Tail gas recovery and utilization device in urea production process

Abstract

This utility model relates to the field of large-scale urea production industrial technology, and is a tail gas recovery and utilization device in the urea production process. It includes an atmospheric pressure absorption tower, a first condenser, an ammonia tank, a second condenser, a tail gas venting cylinder, and a pre-concentrator. A first liquid phase pipeline connects the atmospheric pressure absorption tower and the tail gas venting cylinder; a venting pipeline connects the atmospheric pressure absorption tower and the tail gas venting cylinder; a first gas phase pipeline connects the venting pipeline and the first condenser; a second gas phase pipeline connects the first condenser and the second condenser; a third gas phase pipeline connects the second condenser and the venting pipeline; a second liquid phase pipeline connects the second condenser and the ammonia tank; a third liquid phase pipeline connects the first condenser and the second liquid phase pipeline; and a fourth gas phase pipeline connects the pre-concentrator and the first gas phase pipeline. This utility model has a reasonable and compact structure, is easy to use, improves the urea production efficiency of enterprises, and reduces environmental emission pressure.

Description

Technical Field

[0001] This utility model relates to the field of large-scale urea production industrial technology, and is a tail gas recovery and utilization device in the urea production process. Background Technology

[0002] The industrial synthesis of urea is a multi-step production process. Urea synthesis is a high-pressure synthesis reaction. The core is to react ammonia (NH3) and carbon dioxide (CO2) in a urea synthesis tower (high-pressure reactor) to produce urea (CO(NH2)2).

[0003] The urea synthesis rate of a urea synthesis tower is generally between 50% and 70%. To improve raw material utilization, unreacted gases (NH3 and CO2) in the urea synthesis liquid generated by the tower need to be recovered and reused through medium-pressure and low-pressure systems. The urea synthesis liquid produced by the tower, after being recovered and reused through the medium-pressure and low-pressure systems, enters the urea evaporation section for concentration and granulation to obtain the urea product. Process wastewater generated during urea production is treated through a hydrolysis system to reduce CO2 emissions and achieve zero wastewater discharge, meeting environmental protection requirements.

[0004] However, when the medium-pressure system is coupled with the low-pressure system, the low-pressure system experiences a heavy operating load, resulting in a large amount of ammonia being directly released into the atmosphere without being recovered and utilized. This significant ammonia escape increases urea production costs and places enormous pressure on the company's environmental emissions.

[0005] In summary, the low production efficiency and high environmental emission pressure in the urea production process have become urgent technical problems that urea production enterprises need to solve. Summary of the Invention

[0006] This utility model provides a tail gas recovery and utilization device in the urea production process, which overcomes the shortcomings of the above-mentioned prior art and can effectively solve the problems of low production efficiency and high environmental emission pressure in the existing urea production process.

[0007] The technical solution of this utility model is achieved through the following measures: a tail gas recovery and utilization device in the urea production process, comprising an atmospheric pressure absorption tower, a first condenser, an ammonia water tank, a second condenser, a tail gas venting cylinder, and a pre-concentrator. A dilute ammonia water pipeline is fixedly connected to the upper inlet of the atmospheric pressure absorption tower; a low-pressure gas phase pipeline is fixedly connected to the lower inlet of the atmospheric pressure absorption tower; a first liquid phase pipeline is fixedly connected between the lower outlet of the atmospheric pressure absorption tower and the lower inlet of the tail gas venting cylinder; a venting pipeline is fixedly connected between the top outlet of the atmospheric pressure absorption tower and the middle inlet of the tail gas venting cylinder; and a first gas phase pipeline is fixedly connected between the venting pipeline and the top inlet of the first condenser. A second gas phase pipeline is fixedly connected between the first outlet at the bottom of the condenser and the top inlet of the second condenser. A third gas phase pipeline is fixedly connected between the top outlet of the second condenser and the vent pipeline between the first gas phase pipeline and the middle inlet of the tail gas venting cylinder. A second liquid phase pipeline is fixedly connected between the bottom outlet of the second condenser and the first inlet at the top of the ammonia tank. A third liquid phase pipeline is fixedly connected between the second outlet at the bottom of the first condenser and the second liquid phase pipeline. A dilute urine pipeline is fixedly connected to the upper inlet of the pre-concentrator. A fourth gas phase pipeline is fixedly connected between the top outlet of the pre-concentrator and the first gas phase pipeline. A urine pipeline is fixedly connected to the bottom outlet of the pre-concentrator.

[0008] The following are further optimizations and / or improvements to the above-mentioned utility model technical solution: The aforementioned device also includes a cooler, with a first circulation pipeline fixedly connected between the bottom outlet of the cooler and the middle inlet of the atmospheric pressure absorption tower, and a second circulation pipeline fixedly connected between the bottom outlet of the atmospheric pressure absorption tower and the top inlet of the cooler, with a first circulation pump fixedly installed on the second circulation pipeline.

[0009] The aforementioned device also includes a third condenser, a fifth gas phase pipeline fixedly connected between the first gas phase pipeline between the vent pipeline and the fourth gas phase pipeline and the top inlet of the third condenser, a fourth liquid phase pipeline fixedly connected between the bottom outlet of the third condenser and the second liquid phase pipeline between the third liquid phase pipeline and the first inlet at the top of the ammonia tank, and a sixth gas phase pipeline fixedly connected between the fourth liquid phase pipeline and the vent pipeline between the first and third gas phase pipelines.

[0010] A steam extractor is fixedly installed on the second gas phase pipeline, and a steam pipeline is fixedly connected to the steam extractor.

[0011] The inlet of the pre-concentrator is fixedly connected to a flash steam pipeline, and a potassium ammonia liquid input pipeline is fixedly connected to the flash steam pipeline. The outlet of the pre-concentrator is fixedly connected to a potassium ammonia liquid output pipeline, and a potassium ammonia liquid diversion pipeline is fixedly connected between the potassium ammonia liquid input pipeline and the potassium ammonia liquid output pipeline.

[0012] A fifth liquid phase pipeline is fixedly connected between the lower outlet of the ammonia tank and the upper inlet of the tail gas venting cylinder. A second circulation pump is fixedly installed on the fifth liquid phase pipeline. A sixth liquid phase pipeline is fixedly connected between the lower outlet of the tail gas venting cylinder and the second inlet at the top of the ammonia tank.

[0013] The left-end inlets of the first condenser, second condenser, cooler, and third condenser are all fixedly connected to condensate input pipelines, and the right-end outlets of the first condenser, second condenser, cooler, and third condenser are all fixedly connected to condensate output pipelines.

[0014] Temperature gauges are fixedly installed on the second liquid phase pipeline between the bottom outlet of the second condenser and the third liquid phase pipeline, the third liquid phase pipeline, and the fourth liquid phase pipeline between the bottom outlet of the third condenser and the sixth gas phase pipeline.

[0015] Control valves are fixedly installed on the vent line between the first gas phase pipeline and the sixth gas phase pipeline, the first gas phase pipeline between the vent line and the fifth gas phase pipeline, the first gas phase pipeline between the fifth gas phase pipeline and the fourth gas phase pipeline, the third gas phase pipeline, the fifth gas phase pipeline, the sixth gas phase pipeline, and the steam pipeline.

[0016] The aforementioned device also includes a controller, and the thermometer and control valve are all electrically connected to the controller.

[0017] This utility model has a reasonable and compact structure and is easy to use. It can recycle and utilize the ammonia-containing tail gas generated in urea production, which can effectively solve the problems of low production efficiency and high environmental emission pressure in the urea production process. It has the advantages of high efficiency and environmental protection. Attached Figure Description

[0018] Appendix Figure 1 This is a schematic diagram of the process flow of this utility model.

[0019] Appendix Figure 1The codes in the diagram are as follows: 1 for atmospheric pressure absorption tower, 2 for first condenser, 3 for ammonia tank, 4 for second condenser, 5 for tail gas vent, 6 for pre-concentrator, 7 for dilute ammonia pipeline, 8 for low-pressure gas phase pipeline, 9 for first liquid phase pipeline, 10 for vent pipeline, 11 for first gas phase pipeline, 12 for second gas phase pipeline, 13 for third gas phase pipeline, 14 for second liquid phase pipeline, 15 for third liquid phase pipeline, 16 for dilute urine pipeline, 17 for fourth gas phase pipeline, 18 for urine pipeline, 19 for cooler, 20 for first circulation pipeline, 21 for second circulation pipeline, 2 2 is the first circulating pump, 23 is the third condenser, 24 is the fifth gas phase pipeline, 25 is the fourth liquid phase pipeline, 26 is the sixth gas phase pipeline, 27 is the steam extractor, 28 is the steam pipeline, 29 is the flash steam pipeline, 30 is the potassium ammonia solution input pipeline, 31 is the potassium ammonia solution output pipeline, 32 is the potassium ammonia solution diversion pipeline, 33 is the condensate input pipeline, 34 is the condensate output pipeline, 35 is the thermometer, 36 is the control valve, 37 is the fifth liquid phase pipeline, 38 is the second circulating pump, 39 is the sixth liquid phase pipeline, 40 is the condensate spray device, and 41 is the condensate collection tank. Detailed Implementation

[0020] This utility model is not limited to the following embodiments, and the specific implementation method can be determined according to the technical solution of this utility model and the actual situation.

[0021] Unless otherwise specified, all equipment and devices used in this invention are existing, publicly known, and commonly used equipment and devices in the field.

[0022] In this utility model, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 1 The layout is described using a diagrammatic method, such as the positional relationships of front, back, top, bottom, left, and right, which are based on the instructions attached. Figure 1 The orientation of the layout is determined by the direction of the map.

[0023] The present invention will be further described below with reference to the embodiments and accompanying drawings: Example 1: As shown in the attached document Figure 1As shown, the tail gas recovery and utilization device in the urea production process includes an atmospheric pressure absorption tower 1, a first condenser 2, an ammonia water tank 3, a second condenser 4, a tail gas venting cylinder 5, and a pre-concentrator 6. A dilute ammonia water pipeline 7 is fixedly connected to the upper inlet of the atmospheric pressure absorption tower 1, a low-pressure gas phase pipeline 8 is fixedly connected to the lower inlet of the atmospheric pressure absorption tower 1, a first liquid phase pipeline 9 is fixedly connected between the lower outlet of the atmospheric pressure absorption tower 1 and the lower inlet of the tail gas venting cylinder 5, a venting pipeline 10 is fixedly connected between the top outlet of the atmospheric pressure absorption tower 1 and the middle inlet of the tail gas venting cylinder 5, a first gas phase pipeline 11 is fixedly connected between the venting pipeline 10 and the top inlet of the first condenser 2, and a first outlet at the bottom of the first condenser 2 is connected to the second condenser 6. A second gas phase pipeline 12 is fixedly connected between the top inlet of the second condenser 4 and the first gas phase pipeline 11 and the middle inlet of the tail gas venting cylinder 5. A third gas phase pipeline 13 is fixedly connected between the top outlet of the second condenser 4 and the venting pipeline 10 between the first gas phase pipeline 11 and the middle inlet of the tail gas venting cylinder 5. A second liquid phase pipeline 14 is fixedly connected between the bottom outlet of the second condenser 4 and the top first inlet of the ammonia tank 3. A third liquid phase pipeline 15 is fixedly connected between the bottom second outlet of the first condenser 2 and the second liquid phase pipeline 14. A dilute urine pipeline 16 is fixedly connected to the upper inlet of the pre-concentrator 6. A fourth gas phase pipeline 17 is fixedly connected between the top outlet of the pre-concentrator 6 and the first gas phase pipeline 11. A urine pipeline 18 is fixedly connected to the bottom outlet of the pre-concentrator 6.

[0024] As needed, a stuffing box is installed inside the atmospheric pressure absorption tower 1 to ensure full contact between the liquid and gaseous media inside the atmospheric pressure absorption tower 1, thereby promoting the absorption of ammonia from the mixed gas by dilute ammonia water.

[0025] The dilute ammonia water and mixed gas (mainly composed of ammonia) discharged from the upstream low-pressure process system enter the atmospheric pressure absorption tower 1. After the dilute ammonia water in the atmospheric pressure absorption tower 1 absorbs the ammonia in the mixed gas, the mixed gas discharged from the top of the atmospheric pressure absorption tower 1 is condensed in sequence by the first condenser 2 and the second condenser 4. The condensate after condensation is collected in the ammonia water tank 3, and the gas phase discharged after condensation is discharged into the tail gas venting cylinder 5 for venting.

[0026] The upstream low-pressure process system also discharges dilute urine. The dilute urine is heated and concentrated by concentrator 6. The resulting gas phase (mainly containing ammonia) is condensed by the first condenser 2 and the second condenser 4. The condensate is collected in the ammonia tank 3. The gas phase discharged after condensation is released into the tail gas venting cylinder 5 for venting. The dilute urine is heated and concentrated by concentrator 6 to obtain urea solution, which enters the downstream evaporation process system to produce urea products.

[0027] This invention recycles and utilizes ammonia-containing tail gas generated during urea production, effectively solving the problems of low production efficiency and high environmental emission pressure in the urea production process, and has the advantages of high efficiency and environmental protection.

[0028] The exhaust gas recovery and utilization device in the above-mentioned urea production process can be further optimized and / or improved according to actual needs: Example 2: Its difference from Example 1 is as follows: (See attached) Figure 1 As shown, the device also includes a cooler 19. A first circulation pipeline 20 is fixedly connected between the bottom outlet of the cooler 19 and the middle inlet of the atmospheric pressure absorption tower 1. A second circulation pipeline 21 is fixedly connected between the bottom outlet of the atmospheric pressure absorption tower 1 and the top inlet of the cooler 19. A first circulation pump 22 is fixedly installed on the second circulation pipeline 21.

[0029] As required, the stuffing box of the atmospheric pressure absorption tower 1 includes an upper stuffing box section and a lower stuffing box section. A condensate spraying device is installed between the upper stuffing box section and the lower stuffing box section. The dilute ammonia water in the lower part of the lower stuffing box section enters the cooler 19, is condensed, and then returns to the spraying device in the upper part of the lower stuffing box section, thus establishing a circulating condensation system for the liquid phase medium in the lower part of the atmospheric pressure absorption tower 1. This can promote the absorption of ammonia gas by the dilute ammonia water in the atmospheric pressure absorption tower 1. When the liquid level of the lower liquid phase in the atmospheric pressure absorption tower 1 exceeds the allowable liquid level of the production process design, the liquid phase medium in the lower part of the atmospheric pressure absorption tower 1 enters the tail gas venting cylinder 5 through its own liquid level pressure difference.

[0030] Example 3: Its difference from Examples 1 to 2 is as follows: (See attached) Figure 1 As shown, the device also includes a third condenser 23, a fifth gas phase pipeline 24 fixedly connected between the first gas phase pipeline 11 between the vent pipeline 10 and the fourth gas phase pipeline 17, a fourth liquid phase pipeline 25 fixedly connected between the bottom outlet of the third condenser 23 and the second liquid phase pipeline 14 between the third liquid phase pipeline 15 and the first inlet at the top of the ammonia tank 3, and a sixth gas phase pipeline 26 fixedly connected between the fourth liquid phase pipeline 25 and the vent pipeline 10 between the first gas phase pipeline 11 and the third gas phase pipeline 13.

[0031] Example 4: Its difference from Examples 1 to 3 is as follows: (See attached) Figure 1 As shown, a steam extractor 27 is fixedly installed on the second gas phase pipeline 12, and a steam pipeline 28 is fixedly connected to the steam extractor 27.

[0032] If required, when the vacuum degree (stripping capacity) inside the pre-concentrator 6 drops to the minimum allowable index of the production process, the steam consumption of the steam extractor 27 can be increased to ensure the vacuum degree requirement of the pre-concentrator 6 during normal production operation. If the steam extractor 27 still cannot guarantee the vacuum requirement of the pre-concentrator 6, the air intake of the first condenser 2 needs to be reduced.

[0033] Example 5: It differs from Examples 1 to 4 in that: as shown in the appendix Figure 1As shown, a flash steam pipeline 29 is fixedly connected to the inlet of the pre-concentrator 6, and a potassium ammonia liquid input pipeline 30 is fixedly connected to the flash steam pipeline 29. A potassium ammonia liquid output pipeline 31 is fixedly connected to the outlet of the pre-concentrator 6, and a potassium ammonia liquid diversion pipeline 32 is fixedly connected between the potassium ammonia liquid input pipeline 30 and the potassium ammonia liquid output pipeline 31.

[0034] As needed, a shell-and-tube heat exchanger is installed inside the pre-concentrator 6. The pre-concentrator 6 heats and concentrates the dilute urine entering it through the shell-and-tube heat exchanger. Before the flash steam enters the pre-concentrator 6 through the flash steam pipeline 29, the low-pressure potassium ammonia solution discharged from the upstream low-pressure process system is injected into the flash steam pipeline 29 through the potassium ammonia solution input pipeline 30. After the low-pressure potassium ammonia solution and flash steam are mixed, a stable steam flow is obtained, which then enters the shell side of the heat exchanger of the pre-concentrator 6 to heat and concentrate the dilute urine entering the tube side of the heat exchanger.

[0035] If required, when the flash steam transported by flash steam pipeline 29 does not require a large amount of low-pressure potassium ammonia solution to be mixed, the low-pressure potassium ammonia solution transported by potassium ammonia solution input pipeline 30 can also be diverted to potassium ammonia solution output pipeline 31 via potassium ammonia solution diversion pipeline 32 to enter the downstream medium-pressure process system.

[0036] Example 6: Its difference from Examples 1 to 5 is as follows: (See attached) Figure 1 As shown, a fifth liquid phase pipeline 37 is fixedly connected between the lower outlet of the ammonia tank 3 and the upper inlet of the tail gas venting cylinder 5. A second circulation pump 38 is fixedly installed on the fifth liquid phase pipeline 37. A sixth liquid phase pipeline 39 is fixedly connected between the lower outlet of the tail gas venting cylinder 5 and the second inlet at the top of the ammonia tank 3.

[0037] As needed, a condensate spraying device 40 is installed at the upper part of the gas phase inlet of the tail gas venting cylinder 5, and a condensate collection tank 41 is installed at the bottom of the tail gas venting cylinder 5. The liquid phase medium at the bottom of the atmospheric pressure absorption tower 1 enters the condensate collection tank 41. When the liquid level in the condensate collection tank 41 exceeds the allowable liquid level of the production process design, the solution in the condensate collection tank 41 is discharged into the ammonia water tank 3. The ammonia water in the ammonia water tank 3 can enter the condensate spraying device 40 to spray and condense the gas phase medium entering the tail gas venting cylinder 5, and then the gas in the tail gas venting cylinder 5 is vented.

[0038] Example 7: Its difference from Examples 1 to 6 is as follows: (See attached) Figure 1 As shown, the liquid inlets at the left ends of the first condenser 2, the second condenser 4, the cooler 19, and the third condenser 23 are all fixedly connected to condensate input pipelines 33, and the liquid outlets at the right ends of the first condenser 2, the second condenser 4, the cooler 19, and the third condenser 23 are all fixedly connected to condensate output pipelines 34.

[0039] As required, the first condenser 2, the second condenser 4, the cooler 19 and the third condenser 23 are all shell and tube heat exchangers. The condensate enters the tube side of the shell and tube heat exchanger to cool and condense the medium in the shell side of the shell and tube heat exchanger.

[0040] Example 8: It differs from Examples 1 to 7 in that, as shown in the appendix... Figure 1 As shown, thermometers 35 are fixedly installed on the second liquid phase pipeline 14 between the bottom outlet of the second condenser 4 and the third liquid phase pipeline 15, the fourth liquid phase pipeline 25 between the bottom outlet of the third condenser 23 and the sixth gas phase pipeline 26.

[0041] As needed, the real-time temperature values ​​displayed on thermometer 35 are the liquid outlet temperatures at the bottom of the first condenser 2, the second condenser 4, and the third condenser 23. Observing the liquid outlet temperatures of each condenser helps determine their operating status and prevents excessive condensation that could cause pipe blockage. When the liquid outlet temperatures of any condenser are too low, the air intake at the top of the first condenser 2, the second condenser 4, and the third condenser 23 can be increased, or the amount of condensate used in the first condenser 2, the second condenser 4, and the third condenser 23 can be reduced.

[0042] Example 9: It differs from Examples 1 to 8 in that: as shown in the appendix Figure 1 As shown, control valves 36 are fixedly installed on the vent line 10 between the first gas phase line 11 and the sixth gas phase line 26, the first gas phase line 11 between the vent line 10 and the fifth gas phase line 24, the first gas phase line 11 between the fifth gas phase line 24 and the fourth gas phase line 17, the third gas phase line 13, the fifth gas phase line 24, the sixth gas phase line 26, and the steam line 28.

[0043] Example 10: It differs from Examples 1 to 9 in that, as shown in the appendix... Figure 1 As shown, the device also includes a controller, and the thermometer 35 and the control valve 36 are electrically connected to the controller.

[0044] Depending on the needs, the pipelines and equipment of the urea production process tail gas recovery and utilization device may also be equipped with conventional valves, thermometers, and pressure gauges known and commonly used in the field, according to production requirements. The controller is a PLC controller, and the model of the PLC controller can be Zhejiang University Control FCU711-S, which is equipped with the Zhejiang University Control ECS-700 control system.

[0045] The above technical features constitute various embodiments of this utility model, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

[0046] The usage process of this utility model embodiment is as follows: First, the dilute ammonia water output from the upstream low-pressure process system enters the atmospheric pressure absorption tower 1 through the dilute ammonia water pipeline 7. The mixed tail gas (mainly containing ammonia) output from the upstream low-pressure process system enters the atmospheric pressure absorption tower 1 through the low-pressure gas phase pipeline 8. The dilute ammonia water in the atmospheric pressure absorption tower 1 absorbs the ammonia in the mixed gas. The ammonia water at the bottom of the atmospheric pressure absorption tower 1 enters the tail gas venting cylinder 5 for buffering through the first liquid phase pipeline 9. Second, the unabsorbed gas at the top of the atmospheric pressure absorption tower 1 enters the first condenser 2 for condensation through the venting pipeline 10 and the first gas phase pipeline 11. The resulting dilute ammonia water enters the ammonia water tank 3 for storage through the third liquid phase pipeline 15 and the second liquid phase pipeline 14. Third, the gas that is not completely condensed in the first condenser 2 enters the second condenser 4 for condensation through the second gas phase pipeline 12. The resulting dilute ammonia water enters the ammonia water tank 3 for storage through the second liquid phase pipeline 14. The gas that is not completely condensed in the second condenser 4 enters the second condenser 4 for condensation again. The gas is condensed and then vented through the third gas phase pipeline 13 and the vent pipeline 10 into the tail gas venting cylinder 5. In the fourth step, when the condensation capacity of the first condenser 2 reaches full load, the unabsorbed gas in the upper part of the atmospheric pressure absorption tower 1 is diverted to the third condenser 23 through the fifth gas phase pipeline 24 for condensation. The resulting dilute ammonia water is stored in the ammonia water tank 3 through the fourth liquid phase pipeline 25 and the second liquid phase pipeline 14. A small amount of uncondensed gas in the fourth liquid phase pipeline 25 is condensed and then vented through the sixth gas phase pipeline 26 and the vent pipeline 10 into the tail gas venting cylinder 5. In the fifth step, the dilute urine output from the upstream low-pressure process system enters the pre-concentrator 6 through the dilute urine pipeline 16 for heating and concentration. The gas in the upper part of the pre-concentrator 6 enters the first condenser 2 through the fourth gas phase pipeline 17 and the first gas phase pipeline 11 for condensation. The urea solution obtained by the pre-concentrator 6 is entered into the downstream evaporation system through the urine pipeline 18 to produce urea products.

Claims

1. A tail gas recovery unit in a urea production process, characterized by The system includes an atmospheric pressure absorption tower, a first condenser, an ammonia water tank, a second condenser, a tail gas venting cylinder, and a pre-concentrator. A dilute ammonia water pipeline is fixedly connected to the upper inlet of the atmospheric pressure absorption tower. A low-pressure gas phase pipeline is fixedly connected to the lower inlet of the atmospheric pressure absorption tower. A first liquid phase pipeline is fixedly connected between the lower outlet of the atmospheric pressure absorption tower and the lower inlet of the tail gas venting cylinder. A venting pipeline is fixedly connected between the top outlet of the atmospheric pressure absorption tower and the middle inlet of the tail gas venting cylinder. A first gas phase pipeline is fixedly connected between the venting pipeline and the top inlet of the first condenser. The first outlet at the bottom of the first condenser is connected to the top inlet of the second condenser. A second gas phase pipeline is fixedly connected between the top outlet of the second condenser and the vent pipeline between the first gas phase pipeline and the middle inlet of the tail gas venting cylinder. A third gas phase pipeline is fixedly connected between the bottom outlet of the second condenser and the first inlet at the top of the ammonia tank. A third liquid phase pipeline is fixedly connected between the second outlet at the bottom of the first condenser and the second liquid phase pipeline. A dilute urine pipeline is fixedly connected to the upper inlet of the pre-concentrator. A fourth gas phase pipeline is fixedly connected between the top outlet of the pre-concentrator and the first gas phase pipeline. A urine pipeline is fixedly connected to the bottom outlet of the pre-concentrator.

2. The off-gas recovery device in a urea production process according to claim 1, characterized in that It also includes a cooler, with a first circulation pipeline fixedly connected between the bottom outlet of the cooler and the middle inlet of the atmospheric pressure absorption tower, and a second circulation pipeline fixedly connected between the bottom outlet of the atmospheric pressure absorption tower and the top inlet of the cooler, with a first circulation pump fixedly installed on the second circulation pipeline.

3. The off-gas recovery device in a urea production process according to claim 1 or 2, characterized in that It also includes a third condenser, a fifth gas phase pipeline that is fixedly connected between the first gas phase pipeline between the vent pipeline and the fourth gas phase pipeline and the top inlet of the third condenser, a fourth liquid phase pipeline that is fixedly connected between the bottom outlet of the third condenser and the second liquid phase pipeline between the third liquid phase pipeline and the first inlet at the top of the ammonia tank, and a sixth gas phase pipeline that is fixedly connected between the fourth liquid phase pipeline and the vent pipeline between the first and third gas phase pipelines.

4. The off-gas recovery apparatus in a urea production process according to claim 3, characterized in that A steam extractor is fixedly installed on the second gas phase pipeline, and a steam pipeline is fixedly connected to the steam extractor.

5. The urea production process off-gas recovery device according to claim 1 or 2 or 4, characterized in that A flash steam pipeline is fixedly connected to the inlet of the pre-concentrator, and a potassium ammonia liquid input pipeline is fixedly connected to the flash steam pipeline. A potassium ammonia liquid output pipeline is fixedly connected to the outlet of the pre-concentrator, and a potassium ammonia liquid diversion pipeline is fixedly connected between the potassium ammonia liquid input pipeline and the potassium ammonia liquid output pipeline.

6. The off-gas recovery device in a urea production process according to claim 5, characterized in that A fifth liquid phase pipeline is fixedly connected between the lower outlet of the ammonia tank and the upper inlet of the tail gas venting cylinder. A second circulation pump is fixedly installed on the fifth liquid phase pipeline. A sixth liquid phase pipeline is fixedly connected between the lower outlet of the tail gas venting cylinder and the second inlet at the top of the ammonia tank.

7. The off-gas recovery device in a urea production process according to claim 4 or 6, characterized in that The left inlets of the first condenser, second condenser, cooler, and third condenser are all fixedly connected to condensate input pipelines, and the right outlets of the first condenser, second condenser, cooler, and third condenser are all fixedly connected to condensate output pipelines.

8. The off-gas recovery device in a urea production process according to claim 7, characterized in that Temperature gauges are fixedly installed on the second liquid phase pipeline between the bottom outlet of the second condenser and the third liquid phase pipeline, the third liquid phase pipeline, and the fourth liquid phase pipeline between the bottom outlet of the third condenser and the sixth gas phase pipeline.

9. The off-gas recovery device in a urea production process according to claim 8, characterized in that Control valves are fixedly installed on the vent line between the first and sixth gas phase lines, the first gas phase line between the vent line and the fifth gas phase line, the first gas phase line between the fifth and fourth gas phase lines, the third gas phase line, the fifth gas phase line, the sixth gas phase line, and the steam line.

10. The off-gas recovery device in a urea production process according to claim 9, characterized in that It also includes a controller, a thermometer, and a control valve, all of which are electrically connected to the controller.

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