Energy-saving and efficiency-improving urea production system and method thereof

Abstract

The invention discloses an energy-saving and efficiency-improving urea production system. The system comprises a synthesis unit, a hydrolysis analysis unit, an evaporation granulation unit and a circulating absorption unit, the method has the advantages that through full-tower operation transformation of the synthetic tower and additional arrangement of the tower plates, idle space in the tower is fully utilized, the material reaction time is prolonged, the urea synthesis conversion rate is remarkably improved, the unreacted material amount is reduced, and the circulating load is reduced, so that the raw material feeding amount can be increased, the capacity of the device is greatly improved, and the problem that the capacity of a traditional process is limited is solved; and sufficient fertilizer guarantee is provided for grain production. The waste heat of 98 DEG C hydrolysis water purification of the hydrolysis system is used for preheating liquid ammonia, energy waste caused by the fact that waste heat is cooled through circulating water in a traditional process is avoided, consumption of extra energy for liquid ammonia preheating is reduced, gradient utilization of heat is achieved, steam consumption and circulating water consumption of the device are remarkably reduced, and the energy-saving effect is outstanding.

Description

Technical Field

[0001] This invention relates to the field of urea production, and more specifically to an energy-saving and efficiency-enhancing urea production system and method. Background Technology

[0002] Urea is an indispensable core fertilizer in agricultural production. The energy consumption level and production efficiency of its production equipment are directly related to agricultural production costs and national food security. A stable and efficient urea supply is the key to ensuring high grain yields and enhancing the stability of national food security.

[0003] However, existing urea production plants have two major technical pain points: First, the temperature of the hydrolyzed purified water produced by the hydrolysis system is still as high as 98°C after exchanging heat with the dilute ammonia water entering the desorption tower. In the current process, it is only cooled to 40°C by circulating water before reuse, resulting in a large amount of waste heat not being recovered, causing energy waste and increasing the operating load of the circulating water system. Second, the urea synthesis tower has the problem of insufficient space utilization. In the traditional process, the space of about 10 meters above the synthesis tower is not effectively utilized, and the overflow pipe discharge mode results in insufficient material reaction time and low urea conversion rate (the urea concentration of the material at the outlet of the synthesis tower is only about 33%). This leads to a large amount of circulating material, limiting the plant's capacity and increasing steam consumption, which does not meet the development requirements of energy conservation and carbon reduction.

[0004] In existing technologies, improvements to urea synthesis efficiency and waste heat recovery are mostly single-dimensional optimizations, lacking a systematic solution that combines enhanced synthesis reactions with cascaded utilization of waste heat. Simply improving the conversion rate of the synthesis tower often overlooks the potential for waste heat recovery, while purely waste heat utilization technologies fail to link with the optimization of the synthesis system, resulting in limited overall energy-saving and efficiency-enhancing effects, and also presenting problems such as high investment costs and difficulties in widespread adoption. Therefore, there is an urgent need to develop an integrated urea production control technology that can fully exploit the reaction potential of the synthesis tower while efficiently recovering waste heat from the hydrolysis system, achieving synergistic optimization of capacity increase and energy consumption reduction, and meeting the industry's dual needs for energy conservation, carbon reduction, and capacity assurance. Summary of the Invention

[0005] To address the aforementioned problems, the first objective of this invention is to provide an energy-saving and efficiency-enhancing urea production system, and the second objective of this invention is to provide an energy-saving and efficiency-enhancing urea production method.

[0006] The first objective of this invention is achieved by the following technical solution: An energy-saving and efficiency-enhancing urea production system includes a synthesis unit, a hydrolysis and desorption unit, an evaporation and granulation unit, and a recycling and absorption unit. The liquid ammonia outlet of the liquid ammonia storage tank of the synthesis unit is connected to the cold medium inlet of the second heat exchanger of the hydrolysis and desorption unit via a pipeline, and the cold medium outlet of the second heat exchanger is connected to the inlet of the mixer of the synthesis unit via a pipeline. The outlet of the stripping tower of the synthesis unit is connected to the inlet of the low-pressure separator of the circulating absorption unit via a pipeline. The outlet of the desorption tower of the hydrolysis and desorption unit is connected to the inlet of the low-pressure separator of the circulating absorption unit via a pipeline. The outlet of the absorbent circulation pump of the circulating absorption unit is connected to the inlet of the high-pressure scrubber of the synthesis unit via a pipeline. The liquid phase outlet of the low-pressure separator of the circulating absorption unit is connected to the inlet of the multi-effect evaporator of the evaporation and granulation unit via a pipeline. The mother liquor outlet of the multi-effect evaporator is connected to the inlet of the ammonia tank of the hydrolysis and desorption unit via a pipeline.

[0007] Furthermore, the synthesis unit includes a liquid ammonia storage tank, a carbon dioxide source, a mixer, a pool condenser, a synthesis tower, a liquid collection tank, a stripping tower, and a high-pressure scrubber. The synthesis tower has several trays arranged from top to bottom, and a discharge port is located at the top. The discharge port is connected to the inlet of the liquid collection tank via a pipeline. The gas phase outlet of the liquid collection tank is connected to the air inlet of the high-pressure scrubber via a pipeline. The outlet of the high-pressure scrubber is connected to the inlet of the mixer via a pipeline. The outlet of the mixer is connected to the liquid inlet of the pool condenser via a pipeline. The liquid phase outlet of the liquid collection tank is connected to the liquid inlet of the stripping tower via a pipeline. The outlet of the carbon dioxide source is connected to the air inlet of the stripping tower via a pipeline. The gas outlet of the stripping tower is connected to the air inlet of the pool condenser via a pipeline. The outlet of the pool condenser is connected to the feed inlet of the synthesis tower via a pipeline.

[0008] Furthermore, the hydrolysis and desorption unit includes an ammonia tank, a desorption tower, a first heat exchanger, a second heat exchanger, a hydrolysis tower, and a third heat exchanger. The outlet of the ammonia tank is connected to the cold medium inlet of the first heat exchanger via a pipeline. The cold medium outlet of the first heat exchanger is connected to the liquid inlet of the analytical tower via a pipeline. The hydrolyzed purified water outlet at the bottom of the analytical tower is connected to the hot medium inlet of the first heat exchanger via a pipeline. The hot medium outlet of the first heat exchanger is connected to the hot medium inlet of the second heat exchanger via a pipeline. The hot medium outlet of the second heat exchanger is connected to the inlet of the circulating water system via a pipeline. The liquid outlet in the middle of the analytical column is connected to the cold medium inlet of the third heat exchanger via a pipeline; the cold medium outlet of the third heat exchanger is connected to the feed inlet of the hydrolysis column via a pipeline; the liquid outlet at the bottom of the hydrolysis column is connected to the hot medium inlet of the third heat exchanger via a pipeline; the hot medium outlet of the third heat exchanger is connected to the middle inlet of the analytical column via a pipeline; and the outlet at the top of the hydrolysis column is connected to the upper inlet of the analytical column via a pipeline.

[0009] Furthermore, the evaporation granulation unit includes a multi-effect evaporator, an atomizing granulation tower, and a crude product silo; The concentrated liquid outlet of the multi-effect evaporator is connected to the inlet of the high-pressure pump via a pipeline, the outlet of the high-pressure pump is connected to the nozzle inlet of the atomizing granulation tower via a pipeline, and the particle outlet of the atomizing granulation tower is connected to the inlet of the crude product silo via a pipeline.

[0010] Furthermore, the circulating absorption unit includes a low-pressure absorption tower, a low-pressure condenser, a low-pressure separator, an absorbent circulation pump, and a tail gas scrubber. The gas phase outlet of the low-pressure separator is connected to the air inlet at the bottom of the low-pressure absorption tower via a pipeline. The top outlet of the low-pressure absorption tower is connected to the air inlet of the low-pressure condenser via a pipeline. The outlet of the low-pressure condenser is connected to the inlet of the condensate pump via a pipeline. The outlet of the condensate pump is connected to the inlet of the ammonia tank via a pipeline. The uncondensed gas outlet of the low-pressure condenser is connected to the air inlet of the tail gas scrubber via a pipeline. The outlet of the tail gas scrubber is led to high altitude for discharge via a pipeline. The liquid outlet of the tail gas scrubber is connected to the inlet of the ammonia tank via a pipeline. The liquid outlet at the bottom of the low-pressure absorption tower is connected to the inlet of the absorption liquid circulation pump via a pipeline, and the outlet of the absorption liquid circulation pump is also connected to the spray liquid inlet at the top of the low-pressure absorption tower via a pipeline.

[0011] Another objective of this invention is achieved by the following technical solution: An energy-saving and efficiency-enhancing urea production method includes the following steps: (1) Synthesis reaction: After the liquid ammonia is heated by heat exchange with waste heat, it is mixed with carbon dioxide, recycled ammonia and carbon dioxide, and then enters the pool condenser to generate ammonium carbamate, and then sent to the synthesis tower. The full tower operation mode is adopted, and the reaction time of the material is extended by multiple tower plates in the tower to generate urea mixture. (2) Stripping separation: The urea mixture discharged from the top of the synthesis tower is sent to the collection tank for buffering, and then introduced into the stripping tower. Raw material carbon dioxide is introduced for stripping treatment to separate some unreacted ammonia and carbon dioxide. (3) Recycled absorption: The stripped material enters the low-pressure absorption unit. After low-pressure absorption and condensation separation, the liquid phase material is sent to the evaporation granulation system, and the ammonia and carbon dioxide in the gas phase are recovered and returned to the pool condenser for recycling. (4) Evaporation granulation: The material from the low-pressure absorption unit is concentrated to a urea concentration of ≥99.5% by multi-effect evaporation, and then urea product is obtained by atomization granulation; (5) Hydrolysis and waste heat utilization: Ammonia, carbon dioxide and water separated during the evaporation and concentration process enter the ammonia tank to form dilute ammonia water. The dilute ammonia water is sent to the hydrolysis and desorption unit. After hydrolysis in the hydrolysis tower and desorption in the desorption tower to recover ammonia and carbon dioxide, hydrolyzed purified water at about 98°C is produced. The hydrolyzed purified water is used to exchange heat with the liquid ammonia in step (1) to raise the temperature of the liquid ammonia to 65-80°C. The hydrolyzed purified water after heat exchange is cooled to 41-48°C and sent directly to the circulating water system for reuse.

[0012] Furthermore, in step (1), the synthesis tower is operated at full capacity, and the reaction time of the material in the synthesis tower is extended by more than 30% compared with the traditional process; the initial temperature of liquid ammonia is 38°C, and after heat exchange with hydrolyzed purified water, the temperature is raised to 65-80°C. The heat exchange process between hydrolyzed purified water and liquid ammonia is carried out in the second heat exchanger, and the temperature of hydrolyzed purified water is controlled at 41-48°C after heat exchange.

[0013] Furthermore, in step (2), the operating pressure of the stripping tower is 1.5 to 2.5 MPa, the operating temperature is 170 to 190°C, and the concentration of the urea mixture after stripping is increased to more than 53%.

[0014] Furthermore, in step (3), the operating pressure of the low-pressure absorption unit is 0.1 to 0.3 MPa, and the operating temperature is 40 to 60°C. After low-pressure absorption, the urea concentration of the material is increased to more than 70%.

[0015] Furthermore, in step (4), the multi-effect evaporator adopts a 2-3 effect evaporation process with an evaporation temperature of 120-140℃. The ammonia and carbon dioxide recovered during the evaporation process are concentrated by the hydrolysis and desorption unit and then sent to the high-pressure scrubber and then introduced into the pool condenser for circulation reaction.

[0016] Advantages of this invention: 1. By modifying the synthesis tower to operate at full capacity and adding trays, the idle space inside the tower is fully utilized, the reaction time of materials is extended, the urea synthesis conversion rate is significantly improved, the amount of unreacted materials is reduced, and the circulating load is reduced, thereby increasing the feed rate of raw materials and achieving a significant increase in the capacity of the unit. This solves the problem of limited capacity in traditional processes and provides sufficient fertilizer for grain production.

[0017] 2. The waste heat from the 98℃ hydrolysis of purified water in the hydrolysis system is used to preheat liquid ammonia, avoiding the energy waste caused by cooling the waste heat through circulating water in the traditional process. At the same time, it reduces the consumption of additional energy by the waste heat of liquid ammonia, realizes the cascade utilization of heat, significantly reduces the steam consumption and circulating water consumption of the unit, and has outstanding energy-saving effect.

[0018] 3. By improving reaction conversion rate and resource recovery rate, the emission and waste of unreacted materials are reduced, carbon emission intensity is lowered, and the requirements of national energy conservation and carbon reduction policies are met. At the same time, the increase in production capacity and the reduction in energy consumption are directly converted into significant economic benefits, helping enterprises to enhance market competitiveness and achieve green and sustainable development.

[0019] 4. By organically integrating processes such as synthesis reaction optimization, waste heat recovery and recycling, a synergistic and efficient urea production system is formed, which solves the problem of limited effects of traditional single-modification methods and achieves simultaneous optimization of production capacity, energy consumption and environmental protection indicators, providing a brand-new solution for the technological upgrading of the urea industry. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system connection in Example 1.

[0021] In the diagram: Synthesis Unit 1, Liquid Ammonia Storage Tank 11, Carbon Dioxide Source 12, Mixer 13, Pool-type Condenser 14, Synthesis Tower 15, Liquid Collection Tank 16, Stripping Tower 17, High-Pressure Scrubber 18, Hydrolysis and Desorption Unit 2, Ammonia Water Tank 21, Desorption Tower 22, First Heat Exchanger 23, Second Heat Exchanger 24, Hydrolysis Tower 25, Third Heat Exchanger 26, Evaporation and Granulation Unit 3, Multi-Effect Evaporator 31, Atomizing Granulation Tower 32, Crude Product Silo 33, Circulating Absorption Unit 4, Low-Pressure Absorption Tower 41, Low-Pressure Condenser 42, Low-Pressure Separator 43, Absorption Liquid Circulating Pump 44, Tail Gas Scrubber 45. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 like Figure 1 The energy-saving and efficiency-enhancing urea production system includes a synthesis unit 1, a hydrolysis and desorption unit 2, an evaporation and granulation unit 3, and a circulation and absorption unit 4. The synthesis unit 1 includes a liquid ammonia storage tank 11, a carbon dioxide source 12, a mixer 13, a pool condenser 14, a synthesis tower 15, a collection tank 16, a stripping tower 17, and a high-pressure scrubber 18; the hydrolysis and desorption unit 2 includes an ammonia water tank 21, a desorption tower 22, a first heat exchanger 23, a second heat exchanger 24, a hydrolysis tower 25, and a third heat exchanger 26; the circulating absorption unit 4 includes a low-pressure absorption tower 41, a low-pressure condenser 42, a low-pressure separator 43, an absorption liquid circulation pump 44, and a tail gas scrubber 45; and the evaporation and granulation unit 3 includes a multi-effect evaporator 31, an atomizing granulation tower 32, and a crude product silo 33.

[0024] Specifically, the synthesis tower 15 has an inner diameter of 4.2m and a total height of 38m. It has 20 trays (including 8 newly added trays at the top) arranged from top to bottom. A discharge port is located at the top of the synthesis tower 15. The discharge port of the synthesis tower 15 is connected to the inlet of the liquid collection tank 16 via a pipeline. The gas phase outlet of the liquid collection tank 16 is connected to the air inlet of the high-pressure scrubber 18 via a pipeline. The outlet of the high-pressure scrubber 18 is connected to the inlet of the mixer 13 via a pipeline. The outlet of the mixer 13 is connected to the liquid inlet of the pool condenser 14. The liquid phase outlet of the liquid collection tank 16 is connected to the liquid inlet of the stripping tower 17 via a pipeline. The outlet of the carbon dioxide source 12 is connected to the air inlet of the stripping tower 17 via a pipeline. The gas outlet of the stripping tower 17 is connected to the air inlet of the pool condenser 14 via a pipeline. The outlet of the pool condenser 14 is connected to the feed port of the synthesis tower 15 via a pipeline.

[0025] The outlet of stripping tower 17 is connected to the inlet of low-pressure separator 43 via a pipeline. The gas phase outlet of low-pressure separator 43 is connected to the lower inlet of low-pressure absorption tower 41 via a pipeline. The top outlet of low-pressure absorption tower 41 is connected to the inlet of low-pressure condenser 42 via a pipeline. The outlet of low-pressure condenser 42 is connected to the inlet of condensate pump via a pipeline. The outlet of condensate pump is connected to the inlet of ammonia tank 21 via a pipeline. The uncondensed gas outlet of low-pressure condenser 42... The exhaust gas scrubber 45 is connected to the air inlet of the exhaust gas scrubber 45 via a pipeline. The exhaust gas scrubber 45 is led to the high-altitude air discharge via a pipeline. The liquid outlet of the exhaust gas scrubber 45 is connected to the inlet of the ammonia tank 21 via a pipeline. The liquid outlet at the bottom of the low-pressure absorption tower 41 is connected to the inlet of the absorption liquid circulation pump 44 via a pipeline. The outlet of the absorption liquid circulation pump 44 is connected to the liquid inlet of the high-pressure scrubber 18 via a pipeline, and is also connected to the spray liquid inlet at the top of the low-pressure absorption tower 41 via a pipeline.

[0026] The outlet of ammonia tank 21 is connected to the cold medium inlet of the first heat exchanger 23 via a pipeline. The cold medium outlet of the first heat exchanger 23 is connected to the liquid inlet of the desorption tower 22 via a pipeline. The hydrolysis purified water outlet at the bottom of the desorption tower 22 is connected to the hot medium inlet of the first heat exchanger 23 via a pipeline. The hot medium outlet of the first heat exchanger 23 is connected to the hot medium inlet of the second heat exchanger 24 via a pipeline. The hot medium outlet of the second heat exchanger 24 is connected to the inlet of the circulating water system via a pipeline. The liquid outlet in the middle of the analytical tower 22 is connected to the cold medium inlet of the third heat exchanger 26 via a pipeline. The cold medium outlet of the third heat exchanger 26 is connected to the feed inlet of the hydrolysis tower 25 via a pipeline. The liquid outlet at the bottom of the hydrolysis tower 25 is connected to the hot medium inlet of the third heat exchanger 26 via a pipeline. The hot medium outlet of the third heat exchanger 26 is connected to the middle inlet of the analytical tower 22 via a pipeline. The outlet at the top of the hydrolysis tower 25 is connected to the upper inlet of the analytical tower 22 via a pipeline. The gas outlet of the analytical tower 22 is connected to the gas inlet of the low-pressure separator 43 via a pipeline.

[0027] The liquid ammonia outlet of the liquid ammonia storage tank 11 is connected to the cold medium inlet of the second heat exchanger 24 via a pipeline, and the cold medium outlet of the second heat exchanger 24 is connected to the inlet of the mixer 13 via a pipeline. The liquid outlet of the low-pressure separator 43 is connected to the inlet of the multi-effect evaporator 31 via a pipeline, and the mother liquor outlet of the multi-effect evaporator 31 is connected to the inlet of the ammonia tank 21 via a pipeline. The concentrated liquid outlet of the multi-effect evaporator 31 is connected to the inlet of the high-pressure pump via a pipeline, the outlet of the high-pressure pump is connected to the nozzle inlet of the atomizing granulation tower 32 via a pipeline, and the particle outlet of the atomizing granulation tower 32 is connected to the inlet of the crude product silo 33 via a pipeline.

[0028] Example 2 An energy-saving and efficiency-enhancing urea production method, utilizing the energy-saving and efficiency-enhancing urea production system provided in Example 1, includes the following steps: (1) Synthesis reaction: Liquid ammonia at 38°C in liquid ammonia storage tank 11 is sent to the cold medium channel of the second heat exchanger 24 to exchange heat with the 98°C hydrolyzed purified water from the stripping tower 22. After the heat exchange, the temperature of the hydrolyzed purified water drops to 45°C. After the liquid ammonia is heated to 75°C, it is mixed with carbon dioxide at 130°C, recycled ammonia and carbon dioxide, and enters the pool condenser 14 in sequence. It reacts at 13.5MPa and 185°C to generate ammonium carbamate. The material at the outlet of the pool condenser 14 (containing ammonium carbamate and a small amount of urea) is sent to the synthesis tower 15 and passes through 20 tower plates from bottom to top. The full tower operation mode is adopted, and the reaction time of the material in the tower is extended by 40% compared with the traditional process, and finally a urea mixture is generated.

[0029] (2) Stripping separation: The urea mixture (urea concentration 45%) discharged from the top of the synthesis tower 15 is sent to the collection tank 16 for buffering, and then introduced into the stripping tower 17. Raw material carbon dioxide is introduced for stripping treatment. Under the conditions of 180℃ and 2.0MPa, some unreacted ammonia and carbon dioxide are separated. After stripping, the concentration of the urea mixture is increased to 55%.

[0030] (3) Circulation absorption: The stripped material enters the low-pressure absorption tower 41 and is absorbed under the conditions of 0.2MPa and 50℃. After the gas phase is condensed by the low-pressure condenser 42, the condensate is sent to the ammonia water tank 21. The uncondensed gas is treated by the tail gas scrubber 45 and then returned to the low-pressure absorption tower 41. The liquid phase material (urea concentration 72%) at the bottom of the low-pressure absorption tower 41 is partially circulated and sprayed by the absorption liquid circulation pump 44, and partially sent to the multi-effect evaporator 31.

[0031] (4) Evaporation granulation: The liquid material sent from the low-pressure absorption unit is concentrated to a urea concentration of 99.7% by a triple-effect evaporator, and then pressurized by a high-pressure pump and sent to the atomizing granulation tower 32. After being atomized by the nozzle, it comes into contact with hot air at 380°C to granulate, generating urea particles with a particle size of 0.8 to 2.5 mm, which fall into the crude product silo 33.

[0032] (5) Hydrolysis and waste heat utilization: Ammonia, carbon dioxide and water separated during the evaporation and concentration process enter the ammonia tank 21 to form dilute ammonia water. The dilute ammonia water is pumped into the first heat exchanger 23 for preheating and then introduced into the desorption tower 22. Under the conditions of 145℃ and 0.4MPa, some ammonia and carbon dioxide are desorbed. The material discharged from the middle of the desorption tower 22 is sent to the third heat exchanger 26 for preheating and then introduced into the hydrolysis tower 25. Under the conditions of 190℃ and 2.2MPa, the residual urea is hydrolyzed into ammonia and carbon dioxide. The hydrolysis product is returned to the desorption tower 22 for further desorption. The hydrolyzed purified water at 98℃ is produced at the bottom of the desorption tower 22. After exchanging heat with the dilute ammonia water in the first heat exchanger 23, it is introduced into the second heat exchanger 24 for preheating liquid ammonia.

[0033] After operation in this embodiment, the conversion rate of urea synthesis tower 15 increased from 33% in the traditional process to 45%, and the amount of unreacted ammonia and carbon dioxide decreased by 36%; the urea plant capacity increased by 25% compared to the traditional process, with a daily increase of 120 tons of urea per unit; liquid ammonia preheating no longer requires additional steam consumption, and through waste heat recovery from hydrolysis purification water, the plant's steam consumption is reduced by 18 kg / t urea, saving 10,800 tons of steam annually; the waste heat recovery rate from hydrolysis purification water reaches 92%, and circulating water consumption is reduced by 20%, saving 150,000 m³ of circulating water annually. 3 The total recovery rate of ammonia and carbon dioxide is ≥99.2%, and the pollutant emissions meet the requirements of GB 13223-2011 "Emission Standard of Air Pollutants for Thermal Power Plants".

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An energy-saving and efficiency-enhancing urea production system, characterized in that, It includes a synthesis unit, a hydrolysis and desorption unit, an evaporation and granulation unit, and a recycling and absorption unit; The liquid ammonia outlet of the liquid ammonia storage tank of the synthesis unit is connected to the cold medium inlet of the second heat exchanger of the hydrolysis and desorption unit via a pipeline, and the cold medium outlet of the second heat exchanger is connected to the inlet of the mixer of the synthesis unit via a pipeline. The outlet of the stripping tower of the synthesis unit is connected to the inlet of the low-pressure separator of the circulating absorption unit via a pipeline. The outlet of the desorption tower of the hydrolysis and desorption unit is connected to the inlet of the low-pressure separator of the circulating absorption unit via a pipeline. The outlet of the absorbent circulation pump of the circulating absorption unit is connected to the inlet of the high-pressure scrubber of the synthesis unit via a pipeline. The liquid phase outlet of the low-pressure separator of the circulating absorption unit is connected to the inlet of the multi-effect evaporator of the evaporation and granulation unit via a pipeline. The mother liquor outlet of the multi-effect evaporator is connected to the inlet of the ammonia tank of the hydrolysis and desorption unit via a pipeline.

2. The energy-saving and efficiency-enhancing urea production system according to claim 1, characterized in that, The synthesis unit includes a liquid ammonia storage tank, a carbon dioxide source, a mixer, a pool condenser, a synthesis tower, a liquid collection tank, a stripping tower, and a high-pressure scrubber. The synthesis tower has several trays arranged from top to bottom, and a discharge port is located at the top. The discharge port is connected to the inlet of the liquid collection tank via a pipeline. The gas phase outlet of the liquid collection tank is connected to the air inlet of the high-pressure scrubber via a pipeline. The outlet of the high-pressure scrubber is connected to the inlet of the mixer via a pipeline. The outlet of the mixer is connected to the liquid inlet of the pool condenser via a pipeline. The liquid phase outlet of the liquid collection tank is connected to the liquid inlet of the stripping tower via a pipeline. The outlet of the carbon dioxide source is connected to the air inlet of the stripping tower via a pipeline. The gas outlet of the stripping tower is connected to the air inlet of the pool condenser via a pipeline. The outlet of the pool condenser is connected to the feed inlet of the synthesis tower via a pipeline.

3. The energy-saving and efficiency-enhancing urea production system according to claim 1, characterized in that, The hydrolysis and desorption unit includes an ammonia tank, a desorption tower, a first heat exchanger, a second heat exchanger, a hydrolysis tower, and a third heat exchanger. The outlet of the ammonia tank is connected to the cold medium inlet of the first heat exchanger via a pipeline. The cold medium outlet of the first heat exchanger is connected to the liquid inlet of the analytical tower via a pipeline. The hydrolyzed purified water outlet at the bottom of the analytical tower is connected to the hot medium inlet of the first heat exchanger via a pipeline. The hot medium outlet of the first heat exchanger is connected to the hot medium inlet of the second heat exchanger via a pipeline. The hot medium outlet of the second heat exchanger is connected to the inlet of the circulating water system via a pipeline. The liquid outlet in the middle of the analytical column is connected to the cold medium inlet of the third heat exchanger via a pipeline; the cold medium outlet of the third heat exchanger is connected to the feed inlet of the hydrolysis column via a pipeline; the liquid outlet at the bottom of the hydrolysis column is connected to the hot medium inlet of the third heat exchanger via a pipeline; the hot medium outlet of the third heat exchanger is connected to the middle inlet of the analytical column via a pipeline; and the outlet at the top of the hydrolysis column is connected to the upper inlet of the analytical column via a pipeline.

4. The energy-saving and efficiency-enhancing urea production system according to claim 1, characterized in that, The evaporation granulation unit includes a multi-effect evaporator, an atomizing granulation tower, and a crude product silo. The concentrated liquid outlet of the multi-effect evaporator is connected to the inlet of the high-pressure pump via a pipeline, the outlet of the high-pressure pump is connected to the nozzle inlet of the atomizing granulation tower via a pipeline, and the particle outlet of the atomizing granulation tower is connected to the inlet of the crude product silo via a pipeline.

5. The energy-saving and efficiency-enhancing urea production system according to claim 1, characterized in that, The circulating absorption unit includes a low-pressure absorption tower, a low-pressure condenser, a low-pressure separator, an absorbent circulation pump, and a tail gas scrubber. The gas phase outlet of the low-pressure separator is connected to the air inlet at the bottom of the low-pressure absorption tower via a pipeline. The top outlet of the low-pressure absorption tower is connected to the air inlet of the low-pressure condenser via a pipeline. The outlet of the low-pressure condenser is connected to the inlet of the condensate pump via a pipeline. The outlet of the condensate pump is connected to the inlet of the ammonia tank via a pipeline. The uncondensed gas outlet of the low-pressure condenser is connected to the air inlet of the tail gas scrubber via a pipeline. The outlet of the tail gas scrubber is led to high altitude for discharge via a pipeline. The liquid outlet of the tail gas scrubber is connected to the inlet of the ammonia tank via a pipeline. The liquid outlet at the bottom of the low-pressure absorption tower is connected to the inlet of the absorption liquid circulation pump via a pipeline, and the outlet of the absorption liquid circulation pump is also connected to the spray liquid inlet at the top of the low-pressure absorption tower via a pipeline.

6. The energy-saving and efficiency-enhancing urea production method according to claim 1, utilizing the energy-saving and efficiency-enhancing urea production system according to any one of claims 1-5, is characterized in that... Includes the following steps: (1) Synthesis reaction: After the liquid ammonia is heated by heat exchange with waste heat, it is mixed with carbon dioxide, recycled ammonia and carbon dioxide, and then enters the pool condenser to generate ammonium carbamate, and then sent to the synthesis tower. The full tower operation mode is adopted, and the reaction time of the material is extended by multiple tower plates in the tower to generate urea mixture. (2) Stripping separation: The urea mixture discharged from the top of the synthesis tower is sent to the collection tank for buffering, and then introduced into the stripping tower. Raw material carbon dioxide is introduced for stripping treatment to separate some unreacted ammonia and carbon dioxide. (3) Recycled absorption: The stripped material enters the low-pressure absorption unit. After low-pressure absorption and condensation separation, the liquid phase material is sent to the evaporation granulation system, and the ammonia and carbon dioxide in the gas phase are recovered and returned to the pool condenser for recycling. (4) Evaporation granulation: The material from the low-pressure absorption unit is concentrated to a urea concentration of ≥99.5% by multi-effect evaporation, and then urea product is obtained by atomization granulation; (5) Hydrolysis and waste heat utilization: Ammonia, carbon dioxide and water separated during the evaporation and concentration process enter the ammonia tank to form dilute ammonia water. The dilute ammonia water is sent to the hydrolysis and desorption unit. After hydrolysis in the hydrolysis tower and desorption in the desorption tower to recover ammonia and carbon dioxide, hydrolyzed purified water at about 98°C is produced. The hydrolyzed purified water is used to exchange heat with the liquid ammonia in step (1) to raise the temperature of the liquid ammonia to 65-80°C. The hydrolyzed purified water after heat exchange is cooled to 41-48°C and sent directly to the circulating water system for reuse.

7. The energy-saving and efficiency-enhancing urea production method according to claim 6, characterized in that, In step (1), the synthesis tower is operated at full capacity, and the reaction time of the material in the synthesis tower is extended by more than 30% compared with the traditional process. The initial temperature of liquid ammonia is 38°C, and after heat exchange with hydrolyzed purified water, the temperature is raised to 65-80°C. The heat exchange process between hydrolyzed purified water and liquid ammonia is carried out in the second heat exchanger. After heat exchange, the temperature of hydrolyzed purified water is controlled at 41-48°C.

8. The energy-saving and efficiency-enhancing urea production method according to claim 6, characterized in that, In step (2), the operating pressure of the stripping tower is 1.5 to 2.5 MPa, the operating temperature is 170 to 190°C, and the concentration of the urea mixture after stripping is increased to more than 53%.

9. The energy-saving and efficiency-enhancing urea production method according to claim 7, characterized in that, In step (3), the operating pressure of the low-pressure absorption unit is 0.1 to 0.3 MPa, and the operating temperature is 40 to 60°C. After low-pressure absorption, the urea concentration of the material is increased to more than 70%.

10. The energy-saving and efficiency-enhancing urea production method according to claim 7, characterized in that, In step (4), the multi-effect evaporator adopts a 2-3 effect evaporation process with an evaporation temperature of 120-140℃. The ammonia and carbon dioxide recovered during the evaporation process are concentrated by the hydrolysis and desorption unit and then sent to the high-pressure scrubber and then introduced into the pool condenser for circulation reaction.

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