Stripping tower condensate treatment process based on synthetic ammonia production

Abstract

The invention belongs to the technical field of synthesis ammonia production, and particularly relates to a stripping tower condensate treatment process based on synthesis ammonia production. By adopting the novel composite adsorbent and coupling a multi-stage process, the treatment efficiency and the resource recovery rate are synchronously improved. The unique adsorbent can efficiently remove sulfides and carbon dioxide at low temperature, so that the pretreatment effect is ensured to be stable and reach the standard, and a good foundation is laid for subsequent steps. The process realizes efficient cyclic utilization of energy and substances. In the process, waste heat of condensate is recycled to preheat desalted water, energy consumption of the system is reduced, pollutant ammonia is converted into an ammonium bicarbonate product with economic value through multi-stage ammonia absorption and carbonization steps, and waste is turned into wealth. Moreover, by integrating an advanced treatment unit, especially a reverse osmosis process, the final effluent quality can meet the harsh desalted water standard, so that a complete recycling closed loop is formed, and the consumption of fresh water and the discharge of wastewater are remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of synthetic ammonia production technology, specifically relating to a process for treating stripping tower condensate based on synthetic ammonia production. Background Technology

[0002] In ammonia synthesis, the stripping tower in the shift conversion section generates a large amount of high-temperature condensate, which contains pollutants such as ammonia, carbon dioxide, trace organic matter (e.g., methanol, formic acid), and suspended solids. Direct discharge of this condensate not only causes eutrophication and other environmental pollution due to high ammonia nitrogen and organic matter content, but also wastes the heat energy and ammonia resources that can be recovered from the condensate. Existing treatment processes typically employ single stripping or biochemical treatment, but these suffer from high energy consumption, low ammonia recovery rates, and failure to meet water quality reuse standards. For example, traditional stripping towers have insufficient ammonia removal efficiency and do not fully utilize the waste heat in the condensate, leading to energy waste. Furthermore, the deep purification of the condensate is incomplete, resulting in low reuse rates and difficulty in achieving zero emissions. In addition, the recovery and utilization of CO2 gas and ammonia in existing technologies are inadequate, increasing operating costs and environmental burden.

[0003] Therefore, there is an urgent need to develop an integrated, low-energy-consumption, and high-efficiency condensate treatment process that can synergistically achieve the cascade utilization of waste heat, the resource-based conversion of ammonia and CO2 (such as the preparation of high-value-added ammonium salts), and the deep purification and reuse of wastewater, thereby meeting the industry's dual needs for green environmental protection and cost reduction and efficiency improvement. Summary of the Invention

[0004] The purpose of this invention is to address existing problems by providing a process for treating stripping tower condensate from ammonia synthesis.

[0005] This invention is achieved through the following technical solution:

[0006] A process for treating stripping tower condensate from ammonia synthesis includes the following steps:

[0007] S1. Condensate pretreatment:

[0008] The hot condensate (temperature 80~100℃, ammonia nitrogen content 3000~3500mg / L) discharged from the bottom of the ammonia conversion stripping tower is sent to the pretreatment unit. It is then passed through the desulfurization adsorption column to remove H2S to ≤5mg / L, and then through the propylene carbonate absorption tower to remove CO2 to ≤100mg / L, to obtain the pretreated condensate.

[0009] S2, Waste Heat Recovery:

[0010] The condensate after pretreatment in step S1 is sent to a plate heat exchanger to exchange heat with the fresh water in the demineralized water system to complete the waste heat recovery.

[0011] S3, Multi-stage ammonia absorption:

[0012] The condensate after cooling in step S2 is divided into two streams. One stream is sent to the first-stage ammonia absorber and comes into countercurrent contact with the ammonia gas condensed and evaporated from the synthetic ammonia to generate dilute ammonia water with an ammonia concentration of 5-8 wt%. The other stream is sent to the second-stage ammonia absorber and comes into contact with the remaining ammonia gas at the outlet of the first-stage ammonia absorber to generate concentrated ammonia water with an ammonia concentration of 10-12 wt%.

[0013] S4, Carbonization Utilization:

[0014] The concentrated ammonia obtained in step S3 is fed into a carbonization tower and reacted with compressed CO2 (purity ≥99%) to generate ammonium bicarbonate crystals. After separation and drying, the ammonium bicarbonate product is obtained.

[0015] Furthermore, the desulfurization adsorption column described in step S1 is filled with a ZnO-CeO2-MgO@graphene aerogel composite adsorbent. The preparation of the ZnO-CeO2-MgO@graphene aerogel composite adsorbent includes the following steps:

[0016] (1) Place a 0.5~2 mg / mL GO (graphene oxide) dispersion in a three-necked flask, and add the prepared metal precursor mixture dropwise at 30~40℃ and 300~500 rpm. After the addition is complete, continue stirring for 1~2 h. During this period, adjust the pH of the solution to 7.0~8.0 with ammonia or nitric acid, raise the temperature to 50~60℃, and keep it warm and stir for 2~3 h to form a uniform and transparent sol.

[0017] (2) The above sol was transferred to a polytetrafluoroethylene-lined reactor and then placed in an oven. The hydrothermal reaction was carried out at 120~180℃ for 6~12h. After the reaction was completed, the product was naturally cooled to room temperature and the product was taken out. At this time, GO was partially reduced to reduced graphene oxide and self-assembled into a three-dimensional porous framework. Metal hydroxide was uniformly loaded on the surface of the reduced graphene oxide sheets to form an elastic hydrogel.

[0018] (3) Cut the hydrogel into 2-5cm pieces. 3 The block-shaped aerogel was placed in a supercritical drying reactor, sealed, and CO2 was introduced to replace the air inside the reactor. The temperature was raised to 40~60℃ and the pressure was raised to 8~12MPa. After holding the temperature and pressure for 1~2h, the pressure was released at a rate of 0.1~0.2MPa / h while maintaining a stable temperature. After the pressure was released, CO2 was introduced to purge for 1~2h, and finally a black, lightweight aerogel precursor was obtained.

[0019] (4) Place the aerogel precursor in a quartz boat, put it into a tube furnace, and heat it to 300-400°C at a rate of 2-5°C under N2 atmosphere. After calcining for 2-4 hours, let it cool naturally to room temperature and then take it out.

[0020] Furthermore, the preparation method of the metal precursor solution in step (1) is as follows: according to the target active component molar ratio Zn 2+ :Ce 3+ :Mg 2+ =1:(0.1~0.3):(0.05~0.15) Prepare Zn(NO3)2·6H2O, Ce(NO3)3·6H2O, and Mg(NO3)2·6H2O by adding them to a beaker, adding water and stirring until completely dissolved;

[0021] The amount of GO used accounts for 5-15% of the total mass of the adsorbent;

[0022] The total concentration of metal precursors in the mixed solution was controlled at 0.1~0.3 mol / L.

[0023] Furthermore, after the ZnO-CeO2-MgO@graphene aerogel composite adsorbent is saturated, it is regenerated at 250-280°C using a nitrogen mixture containing a low concentration of oxygen (2-5%). The regenerated adsorbent has a high performance recovery rate and can be recycled more than 500 times without replacement.

[0024] Furthermore, in step S1, the adsorption temperature during the passage through the desulfurization adsorption column is 20~40℃, and the space velocity is 1~2h. -1 ;

[0025] The absorption pressure when passing through the propylene carbonate absorption tower is 0.3~0.5MPa and the temperature is 30~45℃.

[0026] Furthermore, the heat exchange described in step S2 specifically involves the condensate temperature dropping to 50~60℃ and the demineralized water temperature rising to 45~50℃ before being sent to the demineralized water heater to complete the waste heat recovery.

[0027] Furthermore, in step S3, the proportion of condensate fed into the primary ammonia absorber is 60-70%, and the proportion of condensate fed into the secondary ammonia absorber is 30-40%.

[0028] Furthermore, the operating temperature of the two-stage ammonia absorbers described in step S3 is 15~25℃, and the pressure is 0.2~0.3MPa.

[0029] Furthermore, in step S4, the temperature is controlled at 40~50℃ and the pressure at 0.4~0.6MPa during the reaction with compressed CO2.

[0030] Furthermore, it also includes S5, wastewater reuse: collect the wastewater discharged from the carbonization tower in step S4 (ammonia nitrogen ≤ 50 mg / L), and pass it sequentially through quartz sand filtration, activated carbon adsorption, and reverse osmosis membrane separation. The operating pressure is 1.5~2.0 MPa. After treatment, the water quality meets the desalination water index (conductivity ≤ 10 μS / cm) and is reused in the desalination water system to realize water resource recycling.

[0031] The present invention has the following advantages over the prior art:

[0032] 1. This invention achieves a simultaneous leap in treatment efficiency and resource recovery rate by coupling a specially formulated ZnO-CeO2-MgO@graphene aerogel composite adsorbent with a multi-stage process. Its unique composite adsorbent can efficiently remove sulfides and carbon dioxide at low temperatures of 20~40℃, which not only ensures that the pretreatment effect is stable and meets the standards, providing high-quality raw materials for subsequent ammonia absorption, carbonization and other steps, but also greatly reduces the cost of adsorbent replacement due to its low oxygen and nitrogen regeneration capability, thus solving the problems of low efficiency and short life of traditional adsorbents.

[0033] 2. This invention recovers waste heat from the condensate using a plate heat exchanger to preheat the demineralized water, significantly reducing steam consumption in the demineralized water heating process. Simultaneously, through a 65%:35% condensate split design and a two-stage ammonia absorption process, it achieves efficient ammonia absorption, which is then converted into ammonium bicarbonate with a purity of ≥99% via a carbonization reaction. This transforms the ammonia nitrogen pollutants that originally needed to be treated into high-value-added chemical raw materials, turning waste into treasure.

[0034] 3. This invention forms a complete resource recovery closed loop through integrated deep treatment, achieving near-zero wastewater discharge and high-quality reuse. After treatment by quartz sand filtration, activated carbon adsorption and reverse osmosis, the effluent ammonia nitrogen is ≤42mg / L and conductivity is ≤8.8µS / cm, meeting the standards for desalinated water reuse. This can significantly reduce the consumption of fresh water and avoid the environmental pressure of wastewater discharge. Detailed Implementation

[0035] To further explain the present invention, the following specific embodiments are described.

[0036] Example 1

[0037] A process for treating stripping tower condensate from ammonia synthesis includes the following steps:

[0038] S1. Condensate pretreatment:

[0039] The hot condensate (temperature 80~100℃, ammonia nitrogen content 3000~3500 mg / L) discharged from the bottom of the ammonia conversion stripping tower is sent to the pretreatment unit and sequentially passed through a desulfurization adsorption column packed with ZnO-CeO2-MgO@graphene aerogel composite adsorbent at an adsorption temperature of 20℃ and a space velocity of 1 h⁻¹. -1 H2S is removed to ≤5mg / L, and then the solution is passed through a propylene carbonate absorption tower at an absorption pressure of 0.3MPa and a temperature of 30℃ to remove CO2 to ≤100mg / L, yielding pretreated condensate.

[0040] The preparation of the ZnO-CeO2-MgO@graphene aerogel composite adsorbent includes the following steps:

[0041] (1) Place the 0.5 mg / mL GO (graphene oxide) dispersion in a three-necked flask, and add the prepared metal precursor mixture dropwise under stirring conditions of 30°C and 300 rpm. After the addition is complete, continue stirring for 1 h. During this period, adjust the pH of the solution to 7.0 with ammonia or nitric acid, raise the temperature to 50°C, and keep stirring for 2 h to form a uniform and transparent sol.

[0042] The method for preparing the metal precursor solution is as follows: according to the target active component molar ratio Zn 2+ :Ce 3+ :Mg 2+ =1:0.1:0.05 Prepare Zn(NO3)2·6H2O, Ce(NO3)3·6H2O, and Mg(NO3)2·6H2O by adding them to a beaker, adding water and stirring until completely dissolved;

[0043] The amount of GO used accounts for 5% of the total mass of the adsorbent;

[0044] The total concentration of the metal precursor in the mixed solution was controlled at 0.1 mol / L;

[0045] (2) The above sol was transferred to a polytetrafluoroethylene-lined reactor and then placed in an oven. The hydrothermal reaction was carried out at 120°C for 6 hours. After the reaction was completed, the product was naturally cooled to room temperature and the product was taken out. At this time, GO was partially reduced to reduced graphene oxide and self-assembled into a three-dimensional porous framework. Metal hydroxide was uniformly loaded on the surface of the reduced graphene oxide sheets to form an elastic hydrogel.

[0046] (3) Cut the hydrogel into 2cm pieces 3 The block-shaped aerogel precursor was placed in a supercritical drying reactor, sealed, and CO2 was introduced to replace the air in the reactor. The temperature was raised to 40°C and the pressure was increased to 8 MPa. After holding the temperature and pressure for 1 hour, the pressure was released at a rate of 0.1 MPa / h while maintaining a stable temperature. After the pressure was released, CO2 was introduced to purge for another 1 hour, and finally a black, lightweight aerogel precursor was obtained.

[0047] (4) Place the aerogel precursor in a quartz boat, put it into a tube furnace, and heat it to 300°C at a rate of 2°C under N2 atmosphere. After holding it at the temperature for 2 hours, let it cool naturally to room temperature and then take it out.

[0048] After the ZnO-CeO2-MgO@graphene aerogel composite adsorbent is saturated, it is regenerated at 250°C using a nitrogen mixture containing a low concentration of oxygen (2%).

[0049] S2, Waste Heat Recovery:

[0050] The condensate after pretreatment in step S1 is sent to a plate heat exchanger to exchange heat with the fresh water in the demineralized water system. The temperature of the condensate drops to 50°C and the temperature of the demineralized water rises to 45°C before being sent to the demineralized water heater to complete the waste heat recovery.

[0051] S3, Multi-stage ammonia absorption:

[0052] The condensate after cooling in step S2 is divided into two streams. One stream is sent to the primary ammonia absorber (accounting for 60%), which comes into countercurrent contact with the ammonia gas condensed and evaporated from the synthetic ammonia to generate dilute ammonia water with an ammonia concentration of 5-8 wt%. The other stream is sent to the secondary ammonia absorber (accounting for 30%), which comes into contact with the remaining ammonia gas at the outlet of the primary ammonia absorber to generate concentrated ammonia water with an ammonia concentration of 10-12 wt%.

[0053] The operating temperature of both stages of ammonia absorbers is 15℃, and the pressure is 0.2MPa.

[0054] S4, Carbonization Utilization:

[0055] The concentrated ammonia obtained in step S3 is fed into a carbonization tower and reacted with compressed CO2 (purity ≥99%) at 40℃ and 0.4MPa to generate ammonium bicarbonate crystals. After separation and drying, the ammonium bicarbonate product is obtained.

[0056] S5. Wastewater Reuse: Collect the wastewater discharged from the carbonization tower in step S4 (ammonia nitrogen ≤ 50 mg / L), and sequentially pass it through quartz sand filtration, activated carbon adsorption, and reverse osmosis membrane separation. The operating pressure is 1.5 MPa. After treatment, the water quality meets the desalination water index (conductivity ≤ 10 μS / cm) and is reused in the desalination water system to achieve water resource recycling.

[0057] Example 2

[0058] A process for treating stripping tower condensate from ammonia synthesis includes the following steps:

[0059] S1. Condensate pretreatment:

[0060] The hot condensate (temperature 80~100℃, ammonia nitrogen content 3000~3500 mg / L) discharged from the bottom of the ammonia synthesis shift stripping tower is sent to the pretreatment unit and sequentially passed through a desulfurization adsorption column packed with ZnO-CeO2-MgO@graphene aerogel composite adsorbent at an adsorption temperature of 30℃ and a space velocity of 1.5 h⁻¹. -1 H2S is removed to ≤5mg / L, and then the mixture is passed through a propylene carbonate absorption tower at an absorption pressure of 0.4MPa and a temperature of 40℃ to remove CO2 to ≤100mg / L, yielding the treated condensate.

[0061] The preparation of the ZnO-CeO2-MgO@graphene aerogel composite adsorbent includes the following steps:

[0062] (1) Place a 1 mg / mL GO (graphene oxide) dispersion in a three-necked flask and add the prepared metal precursor mixture dropwise under stirring conditions of 35°C and 400 rpm. After the addition is complete, continue stirring for 1.5 h. During this period, adjust the pH of the solution to 7.5 with ammonia or nitric acid, raise the temperature to 55°C, and keep stirring for 2.5 h to form a uniform and transparent sol.

[0063] The method for preparing the metal precursor solution is as follows: according to the target active component molar ratio Zn 2+ :Ce 3+ :Mg 2+ =1:0.2:0.1 Prepare Zn(NO3)2·6H2O, Ce(NO3)3·6H2O, and Mg(NO3)2·6H2O by adding them to a beaker, adding water and stirring until completely dissolved;

[0064] The amount of GO used accounts for 10% of the total mass of the adsorbent;

[0065] The total concentration of the metal precursor in the mixed solution was controlled at 0.2 mol / L;

[0066] (2) The above sol was transferred to a polytetrafluoroethylene-lined reactor and then placed in an oven. The hydrothermal reaction was carried out at 150°C for 9 hours. After the reaction was completed, the product was naturally cooled to room temperature and the product was taken out. At this time, GO was partially reduced to reduced graphene oxide and self-assembled into a three-dimensional porous framework. Metal hydroxide was uniformly loaded on the surface of the reduced graphene oxide sheets to form an elastic hydrogel.

[0067] (3) Cut the hydrogel into 3cm pieces 3 The block-shaped aerogel was placed in a supercritical drying reactor, sealed, and CO2 was introduced to replace the air in the reactor. The temperature was raised to 50°C and the pressure was increased to 10 MPa. After holding the temperature and pressure for 1.5 h, the pressure was released at a rate of 0.15 MPa / h while maintaining a stable temperature. After the pressure was released, CO2 was introduced to purge for another 1.5 h, and finally a black, lightweight aerogel precursor was obtained.

[0068] (4) Place the aerogel precursor in a quartz boat, put it in a tube furnace, and heat it to 350°C at a rate of 3°C under N2 atmosphere. After calcining at this temperature for 3 hours, let it cool naturally to room temperature and then take it out.

[0069] After the ZnO-CeO2-MgO@graphene aerogel composite adsorbent is saturated, it is regenerated at 260°C using a nitrogen mixture containing a low concentration of oxygen (3%).

[0070] S2, Waste Heat Recovery:

[0071] The condensate after pretreatment in step S1 is sent to a plate heat exchanger to exchange heat with the fresh water in the demineralized water system. The temperature of the condensate drops to 55°C and the temperature of the demineralized water rises to 48°C before being sent to the demineralized water heater to complete the waste heat recovery.

[0072] S3, Multi-stage ammonia absorption:

[0073] The condensate after cooling in step S2 is divided into two streams. One stream is sent to the primary ammonia absorber (accounting for 65%), which comes into countercurrent contact with the ammonia gas condensed and evaporated from the synthetic ammonia to generate dilute ammonia water with an ammonia concentration of 5-8 wt%. The other stream is sent to the secondary ammonia absorber (accounting for 35%), which comes into contact with the remaining ammonia gas at the outlet of the primary ammonia absorber to generate concentrated ammonia water with an ammonia concentration of 10-12 wt%.

[0074] The operating temperature of both stages of ammonia absorbers is 20℃, and the pressure is 0.25MPa.

[0075] S4, Carbonization Utilization:

[0076] The concentrated ammonia obtained in step S3 is fed into a carbonization tower and reacted with compressed CO2 (purity ≥99%) at 45°C and 0.5MPa to generate ammonium bicarbonate crystals. After separation and drying, the ammonium bicarbonate product is obtained.

[0077] S5. Wastewater Reuse: Collect the wastewater discharged from the carbonization tower in step S4 (ammonia nitrogen ≤ 50 mg / L), and sequentially pass it through quartz sand filtration, activated carbon adsorption, and reverse osmosis membrane separation. The operating pressure is 1.7 MPa. After treatment, the water quality meets the desalination water index (conductivity ≤ 10 μS / cm) and is reused in the desalination water system to achieve water resource recycling.

[0078] Example 3

[0079] A process for treating stripping tower condensate from ammonia synthesis includes the following steps:

[0080] S1. Condensate pretreatment:

[0081] The hot condensate (temperature 80~100℃, ammonia nitrogen content 3000~3500 mg / L) discharged from the bottom of the ammonia conversion stripping tower is sent to the pretreatment unit and sequentially passed through a desulfurization adsorption column packed with ZnO-CeO2-MgO@graphene aerogel composite adsorbent at an adsorption temperature of 40℃ and a space velocity of 2h. -1 H2S is removed to ≤5mg / L, and then the solution is passed through a propylene carbonate absorption tower at an absorption pressure of 0.5MPa and a temperature of 45℃ to remove CO2 to ≤100mg / L, yielding pretreated condensate.

[0082] The preparation of the ZnO-CeO2-MgO@graphene aerogel composite adsorbent includes the following steps:

[0083] (1) Place the GO (graphene oxide) dispersion with a concentration of 2 mg / mL in a three-necked flask, and add the prepared metal precursor mixture dropwise under stirring conditions of 40℃ and 500 rpm. After the addition is complete, continue stirring for 2 hours. During this period, adjust the pH of the solution to 8.0 with ammonia or nitric acid, raise the temperature to 60℃, and keep stirring for 3 hours to form a uniform and transparent sol.

[0084] The method for preparing the metal precursor solution is as follows: according to the target active component molar ratio Zn 2+ :Ce 3+ :Mg 2+ =1:0.3:0.15 Prepare Zn(NO3)2·6H2O, Ce(NO3)3·6H2O, and Mg(NO3)2·6H2O by adding them to a beaker, adding water and stirring until completely dissolved;

[0085] The amount of GO used accounts for 15% of the total mass of the adsorbent;

[0086] The total concentration of the metal precursor in the mixed solution was controlled at 0.3 mol / L;

[0087] (2) The above sol was transferred to a polytetrafluoroethylene-lined reactor and then placed in an oven. The hydrothermal reaction was carried out at 180°C for 12 hours. After the reaction was completed, the product was naturally cooled to room temperature and removed. At this time, GO was partially reduced to reduced graphene oxide and self-assembled into a three-dimensional porous framework. Metal hydroxide was uniformly loaded on the surface of the reduced graphene oxide sheets to form an elastic hydrogel.

[0088] (3) Cut the hydrogel into 5cm pieces 3 The block-shaped aerogel precursor was placed in a supercritical drying reactor, sealed, and CO2 was introduced to replace the air in the reactor. The temperature was raised to 60°C and the pressure was increased to 12 MPa. After holding the temperature and pressure for 2 hours, the pressure was released at a rate of 0.2 MPa / h while maintaining a stable temperature. After the pressure was released, CO2 was introduced to purge for another 2 hours, and finally a black, lightweight aerogel precursor was obtained.

[0089] (4) Place the aerogel precursor in a quartz boat, put it into a tube furnace, and heat it to 400°C at a rate of 5°C under N2 atmosphere. After calcining at this temperature for 4 hours, let it cool naturally to room temperature and then take it out.

[0090] After the ZnO-CeO2-MgO@graphene aerogel composite adsorbent is saturated, it is regenerated at 280°C using a nitrogen mixture containing a low concentration of oxygen (5%).

[0091] S2, Waste Heat Recovery:

[0092] The condensate after pretreatment in step S1 is sent to a plate heat exchanger to exchange heat with the fresh water in the demineralized water system. The temperature of the condensate drops to 60°C and the temperature of the demineralized water rises to 50°C before being sent to the demineralized water heater to complete the waste heat recovery.

[0093] S3, Multi-stage ammonia absorption:

[0094] The condensate after cooling in step S2 is divided into two streams. One stream is sent to the primary ammonia absorber (accounting for 70%), which comes into countercurrent contact with the ammonia gas condensed and evaporated from the synthetic ammonia to generate dilute ammonia water with an ammonia concentration of 5-8 wt%. The other stream is sent to the secondary ammonia absorber (accounting for 30%), which comes into contact with the remaining ammonia gas at the outlet of the primary ammonia absorber to generate concentrated ammonia water with an ammonia concentration of 10-12 wt%.

[0095] The operating temperature of both stages of ammonia absorbers is 25℃, and the pressure is 0.3MPa.

[0096] S4, Carbonization Utilization:

[0097] The concentrated ammonia obtained in step S3 is fed into a carbonization tower and reacted with compressed CO2 (purity ≥99%) at 50°C and 0.6MPa to generate ammonium bicarbonate crystals. After separation and drying, the ammonium bicarbonate product is obtained.

[0098] S5. Wastewater Reuse: Collect the wastewater discharged from the carbonization tower in step S4 (ammonia nitrogen ≤ 50 mg / L), and sequentially pass it through quartz sand filtration, activated carbon adsorption, and reverse osmosis membrane separation. The operating pressure is 2.0 MPa. After treatment, the water quality meets the desalination water index (conductivity ≤ 10 μS / cm) and is reused in the desalination water system to achieve water resource recycling.

[0099] Preparation Example

[0100] The preparation of the ZnO@graphene aerogel composite adsorbent includes the following steps:

[0101] (1) Place a 1 mg / mL GO (graphene oxide) dispersion in a three-necked flask and add the prepared metal precursor mixture dropwise under stirring conditions of 35°C and 400 rpm. After the addition is complete, continue stirring for 1.5 h. During this period, adjust the pH of the solution to 7.5 with ammonia or nitric acid, raise the temperature to 55°C, and keep stirring for 2.5 h to form a uniform and transparent sol.

[0102] The method for preparing the metal precursor solution is as follows: add Zn(NO3)2·6H2O into a beaker, add water and stir until completely dissolved;

[0103] The amount of GO used accounts for 10% of the total mass of the adsorbent;

[0104] The total concentration of the metal precursor in the mixed solution was controlled at 0.2 mol / L;

[0105] (2) The above sol was transferred to a polytetrafluoroethylene-lined reactor and then placed in an oven. The hydrothermal reaction was carried out at 150°C for 9 hours. After the reaction was completed, the product was naturally cooled to room temperature and the product was taken out. At this time, GO was partially reduced to reduced graphene oxide and self-assembled into a three-dimensional porous framework. Metal hydroxide was uniformly loaded on the surface of the reduced graphene oxide sheets to form an elastic hydrogel.

[0106] (3) Cut the hydrogel into 3cm pieces 3 The block-shaped aerogel was placed in a supercritical drying reactor, sealed, and CO2 was introduced to replace the air in the reactor. The temperature was raised to 50°C and the pressure was increased to 10 MPa. After holding the temperature and pressure for 1.5 h, the pressure was released at a rate of 0.15 MPa / h while maintaining a stable temperature. After the pressure was released, CO2 was introduced to purge for another 1.5 h, and finally a black, lightweight aerogel precursor was obtained.

[0107] (4) Place the aerogel precursor in a quartz boat, put it into a tube furnace, and heat it to 350°C at a rate of 3°C under N2 atmosphere. After calcining at this temperature for 3 hours, let it cool naturally to room temperature and take it out to obtain the ZnO@graphene aerogel composite adsorbent.

[0108] Comparative Example 1

[0109] Compared with Example 2, Comparative Example 1 omits the composite adsorbent and uses a single ZnO adsorbent instead, while the other steps are the same as in Example 2.

[0110] Comparative Example 2

[0111] Compared with Example 2, Comparative Example 2 replaces the ZnO-CeO2-MgO@graphene aerogel composite adsorbent in step S1 with the ZnO@graphene aerogel composite adsorbent prepared in the preparation example, while the other steps are the same as in Example 2.

[0112] Comparative Example 3

[0113] Compared with Example 2, Comparative Example 3 increased the desulfurization adsorption temperature to 50°C and the space velocity to 2.5 h⁻¹. -1 The other steps are the same as in Example 2.

[0114] Comparative Example 4

[0115] Compared with Example 2, Comparative Example 4 adjusts the condensate distribution ratio to 75% (first-stage ammonia absorber): 25% (second-stage ammonia absorber), raises the operating temperature to 30°C, and the other steps are the same as in Example 2.

[0116] Comparative Example 5

[0117] Compared with Example 2, Comparative Example 5 increased the carbonization temperature to 55°C and reduced the pressure to 0.3 MPa, while the other steps were the same as in Example 2.

[0118] Comparative Example 6

[0119] Compared with Example 2, Comparative Example 6 eliminates reverse osmosis membrane separation in the wastewater reuse treatment process, and only uses quartz sand filtration + activated carbon adsorption. The other steps are the same as in Example 2.

[0120] All examples and comparative examples used the same raw materials. The hot condensate discharged from the bottom of the ammonia conversion stripping tower was kept at a stable temperature of 85-95°C and an ammonia nitrogen content of 3200-3400 mg / L. Performance tests were then conducted, and the test indicators and methods are shown in Table 1 below.

[0121] Table 1. Methods for detecting indicators

[0122] Testing process Key Indicators Detection methods Condensate pretreatment [H2S content, CO2 content] Gas chromatography (GB / T 14685-2011), volumetric method (GB / T 15453-2019) Waste heat recovery Cooling range of condensate, heating range of demineralized water Platinum resistance thermometer (accuracy ±0.1℃) for real-time monitoring Multi-stage ammonia recovery Ammonia absorption rate, dilute / concentrated ammonia concentration Ammonia gas detector (accuracy ±1%) Carbonization utilization ammonium bicarbonate yield and purity Gravimetric method (weighing the product after drying) and high performance liquid chromatography (GB / T 18881-2002) Wastewater reuse Ammonia nitrogen and conductivity of effluent Nessler trial spectrophotometer (HJ535-2009) and conductivity meter (accuracy ±0.1µS / cm)

[0123] All examples and comparative examples were run continuously for 72 hours, with tests performed every 12 hours. The average value was taken as the final result. The test results are shown in Table 2 below.

[0124] Table 2 Comparison results of experiments for each embodiment and comparative example

[0125]

[0126] As can be seen from Table 2 above, the pretreatment effect, ammonia nitrogen absorption efficiency, carbonization yield and purity, and wastewater reuse quality of Examples 1-3 are all better than those of the comparative example.

[0127] The pretreatment results of Comparative Example 1 and Comparative Example 2 were significantly worse than those of Example 2, indicating that the ZnO-CeO2-MgO@graphene aerogel composite adsorbent of the present invention is the key to pretreatment.

[0128] In Comparative Example 3, neither H2S nor CO2 met the standards, and the temperature rise of the demineralized water in waste heat recovery was lower than that in Example 2. This shows that excessively high adsorption desulfurization temperature will reduce the adsorption capacity of the adsorbent for H2S, while excessively high space velocity will result in insufficient contact time between the condensate and the adsorbent, leading to incomplete treatment. At the same time, the temperature of the condensate after pretreatment is too high, which affects the subsequent heat exchange efficiency.

[0129] The ammonia absorption rate of Comparative Example 4 is much lower than that of Example 2. It can be seen that the 65%:35% split ratio of Example 2 can ensure that the first-stage ammonia absorber can fully absorb most of the ammonia, and the operating temperature of 20°C can suppress ammonia volatilization and improve the absorption rate.

[0130] The yield of ammonium bicarbonate in Comparative Example 5 was only 73.6% of that in Example 2, and the purity of 97.5% was also significantly reduced. This may be because the temperature was too high, causing the ammonium bicarbonate to decompose, while the pressure was too low, reducing the solubility of CO2. Both of these factors affected the crystal formation efficiency and purity.

[0131] The conductivity of the effluent from Comparative Example 6 far exceeded that of Example 2, failing to meet the desalination water quality standards. This indicates that quartz sand filtration combined with activated carbon adsorption can only remove suspended solids and organic matter, but cannot remove ionic impurities in the water. Therefore, deep desalination must be achieved through a reverse osmosis membrane to ensure the quality of the recycled water.

[0132] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A process for treating condensate from a stripping tower in ammonia synthesis, characterized in that, Includes the following steps: S1. Condensate pretreatment: The hot condensate discharged from the bottom of the ammonia conversion stripping tower is sent to the pretreatment unit, and then passes through the desulfurization adsorption column to remove H2S to ≤5mg / L, and then passes through the propylene carbonate absorption tower to remove CO2 to ≤100mg / L, to obtain the pretreated condensate. S2, Waste Heat Recovery: The condensate after pretreatment in step S1 is sent to a plate heat exchanger to exchange heat with the fresh water in the demineralized water system to complete the waste heat recovery. S3, Multi-stage ammonia absorption: The condensate after cooling in step S2 is divided into two streams. One stream is sent to the first-stage ammonia absorber and comes into countercurrent contact with the ammonia gas condensed and evaporated from the synthetic ammonia to generate dilute ammonia water with an ammonia concentration of 5-8 wt%. The other stream is sent to the second-stage ammonia absorber and comes into contact with the remaining ammonia gas at the outlet of the first-stage ammonia absorber to generate concentrated ammonia water with an ammonia concentration of 10-12 wt%. S4, Carbonization Utilization: The concentrated ammonia obtained in step S3 is fed into a carbonization tower and reacted with compressed CO2 to generate ammonium bicarbonate crystals, which are then separated and dried to obtain the ammonium bicarbonate product.

2. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, The desulfurization adsorption column described in step S1 is filled with a ZnO-CeO2-MgO@graphene aerogel composite adsorbent. The preparation of the ZnO-CeO2-MgO@graphene aerogel composite adsorbent includes the following steps: (1) Place the graphene oxide dispersion with a concentration of 0.5~2mg / mL in a three-necked flask, and add the prepared metal precursor mixed solution dropwise under the stirring conditions of 30~40℃ and 300~500rpm. After the addition is completed, continue stirring for 1~2h. During this period, adjust the pH of the solution to 7.0~8.0 with ammonia or nitric acid, raise the temperature to 50~60℃, and keep it warm and stir for 2~3h to form a uniform and transparent sol. (2) The above sol was transferred to a polytetrafluoroethylene-lined reactor and then placed in an oven. The hydrothermal reaction was carried out at 120~180℃ for 6~12h. After the reaction was completed, the product was naturally cooled to room temperature and the product was taken out. At this time, GO was partially reduced to reduced graphene oxide and self-assembled into a three-dimensional porous framework. Metal hydroxide was uniformly loaded on the surface of the reduced graphene oxide sheets to form an elastic hydrogel. (3) Cut the hydrogel into 2-5cm pieces. 3 The block-shaped aerogel was placed in a supercritical drying reactor, sealed, and CO2 was introduced to replace the air in the reactor. The temperature was raised to 40~60℃ and the pressure was raised to 8~12MPa. After holding the temperature and pressure for 1~2h, the pressure was released at a rate of 0.1~0.2MPa / h while maintaining a stable temperature. After the pressure was released, CO2 was introduced to purge for 1~2h, and finally a black, lightweight aerogel precursor was obtained. (4) Place the aerogel precursor in a quartz boat, put it into a tube furnace, and heat it to 300-400°C at a rate of 2-5°C under N2 atmosphere. After calcining for 2-4 hours, let it cool naturally to room temperature and then take it out.

3. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 2, characterized in that, The preparation method of the metal precursor solution in step (1) is as follows: according to the target active component molar ratio Zn 2+ :Ce 3+ :Mg 2+ =1:(0.1~0.3):(0.05~0.15) Prepare Zn(NO3)2·6H2O, Ce(NO3)3·6H2O, and Mg(NO3)2·6H2O by adding them to a beaker, adding water and stirring until completely dissolved; The amount of graphene oxide used accounts for 5-15% of the total mass of the adsorbent; The total concentration of metal precursors in the mixed solution was controlled at 0.1~0.3 mol / L.

4. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 2, characterized in that, After the ZnO-CeO2-MgO@graphene aerogel composite adsorbent is saturated, it is regenerated at 250~280℃ using a nitrogen mixture containing a low concentration of oxygen, with an oxygen concentration of 2~5%.

5. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, In step S1, the adsorption temperature during the desulfurization adsorption column is 20~40℃, and the space velocity is 1~2h. -1 ; The absorption pressure when passing through the propylene carbonate absorption tower is 0.3~0.5MPa and the temperature is 30~45℃.

6. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, The heat exchange described in step S2 specifically involves the condensate temperature dropping to 50~60℃ and the demineralized water temperature rising to 45~50℃ before being sent to the demineralized water heater to complete the waste heat recovery.

7. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, In step S3, the proportion of condensate fed into the primary ammonia absorber is 60-70%, and the proportion of condensate fed into the secondary ammonia absorber is 30-40%.

8. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, The operating temperature of the two-stage ammonia absorbers described in step S3 is 15~25℃, and the pressure is 0.2~0.3MPa.

9. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, In step S4, the temperature is controlled at 40~50℃ and the pressure at 0.4~0.6MPa during the reaction with compressed CO2.

10. The stripping tower condensate treatment process based on ammonia synthesis production according to claim 1, characterized in that, It also includes S5, wastewater reuse: the wastewater discharged from the carbonization tower in step S4 is collected and sequentially filtered through quartz sand, activated carbon adsorption, and reverse osmosis membrane separation. The operating pressure is 1.5~2.0MPa. After treatment, the water quality meets the desalination index and is reused in the desalination system to realize water resource recycling.

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