阅读说明：本技术 缓释尿素的制备系统及制备方法 (Preparation system and preparation method of slow-release urea ) 是由 王威 于 2020-12-24 设计创作，主要内容包括：本发明提供一种缓释尿素的制备系统及制备方法。缓释尿素的制备系统包括第一输送管路、第二输送管路、吹扫冷却管路、尿素蒸发装置和尿素造粒装置；第一输送管路连通尿素蒸发装置的进料口；尿素蒸发装置的出料口通过第二输送管路连通尿素造粒装置的进料口；吹扫冷却管路连通尿素造粒装置的进气口。本发明提供的缓释尿素的制备系统及制备方法,通过草酸铵与尿素结合能形成一种既有缓释作用又具有速效功能的肥料,延长了肥效时间,产品的氮素有效利用率能提高60％以上；草酸铵与尿素配比灵活,可以根据需要生产草酸铵含量不同的产品；产品颗粒大,强度高；所需要的缓释原料安全可靠,来源广泛,能适用于规模化生产。(The invention provides a preparation system and a preparation method of slow-release urea. The preparation system of the slow-release urea comprises a first conveying pipeline, a second conveying pipeline, a purging and cooling pipeline, a urea evaporation device and a urea granulation device; the first conveying pipeline is communicated with a feed inlet of the urea evaporation device; the discharge hole of the urea evaporation device is communicated with the feed hole of the urea granulation device through a second conveying pipeline; the blowing and cooling pipeline is communicated with an air inlet of the urea granulation device. According to the preparation system and the preparation method of the slow release urea, the fertilizer with slow release function and quick-acting function can be formed by combining the ammonium oxalate and the urea, the fertilizer efficiency time is prolonged, and the effective utilization rate of nitrogen in the product can be improved by over 60%; the mixture ratio of the ammonium oxalate and the urea is flexible, and products with different ammonium oxalate contents can be produced according to requirements; the product has large particles and high strength; the required sustained-release raw materials are safe and reliable, have wide sources and can be suitable for large-scale production.)

1. A preparation system of slow-release urea is characterized by comprising a first conveying pipeline, a second conveying pipeline, a purging and cooling pipeline, a urea evaporation device and a urea granulation device;

the first conveying pipeline is communicated with a feed inlet of the urea evaporation device and is used for conveying mixed liquor containing ammonium oxalate solution and urea solution into the urea evaporation device for evaporation and concentration;

the discharge port of the urea evaporation device is communicated with the feed port of the urea granulation device through the second conveying pipeline and is used for feeding the evaporated and concentrated melt liquid into the urea granulation device for granulation so as to obtain a urea product;

and the blowing and cooling pipeline is communicated with an air inlet of the urea granulation device and is used for sending compressed air into the urea granulation device.

2. The system for preparing slow-release urea according to claim 1, wherein the first delivery line comprises a liquid delivery pump, an ammonium oxalate-containing solution supply line and a urea solution supply line;

the outlet end of the ammonium oxalate-containing solution supply pipeline and the outlet end of the urea solution supply pipeline are both communicated with the inlet of the liquid delivery pump;

and the outlet of the liquid delivery pump is communicated with the feed inlet of the urea evaporation device.

3. The system for preparing the slow release urea according to claim 1, further comprising a dust and ammonia removal tail gas treatment device;

and the gas outlet of the urea granulation device is communicated with the gas inlet of the dust and ammonia removal tail gas treatment device.

4. The system for preparing slow-release urea according to claim 3, wherein the first conveying pipeline comprises a liquid conveying pump, an ammonium oxalate-containing solution supply pipeline, a urea solution supply pipeline, an oxalic acid solution inlet pipeline and a flash tank;

a liquid inlet and a liquid outlet of the dust-removing and ammonia-removing tail gas treatment device are respectively communicated with the outlet end of the oxalic acid solution liquid inlet pipeline and the inlet end of the ammonium oxalate-containing solution supply pipeline;

the first liquid inlet, the second liquid inlet and the liquid outlet of the flash tank are respectively communicated with the outlet end of the ammonium oxalate-containing solution supply pipeline, the outlet end of the urea solution supply pipeline and the inlet of the liquid delivery pump;

and the outlet of the liquid delivery pump is communicated with the feed inlet of the urea evaporation device.

5. The system for preparing slow-release urea according to claim 1, wherein the first conveying pipeline comprises a liquid conveying pump, an ammonia-containing wastewater supply pipeline, an oxalic acid supply pipeline, a urea solution supply pipeline and a flash tank;

the outlet end of the ammonia-containing wastewater supply pipeline and the outlet end of the oxalic acid supply pipeline are both communicated with a first liquid inlet of the flash tank;

a second liquid inlet and a second liquid outlet of the flash tank are respectively communicated with the outlet end of the urea solution supply pipeline and the inlet of the liquid delivery pump;

and the outlet of the liquid delivery pump is communicated with the feed inlet of the urea evaporation device.

6. The system for the preparation of urea for extended release of claim 4 or 5, further comprising a first return conduit;

the inlet end of the first return pipeline is communicated with the gas outlet of the flash tank.

7. The system for preparing slow-release urea according to claim 1, wherein the second conveying pipeline comprises a melting pump, and an inlet and an outlet of the melting pump are respectively communicated with a discharge hole of the urea evaporation device and a feed hole of the urea granulation device.

8. The system for preparing urea for slow release according to claim 1, wherein said purge cooling circuit comprises an air booster, the outlet of which communicates with the air inlet of said urea granulation device.

9. The system for preparing urea for extended release of claim 1, further comprising a second return conduit;

and the inlet end of the second return pipeline is communicated with the air outlet of the urea evaporation device.

10. A preparation method of slow-release urea is characterized by comprising the following steps:

preparing an ammonium oxalate-containing solution;

mixing the ammonium oxalate-containing solution with 65-85 wt% of urea solution to obtain a mixed solution;

feeding the mixed solution into a urea evaporation device through a first conveying pipeline for evaporation and concentration to obtain 95-99.7 wt% molten liquid;

and feeding the molten liquid into the urea granulation device through a second conveying pipeline for granulation so as to obtain a urea product.

Technical Field

The invention relates to the technical field of fertilizer processing, in particular to a preparation system and a preparation method of slow-release urea.

Background

Nitrogen is the most important nutrient element for crop growth, and urea is used as a main solid nitrogen fertilizer and is widely used due to the advantages of high nitrogen content (about 46%), stable property, easy storage and transportation, convenient application, no adverse effect on soil after long-term application, suitability for various soils and crops and the like.

However, urea is in a molecular state before conversion and cannot be adsorbed by soil, urea solution can run off along with water after being dissolved, ammonia formed after conversion is volatile, loss in soil is too high, the utilization rate of urea in China is lower than 30% at present, the fertilizer efficiency is only about 50 days, a large amount of economic loss is caused, the ecological environment is seriously damaged, value-added urea products are researched, the slow release performance of the urea products is improved, and the improvement of the utilization rate of nitrogen in soil is a practical problem to be solved urgently in the current agricultural field.

Disclosure of Invention

The invention provides a preparation system and a preparation method of slow-release urea, aiming at improving the slow-release performance of a urea product so as to improve the utilization rate of nitrogen in soil.

The invention provides a preparation system of slow-release urea, which comprises a first conveying pipeline, a second conveying pipeline, a purging and cooling pipeline, a urea evaporation device and a urea granulation device, wherein the first conveying pipeline is connected with the urea evaporation device;

the first conveying pipeline is communicated with a feed inlet of the urea evaporation device and is used for conveying mixed liquor containing ammonium oxalate solution and urea solution into the urea evaporation device for evaporation and concentration;

the discharge port of the urea evaporation device is communicated with the feed port of the urea granulation device through the second conveying pipeline and is used for feeding the evaporated and concentrated melt liquid into the urea granulation device for granulation so as to obtain a urea product;

and the blowing and cooling pipeline is communicated with an air inlet of the urea granulation device and is used for sending compressed air into the urea granulation device.

According to the preparation system of the slow-release urea provided by the invention, the first conveying pipeline comprises a liquid conveying pump, an ammonium oxalate-containing solution supply pipeline and a urea solution supply pipeline;

the outlet end of the ammonium oxalate-containing solution supply pipeline and the outlet end of the urea solution supply pipeline are both communicated with the inlet of the liquid delivery pump;

and the outlet of the liquid delivery pump is communicated with the feed inlet of the urea evaporation device.

The invention provides a preparation system of slow release urea, which also comprises a dust and ammonia removal tail gas treatment device;

and the gas outlet of the urea granulation device is communicated with the gas inlet of the dust and ammonia removal tail gas treatment device.

According to the preparation system of the slow-release urea provided by the invention, the first conveying pipeline comprises a liquid conveying pump, an ammonium oxalate-containing solution supply pipeline, a urea solution supply pipeline, an oxalic acid solution inlet pipeline and a flash evaporation tank;

a liquid inlet and a liquid outlet of the dust-removing and ammonia-removing tail gas treatment device are respectively communicated with the outlet end of the oxalic acid solution liquid inlet pipeline and the inlet end of the ammonium oxalate-containing solution supply pipeline;

the first liquid inlet, the second liquid inlet and the liquid outlet of the flash tank are respectively communicated with the outlet end of the ammonium oxalate-containing solution supply pipeline, the outlet end of the urea solution supply pipeline and the inlet of the liquid delivery pump;

and the outlet of the liquid delivery pump is communicated with the feed inlet of the urea evaporation device.

According to the preparation system of the slow release urea provided by the invention, the first conveying pipeline comprises a liquid conveying pump, an ammonia-containing wastewater supply pipeline, an oxalic acid supply pipeline, a urea solution supply pipeline and a flash tank;

the outlet end of the ammonia-containing wastewater supply pipeline and the outlet end of the oxalic acid supply pipeline are both communicated with a first liquid inlet of the flash tank;

a second liquid inlet and a second liquid outlet of the flash tank are respectively communicated with the outlet end of the urea solution supply pipeline and the inlet of the liquid delivery pump;

and the outlet of the liquid delivery pump is communicated with the feed inlet of the urea evaporation device.

According to the preparation system of the slow release urea provided by the invention, the preparation system of the slow release urea further comprises a first return pipeline;

the inlet end of the first return pipeline is communicated with the gas outlet of the flash tank.

According to the preparation system of the slow-release urea provided by the invention, the second conveying pipeline comprises a melting pump, and an inlet and an outlet of the melting pump are respectively communicated with a discharge hole of the urea evaporation device and a feed hole of the urea granulation device.

According to the preparation system of the slow release urea provided by the invention, the purging and cooling pipeline comprises an air supercharger, and the outlet of the air supercharger is communicated with the air inlet of the urea granulation device.

According to the preparation system of the slow release urea provided by the invention, the preparation system of the slow release urea further comprises a second return pipeline;

and the inlet end of the second return pipeline is communicated with the air outlet of the urea evaporation device.

The invention also provides a preparation method of the slow release urea, which comprises the following steps:

preparing an ammonium oxalate-containing solution;

mixing the ammonium oxalate-containing solution with 65-85 wt% of urea solution to obtain a mixed solution;

feeding the mixed solution into a urea evaporation device through a first conveying pipeline for evaporation and concentration to obtain 95-99.7 wt% molten liquid;

and feeding the molten liquid into the urea granulation device through a second conveying pipeline for granulation so as to obtain a urea product.

According to the preparation system and the preparation method of the slow release urea, the fertilizer with slow release function and quick-acting function can be formed by combining the ammonium oxalate and the urea, the fertilizer efficiency time is prolonged, and the effective utilization rate of nitrogen in the product can be improved by over 60%; the mixture ratio of the ammonium oxalate and the urea is flexible, and products with different ammonium oxalate contents can be produced according to requirements; the product has large particles and high strength; the required sustained-release raw materials are safe and reliable, have wide sources and can be suitable for large-scale production.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a system for preparing slow-release urea provided by the present invention;

FIG. 2 is a second schematic structural diagram of a system for preparing urea with sustained release provided by the present invention;

FIG. 3 is a third schematic diagram of the structure of a system for preparing slow-release urea provided by the present invention;

FIG. 4 is a schematic flow chart of a process for preparing slow release urea provided by the present invention.

Reference numerals:

100: a system for the preparation of slow release urea; 1: a urea evaporation device; 2: a urea granulation device; 3: a liquid delivery pump; 4: a supply line for an ammonium oxalate-containing solution; 5: a urea solution supply line; 6: a dust and ammonia removal tail gas treatment device; 7: a flash tank; 8: an ammonia-containing wastewater supply line; 9: an oxalic acid supply conduit; 10: a first return conduit; 11: a melt pump; 12: an air supercharger; 13: a second return conduit; 14: and an oxalic acid solution inlet pipeline.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; the connection can be mechanical connection or point connection; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Referring to fig. 1 to 3, a slow release urea preparation system 100 according to the present invention is described, as shown in fig. 1, including a first delivery line, a second delivery line, a purge cooling line, a urea evaporation device 1, and a urea granulation device 2.

As shown in fig. 1, the first conveying pipeline is communicated with a feed inlet of the urea evaporation device 1, and is used for feeding the mixed solution of the ammonium oxalate-containing solution and the urea solution into the urea evaporation device 1 for evaporation and concentration. The ratio of ammonium oxalate to urea may be set to any ratio according to actual needs. Optionally, in this embodiment, the urea solution is 65-85 wt% of urea solution; further, in this embodiment, the urea solution is 70-80 wt% of urea solution. Alternatively, in this embodiment, the ammonium oxalate containing solution may include at least one of an ammonium oxalate solution and an ammonium oxalate containing urea solution. The mixed solution of the ammonium oxalate-containing solution and the urea solution is an ammonium oxalate-containing urea solution, and the ammonium oxalate-containing urea solution is sent to the urea evaporation device 1 for evaporation concentration, optionally, in this embodiment, the ammonium oxalate-containing urea solution is evaporated and concentrated to 95-99.7 wt%, so as to obtain a molten solution.

Optionally, as shown in fig. 1, in this embodiment, the slow release urea preparation system 100 further includes a second return pipeline 13; the inlet end of the second return duct 13 communicates with the outlet of the urea evaporation device 1. The gases produced by the urea evaporation plant 1 can be returned to the production system (of which the system 100 for the slow release urea preparation can be part) via a second return conduit 13.

As shown in fig. 1, a discharge port of the urea evaporation device 1 is communicated with a feed port of the urea granulation device 2 through a second conveying pipeline, and is used for feeding the evaporated and concentrated melt into the urea granulation device 2 for granulation to obtain a urea product. The molten liquid obtained by the evaporation and concentration of the urea evaporation device 1 is sent to the urea granulation device 2 for granulation through a second conveying pipeline, and a urea product is output. Specifically, as shown in fig. 1, in the present embodiment, the second conveying pipeline includes a melting pump 11, an inlet and an outlet of the melting pump 11 are respectively communicated with a discharge port of the urea evaporation device 1 and a feed port of the urea granulation device 2, and the molten liquid is sent to the urea granulation device 2 through the melting pump 11.

As shown in fig. 1, the purge cooling line is connected to an air inlet of the urea granulation apparatus 2 for feeding compressed air into the urea granulation apparatus 2. Specifically, as shown in fig. 1, in the present embodiment, the purge cooling line includes an air supercharger 12, and an outlet of the air supercharger 12 is communicated with an air inlet of the urea granulation device 2, and after passing through the air supercharger 12, the purge cooling line is sent to the urea granulation device 2 to purge and cool the urea. And the ammonia-containing tail gas generated by the urea granulation device 2 can be sent to a tail gas treatment system of the production system and then discharged.

The first conveying pipeline can convey a mixed solution of an ammonium oxalate-containing solution and a urea solution into the urea evaporation device 1, wherein the ammonium oxalate-containing solution can be an ammonium oxalate solution prepared by using ammonium oxalate, and specifically, as shown in fig. 1, the first conveying pipeline comprises a liquid conveying pump 3, an ammonium oxalate-containing solution supply pipeline 4 and a urea solution supply pipeline 5; the outlet end of the ammonium oxalate-containing solution supply pipeline 4 and the outlet end of the urea solution supply pipeline 5 are both communicated with the inlet of the liquid delivery pump 3; the outlet of the liquid delivery pump 3 is communicated with the feeding hole of the urea evaporation device 1. The ammonium oxalate solution prepared from ammonium oxalate is fed into the system 100 for preparing slow-release urea through the supply pipe 4 containing the ammonium oxalate solution.

The ammonium oxalate-containing solution may also be an ammonium oxalate solution discharged from the ammonia-containing tail gas washed by oxalic acid, and specifically, as shown in fig. 2, in this embodiment, the slow-release urea preparation system 100 further includes a dust removal and ammonia removal tail gas treatment device 6; the gas outlet of the urea granulation device 2 is communicated with the gas inlet of the dust and ammonia removal tail gas treatment device 6; and the first conveying pipeline comprises a liquid conveying pump 3, an ammonium oxalate-containing solution supply pipeline 4, a urea solution supply pipeline 5, an oxalic acid solution inlet pipeline 14 and a flash tank 7; a liquid inlet and a liquid outlet of the dust-removing and ammonia-removing tail gas treatment device 6 are respectively communicated with an outlet end of an oxalic acid solution inlet pipeline 14 and an inlet end of an ammonium oxalate-containing solution supply pipeline 4; a first liquid inlet, a second liquid inlet and a liquid outlet of the flash tank 7 are respectively communicated with the outlet end of the ammonium oxalate-containing solution supply pipeline 4, the outlet end of the urea solution supply pipeline 5 and the inlet of the liquid delivery pump 3; the outlet of the liquid delivery pump 3 is communicated with the feeding hole of the urea evaporation device 1. The liquid after the oxalic acid is used for washing ammonia is comprehensively utilized, so that the environmental pollution is reduced, and the efficient slow-release urea product is produced.

Further, as shown in fig. 2, in the embodiment, the system 100 for preparing slow release urea further includes a first return pipeline 10; the inlet end of the first return conduit 10 communicates with the outlet of the flash tank 7. The gas produced by the flash tank 7 can be returned to the production system via a first return conduit 10.

For example, as shown in fig. 2, the ammonium oxalate-containing solution is derived from ammonia-containing tail gas generated by washing a urea granulation device 2 with oxalic acid, the urea granulation device 2 generates ammonia-containing tail gas, ammonia and urea dust in the ammonia-containing tail gas are washed with oxalic acid solution in a dust removal and ammonia removal tail gas treatment device 6 to generate an ammonium oxalate-containing urea solution, the ammonium oxalate-containing urea solution and 65-85 wt% of the urea solution enter a flash evaporation tank 7 to be flashed, the flashed ammonium oxalate-containing urea solution is sent to a urea evaporation device 1 by a liquid delivery pump 3, the ammonium oxalate-containing urea solution is evaporated and concentrated to 95-99.7 wt%, and is sent to the urea granulation device 2 by a melt pump 11 to be granulated, and a urea product is output; the gas that flash drum 7 and urea evaporation plant 1 produced returns the production system respectively, and the air is after air booster 12, send into urea prilling granulator 2 and sweep cooling urea, and the tail gas that contains ammonia that produces sends to and removes ammonia tail gas processing apparatus 6 and discharges the atmosphere after removing ammonia, and exhaust ammonium oxalate solution circulates back to flash drum 7. When the ammonium oxalate generated from ammonia and urea dust in the tail gas from the washing with oxalic acid cannot satisfy the amount of ammonium oxalate required by the urea product, ammonium oxalate can be added into the flash tank 7 to satisfy the mixture ratio of ammonium oxalate and urea in the urea product.

The ammonium oxalate-containing solution can also be prepared by adding oxalic acid into a part of waste liquor containing at least one of ammonia or urea in urea production to generate an ammonium oxalate solution, specifically, as shown in fig. 3, in the present embodiment, the first conveying pipeline comprises a liquid conveying pump 3, an ammonia-containing wastewater supply pipeline 8, an oxalic acid supply pipeline 9, a urea solution supply pipeline 5 and a flash tank 7; the outlet end of the ammonia-containing wastewater supply pipeline 8 and the outlet end of the oxalic acid supply pipeline 9 are both communicated with a first liquid inlet of the flash tank 7; a second liquid inlet and a second liquid outlet of the flash tank 7 are respectively communicated with the outlet end of the urea solution supply pipeline 5 and the inlet of the liquid delivery pump 3; the outlet of the liquid delivery pump 3 is communicated with the feeding hole of the urea evaporation device 1.

For example, as shown in fig. 3, oxalic acid is added into ammonia-containing wastewater to generate an ammonium oxalate solution, the ammonium oxalate solution and 65-85 wt% of urea solution enter a flash evaporation tank 7 to be flashed, the flashed ammonium oxalate-containing urea solution is sent to a urea evaporation device 1 through a liquid delivery pump 3, the ammonium oxalate-containing urea solution is evaporated and concentrated to 95-99.7 wt%, and then is sent to a urea granulation device 2 through a melt pump 11 to be granulated, and a urea product is output; the gas that flash drum 7 and urea evaporation plant 1 produced returns the production system respectively, and the air is after air booster 12, send into urea prilling granulator 2 and sweep cooling urea, and the tail gas that contains ammonia that produces can send to and remove ammonia tail gas processing system emission atmosphere after removing ammonia, and exhaust ammonium oxalate solution circulates back to flash drum 7. In order to maintain water balance and reduce energy consumption of the urea evaporation device 1, the amount of ammonia-containing wastewater added is limited, and when the amount of ammonium oxalate generated by ammonia-containing wastewater and oxalic acid cannot meet the amount of ammonium oxalate required by a urea product, ammonium oxalate can be added into the flash tank 7 to meet the proportion of ammonium oxalate and urea in the urea product.

The slow release urea preparation system 100 has the following advantages:

1. the slow-release urea preparation system 100 can comprehensively utilize the liquid obtained after ammonia is washed by oxalic acid, so that the environment pollution is reduced, and a high-efficiency slow-release urea product is produced;

2. the ammonium oxalate is a good slow-release nitrogen fertilizer, is nontoxic and has a quick-acting function, the ammonium oxalate and the urea can be complemented with each other, and the ammonium oxalate and the urea can be combined to form a fertilizer with slow-release function and quick-acting function, so that the fertilizer efficiency time can be prolonged, and the effective utilization rate of nitrogen in the product is improved by over 60 percent;

3. the existing urea production process device can be directly utilized or simply modified, so that the equipment investment cost is low;

4. the mixture ratio of the ammonium oxalate and the urea is flexible, and products with different ammonium oxalate contents can be produced according to requirements;

5. the product produced by the slow-release urea preparation system 100 has large particles and high strength;

6. the slow-release raw material oxalic acid or ammonium oxalate required by the preparation system 100 of the slow-release urea is safe and reliable, has wide sources and can be suitable for large-scale production.

The invention also provides a preparation method of the slow release urea, which is realized based on the preparation system of the slow release urea as described above, and as shown in fig. 4, the preparation method of the slow release urea comprises steps S410 to S440.

Step S410: an ammonium oxalate containing solution is prepared.

Specifically, the ammonium oxalate-containing solution can be prepared in various ways, for example, by preparing an ammonium oxalate solution from ammonium oxalate; for another example, adding oxalic acid into a part of waste liquid containing at least one of ammonia or urea in urea production to generate an ammonium oxalate solution; for another example, the ammonium oxalate solution discharged from the oxalic acid washing ammonia-containing tail gas is recycled.

Step S420: and mixing the ammonium oxalate-containing solution with 65-85 wt% of urea solution to obtain a mixed solution.

Step S430: and (3) feeding the mixed solution into a urea evaporation device through a first conveying pipeline for evaporation concentration to obtain 95-99.7 wt% molten liquid.

Specifically, the flashed urea solution containing ammonium oxalate is delivered into a urea evaporation device by a liquid delivery pump, and is evaporated and concentrated to 95-99.7 wt%

Step S440: and feeding the molten liquid into the urea granulation device through a second conveying pipeline for granulation so as to obtain a urea product.

Specifically, the melt after evaporation and concentration is sent to a urea granulation system through a melting pump, and is granulated and output as a urea product.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.