Production process for increasing ammonia net value by using waste heat refrigeration in synthetic ammonia process

Abstract

The application relates to the technical field of waste heat refrigeration, and particularly discloses a production process for improving ammonia net value in a synthetic ammonia process by using waste heat refrigeration, which comprises the following steps: cooling ammonia synthesis gas after cooling is sequentially subjected to staged deep cooling through a first ammonia cooler and a second ammonia cooler, the ammonia synthesis gas is first cooled to 12-10 DEG C through the first ammonia cooler, then is deeply cooled to-10 DEG C to-25 DEG C through the second ammonia cooler, gaseous ammonia is liquefied, and ammonia synthesis material in a gas-liquid mixture is obtained; the ammonia synthesis material is sent into an ammonia separator to complete gas-liquid separation, liquid ammonia obtained through separation flows to a next section, and low-temperature circulating gas obtained through separation is recycled and reused. The application has the effect of improving ammonia net value in a synthetic ammonia process.

Description

Technical Field

[0001] This invention relates to the field of waste heat refrigeration technology, and in particular to a production process for improving the net value of ammonia by utilizing waste heat refrigeration in ammonia synthesis. Background Technology

[0002] Net ammonia value is a core indicator for evaluating the advancement of ammonia synthesis technology, directly determining the production capacity, raw material consumption, and overall operational efficiency of the ammonia synthesis unit. Ammonia synthesis is a typical reversible exothermic reaction, its progress strictly limited by chemical equilibrium. Under given reaction pressure, temperature, hydrogen-nitrogen ratio, and catalyst conditions, the ammonia content in the outlet gas of the synthesis tower has a theoretical upper limit. The core path to improving the system's net ammonia value is to reduce the residual ammonia content in the circulating gas at the synthesis tower inlet, breaking the reaction equilibrium limitation, increasing the driving force of the forward ammonia synthesis reaction, thereby improving the single-pass conversion rate of the synthesis reaction, and ultimately achieving an increase in the system's net ammonia value. Existing ammonia synthesis processes face insurmountable technical bottlenecks in improving net ammonia value; the core issues are as follows: The insufficient cooling depth of existing refrigeration systems, which cannot achieve deep liquefaction and separation of gaseous ammonia in syngas, is the core bottleneck restricting the reduction of ammonia content in circulating gas. Traditional ammonia synthesis processes generally use electrically driven ammonia chillers as the cold source supply equipment for ammonia coolers. Due to multiple limitations such as the upper limit of compressor compression ratio, equipment investment cost, operating energy consumption, and safe operating boundaries, the ammonia chiller in industrial-scale plants can usually only stably maintain the syngas temperature at the outlet of the ammonia cooler above -5℃, and cannot achieve a long-term stable deep cooling range of -10℃ to -25℃.

[0003] Insufficient refrigeration depth directly leads to persistently high residual ammonia content in the circulating gas, creating a rigid upper limit for improving the net ammonia value. At a conventional refrigeration temperature of -5℃, the saturated vapor pressure of gaseous ammonia in the ammonia synthesis gas is relatively high, limiting the liquefaction separation efficiency. The residual ammonia content in the circulating gas at the ammonia separator outlet is generally higher than 3.5%. The high residual ammonia content re-enters the synthesis tower with the circulating gas, resulting in a significant increase in the ammonia content of the reaction mixture at the synthesis tower inlet. This directly inhibits the forward reaction of ammonia synthesis, greatly weakens the driving force of the chemical equilibrium reaction, and makes it impossible to effectively improve the single-pass conversion rate of the synthesis reaction.

[0004] Current processes are caught in a dilemma between "improving ammonia net value" and "controlling energy consumption," making it impossible to achieve a breakthrough in ammonia net value. If deep refrigeration is forcibly achieved through multi-stage compression of ammonia ice machines to reduce the ammonia content in circulating gas, the equipment investment and power consumption of ammonia ice machines will increase exponentially, accounting for more than 40% of the total power consumption of the synthetic ammonia plant. This will significantly increase the operating costs and carbon emissions of the equipment, completely negating the economic viability for industrial application. The few existing processes that attempt waste heat refrigeration mostly use single-stage refrigeration units, which cannot stably achieve deep refrigeration, nor can they solve the closed-loop matching problem between refrigeration depth, circulating gas ammonia content, and reaction equilibrium conversion rate. Ultimately, they cannot break through the rigid bottleneck of ammonia net value, and the system ammonia net value of conventional synthetic ammonia processes in the industry has stagnated in the low range for a long time, failing to achieve a leapfrog improvement. Summary of the Invention

[0005] In order to improve the net ammonia value in the ammonia synthesis process, this application provides a production process for improving the net ammonia value by utilizing waste heat for refrigeration in the ammonia synthesis process.

[0006] This application provides a production process for improving the net value of ammonia through waste heat refrigeration in a synthetic ammonia process, which adopts the following technical solution: A production process for improving the net value of ammonia by utilizing waste heat refrigeration in a synthetic ammonia process includes the following steps: The cooled ammonia synthesis gas is sequentially cooled in stages by the first ammonia cooler and the second ammonia cooler. The first ammonia cooler cools the gas to 12 to -10°C, and the second ammonia cooler cools it to -10°C to -25°C, so that the gaseous ammonia is liquefied, and a gas-liquid mixed ammonia synthesis material is obtained. The ammonia synthesis material is fed into an ammonia separator to complete gas-liquid separation. The separated liquid ammonia flows to the next stage, and the separated low-temperature circulating gas is recycled for reuse.

[0007] Optionally, the cooled ammonia synthesis gas is obtained through the following steps: Compressed gas containing raw materials with a hydrogen-nitrogen molar ratio of 1:(2.7-3.2) and a pressure of 13-18 MPaG is fed into the ammonia synthesis reaction system to generate a high-temperature ammonia synthesis gas through an exothermic ammonia synthesis reaction. The high-temperature ammonia synthesis gas is fed into a waste heat boiler to recover the waste heat from the reaction, resulting in primary ammonia synthesis gas with a temperature of 160-170°C. At the same time, the waste heat boiler utilizes the recovered waste heat to produce low-pressure steam with a pressure of 0.3-0.5 MPaG as a byproduct. The primary ammonia synthesis gas is cooled step by step through a multi-stage heat exchange system and discharged to obtain secondary ammonia synthesis gas with a temperature of 35-42℃; The secondary ammonia synthesis gas is cooled by a cold exchange cooling system and discharged to obtain tertiary ammonia synthesis gas with a temperature of 25-32°C. The tertiary ammonia synthesis gas is the cooled ammonia synthesis gas.

[0008] Optionally, a dual-stage independent waste heat refrigeration unit is provided, comprising a first waste heat refrigeration unit and a second waste heat refrigeration unit that operate independently. Both the first and second waste heat refrigeration units use low-pressure steam, a byproduct of the ammonia synthesis reaction, as their driving heat source. The first waste heat refrigeration unit provides cooling energy to the first ammonia cooler, and the second waste heat refrigeration unit provides cooling energy to the second ammonia cooler. The two units can dynamically adjust the low-pressure steam input according to the real-time cooling load of the corresponding ammonia cooler to achieve dynamic matching between cooling supply and demand.

[0009] Optionally, the recycling of the low-temperature circulating gas is specifically as follows: the low-temperature circulating gas separated by the ammonia separator at a temperature of -10 to -25°C is first sent to the cold exchange cooling system to complete the recovery of cold energy, and then pressurized by the circulating gas compression system, mixed with fresh gas to form raw material compressed gas, which is then sent to the ammonia synthesis reaction system for recycling reaction.

[0010] Optionally, a cold exchange cooling system is provided to recover the cold energy of the low-temperature circulating gas. The cold exchange cooling system includes a primary cold exchanger. The tertiary ammonia synthesis gas first enters the primary cold exchanger and exchanges heat with the low-temperature circulating gas separated by the ammonia separator to cool it down, thus completing the cold energy recovery.

[0011] Optionally, the cold exchange cooling system further includes: A pre-cooled water cooler and a secondary cold exchanger are connected in series with the primary cold exchanger, with the pre-cooled water cooler connected between the primary and secondary cold exchangers. The ammonia synthesis gas cooled by the primary cold exchanger enters the pre-cooled water cooler and then enters the secondary cold exchanger. The low-temperature circulating gas separated by the ammonia separator first enters the secondary cold exchanger and then enters the primary cold exchanger. The secondary ammonia synthesis gas and the low-temperature circulating gas separated by the ammonia separator complete a three-stage heat exchange and cooling process, achieving gradient recovery of cooling capacity. The supporting lithium bromide refrigeration unit uses low-pressure steam, a byproduct of the ammonia synthesis reaction, as the driving heat source to provide chilled water at 5-7°C to the pre-cooled water cooler, and performs secondary pre-cooling on the ammonia synthesis gas after it has been cooled by the primary heat exchanger.

[0012] Optionally, a GVX heat exchanger is provided. The high-pressure liquid ammonia output from the first waste heat refrigeration unit and the second waste heat refrigeration unit is first pre-cooled by the GVX heat exchanger before being sent to the corresponding ammonia cooler for evaporation and refrigeration. The GVX heat exchanger uses the low-temperature product liquid ammonia separated by the ammonia separator after throttling and depressurization as the cold source to recover the cold energy of the product liquid ammonia.

[0013] Optionally, the multi-stage heat exchange system includes a boiler feedwater preheater, a raw material gas heat exchanger, and a water cooler connected in series: the primary ammonia synthesis gas first enters the boiler feedwater preheater, exchanges heat with the boiler feedwater to cool down, and the preheated boiler feedwater is then sent to the waste heat boiler for steam generation; the cooled synthesis gas then enters the raw material gas heat exchanger, exchanges heat with the raw material compressed gas that has passed through the raw material gas heat exchanger to cool down, and the preheated raw material compressed gas is then sent to the ammonia synthesis reaction system; finally, the synthesis gas passes through the water cooler and is cooled to 35-42°C by circulating water to obtain the secondary ammonia synthesis gas.

[0014] Optionally, a supplementary steam heat exchanger is connected in series on the pipeline from the raw material gas heat exchanger to the delivery pipeline of the ammonia synthesis reaction system. The supplementary steam heat exchanger uses the high-temperature ammonia synthesis gas output from the ammonia synthesis reaction system as a heat source to supplement and raise the temperature of the raw material gas, ensuring that the raw material gas reaches the trigger temperature required for the ammonia synthesis reaction.

[0015] Optionally, a circulating gas compression system is provided, which includes two circulating compressors; one circulating compressor is connected to the main pipeline of the raw material compressed gas and is used to replenish fresh gas to the ammonia synthesis reaction system; the inlet of the other circulating compressor is connected to the circulating gas outlet of the cold exchange cooling system, and the outlet merges with the main pipeline of the raw material compressed gas to provide circulating power for the circulating gas and overcome the pressure drop of the pipeline and equipment in the synthesis loop.

[0016] In summary, this application includes at least one of the following beneficial technical effects: 1. Deep cooling of -10℃ to -25℃ is achieved through a dual-stage independent waste heat refrigeration unit, which greatly improves the liquefaction and separation efficiency of gaseous ammonia in ammonia synthesis gas. The residual ammonia content in the circulating gas at the outlet of the ammonia separator can be reduced to below 1.5%, significantly reducing the ammonia content in the circulating gas at the inlet of the synthesis tower, greatly enhancing the chemical equilibrium driving force of the ammonia synthesis forward reaction, and improving the single-pass conversion rate of the reaction. 2. The refrigeration system is entirely driven by low-pressure steam produced from the waste heat of the ammonia synthesis reaction, replacing the traditional electric ammonia ice machine. The power consumption of the refrigeration process is reduced by more than 90% compared with the traditional process. It avoids the problems of equipment investment and exponential growth in energy consumption caused by the multi-stage compression deep refrigeration of the traditional process. The energy utilization efficiency of the entire system is improved, while significantly reducing the carbon emissions and operating costs of the device, and has excellent economic benefits for industrial application. 3. Within the entire range of 20% to 110% of rated load, the low-pressure steam produced by the waste heat boiler can completely cover the steam consumption of the refrigeration unit, realizing the dynamic coupling of waste heat output and cooling demand. Through supporting designs such as cascade cooling recovery, staged refrigeration, and feed gas supplementary heating, the cascade utilization of cooling capacity is realized. At the same time, the problem of insufficient preheating temperature of feed gas under high cooling capacity conditions is solved, ensuring the stability of the synthesis reaction conversion rate within the entire load range, and significantly improving the system's operational reliability and adaptability to operating conditions. Attached Figure Description

[0017] Figure 1 This is a production process flow diagram of Embodiment 1 of this application; Figure 2 This is a schematic diagram of the structure of the two-stage independent waste heat refrigeration unit in Embodiment 1 of this application; Figure 3 This is a parameter comparison diagram of the ammonia cooler in Embodiment 1 of this application; Figure 4 This is a production process flow diagram of Embodiment 2 of this application; Figure 5 This is a production process flow diagram of Embodiment 3 of this application; Figure 6 This is a schematic diagram of the lithium bromide refrigeration unit structure of Embodiment 3 of this application; Figure 7 This is a production process flow diagram of Embodiment 4 of this application; Figure 8 This is a production process flow diagram of Embodiment 5 of this application; Figure 9 This is a production process flow diagram of Embodiment 6 of this application; Figure 10 This is a production process flow diagram of Embodiment 7 of this application.

[0018] Explanation of reference numerals in the attached figures: 1. Ammonia synthesis reaction system; 11. Heating unit; 12. Ammonia synthesis tower; 13. Replenishment steam heat exchanger; 2. Waste heat boiler; 3. Two-stage independent waste heat refrigeration unit; 31. First waste heat refrigeration unit; 311. First generator; 312. First GAX heat exchanger; 313. First absorber; 314. First condenser; 315. First throttle valve; 316. First solution circulation pump; 32. Second waste heat refrigeration unit; 321. Second generator; 322. Second GAX heat exchanger; 323. Second absorber; 324. Second condenser; 325. Second throttle valve; 326. Second solution circulation pump 33. GVX heat exchanger; 4. Multi-stage heat exchange system; 41. Boiler feedwater preheater; 42. Raw gas heat exchanger; 43. Water cooler; 5. Cold exchange cooling system; 51. Primary cold exchanger; 52. Secondary cold exchanger; 53. Pre-cooled water cooler; 6. First ammonia cooler; 7. Second ammonia cooler; 8. Lithium bromide refrigeration unit; 81. Third generator; 82. Third solution heat exchanger; 83. Third absorber; 84. Third condenser; 85. Built-in evaporator; 86. Third throttle valve; 87. Third solution circulation pump; 88. Chilled water pump; 9. Circulating compressor; 10. Ammonia separator. Detailed Implementation

[0019] The following is in conjunction with the appendix Figure 1-10This application will be described in further detail. Example

[0020] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figures 1-2 The production process includes: Step 1. The raw material compressed gas (a mixture of fresh gas and recirculated gas) with a pressure of 13-18 MPaG, a hydrogen-nitrogen molar ratio of 1:(2.7-3.2), and a temperature of 25-35℃ is transported to the ammonia synthesis reaction system. After preheating and supplemental heating, the ammonia synthesis reaction trigger temperature is reached. An exothermic ammonia synthesis reaction occurs in the catalyst bed of the ammonia synthesis tower to generate high-temperature ammonia synthesis gas.

[0021] Step 2. The high-temperature ammonia synthesis gas from the outlet of the ammonia synthesis reaction system is first fed into the waste heat boiler to recover the waste heat of the reaction before being discharged, resulting in primary ammonia synthesis gas with a temperature of 160-170℃. At the same time, the waste heat boiler utilizes the recovered reaction heat to produce low-pressure steam with a pressure of 0.3-0.5 MPaG as a byproduct. The low-pressure steam is transported through the steam header to the first waste heat refrigeration unit and the second waste heat refrigeration unit, respectively, as the driving heat source for the refrigeration system.

[0022] Step 3. The primary ammonia synthesis gas is cooled step by step through a multi-stage heat exchange system to obtain secondary ammonia synthesis gas at a temperature of 35-42℃. The multi-stage heat exchange system includes a boiler feedwater preheater, a feed gas heat exchanger, and a water cooler connected in series: the primary ammonia synthesis gas first enters the boiler feedwater preheater to exchange heat with the boiler feedwater and cool down. The preheated boiler feedwater is then sent to the waste heat boiler for steam generation. The cooled synthesis gas then enters the feed gas heat exchanger to exchange heat with the feed gas compressed from Step 1 and cool down. The preheated feed gas compressed from the feed gas is then sent to the ammonia synthesis reaction system. Finally, the synthesis gas is cooled to 35-42℃ by the water cooler and circulating water to obtain secondary ammonia synthesis gas.

[0023] Step 4. The secondary ammonia synthesis gas is cooled by a cold exchange cooling system and discharged to obtain tertiary ammonia synthesis gas with a temperature of 25-32℃. The cold exchange cooling system includes a primary cold exchanger: the secondary ammonia synthesis gas enters the primary cold exchanger and exchanges heat with the circulating gas separated from the ammonia separator to cool down; the low-temperature circulating gas separated from the ammonia separator with a temperature of -10 to -25℃ enters the primary cold exchanger in a countercurrent flow, and after completing the cold recovery with the synthesis gas, the temperature rises to 30-35℃ and is incorporated into the raw material compressed gas and transported to the ammonia synthesis reaction system.

[0024] Step 5. The three-stage ammonia synthesis gas is sequentially cooled and liquefied by the first and second ammonia coolers: The ammonia synthesis gas is first cooled to 12 to -10°C by the first ammonia cooler, and then further cooled to -10 to -25°C by the second ammonia cooler, so that the gaseous ammonia is liquefied to form a gas-liquid mixture of ammonia synthesis materials; This step is equipped with a dual-stage independent waste heat refrigeration unit to provide cooling energy: the first waste heat refrigeration unit provides cooling energy to the first ammonia cooler, and the second waste heat refrigeration unit provides cooling energy to the second ammonia cooler. The two units are independently regulated and do not interfere with each other. The low-pressure steam input can be dynamically adjusted according to the real-time cooling load of the corresponding ammonia cooler to achieve dynamic matching between cooling supply and demand.

[0025] Step 6. The ammonia synthesis material obtained in Step 5 is transported to the ammonia separator to complete the separation of liquid ammonia and non-condensable gas: the separated liquid ammonia is stored; the separated non-condensable gas is a low-temperature circulating gas, which is first sent to the cold exchange cooling system in Step 4 to complete the cold energy recovery, and then pressurized by the circulating gas compression system, and finally returned to the raw material compressed gas in Step 1 to enter the ammonia synthesis reaction system for cyclic reaction.

[0026] Furthermore, the circulating gas compression system in this embodiment includes two circulating compressors connected in series; one of the circulating compressors is connected to the main pipeline of the raw material compressed gas to replenish fresh gas; the inlet of the other circulating compressor is connected to the circulating gas outlet of the first-stage cold exchanger, and the outlet merges with the main pipeline of the raw material compressed gas to overcome the pressure drop of the pipeline and equipment in the synthesis loop and provide circulating power for the circulating gas.

[0027] Furthermore, the ammonia synthesis reaction system in this embodiment includes a heating unit and an ammonia synthesis tower connected in series. The heating unit is used to heat the raw material compressed gas to the trigger temperature required for the ammonia synthesis reaction. The heating unit is a backup heating device and is only put into use when the system is cold-started or under extremely low load conditions.

[0028] Furthermore, this embodiment is equipped with a dual-stage independent waste heat refrigeration unit, including a first waste heat refrigeration unit and a second waste heat refrigeration unit, both of which use low-pressure steam produced by the waste heat boiler as the driving heat source to achieve graded refrigeration and cascade utilization of cooling capacity.

[0029] The first waste heat refrigeration unit corresponds to the first ammonia cooler for cooling, which includes a first generator, a first GAX heat exchanger, a first absorber, a first condenser, a first throttle valve, and a first solution circulation pump. The first generator is equipped with a low-pressure steam inlet, an ammonia steam outlet, a condensate outlet, a lean liquor outlet, and a rich liquor inlet. The low-pressure steam inlet is connected to the steam header of the waste heat boiler to provide a driving heat source for the unit. The ammonia vapor inlet of the first condenser is connected to the ammonia vapor outlet of the first generator. The liquid ammonia outlet pipe of the first condenser is connected to the liquid ammonia inlet of the first ammonia cooler through the first throttling valve to reduce pressure. The ammonia inlet of the first absorber is connected to the ammonia outlet of the first ammonia cooler, the lean liquid inlet of the first absorber is connected to the lean liquid outlet of the first GAX heat exchanger, and the rich liquid outlet of the first absorber is connected to the rich liquid inlet of the first GAX heat exchanger through the first solution circulation pump. The rich liquid outlet of the first GAX heat exchanger is connected to the rich liquid inlet of the first generator, and the lean liquid inlet of the first GAX heat exchanger is connected to the lean liquid outlet of the first generator. This is used to recover waste heat from the lean liquid, preheat the rich liquid, and improve the unit's energy efficiency. Both the first absorber and the first condenser are equipped with cooling water circulation interfaces to remove heat from the absorption and condensation processes, ensuring stable operation of the refrigeration cycle.

[0030] The second waste heat refrigeration unit corresponds to the second ammonia cooler for cooling, and it includes a second generator, a second GAX heat exchanger, a second absorber, a second condenser, a second throttle valve, and a second solution circulation pump. The second generator is equipped with a low-pressure steam inlet, an ammonia steam outlet, a condensate outlet, a lean liquor outlet, and a rich liquor inlet. The low-pressure steam inlet is connected to the steam header of the waste heat boiler. The ammonia vapor inlet of the second condenser is connected to the ammonia vapor outlet of the second generator. The liquid ammonia outlet pipe of the second condenser is connected to the liquid ammonia inlet of the second ammonia cooler through the second throttling valve to reduce pressure. The ammonia inlet of the second absorber is connected to the ammonia outlet of the second ammonia cooler, the lean liquid inlet of the second absorber is connected to the lean liquid outlet of the second GAX heat exchanger, and the rich liquid outlet of the second absorber is connected to the rich liquid inlet of the second GAX heat exchanger via the second solution circulation pump. The rich liquid outlet of the second GAX heat exchanger is connected to the rich liquid inlet of the second generator, and the lean liquid inlet of the second GAX heat exchanger is connected to the lean liquid outlet of the second generator. Both the second absorber and the second condenser are equipped with cooling water circulation interfaces to ensure stable operation of the refrigeration cycle.

[0031] Figure 3This is a comparison chart of the cooling temperatures of the first and second ammonia coolers. For example, in this embodiment of the application, the production process is a synthetic ammonia project with an annual output of 300,000 tons; the pressure of the raw material compressed gas is 15 MPaG, the hydrogen-nitrogen molar ratio is 1:2.7, and the temperature is 25℃; the temperature of the first-stage ammonia synthesis gas is 165℃; the pressure of the by-product low-pressure steam is 0.3 MPaG; the temperature of the second-stage ammonia synthesis gas is 40℃; and the temperature of the third-stage ammonia synthesis gas is 25℃. When the cooling temperature of the first ammonia cooler is -10℃ and the cooling temperature of the second ammonia cooler is -25℃, the ammonia content in the circulating gas is 1.91%, and the ammonia output is 45491 kg / h. Compared with the traditional second ammonia cooler cooling temperature of -10℃, the ammonia content in the circulating gas is reduced by 1.51%, the ammonia output is increased by 3608 kg / h, and the flow rate of the circulating compressor is reduced to 129707 kg / h, thus reducing the load on the circulating compressor.

[0032] The full-condition adaptability and technical effects of this embodiment are as follows: Firstly, the closed-loop logic for improving ammonia net value is as follows: By reducing the outlet temperature of the second ammonia cooler to -10℃ to -25℃ through the second waste heat refrigeration unit, the condensation temperature is significantly reduced, the liquefaction rate of gaseous ammonia in the ammonia synthesis gas is significantly improved, the liquid ammonia recovery rate of the ammonia separator is increased, and the ammonia content in the separated circulating gas is significantly reduced. The lower the ammonia content in the circulating gas, the lower the ammonia content in the inlet gas of the synthesis tower, the stronger the chemical equilibrium driving force of the ammonia synthesis reaction, the significantly improved single-pass conversion rate of the synthesis tower, and ultimately, a significant increase in the net ammonia value of the system is achieved.

[0033] Secondly, dynamic matching of waste heat and cooling capacity: The increased cooling capacity demand brought about by the improvement of ammonia net value corresponds to a synchronous increase in the low-pressure steam consumption of the waste heat chiller unit; while the increase in the load of the synthesis system and the improvement of the ammonia synthesis reaction conversion rate also lead to a synchronous increase in the amount of low-pressure steam produced by the waste heat boiler. Within the entire range of 20% to 110% of the rated load, the amount of low-pressure steam produced by the waste heat boiler completely covers the maximum steam consumption of the two chiller units, and always maintains a surplus of steam, realizing the dynamic coupling of waste heat production and cooling capacity demand; by optimizing the steam pressure of the waste heat boiler, under the premise of meeting the temperature requirements of the heat source driving the chiller unit, matching a lower steam pressure can maximize the recovery of reaction waste heat and improve the overall heat utilization rate.

[0034] Third, quantitative energy saving and production improvement effects: Under rated load conditions, this process can stably control the outlet temperature of the second ammonia cooler at -25℃, reduce the ammonia content in the circulating gas, and improve the net ammonia value of the system compared with the traditional process; the refrigeration system is driven entirely by the waste heat of the synthesis reaction, which reduces the power consumption of the refrigeration link by more than 90% compared with the traditional electric ammonia ice machine process, and improves the energy utilization efficiency of the entire system. Example

[0035] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figure 4 The only difference from Example 1 is the direction of the liquid ammonia separated by the ammonia separator in step 6. All other processes, equipment, and parameters are completely consistent with Example 1. Step 6. The ammonia synthesis material obtained in Step 5 is transported to the ammonia separator to complete the separation of liquid ammonia and non-condensable gas: the separated liquid ammonia is heated by the GVX heat exchanger (the GVX heat exchanger is a refrigerant pre-cooling heat exchanger used to recover the cold energy of the product liquid ammonia) before being used; the separated non-condensable gas is a low-temperature circulating gas, which is first sent to the cold exchange cooling system in Step 4 to complete the cold energy recovery, and then pressurized by the circulating gas compression system, and finally flows back to the raw material compressed gas in Step 1 to enter the ammonia synthesis reaction system for cyclic reaction.

[0036] The ammonia vapor inlet of the first condenser is connected to the ammonia vapor outlet of the first generator. The liquid ammonia outlet pipe of the first condenser is cooled by heat exchange in the second shell side of the GVX heat exchanger, and then throttled and depressurized by the first throttling valve before being connected to the liquid ammonia inlet of the first ammonia cooler.

[0037] The ammonia vapor inlet of the second condenser is connected to the ammonia vapor outlet of the second generator. The liquid ammonia outlet pipe of the second condenser is cooled by heat exchange in the second shell side of the GVX heat exchanger, and then throttled and depressurized by the second throttling valve before being connected to the liquid ammonia inlet of the second ammonia cooler.

[0038] Furthermore, the GVX heat exchanger can be a shell-and-tube heat exchanger, a plate heat exchanger, etc. In this embodiment, the GVX heat exchanger is preferably a shell-and-tube heat exchanger. The tube side inlet is connected to the liquid ammonia outlet of the ammonia separator through a throttling valve. The tube side carries the low-temperature product liquid ammonia separated by the ammonia separator and depressurized by the throttling valve. The shell side is divided into a first shell side and a second shell side, carrying the high-pressure liquid ammonia output from the first waste heat refrigeration unit and the second waste heat refrigeration unit, respectively. The depressurized product liquid ammonia evaporates in the tube side, recovering its own cooling capacity, and precools the high-pressure liquid ammonia of the refrigeration unit in the shell side, further improving the cooling capacity utilization efficiency and reducing the refrigeration load of the ammonia cooler. The precooled product liquid ammonia is transported to the product storage tank, and the precooled refrigeration unit liquid ammonia is sent to the corresponding ammonia cooler for evaporative cooling.

[0039] Based on the technical effects of Embodiment 1, this embodiment achieves efficient recovery of the low-temperature cooling capacity of liquid ammonia through a GVX heat exchanger. This pre-cools the high-pressure liquid ammonia output from the refrigeration unit, reducing the refrigeration load of the ammonia cooler and the steam consumption of the waste heat refrigeration unit, thus further improving the overall system energy utilization efficiency. At the same time, it avoids the ineffective loss of the cooling capacity of the liquid ammonia and realizes the full-process cascade utilization of cooling capacity. Under the same refrigeration depth, the device has lower steam consumption and better operating costs. Example

[0040] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figures 5-6 The difference from Example 2 lies in the structure of steps 2 and 4, with the addition of a lithium bromide refrigeration unit and a supporting precooling system. The remaining processes, equipment, and parameters are completely consistent with Example 2. Step 2. The high-temperature ammonia synthesis gas from the outlet of the ammonia synthesis tower is first fed into the waste heat boiler to recover the waste heat of the reaction before being discharged, resulting in primary ammonia synthesis gas with a temperature of 160-170℃. At the same time, the waste heat boiler uses the recovered reaction heat to produce low-pressure steam with a pressure of 0.3-0.5 MPaG as a byproduct. The low-pressure steam is transported through the steam header to the first waste heat refrigeration unit, the second waste heat refrigeration unit, and the lithium bromide refrigeration unit, respectively, as the driving heat source for the refrigeration system.

[0041] Step 4. The secondary ammonia synthesis gas is cooled by a cold exchange cooling system and discharged to obtain tertiary ammonia synthesis gas at a temperature of 25-32℃. The cold exchange cooling system includes a primary cold exchanger, a pre-chilled water cooler, and a secondary cold exchanger connected in series. The secondary ammonia synthesis gas first enters the primary cold exchanger and undergoes a first heat exchange with the reheated circulating gas from the secondary cold exchanger. The cooled synthesis gas then enters the pre-chilled water cooler and undergoes a second cooling with 5-7℃ chilled water provided by a lithium bromide refrigeration unit. The second-cooled synthesis gas then enters the secondary cold exchanger and undergoes a third deep heat exchange with the low-temperature circulating gas separated from the ammonia separator, finally obtaining tertiary ammonia synthesis gas at a temperature of 25-32℃. The low-temperature circulating gas separated from the ammonia separator at a temperature of -10 to -25℃ flows counter-currently into the secondary cold exchanger and then the primary cold exchanger. After recovering the cold energy with the synthesis gas, the temperature rises to 30-35℃ and is then incorporated into the raw material compressed gas and transported to the ammonia synthesis reaction system.

[0042] The lithium bromide refrigeration unit is a vacuum-type lithium bromide-water absorption refrigeration unit, which is supplied with a pre-cooled chilled water cooler. It includes a third generator, a third solution heat exchanger, a third absorber, a third condenser, a built-in evaporator, a third throttle valve, a third solution circulation pump, and a chilled water pump. The third generator is equipped with a low-pressure steam inlet, a refrigerant steam outlet, a condensate outlet, a concentrated lithium bromide solution outlet, and a dilute lithium bromide solution inlet. The low-pressure steam inlet is connected to the steam header of the waste heat boiler. The refrigerant vapor inlet of the third condenser is connected to the refrigerant vapor outlet of the third generator. The liquid refrigerant water outlet of the third condenser, after being throttled and depressurized by the third throttle valve, enters the unit's built-in evaporator, where it evaporates and cools under vacuum to produce chilled water at 5-7°C. The refrigerant vapor inlet of the third absorber is connected to the refrigerant vapor outlet of the unit's built-in evaporator. The concentrated lithium bromide solution inlet of the third absorber is connected to the concentrated solution outlet of the third solution heat exchanger. The dilute lithium bromide solution outlet of the third absorber is connected to the dilute solution inlet of the third solution heat exchanger via the third solution circulation pump. The dilute solution outlet of the third solution heat exchanger is connected to the dilute lithium bromide solution inlet of the third generator, and the concentrated solution inlet of the third solution heat exchanger is connected to the concentrated lithium bromide solution outlet of the third generator. The unit is equipped with a closed chilled water circulation loop: the chilled water prepared by the evaporator is pumped to the shell side of the pre-chilled water cooler, where it exchanges heat with the ammonia synthesis gas in the tube side and is heated up. Then it returns to the unit's built-in evaporator for circulation and cooling. The chilled water and ammonia synthesis gas are completely isolated throughout the process, and there is no risk of ammonia synthesis catalyst poisoning. Both the third absorber and the third condenser are equipped with cooling water circulation interfaces to ensure stable operation of the unit's vacuum environment and refrigeration cycle.

[0043] Based on the technical effects of Embodiment 2, this embodiment adds the following technical advantages: By combining two-stage heat exchangers with a pre-cooled water cooler, the three-stage recovery of cooling capacity is achieved, further reducing the inlet temperature of the synthesis gas entering the ammonia cooler, thus reducing the refrigeration load of the first ammonia cooler and significantly reducing the steam consumption of the absorption chiller unit. Using lithium bromide refrigeration units to handle the pre-cooling load in the medium temperature range, the COP of lithium bromide refrigeration units can reach over 1, which has a higher heat utilization rate than ammonia absorption refrigeration units, reduces the total steam consumption of the entire system by more than 1%, and further improves the efficiency of waste heat recovery and utilization. Example

[0044] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figure 7 The only difference from Example 3 is the addition of a raw material gas supplementary steam heat exchanger system; all other processes, equipment, and parameters are completely identical to Example 3. Furthermore, in this embodiment, a supplementary steam heat exchanger is connected in series on the pipeline that supplies the compressed raw material gas to the ammonia synthesis tower via the raw material gas heat exchanger. The supplementary steam heat exchanger can be a shell-and-tube heat exchanger, and the specific type can be selected according to actual use. The tube side is connected in series between the raw material gas heat exchanger and the heating unit of the ammonia synthesis reaction system, and the compressed raw material gas flows through the tube side. The shell side inlet is connected to the high-temperature ammonia synthesis gas discharge pipeline of the ammonia synthesis tower, and the ammonia synthesis gas flows through the shell side. The ammonia synthesis gas after heat exchange merges into the pipeline for conveying the primary ammonia synthesis gas, and the temperature is stabilized at 160-170°C after mixing. When the synthesis system is in a high-cooling-capacity operating condition, the steam consumption of the waste heat refrigeration unit increases, the heat load of the waste heat boiler increases, and the temperature of the primary ammonia synthesis gas at the outlet of the waste heat boiler decreases, resulting in a decrease in the heat exchange capacity of the raw material gas heat exchanger. When the preheating temperature of the compressed raw material gas is insufficient, the supplementary steam heat exchanger uses the ammonia synthesis gas to supplement and raise the temperature of the compressed raw material gas, ensuring that the raw material gas reaches the inlet temperature required for the synthesis reaction.

[0045] The technical effect of this embodiment is based on that of embodiment 3. By adding a supplementary heating steam heat exchanger, the inlet temperature of the raw material gas is precisely controlled, avoiding the problem of insufficient synthesis reaction trigger temperature under high refrigeration conditions, ensuring the stability of the synthesis conversion rate in the full load range of the system, and further improving the stability of the ammonia net value. Example

[0046] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figure 8 The only difference from Example 2 is the addition of a raw material gas supplementary steam heat exchanger system; all other processes, equipment, and parameters are completely identical to Example 2. Furthermore, in this embodiment, a supplementary steam heat exchanger is connected in series on the pipeline that supplies the compressed raw material gas to the ammonia synthesis tower via the raw material gas heat exchanger. The supplementary steam heat exchanger can be a shell-and-tube heat exchanger, and the specific type can be selected according to actual use. The tube side is connected in series between the raw material gas heat exchanger and the heating unit of the ammonia synthesis reaction system, and the compressed raw material gas flows through the tube side. The shell side inlet is connected to the high-temperature ammonia synthesis gas discharge pipeline of the ammonia synthesis tower, and the ammonia synthesis gas flows through the shell side. The ammonia synthesis gas after heat exchange merges into the pipeline for conveying the primary ammonia synthesis gas, and the temperature is stabilized at 160-170°C after mixing. When the synthesis system is in a high-cooling-capacity operating condition, the steam consumption of the waste heat refrigeration unit increases, the heat load of the waste heat boiler increases, and the temperature of the primary ammonia synthesis gas at the outlet of the waste heat boiler decreases, resulting in a decrease in the heat exchange capacity of the raw material gas heat exchanger. When the preheating temperature of the compressed raw material gas is insufficient, the supplementary steam heat exchanger uses the ammonia synthesis gas to supplement and raise the temperature of the compressed raw material gas, ensuring that the raw material gas reaches the inlet temperature required for the synthesis reaction.

[0047] The technical advantages of this embodiment, based on Embodiment 2, are achieved by adding a supplementary steam heat exchanger to precisely control the inlet temperature of the raw material gas. This avoids the problem of insufficient synthesis reaction trigger temperature under high refrigeration conditions, ensuring stable synthesis conversion rate across the entire system load range and further improving the stability of ammonia net value. Under all operating conditions, the amount of by-product steam from the waste heat boiler in this embodiment completely covers the maximum steam consumption of both refrigeration units. Example

[0048] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figure 9 The difference from Example 3 is that: The circulating gas compression system in this embodiment includes two circulating compressors. One circulating compressor is connected to the pipeline of raw material compressed gas, and the circulating gas pipeline of the first-stage heat exchanger is connected to the pipeline of the circulating compressor that supplies raw material compressed gas to the raw material gas heat exchanger. The other circulating compressor is connected to the pipeline of the second-stage heat exchanger that supplies circulating gas to the first-stage heat exchanger.

[0049] Because the circulating gas temperature is low, the circulating compressor can more easily compress the low-temperature circulating gas when it is working, which reduces the unit power consumption of the circulating compressor and further reduces the overall energy consumption of the entire system. Example

[0050] This application discloses a production process for increasing the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis. (Refer to...) Figure 10 The difference from Example 3 is that: The circulating gas compression system in this embodiment includes two circulating compressors. One circulating compressor is connected to the pipeline of raw material compressed gas, and the circulating gas pipeline of the first-stage heat exchanger is connected to the pipeline of the circulating compressor that supplies raw material compressed gas to the raw material gas heat exchanger. The other circulating compressor is connected to the pipeline of the ammonia separator that supplies circulating gas to the second-stage heat exchanger.

[0051] Because the circulating gas temperature is low, the circulating compressor can more easily compress the low-temperature circulating gas when it is working, which reduces the unit power consumption of the circulating compressor and further reduces the overall energy consumption of the entire system.

[0052] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A production process for improving the net value of ammonia by utilizing waste heat for refrigeration in ammonia synthesis, characterized in that, Includes the following steps: The cooled ammonia synthesis gas is sequentially cooled in stages by the first ammonia cooler and the second ammonia cooler. The first ammonia cooler cools the gas to 12 to -10°C, and the second ammonia cooler cools it to -10°C to -25°C, so that the gaseous ammonia is liquefied, and a gas-liquid mixed ammonia synthesis material is obtained. The ammonia synthesis material is fed into an ammonia separator to complete gas-liquid separation. The separated liquid ammonia flows to the next stage, and the separated low-temperature circulating gas is recycled for reuse.

2. The production process according to claim 1, characterized in that, The cooled ammonia synthesis gas is obtained through the following steps: Compressed gas containing raw materials with a hydrogen-nitrogen molar ratio of 1:(2.7-3.2) and a pressure of 13-18 MPaG is fed into the ammonia synthesis reaction system to generate a high-temperature ammonia synthesis gas through an exothermic ammonia synthesis reaction. The high-temperature ammonia synthesis gas is fed into a waste heat boiler to recover the waste heat from the reaction, resulting in primary ammonia synthesis gas with a temperature of 160-170°C. At the same time, the waste heat boiler utilizes the recovered waste heat to produce low-pressure steam with a pressure of 0.3-0.5 MPaG as a byproduct. The primary ammonia synthesis gas is cooled step by step through a multi-stage heat exchange system and discharged to obtain secondary ammonia synthesis gas with a temperature of 35-42℃; The secondary ammonia synthesis gas is cooled by a cold exchange cooling system and discharged to obtain tertiary ammonia synthesis gas with a temperature of 25-32°C. The tertiary ammonia synthesis gas is the cooled ammonia synthesis gas.

3. The production process according to claim 2, characterized in that, The system is equipped with a dual-stage independent waste heat refrigeration unit, which includes a first waste heat refrigeration unit and a second waste heat refrigeration unit that operate independently. Both the first and second waste heat refrigeration units use low-pressure steam, a byproduct of the ammonia synthesis reaction, as their driving heat source. The first waste heat refrigeration unit provides cooling energy to the first ammonia cooler, and the second waste heat refrigeration unit provides cooling energy to the second ammonia cooler. The two units can dynamically adjust the low-pressure steam input according to the real-time cooling load of the corresponding ammonia cooler to achieve dynamic matching between cooling supply and demand.

4. The production process according to claim 2, characterized in that, The recycling of the low-temperature circulating gas is specifically as follows: the low-temperature circulating gas separated by the ammonia separator at a temperature of -10 to -25°C is first sent to the cold exchange cooling system to complete the recovery of cold energy, and then pressurized by the circulating gas compression system, mixed with fresh gas to form raw material compressed gas, which is then sent to the ammonia synthesis reaction system for recycling reaction.

5. The production process according to claim 4, characterized in that, A cooling system is provided to recover the cold energy of the low-temperature circulating gas. The cooling system includes a primary cooling exchanger. The tertiary ammonia synthesis gas first enters the primary cooling exchanger and exchanges heat with the low-temperature circulating gas separated by the ammonia separator to cool it down, thus completing the cold energy recovery.

6. The production process according to claim 5, characterized in that, The cold exchange cooling system also includes: A pre-cooled water cooler and a secondary cold exchanger are connected in series with the primary cold exchanger, with the pre-cooled water cooler connected between the primary and secondary cold exchangers. The ammonia synthesis gas cooled by the primary cold exchanger enters the pre-cooled water cooler and then enters the secondary cold exchanger. The low-temperature circulating gas separated by the ammonia separator first enters the secondary cold exchanger and then enters the primary cold exchanger. The secondary ammonia synthesis gas and the low-temperature circulating gas separated by the ammonia separator complete a three-stage heat exchange and cooling process, achieving gradient recovery of cooling capacity. The supporting lithium bromide refrigeration unit uses low-pressure steam, a byproduct of the ammonia synthesis reaction, as the driving heat source to provide chilled water at 5-7°C to the pre-cooled water cooler, and performs secondary pre-cooling on the ammonia synthesis gas after it has been cooled by the primary heat exchanger.

7. The production process according to claim 3, characterized in that, A GVX heat exchanger is provided. The high-pressure liquid ammonia output from the first waste heat refrigeration unit and the second waste heat refrigeration unit is first pre-cooled by the GVX heat exchanger before being sent to the corresponding ammonia cooler for evaporation and refrigeration. The GVX heat exchanger uses the low-temperature product liquid ammonia separated by the ammonia separator after throttling and pressure reduction as the cold source to recover the cold energy of the product liquid ammonia.

8. The production process according to claim 2, characterized in that, The multi-stage heat exchange system includes a boiler feedwater preheater, a feed gas heat exchanger, and a water cooler connected in series: the primary ammonia synthesis gas first enters the boiler feedwater preheater, where it exchanges heat with the boiler feedwater to cool down, and the preheated boiler feedwater is then sent to the waste heat boiler for steam generation; the cooled synthesis gas then enters the feed gas heat exchanger, where it exchanges heat with the compressed feed gas that has passed through the feed gas heat exchanger to cool down, and the preheated compressed feed gas is then sent to the ammonia synthesis reaction system; finally, the synthesis gas passes through the water cooler and is cooled to 35-42°C by circulating water to obtain the secondary ammonia synthesis gas.

9. The production process according to claim 8, characterized in that, The compressed raw material gas discharged from the raw material gas heat exchanger is sent to the conveying pipeline of the ammonia synthesis reaction system, and a supplementary heating steam heat exchanger is installed in series. The supplementary heating steam heat exchanger uses the high-temperature ammonia synthesis gas output from the ammonia synthesis reaction system as a heat source to supplement and raise the temperature of the compressed raw material gas, ensuring that the compressed raw material gas reaches the trigger temperature required for the ammonia synthesis reaction.

10. The production process according to claim 4, characterized in that, A circulating gas compression system is provided, which includes two circulating compressors; One of the circulating compressors is connected to the main pipeline of the raw material compressed gas and is used to supply fresh gas to the ammonia synthesis reaction system; the inlet of the other circulating compressor is connected to the circulating gas outlet of the cold exchange cooling system, and the outlet merges with the main pipeline of the raw material compressed gas to provide circulating power for the circulating gas and overcome the pressure drop of the pipeline and equipment in the synthesis loop.

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