Low-energy consumption and low-emission fluidized bed urea granulation system

Abstract

A low-energy consumption and low-emission fluidized bed urea granulation system, comprising: an ammonia recovery tower (P), a fluidized bed granulator (A), a first screening machine (B), a second screening machine (F), a cooler (C), a first bucket elevator (E), a second bucket elevator (D), a combined dust collector (J) and a melting tank (L).

Description

A low-energy, low-emission fluidized bed urea granulation system Technical Field

[0001] This invention belongs to the field of chemical equipment, and specifically relates to an apparatus for preparing granular urea from urea solution. Background Technology

[0002] Urea is the nitrogen fertilizer with the highest nitrogen content, and the global annual production of urea exceeds 200 million tons. For ease of use, storage, and transportation, the vast majority of urea products are in granular form. Various methods for producing granules are well-known, generally falling into two main categories: granulation tower methods and mechanical granulation methods. Mechanical granulation methods can be further divided into fluidized bed granulation and rotary drum granulation.

[0003] Granulation tower granulation involves dropping molten urea with a moisture content below 0.4% (wt) from a granulation nozzle (rotary or vibrating) at the top of a granulation tower as small droplets. These droplets come into counter-current contact with rising air from the bottom of the tower. The urea droplets undergo a cooling-solidification-cooling process to produce granulated urea. Air enters from the bottom of the tower and its temperature rises during the urea cooling process. No additional power is required; the air rises naturally, and power consumption is negligible. Urea granules prepared by this method are generally between 0.5 and 3.5 mm in size and have low mechanical strength, making them prone to crushing during transport and caking during long-term storage. Urea products granulated by granulation towers are not suitable for long-term storage, transportation, or mechanized fertilization operations.

[0004] Mechanical granulation involves spraying high-concentration urine onto seed urea crystals to gradually increase particle size. Anti-caking agents are added during the granulation process to improve particle size and strength. Mechanically granulated urea produces large, high-strength particles suitable for long-term storage and long-distance transport. Drum granulation, limited by drum size, generally has a small production capacity, requiring multiple lines for large-scale production. Currently, the mainstream mechanical granulation process for large-scale production worldwide is fluidized bed granulation. In a fluidized bed granulator, seed crystals exist in a fluidized state under the influence of fluidizing air. Urine with a concentration of 95% (wt) or higher is sprayed through nozzles as fine droplets onto the seed crystal surface, followed by drying, solidification, and cooling to produce large-particle urea. Fluidized bed granulation produces granulated urea with larger particle sizes (2-8 mm) and higher mechanical strength than that produced by granulation tower methods, as disclosed in US 4,219,589, US 3,067,177, US 3,112,343, EP0289074A1, JP-B-4-63729, and JP-B-50-34536. It is well known that regardless of the fluidized bed granulation process, additives are added to the urea solution to improve the mechanical strength and anti-caking properties of the large-particle urea product and increase granulation efficiency. This means that dust generation during granulation can be reduced. These additives are generally formaldehyde aqueous solutions or reactants of urea and formaldehyde (trade names such as UF85).

[0005] The main process of fluidized bed granulation can be divided into several steps: granulation, cooling, screening, crushing (for seed crystal preparation), final product cooling, and dust-laden gas treatment. Fluidized bed granulators and fluidized bed coolers can be installed separately or combined in one unit. Whether separate or combined, fluidized air is required to establish the fluidized bed and cool the granulated urea, typically to 70-90°C. This requires a large amount of compressed air, usually supplied by a blower. The amount of compressed air depends on the granulated urea production capacity and the temperature to which the granulated urea is cooled. Throughout the granulation process, the equipment for granulation, cooling, screening, and dust recovery needs to operate under negative pressure, requiring an induced draft fan to maintain the necessary negative pressure. Because the fluidized bed granulation process requires a very large amount of air, the blowers and induced draft fans have very high power consumption. During the fluidized bed granulation process, a certain amount of dust will inevitably be generated because granulation and cooling are carried out in a fluidized state. Even with the addition of additives, the amount of dust generated during the production process accounts for about 5% (wt) of the finished urea product. Such a large amount of dust must be recycled.

[0006] The urea solution used in fluidized bed granulation originates from an upstream molten urea unit. This urea solution contains a certain amount of free ammonia (partly from free ammonia dissolved during urea concentration and partly from free ammonia generated during biuret formation during pipeline transport). Before leaving the nozzle, the free ammonia content in the urea solution is approximately 500–1200 ppm (wt). This free ammonia is released during granulation and enters the dust-laden exhaust gas of the granulator. Ammonia released into the atmosphere is a pollutant, and the ammonia in the granulation exhaust gas must be controlled before being released into the atmosphere. Currently, the World Bank's atmospheric emission standards stipulate that the ammonia concentration in the exhaust gas should not exceed 50 mg / Nm3, while the EU standard is no higher than 20 mg / Nm3.

[0007] Currently, all commercially operational fluidized bed granulation processes worldwide employ wet scrubbing. First, water is used to wash away dust from the exhaust gas, which is then recovered as a diluted solution. Next, acid is used to neutralize and wash away ammonia from the exhaust gas, forming ammonium salts as a byproduct, as disclosed in US2015 / 0133689 A1 and US10,829,44. The acid used for acid washing can be sulfuric acid, nitric acid, phosphoric acid, etc., with sulfuric acid and nitric acid being preferred.

[0008] The wet exhaust gas dust removal and ammonia removal technology used in fluidized bed granulation has obvious drawbacks. One drawback is that the dust content in the exhaust gas after wet exhaust gas treatment is about 20 mg / Nm³. 3 The ammonia content is approximately 30 mg / Nm³. 3 This method fails to achieve ultra-low emissions. Especially during winter operation (particularly in cold northern regions), the exhaust gas contains nearly saturated water, which condenses upon entering the atmosphere, forming droplets or snowflakes that fall onto the ground, equipment surfaces, and factory roofs. These liquids or snowflakes contain urea and ammonium salts, corroding the surfaces, equipment, and roofs. Over time, the accumulated urea and ammonium salts can enter the water system with rainwater or snowmelt, causing environmental pollution. Secondly, the dust and ammonia removal process after the exhaust gas is inadequate. The scrubber discharges saturated gas, while the air entering the fluidized bed granulation process is relatively low in humidity. This means the exhaust gas carries away a large amount of water, which needs to be replenished during the exhaust gas treatment process, resulting in water waste. Thirdly, the large volume of exhaust gas requires a two-stage washing process (water washing followed by acid washing), leading to a significant drop in resistance. The scrubber's induced draft fan is the most power-consuming component in the entire fluidized bed granulation process.

[0009] Electricity consumption is the largest energy-consuming component of fluidized bed granulation equipment. Reducing the electricity consumption of fluidized bed granulation is also the main direction for the development of fluidized bed granulation technology.

[0010] Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of existing fluidized bed granulation processes by providing a low-energy-consumption fluidized bed granulation process device that can achieve ultra-low concentration emissions of ammonia and urea dust in the exhaust gas.

[0012] To achieve the above objectives, the present invention adopts the following technical solution: a low-energy-consumption and low-emission fluidized bed urea granulation system, comprising: an ammonia recovery tower, a fluidized bed granulator, a first screening machine, a second screening machine, a cooler, a first bucket elevator, a second bucket elevator, a combined dust collector, and a melting tank;

[0013] The ammonia recovery tower is located before the inlet of the fluidized bed granulator. After free ammonia is removed in the ammonia recovery tower, the raw material molten urea is granulated in the fluidized bed granulator.

[0014] The granular urea material generated by the fluidized bed granulator is screened by the first screening machine into three specifications: large urea, powder urea and intermediate granular urea.

[0015] Large pieces of urea separated by screening are recycled.

[0016] After being cooled by a cooler, the intermediate granular urea is lifted to a certain height by the first bucket elevator and then screened by the second screening machine. The screening results in three specifications of material: finished urea, powdered urea, and large granular urea. The finished urea is cooled to below 50°C and sent to the outside of the boundary as the final urea product. The large granular urea is crushed into powder and then sent through pipelines to the fluidized bed granulator along with the powdered urea and the powdered urea screened by the first screening machine as seed crystals for granulation.

[0017] The combined dust collector and the melting tank are sequentially connected to the fluidized bed granulator. The dust-laden exhaust gas generated by the fluidized bed granulator first enters the combined dust collector, which removes more than 80% of the dust particles larger than 10μm from the exhaust gas, reducing the dust concentration in the exhaust gas to 10mg / Nm³. 3 The dust removed by the combined dust collector is sent to the melting tank, where it is melted into liquid and sent to the inlet urea solution pipeline of the fluidized bed granulator. The urea solution is then mixed with the raw material urea solution before entering the fluidized bed granulator for granulation.

[0018] Furthermore, the ammonia recovery tower includes a lower ammonia stripping section and an upper condensation section. The ammonia stripping section uses hot CO2 gas at a temperature above 120°C as the stripping medium to extract free ammonia from the raw material molten urea. The free ammonia is then condensed into a dilute ammonium carbonate solution in the upper condensation section using a cooling medium for recycling.

[0019] Furthermore, after the free ammonia in the ammonia recovery tower is removed from the raw material molten urea, the free ammonia is reduced to below 100 ppm.

[0020] Furthermore, the cooler is a corrugated plate cooler, which uses circulating water and intermediate granular urea for indirect heat exchange between the corrugated plates.

[0021] Furthermore, the cooler reduces the temperature of the intermediate urea particles from 100-110°C to 60-70°C.

[0022] Furthermore, the finished urea is cooled using a corrugated plate cooler.

[0023] Furthermore, the fluidized bed granulator is divided into upper and lower chambers by a perforated plate as the interface. The lower chamber is equipped with granulation nozzles, a fluidized bed perforated plate, atomizing air and fluidized air distribution pipes, while the upper chamber is the fluidized bed layer and gas phase space.

[0024] Furthermore, the combined dust collector includes an upper bag filter section, a middle cyclone separator section, and a lower conical outlet. The dust-laden exhaust gas from the fluidized bed granulator first enters the cyclone separator section to remove more than 80% of the dust particles larger than 10μm. The exhaust gas then enters the upper bag filter section to remove dust down to 10mg / Nm³. 3 The dust is then discharged into the atmosphere via an induced draft fan; the removed dust is discharged from the lower conical outlet and sent to the melting tank.

[0025] Furthermore, the second screening machine consists of two layers of screens.

[0026] Furthermore, the system also includes a crusher for breaking large urea particles into powder.

[0027] The fluidized bed granulation technology of this invention is used to prepare granular urea products. By removing ammonia from the urea solution before it enters the granulator, the free ammonia content in the urea solution entering the granulator is significantly reduced, decreasing from 800-1100 ppm (wt) to below 100 ppm (wt). Consequently, the free ammonia content in the granulator exhaust gas can be lower than 10 mg / Nm³. 3 This meets the emission standards for ammonia in the exhaust gas. Using the technology of this patented invention, there is no need to install ammonia removal facilities in the granulation exhaust gas treatment system, reducing equipment investment and operating costs.

[0028] The fluidized bed granulation technology of this invention is used to prepare granular urea products. The screening machine B following the fluidized bed granulator A separates the product into three specifications: large urea, powder urea, and intermediate granular urea. The intermediate granular urea goes to the cooler, while the powder urea is directly lifted by a bucket elevator and returned to the fluidized bed granulator along with the crushed powder as seed crystals. The large urea is recycled. The cooler is a corrugated plate cooler C, which uses circulating water to reduce the temperature of the granular urea from 100-110℃ to 60-70℃. This reduces the amount of fluidization and cooling air required and the amount of dust generated during the cooling process. Compared to the fluidized bed cooler used in traditional fluidized bed granulation processes, which requires a separate cooling fan to provide the large amount of fluidization and cooling air needed for the fluidized bed cooler and generates a certain amount of dust during the cooling process, this method is more efficient. For example, to produce 100 tons of granular urea per hour, the temperature of the granules from the granulator needs to be cooled from 110℃ to 70℃, requiring approximately 220,000 Nm³ of air. 3 The fluidizing air pressure required for fluidization and cooling is 2.5 kPa, and the exhaust gas treatment fan pressure is 4.5 kPa. Therefore, the power consumption of the fluidizing fan is approximately 190 kWh / h, and the power consumption of the exhaust fan is approximately 345 kWh / h. In contrast, using a corrugated plate water cooler consumes 380 m³ of circulating water. 3 / h, which translates to approximately 60kWh / h of electricity consumption. Assuming 8000 hours of production per year, this translates to approximately 380,000kWh of electricity savings annually.

[0029] The fluidized bed granulation technology of this invention is used to prepare granular urea products. A combined dust collector is used for treating the dust-laden exhaust gas. The combined dust collector and the melting tank are sequentially connected to the fluidized bed granulator. The dust-laden exhaust gas generated by the fluidized bed granulator first enters the combined dust collector, where more than 80% of the 10μm dust is removed in the lower part, and the dust concentration in the exhaust gas is reduced to 10mg / Nm³ in the upper part. 3 The exhaust gas is then discharged into the atmosphere via an induced draft fan. The treated dust, in the form of dry material, is collected, melted, and then pumped to a raw urea solution for granulation. The urea dust content in the exhaust gas after dust removal is reduced to 10 mg / Nm³. 3 The following is true, while traditional water washing processes can only achieve 20mg / Nm³. 3 This invention can recover more urea dust, not only reducing dust emissions but also increasing economic benefits. Generally, fluidized bed granulation processes generate 35-55 kg of dust per ton of final urea product. Water washing dust removal recovers approximately 45% (wt) urea solution (or a urea solution containing ammonium salts). Concentrating this urea solution to the concentration required for granulation requires a certain amount of steam and circulating cooling water. Taking the recovery of 1 ton of dust as an example, the water washing process consumes approximately 1.75 tons of low-pressure steam and approximately 75 cubic meters of circulating cooling water. 3The technology of this invention only requires 0.18t of low-pressure steam, resulting in significant energy savings. In addition, the exhaust gas discharged from the water washing dust removal process is close to saturation, requiring the addition of a certain amount of water. This water is released into the atmosphere and is lost (approximately 170kg of water is lost for every 1t of urea final product produced). Attached Figure Description

[0030] Figure 1 is a schematic diagram of the low-energy-consumption and low-emission fluidized bed urea granulation system of the embodiment.

[0031] Figure 2 is a schematic diagram of the structure of the combined dust collector in the embodiment. Detailed Implementation

[0032] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0033] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification, claims and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product or device.

[0034] This low-energy-consumption, low-emission fluidized bed urea granulation system includes an ammonia recovery tower before the urea solution enters the fluidized bed granulator A. The ammonia recovery tower consists of an ammonia stripping section and a condensation section. In the ammonia stripping section, hot CO2 gas at above 120°C is used as the stripping medium to extract free ammonia from the urea solution. This ammonia is then condensed into a dilute ammonium carbonate solution in the upper condensation section using a cooling medium for recycling. The non-condensable gas is sent to the induced draft fan after dust recovery. By removing ammonia before the urea solution enters the granulator, the free ammonia content in the urea solution entering the granulator is significantly reduced, from 800–1100 ppm (wt) to below 100 ppm (wt). Therefore, the free ammonia content in the granulator exhaust gas can be below 10 mg / Nm³. 3 Therefore, no further ammonia removal is required before the exhaust gas is released into the atmosphere, achieving ultra-low concentration emissions of ammonia in the exhaust gas.

[0035] Screening machine B, installed after fluidized bed granulator A, separates the product into three grades: large urea, powder urea, and intermediate urea. The intermediate urea goes to urea cooler C, while the powder urea is directly lifted by bucket elevator E and returned to fluidized bed granulator A along with crushed powder as seed crystals. The large urea is recycled. The intermediate urea from the screening machine is cooled by circulating cooling water in urea cooler C. Urea cooler C is a vertical corrugated plate type, where granular urea and circulating cooling water exchange heat indirectly through the corrugated plates. The circulating cooling water removes heat, cooling the granular urea material from 100–110°C at the fluidized bed granulator A to 60–70°C. The outlet temperature of fluidized bed granulator A is controlled at 100–110°C to reduce the length of the fluidized bed granulator and decrease fluidizing air consumption. The system also includes granular urea screening, crushing, and final product cooling. The granular urea exiting urea cooler C has a temperature of 60-70℃. After being lifted to a certain height by bucket elevator D, it is screened. Screening machine F has two layers of screens and separates three materials: product urea 7, powder urea 9, and large granular urea 8. Large granular urea 8 is crushed into powder urea 10 by crusher H. It is then returned to fluidized bed granulator A as return seed crystals along with the powder urea 9 screened out and the powder urea 14 screened out by screening machine B and lifted up by powder bucket elevator E.

[0036] Dust-laden exhaust gas generated during the granulation process is treated by a combined dust collector J. The powder obtained from the combined dust collector J is then conveyed to a dust silo for packaging via a discharge device (screw type, vibrating type, or other type) for sale as a powder product. Alternatively, the powder can be melted in a melter L, mixed with the feed urea solution, and then fed into a fluidized bed granulator A for granulation, with melting before granulation being preferred. The dust content in the exhaust gas after dust removal is no higher than 10 mg / Nm³. 3 The dust is discharged directly into the atmosphere via an induced draft fan. The entire inner wall of the combined dust collector J is mirror-polished, with a surface finish requirement of not less than grade 9 (≤Ra0.4).

[0037] Example

[0038] Referring to Figure 1, urea solution (95–98.5% (wt)) from the upstream urea unit is sent to fluidized bed granulator A via pipeline 1. An ammonia recovery tower P is installed before entering fluidized bed granulator A. Ammonia recovery tower P consists of an ammonia stripping section and a condensation section. The ammonia stripping section uses hot CO2 gas 20 (above 120°C) as the stripping medium to extract free ammonia from the urea solution. This ammonia is then condensed into a dilute ammonium carbonate solution in the upper condensation section using a cooling medium for recycling. The non-condensable gas 22 is sent to the induced draft fan K after dust recovery. By removing ammonia before the urea solution enters the granulator, the free ammonia content in the urea solution entering the granulator is significantly reduced, decreasing from 800–1100 ppm (wt) to below 100 ppm (wt). Consequently, the free ammonia content in the granulator exhaust gas can be below 10 mg / Nm³. 3 The urea solution 2, after being treated by the ammonia recovery tower P, is sent to the fluidized bed granulator A for granulation. Fluidized bed granulator A is a fluidized bed chamber device, divided into upper and lower chambers by a perforated plate. The lower chamber houses the granulation nozzles, the fluidized bed perforated plate, atomizing air, and fluidizing air distribution pipes. The upper chamber contains the fluidized bed layer and gas phase space, where the incoming seed crystals 11 and the generated granular urea material form a fluidized bed layer above the perforated plate. Urea droplets sprayed from the nozzles in the lower chamber are atomized by the air and sprayed onto the seed crystal surface, where they are cooled and solidified by the fluidized air. Along the length of fluidized bed granulator A, the seed crystals gradually grow into granular urea products. The heat released during cooling and solidification is carried away by the fluidized air, along with the dust generated during the granulation process, and exits fluidized bed granulator A. The granular urea material 3 from fluidized bed granulator A enters screening machine B, which separates the product into three specifications: large urea 26 (no large granules are present in normal production), powdered urea 13, and intermediate granular urea 4. The intermediate granular urea 4 is sent to corrugated plate urea cooler C. Powdered urea 13 is directly lifted by bucket elevator E and returned to fluidized bed granulator A along with crushed powder 10 and powdered material 9 screened by screening machine F as seed crystals. Large urea 26 is recycled. Corrugated plate urea cooler C is a solid material cooler where granular urea and circulating cooling water exchange heat between corrugated plates. The circulating cooling water cools the granular urea material to 60-70℃. The cooled material 5 is then lifted to a certain height by bucket elevator D and enters screening machine F for sieving. Inside the screening machine F, material 6 is screened into three specifications: finished urea 7, powdered urea 9, and large-particle urea 8. Finished urea 7 is cooled to below 50°C by the final product cooler G and sent outside the boundary as final urea product 12. Large-particle urea 8 is crushed into powder 10 by the crusher H and combined with the powdered urea 9 screened by the screening machine F. This powder is then sent through a pipeline to the fluidized bed granulator A as seed crystals for granulation. The final product cooler G can be a corrugated plate cooler or a fluidized bed cooler, with a corrugated plate cooler being preferred.

[0039] Dust generated during urea production is produced in fluidized bed granulator A. Trace amounts of dust generated during the operation of other equipment such as granular material conveying, bucket elevators, screening, and cooling systems are collected by dust collector fans and sent to the dust recovery system. The dust-laden exhaust gas 15 from fluidized bed granulator A enters the N1 port of the cyclone dust collector section of the combined dust collector J (see Figure 2). In the cyclone dust collector section, more than 80% of the 10μm dust is removed. The gas exiting the cyclone dust collector section enters the upper high-efficiency bag filter section, where the dust concentration is reduced to 10mg / Nm³. 3 Below, or even lower concentrations, such as 5 mg / Nm 3 The exhaust gas 16, after meeting the emission standards, is discharged into the atmosphere via N3 through the induced draft fan K. The dust 24 removed by the combined dust collector J is sent to the melting tank L through the N3 port, where the dust is melted into liquid material 25 and sent to the inlet urea solution pipeline 2 of the fluidized bed granulator A. The mixed urea solution then enters the fluidized bed granulator A for granulation.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A low-energy-consumption, low-emission fluidized bed urea granulation system, characterized in that... include: Ammonia recovery tower, fluidized bed granulator, first screening machine, second screening machine, cooler, first bucket elevator, second bucket elevator, combined dust collector and melting tank; The ammonia recovery tower is located before the inlet of the fluidized bed granulator. After the free ammonia is removed in the ammonia recovery tower, the raw material molten urea is granulated in the fluidized bed granulator. The granular urea material generated by the fluidized bed granulator is screened by the first screening machine into three specifications: large urea, powder urea and intermediate granular urea. Large pieces of urea separated by screening are recycled. After being cooled by a cooler, the intermediate granular urea is lifted to a certain height by the first bucket elevator and then screened by the second screening machine. The screening results in three specifications of material: finished urea, powdered urea, and large granular urea. The finished urea is cooled to below 50°C and sent to the outside of the boundary as the final urea product. The large granular urea is crushed into powder and then sent through pipelines to the fluidized bed granulator along with the powdered urea and the powdered urea screened by the first screening machine as seed crystals for granulation. The combined dust collector and the melting tank are sequentially connected to the fluidized bed granulator. The dust-laden exhaust gas generated by the fluidized bed granulator first enters the combined dust collector, which removes more than 80% of the dust particles larger than 10μm from the exhaust gas, reducing the dust concentration in the exhaust gas to 10mg / Nm³. 3 The dust removed by the combined dust collector is sent to the melting tank, where it is melted into liquid and sent to the inlet urea solution pipeline of the fluidized bed granulator. The urea solution is then mixed with the raw material urea solution before entering the fluidized bed granulator for granulation.

2. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The ammonia recovery tower includes a lower ammonia stripping section and an upper condensation section. The ammonia stripping section uses hot CO2 gas at a temperature above 120°C as the stripping medium to extract free ammonia from the raw material molten urea. The free ammonia is condensed into a dilute ammonium carbonate solution in the upper condensation section using a cooling medium for recycling.

3. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: After the molten urea raw material is deaerated in the ammonia recovery tower, the free ammonia content is reduced to below 100 ppm.

4. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The cooler is a corrugated plate cooler, which uses circulating water and intermediate granular urea for indirect heat exchange between the corrugated plates.

5. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The cooler reduces the temperature of the intermediate urea particles from 100-110°C to 60-70°C.

6. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The finished urea is cooled using a corrugated plate cooler.

7. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The fluidized bed granulator is divided into upper and lower chambers by a perforated plate as the interface. The lower chamber is equipped with granulation nozzles, a fluidized bed perforated plate, atomizing air and fluidized air distribution pipes, while the upper chamber is the fluidized bed layer and gas phase space.

8. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The combined dust collector includes an upper bag filter section, a middle cyclone separator section, and a lower conical outlet. The dust-laden exhaust gas from the fluidized bed granulator first enters the cyclone separator section to remove more than 80% of the dust particles larger than 10μm. The exhaust gas then enters the upper bag filter section to further reduce the dust concentration to 10mg / Nm³. 3 The dust is then discharged into the atmosphere via an induced draft fan; the removed dust is discharged from the lower conical outlet and sent to the melting tank.

9. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The second screening machine has two layers of screens.

10. The low-energy-consumption, low-emission fluidized bed urea granulation system according to claim 1, characterized in that: The system also includes a crusher for crushing large urea particles into powder.

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