A system for controlling the water-to-carbon ratio in the co-production of urea and triamine

Abstract

The application provides a water-carbon ratio control system for urea and triamine coproduction, comprising a urea synthesis loop, a triamine tail gas introduction unit and a split processing unit, the urea synthesis loop is sequentially connected with a high-pressure synthesis unit, a medium-pressure unit and a low-pressure unit; the triamine tail gas introduction unit sends triamine tail gas into the low-pressure unit to form a low-pressure recovery liquid phase, the split processing unit splits the liquid phase and separates it into a first gas phase and a first liquid phase, the first gas phase is sent to a pre-concentration separation unit to recover heat, and the first liquid phase is connected to the medium-pressure unit, so that the water bypasses the high-pressure synthesis unit, enters the low-pressure unit through the medium-pressure unit and is discharged from the system; the application solves the problem that the water in the triamine tail gas enters the high-pressure synthesis unit, resulting in the uncontrolled increase of the water-carbon ratio, maintains the water-carbon ratio in an ideal range, improves the urea synthesis conversion rate, reduces unreacted substances, reduces the steam consumption of the stripping tower and the operation load of the medium and low-pressure units, does not need to passively increase the ammonia-carbon ratio, avoids the waste of ammonia raw materials and the loss of venting.

Description

Technical Field

[0001] This application generally relates to the field of urea production technology, and specifically to a water-to-carbon ratio control system for the co-production of urea and melamine. Background Technology

[0002] Co-production of urea and melamine is an important production model for achieving resource recycling in the chemical industry. The melamine unit uses urea solution as raw material for production, while simultaneously producing melamine tail gas containing ammonia and carbon dioxide as a byproduct. To improve the overall raw material utilization rate, the effective gases in these tail gases need to be reintroduced into the urea system to participate in the synthesis reaction. In existing co-production processes, the melamine tail gas is usually recovered by adding water to form an aqueous solution, which is then cooled and condensed before entering the low-pressure ammonium carbamate condenser of the urea unit. Subsequently, it follows a fixed process path, sequentially entering the medium-pressure and high-pressure systems, and finally converging into the urea synthesis tower.

[0003] However, existing process routes have inherent design limitations, leading to a series of long-term technical challenges for the intermodal system. Because the triamine tail gas aqueous solution carries a large amount of water, and the existing process forces it into the high-pressure system, the water-to-carbon ratio in the urea synthesis tower rises uncontrollably. As a key parameter affecting the equilibrium of the urea synthesis reaction, an increase in the water-to-carbon ratio directly leads to a decrease in the synthesis conversion rate, resulting in a significant increase in unreacted ammonia and carbon dioxide. To avoid unreacted materials exceeding the processing capacity of the high, medium, and low-pressure systems and causing system shutdowns, the existing process can only passively increase the ammonia-to-carbon ratio to maintain operation. While this adjustment can temporarily stabilize the conversion rate, it introduces further problems: the excess ammonia needs to be absorbed by more water, pushing the water-to-carbon ratio further up, creating a vicious cycle; or it may have to be vented through the low-pressure absorption tower, resulting in raw material waste. Furthermore, the increase in unreacted materials also significantly increases the steam consumption of the stripping tower, while simultaneously increasing the operating load of the medium- and low-pressure recovery systems, affecting the long-term stable operation of the unit. Summary of the Invention

[0004] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a water-carbon ratio control system for the co-production of urea and triamine that can solve the above-mentioned technical problems.

[0005] This application provides a water-to-carbon ratio control system for the co-production of urea and triamine, comprising: A urea synthesis circuit, comprising a high-pressure synthesis unit, a medium-pressure unit, and a low-pressure unit connected in sequence. The triamine tail gas introduction unit is connected to the low-pressure unit. The triamine tail gas introduction unit is used to send the triamine tail gas into the low-pressure unit, and after being condensed and absorbed by the low-pressure unit, it forms a low-pressure recovery liquid phase. The diversion processing unit has its inlet connected to the output pipeline of the low-pressure recovered liquid phase. The diversion processing unit is used to divert part of the low-pressure recovered liquid phase and separate it into a first liquid phase and a first gas phase. The diversion processing unit has a first gas phase outlet and a first liquid phase outlet; the first gas phase outlet is connected to the inlet of the pre-concentration separation unit so that the first gas phase is sent to the pre-concentration separation unit for heat recovery; the first liquid phase outlet is connected to the inlet of the medium-pressure unit so that the water contained in the first liquid phase enters the low-pressure unit through the medium-pressure unit, thereby bypassing the high-pressure synthesis unit.

[0006] According to the technical solution provided in this application, the traffic splitting processing unit includes: The first heat exchanger has its inlet connected to the output pipeline of the low-pressure recovered liquid phase, and is used to heat the diverted low-pressure recovered liquid phase. The first separator has its inlet connected to the outlet of the first heat exchanger. The first gas phase outlet and the first liquid phase outlet are both located on the first separator. The first separator is used to separate the heated low-pressure recovered liquid phase into the first liquid phase and the first gas phase.

[0007] According to the technical solution provided in this application, the diversion processing unit further includes: a regulating valve, which is disposed at the inlet of the first heat exchanger and is used to regulate the flow rate into the first heat exchanger.

[0008] According to the technical solution provided in this application, it further includes: a control device, which is connected to the regulating valve, and the control device is configured to control the opening degree of the regulating valve according to the water-carbon ratio feedback signal of the high-pressure synthesis unit.

[0009] According to the technical solution provided in this application, the medium-pressure unit includes: A medium-pressure decomposition tower, the inlet of which is connected to the high-pressure synthesis unit, is used to receive the reaction mixture from the high-pressure synthesis unit and perform gas-liquid separation to output a second gas phase and a second liquid phase. The medium-pressure decomposition tower has a second gas phase outlet and a second liquid phase outlet; the second liquid phase outlet is connected to the inlet of the low-pressure unit; the second gas phase outlet is connected to the heat source medium inlet of the pre-concentration separation unit. A medium-pressure ammonium carbamate condenser, wherein the inlet of the medium-pressure ammonium carbamate condenser is connected to the shell-side outlet of the pre-concentration separation unit, and the medium-pressure ammonium carbamate condenser is used to condense the gas-liquid mixture from the pre-concentration separation unit; A medium-pressure separator is provided, with its inlet connected to the outlet of the medium-pressure ammonium carbamate condenser. The medium-pressure separator is used to separate the condensed gas-liquid mixture into a medium-pressure recovered liquid phase and a medium-pressure recovered gas phase. The medium-pressure separator has a third liquid phase outlet and a third gas phase outlet. The third liquid phase outlet is connected to the high-pressure synthesis unit and is used to feed the medium-pressure recovered liquid phase into the high-pressure synthesis unit. The third gas phase outlet is connected to the low-pressure unit and is used to feed the medium-pressure recovered gas phase into the low-pressure unit.

[0010] According to the technical solution provided in this application, the low-voltage unit includes: A low-pressure decomposition tower, wherein the inlet of the low-pressure decomposition tower is connected to the outlet of the second liquid phase, for receiving the second liquid phase and performing gas-liquid separation to output a fourth gas phase and a fourth liquid phase, the low-pressure decomposition tower having a fourth gas phase outlet and a fourth liquid phase outlet; the fourth liquid phase outlet is connected to the liquid phase inlet of the pre-concentration separation unit; A low-pressure ammonium carbamate condenser, the inlet of which is connected to the fourth gas phase outlet, the third gas phase outlet, and the outlet of the melamine tail gas inlet unit; the low-pressure ammonium carbamate condenser is used to condense the fourth gas phase, the medium-pressure recovery gas phase, and the melamine tail gas to generate a first mixture; A low-pressure separator, the inlet of which is connected to the outlet of the low-pressure ammonium carbamate condenser, is used to separate the first mixture into a low-pressure recovery liquid phase and a low-pressure recovery gas phase; the low-pressure separator has a fifth gas phase outlet and a fifth liquid phase outlet, the fifth gas phase outlet being connected to a low-pressure absorption unit, and the fifth liquid phase outlet being connected to the heat source medium inlet of the pre-concentration separation unit; The output pipeline between the fifth liquid phase outlet and the heat source medium inlet is connected to the inlet of the first heat exchanger.

[0011] According to the technical solution provided in this application, the pre-concentration separation unit includes: A pre-concentrating separator, comprising a heat source medium inlet, a liquid phase inlet, a shell-side outlet, a sixth gas phase outlet, and a sixth liquid phase outlet; wherein: The heat source medium inlet is connected to the second gas phase outlet, the fifth liquid phase outlet and the first gas phase outlet respectively, and is used to receive the second gas phase, the low-pressure recovered liquid phase and the first gas phase as heat source medium to provide the heat required for liquid phase concentration. The liquid phase inlet is connected to the fourth liquid phase outlet and is used to receive the fourth liquid phase to be concentrated; The shell-side outlet is connected to the inlet of the medium-pressure ammonium carbamate condenser, and is used to send the heat-exchanged gas-liquid mixture to the medium-pressure ammonium carbamate condenser for recovery. The sixth liquid phase outlet is connected to the urine tank and is used to deliver concentrated liquid phase to the urine tank; The sixth gas phase outlet is connected to the first condenser and is used to output the evaporated gas phase; the first condenser has a seventh liquid phase outlet and a seventh gas phase outlet, the seventh liquid phase outlet is connected to the inlet of the ammonia water tank and is used to send the ammonia water formed by condensing the evaporated gas phase into the ammonia water tank; the seventh gas phase outlet is connected to the venting system.

[0012] According to the technical solution provided in this application, the melamine tail gas introduction unit includes: The tail gas condenser has an inlet for receiving melamine tail gas and an outlet connected to the inlet of the low-pressure ammonium carbamate condenser for sending the condensed melamine tail gas into the low-pressure ammonium carbamate condenser.

[0013] According to the technical solution provided in this application, the high-pressure synthesis unit includes: a high-pressure ammonium carbamate condenser, a stripping tower, a urea synthesis tower, and a high-pressure scrubber; the stripping tower has an eighth liquid phase outlet and an eighth gas phase outlet, the urea synthesis tower has a ninth liquid phase outlet and a ninth gas phase outlet, and the high-pressure scrubber has a tenth liquid phase outlet and a tenth gas phase outlet. The inlet of the high-pressure ammonium carbamate condenser is connected to the ammonia source, the tenth liquid phase outlet and the eighth gas phase outlet, respectively. The high-pressure ammonium carbamate condenser is used to generate and output an ammonium carbamate mixture. The inlet of the urea synthesis tower is connected to the outlet of the high-pressure ammonium carbamate condenser. The urea synthesis tower is used to receive the ammonium carbamate mixture and carry out the urea synthesis reaction to generate a synthesis liquid phase and a synthesis gas phase. The inlet of the stripping tower is connected to a carbon dioxide source and a ninth liquid phase outlet, respectively, and the eighth liquid phase outlet is connected to the inlet of the medium-pressure decomposition tower. The stripping tower is used to strip the synthetic liquid phase using carbon dioxide, separate the reaction mixture and the stripping gas phase, and input the reaction mixture into the medium-pressure decomposition tower and the stripping gas phase into the high-pressure ammonium carbamate condenser. The inlet of the high-pressure scrubber is connected to the ninth gas phase outlet, and the tenth gas phase outlet is connected to the low-pressure absorption unit. The high-pressure scrubber is used to wash the unreacted substances in the synthesis gas phase and input the resulting ammonium carbamate solution into the high-pressure ammonium carbamate condenser.

[0014] According to the technical solution provided in this application, the low-pressure absorption unit includes: The first absorption tower has a first air inlet, a first liquid inlet, a first liquid outlet, and a first air outlet. The first air inlet is connected to the tenth gas phase outlet and is used to receive the exhaust gas from the high-pressure scrubber. The first liquid inlet is connected to the outlet of the ammonia tank and is used to receive ammonia water from the ammonia tank as the absorption liquid. The first air outlet is connected to the venting system. The second absorption tower has a second air inlet, a second liquid inlet, a second liquid outlet, and a second air outlet. The second air inlet is connected to the fifth gas phase outlet and is used to receive the low-pressure recovered gas phase. The second liquid inlet is connected to the first liquid outlet and is used to receive the liquid phase from the first absorption tower as the absorbent. The second air outlet is connected to the venting system. The second liquid outlet is connected to the inlet of the ammonia water tank and is used to send the absorbed ammonia water into the ammonia water tank.

[0015] The beneficial effects of this application are as follows: This application provides a water-to-carbon ratio control system for the co-production of urea and triamine, including a urea synthesis circuit, a triamine tail gas inlet unit, and a diversion treatment unit. The urea synthesis circuit includes a high-pressure synthesis unit, a medium-pressure unit, and a low-pressure unit connected in sequence. The triamine tail gas inlet unit is connected to the low-pressure unit and is used to send triamine tail gas into the low-pressure unit, where it is condensed and absorbed to form a low-pressure recovered liquid phase. The inlet of the diversion treatment unit is connected to the output pipeline of the low-pressure recovered liquid phase, and the diversion treatment unit is used to divert part of the low-pressure recovered liquid phase and separate it into a first liquid phase and a first gas phase. The diversion treatment unit has a first gas phase outlet and a first liquid phase outlet. The first gas phase outlet is connected to the inlet of a pre-concentration separation unit so that the first gas phase is sent to the pre-concentration separation unit for heat recovery. The first liquid phase outlet is connected to the inlet of the medium-pressure unit so that the water contained in the first liquid phase enters the low-pressure unit through the medium-pressure unit, thereby bypassing the high-pressure synthesis unit.

[0016] This application introduces a diversion treatment unit into the low-pressure recovered liquid phase output pipeline to divert and separate the low-pressure recovered liquid phase containing triamine tail gas components from the low-pressure unit. The first gas phase obtained from the separation is sent to the pre-concentration separation unit to recover heat and materials, while the first liquid phase obtained from the separation is returned to the inlet of the medium-pressure unit. This allows the water carried in the first liquid phase to flow along the process paths of the medium-pressure and low-pressure units and finally be discharged from the system, bypassing the high-pressure synthesis unit entirely. This fundamentally solves the technical problem in existing urea and triamine co-production processes where the water carried by the triamine tail gas passively enters the high-pressure synthesis unit, leading to an uncontrollable increase in the system's water-to-carbon ratio. Since external water no longer enters the high-pressure synthesis unit to participate in the urea synthesis reaction, the water-to-carbon ratio in the high-pressure synthesis unit is stably maintained within the ideal range, effectively avoiding a decrease in synthesis conversion rate due to an abnormal increase in the water-to-carbon ratio, thereby reducing the generation of unreacted ammonia and carbon dioxide in the system. The reduction of unreacted substances not only effectively reduces the steam consumption of the stripping tower, but also reduces the recovery operation load of the medium-pressure and low-pressure units; it also eliminates the need to maintain system operation by passively increasing the ammonia-carbon ratio, fundamentally avoiding raw material waste and system venting losses caused by excessive ammonia, and achieving efficient, low-consumption, and stable operation of the cogeneration system. Attached Figure Description

[0017] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a water-to-carbon ratio control system for the co-production of urea and triamine provided in Embodiment 1 of this application; Figure 2 This is a schematic diagram of the diversion processing unit provided in Embodiment 1 of this application.

[0018] In the diagram: 1. First heat exchanger; 2. First separator; 21. First gas phase outlet; 22. First liquid phase outlet; 3. Control valve; 4. Medium-pressure decomposition tower; 41. Second gas phase outlet; 42. Second liquid phase outlet; 5. Medium-pressure ammonium carbamate condenser; 6. Medium-pressure separator; 61. Third gas phase outlet; 62. Third liquid phase outlet; 7. Low-pressure decomposition tower; 71. Fourth gas phase outlet; 72. Fourth liquid phase outlet; 8. Low-pressure ammonium carbamate condenser; 9. Low-pressure separator; 91. Fifth gas phase outlet; 92. Fifth liquid phase outlet; 10. Pre-concentration section 101. Heat source medium inlet; 102. Liquid phase inlet; 103. Shell side outlet; 104. Sixth gas phase outlet; 105. Sixth liquid phase outlet; 11. Urea tank; 12. First condenser; 13. Ammonia tank; 14. Tail gas condenser; 15. High-pressure ammonium carbamate condenser; 16. Urea synthesis tower; 161. Ninth gas phase outlet; 162. Ninth liquid phase outlet; 17. Stripping tower; 171. Eighth gas phase outlet; 172. Eighth liquid phase outlet; 18. High-pressure scrubber; 19. First absorption tower; 20. Second absorption tower. Detailed Implementation

[0019] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] Example 1 Please refer to Figures 1-2 This application provides a water-to-carbon ratio control system for the co-production of urea and triamine, comprising: The urea synthesis circuit includes a high-pressure synthesis unit, a medium-pressure unit, and a low-pressure unit connected in sequence. The melamine tail gas introduction unit is connected to the low-pressure unit. The melamine tail gas introduction unit is used to send the melamine tail gas into the low-pressure unit, where it is condensed and absorbed to form a low-pressure recovered liquid phase. The diversion processing unit has its inlet connected to the output pipeline of the low-pressure recovered liquid phase. The diversion processing unit is used to divert part of the low-pressure recovered liquid phase and separate it into a first liquid phase and a first gas phase. The diversion processing unit has a first gas phase outlet 21 and a first liquid phase outlet 22; the first gas phase outlet 21 is connected to the inlet of the pre-concentration separation unit so that the first gas phase is sent to the pre-concentration separation unit for heat recovery; the first liquid phase outlet 22 is connected to the inlet of the medium-pressure unit so that the water contained in the first liquid phase enters the low-pressure unit through the medium-pressure unit, thereby bypassing the high-pressure synthesis unit.

[0022] Specifically, the urea synthesis loop of this application adopts a high-pressure urea generation process, consisting of a high-pressure synthesis unit, a medium-pressure unit, and a low-pressure unit connected in sequence. Each unit works collaboratively to complete the urea synthesis reaction and the recovery and recycling of unreacted ammonia and carbon dioxide. Based on this conventional process, a melamine tail gas introduction unit is added. This unit is connected to the low-pressure unit and is used to send the melamine tail gas containing ammonia, carbon dioxide, and water, a byproduct of the melamine unit, into the low-pressure unit. After entering the low-pressure unit, the melamine tail gas undergoes a condensation and absorption process to form a low-pressure recovered liquid phase containing ammonia, carbon dioxide, and water. In existing co-production processes, this low-pressure recovered liquid phase flows back to the high-pressure synthesis unit via a fixed process path through the medium-pressure unit, directly causing an uncontrollable increase in the water-to-carbon ratio within the high-pressure synthesis unit. This leads to a series of cascading technical problems, such as a decrease in urea synthesis conversion rate, a significant increase in system ammonia consumption, and a surge in energy consumption in each unit.

[0023] To solve this technical problem, such as Figure 1 As shown, this application includes a diversion processing unit on the output pipeline of the low-pressure recovered liquid phase. The inlet of the diversion processing unit is connected to the output pipeline of the low-pressure recovered liquid phase, and it is used to divert a portion of the stream from the low-pressure recovered liquid phase for specific treatment. This application adopts a partial diversion processing method, rather than processing the entire low-pressure recovered liquid phase. This allows for precise and effective adjustment of the water-to-carbon ratio in the high-pressure synthesis unit, while also allowing the main stream material of the low-pressure recovered liquid phase to enter the pre-concentration and separation unit according to the original process path, ensuring the stable operation of the entire urea and melamine co-production system. The core function of the diversion processing unit is to separate the diverted low-pressure recovered liquid phase into a first liquid phase and a first gas phase after heating. This separation process is based on the difference in the volatility characteristics of ammonia, carbon dioxide, and water. Ammonia and carbon dioxide preferentially vaporize under heating conditions to form the first gas phase, while water mainly remains in the liquid phase, thus achieving an effective preliminary separation of gas and water. The first gas phase is a gas mixture rich in ammonia and carbon dioxide, which may contain a small amount of water vapor; the first liquid phase is a liquid mixture mainly composed of water, with dissolved small amounts of ammonia and carbon dioxide.

[0024] The diversion processing unit has a first gas phase outlet 21 and a first liquid phase outlet 22. The first gas phase outlet 21 is connected to the inlet of the pre-concentration separation unit, sending the separated first gas phase, rich in ammonia and carbon dioxide, to the pre-concentration separation unit for heat recovery. This setup has two considerations: firstly, the ammonia and carbon dioxide in the first gas phase can be absorbed by the urine in the pre-concentration separation unit, achieving efficient recovery of effective reactants and avoiding raw material waste; secondly, the process heat carried by the first gas phase can be directly used in the urine concentration process, making full use of waste heat to reduce the overall energy consumption of the system. The first liquid phase outlet 22 is connected to the inlet of the medium-pressure unit, sending the separated first liquid phase, containing a large amount of water, back to the medium-pressure unit. After entering the medium-pressure unit, the first liquid phase is thoroughly mixed with the reaction mixture from the high-pressure synthesis unit. The water contained therein will flow sequentially through the medium-pressure unit and the low-pressure unit along the main urine process path, finally entering the pre-concentration separation unit for heating and concentration. In the pre-concentration and separation unit, most of the water is discharged as an evaporated gas phase, which is then condensed to form ammonia water. The residual water enters the subsequent processing steps with the concentrated liquid phase and is finally discharged from the device through the desorption and hydrolysis system. Through this setup, the water in the first liquid phase successfully bypasses the high-pressure synthesis unit and no longer participates in the urea synthesis reaction under high pressure. This fundamentally avoids interference from external water on the high-pressure synthesis reaction, allowing the water-to-carbon ratio of the high-pressure synthesis unit to be stably maintained within the ideal process range.

[0025] Working Principle: This application introduces a diversion treatment unit into the low-pressure recovered liquid phase output pipeline to divert and separate the low-pressure recovered liquid phase containing triamine tail gas components from the low-pressure unit. The first gas phase obtained from the separation is sent to the pre-concentration separation unit to recover heat and materials, while the first liquid phase obtained from the separation is returned to the inlet of the medium-pressure unit. This allows the water carried in the first liquid phase to flow along the process paths of the medium-pressure and low-pressure units and finally be discharged from the system, bypassing the high-pressure synthesis unit entirely. This fundamentally solves the technical problem in existing urea and triamine co-production processes where the water carried by the triamine tail gas passively enters the high-pressure synthesis unit, leading to an uncontrollable increase in the system's water-to-carbon ratio. Since external water no longer enters the high-pressure synthesis unit to participate in the urea synthesis reaction, the water-to-carbon ratio in the high-pressure synthesis unit is stably maintained within the ideal range, effectively avoiding a decrease in synthesis conversion rate due to an abnormal increase in the water-to-carbon ratio, thereby reducing the amount of unreacted ammonia and carbon dioxide produced in the system. The reduction of unreacted substances not only effectively reduces the steam consumption of stripping tower 17, but also reduces the recovery operation load of the medium-pressure unit and the low-pressure unit; it also eliminates the need to maintain system operation by passively increasing the ammonia-carbon ratio, fundamentally avoiding raw material waste and system venting losses caused by excessive ammonia, and achieving efficient, low-consumption and stable operation of the cogeneration system.

[0026] In some implementations, the traffic splitting unit includes: The first heat exchanger 1 has its inlet connected to the output pipeline of the low-pressure recovered liquid phase. The first heat exchanger 1 is used to heat the diverted low-pressure recovered liquid phase. The first separator 2 has its inlet connected to the outlet of the first heat exchanger 1. The first gas phase outlet 21 and the first liquid phase outlet 22 are both located on the first separator 2. The first separator 2 is used to separate the heated low-pressure recovered liquid phase into a first liquid phase and a first gas phase.

[0027] Specifically, such as Figure 2 As shown, the diversion processing unit consists of a first heat exchanger 1 and a first separator 2, which work together to achieve heating and gas-liquid separation of the diverted low-pressure recovered liquid phase. In this embodiment, the first heat exchanger 1 is a shell-and-tube heat exchanger, with a utility heat source stream flowing through its shell side and the inlet on its tube side connected to the output pipeline of the low-pressure recovered liquid phase, through which the diverted low-pressure recovered liquid phase is introduced. The low-pressure recovered liquid phase is heated through heat exchange between the heat source and the material, causing ammonia and carbon dioxide in the low-pressure recovered liquid phase to preferentially vaporize based on their volatility characteristics, laying the foundation for subsequent gas-liquid separation. According to the process requirements of urea and triamine co-production, the temperature of this heating process can be controlled within the range of 125°C to 160°C. This temperature range can ensure efficient gas-liquid separation of ammonia, carbon dioxide, and water, while avoiding unnecessary increases in system energy consumption due to excessively high heating temperatures, achieving an optimal balance between separation effect and energy consumption control.

[0028] The low-pressure recovered liquid phase, heated by the first heat exchanger 1, is in a gas-liquid mixed state. After flowing out of the outlet of the first heat exchanger 1, it enters the first separator 2 connected to it. The first separator 2, as the core equipment for gas-liquid separation, efficiently separates the input gas-liquid mixture. It has a first gas phase outlet 21 at the top and a first liquid phase outlet 22 at the bottom. During the separation process, the gas phase component rich in ammonia and carbon dioxide is discharged from the first gas phase outlet 21 to form the first gas phase, while the liquid phase component with a high water content is discharged from the first liquid phase outlet 22 to form the first liquid phase. The first gas phase obtained from the separation is sent to the pre-concentration separation unit, which serves as a heat source medium to provide heat for the urine concentration process, realizing the recovery and utilization of process waste heat. During the pre-concentration process, ammonia and carbon dioxide in the gas phase are absorbed by the urine and returned to the urea synthesis loop, achieving the recovery of effective reactants. The first liquid phase obtained from the separation, enriched with moisture carried by the triamine tail gas, is transported to the inlet of the medium-pressure unit. It then flows sequentially through the medium-pressure unit and low-pressure unit along the main path of urea synthesis into subsequent processing steps, finally being discharged from the device through the desorption and hydrolysis system. This design achieves the recovery and reuse of effective gases, while ensuring that the external moisture carried by the triamine tail gas bypasses the high-pressure synthesis unit and no longer participates in the urea synthesis reaction under high pressure. This prevents external moisture from interfering with the water-to-carbon ratio of the high-pressure synthesis unit from the material path, laying a key technological foundation for achieving active and precise control of the water-to-carbon ratio.

[0029] In some embodiments, the diversion processing unit further includes a regulating valve 3, which is disposed at the inlet of the first heat exchanger 1 and is used to regulate the flow rate into the first heat exchanger 1.

[0030] Specifically, in the process of co-producing urea and triamine, the water-to-carbon ratio of the high-pressure synthesis unit is easily affected by various process factors such as fluctuations in the water content of the triamine tail gas and changes in the system production load. If the split ratio of the low-pressure recovered liquid phase remains constant, it cannot adapt to these dynamic changes, resulting in unsatisfactory water-to-carbon ratio control. Therefore, this application installs a regulating valve 3 at the inlet of the first heat exchanger 1. By controlling the opening of the regulating valve 3, the flow rate of the low-pressure recovered liquid phase entering the first heat exchanger 1 can be flexibly adjusted, thereby precisely changing the overall split ratio of the low-pressure recovered liquid phase. This ensures that the operating state of the splitting treatment unit is adapted to the system operating conditions, guaranteeing that the water-to-carbon ratio of the high-pressure synthesis unit is within the ideal process range, and allowing the system to maintain optimal operating conditions.

[0031] Specifically, when the water-to-carbon ratio of the high-pressure synthesis unit is detected to be too high, the opening of regulating valve 3 is increased to increase the diversion ratio, allowing more low-pressure recovered liquid phase containing triamine tail gas components to enter the diversion treatment unit for heating and separation. This allows more water introduced with the triamine tail gas to bypass the high-pressure synthesis unit, quickly causing the water-to-carbon ratio of the high-pressure synthesis unit to drop back to the ideal range (in this embodiment, the ideal range of the water-to-carbon ratio is between 0.45 and 0.5). Conversely, when the water-to-carbon ratio of the high-pressure synthesis unit is detected to be too low, the opening of regulating valve 3 can be appropriately reduced to decrease the diversion ratio, reducing the processing volume of the low-pressure recovered liquid phase. This avoids excessive diversion affecting the normal circulation of materials within the system and ensures the stable operation of the urea and triamine co-production system.

[0032] In some embodiments, the system further includes a control device connected to the regulating valve 3, the control device being configured to control the opening degree of the regulating valve 3 based on the water-to-carbon ratio feedback signal from the high-pressure synthesis unit.

[0033] Specifically, in this application, the water-to-carbon ratio feedback signal is obtained collaboratively by an online analytical instrument adapted to the urea process and a calculation unit: an online analytical instrument adapted to its high-temperature, high-pressure, and corrosive media conditions is set in the high-pressure synthesis unit to detect the carbon dioxide and water content in the reactants in the high-pressure synthesis unit in real time; the calculation unit is a conventional calculation unit in the field of chemical process control (which can be built into the control device), which has a built-in water-to-carbon ratio calculation algorithm, receives the real-time detection data from the online analytical instrument and performs ratio calculations to generate the water-to-carbon ratio feedback signal.

[0034] The control device can adopt a distributed control system (DCS) or programmable logic controller (PLC) commonly used in chemical production. Its signal input terminal is communicatively connected to the computing unit to receive the water-carbon ratio feedback signal in real time, and its signal output terminal is electrically or pneumatically connected to the regulating valve 3 to achieve stable transmission of control signals. The control device has a pre-stored preset ideal range of water-carbon ratio for the high-pressure synthesis unit (in this embodiment, the preset ideal range of water-carbon ratio is 0.45~0.5), and has built-in automatic valve opening adjustment logic. This logic can compare and analyze the real-time received water-carbon ratio feedback signal with the preset ideal range, and automatically adjust the opening of the regulating valve 3 according to the comparison result, thereby dynamically controlling the flow rate and diversion ratio of the low-pressure recovered liquid phase entering the diversion treatment unit. Ultimately, the water-carbon ratio in the high-pressure synthesis unit is accurately and stably controlled within the preset ideal process range, realizing automated active control of the water-carbon ratio.

[0035] In some embodiments, the medium-pressure unit includes: The medium-pressure decomposition tower 4 has an inlet connected to the high-pressure synthesis unit and is used to receive the reaction mixture from the high-pressure synthesis unit and perform gas-liquid separation to output a second gas phase and a second liquid phase. The medium-pressure decomposition tower 4 has a second gas phase outlet 41 and a second liquid phase outlet 42. The second liquid phase outlet 42 is connected to the inlet of the low-pressure unit. The second gas phase outlet 41 is connected to the heat source medium inlet 101 of the pre-concentration separation unit. The medium-pressure ammonium carbamate condenser 5 has its inlet connected to the shell-side outlet 103 of the pre-concentration separation unit. The medium-pressure ammonium carbamate condenser 5 is used to condense the gas-liquid mixture from the pre-concentration separation unit. The medium-pressure separator 6 has its inlet connected to the outlet of the medium-pressure ammonium carbamate condenser 5. The medium-pressure separator 6 is used to separate the condensed gas-liquid mixture into a medium-pressure recovered liquid phase and a medium-pressure recovered gas phase. The medium-pressure separator 6 has a third liquid phase outlet 62 and a third gas phase outlet 61. The third liquid phase outlet 62 is connected to the high-pressure synthesis unit and is used to send the medium-pressure recovered liquid phase into the high-pressure synthesis unit. The third gas phase outlet 61 is connected to the low-pressure unit and is used to send the medium-pressure recovered gas phase into the low-pressure unit.

[0036] Specifically, the inlet of the medium-pressure decomposition tower 4 (in this embodiment, the medium-pressure decomposition tower 4 is a packed tower structure) is connected to the high-pressure synthesis unit and is used to receive the reaction mixture from the high-pressure synthesis unit after stripping. Before entering the medium-pressure decomposition tower 4, the stream is reduced from high pressure (approximately 14 MPa) to medium-pressure process pressure (approximately 2 MPa) by a pressure reducing valve. Inside the medium-pressure decomposition tower 4, residual ammonium carbamate in the reaction mixture is further decomposed by heating, while efficient gas-liquid separation is achieved. The processed stream is separated into a second gas phase and a second liquid phase. The second liquid phase is urine with a further increased urea concentration. It is output from the second liquid phase outlet 42 of the medium-pressure decomposition tower 4 and enters the inlet of the low-pressure unit, continuing to complete the subsequent ammonium carbamate decomposition and urine concentration along the low-pressure unit process path. The second gas phase is a gas mixture rich in ammonia, carbon dioxide, and water vapor. It is output from the second gas phase outlet 41 of the medium-pressure decomposition tower 4 and merges with the first gas phase from the diversion processing unit, jointly entering the heat source medium inlet 101 of the pre-concentration separation unit, serving as a heat source medium to provide heat for the urine concentration process in the pre-concentration separation unit. This application achieves deep decomposition of residual ammonium carbamate in the reaction mixture and increases the concentration of urea solution through decompression and heating treatment in medium-pressure decomposition tower 4. It also obtains a second gas phase rich in effective gases. At the same time, the second gas phase is combined with the first gas phase as a heat source for the pre-concentration separation unit, realizing the cascade utilization of process energy and reducing the overall energy consumption of the system.

[0037] The pre-concentration and separation unit utilizes the heat from the aforementioned mixed gas phase to heat and concentrate the urine from the low-pressure unit. Its shell-side outlet 103 outputs a gas-liquid mixture containing ammonia and carbon dioxide, which then enters the inlet of the medium-pressure ammonium carbamate condenser 5. In this embodiment, the medium-pressure ammonium carbamate condenser 5 is a shell-and-tube heat exchanger. Through heat exchange between the cooling medium and the material, most of the ammonia and carbon dioxide in the gas-liquid mixture react to form ammonium carbamate and liquefy it, achieving preliminary condensation and recovery of the effective components. The gas-liquid mixture condensed by the medium-pressure ammonium carbamate condenser 5 enters the medium-pressure separation tank 6, which is connected to its outlet, to complete the final gas-liquid separation operation. In this embodiment, the medium-pressure separation tank 6 is a conventional gas-liquid separation tank used in the chemical industry, which can accurately separate the condensed material into a medium-pressure recovery liquid phase and a medium-pressure recovery gas phase. The medium-pressure recovery liquid phase is an aqueous solution rich in ammonium methyl ...

[0038] In some embodiments, the low-voltage unit includes: The low-pressure decomposition tower 7 has an inlet connected to the second liquid phase outlet 42, which is used to receive the second liquid phase and perform gas-liquid separation to output a fourth gas phase and a fourth liquid phase. The low-pressure decomposition tower 7 has a fourth gas phase outlet 71 and a fourth liquid phase outlet 72; the fourth liquid phase outlet 72 is connected to the liquid phase inlet 102 of the pre-concentration separation unit. The low-pressure ammonium carbamate condenser 8 has its inlet connected to the fourth gas phase outlet 71, the third gas phase outlet 61, and the outlet of the melamine tail gas inlet unit, respectively. The low-pressure ammonium carbamate condenser 8 is used to condense the fourth gas phase, the medium-pressure recovery gas phase, and the melamine tail gas to generate the first mixture. The low-pressure separator 9 has an inlet connected to the outlet of the low-pressure ammonium carbamate condenser 8. The low-pressure separator 9 is used to separate the first mixture into a low-pressure recovery liquid phase and a low-pressure recovery gas phase. The low-pressure separator 9 has a fifth gas phase outlet 91 and a fifth liquid phase outlet 92. The fifth gas phase outlet 91 is connected to the low-pressure absorption unit, and the fifth liquid phase outlet 92 is connected to the heat source medium inlet 101 of the pre-concentration separation unit. The output pipeline between the fifth liquid phase outlet 92 and the heat source medium inlet 101 is connected to the inlet of the first heat exchanger 1.

[0039] Specifically, the inlet of the low-pressure decomposition tower 7 is connected to the second liquid phase outlet 42 of the medium-pressure decomposition tower 4, and is used to receive the second liquid phase from the medium-pressure unit. Before entering the low-pressure decomposition tower 7, this stream is depressurized from medium pressure to low-pressure process pressure (approximately 0.3-0.5 MPa) by a pressure reducing valve, and then enters the low-pressure decomposition tower 7 to complete the depressurization heating decomposition and gas-liquid separation operation. Inside the tower, the residual ammonium carbamate in the second liquid phase is further decomposed by heating, while achieving efficient gas-liquid separation. The processed material is separated into a fourth gas phase and a fourth liquid phase. The fourth liquid phase is urine with a further increased urea concentration (up to approximately 70%), which is output from the fourth liquid phase outlet 72 of the low-pressure decomposition tower 7 and enters the liquid phase inlet 102 of the pre-concentration separation unit, where it is heated and concentrated as urine to be concentrated. The fourth gas phase is a gas mixture rich in ammonia, carbon dioxide, and water vapor, which is output from the fourth gas phase outlet 71 of the low-pressure decomposition tower 7 and enters the low-pressure ammonium carbamate condenser 8 to participate in the condensation absorption process.

[0040] The low-pressure ammonium carbamate condenser 8 (in this embodiment, the low-pressure ammonium carbamate condenser 8 is a shell-and-tube heat exchanger) is the core condensation and absorption equipment of the low-pressure unit. Its inlet is simultaneously connected to three gaseous streams: the fourth gas phase output from the low-pressure decomposition tower 7, the medium-pressure recovery gas phase output from the medium-pressure separator 6, and the melamine tail gas transported by the melamine tail gas introduction unit. The three streams are in full contact with the circulating absorption liquid in the low-pressure ammonium carbamate condenser 8. The ammonia and carbon dioxide in the liquid are condensed and absorbed and react to generate ammonium carbamate, while releasing the heat of reaction of ammonium carbamate synthesis. The material after condensation and absorption forms a first mixture of gas and liquid, which is output from the outlet of the low-pressure ammonium carbamate condenser 8 to the low-pressure separator 9.

[0041] The inlet of the low-pressure separator 9 (in this embodiment, the low-pressure separator 9 is a conventional gas-liquid separator in the chemical industry) is connected to the outlet of the low-pressure ammonium carbamate condenser 8, and is used to perform gas-liquid separation on the first mixture to obtain a low-pressure recovered liquid phase and a low-pressure recovered gas phase. Among them, the low-pressure recovered liquid phase is a low-pressure ammonium carbamate liquid containing ammonium carbamate, ammonia, carbon dioxide and water, which is output from the fifth liquid phase outlet 92 of the low-pressure separator 9; the main stream of this low-pressure recovered liquid phase is powered by an electromagnetic pump and sent through a pipeline to the heat source medium inlet 101 of the pre-concentration separation unit, where it participates in the urine concentration process as a heat source medium, and the output pipeline is connected to the inlet of the first heat exchanger 1 of the diversion processing unit, providing the diversion processing unit with the low-pressure recovered liquid phase to be processed, which is the core material basis for realizing the active control of the water-carbon ratio. The low-pressure recovery gas phase consists of residual gas that has not been condensed and absorbed, mainly containing inert gases and trace amounts of ammonia. After being output from the fifth gas phase outlet 91 of the low-pressure separator 9, it enters the low-pressure absorption unit. After further washing and absorption treatment, it meets the standards and is released into the atmosphere, effectively reducing the fugitive emissions of ammonia.

[0042] The low-pressure unit of this application, through the coordinated operation of the aforementioned equipment, achieves, on the one hand, deep concentration of the liquid from the medium-pressure unit, providing high-concentration urea raw material for subsequent urea product preparation; on the other hand, it realizes centralized condensation absorption and gas-liquid separation of the fourth gas phase, the medium-pressure recovery gas phase, and the triamine tail gas. The produced low-pressure recovery liquid phase serves as a heat source medium in the pre-concentration process and also provides materials to be processed for the diversion treatment unit, realizing the process linkage of material recovery, heat utilization, and water-carbon ratio control. At the same time, through deep washing in the low-pressure absorption unit, the system ammonia consumption is reduced, ensuring the environmental friendliness and economy of the co-production process.

[0043] In some embodiments, the pre-concentration separation unit includes: The pre-concentrating separator 10 has a heat source medium inlet 101, a liquid phase inlet 102, a shell-side outlet 103, a sixth gas phase outlet 104, and a sixth liquid phase outlet 105; wherein: The heat source medium inlet 101 is connected to the second gas phase outlet 41, the fifth liquid phase outlet 92 and the first gas phase outlet 21 respectively, and is used to receive the second gas phase, the low-pressure recovered liquid phase and the first gas phase as heat source medium to provide the heat required for liquid phase concentration. The liquid phase inlet 102 is connected to the fourth liquid phase outlet 72 and is used to receive the fourth liquid phase to be concentrated; Shell-side outlet 103 is connected to inlet of medium-pressure ammonium carbamate condenser 5, and is used to send the heat-exchanged gas-liquid mixture to medium-pressure ammonium carbamate condenser 5 for recovery; The sixth liquid phase outlet 105 is connected to the urine tank 11 and is used to deliver concentrated liquid phase to the urine tank 11; The sixth gas phase outlet 104 is connected to the first condenser 12 and is used to output the evaporated gas phase; the first condenser 12 has a seventh liquid phase outlet and a seventh gas phase outlet, the seventh liquid phase outlet is connected to the inlet of the ammonia water tank 13 and is used to send the ammonia water formed by condensing the evaporated gas phase into the ammonia water tank 13; the seventh gas phase outlet is connected to the venting system.

[0044] Specifically, the heat source medium inlet 101 of the pre-concentrating separator 10 is simultaneously connected to three materials: the second gas phase output from the medium-pressure decomposition tower 4, the main stream of low-pressure recovered liquid phase output from the low-pressure separator 9, and the first gas phase output from the diversion processing unit. The second and first gas phases are both high-temperature gas phases rich in ammonia and carbon dioxide, carrying a large amount of process reaction heat. The low-pressure recovered liquid phase is a liquid material that, after entering the shell side of the pre-concentrating separator 10, partially vaporizes under the high-temperature conditions of the shell side, while simultaneously absorbing ammonia and carbon dioxide from the second and first gas phases. These three materials work together as a heat source medium, providing the necessary heat for urine concentration while achieving cascaded utilization of process heat within the system, as well as deep enrichment and recovery of effective gases such as ammonia and carbon dioxide, thus improving the utilization rate of raw materials and energy.

[0045] The liquid inlet 102 of the pre-concentrating separator 10 is connected to the fourth liquid outlet 72 of the low-pressure decomposition tower 7, and is used to receive the fourth liquid phase to be concentrated. The fourth liquid phase is urine with a urea concentration of about 70% after two-stage decomposition treatment at medium and low pressure, and is the core material processed by the pre-concentrating separator unit. After entering the pre-concentrating separator 10, the urine flows through the tube side and indirectly exchanges heat with the heat source medium in the shell side. The heat from the heat source in the shell side is used to heat and concentrate the urine in the tube side, thus completing the urine concentration process.

[0046] Inside the pre-concentrating separator 10, after the three heat source media in the shell side and the urine in the tube side complete heat exchange, partial condensation and vaporization reactions occur, forming a gas-liquid mixture, which is output from the shell side outlet 103 (in this embodiment, the gas-liquid mixture is a mixture of a gas phase component containing ammonia, carbon dioxide, water vapor and a small amount of inert gas and a liquid phase component containing ammonium carbamate, ammonia, carbon dioxide and water); the gas-liquid mixture is sent to the inlet of the medium-pressure ammonium carbamate condenser 5 through pipelines, and enters the recovery process of the medium-pressure unit, so that the effective components such as ammonia and carbon dioxide that have not been absorbed in the heat source media continue to be recycled and recovered in the medium-pressure system, thus avoiding the waste of effective raw materials from the process closed loop.

[0047] After the urine in the tube is heated and concentrated, some of the water evaporates during the heating process, forming a gas-liquid two-phase mixture that enters the separation section of the pre-concentration separator 10. After gas-liquid separation in the separation section, the concentrated liquid phase is output from the sixth liquid phase outlet 105 and sent to the urine tank 11. This concentrated liquid phase is urine with a urea concentration of 75-80%. The residual water contained in the concentrated liquid phase enters the subsequent processing steps along with the concentrated liquid phase, and is finally discharged from the device through the desorption hydrolysis system to generate finished urea. The evaporated gas phase generated during the urine concentration process is mainly water vapor and a small amount of ammonia and carbon dioxide. It is output from the sixth gas phase outlet 104 and enters the first condenser 12 for cooling and condensation. In this embodiment, the desorption hydrolysis system is a standard supporting unit for processing the condensate in the urea plant. It is used to recover ammonia and urea from the dilute ammonia water collected in the ammonia water tank 13 and to discharge the treated purified water from the system. Its specific structure and operation are known prior art in the field and will not be described in detail here.

[0048] The first condenser 12 cools and condenses the evaporated gas phase, condensing condensable water vapor and ammonia into ammonia water. The condensed ammonia water is output from the seventh liquid phase outlet and sent to the ammonia water tank 13 for storage. The uncondensed inert gases (mainly nitrogen, hydrogen, etc.) are discharged from the seventh gas phase outlet and enter the venting system to maintain system pressure balance. In this embodiment, the venting system is a conventional tail gas treatment device in the urea production field. Its specific structure and operation are known to those skilled in the art and will not be described in detail here.

[0049] The pre-concentration separation unit of this application, through the coordinated operation of the aforementioned equipment, completes the heating and concentration of urine from the low-pressure unit, heat recovery and effective gas absorption of the three heat source media, gas-liquid separation and directional output of the concentrated liquid phase and the evaporated gas phase, and simultaneously achieves process docking with the medium-pressure recovery system, urine tank 11, ammonia tank 13, and venting system, becoming the core link connecting the low-pressure unit, medium-pressure unit, and subsequent processing steps. In this embodiment, the pre-concentration separator 10 can be selected as a combined structure or a split structure according to process requirements and equipment layout. The combined structure integrates the heat exchange section and the separation section into one unit, while the split structure separates the pre-concentrator and the pre-concentration separator 10. In this embodiment, the pre-concentration separator 10 adopts an integrated equipment structure, with its heat exchange section being a shell-and-tube structure and the separation section being a gravity settling structure, which has the advantages of compact structure, simple operation, and high heat exchange and separation efficiency.

[0050] In some embodiments, the triamine tail gas introduction unit includes: The tail gas condenser 14 has an inlet for receiving melamine tail gas and an outlet connected to the inlet of the low-pressure ammonium carbamate condenser 8 for sending the condensed melamine tail gas into the low-pressure ammonium carbamate condenser 8.

[0051] Specifically, the melamine tail gas is a process tail gas produced as a byproduct of the melamine production unit, mainly containing components such as ammonia, carbon dioxide, and water vapor. The tail gas condenser 14 is used to pre-treat the melamine tail gas by cooling and condensing it. Through cooling and heat exchange, some of the water vapor and condensable components in the tail gas are condensed and removed in advance, reducing the temperature and water content of the melamine tail gas, making it more suitable for the condensation and absorption conditions of the subsequent low-pressure ammonium carbamate condenser 8, and improving the absorption efficiency of the effective components.

[0052] The melamine tail gas, after being condensed by the tail gas condenser 14, is sent from its outlet to the inlet of the low-pressure ammonium carbamate condenser 8, where it merges with the fourth gas phase from the low-pressure decomposition tower 7 and the medium-pressure recovery gas phase from the medium-pressure separator 6. Together, they are condensed and absorbed in the low-pressure ammonium carbamate condenser 8, realizing the recovery and reuse of effective reaction components such as ammonia and carbon dioxide in the melamine tail gas.

[0053] In this embodiment, the exhaust gas condenser 14 is a conventional heat exchange and condensation device in the co-production process of urea and melamine. Its specific structure and operation method are known prior art in this field and will not be described in detail here.

[0054] In some embodiments, the high-pressure synthesis unit includes: a high-pressure ammonium carbamate condenser 15, a stripping tower 17, a urea synthesis tower 16, and a high-pressure scrubber 18; the stripping tower 17 has an eighth liquid phase outlet 172 and an eighth gas phase outlet 171, the urea synthesis tower 16 has a ninth liquid phase outlet 162 and a ninth gas phase outlet 161, and the high-pressure scrubber 18 has a tenth liquid phase outlet and a tenth gas phase outlet. The inlet of the high-pressure ammonium carbamate condenser 15 is connected to the ammonia source, the tenth liquid phase outlet and the eighth gas phase outlet 171 respectively. The high-pressure ammonium carbamate condenser 15 is used to generate and output the ammonium carbamate mixture. The inlet of the urea synthesis tower 16 is connected to the outlet of the high-pressure ammonium carbamate condenser 15. The urea synthesis tower 16 is used to receive the ammonium carbamate mixture and carry out the urea synthesis reaction to generate the synthesis liquid phase and the synthesis gas phase. The inlet of stripping tower 17 is connected to a carbon dioxide source and the ninth liquid phase outlet 162, respectively, and the eighth liquid phase outlet 172 is connected to the inlet of medium-pressure decomposition tower 4. Stripping tower 17 is used to strip the synthetic liquid phase with carbon dioxide, separate the reaction mixture and stripping gas phase, and input the reaction mixture into medium-pressure decomposition tower 4, and input the stripping gas phase into high-pressure ammonium carbamate condenser 15. The inlet of the high-pressure scrubber 18 is connected to the ninth gas phase outlet 161, and the tenth gas phase outlet is connected to the low-pressure absorption unit. The high-pressure scrubber 18 is used to wash unreacted substances in the synthesis gas phase and inputs the resulting ammonium carbamate solution into the high-pressure ammonium carbamate condenser 15.

[0055] Specifically, the high-pressure synthesis unit is the core reaction unit of the urea synthesis loop. This application adopts a carbon dioxide stripping high-pressure urea synthesis process. Through the coordinated operation of the high-pressure ammonium carbamate condenser 15, urea synthesis tower 16, stripping tower 17 and high-pressure scrubber 18, the reaction of raw material ammonia and carbon dioxide, urea synthesis, stripping and recovery of unreacted substances are completed, forming a complete reaction and circulation loop of the high-pressure system.

[0056] The high-pressure ammonium carbamate condenser 15 serves as the core reaction pretreatment equipment of the high-pressure system. Its inlet simultaneously receives three materials: the process raw material ammonia source, the tenth liquid phase (ammonium carbamate liquid) output from the high-pressure scrubber 18, and the stripping gas phase output from the stripping tower 17. The above materials undergo heat exchange and reaction within the high-pressure ammonium carbamate condenser 15 to generate a liquid ammonium carbamate mixture, which is then transported to the urea synthesis tower 16 to provide the core reaction materials for the urea synthesis reaction.

[0057] Urea synthesis tower 16 is a high-pressure synthesis reaction vessel for urea. It receives a mixture of ammonium carbamate from the high-pressure ammonium carbamate condenser 15 and carries out the urea synthesis reaction under high temperature and high pressure conditions to convert ammonium carbamate into urea. After the reaction is completed, a synthesis liquid phase mainly composed of urea solution and a synthesis gas phase containing unreacted ammonia and carbon dioxide are generated.

[0058] Stripping tower 17 uses carbon dioxide as the stripping medium. Its inlet receives the synthetic liquid phase from the ninth liquid phase outlet 162 of urea synthesis tower 16, and also receives the process carbon dioxide source. Inside stripping tower 17, unconverted ammonium carbamate in the synthetic liquid phase is decomposed using carbon dioxide stripping, and the ammonia and carbon dioxide are separated, forming a stripping gas phase and a reaction mixture. The stripping gas phase is a gaseous mixture rich in ammonia and carbon dioxide, and may contain a small amount of water vapor. The reaction mixture is a liquid mixture mainly composed of urea and water, containing a small amount of undecomposed ammonium carbamate. The stripping gas phase returns to the high-pressure ammonium carbamate condenser 15 from the eighth gas phase outlet 171, achieving high-pressure internal circulation of unreacted effective components. The reaction mixture is transported to the medium-pressure decomposition tower 4 from the eighth liquid phase outlet 172, entering the subsequent medium- and low-pressure recovery and urea concentration processes.

[0059] The high-pressure scrubber 18 is used to scrub the synthesis gas phase output from the ninth gas phase outlet 161 of the urea synthesis tower 16. The scrubbing liquid absorbs the unreacted ammonia and carbon dioxide remaining in the synthesis gas phase to form ammonium carbamate liquid, which is returned to the high-pressure ammonium carbamate condenser 15 from the tenth liquid phase outlet, further improving the raw material utilization rate. The residual gas phase after high-pressure scrubbing is transported to the low-pressure absorption unit from the tenth gas phase outlet for subsequent deep scrubbing and venting treatment.

[0060] It should be noted that this embodiment uses a carbon dioxide stripping process as an example for description, but the invention lies in the diversion treatment of the low-pressure recovered liquid phase to control the water-to-carbon ratio, and does not depend on a specific high-pressure stripping medium. Based on the same inventive concept, this invention is also applicable to other urea production processes such as ammonia stripping and aqueous solution full-cycle processes.

[0061] In some embodiments, the low-pressure absorption unit includes: The first absorption tower 19 has a first air inlet, a first liquid inlet, a first liquid outlet and a first air outlet. The first air inlet is connected to the tenth gas phase outlet and is used to receive the tail gas of the high-pressure scrubber 18. The first liquid inlet is connected to the outlet of the ammonia tank 13 and is used to receive ammonia water from the ammonia tank 13 as the absorption liquid. The first air outlet is connected to the venting system. The second absorption tower 20 has a second air inlet, a second liquid inlet, a second liquid outlet, and a second air outlet. The second air inlet is connected to the fifth gas phase outlet 91 and is used to receive the low-pressure recovered gas phase. The second liquid inlet is connected to the first liquid outlet and is used to receive the liquid phase from the first absorption tower 19 as the absorbent. The second air outlet is connected to the venting system. The second liquid outlet is connected to the inlet of the ammonia water tank 13 and is used to send the absorbed ammonia water into the ammonia water tank 13.

[0062] Specifically, the low-pressure absorption unit is used to perform step-by-step washing and absorption of the two low-pressure exhaust gases in the system, recover the trace ammonia components remaining in the exhaust gas, reduce the ammonia consumption of the system, and at the same time, allow the exhaust gas to be vented after meeting the standards. The first absorption tower 19 and the second absorption tower 20 are connected in series to form a two-stage absorption system.

[0063] The first absorption tower 19 is used for primary absorption treatment of the exhaust gas discharged from the high-pressure scrubber 18. Its first inlet is connected to the tenth gas phase outlet of the high-pressure scrubber 18, receiving high-pressure exhaust gas containing trace amounts of ammonia and inert gases. The first liquid inlet introduces dilute ammonia water output from the ammonia water tank 13 as the absorbent, which performs countercurrent absorption of ammonia in the exhaust gas to remove residual ammonia components. The clean exhaust gas after primary absorption treatment is transported to the venting system through the first outlet, while the ammonia water after ammonia absorption is discharged through the first liquid outlet and reused as the absorbent in the second absorption tower 20.

[0064] The second absorption tower 20 is used for secondary absorption treatment of the low-pressure recovery gas phase discharged from the low-pressure separator 9. Its second inlet is connected to the fifth gas phase outlet 91 of the low-pressure separator 9, receiving the low-pressure recovery gas phase containing trace amounts of ammonia. The second liquid inlet receives ammonia water discharged from the first absorption tower 19, further absorbing the ammonia in the low-pressure recovery gas phase to maximize the recovery of ammonia resources within the system. The tail gas after secondary absorption treatment is transported to the venting system through the second outlet for final venting. The ammonia water after absorption saturation flows back to the ammonia water tank 13 through the second liquid outlet, where it is combined with other ammonia water in the system and then uniformly transported to subsequent processes for treatment, forming a recycling of the absorption liquid.

[0065] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A water-to-carbon ratio control system for the co-production of urea and triamine, characterized in that, include: A urea synthesis circuit, comprising a high-pressure synthesis unit, a medium-pressure unit, and a low-pressure unit connected in sequence. The triamine tail gas introduction unit is connected to the low-pressure unit. The triamine tail gas introduction unit is used to send the triamine tail gas into the low-pressure unit, and after being condensed and absorbed by the low-pressure unit, it forms a low-pressure recovery liquid phase. The diversion processing unit has its inlet connected to the output pipeline of the low-pressure recovered liquid phase. The diversion processing unit is used to divert part of the low-pressure recovered liquid phase and separate it into a first liquid phase and a first gas phase. The diversion processing unit has a first gas phase outlet (21) and a first liquid phase outlet (22); the first gas phase outlet (21) is connected to the inlet of the pre-concentration separation unit so that the first gas phase is sent to the pre-concentration separation unit for heat recovery; the first liquid phase outlet (22) is connected to the inlet of the medium-pressure unit so that the water contained in the first liquid phase enters the low-pressure unit through the medium-pressure unit, thereby bypassing the high-pressure synthesis unit.

2. The water-to-carbon ratio control system for the co-production of urea and melamine according to claim 1, characterized in that, The traffic splitting processing unit includes: The first heat exchanger (1) has its inlet connected to the output pipeline of the low-pressure recovered liquid phase. The first heat exchanger (1) is used to heat the diverted low-pressure recovered liquid phase. The first separator (2) has its inlet connected to the outlet of the first heat exchanger (1). The first gas phase outlet (21) and the first liquid phase outlet (22) are both located on the first separator (2). The first separator (2) is used to separate the heated low-pressure recovered liquid phase into the first liquid phase and the first gas phase.

3. A water-to-carbon ratio control system for the co-production of urea and triamine according to claim 2, characterized in that, The diversion processing unit further includes a regulating valve (3), which is located at the inlet of the first heat exchanger (1) and is used to regulate the flow rate into the first heat exchanger (1).

4. A water-to-carbon ratio control system for the co-production of urea and triamine according to claim 3, characterized in that, Also includes: A control device is connected to the regulating valve (3) and is configured to control the opening degree of the regulating valve (3) according to the water-carbon ratio feedback signal of the high-pressure synthesis unit.

5. A water-to-carbon ratio control system for the co-production of urea and triamine according to claim 2, characterized in that, The medium-pressure unit includes: A medium-pressure decomposition tower (4) is provided, the inlet of which is connected to the high-pressure synthesis unit. The tower is used to receive the reaction mixture from the high-pressure synthesis unit and perform gas-liquid separation to output a second gas phase and a second liquid phase. The medium-pressure decomposition tower (4) has a second gas phase outlet (41) and a second liquid phase outlet (42). The second liquid phase outlet (42) is connected to the inlet of the low-pressure unit. The second gas phase outlet (41) is connected to the heat source medium inlet (101) of the pre-concentration separation unit. A medium-pressure ammonium carbamate condenser (5) is provided, the inlet of which is connected to the shell-side outlet (103) of the pre-concentration separation unit. The medium-pressure ammonium carbamate condenser (5) is used to condense the gas-liquid mixture from the pre-concentration separation unit. A medium-pressure separator (6) is provided, the inlet of which is connected to the outlet of the medium-pressure ammonium carbamate condenser (5). The medium-pressure separator (6) is used to separate the condensed gas-liquid mixture into a medium-pressure recovered liquid phase and a medium-pressure recovered gas phase. The medium-pressure separator (6) has a third liquid phase outlet (62) and a third gas phase outlet (61). The third liquid phase outlet (62) is connected to the high-pressure synthesis unit and is used to send the medium-pressure recovered liquid phase into the high-pressure synthesis unit. The third gas phase outlet (61) is connected to the low-pressure unit and is used to send the medium-pressure recovered gas phase into the low-pressure unit.

6. A water-to-carbon ratio control system for the co-production of urea and melamine according to claim 5, characterized in that, The low-voltage unit includes: A low-pressure decomposition tower (7) is provided, the inlet of which is connected to the second liquid phase outlet (42), for receiving the second liquid phase and performing gas-liquid separation to output a fourth gas phase and a fourth liquid phase. The low-pressure decomposition tower (7) has a fourth gas phase outlet (71) and a fourth liquid phase outlet (72). The fourth liquid phase outlet (72) is connected to the liquid phase inlet (102) of the pre-concentration separation unit. The low-pressure ammonium carbamate condenser (8) has its inlet connected to the fourth gas phase outlet (71), the third gas phase outlet (61), and the outlet of the melamine tail gas inlet unit, respectively. The low-pressure ammonium carbamate condenser (8) is used to condense the fourth gas phase, the medium-pressure recovery gas phase, and the melamine tail gas to generate a first mixture. A low-pressure separator (9) is provided, the inlet of which is connected to the outlet of the low-pressure ammonium carbamate condenser (8). The low-pressure separator (9) is used to separate the first mixture into a low-pressure recovery liquid phase and a low-pressure recovery gas phase. The low-pressure separator (9) has a fifth gas phase outlet (91) and a fifth liquid phase outlet (92). The fifth gas phase outlet (91) is connected to the low-pressure absorption unit, and the fifth liquid phase outlet (92) is connected to the heat source medium inlet (101) of the pre-concentration separation unit. The output pipeline between the fifth liquid phase outlet (92) and the heat source medium inlet (101) is connected to the inlet of the first heat exchanger (1).

7. A water-to-carbon ratio control system for the co-production of urea and melamine according to claim 6, characterized in that, The pre-concentration separation unit includes: A pre-concentrating separator (10) has a heat source medium inlet (101), a liquid phase inlet (102), a shell-side outlet (103), a sixth gas phase outlet (104), and a sixth liquid phase outlet (105); wherein: The heat source medium inlet (101) is connected to the second gas phase outlet (41), the fifth liquid phase outlet (92) and the first gas phase outlet (21) respectively, and is used to receive the second gas phase, the low-pressure recovered liquid phase and the first gas phase as heat source medium to provide the heat required for liquid phase concentration. The liquid phase inlet (102) is connected to the fourth liquid phase outlet (72) and is used to receive the fourth liquid phase to be concentrated; The shell-side outlet (103) is connected to the inlet of the medium-pressure ammonium carbamate condenser (5) for sending the heat-exchanged gas-liquid mixture to the medium-pressure ammonium carbamate condenser (5) for recovery. The sixth liquid phase outlet (105) is connected to the urine tank (11) and is used to deliver concentrated liquid phase to the urine tank (11); The sixth gas phase outlet (104) is connected to the first condenser (12) and is used to output the evaporating gas phase; the first condenser (12) has a seventh liquid phase outlet and a seventh gas phase outlet, the seventh liquid phase outlet is connected to the inlet of the ammonia water tank (13) and is used to send the ammonia water formed by condensing the evaporating gas phase into the ammonia water tank (13); the seventh gas phase outlet is connected to the venting system.

8. A water-to-carbon ratio control system for the co-production of urea and triamine according to claim 6, characterized in that, The melamine tail gas introduction unit includes: The tail gas condenser (14) has an inlet for receiving triamine tail gas and an outlet connected to the inlet of the low-pressure ammonium carbamate condenser (8) for sending the condensed triamine tail gas into the low-pressure ammonium carbamate condenser (8).

9. A water-to-carbon ratio control system for the co-production of urea and triamine according to claim 7, characterized in that, The high-pressure synthesis unit includes: a high-pressure ammonium carbamate condenser (15), a stripping tower (17), a urea synthesis tower (16), and a high-pressure scrubber (18); the stripping tower (17) has an eighth liquid phase outlet (172) and an eighth gas phase outlet (171), the urea synthesis tower (16) has a ninth liquid phase outlet (162) and a ninth gas phase outlet (161), and the high-pressure scrubber (18) has a tenth liquid phase outlet and a tenth gas phase outlet; The inlet of the high-pressure ammonium carbamate condenser (15) is connected to the ammonia source, the tenth liquid phase outlet and the eighth gas phase outlet (171) respectively. The high-pressure ammonium carbamate condenser (15) is used to generate and output ammonium carbamate mixture. The inlet of the urea synthesis tower (16) is connected to the outlet of the high-pressure ammonium carbamate condenser (15). The urea synthesis tower (16) is used to receive the ammonium carbamate mixture and carry out the urea synthesis reaction to generate a synthesis liquid phase and a synthesis gas phase. The inlet of the stripping tower (17) is connected to the carbon dioxide source and the ninth liquid phase outlet (162), respectively, and the eighth liquid phase outlet (172) is connected to the inlet of the medium-pressure decomposition tower (4); the stripping tower (17) is used to strip the synthetic liquid phase with carbon dioxide, separate the reaction mixture and the stripping gas phase, and input the reaction mixture into the medium-pressure decomposition tower (4), and input the stripping gas phase into the high-pressure ammonium carbamate condenser (15). The inlet of the high-pressure scrubber (18) is connected to the ninth gas phase outlet (161), and the tenth gas phase outlet is connected to the low-pressure absorption unit. The high-pressure scrubber (18) is used to wash the unreacted substances in the synthesis gas phase and input the ammonium carbamate solution formed by washing into the high-pressure ammonium carbamate condenser (15).

10. A water-to-carbon ratio control system for the co-production of urea and triamine according to claim 9, characterized in that, The low-pressure absorption unit includes: The first absorption tower (19) has a first air inlet, a first liquid inlet, a first liquid outlet and a first air outlet. The first air inlet is connected to the tenth gas phase outlet and is used to receive the tail gas of the high-pressure scrubber (18). The first liquid inlet is connected to the outlet of the ammonia tank (13) and is used to receive ammonia water from the ammonia tank (13) as the absorption liquid. The first air outlet is connected to the venting system. The second absorption tower (20) has a second air inlet, a second liquid inlet, a second liquid outlet and a second air outlet. The second air inlet is connected to the fifth gas phase outlet (91) and is used to receive the low-pressure recovered gas phase. The second liquid inlet is connected to the first liquid outlet and is used to receive the liquid phase from the first absorption tower (19) as the absorbent. The second air outlet is connected to the venting system. The second liquid outlet is connected to the inlet of the ammonia water tank (13) and is used to send the absorbed ammonia water into the ammonia water tank (13).

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