A production process for ultrapure liquid automotive urea

Abstract

This application discloses a process for producing ultrapure liquid automotive urea, comprising the following steps: Step 1: introducing a urea solution into a flash evaporator for purification to obtain molten urea, adding carbon dioxide to the lower liquid of the flash evaporator, and stripping ammonia from the molten urea with the carbon dioxide to obtain molten urine; Step 2: introducing ultrapure water and the molten urine obtained in Step 1 into a mixer in a proportional manner and mixing them uniformly to obtain mixed urine; Step 3: introducing the mixed urine obtained in Step 2 into a filtration device for filtration to obtain a urea solution for automotive use. The automotive urea produced using this production process has low biuret and ammonia content.

Description

Technical Field

[0001] The present application relates to the technical field of urea production, and specifically to a process for producing ultrapure liquid automotive urea. Background Art

[0002] Currently, heavy-duty trucks, buses, and other diesel vehicles must meet emission standards by using a suitable SCR system for exhaust treatment. This system utilizes a urea solution to treat nitrogen oxides in the exhaust. Working with the SCR catalyst, it converts harmful nitrogen oxides emitted by diesel engines into harmless water vapor and nitrogen. Therefore, automotive urea solution has become an essential product for heavy-duty trucks and buses to meet emission standards.

[0003] However, the traditional automotive urea production process still has the following defects: (1) The produced automotive urea has a high content of biuret (usually 0.3%), which is converted into water-insoluble impurities such as melamine and calcium-magnesium compounds during use. This is more serious than ordinary scale and the damage it causes to the SCR system is almost fatal; (2) The produced automotive urea also has a relatively high content of ammonia and has a noticeable ammonia smell.

[0004] Therefore, how to improve the traditional automotive urea production process to overcome the above-mentioned shortcomings is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0005] One object of the present application is to provide a process for producing ultrapure liquid automotive urea with low biuret content and low ammonia content.

[0006] To achieve the above objectives, the technical solution adopted in this application is: a process for producing ultrapure liquid automotive urea, comprising the following steps:

[0007] Step 1: inputting the urea solution into a flash evaporator for purification to obtain molten urea, and adding carbon dioxide to the lower liquid of the flash evaporator, and stripping ammonia in the molten urea by the carbon dioxide, thereby obtaining molten urine;

[0008] Step 2: Inputting ultrapure water and the molten urine in step 1 into a mixer in proportion and mixing them evenly to obtain mixed urine;

[0009] Step 3: The mixed urine in step 2 is input into a filtering device for filtration to obtain a vehicle urea solution.

[0010] Preferably, in step 2, the flow ratio of the ultrapure water to the molten urine is (1.59-1.63):1.

[0011] Preferably, in step three, the filtering device includes a fine filtration tank and an ultra-fine filtration tank; the mixed urine is first filtered through the fine filtration tank and then filtered through the ultra-fine filtration tank.

[0012] Preferably, the filtration accuracy of the fine filtration tank is 5 microns.

[0013] Preferably, the filtration accuracy of the ultra-fine filtration tank is 1 micron.

[0014] Preferably, in step 2, the preparation process of the ultrapure water is as follows: adding the soft water obtained after tap water treatment into the EDI raw water tank, starting the EDI system after controlling the liquid level to be qualified, and when the resistivity of the pure water is within the index > 10 megohms and the liquid level in the pure water tank reaches 70%, starting the pure water pump and the outlet regulating valve to control the ultrapure water to be input into the mixer.

[0015] Preferably, in step three, the mixed urine is first input into a urine trough and a density test is performed; when the density of the mixed urine is 31.0-31.2, the mixed urine is then input into the filtration device for filtration.

[0016] Preferably, in step 2, the mixer includes a first pipe, a second pipe and a third pipe; a first interface for inputting the molten urine is formed at the upper end of the first pipe, a chamber is formed radially outward at the lower end of the first pipe, and the chamber is connected to the first pipe through a truncated cone hole; the upper end of the second pipe is coaxially embedded in the chamber, and a gap is left between the outer side surface of the second pipe and the inner side surface of the chamber; the lower end of the second pipe is provided with a second interface for inputting the ultrapure water, and the upper end of the second pipe is sealed by a conical structure; a channel is formed between the outer side surface of the conical structure and the inner side surface of the truncated cone hole, and a drainage hole for connecting the channel with the second interface is provided on the conical structure; a third interface for discharging the mixed urine is formed at the left end of the third pipe, and a liquid collecting cup with an open upper end is formed at the right end of the third pipe; the upper end of the liquid collecting cup is sealed with the lower end of the chamber, the side surface of the liquid collecting cup is connected to the third interface, and the lower end of the liquid collecting cup is provided with a threaded hole for threaded connection with the outer side surface of the second pipe.

[0017] Preferably, the mixer further comprises a spiral partition, which is arranged in the chamber, wherein a seal is formed between the outer side surface of the partition and the inner side surface of the chamber, and a seal is formed between the inner side surface of the partition and the outer side surface of the second pipe.

[0018] Preferably, the drainage holes are arranged along the tangential direction of the second pipe, so that the ultrapure water discharged from the drainage holes is mixed with the molten urine in the channel to generate spin, and the spin direction is the same as the spiral direction of the partition.

[0019] Compared with the prior art, the beneficial effects of the present application are: (1) under the action of the flash evaporator, the concentration and purification efficiency of the urea solution is higher, thereby effectively reducing the residence time of the molten urea in the lower evaporator, and further effectively reducing the generation rate of biuret.

[0020] (2) After the carbon dioxide is added to the lower liquid of the flash evaporator, it will strip ammonia from the urine, thereby effectively reducing the ammonia content in the liquid automotive urea, making the liquid automotive urea purer and removing the slight ammonia odor. The high purity reduces the pollution to the atmosphere during use. At the same time, the carbon dioxide is consumed during the production process, solving the problem of carbon dioxide waste and pollution in exhaust emissions.

[0021] (3) Under the action of the mixer, the molten urine first enters the interior of the first pipe through the first interface, and then enters the channel between the outer side of the conical structure and the inner side of the truncated cone hole; the ultrapure water first enters the interior of the second pipe through the second interface, and then is discharged into the channel through the drainage hole on the conical structure, thereby mixing with the molten urine and entering the chamber. After further mixing in the chamber, the mixed urine is obtained. The mixed urine is first discharged into the liquid collection cup, and then discharged into the interior of the third pipe, and finally discharged from the third interface. From the above content, it can be seen that the mixer has a simple structure, a compact size, takes up little space, has low production and maintenance costs, and can operate for a long period of time.

[0022] (4) Under the action of the threaded hole at the lower end of the liquid collecting cup, the position of the second pipe can be adjusted in the vertical direction (i.e., the axial direction of the second pipe) by rotating the second pipe, thereby adjusting the size of the channel between the outer side surface of the conical structure and the inner side surface of the truncated cone hole, and further adjusting the flow rate of the molten urine. In other words, while ensuring that the flow rate of the ultrapure water remains unchanged, the flow rate ratio of the molten urine to the ultrapure water can be adjusted by adjusting the flow rate of the molten urine, and the entire adjustment process is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention provides a flow chart of a process for producing ultrapure liquid automotive urea.

[0024] Figure 2 Provided for this application Figure 1A perspective view of the mixer.

[0025] Figure 3 Provided for this application Figure 2 Exploded view of the mixer.

[0026] Figure 4 Provided for this application Figure 2 A cross-sectional view of the mixer shows the internal structure of the mixer.

[0027] Figure 5 Provided for this application Figure 2 Cross-sectional view of the mixer along the drain hole.

[0028] In the figure: 1. Flash evaporator; 2. Mixer; 21. First pipe; 211. First interface; 212. Chamber; 213. Cone hole; 22. Second pipe; 221. Second interface; 222. Conical structure; 223. Drain hole; 224. Channel; 23. Third pipe; 231. Third interface; 232. Liquid collecting cup; 233. Threaded hole; 24. Partition; 25. Sealing ring; 3. First filter tank; 4. Second filter tank; 5. Third filter tank; 6. Fourth filter tank; 7. Urine tank. DETAILED DESCRIPTION

[0029] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0030] In the description of the present application, it should be noted that for directional words, such as the terms "center", "transverse", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction, and cannot be understood as limiting the specific scope of protection of the present application. The terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. The terms "including" and "having" in the description and claims of the present application and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0031] Reference Figure 1 One embodiment of the present application provides a process for producing ultrapure liquid automotive urea, comprising the following steps:

[0032] Step 1: The urea solution is input into the flash evaporator 1 for purification to obtain molten urea, and carbon dioxide is added to the lower liquid of the flash evaporator 1 to strip ammonia in the molten urea by the carbon dioxide, thereby obtaining molten urine;

[0033] Step 2: The ultrapure water and the molten urine in step 1 are input into the mixer 2 in proportion and mixed evenly to obtain mixed urine;

[0034] Step 3: The mixed urine in step 2 is input into a filtering device for filtration to obtain a vehicle urea solution.

[0035] The flash evaporator 1 achieves higher concentration and purification efficiency for the urea solution, effectively reducing the residence time of the molten urea in the lower evaporator and, in turn, the rate of biuret formation. When carbon dioxide is added to the lower liquid of the flash evaporator 1, it strips ammonia from the urine, effectively reducing the ammonia content in the liquid automotive urea, making it purer and removing the slight ammonia odor. This high purity reduces atmospheric pollution during use. Furthermore, carbon dioxide is consumed during the production process, eliminating the waste and pollution issues associated with carbon dioxide emissions.

[0036] In some embodiments of the present application, in step 2, the flow ratio of ultrapure water to molten urine is (1.59-1.63): 1. Experiments have shown that within this flow ratio range, the final production of 32.5% ultrapure liquid automotive urea has a biuret content of 0.12% and an ammonia content of <0.02%.

[0037] In some embodiments of the present application, in step 3, the filtration device includes a fine filter tank and an ultra-fine filter tank; the mixed urine is first filtered through the fine filter tank and then through the ultra-fine filter tank. The filtration accuracy of the fine filter tank is preferably 5 microns, and the filtration accuracy of the ultra-fine filter tank is preferably 1 micron.

[0038] In some embodiments of the present application, in step 2, the preparation process of ultrapure water is as follows: soft water obtained after tap water treatment is added to the EDI raw water tank, the EDI system is started after the liquid level is controlled to be qualified, and when the resistivity of pure water is within the index > 10 megohms and the liquid level in the pure water tank reaches 70%, the pure water pump and the outlet regulating valve are started to control the ultrapure water input into the mixer 2.

[0039] In some embodiments of the present application, in step three, the mixed urine is first input into the urine tank 7 and the density is tested; when the density of the mixed urine is 31.0-31.2, the mixed urine is then input into the filtration device for filtration.

[0040] Example 1

[0041] like Figure 1 As shown, a urea solution is pumped into a flash evaporator 1 by a urea pump to be purified to obtain molten urea, so as to reduce the time consumed in the purification process and thus reduce the productivity of biuret; and the carbon dioxide gas in the tail gas is input into the lower liquid of the flash evaporator 1, and the ammonia in the molten urea is stripped by the carbon dioxide gas to reduce the ammonia content in the molten urine.

[0042] The molten urine from the flash evaporator 1 and the ultrapure water from the EDI are input into the mixer 2 and mixed evenly, and then first input into the urine tank 7 to exclude urine that does not meet the initial mixing standards; at the same time, the density of the mixed urine is tested. When the density of the mixed urine is 31.1, the mixed urine is input into the filtration device for filtration.

[0043] Among them, there are two filtration routes. One route first passes through the 32.5 intermediate tank, then is pumped into the first filter tank 3 (i.e., 5 micron fine filter tank) through the 32.5 intermediate pump (15KW) to filter and arrive at the 32.5 product tank. Then, it is pumped into the third filter tank 5 (i.e., 1 micron ultra-fine filter tank) through the 32.5 filling pump (15KW) to filter and then go to filling. The other route first passes through the 40 intermediate tank, then is pumped into the second filter tank 4 (i.e., 5 micron fine filter tank) through the 40 intermediate pump (15KW) to filter and arrive at the 40 product tank. Then, it is pumped into the fourth filter tank 6 (i.e., 1 micron ultra-fine filter tank) through the 40 filling pump (15KW) to filter and then go to filling. It should be understood that the three-way valve can be used to control the discharge of mixed urine to the urine tank 7, or control the mixed urine to be filtered through one of the filtration routes.

[0044] Example 2

[0045] It is understandable that in Example 1, a conventional mixer 2 can be used to achieve the mixing function. However, the conventional mixer 2 is usually a tank structure, which occupies a large space and usually requires a stirring device inside. The overall structure is complex and requires regular maintenance, which is costly and requires high subsequent maintenance costs. In addition, this structure makes it difficult to adjust the flow rate ratio of molten urine to ultrapure water in a timely manner.

[0046] Therefore, the difference between the second embodiment and the first embodiment is that: in step 2, if Figures 2 to 4As shown, the mixer 2 includes a first pipe 21, a second pipe 22 and a third pipe 23; a first interface 211 for inputting molten urine is formed at the upper end of the first pipe 21, a chamber 212 is formed radially outward at the lower end of the first pipe 21, and the chamber 212 is connected to the first pipe 21 through a truncated cone hole 213; the upper end of the second pipe 22 is coaxially built into the chamber 212, and a gap is left between the outer side of the second pipe 22 and the inner side of the chamber 212; the lower end of the second pipe 22 is provided with a second interface 221 for inputting ultrapure water, and the upper end of the second pipe 22 is sealed by a conical structure 222; the outer side of the conical structure 222 and the inner side of the truncated cone hole 213 are connected. A channel 224 is formed between them, and a drainage hole 223 for connecting the channel 224 and the second interface 221 is provided on the conical structure 222; a third interface 231 for discharging mixed urine is formed at the left end of the third pipe 23, and a liquid collecting cup 232 with an open upper end is formed at the right end of the third pipe 23; the upper end of the liquid collecting cup 232 is sealed with the lower end of the chamber 212 (for example, the upper end of the liquid collecting cup 232 and the lower end of the chamber 212 are connected by screws, and the sealing between them is strengthened by a sealing ring 25), the side of the liquid collecting cup 232 is connected to the third interface 231, and the lower end of the liquid collecting cup 232 is penetrated by a threaded hole 233 for threaded connection to the outer side surface of the second pipe 22.

[0047] The working principle of the mixer 2 is as follows:

[0048] (1) The molten urine first enters the interior of the first pipe 21 through the first interface 211, and then enters the channel 224 between the outer side of the conical structure 222 and the inner side of the truncated cone hole 213; the ultrapure water first enters the interior of the second pipe 22 through the second interface 221, and then is discharged into the channel 224 through the drainage hole 223 on the conical structure 222, thereby mixing with the molten urine and entering the chamber 212. After further mixing in the chamber 212, mixed urine is obtained. The mixed urine is first discharged into the liquid collection cup 232, and then discharged into the interior of the third pipe 23, and finally discharged from the third interface 231. As can be seen from the above content, the mixer 2 has a simple structure, a compact size, takes up little space, requires no maintenance, can operate for a long period of time, and has low production and maintenance costs.

[0049] (2) Under the action of the threaded hole 233 at the lower end of the liquid collecting cup 232, the position of the second pipe 22 can be adjusted in the up-down direction (i.e., the axial direction of the second pipe 22) by rotating the second pipe 22, thereby adjusting the size of the channel 224 between the outer side surface of the conical structure 222 and the inner side surface of the truncated cone hole 213, and thus adjusting the flow rate of the molten urine; that is, when the second pipe 22 moves upward, the size of the channel 224 becomes smaller, thereby reducing the flow rate of the molten urine; when the second pipe 22 moves downward, the size of the channel 224 becomes larger, thereby increasing the flow rate of the molten urine. In other words, while ensuring that the flow rate of ultrapure water remains unchanged, the flow ratio of molten urine to ultrapure water can be adjusted by adjusting the flow rate of molten urine, and the entire adjustment process is simple to operate.

[0050] (3) When the mixed urine flows through the chamber 212 and the liquid collecting cup 232, it will generate heat exchange with the ultrapure water in the second pipe 22, thereby increasing the initial temperature of the ultrapure water, and further reducing the temperature difference between the ultrapure water and the molten urine, which is beneficial to prevent the ultrapure water from vaporizing when it comes into contact with the molten urine.

[0051] Reference Figure 3 as well as Figure 4 In order to extend the flow path (i.e., residence time) of the mixed urine in chamber 212, in some embodiments of the present application, the mixer 2 further includes a spiral partition 24, which is disposed in chamber 212. A seal is formed between the outer side of partition 24 and the inner side of chamber 212, and between the inner side of partition 24 and the outer side of second pipe 22. Due to the action of partition 24, a spiral flow channel is formed in chamber 212, thereby significantly extending the flow path (i.e., residence time) of the mixed urine in chamber 212. This not only facilitates more uniform mixing of the molten urine and ultrapure water, but also helps the ultrapure water in second pipe 22 gain more heat.

[0052] The present application does not limit the installation method of the partition 24. For example, a spiral groove is provided on the inner side surface of the chamber 212, and the partition 24 is threadedly connected to the spiral groove to achieve the installation and fixation of the partition 24.

[0053] Reference Figure 4 as well as Figure 5 In some embodiments of the present application, the drainage holes 223 are arranged along the tangential direction of the second pipe 22, so that the ultrapure water discharged from the drainage holes 223 and the molten urine in the channel 224 are mixed and spin is generated, and the spin direction is the same as the spiral direction of the partition 24. Figure 5As shown, under the action of the drainage hole 223 of this structure, the ultrapure water discharged from the drainage hole 223 is mixed with the molten urine in the channel 224 and then spins, so that the mixed urine enters the interior of the chamber 212 along the spiral direction of the partition 24, which is conducive to making the ultrapure water and the molten urine mix more evenly.

[0054] The above describes the basic principles, main features, and advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above-described embodiments. The above-described embodiments and the specification merely illustrate the principles of the present application. Various changes and improvements may be made to the present application without departing from the spirit and scope of the present application. These changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the appended claims and their equivalents.

Claims

1. A process for producing ultrapure liquid automotive urea, characterized in that: The following steps are involved: Step 1: inputting the urea solution into a flash evaporator for purification to obtain molten urea, and adding carbon dioxide to the lower liquid of the flash evaporator, and stripping ammonia in the molten urea by the carbon dioxide, thereby obtaining molten urine; Step 2: Inputting ultrapure water and the molten urine in step 1 into a mixer in proportion and mixing them evenly to obtain mixed urine; Step 3: inputting the mixed urine in step 2 into a filtering device for filtering to obtain a vehicle urea solution; In step 2, the mixer includes a first pipe, a second pipe, and a third pipe; a first interface for inputting the molten urine is formed at the upper end of the first pipe, a chamber is formed radially outward at the lower end of the first pipe, and the chamber is connected to the first pipe through a truncated cone hole; the upper end of the second pipe is coaxially embedded in the chamber, and a gap is left between the outer side surface of the second pipe and the inner side surface of the chamber; a second interface for inputting the ultrapure water is provided at the lower end of the second pipe, and the upper end of the second pipe is sealed by a conical structure; a channel is formed between the outer side surface of the conical structure and the inner side surface of the truncated cone hole, and a drainage hole for connecting the channel with the second interface is formed through the conical structure; a third interface for discharging the mixed urine is formed at the left end of the third pipe, and a liquid collecting cup with an open upper end is formed at the right end of the third pipe; the upper end of the liquid collecting cup is sealed with the lower end of the chamber, the side surface of the liquid collecting cup is connected to the third interface, and the lower end of the liquid collecting cup is penetrated by a threaded hole for threaded connection with the outer side surface of the second pipe.

2. The process for producing ultrapure liquid urea for vehicles according to claim 1, wherein: In the step 2, the flow ratio of the ultrapure water to the molten urine is (1.59-1.63):

1.

3. The process for producing ultrapure liquid urea for vehicles according to claim 1, wherein: In the step three, the filtering device includes a fine filtration tank and an ultra-fine filtration tank; the mixed urine is first filtered through the fine filtration tank and then filtered through the ultra-fine filtration tank.

4. The process for producing ultrapure liquid urea for vehicles according to claim 3, wherein: The filtration accuracy of the fine filtration tank is 5 microns.

5. The process for producing ultrapure liquid urea for vehicles according to claim 4, wherein: The filtration accuracy of the ultra-fine filtration tank is 1 micron.

6. The process for producing ultrapure liquid urea for vehicles according to claim 1, wherein: In step 2, the preparation process of the ultrapure water is as follows: Add the soft water obtained after tap water treatment into the EDI raw water tank, start the EDI system after the liquid level is controlled to be qualified, and when the resistivity of pure water is within the index > 10 megohms and the liquid level in the pure water tank reaches 70%, start the pure water pump and the outlet regulating valve to control the ultrapure water to be input into the mixer.

7. The process for producing ultrapure liquid urea for vehicles according to claim 1, wherein: In the step three, the mixed urine is first input into the urine tank and the density is tested; when the density of the mixed urine is 31.0-31.2, the mixed urine is input into the filtering device for filtration.

8. The process for producing ultrapure liquid urea for vehicles according to claim 1, wherein: The mixer further comprises a spiral partition, which is disposed in the chamber. A seal is formed between the outer side of the partition and the inner side of the chamber, and a seal is formed between the inner side of the partition and the outer side of the second pipe.

9. The process for producing ultrapure liquid urea for vehicles according to claim 8, wherein: The drainage holes are arranged along the tangential direction of the second pipe, so that the ultrapure water discharged from the drainage holes is mixed with the molten urine in the channel to generate spin, and the spin direction is the same as the spiral direction of the partition.

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