Compound fertilizer production system and production process

Abstract

The invention discloses a compound fertilizer production system and production process, and belongs to the technical field of urea production, the system comprises a granulation unit and a tail gas treatment unit, the granulation unit comprises a material treatment module, a granulator and a screening cooling device, and the tail gas treatment unit comprises a bag-type dust collector, a washing tower and a flue gas desulfurization device. The invention further provides a production process. Alternate production of the nitrogen-potassium compound fertilizer and common large-particle urea can be achieved through valve switching, an independent production line does not need to be additionally arranged, and the equipment investment and the occupied area are greatly reduced; one set of device meets the production requirements of two products, so that the equipment utilization rate is improved, and the quick response capability of an enterprise to market requirements is enhanced; meanwhile, the system adopts a two-stage tail gas treatment process of'bag dust removal + washing tower absorption ', so that urea dust in the tail gas is efficiently removed, ammonia gas is absorbed through desalted water to generate ammonia water, atmospheric pollution caused by direct emission of the ammonia gas is avoided, and strict environmental protection requirements are met.

Description

Technical Field

[0001] This invention relates to the field of urea production technology, and in particular to a compound fertilizer production system and production process. Background Technology

[0002] In agricultural production, compound fertilizers, as an important fertilizer category, play a vital role in agricultural development through their efficient production and diversified applications. Currently, the market situation for ordinary urea fertilizer products is severe, with fierce competition and significant fluctuations in production efficiency. To achieve greater profits, it is essential to continuously introduce new compound fertilizer products.

[0003] Traditional production often employs separate production lines for each component, resulting in high equipment investment, large land area requirements, and poor production flexibility. Furthermore, current compound fertilizer production technologies primarily utilize solid raw material mixing followed by granulation or simple melting and mixing, which easily leads to uneven material mixing, low particle strength, and uneven nutrient distribution, affecting product quality. Simultaneously, improper handling of exhaust gases such as urea-containing dust and ammonia generated during production not only wastes raw materials but also pollutes the environment.

[0004] Therefore, developing a production system and process that can flexibly switch between producing nitrogen-potassium compound fertilizer and ordinary urea, improve raw material utilization, reduce pollutant emissions, and operate stably has become an urgent technical problem to be solved in the current compound fertilizer production field. Summary of the Invention

[0005] The purpose of this invention is to provide a compound fertilizer production system and process to solve the problems in the background art.

[0006] To achieve the above objectives, the present invention provides a compound fertilizer production system, including a granulation unit and a tail gas treatment unit. The granulation unit includes a material processing module, a granulator, and a screening and cooling device. The material processing module consists of a mixing tank, a common small-particle urea device, and a potash fertilizer silo. The outlet of the common small-particle urea device is connected to the inlet of the mixing tank through a first valve. The outlet of the common small-particle urea device is connected to the inlet of the granulator through a second valve. A third valve is provided on the connecting pipeline between the mixing tank and the granulator. The tail gas outlet of the granulator is connected to the tail gas treatment unit, which includes a bag filter, a scrubbing tower, and a flue gas desulfurization device.

[0007] Preferably, a bucket elevator is provided at the feed end of the potash fertilizer bin, and a static weighing scale is installed at the lower end of the potash fertilizer bin; the static weighing scale is connected to the feed inlet of the mixing tank, a steam inlet pipe is connected to the mixing tank, and a temperature self-regulating valve is provided on the steam inlet pipe.

[0008] Preferably, the discharge port of the ordinary small granule urea device is connected to the feed port of the granulator, and an electromagnetic flow meter is installed at the liquid outlet of the ordinary small granule urea device.

[0009] Preferably, the lower outlet of the melting and mixing tank is connected to the inlet of the granulator in sequence through a filter and a melting pump, and the third valve is installed on the connecting pipeline between the melting pump and the granulator; the granulator outlet is connected to the screening and cooling device, and the exhaust gas outlet of the screening and cooling device is connected to the first induced draft fan and the bag filter dust collector respectively.

[0010] Preferably, the outlet of the first induced draft fan is connected to the air inlet of the scrubbing tower, the scrubbing tower is provided with a demineralized water inlet, the outlet of the scrubbing tower is connected to a scrubbing liquid circulation pump, the outlet of the scrubbing liquid circulation pump is connected to a circulation pipe and an ammonia water delivery pipe through a scrubbing liquid outlet pipe, the ammonia water delivery pipe is connected to the flue gas desulfurization device, and the other end of the circulation pipe is connected to the demineralized water inlet of the scrubbing tower.

[0011] The ammonia water delivery pipe is equipped with a concentration self-adjusting valve, and the washing liquid outlet pipe is equipped with a concentration meter.

[0012] Preferably, the discharge port of the bag filter is connected to a static weighing scale via a star-shaped discharge valve, and the discharge port of the bag filter is connected to a second induced draft fan, the outlet of which is connected to the air inlet of the washing tower.

[0013] This invention also provides a production process based on the above-mentioned compound fertilizer production system, including a nitrogen-potassium compound fertilizer production process and a conventional urea process. In the nitrogen-potassium compound fertilizer production process, the second valve is closed, and the first and third valves are opened. The molten urea in the conventional small-particle urea unit and the potassium chloride in the potassium fertilizer silo enter the mixing tank together. After being fully stirred, a eutectic slurry is formed. After being filtered by a filter and pressurized by a melting pump, the slurry enters the granulator. At the same time, the seed crystals in the conventional small-particle urea unit enter the granulator. After granulation, nitrogen-potassium compound fertilizer is obtained. It is then transported to a screening and cooling device for cooling and screening. The nitrogen-potassium compound fertilizer with qualified particle size is selected by screening.

[0014] In the conventional urea process, the first and third valves are closed, and the second valve is opened. The molten urea in the conventional small-particle urea unit directly enters the granulator. At the same time, the seed crystals in the conventional small-particle urea unit enter the granulator. After granulation, conventional large-particle urea is obtained, which is then transported to the screening and cooling device for cooling and screening. The conventional large-particle urea with qualified particle size is selected by screening.

[0015] Preferably, the urea-containing dust exhaust gas generated during the granulation process of the granulator and the screening and cooling process is transported to a bag filter or a first induced draft fan for treatment. The exhaust gas treated in the first induced draft fan is directly transported to a washing tower for treatment, while the exhaust gas treated in the bag filter is transported to the washing tower by a second induced draft fan. The dust generated in the bag filter is transported to a static weighing scale through a star-shaped discharge valve and pipeline, weighed, and then transported to a melting and mixing tank for recycling.

[0016] Preferably, the specific processing procedure of the washing tower is as follows:

[0017] 1) The exhaust gas enters the lower part of the scrubbing tower through the air inlet, and the demineralized water enters the middle part of the scrubbing tower through the demineralized water feed inlet. It flows from top to bottom and comes into countercurrent contact with the exhaust gas flowing from bottom to top. The demineralized water absorbs the trace amount of ammonia in the exhaust gas, and the qualified exhaust gas is released from the top of the scrubbing tower.

[0018] 2) The demineralized water that absorbs ammonia is converted into washing liquid and stored in the lower part of the washing tower. It is then transported through pipelines to the washing liquid circulation pump for pressurization.

[0019] 3) After pressurization, the washing liquid is tested by a concentration meter. The washing liquid with qualified concentration is transported to the flue gas desulfurization unit through the ammonia water delivery pipe and used as a desulfurizing agent; the washing liquid with unqualified concentration enters the circulation pipe and returns to the washing tower as ammonia absorption liquid, so as to realize recycling.

[0020] Preferably, the specific steps of the nitrogen-potassium compound fertilizer production process are as follows:

[0021] S1. In a typical small-particle urea plant, molten urea is metered by an electromagnetic flowmeter and then enters the mixing tank through the first valve, where an electric agitator is activated. Potassium chloride is transported to the potash fertilizer silo by a bucket elevator, and after being metered by a static weighing scale based on its position difference, it enters the mixing tank for slurry mixing.

[0022] S2. After the molten urine in the mixing tank is thoroughly stirred with potassium chloride, a eutectic slurry is formed. After initial filtration through the filter screen at the bottom of the mixing tank, it enters the filter and is further filtered before being transported to the melting pump for pressurization.

[0023] S3. The treated eutectic slurry enters the granulator, while the seed crystals from the ordinary small-particle urea unit also enter the granulator. Together, they are granulated to obtain nitrogen-potassium compound fertilizer. The fertilizer is then transported to a screening and cooling device for cooling and screening. The nitrogen-potassium compound fertilizer with qualified particle size selected by screening is transported to the outside of the site for packaging through the finished product delivery pipeline.

[0024] Preferably, in step S1, the temperature of the molten urine is 138–142°C; when the molten urine enters the mixing tank and reaches the first blade of the electric stirrer, the static weighing scale is turned on; at the same time, 1.2 MPa steam enters the inner coil of the mixing tank through the steam inlet pipe to heat the slurry in the mixing tank.

[0025] Preferably, in step S2, the temperature of the slurry in the melting tank is controlled by a temperature self-regulating valve, and the temperature of the eutectic slurry is 128-134°C.

[0026] Therefore, the compound fertilizer production system and process of the present invention have the following beneficial effects:

[0027] (1) The system can achieve alternating production of nitrogen-potassium compound fertilizer and ordinary large-particle urea by switching valves, without the need to set up an additional independent production line, which greatly reduces equipment investment and floor space; by using one device to meet the production needs of two products, the equipment utilization rate is improved and the enterprise's ability to respond quickly to market demands is enhanced.

[0028] (2) In the production of nitrogen-potassium compound fertilizer, molten urine and potassium chloride form a eutectic slurry in the mixing tank. Combined with the seed granulation process, the materials are mixed more thoroughly and evenly, which effectively solves the problems of uneven nutrient distribution and insufficient particle strength in the traditional process, and improves the stability and qualification rate of the product.

[0029] (3) In the exhaust gas treatment, the exhaust gas containing urea dust is first filtered by a bag filter before being washed. Compared with a dust-free system where all dust directly enters the scrubber, this method effectively reduces the energy consumption of demineralized water during the washing process while achieving a more significant dust reduction effect. Furthermore, the urea dust collected in the bag filter is returned to the system for reuse via a star-shaped discharge valve, reducing raw material waste. A washing section is located in the middle of the scrubbing tower, employing spray washing to absorb trace amounts of ammonia in the exhaust gas, resulting in a good washing effect. The urea dust content in the emitted exhaust gas is ≤10mg / Nm³. 3 Ammonia content ≤10mg / Nm 3 This avoids environmental pollution; the ammonia water it produces is sent out as a desulfurizing agent, realizing the recycling of resources and reducing production costs and environmental pressure.

[0030] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention;

[0032] Figure label:

[0033] 1. Bucket elevator; 2. Potash fertilizer silo; 3. Melting tank; 4. Electric agitator; 5. Filter; 6. Melting pump; 7. Granulator; 8. Screening and cooling device; 9. First induced draft fan; 10. Bag filter; 11. Second induced draft fan; 12. Scrubber; 13. Scrubber circulation pump; 14. Liquid level self-regulating valve; 15. Concentration self-regulating valve; 16. Temperature self-regulating valve; 17. First valve; 18. Second valve; 19. Third valve 20. Flow meter; 21. Thermometer; 22. Condensate delivery pipe; 23. Steam inlet pipe; 24. Finished product delivery pipe; 25. Demineralized water inlet pipe; 26. Ammonia delivery pipe; 27. Washing liquid outlet pipe; 28. Circulation pipe; 29. ​​Seed crystal feed pipe; 30. Static weighing scale; 31. Ordinary small particle urea unit; 32. Flue gas desulfurization unit; 33. Star valve; 34. Pipeline filter; 35. Concentration meter. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0036] Example

[0037] like Figure 1 As shown, this embodiment provides a compound fertilizer production system, including a granulation unit and a tail gas treatment unit. The granulation unit includes a material processing module, a granulator 7, and a screening and cooling device 8. The material processing module consists of a mixing tank 3, a common small granule urea device 31, and a potash fertilizer bin 2. The tail gas outlet of the granulator 7 is connected to the tail gas treatment unit, which includes a bag filter 10, a scrubbing tower 12, and a flue gas desulfurization device 32.

[0038] A bucket elevator 1 is installed at the feed end of the potash fertilizer silo 2. 60% potassium chloride (special surface potassium) is poured into the inlet of the bucket elevator 1, which is below ground level, and the bucket elevator 1 is turned on to transport it into the potash fertilizer silo 2. A level gauge is installed inside the potash fertilizer silo to detect the amount of fertilizer stored inside. A static weighing scale 30 is installed at the lower end of the potash fertilizer silo 2. The potassium chloride in the potash fertilizer silo 2 enters the static weighing scale 30 for weighing due to the level difference. The static weighing scale 30 is connected to the feed inlet of the mixing tank 3, and the weighed potassium chloride enters the mixing tank 3.

[0039] The outlet of the ordinary small-particle urea unit 31 is connected to the inlet of the mixing tank 3 via a first valve 17 and a delivery pipe. The first valve 17 controls whether the molten urea enters the mixing tank 3. A steam inlet pipe 23 is connected to the mixing tank 3, and a temperature self-regulating valve 16 is installed on the steam inlet pipe 23. A thermometer 21 is installed on the mixing tank 3, and an automatic control circuit is set up between the thermometer 21 and the temperature self-regulating valve 16. 1.2MPa steam enters the inner coil of the mixing tank 3 through the temperature self-regulating valve 16 to heat the slurry in the mixing tank 3, and the temperature of the slurry in the mixing tank 3 is stabilized at a set value by the temperature self-regulating valve 16. A level gauge is installed in the mixing tank to detect the liquid level of the slurry inside.

[0040] The outlet of the ordinary small granule urea device 31 is connected to the inlet of the granulator 7 through the second valve 18 and the delivery pipe. The second valve 18 is used to control whether the molten urea enters the granulator 7.

[0041] An electromagnetic flow meter 20 is installed at the outlet of the ordinary small particle urea device 31 to control the amount of molten urea used.

[0042] When the molten urine enters the mixing tank 3 and reaches the first blade of the electric agitator 4, allowing the urine to be stirred within the mixing tank 3, the static weighing scale 30 is activated. Potassium chloride from the potassium fertilizer silo 2 is metered by the static weighing scale 30 and added to the mixing tank 3 by gravity. Simultaneously, steam at 1.2 MPa is introduced into the inner coil of the mixing tank 3 through the steam inlet pipe 23. The slurry in the mixing tank 3 is continuously stirred and mixed by the agitator blades of the electric agitator 4. Under the heating effect of steam, the potassium chloride and molten urine are fully dissolved and mixed in the mixing tank 3, forming a low-temperature eutectic slurry with a temperature of 128–134°C.

[0043] After heating the slurry, the steam cools and condenses into condensate, which is then transported to an external location for recycling via the condensate delivery pipe 22 at the bottom of the mixing tank 3. The lower outlet of the mixing tank 3 is connected to the inlet of the granulator 7 via a filter 5, a melting pump 6, and a third valve 19 on the delivery pipe between the melting pump 6 and the granulator 7, controlling the flow between them. In this structure, the eutectic slurry is first pre-filtered through the filter screen in the mixing tank 3, which blocks impurities and large pieces of potassium chloride from flowing out of the mixing tank 3. After pre-filtration, the slurry overflows through the bottom outlet pipe of the mixing tank 3 and enters the open filter 5, where impurities are further filtered. The filtered slurry then enters the melting pump 6 via the inlet pipe due to the level difference. After being pressurized by the melting pump 6, it is transported to the granulator 7 for granulation through the outlet pipe. In addition, during actual production, operators can observe the degree of slurry dissolution at the opening of filter 5, thereby adjusting and controlling the temperature in the mixing tank 3. If the degree of slurry dissolution is found to be poor, the set value of thermometer 21 can be increased, and the temperature self-adjusting valve 16 will automatically increase the valve opening to increase the amount of steam added and improve the solubility of the slurry. A pressure gauge can also be installed in the mixing tank to monitor the internal pressure.

[0044] In this embodiment, in order to prevent impurities in the slurry from clogging the nozzle of the granulator 7, a pipeline filter 34 (located at the front end of the third valve 19) is installed on the conveying pipeline between the melt pump 6 and the granulator 7 to perform secondary filtration on the slurry at the outlet of the melt pump 6.

[0045] The discharge port of the ordinary small-particle urea unit 31 is connected to the inlet of the granulator 7 through the seed crystal feed pipe 29, which transports the seed crystals into the granulator 7 for granulation. Inside the granulator 7, the slurry is sprayed onto the outside of the seed crystals, causing them to continuously grow and form nitrogen-potassium compound fertilizer. The discharge port of the granulator 7 is connected to the screening and cooling device 8 through the conveying pipe, which transports the nitrogen-potassium compound fertilizer to the device. The nitrogen-potassium compound fertilizer granules are first cooled, then screened to select the finished nitrogen-potassium compound fertilizer with qualified particle size, and then transported out of the boundary for packaging through the finished product delivery pipe 24.

[0046] The exhaust gas outlet of the screening and cooling device 8 is connected to the first induced draft fan 9 and the bag filter 10 through the exhaust gas outlet pipe. The exhaust gas containing urea dust is transported to the bag filter 10 or the first induced draft fan 9 for treatment through the exhaust gas branch pipe.

[0047] In the initial stage of system startup, or when the bag filter 10 malfunctions or cannot be used due to bag replacement, the exhaust gas containing urea dust can be directly pressurized by entering the first induced draft fan 9 through the inlet pipe. The outlet of the first induced draft fan 9 is connected to the inlet of the scrubbing tower 12, and the exhaust gas is transported to the scrubbing tower 12 for washing and then discharged through the outlet pipe of the first induced draft fan 9.

[0048] The discharge port of the bag filter 10 is connected to the static weighing scale 30 via a star-shaped discharge valve 33 and a urea powder conveying pipe. Since the discharge port of the bag filter 10 is under negative pressure, a star-shaped discharge valve 33 is installed at the discharge port to ensure normal material discharge and prevent external air from being drawn into the bag filter 10 during urea powder discharge, thus maintaining a stable negative pressure and ensuring dust removal efficiency. Simultaneously, by adjusting the impeller speed of the star-shaped discharge valve 33, the amount of urea powder discharged per unit time is controlled, achieving uniform and continuous urea powder discharge. The dust generated by the bag filter 10 is conveyed to the static weighing scale 30 via the star-shaped discharge valve 33 and the urea powder conveying pipe, and after metering, is uniformly conveyed to the mixing tank 3 for recycling.

[0049] The outlet of the bag filter 10 is connected to a second induced draft fan 11, and the outlet of the second induced draft fan 11 is connected to the inlet of the scrubbing tower 12. Inside the bag filter 10, urea dust in the exhaust gas is removed, and then enters the second induced draft fan 11 through the inlet pipe for pressurization, and then enters the lower part of the scrubbing tower 12 through the outlet pipe of the second induced draft fan 11 for washing before being discharged.

[0050] The scrubbing tower 12 is equipped with a demineralized water inlet and connected to a demineralized water inlet pipe 25, which is equipped with a level self-regulating valve 14. The demineralized water enters the middle of the scrubbing tower 12 through the demineralized water inlet pipe 25 and flows downwards, counter-currently contacting the upward-flowing tail gas to absorb trace amounts of ammonia in the tail gas. The qualified tail gas has a urea dust content ≤10mg / Nm³. 3 Ammonia content ≤10mg / Nm 3 The wastewater is vented from the top of the scrubbing tower 12; the demineralized water after absorbing ammonia is converted into scrubbing liquid and stored in the lower part of the scrubbing tower 12.

[0051] The lower outlet of the scrubbing tower 12 is connected to the scrubbing liquid circulation pump 13 via a delivery pipe. The outlet of the scrubbing liquid circulation pump 13 is provided with a scrubbing liquid outlet pipe 27, which is connected to the circulation pipe 28 and the ammonia water delivery pipe 26 respectively. The ammonia water delivery pipe 26 is connected to the flue gas desulfurization device 32. The other end of the circulation pipe 28 is connected to the demineralized water inlet of the scrubbing tower 12. A concentration meter 35 is installed on the scrubbing liquid outlet pipe 27, and a concentration self-adjusting valve 15 is installed on the ammonia water delivery pipe 26.

[0052] The washing liquid at the bottom of the washing tower 12 enters the washing liquid circulation pump 13 through the delivery pipe, and after being pressurized, it is output through the washing liquid outlet pipe 27. The flow path is determined by measuring the concentration through the concentration meter 35.

[0053] When the value of the concentration meter 35 is greater than 6%, that is, the ammonia concentration is greater than 6%, it is qualified. The concentration self-adjusting valve 15 on the ammonia water delivery pipe 26 will open automatically, and the qualified ammonia water will be delivered to the flue gas desulfurization unit 32 through the ammonia water delivery pipe 26 and used as a desulfurizing agent in the production of the flue gas desulfurization unit 32.

[0054] When the concentration meter 35 measures less than 6%, indicating an unqualified concentration, the washing liquid is returned to the washing tower 12 via the circulation pipe 28. In this embodiment, the washing liquid is divided into two paths, which are returned to the middle of the washing tower 12 via the first circulation pipe 28 and the second circulation pipe 28 respectively, and recycled as an ammonia absorbent.

[0055] In this embodiment, the scrubbing tower 12 features a specially designed structure with a scrubbing section in the middle. This section uses spray scrubbing to absorb trace amounts of ammonia in the exhaust gas, which is then discharged into the atmosphere. The scrubbing effect is excellent, and the resistance reduction is minimal. A storage section is located at the bottom, where the scrubbing liquid can be stored, eliminating the need for an external storage tank and saving equipment cost and space. A level gauge is installed in the storage section, forming an automatic adjustment loop with the level self-regulating valve 14 installed on the demineralized water inlet pipe 25. The level self-regulating valve 14 automatically adjusts its opening according to the set level of the scrubbing tower 12, maintaining the liquid level of the scrubbing tower 12 stably near the set value.

[0056] This system can also be equipped with a PLC control system, which transmits the metered data of molten urine, potassium chloride, urine powder, pigment, and seed crystals to the PLC system. The system calculates and controls the amount of each raw material added, thereby accurately producing qualified products.

[0057] This embodiment also provides a production process based on the above-mentioned compound fertilizer production system, including a nitrogen-potassium compound fertilizer production process and a conventional urea process. The conversion between the two processes is achieved through the first valve 17, the second valve 18, and the third valve 19, specifically as follows:

[0058] In the production process of nitrogen-potassium compound fertilizer, the second valve 18 is closed, and the first valve 17 and the third valve 19 are opened. The specific steps are as follows:

[0059] S1. Molten urea solution (biuret <0.9%) with a temperature of 138-142℃ and 99.8% purity in the ordinary small granular urea unit 31 is metered by electromagnetic flowmeter 20 and then enters the mixing tank 3 through the first valve 17, and the electric stirrer 4 is turned on. Potassium chloride is transported to the potash fertilizer bin 2 by bucket elevator 1, and then enters the static weighing scale 30 for metering based on the position difference. After that, it enters the mixing tank 3 for slurry mixing. During this process, steam enters the inner coil of the mixing tank 3 through steam inlet pipe 23 to heat the slurry inside.

[0060] S2. The slurry in the mixing tank 3 is continuously stirred and mixed by the electric stirrer 4. Under the action of steam heating, potassium chloride and molten urine are fully dissolved and mixed in the mixing tank 3 to form a low-temperature eutectic slurry with a temperature of 128-134℃. After initial filtration through the filter screen at the bottom of the mixing tank 3, it enters the filter 5. After further filtration by the filter 5, it is transported to the melting pump 6 for pressurization.

[0061] S3. The treated eutectic slurry enters the granulator 7, and at the same time, the seed crystals in the ordinary small granule urea device 31 enter the granulator 7. The slurry is sprayed on the outside of the seed crystals, causing the seed crystals to grow continuously and form nitrogen-potassium compound fertilizer.

[0062] After granulation, the product is transported to the screening and cooling device 8 for cooling and screening. The nitrogen and potassium compound fertilizer with qualified particle size selected by screening is transported to the outside for packaging through the finished product delivery pipe 24.

[0063] In the conventional urea process, the first valve 17 and the third valve 19 are closed, and the second valve 18 is opened. The molten urea in the conventional small-particle urea device 31 directly enters the granulator 7. At the same time, the seed crystals in the conventional small-particle urea device 31 enter the granulator 7. The slurry is sprayed on the outside of the seed crystals, causing the seed crystals to grow continuously. After granulation, conventional large-particle urea is obtained. It is then transported to the screening and cooling device 8 for cooling and screening. The urea with qualified particle size selected by screening is transported to the outside for packaging through the finished product delivery pipe 24.

[0064] In the two processes described above, the urea-containing dust exhaust gas generated during the granulation process of granulator 7 and the processing of screening and cooling device 8 is transported to bag filter 10 or first induced draft fan 9 for treatment. The exhaust gas treated in the first induced draft fan 9 is directly transported to washing tower 12 for treatment. The exhaust gas treated in bag filter 10 is transported to washing tower 12 through second induced draft fan 11. The dust generated in bag filter 10 is transported to static weighing scale 30 through star-shaped discharge valve 33 and pipeline, weighed, and then transported to melting and mixing tank 3 for recycling.

[0065] The specific processing procedure of scrubbing tower 12 is as follows:

[0066] 1) The exhaust gas enters the lower part of the scrubbing tower 12 through the air inlet of the scrubbing tower 12, and the demineralized water enters the middle part of the scrubbing tower 12 through the demineralized water feed inlet of the scrubbing tower 12 and flows from top to bottom, contacting the exhaust gas flowing from bottom to top in a countercurrent manner. The demineralized water absorbs the trace amount of ammonia in the exhaust gas, and the qualified exhaust gas is released from the top of the scrubbing tower 12.

[0067] 2) The demineralized water that absorbs ammonia is converted into washing liquid and stored in the lower part of the washing tower 12. It is then transported through pipelines to the washing liquid circulation pump 13 for pressurization.

[0068] 3) The pressurized washing liquid is tested by the concentration meter 35. The washing liquid with qualified concentration is transported to the flue gas desulfurization unit 32 through the ammonia water delivery pipe 26 and used as a desulfurizing agent; the washing liquid with unqualified concentration enters the circulation pipe 28 and returns to the washing tower 12 as the ammonia absorption liquid, so as to realize recycling.

[0069] Therefore, the present invention provides a compound fertilizer production system and process that can achieve alternating production of nitrogen-potassium compound fertilizer and ordinary granular urea by switching valves, without the need for additional independent production lines, significantly reducing equipment investment and floor space requirements; one set of equipment meets the production needs of two products, improving equipment utilization and enhancing the company's ability to respond quickly to market demands; at the same time, the system adopts a two-stage tail gas treatment process of "bag filter dust collection + scrubbing tower absorption", which not only efficiently removes urea dust from the tail gas, but also absorbs ammonia gas through demineralized water to generate ammonia water, avoiding air pollution caused by direct ammonia emissions and meeting strict environmental protection requirements.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A compound fertilizer production system, characterized in that: The system includes a granulation unit and a tail gas treatment unit. The granulation unit comprises a material processing module, a granulator, and a screening and cooling device. The material processing module consists of a mixing tank, a common small-particle urea unit, and a potash fertilizer silo. The outlet of the common small-particle urea unit is connected to the inlet of the mixing tank via a first valve. The outlet of the common small-particle urea unit is connected to the inlet of the granulator via a second valve. A third valve is installed on the connecting pipeline between the mixing tank and the granulator. The tail gas outlet of the granulator is connected to the tail gas treatment unit, which includes a bag filter, a scrubbing tower, and a flue gas desulfurization device.

2. The compound fertilizer production system according to claim 1, characterized in that: The potash fertilizer bin is equipped with a bucket elevator at its feed end and a static weighing scale at its lower end. The static weighing scale is connected to the feed inlet of the mixing tank. A steam inlet pipe is connected to the mixing tank and a temperature self-regulating valve is installed on the steam inlet pipe.

3. The compound fertilizer production system according to claim 2, characterized in that: The discharge port of the ordinary small granule urea device is connected to the feed port of the granulator, and an electromagnetic flow meter is installed at the liquid outlet of the ordinary small granule urea device.

4. The compound fertilizer production system according to claim 3, characterized in that: The lower outlet of the melting and mixing tank is connected to the inlet of the granulator in sequence through a filter and a melting pump. The third valve is installed on the connecting pipeline between the melting pump and the granulator. The granulator outlet is connected to the screening and cooling device. The exhaust outlet of the screening and cooling device is connected to the first induced draft fan and the bag filter dust collector, respectively.

5. A compound fertilizer production system according to claim 4, characterized in that: The outlet of the first induced draft fan is connected to the air inlet of the scrubbing tower. The scrubbing tower is provided with a demineralized water inlet. The outlet of the scrubbing tower is connected to a scrubbing liquid circulation pump. The outlet of the scrubbing liquid circulation pump is connected to a circulation pipe and an ammonia water delivery pipe through a scrubbing liquid outlet pipe. The ammonia water delivery pipe is connected to the flue gas desulfurization device. The other end of the circulation pipe is connected to the demineralized water inlet of the scrubbing tower. The ammonia water delivery pipe is equipped with a concentration self-adjusting valve, and the washing liquid outlet pipe is equipped with a concentration meter.

6. A compound fertilizer production system according to claim 5, characterized in that: The discharge port of the bag filter is connected to a static weighing scale via a star-shaped discharge valve, and the discharge port of the bag filter is connected to a second induced draft fan. The outlet of the second induced draft fan is connected to the air inlet of the washing tower.

7. A production process based on the compound fertilizer production system according to any one of claims 1-6, characterized in that: The process includes the production process of nitrogen-potassium compound fertilizer and the ordinary urea process. In the nitrogen-potassium compound fertilizer production process, the second valve is closed and the first and third valves are opened. The molten urea in the ordinary small-particle urea unit and the potassium chloride in the potassium fertilizer silo enter the mixing tank together. After being fully stirred, a eutectic slurry is formed. After being filtered by a filter and pressurized by a melting pump, it enters the granulator. At the same time, the seed crystals in the ordinary small-particle urea unit enter the granulator. After granulation, nitrogen-potassium compound fertilizer is obtained, and then it is transported to a screening and cooling device for cooling and screening. In the conventional urea process, the first and third valves are closed, and the second valve is opened. The molten urea in the conventional small-particle urea unit directly enters the granulator, and the seed crystals in the conventional small-particle urea unit also enter the granulator. After granulation, conventional large-particle urea is obtained, which is then transported to the screening and cooling device for cooling and screening.

8. The production process according to claim 7, characterized in that: The urea-containing dust exhaust gas generated during the granulation process of the granulator and the screening and cooling process is transported to the bag filter or the first induced draft fan for treatment. The exhaust gas treated in the first induced draft fan is directly transported to the washing tower for treatment, while the exhaust gas treated in the bag filter is transported to the washing tower by the second induced draft fan. The dust generated in the bag filter is transported to the static weighing scale through the star-shaped discharge valve and pipeline, weighed, and then transported to the melting and mixing tank for recycling.

9. The production process according to claim 8, characterized in that: The specific processing procedure of the scrubbing tower is as follows: 1) The exhaust gas enters the lower part of the scrubbing tower through the air inlet, and the demineralized water enters the middle part of the scrubbing tower through the demineralized water feed inlet. It flows from top to bottom and comes into countercurrent contact with the exhaust gas flowing from bottom to top. The demineralized water absorbs the trace amount of ammonia in the exhaust gas, and the qualified exhaust gas is released from the top of the scrubbing tower. 2) The demineralized water that absorbs ammonia is converted into washing liquid and stored in the lower part of the washing tower. It is then transported through pipelines to the washing liquid circulation pump for pressurization. 3) After pressurization, the washing liquid is tested by a concentration meter. The washing liquid with qualified concentration is transported to the flue gas desulfurization unit through the ammonia water delivery pipe and used as a desulfurizing agent; the washing liquid with unqualified concentration enters the circulation pipe and returns to the washing tower as ammonia absorption liquid, so as to realize recycling.

10. The production process according to claim 8, characterized in that: The specific steps of the nitrogen-potassium compound fertilizer production process are as follows: S1. In a typical small-particle urea plant, molten urea is metered by an electromagnetic flowmeter and then enters the mixing tank through the first valve, where an electric agitator is activated. Potassium chloride is transported to the potash fertilizer silo by a bucket elevator, and after being metered by a static weighing scale based on its position difference, it enters the mixing tank for slurry mixing. S2. After the molten urine in the mixing tank is thoroughly stirred with potassium chloride, a eutectic slurry is formed. After initial filtration through the filter screen at the bottom of the mixing tank, it enters the filter and is further filtered before being transported to the melting pump for pressurization. S3. The treated eutectic slurry enters the granulator, while the seed crystals from the ordinary small-particle urea unit also enter the granulator. Together, they are granulated to obtain nitrogen-potassium compound fertilizer urea. Subsequently, it is transported to the screening and cooling device for cooling and screening. The nitrogen-potassium compound fertilizer with qualified particle size selected by screening is transported to the outside for packaging through the finished product delivery pipeline.

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