RU2842544C1 - Method of grinding fertilizer plates in two-roll mill - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to a method of producing fertilizer granulate from inorganic substances and an apparatus for producing such a granulate. Method consists in that, as starting material (A), inorganic substances are compacted in a roller press into tile (S), and then slab (S) or the resulting pieces (P) are crushed in a two-roll mill, wherein two-roll mill (3) comprises two driven grinding rolls, the surfaces of which have a profile. Said plate (S) or its lumps (P) are fed into two-roll mill and ground in clearance between grinding rolls to granulate (G). At that, grinding rolls are revolved at peripheral speed exceeding 5 m/s. Grinding roll surfaces are cooled in operation. Proposed plant comprises, at least, one roll press and, at least, one two-roll mill. Wherein rolls of two-roll mill are equipped with roll surface coolers.

EFFECT: method and apparatus provide improved functionality and high profitability.

16 cl, 3 dwg

Description

The invention relates to a method for grinding fertilizer tiles or pieces of tiles in a two-roll mill in the process of producing fertilizer granulate, wherein the two-roll mill comprises two rotating grinding rollers, the surfaces of which have a profile, wherein the tile or pieces of tiles are loaded into the two-roll mill and are ground into granulate in an inter-roll gap formed between the grinding rollers, and wherein the grinding rollers rotate at a peripheral speed (on the surface) of more than 5 m/s. The roller can be made in the form of a solid roller or contain a core and a shell or bandage fixed thereto, which is provided with a profile.

In addition, the invention relates to a method and apparatus for producing fertilizer granules from inorganic substances, wherein the inorganic substances, for example in the form of fertilizer salt, are compacted in a roller press into a tile as the starting material, wherein the tile or pieces obtained from it are crushed/ground in a two-roll mill in the manner described above into fertilizer granules.

This type of production of fertilizer granules is also called press granulation or compact granulation. The starting material (inorganic substances) is pressed in a roller press (high pressure) under high pressure and compacted, resulting in the formation of a so-called "tile". This stage of the process is called press agglomeration. It is followed in the next stage by granulation by crushing the tiles and classification, for example screening. In this case, the tiles coming out of the roller press are usually not fed directly into the two-roll mill, but are pre-crushed by first crushing the tiles in a crusher and/or hammer mill into pieces. They are then fed into the two-roll mill, namely, with intermediate classification, if necessary.

Since the inorganic substances are initially in the form of relatively fine-grained materials, which in this form are unsuitable for mechanical spreading over the fertilized areas, granulation by pressing produces fertilizer granules of a certain grain size, which allow them to be handled flawlessly. The goal is usually to obtain fertilizer granules with a grain size of 1-5 mm.

The inorganic substances used in the context of the invention for producing the fertilizer granulate are, for example, mineral substances or substances obtained by evaporating salt water, such as chlorides or sulfates. Thus, it may preferably be potassium sulfate or potassium chloride.

In the described processes and installations, a distinction must therefore be made between a roller press on the one hand and a two-roll mill on the other. In a roller press, the feedstock is compacted into tiles under high pressure and at relatively low circumferential speeds of the rollers. A two-roll mill serves in a further step of the process for crushing the tiles or pieces of tiles obtained from them after compaction, for example with a roller crusher or hammer mill. In contrast to roller presses, two-roll mills operate at a relatively high circumferential speed and the material is poured into the inter-roll gap unbound in the form of a curtain. The surfaces of the rollers of a two-roll mill have a profile, i.e. the surfaces of the rollers are usually structured. In contrast to a crusher with a plurality of crushing elements (e.g. teeth), which act individually or in small numbers on the material being loaded and crush it, the crushing in a two-roll mill takes place between the grinding surfaces, which, admittedly, can be quite structured, but without the specific effect of individual crushing elements on the particles being crushed. The foreground of the invention is the design of a two-roll mill, which therefore cannot be confused with a roller press and a roller crusher.

The compaction of inorganic substances in a roller press is known, for example, from DE 2824827 B2, DE 3802173 C1 and DE 1758978.

According to DE 2824827 B2, the material is pressed under pressure by a screw conveyor into a roller gap. The material to be pressed is fed at a temperature of over 120°C, and the pressing takes place with a high specific pressing force. The rollers rotate at a circumferential speed of 0.55-0.75 m/s. The surface temperature of the rollers must be maintained below 80°C, namely to avoid melting of the material on the pressing surface and thus to obtain a tile with a shiny, hard surface. This state of the art concerns exclusively high-pressure roller presses.

DE 652349 A describes a device for granulating lumpy products, in particular fertilizers containing ammonium nitrate, consisting of two rollers rotating towards each other, remaining at a distance from each other at their outer periphery, the working surface of which is formed by sharp-edged grooves offset relative to the grooves of the opposite roller.

Furthermore, the above-mentioned two-roll mills are known from practice, which, during the process of obtaining fertilizer granules, are operated at a high peripheral speed and in which the previously obtained pieces of tiles are scattered unbound into the inter-roll gap without pressure.

From DE 21293, grinding of grain on grooved or smooth rollers is known. To avoid damage to the grain due to harmful heating, the rollers are cooled.

Cooling of the rolls is also described in DE 496 543, which discloses the rolling of plastic and soft masses, in particular cocoa and chocolate masses, and alternatively mentions the rolling of rubber, oil paints and other oil- and fat-containing masses. Cooling also serves to avoid damage to the processed masses. In addition, disruption of the rolling process, including by burning of the mass to the rolls, must be prevented. The processing of plastic materials also takes place at relatively low circumferential speeds and under comparatively high pressure.

DE 635879 A describes a roll for mills and rolling mills, equipped with cooling. However, the authors have abandoned the idea of a coolant flowing through the roll. Instead, in order to distribute the heat in the roll, its cavity is filled with a liquid, which is poured in once, after which the filling hole is tightly sealed.

Finally, cooled rollers are also known in roller presses for hot briquetting or hot compaction of material that is processed at high temperatures, for example when processing reduced iron ores or sponge iron at temperatures above 900°C (see DE 102012106527 A1). At such temperatures, the roller tires and, in particular, the pressing tools (e.g., molding recesses) fixed to them are subject to severe wear. In order to limit this, cooling, e.g., water cooling, is generally provided.

These publications have no influence on the design of two-roll mills for grinding fertilizer tiles or pieces thereof.

The invention is based on the technical problem of creating a method for grinding fertilizer tiles or pieces thereof in a two-roll mill of the type described above, which would be distinguished by improved functionality and increased profitability.

This problem of the invention is solved by means of a generic method of grinding fertilizer tiles or pieces thereof in a two-roll mill during the process of obtaining fertilizer granulate due to the fact that the surfaces of the grinding rollers are cooled during operation and, consequently, during the grinding of the tiles or pieces thereof.

According to the invention, therefore, in the process of grinding granular material, namely fertiliser tiles or pieces thereof, previously obtained with the aid of a high-pressure roller press, cooling of the roller surfaces of a two-roll mill is provided, i.e. (preferably) hot fertiliser tiles or pieces thereof are ground in a two-roll mill with cooled roller surfaces. In this case, the invention proceeds from the unexpected fact that in such a two-roll mill, when processing fertilisers, despite the small width of the inter-roll gap, the high circumferential speeds of the roller surfaces and the associated very short contact time of the material with the roller surfaces, clogging of the profiled surfaces of the rollers can be reliably avoided by cooling. Despite the very short contact time, cooling makes it possible to prevent scorching or adhesion of salts or tile pieces to the roller surfaces and, consequently, to the profile of the rollers. In this case, of particular importance is the fact that the granular and preferably hot material, i.e. tiles or crushed pieces thereof (e.g. of size/fraction 4-10 mm) are poured loosely into the roller gap as a curtain of material without compaction, for example via a vibrating chute located above the roller gap and through a subsequent or located below the roller gap discharge shaft, which runs across the entire width of the roller. The width of the rollers can be, for example, 1000-3000 mm, for example 1500-2500 mm. A typical roller width is, for example, 1800-2000 mm. The material is poured as a curtain into the shaft located above the roller gap via a vibrating chute or similar means.

It is further important that the grinding rollers are driven at a high peripheral speed, whereby the speed of both rollers can be the same or different, depending on the material being processed. The speed of both rollers is more than 5 m/s, preferably more than 6 m/s. In the case of different speeds, the slower roller rotates at a speed of more than 5 m/s, preferably more than 6 m/s. Thus, the peripheral speeds can be 5-25 m/s, for example 5-20 m/s, preferably 7-15 m/s. The diameter of the grinding rollers is known to be 200-1000 mm, preferably 400-800 mm, for example 500-700 mm. The rotational speed (of both rollers or of the slower roller) can be 80-2400 rpm, for example 100-1000 rpm, preferably 200-600 rpm, for example 200-500 rpm. The correspondingly realizable peripheral speed then results from the diameter of the grinding rollers and the rotational speed.

The grinding rolls are driven in rotation towards each other. The roll gap is, for example, 0.5-10 mm, for example 1-5 mm. The roll gap can be structurally fixed. Preferably, however, the roll gap can be adjusted in the specified range to a certain value. However, during operation, the roll gap is preferably adjusted fixedly, so that, for example, in contrast to compacting presses, work is not carried out with a roll gap that changes during operation.

The surface of the grinding rollers is preferably provided with a ribbing (as a profile), wherein this ribbing can be formed, for example, by a plurality of grooved depressions and projections. These depressions and projections can extend, for example, across the width of the rollers and are oriented, for example, straight (parallel) or obliquely to the axis of the rollers, spirally or arcuately. Also, two rollers with different profiles can be used in one press, for example, one with a straight and the other with a different ribbing can be combined with each other. The profile of the grinding rollers of a two-roll mill should be distinguished from the individual crushing elements implemented in roller crushers.

Preferably, the tiles (or pieces thereof) are introduced into the two-roll mill dry, whereby the tiles or particles preferably have a moisture content of max. 1.5 wt.%.

The material, i.e. the tile or pieces thereof, is loaded into the two-roll mill, as a rule, in a hot state, for example with a temperature of at least 100°C. Preferably, the temperature is 100-200°C, for example 120-150°C. The stated cooling allows, in general, to avoid accumulation of (granular and hot) material on the surfaces of the rolls. For this purpose, cooling can be implemented with the proviso that the temperature of the surfaces of the rolls does not exceed 100°C, for example 90°C, preferably 80°C.

Cooling of the roll surfaces is important, and for this purpose the rolls can be provided with internal cooling, when, for example, one or more cooling devices are integrated into the rolls. These cooling devices can be designed, for example, as liquid coolers, containing one or more cooling channels for coolant located inside the rolls. Water can be used as a coolant, for example.

Of particular importance, according to the invention, is a method for grinding fertilizer tiles or pieces thereof in such a two-roll mill, namely in the process of producing fertilizer granules based on inorganic substances. The invention also concerns a two-roll mill of the described type for grinding such fertilizer tiles, wherein this two-roll mill is designed to implement the described method and, therefore, is provided with cooling. The roll of such a two-roll mill can be designed as a solid roll or contain, in a fundamentally known manner, on the one hand, a core and, on the other hand, a shell or an annular band located on the core, wherein this shell or annular band is provided with the described profile. The roll shell, which can be made up of several segments, or the annular band can, therefore, be replaced as wearing parts and be detachably fastened to the roll core. The cooling is preferably implemented by one or more cooling channels, which are designed to cool the surface of the roll. For this purpose, cooling channels can be arranged, for example, in the core, the bandage (or the casing) and/or between the core and the bandage/casing. Such channels can be made in the core and/or the bandage, for example in the form of bores. One possible variant is characterized in that the cooling channels or the annular or spiral-shaped enveloping cooling channel are made/is made between the core and the bandage. This is implemented structurally, for example, by the fact that on the side of the outer periphery, a spiral-shaped enveloping annular groove is made in the core, which is closed by the put-on bandage and thereby forms an enveloping spiral-shaped annular channel as a cooling channel on the inside of the bandage. As an alternative, such an annular groove can also be made in the bandage on the side of its inner periphery. It is always advisable to feed the coolant into the roll body via a central or axially parallel feed channel. From there, the coolant can be directed, for example, into a spiral-shaped cooling channel into the surface area, for example via radial feed channels.

The invention also relates to a method for producing fertilizer granules from inorganic substances, wherein the feedstock is first compacted in a roller press (high pressure) into a tile, wherein the tile or pieces obtained from it are then crushed/ground in a two-roll mill in the manner described, wherein the rollers of the two-roll mill are cooled during the crushing. The processing of granular hot material is in the foreground. The feedstock is fed into the roller press as feedstock, preferably with a temperature of at least 100°C. The hot material is therefore processed, so that the tile or pieces thereof are also fed into the two-roll mill in a hot state, preferably also in the form of hot material, namely preferably with a temperature of at least 100°C.

In a preferred embodiment, the tile coming out of the high-pressure roller press is not fed directly into the two-roll mill, but is first pre-crushed in a pre-crushing device. The crushing device may be, for example, a roller crusher and/or a hammer mill. The tile is therefore first processed into pieces or particles, which are fed to the roller mill for granulation.

For this purpose, it is also preferable if between the pre-crushing device and the two-roll mill, a classification of the tile pieces takes place, for example by means of one or more screens. For this, reference should be made to the description of the figures.

The subject of the invention is also a plant for producing fertilizer granules in this manner, 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, according to the invention, with cooling of the roller surfaces. In addition, at least one pre-crushing device and/or classification device is preferably provided. For this purpose, reference should also be made to the description of the figures.

The invention is explained below with the aid of drawings, which show only one example of its implementation. The drawings show the following:

- Fig. 1: simplified diagram of the installation and method for producing fertilizer granules from inorganic substances;

- Fig. 2: Two-roll mill for grinding fertilizer tiles in this way;

- Fig. 3: fragment of the two-roll mill according to Fig. 2.

Fig. 1 shows a schematic and very simplified illustration of a plant for producing fertilizer granules from inorganic substances with a temperature of, for example, at least 100°C. The plant comprises a roller press 1, which is designed as a high-pressure roller press. In this roller press 1, the starting material A, namely the inorganic substances, is pressed and thereby compacted into a tile S. This tile S is then granulated, whereby a preliminary crushing is first optionally provided in at least one preliminary crushing device 2a, 2b. This preliminary crushing device can be designed, for example, as a roller crusher 2a. Alternatively or additionally, it can also be a hammer mill 2b, or several such devices can also be combined with each other for the preliminary crushing. In any case, pieces or particles P are obtained from the tile S, which are crushed and thus granulated in the next step of the method. For this purpose, pieces of tile P, having, for example, a temperature of at least 100°C, are loaded into a two-roll mill 3 and crushed in it into granulate G.

In the example in Fig. 1, classification occurs between the preliminary grinding and the grinding, for which purpose a screen 4 with several screening stages 4a, 4b, 4c is located between the preliminary grinding device 2 and the two-roll mill 3.

The pieces of tiles or particles P are fed to the screen, and in the first screening stage 4a the very large particles with a size of more than 10 mm are screened out as a large fraction a. This large fraction a can be fed, for example, to an additional grinding device 2c, for example a hammer mill, and from there the crushed particles are fed back to the screen 4. In the second screening stage 4b the medium fraction b with a grain size of, for example, 4-10 mm is screened out, which is fed as feed material to the two-roll mill 3 and is ground there in the manner described. The crushed material is circulated and thus fed back to the screen 4. In the third screening stage 4c, the material with a grain size of 2-4 mm and thus the desired granulate G are screened out and discharged as product G. The finest material F that passes through all screening processes is fed back to the compaction and granulation process and thus loaded into the roller press 1 again for compaction.

The design and operating principle of the two-roll mill 3 are of particular importance within the scope of the invention. In order to prevent the accumulation of pieces of tiles on the surfaces of the rolls or in the profile, the surface of the roll is cooled (Fig. 2).

Fig. 2 shows a schematic, simplified view of a two-roll mill 3 with two grinding rollers 7 rotating towards each other, the surfaces of which have a profile 8, made, for example, in the form of corrugation with a plurality of grooved depressions and projections. These grooved depressions and projections extend across the entire width of the rollers and are oriented, for example, obliquely to the axis of the rollers. In the example shown, each of the rollers 7 consists of a core 9 driven into rotation and an annular bandage 10 mounted on it, which, in turn, has a profile 8.

The rolls 7 are equipped with cooling devices, by means of which the surfaces of the rolls are cooled. For this purpose, cooling channels 11 are made in the rolls. In the example shown, these cooling channels 11 are made in the form of spirally enveloping cooling channels 11. Structurally, they are implemented due to the fact that the core 9 is provided from the side of the outer periphery with an annularly enveloping spiral groove, which is closed by a mounted bandage 10, as a result of which a spirally enveloping cooling channel 11 is formed between the core 9 and the bandage 10. The coolant is supplied in this example through the central supply channel 12, located axially in the core. The coolant is supplied to the cooling channel 11 and removed from it through the radial channels 13.

In addition, the figures show that the two-roll mill 3 is provided with a housing 14, forming a casing. Further, a feed shaft 15 is provided, through which the material is fed, and this shaft 15 can be part of the housing or casing 14.

The material is poured into the inter-roll gap without pressure, unbound, in the form of a curtain. For this purpose, a vibrating chute or vibrating platform (not shown) may be provided, through which the material enters the shaft 15 above the inter-roll gap, and from there it is directed into the inter-roll gap.

According to the invention, the cooling of the described two-roll mill is of particular importance, since the cooling makes it possible to unexpectedly prevent the clogging of the profile or the corrugation. This is of great importance, since the clogging of the profile leads to the fact that the shearing effect in the gap is reduced, and thus the material is broken into smaller pieces. Furthermore, the open middle inter-roll gap is reduced, and this also leads to the fact that more fine material is produced. The small pieces and fine material are fed back to the roller press after the next screening process as fine return material and are passed through the process again. Due to this undesired fine material, the rotational load in the plant increases, and thus the product yield decreases. In general, the clogging of the profile leads to a decrease in efficiency and thus to a decrease in the profitability of the plant. According to the invention, these disadvantages are unexpectedly simple prevented by the described cooling of the rollers, namely in the two-roll mill within the framework of the described method.

Claims (16)

1. A method for producing fertilizer granules from inorganic substances, wherein the inorganic substances are compacted in a roller press (1) as the starting material (A) into a tile (S), and then the tile (S) or pieces (P) obtained from it are then ground in a two-roll mill (3), wherein the two-roll mill (3) contains two rotating grinding rollers (7), the surfaces of which have a profile (8), wherein the tile (S) or pieces (P) thereof are loaded into the two-roll mill (3) and ground in an inter-roll gap formed between the grinding rollers (7) into granules (G), wherein the grinding rollers (7) rotate at a peripheral speed or speeds greater than 5 m/s, characterized in that the surfaces of the grinding rollers (7) are cooled during operation. 2. The method according to paragraph 1, characterized in that the cooling of the surfaces of the rolls is performed using internal cooling of the rolls (7) due to the fact that cooling devices are integrated into the rolls (7). 3. The method according to paragraph 2, characterized in that the cooling devices are made in the form of liquid cooling devices containing one or more cooling channels for a liquid coolant, for example cooling water. 4. The method according to any one of paragraphs 1-3, characterized in that the grinding rollers (7) rotate at a peripheral speed or speeds of 5-25 m/s, preferably 5-20 m/s, predominantly 6-15 m/s. 5. The method according to any one of paragraphs. 1-4, characterized in that the grinding rollers (7) have a diameter of 200-1000 mm, preferably 400-800 mm, preferably 500-700 mm, and/or rotate at a rotation speed or speeds of 80-2400 rpm, preferably 120-1000 rpm, preferably 200-500 rpm. 6. The method according to any one of paragraphs. 1-5, characterized in that the tile (S) or its pieces (P) are loaded into a two-roll mill (3) with a temperature of at least 100°C, preferably 100-200°C, preferably 120-150°C. 7. The method according to any one of paragraphs 1-6, characterized in that the cooling of the grinding rollers (7) is carried out so that the temperature of the roller surfaces does not exceed 100°C, preferably 80°C. 8. The method according to any of paragraphs 1-7, characterized in that the inter-roller gap is set with a width of 0.5-10 mm, preferably 0.5-5 mm, or it is adjusted with a variable gap setting to such a width. 9. The method according to any one of paragraphs 1-8, characterized in that the surface of the grinding rollers (7) has a corrugation formed by a plurality of grooved depressions and projections that extend across the width of the rollers and are oriented essentially parallel or obliquely to the axis of the rollers, or in a spiral or arc-shaped manner. 10. The method according to any of paragraphs 1-9, characterized in that the tile (S) or its pieces (P) are poured into the inter-roller gap in the form of an unbound curtain of material. 11. The method according to any one of paragraphs. 1-10, characterized in that the tile (S) is pre-crushed in at least one pre-crushing device, preferably in a roller crusher (2a) and/or a hammer mill (2b) into pieces (P), which are fed to a two-roll mill (3). 12. The method according to claim 11, characterized in that between the preliminary grinding device (2a, 2b) and the two-roll mill (3) and/or behind the two-roll mill (3), classification of the tile pieces is carried out, preferably using one or more screens (4). 13. The method according to any one of paragraphs 1-12, characterized in that the material is circulated due to the fact that the material leaving the two-roll mill (3) is again fed to the screen (4). 14. The method according to any one of paragraphs. 1-13, characterized in that the starting material (A) is loaded into a roller press (1) with a temperature of at least 100°C and/or the tile (S) or its pieces (P) are loaded into a two-roll mill (3) with a temperature of at least 100°C. 15. An installation for producing fertilizer granules from fertilizer salts made from inorganic substances by the method according to any of paragraphs 1-14, comprising at least one roller press (1) and at least one two-roll mill (3), characterized in that the rollers (7) of the two-roll mill (3) are equipped with cooling devices for cooling the surfaces of the rollers. 16. The installation according to item 15, made in the form of a circulation compacting and granulating installation.

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