are screened out as coarse fraction a. This coarse fraction a can, for example, be fed to a further comminution device 2c, e.g. a hammer mill, and from there the comminuted particles are fed again to the screening device 4. In the second screening stage 4b, a medium fraction b with a grain size of, for example, greater than 4 mm up to 10 mm is screened out and this medium fraction b is fed as feed material to the two-roller mill 3 and comminuted there in the manner described. The comminuted material is circulated and thus fed again to the screening device 4. In the third screening stage 4c, a material with a grain size of 2 mm to 4 mm and thus the desired granulate G is screened out and discharged as product G.The finest material F passing through all sieve passes is fed back into the compacting-granulating process and subsequently fed back into the roller press 1 for compaction.

[0037] The design and operation of the two-roll mill 3 is of particular importance within the scope of the invention. To prevent the flakes from sticking to the roller surfaces or in the profiling, the roller surface is cooled. For this purpose, Fig. 2 referred to.

[0038] Fig. 2shows a simplified schematic of a two-roll mill 3 with two counter-rotating grinding rollers 7, the roller surfaces of which are provided with a profiling 8, which is designed, for example, as a corrugation with a plurality of groove-shaped depressions and projections. These groove-shaped depressions and projections extend across the entire roller width and are oriented, for example, obliquely to the roller axis. In the illustrated embodiment, each of the rollers 7 consists of a rotatingly driven roller core 9 and a ring band 10 mounted on the roller core, which in turn is provided with the profiling 8.

[0039] The rollers 7 are each equipped with a cooling device for cooling the roller surfaces. For this purpose, cooling channels 11 are integrated into the rollers. In the illustrated embodiment, these cooling channels 11 are each designed as spiral-shaped cooling channels 11. These can be structurally realized by providing the roller core 9 with an annular spiral groove on its outer circumference, which is closed by the mounted bandage 10, so that a spiral-shaped cooling channel 11 is formed between the roller core 9 and bandage 10. In the exemplary embodiment, the cooling medium is supplied via a central supply channel 12, which is arranged axially in the roller core. The cooling medium can be supplied to and removed from the cooling channel 11 via radial channels 13.

[0040] Furthermore, the figures show that the two-roller mill 3 is provided with a housing 14 that forms an enclosure. Furthermore, a feed chute 15 is provided through which the material is fed; this chute 15 can be part of the housing or enclosure 14.

[0041] The material is spread loosely into the roller gap, like a veil of material, without pressure. For this purpose, a vibrating chute or vibrating platform (not shown) can be provided, through which the material enters the shaft 15 above the roller gap and is guided from there into the roller gap.

[0042] According to the invention, the cooling of the described two-roll mill is of particular importance, as cooling in this process surprisingly prevents clogging of the profiling or corrugation. This is of key importance, as clogging of the profiling reduces the shearing effect in the gap, thus breaking the material into finer pieces. Furthermore, the open, central roller gap is reduced, and this also leads to more fines being produced. Both are fed back into the roller press as fine return material after the next screening pass and undergo the process again. This unwanted fine material increases the circulating load in the system, thereby reducing product output. Overall, clogging of the profiling therefore reduces the efficiency and thus the profitability of the system.These disadvantages are avoided according to the invention in a surprisingly simple manner by the described cooling of the rollers, specifically in a two-roll mill within the described process.

Claims

1. A method for comminuting fertiliser flake (S) or flake pieces (P) in a two-roller mill (3) during the production of fertiliser granulate, wherein the two-roller mill (3) comprises two rotating, driven grinding rollers (7), the roller surfaces of which are provided with a profiling (8), wherein the flake (S) or flake pieces (P) are supplied onto the two-roller mill (3) and comminuted to granulate (G) in the roller gap formed between the grinding rollers (7), wherein the grinding rollers (7) rotate with a circumferential speed or with circumferential speeds of more than 5 m / s, characterised in that the surfaces of the grinding rollers (7) are cooled during operation.

2. The method according to claim 1, characterised in that cooling of the roller surfaces takes place with inner cooling of the rollers (7), in that cooling devices are integrated into the rollers (7).

3. The method according to claim 2, characterised in that the cooling devices are designed as liquid cooling devices which comprise one or more cooling channels for a liquid cooling medium, e.g. cooling water.

4. The method according to any one of claims 1 to 3, characterised in that the grinding rollers (7) rotate with a circumferential speed or with circumferential speeds of 5 to 25 m / sec, e.g. 5 to 20 m / sec, preferably 6 to 15 m / sec.

5. The method according to any one of claims 1 to 4, characterised in that the grinding rollers (7) have a diameter of 200 mm to 1000 mm, preferably 400 mm to 800 mm, e.g. 500 mm to 700 mm and / or rotate with a speed or with speeds of 80 to 2400 revs / min, preferably 120 to 1000 revs / min, e.g. 200 to 500 revs / min.

6. The method according to any one of claims 1 to 5, characterised in that the flake (S) or the flake pieces (P) are supplied onto the two-roller mill with a temperature of at least 100 °C, e.g. 100 °C to 200 °C, preferably 120 °C to 150 °C.

7. The method according to any one of claims 1 to 6, characterised in that cooling of the grinding rollers (7) takes place on the proviso that the temperature of the roller surfaces does not exceed 100 °C, preferably 80 °C.

8. The method according to any one of claims 1 to 7, characterised in that the roller gap has a gap width of 0.5 to 10 mm, e.g. 0.5 to 5 mm, or in the case of a variable gap setting is set to such a gap width.

9. The method according to any one of claims 1 to 8, characterised in that the surface of the grinding rollers (7) has a corrugation that is formed by a plurality of channel-shaped recesses and projections that extend across the width of the roller and, for example, are orientated in parallel or at an angle to the roller axis or in a spiral-shaped or arc-shaped manner.

10. The method according to any one of claims 1 to 9, characterised in that the flake (S) or flake pieces (P) is / are spread into the roller gap as a loose material shroud.

11. The method for producing fertiliser granulate from inorganic substances, wherein initially as starting material (A), inorganic substances are compacted in a roller press (1) to form a flake (S) and wherein subsequently the flake (S) or flake pieces (P) produced from the flake (S) is / are comminuted in a two-roller mill (3) with a method according to any one of claims 1 to 10.

12. The method according to claim 11, characterised in that flake (S) is pre-comminuted with at least one pre-comminution device, e.g. a roller breaker (2a) and / or a hammer mill (2b), into flake pieces (P) which are supplied to the two-roller mill (3).

13. The method according to claim 12, characterised in that between the pre-comminution device (2a, 2b) and the two-roller mill (3) and / or after the two-roller mill (3), classification of the flake pieces takes place with one or more sieving devices (4), for example.

14. The method according to any one of claims 11 to 13, characterised in that the material is moved in a circular flow system, in that preferably the material emerging from the two-roller mill (3) is supplied to the sieving device (4) again.

15. The method according to any one of claims 11 to 14, characterised in that the starting material (A) is supplied with a temperature of at least 100 °C onto the roller press (1) and / or in that the flake (S) or the flake pieces (P) are supplied onto the two-roller mill (3) with a temperature of at least 100 °C.

16. An installation for producing fertiliser granulate from fertiliser salt with a method according to any one of claims 11 to 15 with at least one roller press (1) and at least one two-roller mill (3), characterised in that the rollers (7) of the two-roller mill (3) are equipped with cooling devices for cooling the roller surfaces.

17. The installation according to claim 16 embodied in the form of a circulation system compacting and granulation installation.