A kind of extraction and purification process of urea granules

Abstract

The present invention discloses an extraction and purification process for urea granules. The process is carried out using an extraction and purification device, which includes an extraction system, an auger system, an extractant spraying system, and an extractant recovery system. The process includes the following steps: adding an extractant to the urea granules and extracting them through the extraction system, then transferring them to the extractant spraying system through the auger system and leaching the urea granules, and finally drying them to obtain purified urea granules, and using the extractant recovery system to recover the extractant. The extractant used in the present invention has a higher flash point than the methanol and ethanol used in traditional patents and is safer. The process of the present invention can significantly improve the removal effect of biuret and increase the purity of urea.

Description

Technical Field

[0001] The invention belongs to the technical field of vehicle urea purification, and particularly relates to an extraction and purification process for urea granules. Background Art

[0002] The main harmful substances in diesel vehicle exhaust are nitrogen oxide particles. Technical means can be used to reduce particle emissions inside the engine, and urea can be used in the exhaust after-treatment device to reduce nitrogen oxide emissions. Urea decomposes into ammonia at high temperatures, which reacts with nitrogen oxides under the action of a catalyst to produce harmless nitrogen and water.

[0003] Because diesel engine exhaust cannot meet the current national standards for nitrogen oxide emissions, existing technologies employ exhaust gas treatment devices to achieve denitrification, namely SCR aftertreatment systems. These systems primarily catalyze the reaction of ammonia and nitrogen oxides to produce nitrogen and water. Ammonia is primarily provided by the decomposition of urea solution, which is atomized and injected into the exhaust system by a urea injection system. Due to the unique characteristics of automotive urea solution, fouling can accumulate over long periods of use. This is primarily due to the polycondensation of substances in the urea solution and its byproducts at high temperatures. The accumulation of fouling can easily cause SCR aftertreatment device blockage, leading to engine torque restriction. Biuret is a major impurity in automotive urea solution, which significantly exacerbates fouling and accumulation. The relevant automotive urea standards have clear requirements for this impurity content. Domestic urea granules contain a relatively high content of biuret, resulting in a biuret content in the resulting automotive urea solution that often fails to meet the relevant standards or barely meets them. This contributes to common exhaust system blockage in the industry.

[0004] Currently, the purification process for urea granules mainly relies on recrystallization to remove impurities. However, this method has high energy consumption, the crystallization process is difficult to control, and is difficult to apply industrially. Some domestic manufacturers also use extraction to remove biuret from urea granules, as shown in patent CN105237439A. However, the extraction agents used are methanol and ethanol, both of which are hazardous chemicals. These methods pose a great safety hazard in large-scale production and cannot be widely used.

[0005] It can be seen that providing an extraction and purification process for urea granules is an urgent problem to be solved in this field. Summary of the Invention

[0006] The problem to be solved and the technical solution proposed by the present invention are to improve the existing technology, thereby providing a process for extracting and purifying urea granules. The process of the present invention can significantly improve the removal effect of biuret.

[0007] The above technical objectives of the present invention are achieved through the following technical solutions:

[0008] One embodiment of the present invention provides an extraction and purification process for urea granules. The process is carried out using an extraction and purification device, which includes an extraction system, an auger system, an extractant spraying system, and an extractant recovery system. The process includes the following steps: adding an extractant to urea granules and extracting them through the extraction system, then transferring them to the extractant spraying system through the auger system and eluting the urea granules, and finally drying them to obtain purified urea granules, and recovering the extractant using the extractant recovery system.

[0009] According to an extraction and purification process of urea granules provided in one embodiment of the present invention, the extraction system includes an extraction tank provided with a reflux pump and a heating device, and a coaxial stirring paddle is further provided in the extraction tank.

[0010] According to an extraction and purification process of urea granules provided by one embodiment of the present invention, the auger system includes an auger and a delivery pipe, one end of the auger is arranged at the inner bottom of the extraction tank, and the other end of the auger is connected to the delivery pipe.

[0011] According to the above embodiment of the present invention, a process for extracting and purifying urea granules is provided, wherein the extractant spraying system includes a conveyor belt, a spraying device arranged above the conveyor belt, and a tunnel oven.

[0012] According to an extraction and purification process of urea granules provided by one embodiment of the present invention, the extractant recovery system includes an air collecting hood, a liquid collecting tank, an evaporator, a condensing tower and a liquid storage tank, the air collecting hood is arranged above the spraying device and the tunnel oven, the liquid collecting tank is arranged below the conveyor belt, and the condensing tower is arranged above the liquid storage tank.

[0013] According to one embodiment of the present invention, an extraction and purification process for urea granules is provided, the process comprising the following steps:

[0014] Extraction: Add urea granules and extractant into the extraction tank, turn on the stirring paddle and reflux pump to start extraction, and use the auger to transport the extracted urea granules to the surface of the conveyor belt;

[0015] Spraying and drying: Turn on the conveyor belt to move the urea granules on the conveyor belt surface to the spray device, turn on the spray device to rinse the urea granules, and the washed granular urea is transported to the tunnel oven for drying to obtain purified urea granules;

[0016] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0017] According to the above embodiment of the present invention, a process for extracting and purifying urea granules is provided, wherein the extractant includes N,N-dimethylformamide, ethylene glycol, N-methylpyrrolidone, dipropylene glycol methyl ether or diethylene glycol methyl ether.

[0018] According to the above embodiment of the present invention, a process for extracting and purifying urea granules is provided, wherein the extraction conditions are: temperature 20-80° C., and time 10-240 min.

[0019] According to the extraction and purification process of urea granules provided by one embodiment of the present invention, the conveying speed of the conveyor belt is 1-50 kg / min.

[0020] According to the extraction and purification process of urea granules provided by one embodiment of the present invention, the spray flow rate is 0.5-50 kg / min, and the drying temperature is 60-100°C.

[0021] In summary, the present invention has the following beneficial effects: 1. The extractant used in the present invention has a higher flash point than the methanol and ethanol used in traditional patents and is safer; 2. The process of the present invention can significantly improve the removal effect of biuret and increase the purity of urea. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. Those skilled in the art will readily appreciate that these drawings are merely used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0023] Figure 1 The figure shows the structure of the device for extracting and purifying urea particles of the present invention.

[0024] The numbers in the accompanying drawings are: 10-extraction system; 11-reflux pump; 12-heating device; 13-coaxial stirring paddle; 14-extraction tank; 20-auger system; 21-delivery pipe; 22-auger; 30-extraction agent spraying system; 31-conveyor belt; 32-spraying device; 33-tunnel oven; 40-extraction agent recovery system; 41-air collecting hood; 42-liquid collecting tank; 43-evaporator; 44-condensation tower; 45-liquid storage tank. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the drawings are for illustrative purposes only and are not drawn to scale. In addition, some parts may be enlarged or reduced for ease of description, and some well-known parts may be omitted.

[0026] In the description of this specification, reference to the terms "one embodiment," "example," "specific example," etc., means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples.

[0027] like Figure 1 As shown, a preferred embodiment of the present invention provides an extraction and purification device for urea granules, comprising an extraction system 10, an auger system 20, an extractant spray system 30, and an extractant recovery system 40. The extraction system 10 includes an extraction tank 14, which is equipped with a reflux pump 11 and a heating device 12. A coaxial stirring paddle 13 is also located within the extraction tank 14. The auger system 20 includes an auger 22 and a delivery pipe 21. One end of the auger 22 is located at the inner bottom of the extraction tank 14, and the other end of the auger 22 is connected to the delivery pipe 21. The extractant spray system 30 includes a conveyor belt 31, a spray device 32 disposed above the conveyor belt 31, and a tunnel oven 33. The extractant recovery system 40 includes an air collection hood 41, a liquid collection tank 42, an evaporator 43, a condensation tower 44, and a liquid storage tank 45. The air collection hood 41 is located above the spray device 32 and tunnel oven 33. The liquid collection tank 42 is located below the conveyor belt 31. The condensation tower 44 is disposed above the liquid storage tank 45 .

[0028] The extraction and purification of urea granules is carried out according to the above-mentioned device, which is described below with reference to specific embodiments. Unless otherwise specified, the devices, systems and other equipment mentioned in the process belong to the above-mentioned devices.

[0029] Example 1

[0030] Extraction: Add 1 t of urea granules (initial biuret content is 0.9%) and 1 t of N,N-dimethylformamide into the extraction tank; turn on the stirring paddle and reflux pump, stir at 20°C for 10 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0031] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 1kg / min. The granules on the conveyor belt surface move to the spray device. Turn on the spray device and set the flow rate to 0.5kg / min to rinse the urea granules. The rinsed granules are then transported to a tunnel oven and dried at 60°C to obtain purified urea granules.

[0032] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0033] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0034] Example 2

[0035] Extraction: Add 1 t urea granules (initial biuret content is 0.9%) and 1 t ethylene glycol into the extraction tank, turn on the stirring paddle and reflux pump, stir at 40°C for 200 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0036] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 20kg / min. The granules on the conveyor belt surface move to the spray device, turn on the spray device, set the flow rate to 40kg / min, and rinse the urea granules. The rinsed granules are then transported to a tunnel oven and dried at 80°C to obtain purified urea granules.

[0037] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0038] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0039] Example 3

[0040] Extraction: Add 1 t urea granules (initial biuret content is 0.9%) and 1 t N-methylpyrrolidone into the extraction tank, turn on the stirring paddle and reflux pump, stir at 60°C for 60 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0041] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 10kg / min. The granules on the conveyor belt surface move to the spray device. Turn on the spray device and set the flow rate to 5kg / min to rinse the urea granules. The rinsed granules are then transported to a tunnel oven and dried at 100°C to obtain purified urea granules.

[0042] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0043] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0044] Example 4

[0045] Extraction: Add 1 t urea granules (initial biuret content is 0.9%) and 1 t dipropylene glycol methyl ether into the extraction tank, turn on the stirring paddle and reflux pump, stir at 80°C for 240 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0046] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 20kg / min. The granules on the conveyor belt surface move to the spray device, turn on the spray device, set the flow rate to 8kg / min, and rinse the urea granules. The rinsed granules are then transported to a tunnel oven and dried at 60°C to obtain purified urea granules.

[0047] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0048] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0049] Example 5

[0050] Extraction: Add 1 t urea granules (initial biuret content is 0.9%) and 1 t diethylene glycol methyl ether into the extraction tank, turn on the stirring paddle and reflux pump, stir at 20°C for 100 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0051] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 50kg / min. The granules on the conveyor belt surface move to the spray device, turn on the spray device, set the flow rate to 50kg / min, and rinse the urea granules. The rinsed granular urea is then transported to a tunnel oven and dried at 50°C to obtain purified urea granules.

[0052] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0053] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0054] Example 6

[0055] Extraction: Add 1 t urea granules (initial biuret content is 0.9%) and 1 t diethylene glycol methyl ether into the extraction tank, turn on the stirring paddle and reflux pump, stir at 40°C for 120 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0056] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 20kg / min. The granules on the conveyor belt surface move to the spray device, turn on the spray device, set the flow rate to 20kg / min, and rinse the urea granules. The rinsed granular urea is then transported to a tunnel oven and dried at 60°C to obtain purified urea granules.

[0057] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0058] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0059] Example 7

[0060] Extraction: Add 1 t urea granules (initial biuret content is 0.9%) and 1 t diethylene glycol methyl ether into the extraction tank, turn on the stirring paddle and reflux pump, stir at 60°C for 240 minutes, and use the auger to transport the urea granules to the surface of the conveyor belt;

[0061] Spraying and drying: Turn on the conveyor belt and adjust the urea granule conveying speed to 2kg / min. Move the granules on the conveyor belt surface to the spray device. Turn on the spray device and set the flow rate to 20kg / min to rinse the urea granules. The rinsed granules are then transported to a tunnel oven and dried at 100°C to obtain purified urea granules.

[0062] Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

[0063] The biuret content was tested according to Appendix C of GB 29518. The results are shown in Table 1.

[0064] The biuret content after purification in Example 1 to Implementation 7 was tested according to Appendix C of GB 29518. The test results are shown in the following table:

[0065] Table 1 Parameters of each example and determination of biuret content

[0066] parameter 1 2 3 4 5 6 7 Extraction agent N,N-Dimethylformamide Ethylene glycol N-Methylpyrrolidone Dipropylene glycol methyl ether Diethylene glycol methyl ether Diethylene glycol methyl ether Diethylene glycol methyl ether Extraction temperature / ℃ 20 40 60 80 20 40 60 Extraction time / min 10 200 60 240 100 120 240 Granular urea transmission speed kg / min 1 20 10 20 50 20 2 Spray flow kg / min 0.5 40 5 8 50 20 20 Drying temperature / ℃ 60 80 100 60 50 60 100 Initial biuret content / % 0.9 0.9 0.9 0.9 0.9 0.9 0.9 Biuret content after treatment / % 0.8 0.65 0.77 0.81 0.7 0.55 0.79

[0067] The test results in Table 1 above show that the extraction process of the present invention can effectively reduce the biuret content in urea granules, with a biuret removal rate of over 38.88% in granular urea. Comparison of the examples shows that extending the extraction time and increasing the temperature within a certain range can increase the biuret removal efficiency, and the spraying process and flow rate are also very helpful in removing biuret from the granules.

[0068] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and does not limit the present invention in any form. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the scope of the technical solution of the application.

Claims

1. A urea granular extraction and purification process, characterized in that: The process is carried out using an extraction and purification device, which includes an extraction system, an auger system, an extractant spraying system, and an extractant recovery system. The process includes the following steps: adding an extractant to urea granules and extracting them through the extraction system, then transferring them to the extractant spraying system through the auger system and eluting the urea granules, and finally drying them to obtain purified urea granules, and recovering the extractant using the extractant recovery system.

2. The extraction and purification process of urea granules according to claim 1, characterized in that: The extraction system comprises an extraction tank, a reflux pump and a heating device are provided on the extraction tank, and a coaxial stirring paddle is also provided in the extraction tank.

3. The extraction and purification process of urea granules according to claim 2, characterized in that: The auger system includes an auger and a delivery pipe. One end of the auger is arranged at the inner bottom of the extraction tank, and the other end of the auger is connected to the delivery pipe.

4. The extraction and purification process of urea granules according to claim 3, characterized in that: The extractant spraying system includes a conveyor belt, a spraying device arranged above the conveyor belt, and a tunnel oven.

5. The extraction and purification process of urea granules according to claim 4, characterized in that: The extractant recovery system includes an air collecting hood, a liquid collecting tank, an evaporator, a condensing tower and a liquid storage tank. The air collecting hood is arranged above the spray device and the tunnel oven, the liquid collecting tank is arranged below the conveyor belt, and the condensing tower is arranged above the liquid storage tank.

6. The extraction and purification process of urea granules according to claim 5, characterized in that: The process comprises the following steps: Extraction: Add urea granules and extractant into the extraction tank, turn on the stirring paddle and reflux pump to start extraction, and use the auger to transport the extracted urea granules to the surface of the conveyor belt; Spraying and drying: Turn on the conveyor belt to move the urea granules on the conveyor belt surface to the spray device, turn on the spray device to rinse the urea granules, and the washed granular urea is transported to the tunnel oven for drying to obtain purified urea granules; Recovery: The extractant is vaporized and carried out, and the gas is collected by the wind collecting hood; at the same time, the extractant collected in the liquid collecting tank enters the evaporator for vaporization, and the vaporized gas enters the condensation tower together with the gas collected by the wind collecting hood. The condensed extract enters the liquid storage tank for next use.

7. The extraction and purification process of urea granules according to claim 6, characterized in that: The extractant includes N,N-dimethylformamide, ethylene glycol, N-methylpyrrolidone, dipropylene glycol methyl ether or diethylene glycol methyl ether.

8. The extraction and purification process of urea granules according to claim 6, characterized in that: The extraction conditions are: temperature 20-80° C., time 10-240 min.

9. The extraction and purification process of urea granules according to claim 6, characterized in that: The conveying speed of the conveyor belt is 1-50 kg / min.

10. The extraction and purification process of urea granules according to claim 6, characterized in that: The spray flow rate is 0.5-50 kg / min, and the drying temperature is 60-100°C.

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