Apparatus and method for producing fertilizer particles

Abstract

The invention relates to a plant for producing fertilizer granules, comprising: a compactor (1) for producing strips (S) from an inorganic raw material (A); a crushing device (2) for pre-crushing the strip (S) into strip pieces (P); at least two twin-roller mills (3a, 3b, 3c) arranged one behind the other in the production direction, the twin-roller mills (3a, 3b, 3c) each having two rotationally driven grinding rollers (7), the surfaces of which are provided with profiled sections and between which a roller gap having a roller gap width is formed, according to the invention, the strip pieces (P) can be transported in sequence to two roller mills (3a, 3b, 3c) arranged one behind the other for comminution into granules (E), and the roller gap widths of the two roller mills (3a, 3b, 3c) differ in size or are set to differ and gradually decrease in the production direction from one to the next.

Description

Technical Field

[0001] The invention relates to a device and a method for producing fertilizer granules from inorganic raw materials. The device has at least one compactor in which the inorganic raw material is compacted into strips, thereby producing strips from the inorganic raw material. A crushing device is arranged downstream of the compactor, which serves to pre-crush the strips, i.e. the strips are crushed or pre-crushed into strip fragments in the crushing device. These pre-crushed strip fragments are subsequently crushed into granules of the desired size. Background Art

[0002] This method of producing fertilizer granules is also known as extrusion granulation or compaction granulation. The compactor is preferably designed as a roller press or a high-pressure roller press, in which the raw material (inorganic substance) is squeezed under high pressure and compacted here, thereby forming so-called strips (i.e. flat, compacted material strips). This process step is called pressure agglomeration. The strips are pre-crushed in a mechanical crusher, and then in other crushing equipment (for example in a double-roll mill) these strip fragments are made into particles of the required particle size - usually after one or more classifications. Since the inorganic substance initially exists in the form of relatively fine material, this form of material is not suitable for mechanical spreading on the land to be fertilized, so the extrusion granulation process can produce fertilizer granules with a clear particle size and easy to handle. The usual goal is to produce fertilizer granules with a particle size between 1 mm and 5 mm.

[0003] Inorganic substances used for producing fertilizer granules within the scope of the present invention can be, for example, minerals or substances obtained from the evaporation of seawater, such as chlorides or sulfates, in particular potassium sulfate or potassium chloride. It also includes multi-nutrient fertilizers, such as nitrogen, phosphorus and potassium compound fertilizers.

[0004] In the above-mentioned processes or apparatuses, a distinction needs to be made between roller presses on the one hand and double roller mills on the other hand. In roller presses, the raw material is compacted into strands under high pressure and relatively low roller circumferential speeds. Double roller mills are used in a downstream process step to comminute strand fragments, which are obtained from the strands after compaction, for example by a roller crusher. In contrast to roller presses, double roller mills are operated at relatively high circumferential speeds and the material is thrown into the roller gap in the form of a loose material curtain. The roller surface of a double roller mill is provided with profiles, i.e. the roller surface is usually structured. Double roller mills and crushing devices are therefore also different. In contrast to crushers with a plurality of crushing elements (e.g. teeth), which act individually or in small numbers on the feed material and crush it, the comminution in a double roller mill takes place between the grinding surfaces, which, although they can also be structured, do not result in a specific action of the individual crushing elements on the particles to be comminuted. Thus, in a crusher, comminution is achieved (essentially) by impact and shearing action, whereas in a mill it is achieved (essentially) by pressure and shearing action.

[0005] 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 17 58978.

[0006] A device and a method of the above-mentioned type are described in DE 10 2020 131 638 A1. The strip is first broken into strip fragments in a crusher and / or a hammer mill, which are then conveyed to a double-roll mill and possibly graded in between. The grinding roller surfaces of the double-roll mill are cooled during operation.

[0007] In practice, when producing fertilizer granules, the strands of the strands discharged from the strand crusher are usually not conveyed directly to the double-roll mill, but are first crushed in other comminution devices, for example in an impact crusher, an impact mill and / or a hammer mill. Only the granules from the impact mill or hammer mill are finally fed to the double-roll mill. In the known devices, the double-roll mill thus serves as the "final" comminution device for producing a final product with the desired particle size, since the particle size of the double-roll mill can be adjusted very well by means of a variable roll gap width.

[0008] Furthermore, from EP 3 801 909 B1 a grinding machine with multiple mills for the industrial production of ground products is known. In a multi-roller stand, multiple roller pairs can be arranged and multiple processing lines can also be implemented in parallel. It is mainly used for grain grinding.

[0009] Finally, DE 16 67 147 B1 describes a process in which fine-grained materials are granulated by roller pressing, subsequently comminuted by impact or hammer mills, and classified by means of a classifying device.

[0010] Other devices and methods for comminuting materials are known, for example, from CN 210058412, DE 69 904 770 and GB 1 050158 A. Summary of the invention

[0011] Based on the above-mentioned prior art, the object of the present invention is to provide a device which can economically produce high-quality fertilizer granules. In addition, a corresponding method should be specified.

[0012] To achieve this object, the invention provides a device having the features of claim 1 and a method having the features of claim 9 .

[0013] A device for producing fertilizer granules is proposed, the device comprising:

[0014] - compactors for producing strips from inorganic raw materials (e.g. high-pressure roller presses);

[0015] - a crushing device for pre-crushing the strips into strip fragments;

[0016] - at least two double-roller mills arranged one behind the other in the production direction,

[0017] The double-roll mills each have two rotationally driven grinding rollers, the roller surfaces of the grinding rollers are provided with a shaped portion, and a roller gap with a (preferably adjustable) roller gap width is formed between the grinding rollers;

[0018] The strip fragments can be sequentially conveyed to a series of double-roll mills to be crushed into particles;

[0019] Furthermore, the roll gap widths of the double-roll mills are different in size or are adjusted to be different and gradually decrease from one double-roll mill to the next double-roll mill in the production direction.

[0020] The apparatus may comprise at least a first double roll mill downstream of the crushing device and a second double roll mill downstream of the first double roll mill, wherein the gap width of the second double roll mill is sized or adjusted to be smaller than the gap width of the first double roll mill.

[0021] Alternatively, a plant with, for example, three double-roller mills or at least three double-roller mills can also be realized, wherein a third double-roller mill is arranged downstream of the second double-roller mill, the roll gap width of the third double-roller mill being smaller in size or being adjusted to be smaller than the roll gap width of the second double-roller mill. Of course, embodiments with more than three double-roller mills, for example four or more double-roller mills, can also be realized.

[0022] The invention is based on the recognition that the use of double roller mills has proven to be very effective in the production of fertilizer granules, since high-quality fertilizer granules can be produced in principle due to the structure and mode of operation of the double roller mill. However, according to the invention, the double roller mill is not used as the last comminution device for producing the final product as in the prior art, i.e., not only is a double roller mill with a roll gap width adjusted to the size of the final product used in the last process step, but according to the invention, a plurality of double roller mills, for example two or three double roller mills, are connected in series, so that, for example, the first double roller mill is used as a pre-comminution device for the strip fragments, i.e., the strip fragments from the comminution device do not need to be pre-comminuted in other or additional comminution devices before they enter the double roller mill, but on the one hand, the strip fragments from the comminution device are further pre-comminuted by the double roller mill, and on the other hand, the final product is produced by the last double roller mill arranged in series. It is particularly advantageous here that the roll gap width of the double-roller mill can be adjusted very well, so that, for example, the first double-roller mill is implemented or arranged with a relatively large roll gap, while the downstream and optionally the last double-roller mill is arranged with a (significantly) smaller roll gap, which is preferably matched to the size of the end product.

[0023] In principle, the double-roll mills can be arranged directly one after the other in series, for example, they can also be arranged directly one above the other, so that the material passes directly from the first double-roll mill to the second double-roll mill, and if necessary, to the third double-roll mill, so that the final product is discharged from the corresponding last double-roll mill, for example the second double-roll mill or the third double-roll mill.

[0024] In a particularly preferred embodiment, the device is additionally equipped with a classifying device, such as a screening device. Therefore, the present invention optionally proposes that at least one classifying device, such as a screening device, is respectively provided between the crushing device and a double-roller mill located downstream of the crushing device, such as the first double-roller mill, and / or between two double-roller mills arranged in succession, such as between the first double-roller mill and the second double-roller mill, and / or between the second double-roller mill and the third double-roller mill.

[0025] It is particularly advantageous to design the device as a circulating compaction granulation device in which the double roller mill and one or more classifying devices are arranged so that the strip fragments are circulated through the double roller mill and the screening device in sequence. An example of such a circulating compaction granulation device is shown and explained in the accompanying drawings. By using a screening device, double roller mills with different roller gap widths can be operated particularly effectively, because with the help of the screening device, materials with suitable sizes are transported to the corresponding double roller mills in a targeted manner, thereby avoiding the double roller mills with, for example, relatively small roller gap widths to process larger materials. The use of screening devices and the realization of circulating grinding devices are known in principle from the prior art. However, according to the invention, this design is of special significance because a plurality of double roller mills with different roller gap widths are successively integrated in the device, so that the rational loading of the double roller mills is particularly important.

[0026] Particularly preferably, a plant can be realized in which only a double roller mill is arranged as a comminution device downstream of the comminution device or the strip breaker, i.e. after the strip breaker, preferably without using any other comminution devices (e.g. hammer mills, impact mills, etc.). Instead, the strip fragments emerging from the strip breaker are preferably comminuted only by a plurality of double roller mills arranged in series, thereby achieving a particularly efficient granulation based on a double roller mill with an adjustable roll gap width. Reference is also made to the description of the drawings in this regard.

[0027] In the specific design and construction of the double-roll mill, the experience of the prior art can in principle be used. The double-roll mill is preferably equipped with two counter-rotating grinding rollers, whose surfaces have a texture formed by a plurality of groove-shaped recesses and protrusions, which extend over the width of the roller and are oriented, for example, parallel to or obliquely to the roller axis or in a spiral or arc shape. In this case, the two rollers can be provided with textures of different designs, and usually the spiral or arc shape is only provided on one of the rollers.

[0028] The roll gap width of the double-roll mill can each be in the range of 0.5 mm to 30 mm, for example 0.5 mm to 15 mm, and can be adjusted to the desired roll gap width in a particularly targeted manner depending on the design of the plant.

[0029] It is also possible to use a double-roll mill in which the grinding rollers are equipped with a cooling device for cooling the roller surface. For example, the double-roll mill known from DE 10 2020 131 638 A1 can be used.

[0030] The invention relates not only to the above-mentioned device, but also to a method for producing fertilizer granules from inorganic raw materials, which method preferably uses a device of the above-mentioned type. The raw material is compacted into strips in a compactor, and the strips are pre-comminuted into strip fragments in a crushing device. The strip fragments are comminuted into particles in at least two double-roll mills arranged in succession, wherein the roll gap widths of the double-roll mills arranged in succession are different in size or are adjusted to be different, and the roll gap width gradually decreases from one double-roll mill to the next double-roll mill, so that the material passes through a plurality of double-roll mills with gradually decreasing roll gaps in sequence. The last double-roll mill arranged in series is preferably adjusted according to the particle size to be produced. It is particularly preferred that the strip fragments coming out of the crushing device are subsequently comminuted only in a plurality of double-roll mills and not in other comminution devices arranged upstream or downstream (such as impact mills, hammer mills, etc.). Therefore, preferably, no other comminution devices other than the double-roll mill are used after the strip crusher, so that the invention in a preferred embodiment only utilizes the advantages of the double-roll mill.

[0031] Nevertheless, independently of this, a classification device can also be provided in addition, i.e., between the crushing device and the double roller mill located downstream of the crushing device and / or between two double roller mills arranged in succession, preferably the strip fragments can be classified, for example, using one or more screening devices. For the screening device, structures known from the prior art can be used, such as screening devices with one screening plate and / or screening devices with two, three or more screening plates, so that the material can be classified into two or more levels in the screening device.

[0032] Double-roll mills of particular significance within the context of the present invention are preferably operated at a peripheral speed of at least 5 m / s, for example 5 to 30 m / s or 5 to 25 m / s, preferably 6 to 20 m / s or alternatively 6 to 15 m / s.

[0033] The surface of the grinding roller may be cooled during operation.The diameter of the grinding roller may be 200 mm to 1000 mm, preferably 400 mm to 800 mm, for example 500 mm to 700 mm.

[0034] The double-roll mills can rotate (in each case) at a rotational speed of 100 to 3000 rpm, preferably 120 to 1000 rpm, for example 150 to 800 rpm.

[0035] When the diameter is 200 mm to 1000 mm and the peripheral speed is 5 to 30 m / s, the rotation speed is 100 to 2860 rpm. When the diameter is 200 mm to 1000 mm and the peripheral speed is 6 to 20 m / s, the rotation speed is 110 to 1910 rpm.

[0036] When the diameter is 400 mm to 800 mm and the peripheral speed is 5 to 30 m / s, the rotation speed is 120 to 1400 rpm. When the diameter is 400 mm to 800 mm and the peripheral speed is 6 to 20 m / s, the rotation speed is 140 to 950 rpm.

[0037] When the diameter is 500 mm to 700 mm and the peripheral speed is 5 to 30 m / s, the rotation speed is 140 to 1100 rpm. When the diameter is 500 mm to 700 mm and the peripheral speed is 6 to 20 m / s, the rotation speed is 160 to 760 rpm.

[0038] There is the possibility that all double-roll mills in the device are operated with the same peripheral speed or rotational speed and / or are designed to be of the same size. However, it is also preferably possible to design the double-roll mills in the device to different sizes and / or different operating parameters, for example with different rotational speeds.

[0039] In any case, the double-roll mills implemented in the equipment are operated with different roll gap widths. The roll gap widths of the roll gaps are set to 0.5 mm to 30 mm respectively. Therefore, it may be appropriate to set the roll gap width of the first double-roll mill to 10 mm to 30 mm and the roll gap width of the second double-roll mill to 0.5 mm to 7 mm. If three double-roll mills are implemented in succession, similar classification can be performed. For example, for three double-roll mills arranged in succession, the roll gap width of the first double-roll mill can be adjusted to 10 mm to 30 mm, the roll gap width of the second double-roll mill can be adjusted to or set to 5 mm to 15 mm in size, and the roll gap width of the third double-roll mill can be adjusted to or set to 0.5 mm to 5 mm in size.

[0040] The invention also includes embodiments with more than three twin-roll mills arranged in series, for example four or more twin-roll mills. In this case, a suitable roll gap grading setting will also be carried out.

[0041] Therefore, within the scope of the present invention, double roller mills, more precisely in combination with compactors (which are preferably designed as roller presses), are of special significance. Roller presses are therefore distinguished from double roller mills. Roller presses for fertilizer pressure agglomeration have two counter-rotating and driven squeezing rollers or compacting rollers, which form a roller gap, in which the raw material is squeezed under high pressure and compacted here to form strips. The roller press is preferably operated at a pressure of 40 kN to 100 kN per centimeter of roller width. The roller surface circumferential speed of the squeezing rollers of the roller press is generally 0.3 to 1.8 m / s, and the roller diameter can be, for example, 0.5 to 1.5 m. The roller width of the squeezing roller is selected according to the roller diameter and the required output. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The present invention will be described in more detail below with reference to the accompanying drawings, which are only examples and do not limit the scope of protection. In the accompanying drawings:

[0043] Figure 1 A first embodiment of a device for producing fertilizer granules according to the invention is schematically and simplified;

[0044] Figure 2 A second embodiment of the present invention is shown;

[0045] Figure 3 A third embodiment of the present invention is presented; and

[0046] Figure 4 A double-roll mill which can be used in the apparatus according to the invention is shown by way of example. DETAILED DESCRIPTION

[0047] In the figures, a plant for producing fertilizer granules is shown in different embodiments. The plant has a compactor 1 for producing strips from an inorganic raw material. The compactor is preferably a high-pressure roller press 1, with which the inorganic raw material A is compacted into strips S, i.e. flat material strips, which are discharged from the roller gap of the roller press 1. A crushing device 2 is connected downstream of the roller press 1, by which the strips S discharged from the roller press 1 are pre-crushed into strip fragments P and thus become large-sized and non-uniform block-shaped materials. The crushing device 2 is also called a strip crusher and is equipped with a plurality of crushing elements, such as teeth, which act on the feed material individually or in a small number and crush it.

[0048] In all embodiments, a plurality of double roller mills 3a, 3b, 3c are respectively arranged downstream of the strip crusher 2, so that the bulk material P passes through the plurality of double roller mills in sequence after being discharged from the strip crusher. Figure 1 , Figure 2 and Figure 3 All embodiments shown in .

[0049] The basic structure of the double roller mills 3a, 3b, 3c is as follows: Figure 4 As shown. The double-roll mill 3a, 3b, 3c has two counter-rotating grinding rollers 7, whose roller surfaces are provided with profiles, such as patterns consisting of multiple groove-shaped recesses and protrusions. These groove-shaped recesses and protrusions (not shown) extend over the entire roller width and are oriented, for example, obliquely relative to the roller axis. Each roller 7 can be composed of a rotationally driven roller core and an endless belt mounted on the roller core, which in turn is provided with a profile. Each roller 7 can be equipped with a cooling device, by means of which the roller surface can be cooled. Specific details are in Figure 4 Not shown. But from Figure 4 As can be seen in the figure, the double roller mill is provided with a housing 8, which forms an encapsulation shell. In addition, a feed chute 9 is provided, through which the material is fed, and which can be part of the housing 8 or the encapsulation shell. In contrast to the feeding of a high-pressure roller press, the material is thrown into the roller gap without pressure in the form of a loose material curtain. For this purpose, a Figure 4 The material passes through a vibration trough 5 or a vibration platform not shown in the figure to reach the feed trough above the roll gap and is introduced into the roll gap of the double-roll mill from there.

[0050] According to the present invention, in the above-mentioned device, not only a single double-roll mill is installed as the final comminution device for manufacturing the final product, but a plurality of double-roll mills are arranged accordingly, and the material or at least a part of the material passes through these double-roll mills in sequence during the production process, that is, the strip fragments P discharged from the strip crusher 2 are transported to the successively arranged double-roll mills 3a, 3b or 3c in sequence, and the roll gap widths of the double-roll mills in one device are different in size or adjusted to be different, and preferably gradually decrease from one double-roll mill to the next double-roll mill in the production direction. In addition, according to Figure 1 and Figure 2 In the embodiment, a plurality of grading devices 4a, 4b, 4c are respectively integrated in the device, that is, screening devices in the embodiment. Figure 1 and Figure 2The devices shown are all constructed as circulating compaction granulation devices, that is, the double-roll mills and the classifying devices 4a, 4b, 4c are arranged and connected to each other so that the material circulates through the double-roll mills 3a, 3b, 3c and the screening devices 4a, 4b, 4c in sequence until the finished particles E are discharged from the last double-roll mill 3b or 3c.

[0051] First, based on Figure 1 This is explained using the device as an example.

[0052] The inorganic raw material A enters the high-pressure roller press 1, for example, via a conveying device, such as a bucket elevator 6, where it is compacted into a strip S. The strip S is then broken into strip fragments P in a strip crusher 2. Figure 1 In the embodiment of the invention, two double roller mills 3a, 3b are connected downstream of the strip crusher 2, through which the material passes in succession in the sense of a circulating grinding device. For this purpose, the strip fragments P are conveyed (possibly via a further bucket elevator 10) to a first screening device 4a, which is equipped with a screening plate. The coarse fraction, i.e. the oversize, is conveyed, for example, via a vibrating trough 5 to the first double roller mill 3a, which is set to a first roller gap width. The material discharged from the first double roller mill 3a is circulated again to the first screening device 4a.

[0053] The undersize material discharged from the first screening device 4a, i.e., the finer material, reaches the second screening device 4b, which is designed to be classified into three parts in this embodiment. The oversize material of the second screening device 4b is transported to the second double-roll mill 3b through the second vibrating trough 5, and is circulated back to the first screening device 4a from there. The middle part of the second screening device 4b is discharged as the final product, i.e., the particles E of the required size. The finest raw material F, i.e., the undersize material of the second screening device 4b, is re-sent to the production process, i.e., re-sent to the double-roll press 1 together with the raw material A for compaction.

[0054] Through this Figure 1It can be seen that at least a corresponding portion of the material is sent to the first double-roll mill 3a through the first screening device 4a after the strip crusher 2, and the material crushed in the first double-roll mill is then sent to the second double-roll mill 3b through the first screening device 4a and part of it through the second screening device 4b, so that it passes through the first screening device 4a and the second screening device 4b and is discharged from the second screening device as an intermediate particle size and provided as a final product. Therefore, the two double-roll mills 3a and 3b are arranged successively in the circulation process. However, this does not exclude that a portion of the material coming out of the strip crusher 2, that is, the material that has been formed to be fine enough, passes through the first screening device 4a and is directly transported to the second double-roll mill 3b through the second screening device 4b. Similarly, some of the material is already very fine when it is discharged from the strip crusher 2, so that it has been screened out as the final product E in the second screening device or is sent to the roller press 1 again as a return material F. However, this does not affect the fact that most of the material passes through the two double-roll mills 3a and 3b in sequence in the circulation process. It is important that according to Figure 2 In the embodiment of (the rest is the same as other embodiments), only double roller mills 3a, 3b are arranged after the strip crusher 2 as additional comminution equipment, that is, in the production process, once the strip fragments P exist, no other comminution equipment except the double roller mill is used. In addition, it is advantageous that the roll gap widths of the double roller mills 3a, 3b can be adjusted separately. The roll gap width of the first double roller mill 3a is set larger than the roll gap width of the second double roller mill 3b, because the first double roller mill 3a is used for further pre-comminution, that is, the first double roller mill 3a should be mainly used to process and pre-compress relatively large strip fragments, so that the material discharged from the first double roller mill 3a is still (obviously) larger than the final product. The roll gap width of the second double roller mill 3b is set so that particles of a size corresponding to the final product E are discharged from the double roller mill 3b, that is, the roll gap width is (obviously) set to be smaller than the roll gap width of the first double roller mill 3a. It is important here that the series arrangement of the double-roll mills 3a, 3b and the screening devices 4a, 4b ensures that the material suitable for the subsequent double-roll mill is supplied in a targeted manner, i.e., avoids the feeding of oversized material to the second double-roll mill with a smaller roll gap width. The screening devices 4a, 4b arranged in between can reduce the feed load and adjust the material size, so that the overall size of each double-roll mill 3a, 3b can be designed relatively small. These machines work particularly efficiently because the difference between the feed size and the discharge size and the resulting comminution ratio are small.

[0055] In accordance with Figure 2The same advantages are achieved in the embodiment of , in which three double-roller mills 3a, 3b, 3c are connected in succession, namely the first double-roller mill 3a, the second double-roller mill 3b and the third double-roller mill 3c. Accordingly, a first screening device 4a, a second screening device 4b and a third screening device 4c are also provided. The material passes through the screening devices 4a, 4b, 4c and the double-roller mills 3a, 3b, 3c in the manner described. The final product is discharged from the third screening device 4c as an intermediate part, i.e. as an intermediate particle size. By means of this design with three double-roller mills, the respective roll gap widths of the respective mills can be more accurately matched to the material to be processed, so that the respective double-roller mills only process material sizes that are suitable for the efficient operation of the respective double-roller mills 3a, 3b, 3c. By means of the screening devices 4a, 4b, 4c arranged in the middle, the feed load is also reduced here and the feed size is well adjusted, so that relatively small machines can be used.

[0056] Figure 3 A variant embodiment of the present invention is shown. In this device, a plurality of double roller mills 3a, 3b, 3c are also arranged in series, that is, three double roller mills in this embodiment. However, in this simplified embodiment, the intermediate screening device is omitted. The material enters the first double roller mill 3a from the strip crusher 2, from there into the second double roller mill 3b, and finally into the third double roller mill 3c, thereby realizing the series connection of three double roller mills arranged in series. The roll gap width is graded in such a way that only materials smaller than the required maximum particle size, for example, materials not larger than 4 mm, are discharged from the third double roller mill 3c. Since it is inevitable that extremely fine materials that cannot be used as particles are also discharged from the third double roller mill, in this embodiment, a screening device 4a is also connected downstream of the series structure of multiple double roller mills, so that only the overscreen is used as particles, that is, the final product E, and the extremely fine materials passing through the screening device 4a are returned to the process together with the raw material A, that is, to the roller press 1. In this embodiment, only double-roller mills 3 a , 3 b , 3 c are provided downstream of the strip crusher 2 as comminution devices.

[0057] Figure 3 The characteristic of the mill is that the structure is particularly simple, because the screening device between the crushing equipment is omitted. Figure 3 Compared to the embodiment shown, Figure 1 and Figure 2 The embodiment shown has the above advantages, namely, the feed load of each double-roll mill is reduced, and the material delivered to each double-roll mill can be well matched to the corresponding roll gap width, so that the machine can operate efficiently and normally, and the size can be designed to be correspondingly small.

[0058] As mentioned earlier, Figure 1 An embodiment with two double-roller mills 3a, 3b connected in series is shown, Figure 2 and Figure 3 An embodiment with three double-roller mills 3a, 3b, 3c arranged in series is shown. The invention also includes embodiments with four or more double-roller mills arranged in series. In this case, it is also appropriate to increase the number of screening devices accordingly. Figure 2 This is shown in a simplified schematic diagram by the symbols above the third double-roller mill 3c and the third screening device 4c, since further double-roller mills or screening devices can be selectively integrated at the marked positions to achieve an embodiment with more than three double-roller mills. Figure 3 Likewise, the symbol below the third double-roll mill 3c shows the possibility of selectively integrating, for example, a fourth double-roll mill or more double-roll mills.

Claims

1. An apparatus for producing fertilizer granules, the apparatus comprising: - a compactor (1) for producing strips (S) from inorganic raw materials (A); - a crushing device (2) for pre-crushing the strip (S) into strip fragments (P); - at least two double-roller mills (3a, 3b, 3c) arranged one behind the other in the production direction, The double-roller mills (3a, 3b, 3c) each have two rotatably driven grinding rollers (7), the roller surfaces of the grinding rollers are provided with a forming portion, and a roller gap having a roller gap width is formed between the grinding rollers. The strip fragments (P) can be sequentially conveyed to the double roller mills (3a, 3b, 3c) arranged in sequence to be crushed into particles (E), and The roll gap widths of the double-roll mills (3a, 3b, 3c) are different in size or are adjusted to be different and decrease gradually from one double-roll mill to the next in the production direction.

2. The apparatus according to claim 1, comprising at least one first double-roll mill (3a) located downstream of the crushing device (2) and a second double-roll mill (3b) located downstream of the first double-roll mill (3a), wherein: The roll gap width of the second double-roll mill (3b) is smaller in size or is adjusted to be smaller than the roll gap width of the first double-roll mill (3a).

3. The device according to claim 2, characterized in that A third double-roll mill (3c) is arranged downstream of the second double-roll mill (3b), and the roll gap width of the third double-roll mill is smaller in size or is adjusted to be smaller than the roll gap width of the second double-roll mill (3b).

4. The device according to claim 3, characterized in that A fourth double-roller mill and optionally further double-roller mills are arranged downstream of the third double-roller mill ( 3 c ), the roll gap width of the fourth double-roller mill being smaller in size or being adjusted to be smaller than the roll gap width of the third double-roller mill, and so on.

5. The device according to any one of claims 1 to 4, characterized in that At least one classification device (4a, 4b, 4c), for example a screening device, is respectively arranged between the crushing device (2) and a double-roller mill located downstream of the crushing device, for example the first double-roller mill (3a), and / or between two double-roller mills arranged in succession, for example between the first double-roller mill (3a) and the second double-roller mill (3b), and / or between the second double-roller mill (3b) and the third double-roller mill (3c).

6. The device according to any one of claims 1 to 5, wherein the device is implemented as a circulating compaction granulation device, in which the double-roll mill (3a, 3b, 3c) and one or more classification devices (4a, 4b, 4c) are arranged so that the strip fragments (P) at least partially circulate through the double-roll mill (3a, 3b, 3c) and the screening device (4a, 4b, 4c) in sequence.

7. The device according to any one of claims 1 to 6, characterized in that The surface of the grinding rollers (7) of the double-roll mill (3a, 3b, 3c) has a texture formed by a plurality of groove-shaped depressions and elevations, which extend over the roller width and are oriented on one or both rollers, for example parallel to the roller axis or obliquely or in a spiral or arc shape.

8. The device according to any one of claims 1 to 7, characterized in that The roll gap of each of the double-roll mills ( 3 a , 3 b , 3 c ) is respectively sized or adjusted to a roll gap width in the range of 0.5 mm to 30 mm.

9. The device according to claim 8, characterized in that For an apparatus having two double-roller mills (3a, 3b), the roll gap width of the first double-roller mill (3a) is adjusted or sized to be 10 mm to 30 mm, and the roll gap width of the second double-roller mill (3b) is adjusted or sized to be 0.5 mm to 7 mm; or for an apparatus having three double-roller mills, the roll gap width of the first double-roller mill (3a) is sized or adjusted to be 10 mm to 30 mm, the roll gap width of the second double-roller mill (3b) is sized or adjusted to be 5 mm to 15 mm, and the roll gap width of the third double-roller mill (3c) is sized or adjusted to be 0.5 mm to 5 mm.

10. The device according to any one of claims 1 to 9, characterized in that The grinding rollers (7) of each of the double-roll mills (3a, 3b, 3c) or the grinding rollers of at least one double-roll mill are respectively equipped with a cooling device for cooling the roller surface.

11. A method for producing fertilizer granules from an inorganic raw material (A) using the apparatus according to any one of claims 1 to 10, wherein: The raw material (A) is compacted into strips (S) in a compactor (1), The strip (S) is pre-crushed into strip fragments (P) in a crushing device (2), and The strip fragments (P) are comminuted into particles (E) in at least two consecutively arranged double-roll mills (3a, 3b, 3c), The roll gap widths of the consecutively arranged double-roller mills (3a, 3b, 3c) are sized differently or adjusted differently, and the roll gap width decreases gradually from one double-roller mill to the next.

12. The method according to claim 11, characterized in that The strand fragments (P) are comminuted only in a plurality of double-roll mills (3a, 3b, 3c) without the need for further upstream or downstream comminution equipment.

13. The method according to claim 11 or 12, characterized in that: Between the crushing device and a double roller mill (3a) downstream of the crushing device (2), and / or between two consecutively arranged double roller mills (3a, 3b, 3c), the strand fragments are classified, for example using one or more screening devices (4a, 4b, 4c).

14. The method according to claim 13, characterized in that The material is circulated, preferably by feeding the material discharged from a double-roll mill (3a, 3b, 3c) into a screening device (4a, 4b, 4c).

15. The method according to any one of claims 11 to 14, characterized in that The surface of the grinding roller (7) is cooled during operation.

16. The method according to any one of claims 11 to 15, characterized in that The grinding roller ( 7 ) rotates at a peripheral speed or at a plurality of peripheral speeds of at least 5 m / s, for example 5 to 30 m / s, for example 5 to 25 m / s, preferably 6 to 20 m / s.

17. The method according to any one of claims 11 to 16, characterized in that The grinding roller (7) has a diameter of 200 to 1000 mm, preferably 400 to 800 mm, for example 500 to 700 mm, and / or rotates at a speed of 100 to 3000 rpm, preferably 120 to 1000 rpm, for example 150 to 800 rpm.

18. The method according to any one of claims 11 to 17, characterized in that The roll gap width of the roll gap is adjusted to 0.5 mm to 30 mm. Preferably, for an apparatus having two double-roll mills (3a, 3b), the roll gap width of the first double-roll mill (3a) is adjusted to 10 mm to 30 mm, and the roll gap width of the second double-roll mill (3b) is adjusted to 0.5 mm to 7 mm; or for an apparatus having three double-roll mills, the roll gap width of the first double-roll mill (3a) is adjusted to 10 mm to 30 mm, the roll gap width of the second double-roll mill (3b) is adjusted to 5 mm to 15 mm, and the roll gap width of the third double-roll mill (3c) is adjusted to 0.5 mm to 5 mm.

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