A device for preparing low-content biuret automotive urea solution and its application method

Abstract

A device for preparing a low-content biuret automotive urea solution and an application method thereof are urea production and chemical solution preparation technologies. The device uses molten urine as a raw material to produce high-quality automotive urea solution by adjusting the production process.

Description

Technical Field

[0001] The invention relates to urea production and chemical solution preparation technology, in particular to a device for preparing low-content biuret automotive urea solution and an application method. Background Art

[0002] Currently, heavy-duty trucks, buses, and other diesel vehicles must meet China IV emission standards by using a suitable SCR system for exhaust treatment. This system utilizes urea solution to treat nitrogen oxides in the exhaust, making automotive urea solution a must-have for heavy-duty trucks and buses meeting China IV emission standards. SCR technology requires minimal engine modifications, has low fuel and oil requirements, offers advantages in continuous technology upgrades, and eliminates the risk of catalyst clogging. Therefore, SCR technology is the most suitable emission reduction technology for heavy-duty diesel vehicles in my country's national conditions.

[0003] The preparation of automotive urea solution is one of the important conditions for the implementation of SCR technology in diesel vehicles such as heavy-duty trucks and buses. Automotive urea solution is a urea aqueous solution with a concentration of 32.5% and the solvent is ultrapure water. The production raw materials are special raw materials for automotive urea and ultrapure water. The key point lies in the purity of the raw materials. At present, the purity requirements of automotive urea are very high. Ordinary urea or urine cannot meet the high purity requirements of automotive urea. The quality of automotive urea products on the market is difficult to meet international standards, especially the problem of excessive biuret in automotive urea. From the perspective of production technology, the preparation of automotive urea is particularly critical. Only through strict process control and scientific automotive urea production technology can the biuret content in automotive urea be as low as 0.6%-0.7%. The biuret content in the automotive urea solution with a concentration of 32.5% is as low as 0.23%, which is far lower than the national standard GB29518-2013 "Urea Aqueous Solution - Nitrogen Oxide Reductant for Diesel Engines (AUS32)" which requires a biuret content of 0.3% (mass) in the urea aqueous solution. Summary of the Invention

[0004] The purpose of the present invention is to provide a device for preparing a low-content biuret automotive urea solution and an application method thereof. The device uses molten urine as a raw material to produce high-quality automotive urea solution by adjusting the production process. The purpose of the present invention is achieved in that the bottom of the urea synthesis tower is connected to an ammonia preheater and a carbon dioxide pipeline respectively, the middle of the urea synthesis tower is connected to the upper part of the stripping tower, the top of the stripping tower is connected to a high-pressure methylammonium separator, the lower end of the connecting pipeline between the two is equipped with a high-pressure methylammonium condenser, and the pipeline connecting the two is also connected to a medium-pressure absorption The bottom of the collection tower is connected, and a high-pressure methylammonium preheater and a high-pressure methylammonium pump are installed on the connected pipeline; the bottom of the stripping tower is connected to the top of the medium-pressure decomposer, the top of the medium-pressure decomposer is connected to the vacuum pre-concentrator, and the bottom of the medium-pressure decomposer is connected to the top of the low-pressure decomposer; the top of the high-pressure methylammonium separator is connected to the bottom of the medium-pressure decomposer, and the bottom of the high-pressure methylammonium separator is connected to the pipeline at the bottom of the urea synthesis tower; the upper part of the medium-pressure absorption tower is connected to the medium-pressure condenser, the lower end of the medium-pressure condenser is connected to the upper end of the vacuum pre-concentrator, and the top of the medium-pressure absorption tower is connected to the ammonia condenser The ammonia condenser is connected to the liquid ammonia storage tank, and the pipeline below the liquid ammonia storage tank is connected to the pipeline at the upper end of the medium-pressure absorption tower, with an ammonia booster pump installed in the middle; the upper end of the medium-pressure absorption tower is connected to the lower end of the medium-pressure inert gas scrubber, and an ammonia solution pump is installed on the pipeline in the middle. The upper end of the medium-pressure absorption tower is connected to the lower end of the ammonia preheater, and a high-pressure ammonia pump is installed on the pipeline in the middle; the lower end of the medium-pressure inert gas scrubber is connected to the liquid ammonia storage tank; the top of the low-pressure decomposer is connected to the lower end of the ammonia preheater, and the bottom end of the low-pressure decomposer is connected to the top of the vacuum pre-concentrator; the upper end of the ammonia preheater is connected to the low-pressure The lower end of the condenser is connected, the upper end of the low-pressure condenser is connected to the carbon ammonium liquid tank, a gas ammonia absorption tower is installed on the carbon ammonium liquid tank, the carbon ammonium liquid tank is connected to the pipeline connecting the medium-pressure decomposer and the vacuum pre-concentrator by a pipeline, and a medium-pressure carbon ammonium liquid pump is installed on the pipeline of the carbon ammonium liquid tank; the bottom end of the vacuum pre-concentrator is connected to the first vacuum concentrator, and an 85% urine pump is installed on the pipeline connecting the two, the first vacuum concentrator is connected to the first vacuum separation concentrator, the first vacuum separation concentrator is connected to the second vacuum concentrator, and the second vacuum concentrator is connected to the second vacuum separation concentrator.

[0005] The bottom end of the second vacuum separation concentrator is connected to the rough preparation storage tank, and a molten urine pump is installed on the middle pipeline; the bottom end of the bottom rough preparation storage tank is connected to the vehicle urea stock solution storage tank, and a urine pump is installed on the middle pipeline between the two. The vehicle urea stock solution storage tank is connected to the blending tank, and a urine pump is installed on the pipeline connecting the two.

[0006] The top of the rough preparation storage tank at the bottom is connected to the top of the blending tank; a high-purity water pump is installed on the pipeline connecting the two, the high-purity water pump is connected to the high-purity water storage tank, and the top of the high-purity water storage tank is connected to the EDI water making equipment; the top of the finished product tank is connected to the bottom of the blending tank, and the blending tank pump and ultrafiltration filter element are installed in sequence between the two, and the finished product pump is installed at the bottom of the finished product tank, and the finished product pump is connected to the packaging line by a pipeline.

[0007] The application method of the present invention comprises the following steps: raw liquid ammonia enters a liquid ammonia storage tank, is further pressurized by an ammonia booster pump and a high-pressure ammonia pump, and then is sent to a urea synthesis tower through an ammonia preheater. The liquid ammonia entering the synthesis tower is mixed with carbon dioxide pressurized by a compressor and then reacted in the urea synthesis tower. The reaction product exiting the synthesis tower flows to a stripping tower for stripping. During the stripping process, the gas at the top is mixed with the liquid from the medium-pressure absorption tower sent by the high-pressure methylammonium pump and then enters a high-pressure methylammonium condenser to produce by-product steam. The condensed gas-liquid mixture enters a high-pressure methylammonium separator for separation. The separated liquid phase is returned to the synthesis tower through a methylammonium ejector, and the gas is sent to the bottom of the medium-pressure decomposer through a pressure control valve.

[0008] The solution leaving the bottom of the stripping tower is decompressed to 17.6×10 5 Pa (absolute) enters the medium-pressure decomposer, and the solution enters the middle part for heating and decomposition after being separated at the top. The temperature at the bottom of the medium-pressure decomposer is controlled at 150-154°C, and the liquid level is controlled at 40-60%. The gas coming out of the top of the medium-pressure decomposer is mixed with the ammonium carbonate liquid from the medium-pressure ammonium carbonate liquid pump and enters the shell side of the vacuum pre-concentrator for condensation and absorption. The vapor-liquid mixture coming out of the vacuum pre-concentrator enters the medium-pressure condenser. The mixture from the medium-pressure condenser flows into the lower part of the medium-pressure absorption tower. The gas separated from the solution enters the upper distillation section, where CO2 is absorbed and NH3 is distilled off. The gaseous ammonia and inert gas coming out of the top of the medium-pressure absorption tower enter the ammonia condenser for condensation. The condensed liquid ammonia enters the liquid ammonia storage tank. The inert gas saturated with ammonia is sent to the absorption section of the medium-pressure inert gas scrubber, where it is washed and absorbed by countercurrent water to recover the gaseous ammonia. The inert gas is discharged from the tower.

[0009] The solution leaving the bottom of the medium pressure decomposer is decompressed to 5.0×10 5 Pa (absolute) enters the low-pressure decomposer, and the solution is separated at the top and then enters the middle part for heating and decomposition. The temperature at the bottom of the low-pressure decomposer is controlled at 134-138°C, and the liquid level is controlled at 10-30%. The gas coming out of the top of the low-pressure decomposer enters the ammonia preheater and the low-pressure condenser in turn into the ammonium carbonate liquid storage tank. The ammonium carbonate liquid is returned to the shell side of the vacuum pre-concentrator through the medium-pressure ammonium carbonate liquid pump. The gas that is not condensed and absorbed is washed in the low-pressure inert gas scrubber and then discharged.

[0010] The solution coming out from the bottom of the low-pressure decomposer is decompressed to 0.66x10 5Pa (absolute) enters the vacuum pre-concentrator. The upper part of the vacuum pre-concentrator is a separator. When the solution from the bottom of the low-pressure decomposer enters the separator, the flash gas released is separated into vapor and liquid here. The solution enters the heating section of the pre-concentrator, and the liquid level is controlled at 50-70%. The urea solution from the bottom of the vacuum pre-concentrator is sent to the first vacuum concentrator of the evaporation system through the urea solution pump. The water in the solution is evaporated by heating. Its operating pressure is 0.65x10 5 Pa (absolute), the temperature is 125-130 ℃, and the gas-liquid mixture from the first vacuum separation concentrator is separated into gas and liquid in the first vacuum separation concentrator. The urea solution from the first vacuum separation concentrator enters the second vacuum concentrator, which has an operating pressure of 0.05x 105Pa (absolute) and a temperature of 133-137 ℃. The water in the solution is evaporated by heating, and then enters the second vacuum separation concentrator for gas-liquid separation. The separated gas from the first and second stages is condensed and absorbed and then sent to the analytical system. The liquid enters the bottom of the separation concentrator, with the temperature controlled at 133-135 ℃ and the liquid level controlled at 50-70%. It is then sent to the vehicle urea crude preparation tank via the molten urine pump.

[0011] Ultrapure water produced from desalted water by the EDI water production equipment is stored in an ultrapure water storage tank and pumped into the rough urea tank for automotive use via an ultrapure water pump. After the liquid level in the rough urea tank rises to 30%, a portion of the urine from the second vacuum separation concentrator is pumped into the rough urea tank via a molten urea pump. Urine and high-purity water are roughly mixed at a volume flow rate of 1:1 and then pumped into the raw urea tank via a urine pump. From the raw urea tank, the urine pump pumps the urine to a blending tank, where it is mixed with high-purity water to create a urea solution with a urine concentration of approximately 32.5%. The prepared urea solution is then pumped to the finished urea tank via a blending tank pump and ultrafiltration filter element, and then packaged via a finished product pump.

[0012] The significance of the invention:

[0013] 1. The present invention is to produce molten urea with low biuret content after the raw materials liquid ammonia and CO2 react under high temperature and high pressure conditions, and then pass through a stripping tower, a medium-pressure decomposer, a low-pressure decomposer, a vacuum pre-concentrator, a first evaporation stage, and a second evaporation stage. By mixing with ultrapure water, a urea solution for automobiles with low biuret content is produced.

[0014] 2. In order to reduce the content of biuret in the product, the system before the device is adjusted first. The specific process adjustment measures are as follows: reduce the temperature and liquid level of the medium-pressure decomposer. The temperature of the medium-pressure decomposer is adjusted from 155-160℃ to 150-154℃, and the liquid level of the medium-pressure decomposer is adjusted from 50%-80% to 40%-60%; the temperature of the low-pressure decomposer is adjusted from 138-143℃ to 134-138℃, and the liquid level of the low-pressure decomposer is adjusted from 50%-80% to 10%-30%.

[0015] 3. In the ammonia stripping urea process, 61.8% of the biuret in urea granules is produced during the pre-concentration and evaporation stages one and two, and the granulation process in the upper tower. By adjusting the process parameters, the biuret content of the molten urine at the outlet of the molten urea pump was reduced from 0.9% to 0.7%. This was achieved by adjusting the evaporation system, adjusting the liquid level of the falling film vacuum pre-concentrator to 50%-70%, the vacuum (0.65x105 Pa) and temperature (125-130°C) of the evaporation stage one, the vacuum (0.05x 105 Pa) and temperature (133-137°C) of the evaporation stage one, and the temperature (133-135°C) and liquid level (133-135°C) of the separator storage tank in the evaporation stage two.

[0016] 4. Innovation in the extraction of liquid urine using a molten urine pump. Since the urine is directly mixed with ultrapure water after extraction, the urine concentration will quickly drop by about 50% from 98-99%, and the urea solution temperature will drop from 135°C to about 70°C. Through this process, firstly, the urine concentration will drop significantly, which will prevent urea from forming biuret according to the reaction mechanism; secondly, the biuret reaction is an endothermic reaction, and a significant drop in urine temperature will be unfavorable for the formation of biuret.

[0017] 5. The innovative molten urine pump extracts liquid urine. The ammonia content in the molten urine will be significantly lower than that extracted after pre-concentration and evaporation. This can ensure that the ammonia content in the prepared automotive urea solution is the lowest, effectively improving the quality of the automotive urea solution.

[0018] 6. Innovation in extracting liquid urine from the molten urine pump can avoid the biuret produced by the molten urine passing through the upper tower pipeline and the spraying granulation process. In this process, the biuret content in urea can be increased by 0.1%.

[0019] 7. By extracting liquid urine in the molten urine pump, the continuous production of automotive urea solution can be achieved, avoiding the repetition of processes caused by re-dissolving the molten urine to prepare automotive urea solution after solidification of urea granules. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A schematic diagram of a production process for preparing a low-content biuret automotive urea solution, in which 1, a urea synthesis tower 2, a stripping tower 3, a high-pressure methylammonium condenser 4, a high-pressure methylammonium separator 5, a methylammonium ejector 6, a high-pressure methylammonium preheater 7, a medium-pressure decomposer 8, a medium-pressure condenser 9, a medium-pressure absorption tower 10, an ammonia condenser 11, a liquid ammonia storage tank 12, a medium-pressure inert gas scrubber 13, a high-pressure methylammonium pump 14, an ammonia booster pump 15, a high-pressure ammonia pump 16, an ammonia solution pump 17, a low-pressure decomposer 18, an ammonia preheater 19, a low-pressure condenser 20, a carbon Ammonium liquid tank 21, gaseous ammonia absorption tower 22, medium-pressure ammonium carbonate liquid pump 23, vacuum pre-concentrator 24, 85% urine pump 25, first vacuum concentrator 26, first vacuum separation concentrator 27, second vacuum concentrator 28, second vacuum separation concentrator 29, molten urine pump 30, crude preparation storage tank 31, urine pump 32, high-purity water pump 33, high-purity water storage tank 34, EDI water production equipment 35, automotive urea raw liquid storage tank 36, urine pump 37, blending tank 38, blending tank pump 39, ultrafiltration filter element 40, finished product tank 41, finished product pump. DETAILED DESCRIPTION

[0021] Example 1. The device of the present invention is connected to the ammonia preheater 18 and the carbon dioxide pipeline at the bottom of the urea synthesis tower 1, the middle of the urea synthesis tower 1 is connected to the upper part of the stripping tower 2, the top of the stripping tower 2 is connected to the high-pressure methylammonium separator 4, and the lower end of the connecting pipeline between the two is installed with a high-pressure methylammonium condenser 3. The pipeline connecting the two is also connected to the bottom of the medium-pressure absorption tower 9, and the high-pressure methylammonium preheater 6 and the high-pressure methylammonium pump 13 are installed on this connected pipeline; the bottom of the stripping tower 2 is connected to The top of the medium-pressure decomposer 7 is connected, the top of the medium-pressure decomposer 7 is connected to the vacuum pre-concentrator 23, and the bottom of the medium-pressure decomposer 7 is connected to the top of the low-pressure decomposer 17; the top of the high-pressure methylammonium separator 4 is connected to the bottom of the medium-pressure decomposer 7, and the bottom of the high-pressure methylammonium separator 4 is connected to the pipeline at the bottom of the urea synthesis tower 1; the upper part of the medium-pressure absorption tower 9 is connected to the medium-pressure condenser 8, the lower end of the medium-pressure condenser 8 is connected to the upper end of the vacuum pre-concentrator 23, and the top of the medium-pressure absorption tower 9 is connected to the ammonia condenser 1 0 connection; the ammonia condenser 10 is connected to the liquid ammonia storage tank 11, the pipeline below the liquid ammonia storage tank 11 is connected to the pipeline at the upper end of the medium-pressure absorption tower 9, and an ammonia booster pump 14 is installed in the middle; the upper end of the medium-pressure absorption tower 9 is connected to the lower end of the medium-pressure inert gas scrubber 12, and an ammonia solution pump 16 is installed on the pipeline in the middle; the upper end of the medium-pressure absorption tower 9 is connected to the lower end of the ammonia preheater 18, and a high-pressure ammonia pump 15 is installed on the pipeline in the middle; the lower end of the medium-pressure inert gas scrubber 12 is connected to the liquid ammonia storage tank 11; the low-pressure decomposition The top of the decomposer 17 is connected to the lower end of the ammonia preheater 18, and the bottom end of the low-pressure decomposer 17 is connected to the top of the vacuum pre-concentrator 23; the upper end of the ammonia preheater 18 is connected to the lower end of the low-pressure condenser 19, and the upper end of the low-pressure condenser 19 is connected to the carbon ammonium liquid tank 20, and a gas ammonia absorption tower 21 is installed on the carbon ammonium liquid tank 20. The carbon ammonium liquid tank 20 is connected to the pipeline connecting the medium-pressure decomposer 7 and the vacuum pre-concentrator 23 by a pipeline, and a medium-pressure carbon ammonium liquid pump 22 is installed on the pipeline of the carbon ammonium liquid tank 20.

[0022] Example 2: The bottom end of the vacuum pre-concentrator 23 is connected to the first vacuum concentrator 25, and an 85% urine pump 24 is installed on the pipeline connecting the two. The first vacuum concentrator 25 is connected to the first vacuum separation concentrator 26, the first vacuum separation concentrator 26 is connected to the second vacuum concentrator 27, and the second vacuum concentrator 27 is connected to the second vacuum separation concentrator 28.

[0023] Example 3: The bottom end of the second vacuum separation concentrator 28 is connected to the rough preparation storage tank 30, and a molten urine pump 29 is installed on the middle pipeline; the bottom end of the bottom rough preparation storage tank 30 is connected to the vehicle urea stock solution storage tank 35, and a urine pump 31 is installed on the pipeline between the two. The vehicle urea stock solution storage tank 35 is connected to the blending tank 37, and a urine pump 36 is installed on the pipeline connecting the two.

[0024] Example 4: The top of the bottom rough preparation storage tank 30 is connected to the top of the blending tank 37; a high-purity water pump 32 is installed on the pipeline connecting the two, the high-purity water pump 32 is connected to the high-purity water storage tank 33, and the top of the high-purity water storage tank 33 is connected to the EDI water making equipment 34; the top of the finished product tank 40 is connected to the bottom of the blending tank 37, and a blending tank pump 38 and an ultrafiltration filter element 39 are installed in sequence between the two, and a finished product pump 41 is installed at the bottom of the finished product tank 40, and the finished product pump 41 is connected to the packaging line by a pipeline.

[0025] Example 5, an application method of the present invention, wherein the raw liquid ammonia enters the liquid ammonia storage tank 11, is further pressurized by the ammonia booster pump 14 and the high-pressure ammonia pump 15, and then is sent to the urea synthesis tower 1 through the ammonia preheater 18. The liquid ammonia entering the synthesis tower 1 is mixed with the carbon dioxide pressurized by the compressor and then reacted in the urea synthesis tower 1. The reaction product from the synthesis tower 1 flows to the stripping tower 2 for stripping. During the stripping process, the gas at the top is mixed with the liquid from the medium-pressure absorption tower 9 sent by the high-pressure methylammonium pump 13, and then enters the high-pressure methylammonium condenser 3 to produce steam as a by-product. The condensed gas-liquid mixture enters the high-pressure methylammonium separator 4 for separation. After separation, the liquid phase returns to the synthesis tower 1 through the methylammonium ejector 5, and the gas is sent to the bottom of the medium-pressure decomposer 7 through a pressure control valve.

[0026] The solution leaving the bottom of stripping tower 2 is decompressed to 17.6×10 5 Pa (absolute) enters the medium-pressure decomposer 7. The solution is separated at the top and then enters the middle part for thermal decomposition. The temperature at the bottom of the medium-pressure decomposer 7 is controlled at 150-154°C, and the liquid level is controlled at 40-60%. The gas from the top of the medium-pressure decomposer 7 is mixed with the ammonium carbonate liquid from the medium-pressure ammonium carbonate liquid pump 22 and then enters the shell side of the vacuum pre-concentrator 23 for condensation and absorption. The vapor-liquid mixture from the vacuum pre-concentrator 23 enters the medium-pressure condenser 8. The mixture from the medium-pressure condenser 8 flows into the lower part of the medium-pressure absorption tower 9. The gas separated from the solution enters the upper distillation section, where CO2 is absorbed and NH3 is distilled off. The gaseous ammonia and inert gas from the top of the medium-pressure absorption tower 9 enter the ammonia condenser 10 for condensation. The condensed liquid ammonia enters the liquid ammonia storage tank 11. The inert gas saturated with ammonia is sent to the absorption section of the medium-pressure inert gas scrubber 12, where it is washed and absorbed by countercurrent water to recover the gaseous ammonia. The inert gas is discharged from the tower.

[0027] The solution leaving the bottom of the medium pressure decomposer 7 is decompressed to 5.0×10 5Pa (absolute) enters the low-pressure decomposer 17. The solution is separated at the top and then enters the middle part for heating and decomposition. The temperature at the bottom of the low-pressure decomposer 17 is controlled at 134-138°C, and the liquid level is controlled at 10-30%. The gas coming out of the top of the low-pressure decomposer enters the ammonia preheater 18 and the low-pressure condenser 19 in turn and enters the ammonium carbonate liquid storage tank 20. The ammonium carbonate liquid is returned to the shell side of the vacuum pre-concentrator 23 through the medium-pressure ammonium carbonate liquid pump 22. The gas that is not condensed and absorbed is washed in the low-pressure inert gas scrubber 21 and then discharged.

[0028] The solution coming out from the bottom of the low-pressure decomposer 17 is decompressed to 0.66x10 5 Pa (absolute) enters the vacuum pre-concentrator 23. The upper part of the vacuum pre-concentrator is a separator. When the solution from the bottom of the low-pressure decomposer enters the separator, the flash gas released is separated into vapor and liquid here. The solution enters the heating section of the pre-concentrator, and the liquid level is controlled at 50-70%. The urea solution from the bottom of the vacuum pre-concentrator 23 is sent to the first vacuum concentrator 25 of the evaporation system through the urea solution pump 24. The water in the solution is evaporated by heating. Its operating pressure is 0.65x10 5 Pa (absolute) and a temperature of 125-130°C, the gas-liquid mixture exiting the first vacuum concentrator undergoes gas-liquid separation in the first vacuum separation concentrator 26. The urea solution exiting the first vacuum separation concentrator 26 enters the second vacuum concentrator 27, operating at an operating pressure of 0.05 x 105 Pa (absolute) and a temperature of 133-137°C. Heating removes water from the solution, the solution then enters the second vacuum separation concentrator 28 for gas-liquid separation. The separated gases from the first and second stages are condensed and absorbed before being fed into the desorption system. The liquid enters the bottom of the separation concentrator, where its temperature is controlled at 133-135°C and the liquid level is controlled at 50-70%. It is then partially delivered to the vehicle urea crude preparation tank 30 via the molten urine pump 29.

[0029] Ultrapure water prepared from desalted water by EDI water production equipment 34 is stored in ultrapure water storage tank 33 and delivered to vehicle urea crude preparation tank 30 via ultrapure water pump 32. After the liquid level in the vehicle urea crude preparation tank rises to 30%, a portion of the urine from the second vacuum separation concentrator is delivered to the vehicle urea crude preparation tank 30 via molten urea pump 29. Urine and high-purity water are roughly mixed at a volume flow rate of 1:1 and delivered to vehicle urea stock solution storage tank 35 via urine pump 31. The urine from vehicle urea stock solution storage tank 35 is delivered to blending tank 37 via urine pump 36 to be mixed with high-purity water to form a vehicle urea solution with a urine concentration of approximately 32.5%. The prepared vehicle urea solution is then passed through blending tank pump 38 and ultrafiltration filter element 39.

Claims

1. A device for preparing a low-content biuret automotive urea solution, characterized in that: The bottom of the urea synthesis tower (1) is connected to an ammonia preheater (18) and a carbon dioxide pipeline respectively. The middle of the urea synthesis tower (1) is connected to the upper part of the stripping tower (2). The top of the stripping tower (2) is connected to a high-pressure methylammonium separator (4). The lower end of the pipeline connecting the two is equipped with a high-pressure methylammonium condenser (3). The pipeline connecting the two is also connected to the bottom of the medium-pressure absorption tower (9). The high-pressure methylammonium preheater (6) and a high-pressure methylammonium pump (13) are installed on the pipeline connected thereto. The bottom of the stripping tower (2) is connected to the top of the medium-pressure decomposer (7). The top of the medium-pressure decomposer (7) is connected to a vacuum pre-concentrator (23). The bottom of the medium-pressure decomposer (7) is connected to a low-pressure decomposer (17). The top of the high-pressure methylammonium separator (4) is connected to the bottom of the medium-pressure decomposer (7), and the bottom of the high-pressure methylammonium separator (4) is connected to the pipeline at the bottom of the urea synthesis tower (1); the upper part of the medium-pressure absorption tower (9) is connected to the medium-pressure condenser (8), the lower end of the medium-pressure condenser (8) is connected to the upper end of the vacuum pre-concentrator (23), and the top of the medium-pressure absorption tower (9) is connected to the ammonia condenser (10); the ammonia condenser (10) is connected to the liquid ammonia storage tank (11), and the pipeline below the liquid ammonia storage tank (11) is connected to the pipeline at the upper end of the medium-pressure absorption tower (9), and an ammonia booster pump (14) is installed in the middle; the upper end of the medium-pressure absorption tower (9) is connected to the lower end of the medium-pressure inert gas scrubber (12), and the middle An ammonia solution pump (16) is installed on the pipeline, the upper end of the medium-pressure absorption tower (9) is connected to the lower end of the ammonia preheater (18), and a high-pressure ammonia pump (15) is installed on the pipeline in the middle; the lower end of the medium-pressure inert gas scrubber (12) is connected to the liquid ammonia storage tank (11); the top of the low-pressure decomposer (17) is connected to the lower end of the ammonia preheater (18), and the bottom end of the low-pressure decomposer (17) is connected to the top of the vacuum pre-concentrator (23); the upper end of the ammonia preheater (18) is connected to the lower end of the low-pressure condenser (19), and the upper end of the low-pressure condenser (19) is connected to the carbon ammonium liquid tank (20), and the carbon ammonium liquid tank (20) is installed with a gas ammonia absorption tower (21), and the carbon ammonium liquid tank (20) is connected to the medium-pressure A medium-pressure ammonium carbonate liquid pump (22) is installed on the pipeline connecting the decomposer (7) and the vacuum pre-concentrator (23); the bottom end of the vacuum pre-concentrator (23) is connected to the first vacuum concentrator (25), and an 85% urine pump (24) is installed on the pipeline connecting the two. The first vacuum concentrator (25) is connected to the first vacuum separation concentrator (26), the first vacuum separation concentrator (26) is connected to the second vacuum concentrator (27), and the second vacuum concentrator (27) is connected to the second vacuum separation concentrator (28); the bottom end of the second vacuum separation concentrator (28) is connected to the crude preparation storage tank (30), and a molten urine pump (29) is installed on the pipeline between them;The bottom end of the rough preparation storage tank (30) is connected to the vehicle urea raw liquid storage tank (35), and a first urine pump (31) is installed on the pipeline between the two. The vehicle urea raw liquid storage tank (35) is connected to the blending tank (37), and a second urine pump (36) is installed on the pipeline connecting the two. The top end of the rough preparation storage tank (30) is connected to the top end of the blending tank (37); a high-purity water pump (32) is installed on the pipeline connecting the two, and the high-purity water pump (32) is connected to the high-purity water storage tank (33). The top end of the high-purity water storage tank (33) is connected to the EDI water production equipment (34); the top end of the finished product tank (40) is connected to the bottom end of the blending tank (37), and a blending tank pump (38) and an ultrafiltration filter element (39) are installed in sequence between the two. A finished product pump (41) is installed on the bottom end of the finished product tank (40), and the finished product pump (41) is connected to the packaging line by a pipeline.

2. The application method of the device for preparing a low-content biuret vehicle urea solution according to claim 1, characterized in that: The raw liquid ammonia enters the liquid ammonia storage tank (11), is pressurized by the ammonia booster pump (14) and the high-pressure ammonia pump (15), and is then sent to the urea synthesis tower (1) through the ammonia preheater (18). The liquid ammonia entering the urea synthesis tower (1) is mixed with the carbon dioxide pressurized by the compressor and reacts in the urea synthesis tower (1); the reaction product from the urea synthesis tower (1) flows to the stripping tower (2) for stripping. During the stripping process, the gas at the top is mixed with the liquid from the medium-pressure absorption tower (9) sent by the high-pressure methylammonium pump (13) and then enters the high-pressure methylammonium condenser (3) to produce steam as a by-product. The gas-liquid mixture after condensation enters the high-pressure methylammonium separator (4) for separation. After separation, the liquid phase returns to the urea synthesis tower (1) through the methylammonium ejector (5), and the gas is sent to the bottom of the medium-pressure decomposer (7) through the pressure control valve; The solution leaving the bottom of the stripping tower (2) is decompressed to 17.6×10 5 Pa enters the medium-pressure decomposer (7), and the solution is separated at the top and then enters the middle part for heating and decomposition. The temperature at the bottom of the medium-pressure decomposer (7) is controlled at 150-154°C, and the liquid level is controlled at 40-60%. The gas from the top of the medium-pressure decomposer (7) and the ammonium carbonate liquid from the medium-pressure ammonium carbonate liquid pump (22) are mixed and then enter the shell side of the vacuum pre-concentrator (23) for condensation and absorption. The vapor-liquid mixture from the vacuum pre-concentrator (23) enters the medium-pressure condenser (8), and the mixture from the medium-pressure condenser (8) flows into the lower part of the medium-pressure absorption tower (9). The solution at the bottom of the medium-pressure absorption tower (9) is condensed and absorbed by the high-pressure ammonium carbonate pump (1 3) The pressure is increased, and then the gas is sent to the high-pressure methylammonium condenser (3) after passing through the high-pressure methylammonium preheater (6). The gas separated from the solution in the medium-pressure absorption tower (9) enters the upper distillation section, where CO2 is absorbed and NH3 is distilled off. The gaseous ammonia and inert gas coming out of the top of the medium-pressure absorption tower (9) enter the ammonia condenser (10) for condensation. The condensed liquid ammonia enters the liquid ammonia storage tank (11). The inert gas saturated with ammonia is sent to the absorption section of the medium-pressure inert gas scrubber (12) and is washed and absorbed by countercurrent water to recover the gaseous ammonia. The ammonia water produced by washing is sent to the medium-pressure absorption tower (9) through the ammonia solution pump (16). The inert gas not absorbed is discharged from the tower and vented; The solution leaving the bottom of the medium pressure decomposer (7) is decompressed to 5.0×10 5 Pa enters the low-pressure decomposer (17), and the solution is separated at the top and then enters the middle part for heating and decomposition. The temperature at the bottom of the low-pressure decomposer (17) is controlled at 134-138°C, and the liquid level is controlled at 10-30%. The gas coming out of the top of the low-pressure decomposer enters the ammonia preheater (18) and the low-pressure condenser (19) in turn and enters the carbon ammonium liquid tank (20). The carbon ammonium liquid is returned to the shell side of the vacuum pre-concentrator (23) through the medium-pressure carbon ammonium liquid pump (22). The gas that is not condensed and absorbed is washed in the gas ammonia absorption tower (21) and then discharged. The solution coming out of the bottom of the low-pressure decomposer (17) is decompressed to 0.66x10 5 Pa enters the vacuum pre-concentrator (23). The upper part of the vacuum pre-concentrator is a separator. When the solution from the bottom of the low-pressure decomposer enters the separator, the flash gas released is separated into gas and liquid here. The solution enters the heating section of the pre-concentrator. The liquid level is controlled at 50-70%. The urea solution from the bottom of the vacuum pre-concentrator (23) is sent to the first vacuum concentrator (25) of the evaporation system through the 85% urine pump (24). The water in the solution is evaporated by heating. Its operating pressure is 0.65x10 5 Pa, the temperature is 125-130 ° C, the gas-liquid mixture from the first vacuum concentrator is separated into gas and liquid in the first vacuum separation concentrator (26), and the urea solution from the first vacuum separation concentrator (26) enters the second vacuum concentrator (27), the operating pressure of which is 0.05x10 5 Pa, temperature 133-137 ° C, by heating to evaporate the water in the solution, and then enter the second vacuum separation concentrator (28) for gas and liquid separation, the first and second stage separation gas condensation absorption and then sent to the analytical system, the liquid enters the bottom of the separation concentrator, the temperature is controlled at 133-135 ° C, the liquid level is controlled at 50-70%, and part of it is sent to the vehicle urea crude preparation tank (30) through the molten urine pump (29); the high-purity water prepared by the desalted water through the EDI water making equipment (34) is stored in the high-purity water storage tank (33), and is sent to the vehicle urea crude preparation tank (30) through the high-purity water pump (32). When the liquid level of the vehicle urea crude preparation tank is above After the concentration rises to 30%, part of the urine from the second vacuum separation concentrator is transported to the vehicle urea crude preparation tank (30) through the molten urine pump (29), and the urine and high-purity water are roughly mixed according to the volume flow rate of 1:1, and transported to the vehicle urea raw liquid storage tank (35) through the first urine pump (31). The vehicle urea raw liquid storage tank (35) is sent to the blending tank (37) through the second urine pump (36) to be mixed with high-purity water to form a vehicle urea solution with a urine concentration of 32.5%. The prepared vehicle urea solution is sent to the vehicle urea solution finished product tank (40) through the blending tank pump (38) and the ultrafiltration filter element (39), and then packaged through the finished product pump (41).

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