Method for energy-optimised granulation of urea-containing particles and fluidised-bed granulator system

Abstract

The invention relates to a method for energy-optimised granulation of urea-containing particles in a fluidised-bed granulator system (1). In a method in which the energy required for cooling the urea-containing particles is minimised, wherein the method and the operation of the fluidised-bed granulator system (1) are optimised in terms of process technology, the urea-containing particles are, after granulation, cooled in a cooling zone (2) of a fluidised-bed granulator (3) to a temperature in a range between 80°C and 108°C and at least some of the urea-containing particles are, after pre-screening, cooled by means of a bulk flow cooler (4) to a temperature in a range between 30°C and 50°C.

Description

[0001] Description

[0002] Process for energy-optimized granulation of urea-containing particles and flow bed granulation system

[0003] The invention relates to a process for energy-optimized granulation of urea-containing particles in a fluidized bed granulator system.

[0004] The invention also relates to a fluidized bed granulator system for energy-optimized granulation of urea-containing particles.

[0005] Due to the continuous growth of the world's population, there is a constant need for reliable, easily produced, and inexpensive fertilizers. These conventional fertilizers can contain nitrogen, phosphate, sulfur, calcium, selenium, potassium, or micronutrients. A common, widely used fertilizer contains urea as its main component. Urea is water-soluble and rapidly degrades in the soil, producing ammonia and nitrate compounds. Depending on the application, the fertilizer may contain only urea or a combination of urea with one or more of the aforementioned components, e.g., phosphate, sulfur, potassium, or micronutrients.

[0006] Urea can be produced on a large industrial scale by reacting ammonia with carbon dioxide in a (simplified) two-step reaction:

[0007] H2N-COONH4 (NH2)2CO + H2O (2)

[0008] After synthesis, further process steps are required to obtain a transportable and storable urea fertilizer. Common technical processes include various granulation techniques such as prilling, drum granulation, or fluidized-bed granulation. Prilling processes, in particular, have some critical disadvantages, such as relatively soft particles and sometimes deformed, inhomogeneous particles. These problems can be avoided by using a fluidized-bed granulation process, which leads to harder, more stable, and more homogeneous granules. The resulting granulated urea is particularly suitable for bulk blending. In addition, there is less segregation or mechanical damage during mixing and transport of the urea-based fertilizer. The size, size distribution, geometry, and mechanical properties of the final product depend to a large extent on the temperature during the granulation process.Therefore, a controlled temperature environment is essential to achieve reproducible product granules with constant product properties, e.g. in terms of hardness, caking or dust formation.

[0009] Fluid bed granulator systems rely largely on ambient air for cooling. Therefore, the capacity of a fluid bed granulator can be limited, depending on the ambient air temperature or the amount of heat that the ambient air can dissipate. This can lead to high temperatures within the system, reducing the amount of product that can be produced or leading to a reduction in product quality and deterioration of operating conditions. Furthermore, under certain operating conditions (e.g., very high product loads), the granulation temperature can become too high. This is especially true when the system is operating at high capacity or in a high ambient temperature, or both. In addition, many systems are already equipped with a fluid bed cooler to reduce the granule temperature from approximately 95°C to 60-70°C.This requires a large amount of ambient air and can be difficult even under the operating conditions mentioned above.

[0010] Cooling the urea-containing particles requires a high energy input to provide the cooling air. Furthermore, it is important to cool the urea-containing particles at favorable times to ensure the process is as efficient as possible.

[0011] The invention is therefore based on the object of specifying a method for energy-optimized granulation of urea-containing particles and a fluidized-bed granulator system in which the energy required to cool the urea-containing particles is minimized, wherein the method and operation of the fluidized-bed granulator system are optimized in terms of process technology. This object is achieved in the present invention by the features of the characterizing part of patent claim 1, firstly in that the urea-containing particles are cooled after granulation in a cooling zone of a fluidized-bed granulator to a temperature in a range between 80 °C and 108 °C, and in that at least some of the urea-containing particles, after pre-screening, are cooled in a second step by means of a bulk-flow cooler to a temperature in a range between 30 °C and 50 °C.

[0012] The cooling zone can be a fluidized-bed cooler that uses a fan to cool the urea-containing particles. To save investment costs, the fluidized-bed cooler is located within the fluidized-bed granulator. Since the energy required to compress the cooling air is comparatively high, the invention provides for the urea-containing particles to be cooled in the cooling zone to a temperature between 80 °C and 108 °C. The urea-containing particles leave the fluidized-bed granulator, or a granulation zone within the fluidized-bed granulator, at a temperature above 100 °C. The cooling capacity in the cooling zone is therefore energy-efficient compared to the cooling in the second step.

[0013] A bulk flow cooler is a heat exchanger in which the product to be cooled flows relatively gently between welded heat exchanger plates according to the "first in, first out" principle. Cooling water flows at a suitable temperature on the other side of the plates. This indirect method of heat transfer minimizes the need for fans, bag filters, or scrubbers. This provides a cost-effective solution for cooling, but also for heating, bulk materials. Furthermore, the cooling process itself is emission-free.

[0014] With the help of the bulk flow cooler, the urea-containing particles, or a portion of the urea-containing particles—that is, the portion that is fed into the bulk flow cooler after pre-screening—are cooled to a temperature between 30°C and 50°C. The bulk flow cooler therefore assumes the majority of the cooling capacity, whereas the cooling capacity required by the cooling zone in the fluidized bed granulator is low relative to the cooling capacity of the bulk flow cooler. Cooling using a bulk flow cooler with appropriate cooling water is more energy-efficient than cooling in the fluidized bed using compressed air, thus minimizing the overall energy requirements of the fluidized bed granulator system.

[0015] Cooling water is generally available in sufficient quantities at a suitable temperature level (flow / return, for example, 30 / 40 °C) particularly in urea plants and is specifically significantly cheaper than the electrical energy that would otherwise be needed to compress the cooling air.

[0016] Further preferred embodiments of the invention emerge from the remaining features mentioned in the subclaims.

[0017] In a first embodiment of the invention, a two-stage pre-screening process is provided, whereby urea-containing particles with a grain size of > 10 mm are separated first, followed by urea-containing particles with a grain size of > 4 mm. The product leaves the fluidized-bed granulator with a relatively broad grain size range of approximately 0.5 to 10 mm and above. Therefore, it may be advantageous to provide a two-stage pre-screening process, in which the larger particles are separated first, followed by the separation of the so-called coarse material, i.e., particles with a grain size of > 4 mm but < 10 mm.

[0018] In addition, in a further embodiment of the method according to the invention, it can be provided that the urea-containing particles with a grain size of > 4 mm and < 10 mm are cooled and comminuted after separation, and that the cooled and comminuted urea-containing particles are subsequently fed into the fluidized-bed granulator. The coarser fraction, i.e., the oversize material, is present in only a small proportion of the product. The requirements for the sieve used to separate the oversize material, i.e., the urea-containing particles > 4 mm and < 10 mm, are comparatively low, since the majority of the particles with a smaller grain size fall through. The amount of urea attrition or clogging during operation is therefore low.

[0019] After comminution, the urea-containing particles can be returned to the fluidized bed granulator, for example by means of a bucket elevator, so that the crushed urea-containing particles can be further granulated.

[0020] In a particularly advantageous embodiment of the method according to the invention, the urea-containing particles with a grain size of > 4 mm and < 10 mm are fed into the fluidized-bed granulator by means of pneumatic conveying. The advantage of pneumatic conveying or a pneumatic conveying system for conveying the particles back into the fluidized-bed granulator is that no bucket elevator, which is common in the prior art, is required. In this way, the building height can be kept low and only needs to correspond to the height of the bulk flow cooler. For dense-phase conveying, a pressure of approximately 1 to 2 bar and approximately 100 °C in an amount of only < 1% of the fluidizing air of the fluidized-bed granulator is required.

[0021] To simplify further processing of the urea-containing particles with a grain size of > 4 mm and < 10 mm, a further embodiment of the method according to the invention provides for cooling the separated particles to approximately 65 °C. A temperature of "approximately 65 °C" can, for example, be a temperature of 50 °C to 80 °C, in particular also a temperature of 60 °C to 70 °C. During further processing or comminution of the coarse material, it is advantageous for the particles to be cooled beforehand to avoid urea abrasion and clogging.

[0022] For this purpose, a further advantageous embodiment of the invention can provide for the separated particles to be crushed using a roller crusher. A temperature of 65°C for the urea-containing particles is optimal for the roller crusher.

[0023] Optionally, in a further embodiment of the method according to the invention, it can be provided that, after the pre-screening, the urea-containing particles with a grain size of < 4 mm are dedusted. The dedusting can be carried out using any suitable method known from the prior art.

[0024] A practical variant for conveying the particles in a further embodiment of the process involves transporting the urea-containing particles with a grain size of < 4 mm into the bulk flow cooler using a bucket elevator. For urea-containing particles < 4 mm, after pre-screening, both the on-size product (2 to 4 mm) and the fines still to be separated (< 2 mm) are present. The bucket elevator can transport the urea-containing particles to the bulk flow cooler, through which they pass from top to bottom with the aid of gravity. This bucket elevator does not need to be as high as is usual in classic, state-of-the-art concepts because the screening and return of the fines can be arranged at a lower level in the building of the fluid bed granulation system. In this way, the construction costs for the steel structure of the building can be minimized.

[0025] To achieve a desired grain size, a further embodiment of the method according to the invention provides that, after cooling the urea-containing particles to a temperature in a range between 30 °C and 50 °C, urea-containing particles with a grain size of < 2 mm are separated. A corresponding fine sieve, which is arranged downstream of the bulk flow cooler in terms of flow, then operates in a temperature range of 30 to 50 °C and is thus optimally protected against urea abrasion or clogging because the urea-containing particles have already cooled and hardened.

[0026] In a particularly advantageous embodiment of the process according to the invention, the separated particles with a grain size of < 2 mm are fed into the fluidized-bed granulator. The discharge of the fines is below the level of the fluidized-bed granulator. One possible way to convey the fines is therefore to use a bucket elevator.

[0027] In a further preferred embodiment of the invention, the separated particles with a grain size of < 2 mm can be conveyed into the fluidized-bed granulator by means of pneumatic conveying. Similar to the coarse material, pneumatic conveying or a pneumatic conveying system for conveying the particles back into the fluidized-bed granulator has the advantage that no bucket elevator, as is common in the prior art, is required. This allows the building height to be kept low and only needs to correspond to the height of the bulk flow cooler.

[0028] For dense-phase conveying, a conveying air flow of approximately 1 to 2 bar and approximately 100 °C is required, with a quantity of only < 1% of the fluidizing air required for the fluidized-bed granulator. Furthermore, the energy balance of the fluidized-bed granulator can be positively influenced because the cooled fines, i.e., the urea-containing particles < 2 mm, can be fed into various chambers of the fluidized-bed granulator at a temperature of slightly more than 45 °C.

[0029] The above object is also achieved by a fluidized bed granulator system for energy-optimized granulation of urea-containing particles, comprising the following elements in operative connection: a) a fluidized bed granulator for granulating urea-containing particles, b) a cooling zone arranged in the fluidized bed granulator for cooling urea-containing particles with air to a temperature in a range between 80 °C and 108 °C, c) a pre-screening device for separating out urea-containing particles which are too large after granulation, preferably with a grain size of > 4 mm, d) a cooling device for cooling the urea-containing particles to a temperature in a range between 30 °C and 50 °C, the cooling device comprising at least one bulk flow cooler, e) a screening device for separating out urea-containing particles which are too small, preferably with a grain size of < 2 mm.

[0030] In this case, the fluidized bed granulator system can in particular comprise the fluidized bed granulator, which is configured and adapted for granulating urea-containing particles and has a cooling zone arranged in the fluidized bed granulator, which is configured and adapted for cooling urea-containing particles with air to a temperature in a range between 80 °C and 108 °C. The fluidized bed granulator system can further comprise the pre-screening device, which is configured and adapted for separating excessively large urea-containing particles after granulation, preferably for separating urea-containing particles with a grain size > 4 mm, as well as the cooling device, which is configured and adapted for cooling the urea-containing particles to a temperature in a range between 30 °C and 50 °C and which comprises at least one bulk flow cooler.Finally, the fluidized bed granulator system can comprise the screening device which is configured and adapted to separate urea-containing particles which are too small, preferably to separate urea-containing particles with a grain size of < 2 mm, wherein the screening device is arranged fluidically downstream of the bulk flow cooler 4.

[0031] In a first embodiment of the fluidized bed granulator system according to the invention, it is provided that the pre-screening device has at least two screens, wherein urea-containing particles with a grain size > 10 mm can be separated with a first screen and wherein urea-containing particles with a grain size > 10 mm and < 4 mm can be separated with a second screen.

[0032] In a further advantageous embodiment of the fluidized bed granulator system according to the invention, a pneumatic conveying device is provided, wherein separated urea-containing particles with a grain size of > 10 mm and < 4 mm can be conveyed into the fluidized bed granulator by means of the pneumatic conveying device and / or wherein separated urea-containing particles with a grain size of < 2 mm can be conveyed into the fluidized bed granulator by means of the pneumatic conveying device.

[0033] In a further embodiment of the fluidized-bed granulator system according to the invention, it is provided that the fluidized-bed granulator system is designed and configured to carry out a method according to the invention. The above statements regarding the method according to the invention also apply accordingly to the fluidized-bed granulator system according to the invention.

[0034] The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless otherwise stated in the individual case.

[0035] The invention is explained below in exemplary embodiments with reference to the accompanying drawings. They show:

[0036] Figure 1 is a schematic representation of an investment cost-optimized

[0037] State-of-the-art fluid bed granulator system,

[0038] Figure 2 is a schematic representation of a fluid bed granulator system according to a

[0039] Embodiment of a fluid bed granulator system according to the invention and

[0040] Figure 3 shows a schematic design of a fluid bed granulator system according to a particularly preferred embodiment.

[0041] Figure 1 shows an exemplary schematic representation of a fluidized-bed granulation system 1 according to the prior art. The fluidized-bed granulation system 1 comprises a fluidized-bed granulator 3 and a cooling zone 2 arranged in the fluidized-bed granulator 3 or connected to the fluidized-bed granulator 3. The term "connected" within the meaning of the invention generally refers to connecting means capable of / suitable for transporting or transferring process liquids, solids, or gases and / or mixtures thereof, e.g., pipes, channels, pumps, hoses, and further includes tanks, containers, and / or pumps. This definition includes connecting means suitable for gaseous, solid, and liquid media at low pressure (below 1 bar) and for gaseous, solid, and liquid media at high pressure (over 1 bar, preferably up to 10 bar).

[0042] In the cooling zone, the particles are cooled to a temperature range of < 70 °C and then fed into a screening device 9, which is connected to the cooling zone 2. The screening device 9 separates the granular particles from the fluidized-bed granulator 3 into product particles of the desired size, as well as oversized (above the desired product size) particles and undersized (below the desired product size) particles. Additionally, a pre-screening device 7 is provided to separate particles whose grain size is significantly larger than the grain size of the oversized particles. These "lumps" are removed from the process and fed into a collecting container 10. The remaining urea-containing particles are fed into the screening device 9 by means of a bucket elevator 6.

[0043] The structure of the screening device 9 comprises a first screen 11 with a mesh size above the desired particle size and a second screen 12 below the desired particle size, thereby dividing the screening device 9 into three parts. The screening device 9 also comprises an outlet for the final product particles 13 between the first screen 11 and the second screen 12, an outlet for oversized particles 14, e.g., above the first screen 11, and an outlet for undersized particles 15 below the second screen 12. The outlet for the undersized particles 15 is connected to the fluidized bed granulator 1 via a first recirculation inlet 16, and the outlet for the oversized particles 14 is connected to the fluidized bed granulator 1 via a roll crusher 5 or a similar device, thereby producing crushed particles.

[0044] The final product particles are passed from the screening device 9 into a cooler 17 for final curing and cooling. The final product (not shown here) can then be packaged or otherwise processed.

[0045] Figure 2 shows a schematic representation of a fluidized bed granulator system 1 according to an embodiment of a fluidized bed granulator system 1 according to the invention. In comparison to the prior art, the cooling zone 2 within the fluidized bed granulator 3 is kept as small as possible, so that the urea-containing particles leave the fluidized bed granulator 3 or the cooling zone 2 at a temperature in a range between 80 °C and 108 °C. Furthermore, a pre-screening device 7 is provided to separate particles whose grain size is far larger than the grain size of the oversized particles. These "lumps" are removed from the process and fed into a collecting container 10. The remaining urea-containing particles are fed into the screening device 9 by means of a bucket elevator 6. The pre-screening device 7 additionally comprises a first screen 11, which separates the oversized particles from the product particles and the undersized particles.

[0046] The oversized particles, which are generated in a small quantity compared to the remaining urea-containing particles, are then passed through a recirculation cooler 18 before being crushed in a roller crusher 5 and returned to the fluidized-bed granulator 3 by means of a pneumatic conveying device 19. During further processing or comminution of the coarse material, it is advantageous for the particles to be cooled beforehand to avoid urea abrasion and clogging.

[0047] In addition, in this embodiment, a dedusting unit 20 is provided, by which the flow of undersized particles and product particles can be dedusted after pre-screening.

[0048] The undersized particles and the product particles are fed into a cooling device 8 after the pre-screening device 7, wherein the cooling device 8 comprises a bulk flow cooler 4. In the bulk flow cooler 4, the undersized particles and the product particles are cooled to a temperature in a range between 30 and 50 °C. The pneumatic conveying device 19 for conveying the particles back into the fluidized bed granulator 3 has the advantage that no bucket elevator, as is common in the prior art, is required. This allows the building height to be kept low and only needs to correspond to the height of the bulk flow cooler 4.

[0049] With the help of the bulk flow cooler 4, the urea-containing particles, or a portion of the urea-containing particles—that is, the portion that is still fed into the bulk flow cooler 4 after pre-screening—are cooled to a temperature between 30°C and 50°C. The bulk flow cooler 4 therefore assumes the majority of the cooling capacity, whereas the cooling capacity required by cooling zone 2 is low relative to the cooling capacity of the bulk flow cooler 4. Cooling using the bulk flow cooler 4 with appropriate cooling water is more energy-efficient than cooling in the fluidized bed using compressed air, thereby minimizing the overall energy requirements of the fluidized bed granulator system 1.

[0050] The cooled urea-containing particles are then conveyed to a screening device 9, where the undersized particles are separated from the final product particles. The undersized, cooled particles can also be fed back into the fluidized bed granulator 3 via the pneumatic conveying device 19. The final product particles are conveyed to corresponding devices (not shown here) for further processing. A corresponding fine screen, which is arranged downstream of the bulk flow cooler 4 in terms of flow technology, then operates in a temperature range of 30 to 50 °C and is thus optimally protected against urea abrasion or clogging because the urea-containing particles have already cooled and hardened. Figure 3 shows a further embodiment of a fluidized bed granulator system 1. In contrast to Figure 2, the embodiment according to Figure 3 only provides a single-stage pre-screening.The coarse material is screened in the screening device 9 after cooling in the bulk flow cooler and then returned to the recirculation cooler. In this embodiment, the screening device 9 comprises two screens.

[0051] List of reference symbols

[0052] FI ie ß bedgra nu I atorsy stem

[0053] Cooling zone

[0054] Fluid bed granulator

[0055] Bulkflow cooler

[0056] roller crusher

[0057] bucket elevator

[0058] Pre-screening device

[0059] Cooling device

[0060] Screening device

[0061] Collection container

[0062] First sieve

[0063] Second sieve

[0064] Output for final product particles

[0065] Outlet for oversized particles

[0066] Exit for undersized particles

[0067] Return inlet

[0068] cooler

[0069] Recirculation cooler

[0070] Pneumatic conveying system

[0071] Dust extraction unit

Claims

Patent claims 1. A process for energy-optimized granulation of urea-containing particles in a fluidized bed granulator system (1), characterized in that the urea-containing particles are cooled after granulation in a cooling zone (2) of a fluidized bed granulator (3) to a temperature in a range between 80 °C and 108 °C, and in that at least some of the urea-containing particles are cooled after pre-screening by means of a bulk flow cooler (4) to a temperature in a range between 30 °C and 50 °C.

2. Method according to claim 1, characterized in that a two-stage pre-screening is provided, whereby firstly urea-containing particles with a grain size > 10 mm are separated and then urea-containing particles with a grain size > 4 mm.

3. Process according to claim 2, characterized in that the urea-containing particles with a grain size of > 4 mm and < 10 mm are cooled and comminuted after separation and that the cooled and comminuted urea-containing particles are subsequently fed into the fluidized bed granulator (3).

4. The method according to claim 3, characterized in that the urea-containing particles with a grain size > 4 mm and < 10 mm are fed into the fluidized bed granulator (3) after comminution by means of pneumatic conveying.

5. A process according to claim 3 or 4, characterized in that the separated particles are cooled to approximately 65 °C.

6. Method according to one of claims 3 to 5, characterized in that the separated particles are crushed by means of a roller crusher (5).

7. Method according to one of claims 1 to 6, characterized in that after the pre-screening, dedusting of the urea-containing particles with a grain size < 4 mm is carried out.

8. Method according to one of claims 1 to 7, characterized in that the urea-containing particles with a grain size < 4 mm are transported into the bulk flow cooler by means of a bucket elevator (6).

9. Method according to one of claims 1 to 8, characterized in that after cooling the urea-containing particles to a temperature in a range between 30 °C and 50 °C, urea-containing particles with a grain size of < 2 mm are separated.

10. The method according to claim 9, characterized in that the separated particles with a grain size < 2 mm are fed into the fluidized bed granulator (3).

11. The method according to claim 9, characterized in that the separated particles with a grain size < 2 mm are fed into the fluidized bed granulator (3) by means of pneumatic conveying.

12. Fluidized bed granulator system (1) for energy-optimized granulation of urea-containing particles, comprising the following elements in operative connection: a) a fluidized bed granulator (3) for granulating urea-containing particles, b) a cooling zone (2) arranged in the fluidized bed granulator (3) for cooling urea-containing particles with air to a temperature in a range between 80 °C and 108 °C, c) a pre-screening device (7) for separating urea-containing particles that are too large after granulation, preferably with a grain size > 4 mm, d) a cooling device (8) for cooling the urea-containing particles to a temperature in a range between 30 °C and 50 °C, wherein the cooling device comprises at least one bulk flow cooler (4), e) a screening device (9) for separating urea-containing particles that are too small, preferably with a grain size < 2 mm.

13. Fluid bed granulator system (1) according to claim 12, characterized in that the pre-screening device (7) has at least two screens, wherein urea-containing particles with a grain size > 10 mm can be separated with a first screen (11) and urea-containing particles with a grain size < 10 mm and > 4 mm can be separated with a second screen (12).

14. Fluidized bed granulator system (1) according to claim 12 or 13, characterized in that a pneumatic conveying device (19) is provided, wherein separated urea-containing particles with a grain size of < 10 mm and > 4 mm can be conveyed into the fluidized bed granulator (3) by means of the pneumatic conveying device (19) and / or wherein separated urea-containing particles with a grain size of < 2 mm can be conveyed into the fluidized bed granulator (3) by means of the pneumatic conveying device (12).

15. Fluidized bed granulator system (1) according to one of claims 12 to 14, characterized in that the fluidized bed granulator system (1) is designed and configured to carry out a method according to one of claims 1 to 11.

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