A waste heat refrigeration method suitable for dynamic synthesis of green ammonia

Abstract

The present invention relates to the technical field of energy conservation and emission reduction, and in particular to a waste heat refrigeration method adapted to the dynamic synthesis of green ammonia, comprising: S1, exchanging heat between raw compressed gas and synthesis gas after ammonia synthesis reaction in a multi-stage cooler system to achieve preheating; S2, subjecting the preheated raw compressed gas to an ammonia synthesis reaction in a synthetic ammonia reaction system to obtain synthesis gas; the synthesis gas is subjected to a waste heat boiler to recover reaction heat and produce low-pressure steam as a by-product; S3, cooling the synthesis gas treated in step S2 in turn through a multi-stage cooler system and a cooling condenser system to liquefy ammonia, and separating liquid ammonia in a product recovery system; the waste heat refrigeration unit utilizes the low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system. The present invention can utilize low-pressure steam waste heat refrigeration technology to complete direct conversion between cold and hot ends, realize coupling between fluctuating steam production and fluctuating cooling demand, and also conform to the concept and production principles of green hydrogen and green ammonia.

Description

Technical Field

[0001] The invention relates to the technical field of energy conservation and emission reduction, and in particular to a waste heat refrigeration method suitable for dynamic synthesis of green ammonia. Background Art

[0002] Ammonia is one of the most widely produced and used bulk chemicals in the world and is widely used in the production of nitric acid, fertilizers, explosives, refrigerants and other fields. Ammonia synthesis is a typical exothermic reaction, which requires continuous removal of reaction heat to maintain the optimal reaction temperature and ensure the activity of the catalyst. The typical ammonia synthesis process includes four continuous processes: compression, preheating and reaction, waste heat recovery, cooling and separation, and other auxiliary facilities. A waste heat boiler is set at the outlet of the ammonia synthesis tower to achieve heat recovery through the by-product steam of the drum.

[0003] At present, renewable energy sources such as wind and light are developing rapidly, and the industrial application of water electrolysis hydrogen production technology is gradually being promoted. However, due to the timeliness of new energy sources such as wind and light, the power grid cannot digest and regulate a large amount of green electricity. Green ammonia synthesis relies on green hydrogen prepared by upstream new energy as raw material. Due to the timeliness of wind and light, the production load of raw green hydrogen is fluctuating. The fluctuation of the production load of raw green hydrogen brings the fluctuation of the production load of green ammonia, and the amount of by-product steam also fluctuates. At the same time, the liquefaction process of synthesis gas requires electric-driven ammonia ice machine to provide cooling capacity, and the cooling capacity required for cooling condensers (such as primary and secondary ammonia refrigeration) is fluctuating.

[0004] Because the amount of steam produced as a byproduct of green ammonia fluctuates, it needs to be consumed autonomously within the plant boundary. Byproduct steam can generally be used for waste heat power generation. The existing method is to use low-grade steam waste heat to generate electricity. According to research, the minimum operating load of waste heat utilization power generation units on the market must be greater than 30% of the rated load. The power generation unit is designed to produce steam at 100% load of the ammonia synthesis unit. When the load of the ammonia synthesis unit drops below 30%, the power generation unit cannot meet the minimum load operation. It is necessary to add steam accumulators to ensure the normal operation of the power generation unit when the new energy power generation is at a low point and the ammonia synthesis unit is less than 30% load. Designing the scale of the steam accumulator according to the power generation situation has greatly increased the project investment and floor space. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a waste heat refrigeration method suitable for dynamic synthesis of green ammonia, which can utilize low-pressure steam waste heat refrigeration technology to complete the direct conversion of the cold and hot ends, realize the coupling between fluctuating steam production and fluctuating cooling demand, and also conform to the concept and production principles of green hydrogen and green ammonia.

[0006] The present invention provides a waste heat refrigeration method adapted to the dynamic synthesis of green ammonia, comprising the following steps:

[0007] S1, exchanging heat between the raw compressed gas and the synthesis gas after the ammonia synthesis reaction in a multi-stage cooler system to achieve preheating;

[0008] S2, subjecting the preheated raw compressed gas to an ammonia synthesis reaction in a synthetic ammonia reaction system to obtain synthesis gas; the synthesis gas is passed through a waste heat boiler to recover reaction heat and produce low-pressure steam as a by-product;

[0009] S3, cooling the synthesis gas after the treatment in step S2 in a multi-stage cooler system and a cooling condenser system in sequence to liquefy the ammonia, and separating the liquid ammonia in a product recovery system;

[0010] The waste heat refrigeration unit utilizes the low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system.

[0011] Preferably, in step S1, the multi-stage cooler system comprises an inlet and outlet heat exchanger, a water cooler and a cold exchanger connected in sequence;

[0012] The raw compressed gas is heat exchanged with the synthesis gas after the ammonia synthesis reaction in the inlet and outlet heat exchangers to achieve preheating; the temperature of the raw compressed gas after preheating is 140-150°C.

[0013] Preferably, in step S2, the synthetic ammonia reaction system includes an ammonia synthesis tower, a molten salt heater, a molten salt heat storage unit and an electric heater;

[0014] The preheated raw compressed gas undergoes an ammonia synthesis reaction in an ammonia synthesis tower;

[0015] The electric heater is used to heat the raw compressed gas entering the ammonia synthesis tower; the temperature of the heated raw compressed gas is 350-500°C.

[0016] Preferably, in step S2, the pressure adjustment range of the low-pressure steam is 0.3-2.5 MPaG; the temperature of the low-pressure steam is 143.6-226°C; the low-pressure steam enters the steam drum connected to the waste heat boiler;

[0017] The synthesis gas is cooled by a boiler feed water heater after the reaction heat is recovered by a waste heat boiler; the temperature of the synthesis gas after cooling is 160-170°C.

[0018] Preferably, cooling the synthesis gas after the treatment in step S2 through a multi-stage cooler system comprises:

[0019] The synthesis gas treated in step S2 is cooled in turn through the inlet and outlet heat exchangers, the water cooler and the cold exchanger; the temperature of the synthesis gas after cooling through the inlet and outlet heat exchangers is 70-80°C; the temperature of the synthesis gas after cooling through the water cooler is 37-43°C; the temperature of the synthesis gas after cooling through the cold exchanger is 28-33°C.

[0020] Preferably, in step S3, the cooling condenser system comprises a first ammonia cooler and a second ammonia cooler connected in sequence; the synthesis gas cooled by the cold exchanger is cooled to 10-14°C by the first ammonia cooler; and cooled to -10--6°C by the second ammonia cooler.

[0021] Preferably, in step S3, the product recovery system includes an ammonia separator for separating liquid ammonia;

[0022] The gas separated by the ammonia separator enters the multi-stage cooler system to recover the cooling capacity;

[0023] The liquid ammonia separated by the ammonia separator is depressurized to 1.4~1.8 MPaG.

[0024] Preferably, in step S3, the product recovery system further comprises a cold recovery heat exchanger connected to the liquid ammonia outlet of the ammonia separator;

[0025] The liquid ammonia separated by the ammonia separator is preheated to 0~3℃ through the cold recovery heat exchanger and sent to the product tank area.

[0026] Preferably, in step S3, the waste heat refrigeration unit is provided with a low-pressure steam inlet; the low-pressure steam provides a heat source required for evaporation of liquid ammonia in the waste heat refrigeration unit;

[0027] The liquid ammonia discharged from the waste heat refrigeration unit recovers cold in the cold recovery heat exchanger, and then is transported to the first ammonia cooler and the second ammonia cooler for heat exchange and then vaporized, and the gaseous ammonia enters the waste heat refrigeration unit for recycling.

[0028] Preferably, in step S3, the waste heat refrigeration unit includes a first waste heat refrigeration unit and a second waste heat refrigeration unit;

[0029] The first waste heat refrigeration unit comprises:

[0030] The first intermediate pressure cylinder;

[0031] The first condenser; the ammonia vapor inlet of the first condenser is connected to the ammonia vapor outlet of the first intermediate pressure cylinder; the liquid ammonia outlet pipeline of the first condenser is connected to the liquid ammonia inlet of the first ammonia cooler through the first shell side of the cold recovery heat exchanger;

[0032] First low-pressure cylinder: the gas ammonia inlet of the first low-pressure cylinder is connected to the gas ammonia outlet of the first ammonia cooler;

[0033] A first lean-rich liquid heat exchanger; the rich liquid inlet of the first lean-rich liquid heat exchanger is connected to the rich liquid outlet of the first low-pressure cylinder, and the rich liquid outlet of the first lean-rich liquid heat exchanger is connected to the rich liquid inlet of the first intermediate-pressure cylinder; the lean liquid inlet of the first lean-rich liquid heat exchanger is connected to the lean liquid outlet of the first intermediate-pressure cylinder, and the lean liquid outlet of the first lean-rich liquid heat exchanger is connected to the lean liquid inlet of the first low-pressure cylinder;

[0034] The second waste heat refrigeration unit comprises:

[0035] A second intermediate pressure cylinder;

[0036] The second condenser; the ammonia vapor inlet of the second condenser is connected to the ammonia vapor outlet of the second intermediate pressure cylinder; the liquid ammonia outlet pipeline of the second condenser is connected to the liquid ammonia inlet of the second ammonia cooler through the second shell side of the cold recovery heat exchanger;

[0037] Second low-pressure cylinder: the gas ammonia inlet of the second low-pressure cylinder is connected to the gas ammonia outlet of the second ammonia cooler;

[0038] The second lean and rich liquid heat exchanger; the rich liquid inlet of the second lean and rich liquid heat exchanger is connected to the rich liquid outlet of the second low-pressure cylinder, and the rich liquid outlet of the second lean and rich liquid heat exchanger is connected to the rich liquid inlet of the second intermediate-pressure cylinder; the lean liquid inlet of the second lean and rich liquid heat exchanger is connected to the lean liquid outlet of the second intermediate-pressure cylinder, and the lean liquid outlet of the second lean and rich liquid heat exchanger is connected to the lean liquid inlet of the second low-pressure cylinder.

[0039] The present invention provides a waste heat refrigeration method adapted to the dynamic synthesis of green ammonia, comprising the following steps: S1, exchanging heat between raw compressed gas and synthesis gas after ammonia synthesis reaction in a multi-stage cooler system to achieve preheating; S2, subjecting the preheated raw compressed gas to an ammonia synthesis reaction in a synthetic ammonia reaction system to obtain synthesis gas; the synthesis gas recovers reaction heat through a waste heat boiler and produces low-pressure steam as a by-product; S3, cooling the synthesis gas treated in step S2 in turn through a multi-stage cooler system and a cooling condenser system to liquefy ammonia, and separating liquid ammonia in a product recovery system; the waste heat refrigeration unit dynamically matches the cooling capacity required by the cooling condenser system using the low-pressure steam. The waste heat refrigeration method adapted to the dynamic synthesis of green ammonia provided by the present invention can utilize low-pressure steam waste heat refrigeration technology to complete the direct conversion of the cold and hot ends, realize the coupling between the fluctuating steam output and the fluctuating cooling demand, and also conform to the concept and production principles of green hydrogen and green ammonia. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A simplified diagram of a waste heat refrigeration process for dynamically synthesizing green ammonia provided by one embodiment of the present invention;

[0041] Figure 2A waste heat refrigeration process flow chart for dynamic synthesis of green ammonia provided for another embodiment of the present invention; wherein 1 is an inlet and outlet heat exchanger, 2 is a molten salt heater, 3 is a molten salt heat storage unit, 4 is an electric heater, 5 is an ammonia synthesis tower, 6 is a waste heat boiler, 7 is a steam drum, 8 is a water cooler, 9 is a cold exchanger, 10 is a first ammonia cooler, 11 is a second ammonia cooler, 12 is an ammonia separator, 13 is a cold recovery heat exchanger, 14 is a waste heat refrigeration unit, 15 is a boiler feed water heater; 16 is a flow control valve, 17 is a start-up control valve, 18 is a hot standby control valve, 19 is a steam pressure regulating valve, 20 is a first ammonia cooling pressure reducing valve, and 21 is a second ammonia cooling pressure reducing valve;

[0042] Figure 3 A system diagram of a first waste heat refrigeration unit provided for one embodiment of the present invention;

[0043] Figure 4 A system diagram of a second waste heat refrigeration unit provided for one embodiment of the present invention;

[0044] Figure 5 This is a relationship diagram between the amount of by-product low-pressure steam used as a heat source and the ammonia synthesis production load in Example 1 of the present invention;

[0045] Figure 6 This is a relationship diagram between the cooling capacity required by the first ammonia cooler of the present invention and the ammonia synthesis production load;

[0046] Figure 7 This is a relationship diagram between the cooling capacity required for refrigeration of the second ammonia cooler of the present invention and the ammonia synthesis production load. DETAILED DESCRIPTION

[0047] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] The present invention provides a waste heat refrigeration method adapted to the dynamic synthesis of green ammonia, comprising the following steps:

[0049] S1, exchanging heat between the raw compressed gas and the synthesis gas after the ammonia synthesis reaction in a multi-stage cooler system to achieve preheating;

[0050] S2, subjecting the preheated raw compressed gas to an ammonia synthesis reaction in a synthetic ammonia reaction system to obtain synthesis gas; the synthesis gas is passed through a waste heat boiler to recover reaction heat and produce low-pressure steam as a by-product;

[0051] S3, cooling the synthesis gas after the treatment in step S2 in a multi-stage cooler system and a cooling condenser system in sequence to liquefy the ammonia, and separating the liquid ammonia in a product recovery system;

[0052] The waste heat refrigeration unit utilizes the low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system.

[0053] Step S1:

[0054] The raw compressed gas is preheated by exchanging heat with the synthesis gas after the ammonia synthesis reaction in a multi-stage cooler system.

[0055] In certain embodiments of the present invention, the pressure of the raw compressed gas is 13~16 MPaG, such as 14.5 MPaG. The raw compressed gas is obtained by compressing the raw gas through a synthesis gas compressor. The intake air of the synthesis gas compressor is mainly divided into two streams, one is fresh raw gas (i.e., gas that has not been used and comes directly from the gas storage tank, with a volume ratio of N2 to H2 of 1:3), the intake pressure is 1.3~1.5 MPaG, and the other is the circulating gas returned from the synthesis loop (i.e., the circulating gas discharged from the cold exchanger 9). The fresh gas compressor and the circulating gas compressor are separately arranged, and the fresh gas compressor pressurizes the fresh raw gas from 1.3~1.5 MPaG to the pressure required for the ammonia synthesis reaction (e.g., 13~14 MPaG, specifically 13.5 MPaG); the circulating gas compressor is used to compress the circulating gas. The present invention has no special restrictions on the type and source of the fresh gas compressor and the circulating gas compressor, and they can be generally commercially available gas compressors.

[0056] In certain embodiments of the present invention, the multi-stage cooler system comprises an inlet and outlet heat exchanger, a water cooler and a cold exchanger connected in sequence. The raw compressed gas is heat exchanged with the synthesis gas after the ammonia synthesis reaction in the inlet and outlet heat exchanger to achieve preheating. The temperature of the raw compressed gas after preheating is 140-150°C, for example, 145°C.

[0057] Step S2:

[0058] The preheated raw compressed gas is subjected to an ammonia synthesis reaction in a synthetic ammonia reaction system to obtain synthesis gas; the synthesis gas is passed through a waste heat boiler to recover reaction heat and produce low-pressure steam as a by-product.

[0059] In certain embodiments of the present invention, the ammonia synthesis reaction system comprises an ammonia synthesis tower, and the preheated raw compressed gas undergoes an ammonia synthesis reaction in the ammonia synthesis tower.

[0060] In certain embodiments of the present invention, the synthetic ammonia reaction system further comprises: a molten salt heater, a molten salt heat storage unit and an electric heater. The molten salt heater is used to quickly supply heat to the ammonia synthesis tower under low load conditions to ensure the heat balance of the catalyst bed in the ammonia synthesis tower. The molten salt heat storage unit is a safe, energy-efficient and fast high-temperature thermal energy device, which uses a low-temperature binary molten salt mixed with potassium nitrate and sodium nitrite. The molten salt has a melting temperature of 152°C, an operating temperature between 390 and 420°C, and a designed maximum heat load of 3500KW to provide heat for the synthetic ammonia reaction system. The electric heater is used to heat the raw compressed gas entering the ammonia synthesis tower. The temperature of the heated raw compressed gas is 350 to 500°C (also the temperature of the ammonia synthesis reaction). The catalyst in the ammonia synthesis tower is an iron-based catalyst, such as Amomax-10 (oxidized catalyst) or Amomax-10H (pre-reduction catalyst).

[0061] The synthesis gas is recycled through the waste heat boiler. Specifically, the synthesis gas is transported to the waste heat boiler to provide waste heat for the waste heat boiler, and the waste heat boiler produces low-pressure steam as a byproduct. The pressure adjustment range of the low-pressure steam is 0.3~2.5 MPaG, such as 1 MPaG; the temperature of the low-pressure steam is 143.6~226℃, such as 159℃. The low-pressure steam enters a steam drum connected to the waste heat boiler.

[0062] In certain embodiments of the present invention, after the reaction heat is recovered by the waste heat boiler, the synthesis gas is cooled by the boiler feed water heater to obtain the cooled synthesis gas, the temperature of which is 160-170°C, for example, 165°C. The boiler feed water is preheated by the boiler feed water heater and then enters the waste heat boiler. The waste heat boiler is also provided with a boiler waste water outlet for discharging boiler waste water.

[0063] Step S3:

[0064] The synthesis gas treated in step S2 is cooled in a multi-stage cooler system and a cooling condenser system in sequence to liquefy ammonia, and the liquid ammonia is separated in a product recovery system;

[0065] The waste heat refrigeration unit utilizes the low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system.

[0066] In certain embodiments of the present invention, cooling the synthesis gas after the treatment in step S2 through a multi-stage cooler system includes: cooling the synthesis gas after the treatment in step S2 through an inlet and outlet heat exchanger, a water cooler, and a cold exchanger in sequence. The temperature of the synthesis gas after cooling through the inlet and outlet heat exchangers is 70-80°C, such as 76°C. The temperature of the synthesis gas after cooling through the water cooler is 37-43°C, such as 40°C. The synthesis gas after cooling through the water cooler exchanges heat with its shell-side cold air in the cold exchanger, and the temperature of the synthesis gas after cooling through the cold exchanger is 28-33°C, such as 31°C.

[0067] In certain embodiments of the present invention, the cooling condenser system includes a first ammonia cooler and a second ammonia cooler connected in sequence. The synthesis gas cooled by the cold exchanger is cooled to 10-14°C, such as 12°C, by the first ammonia cooler; cooled to -10--6°C, such as -8°C, by the second ammonia cooler; ammonia is liquefied, and liquid ammonia is separated in the product recovery system.

[0068] In certain embodiments of the present invention, the product recovery system includes an ammonia separator for separating liquid ammonia. Specifically, the synthesis gas cooled by the second ammonia cooler enters the ammonia separator to separate liquid ammonia.

[0069] The gas separated by the ammonia separator enters the multi-stage cooler system (cold exchanger) to recover the cold in the shell side, and then enters the synthesis gas compressor circulation section (i.e., circulating gas) for the next cycle.

[0070] The liquid ammonia separated by the ammonia separator is depressurized to 1.4~1.8 MPaG, such as 1.6 MPaG. The flash gas (high-temperature and high-pressure gas, when the pressure drops rapidly, the flashed gas is flash gas) is recycled to the low-pressure section of the fresh gas compressor.

[0071] In certain embodiments of the present invention, the product recovery system further comprises a cold recovery heat exchanger connected to the liquid ammonia outlet of the ammonia separator. The liquid ammonia separated by the ammonia separator is preheated to 0-3°C, such as 0°C, by the cold recovery heat exchanger and sent to the product tank area.

[0072] In the present invention, the waste heat refrigeration unit utilizes the low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system.

[0073] The waste heat refrigeration unit is provided with a low-pressure steam inlet connected to the low-pressure steam outlet of the steam drum. The low-pressure steam provides a heat source required for evaporation of liquid ammonia in the waste heat refrigeration unit.

[0074] The liquid ammonia discharged from the waste heat refrigeration unit recovers cold in the cold recovery heat exchanger, and then is transported to the first ammonia cooler and the second ammonia cooler for heat exchange and then vaporized, and the gaseous ammonia enters the waste heat refrigeration unit for recycling.

[0075] like Figure 1 As shown, the present invention also provides a waste heat refrigeration system adapted to the dynamic synthesis of green ammonia for implementing the method described above, comprising:

[0076] A multi-stage cooler system, wherein the multi-stage cooler system is provided with a raw compressed gas inlet, a raw compressed gas outlet, a synthesis gas inlet, a synthesis gas outlet, a circulating gas inlet and a circulating gas outlet;

[0077] A synthetic ammonia reaction system, wherein a raw material compressed gas inlet of the synthetic ammonia reaction system is connected to a raw material compressed gas outlet of the multi-stage cooler system;

[0078] A waste heat boiler connected to the synthesis gas outlet of the synthetic ammonia reaction system; the waste heat boiler is provided with a synthesis gas inlet, a synthesis gas outlet, a low-pressure steam outlet, a boiler feed water inlet and a boiler waste water outlet; the synthesis gas inlet of the multi-stage cooler system is connected to the synthesis gas outlet of the waste heat boiler;

[0079] A cooling condenser system, wherein the cooling condenser system is provided with a synthesis gas inlet, a synthesis gas outlet, a liquid ammonia inlet and a gaseous ammonia outlet; the synthesis gas inlet of the cooling condenser system is connected to the synthesis gas outlet of the multi-stage cooler system;

[0080] A product recovery system, wherein the product recovery system is provided with a synthesis gas inlet, a circulating gas outlet, and a tube-side liquid ammonia outlet; the synthesis gas inlet of the product recovery system is connected to the synthesis gas outlet of the cooling condenser system; the circulating gas outlet of the product recovery system is connected to the circulating gas inlet of the multi-stage cooler system;

[0081] Waste heat refrigeration unit; the waste heat refrigeration unit is provided with a low-pressure steam inlet, a liquid ammonia outlet and a gaseous ammonia inlet; the low-pressure steam inlet of the waste heat refrigeration unit is connected to the low-pressure steam outlet of the waste heat boiler; the liquid ammonia outlet of the waste heat refrigeration unit is connected to the liquid ammonia inlet of the product recovery system; the gaseous ammonia inlet of the waste heat refrigeration unit is connected to the gaseous ammonia outlet of the cooling condenser system.

[0082] In certain embodiments of the present invention, the multi-stage cooler system includes an inlet and outlet heat exchanger 1, a water cooler 8, and a cold exchanger 9 connected in sequence; the inlet and outlet heat exchanger 1 is provided with a raw compressed gas inlet, a raw compressed gas outlet, a synthesis gas inlet, and a synthesis gas outlet. The synthesis gas inlet of the water cooler 8 is connected to the synthesis gas outlet of the inlet and outlet heat exchanger 1. The synthesis gas inlet of the cold exchanger 9 is connected to the synthesis gas outlet of the water cooler 8; the circulating gas inlet of the cold exchanger 9 is connected to the circulating gas outlet of the product recovery system. The inlet and outlet heat exchanger is a generally commercially available heat exchanger, the water cooler is a generally commercially available water cooler, and the cold exchanger is a generally commercially available cold exchanger.

[0083] In certain embodiments of the present invention, the synthetic ammonia reaction system includes an ammonia synthesis tower 5, a molten salt heater 2, a molten salt heat storage unit 3 and an electric heater 4. The present invention has no special restrictions on the arrangement of the ammonia synthesis tower 5, the molten salt heater 2, the molten salt heat storage unit 3 and the electric heater 4. The molten salt heater is used to quickly supply heat to the ammonia synthesis tower 5 under low load conditions; the molten salt heat storage unit 3 provides heat to the ammonia synthesis tower 5; the electric heater 4 is used to heat the raw compressed gas entering the ammonia synthesis tower 5. The molten salt heat storage unit is a safe, energy-efficient and fast high-temperature thermal energy device. It uses a low-temperature binary molten salt mixed with potassium nitrate and sodium nitrite. The molten salt has a melting temperature of 152°C, an operating temperature between 390 and 420°C, and a designed maximum heat load of 3500KW, which provides heat for the synthetic ammonia reaction system. The ammonia synthesis tower is a commonly available ammonia synthesis tower, the molten salt heater is a commonly available molten salt heater, the molten salt heat storage unit is a commonly available molten salt heating skid, and the electric heater is a commonly available electric heater.

[0084] The present invention also includes a waste heat boiler 6 connected to the synthesis gas outlet of the synthetic ammonia reaction system. The waste heat boiler 6 is provided with a synthesis gas inlet, a synthesis gas outlet, a low-pressure steam outlet, a boiler feed water inlet and a boiler waste water outlet; the synthesis gas inlet of the waste heat boiler 6 is connected to the synthesis gas outlet of the ammonia synthesis tower 5; the synthesis gas inlet of the multi-stage cooler system is connected to the synthesis gas outlet of the waste heat boiler 6. The low-pressure steam outlet of the waste heat boiler 6 is connected to the steam drum 7. The waste heat boiler is a generally commercially available waste heat boiler, and the steam drum is a generally commercially available steam drum.

[0085] In certain embodiments of the present invention, the waste heat refrigeration system further comprises a boiler feed water heater 15. The boiler feed water heater 15 is provided with a boiler feed water inlet, a boiler feed water outlet, a syngas inlet, and a syngas outlet. The syngas inlet of the boiler feed water heater 15 is connected to the syngas outlet of the waste heat boiler 6, and the boiler feed water outlet of the boiler feed water heater 15 is connected to the boiler feed water inlet of the waste heat boiler 6; the syngas outlet of the boiler feed water heater 15 is connected to the syngas inlet of the inlet and outlet heat exchanger 1. The boiler feed water heater is a generally commercially available boiler feed water heater.

[0086] In certain embodiments of the present invention, the cooling condenser system comprises a first ammonia cooler 10 and a second ammonia cooler 11 connected in sequence. The syngas inlet of the first ammonia cooler 10 is connected to the syngas outlet of the cold exchanger 9, and the syngas inlet of the second ammonia cooler 11 is connected to the syngas outlet of the first ammonia cooler 10. The first ammonia cooler and the second ammonia cooler are generally commercially available ammonia coolers.

[0087] In certain embodiments of the present invention, the product recovery system includes: an ammonia separator 12, and a cold recovery heat exchanger 13 connected to the liquid ammonia outlet of the ammonia separator 12. The synthesis gas inlet of the ammonia separator 12 is connected to the synthesis gas outlet of the second ammonia cooler 11; the tube-side liquid ammonia inlet of the cold recovery heat exchanger 13 is connected to the liquid ammonia outlet of the ammonia separator 12. The gas outlet of the ammonia separator 12 is connected to the circulating gas inlet of the cold exchanger 9. The cold exchanger 9 is also provided with a circulating gas outlet. The ammonia separator is a generally commercially available ammonia separator, and the cold recovery heat exchanger is a generally commercially available cold recovery heat exchanger.

[0088] The liquid ammonia product discharged from the liquid ammonia outlet of the tube side of the cold recovery heat exchanger 13 is sent to the product tank area.

[0089] The waste heat refrigeration unit is a waste heat refrigeration unit generally available on the market.

[0090] In some embodiments of the present invention, the number of the waste heat refrigeration units 14 matches the cooling capacity demand of the cooling condenser system. In some specific implementations, two waste heat refrigeration units 14 are provided, including a first waste heat refrigeration unit and a second waste heat refrigeration unit.

[0091] Regarding the first waste heat refrigeration unit, including:

[0092] A first intermediate-pressure cylinder, wherein the first intermediate-pressure cylinder is provided with a low-pressure steam inlet, an ammonia steam outlet, a condensate outlet, a lean liquid outlet, and a rich liquid inlet;

[0093] A first condenser, wherein the first condenser is provided with an ammonia vapor inlet and a liquid ammonia outlet; the ammonia vapor inlet of the first condenser is connected to the ammonia vapor outlet of the first intermediate-pressure cylinder; the liquid ammonia outlet pipeline of the first condenser is connected to the liquid ammonia inlet of the first ammonia cooler through the first shell side of the cold recovery heat exchanger;

[0094] A first low-pressure cylinder, wherein the first low-pressure cylinder is provided with a gas ammonia inlet, a lean liquid inlet, and a rich liquid outlet; the gas ammonia inlet of the first low-pressure cylinder is connected to the gas ammonia outlet of the first ammonia cooler;

[0095] The first rich-lean liquid heat exchanger (first GAX), the first rich-lean liquid heat exchanger is provided with a rich liquid inlet, a rich liquid outlet, a lean liquid inlet and a lean liquid outlet; the rich liquid inlet of the first rich-lean liquid heat exchanger is connected to the rich liquid outlet of the first low-pressure cylinder, and the rich liquid outlet of the first rich-lean liquid heat exchanger is connected to the rich liquid inlet of the first medium-pressure cylinder; the lean liquid inlet of the first rich-lean liquid heat exchanger is connected to the lean liquid outlet of the first medium-pressure cylinder, and the lean liquid outlet of the first rich-lean liquid heat exchanger is connected to the lean liquid inlet of the first low-pressure cylinder.

[0096] Figure 3A system diagram of a first waste heat refrigeration unit provided for an embodiment of the present invention. The structure of the second waste heat refrigeration unit is the same as that of the first waste heat refrigeration unit, except that the direction of the pipeline is different. Specifically, the second waste heat refrigeration unit includes:

[0097] A second intermediate-pressure cylinder, wherein the second intermediate-pressure cylinder is provided with a low-pressure steam inlet, an ammonia steam outlet, a condensate outlet, a lean liquid outlet, and a rich liquid inlet;

[0098] A second condenser, wherein the second condenser is provided with an ammonia vapor inlet and a liquid ammonia outlet; the ammonia vapor inlet of the second condenser is connected to the ammonia vapor outlet of the second intermediate-pressure cylinder; the liquid ammonia outlet pipeline of the second condenser is connected to the liquid ammonia inlet of the second ammonia cooler through the second shell side of the cold recovery heat exchanger;

[0099] A second low-pressure cylinder, wherein the second low-pressure cylinder is provided with a gas ammonia inlet, a lean liquid inlet, and a rich liquid outlet; the gas ammonia inlet of the second low-pressure cylinder is connected to the gas ammonia outlet of the second ammonia cooler;

[0100] The second rich-lean liquid heat exchanger (second GAX), the second rich-lean liquid heat exchanger is provided with a rich liquid inlet, a rich liquid outlet, a lean liquid inlet and a lean liquid outlet; the rich liquid inlet of the second rich-lean liquid heat exchanger is connected to the rich liquid outlet of the second low-pressure cylinder, and the rich liquid outlet of the second rich-lean liquid heat exchanger is connected to the rich liquid inlet of the second medium-pressure cylinder; the lean liquid inlet of the second rich-lean liquid heat exchanger is connected to the lean liquid outlet of the second medium-pressure cylinder, and the lean liquid outlet of the second rich-lean liquid heat exchanger is connected to the lean liquid inlet of the second low-pressure cylinder.

[0101] In some embodiments of the present invention, two outlets are provided on the pipeline of the low-pressure steam outlet of the drum 7, the first outlet is connected to the low-pressure steam inlet of the first intermediate-pressure cylinder, and the second outlet is connected to the low-pressure steam inlet of the second intermediate-pressure cylinder. The distribution of the low-pressure steam is determined according to the cooling load required by the first ammonia cooler 10 and the second ammonia cooler 11.

[0102] In the present invention, low-pressure steam enters the medium-pressure cylinder to heat the TC multi-component working fluid in the medium-pressure cylinder (the commercially available medium-pressure cylinders are all equipped with TC multi-component working fluids for heat transfer, and the present invention has no special restrictions on the components of the TC multi-component working fluids), so that most of the low-boiling-point ammonia in the solution evaporates, and the gaseous ammonia vapor enters the condenser and is cooled by circulating cooling water into saturated liquid ammonia.

[0103] The gas ammonia outlet of the first ammonia cooler 10 is connected to the gas ammonia inlet of the first low-pressure cylinder of the waste heat refrigeration unit, and the gas ammonia outlet of the second ammonia cooler 11 is connected to the gas ammonia inlet of the second low-pressure cylinder of the waste heat refrigeration unit.

[0104] Saturated liquid ammonia is sent out of the waste heat refrigeration boundary, decompressed by the pressure reducing valve, becomes low-temperature liquid ammonia and enters the cold recovery heat exchanger 13. After heat exchange and cooling, it enters the first ammonia cooler 10 and the second ammonia cooler 11. The low-temperature liquid ammonia absorbs heat in the first ammonia cooler 10 and the second ammonia cooler 11 and evaporates into low-temperature gas ammonia, which is sent to the waste heat refrigeration boundary and enters the low-pressure cylinder. The lean liquid in the low-pressure cylinder absorbs gas ammonia, and the concentration increases to form a rich solution. After part of the ammonia evaporates in the medium-pressure cylinder, the remaining lean liquid enters the lean-rich liquid heat exchanger (GAX) to exchange heat with the rich solution in the low-pressure cylinder, and then throttles and reduces the pressure to enter the low-pressure cylinder, absorbs the evaporated low-temperature gas ammonia and restores the solution to its original concentration. The lean solution absorbs liquid ammonia, and the concentration increases to form a rich solution. After the solution pump boosts the pressure, it enters the lean-rich liquid heat exchanger to exchange heat with the lean solution, and then is sent to the medium-pressure cylinder to continue circulating.

[0105] In certain embodiments of the present invention, a first solution pump is provided on the pipeline between the first low-pressure cylinder and the first lean-rich liquid heat exchanger for conveying the rich liquid in the first low-pressure cylinder to the first lean-rich liquid heat exchanger.

[0106] In certain embodiments of the present invention, a second solution pump is provided on the pipeline between the second low-pressure cylinder and the second lean-rich liquid heat exchanger for conveying the rich liquid in the second low-pressure cylinder to the second lean-rich liquid heat exchanger.

[0107] In some embodiments of the present invention, the condensate discharged from the condensate outlet of the first intermediate-pressure cylinder and the condensate discharged from the condensate outlet of the second intermediate-pressure cylinder can be cooled and then sent to a desalted water station as replenishment water.

[0108] In order to further illustrate the present invention, a waste heat refrigeration method adapted to dynamic synthesis of green ammonia provided by the present invention is described in detail below in conjunction with embodiments, but it should not be construed as limiting the scope of protection of the present invention.

[0109] Example 1

[0110] Use Figure 2 The waste heat refrigeration system shown includes:

[0111] Multi-stage cooler system;

[0112] The multi-stage cooler system includes an inlet and outlet heat exchanger 1, a water cooler 8 and a cold exchanger 9 which are connected in sequence; the synthesis gas inlet of the water cooler 8 is connected to the synthesis gas outlet of the inlet and outlet heat exchanger 1; the synthesis gas inlet of the cold exchanger 9 is connected to the synthesis gas outlet of the water cooler 8; the circulating gas inlet of the cold exchanger 9 is connected to the circulating gas outlet of the product recovery system.

[0113] Ammonia synthesis reaction system;

[0114] The synthetic ammonia reaction system includes an ammonia synthesis tower 5, a molten salt heater 2, a molten salt heat storage unit 3 (i.e., a molten salt heating skid) and an electric heater 4; the molten salt heater is used to quickly provide heat to the ammonia synthesis tower 5 under low load conditions; the electric heater 4 is used to heat the raw compressed gas entering the ammonia synthesis tower 5; the molten salt heat storage unit 3 provides heat for the ammonia synthesis tower 5.

[0115] Waste heat boiler 6;

[0116] The synthesis gas inlet of the waste heat boiler 6 is connected to the synthesis gas outlet of the ammonia synthesis tower 5 ; the low-pressure steam outlet of the waste heat boiler 6 is connected to the steam drum 7 .

[0117] Boiler feed water heater 15;

[0118] The synthesis gas inlet of the boiler feed water heater 15 is connected to the synthesis gas outlet of the waste heat boiler 6, and the boiler feed water outlet of the boiler feed water heater 15 is connected to the boiler feed water inlet of the waste heat boiler 6; the synthesis gas outlet of the boiler feed water heater 15 is connected to the synthesis gas inlet of the inlet and outlet heat exchanger 1.

[0119] Cooling condenser system;

[0120] The cooling condenser system includes a first ammonia cooler 10 and a second ammonia cooler 11 which are connected in sequence; the synthesis gas inlet of the first ammonia cooler 10 is connected to the synthesis gas outlet of the cold exchanger 9, and the synthesis gas inlet of the second ammonia cooler 11 is connected to the synthesis gas outlet of the first ammonia cooler 10.

[0121] Product recovery system;

[0122] The product recovery system includes: an ammonia separator 12, and a cold recovery heat exchanger 13 connected to the liquid ammonia outlet of the ammonia separator 12; the synthesis gas inlet of the ammonia separator 12 is connected to the synthesis gas outlet of the second ammonia cooler 11; the tube-side liquid ammonia inlet of the cold recovery heat exchanger 13 is connected to the liquid ammonia outlet of the ammonia separator 12; the gas outlet of the ammonia separator 12 is connected to the circulating gas inlet of the cold exchanger 9.

[0123] The liquid ammonia discharged from the tube-side product liquid ammonia outlet of the cold recovery heat exchanger 13 is sent to the product tank area.

[0124] Two waste heat refrigeration units 14 are provided, including a first waste heat refrigeration unit and a second waste heat refrigeration unit.

[0125] Regarding the first waste heat refrigeration unit (such as Figure 3 shown), including:

[0126] A first intermediate-pressure cylinder, wherein the first intermediate-pressure cylinder is provided with a low-pressure steam inlet, an ammonia steam outlet, a condensate outlet, a lean liquid outlet, and a rich liquid inlet;

[0127] A first condenser, wherein the first condenser is provided with an ammonia vapor inlet and a liquid ammonia outlet; the ammonia vapor inlet of the first condenser is connected to the ammonia vapor outlet of the first intermediate-pressure cylinder; the liquid ammonia outlet pipeline of the first condenser is connected to the liquid ammonia inlet of the first ammonia cooler through the first shell side of the cold recovery heat exchanger;

[0128] A first low-pressure cylinder, wherein the first low-pressure cylinder is provided with a gas ammonia inlet, a lean liquid inlet, and a rich liquid outlet; the gas ammonia inlet of the first low-pressure cylinder is connected to the gas ammonia outlet of the first ammonia cooler 10;

[0129] The first rich-lean liquid heat exchanger (first GAX), the first rich-lean liquid heat exchanger is provided with a rich liquid inlet, a rich liquid outlet, a lean liquid inlet and a lean liquid outlet; the rich liquid inlet of the first rich-lean liquid heat exchanger is connected to the rich liquid outlet of the first low-pressure cylinder, and the rich liquid outlet of the first rich-lean liquid heat exchanger is connected to the rich liquid inlet of the first medium-pressure cylinder; the lean liquid inlet of the first rich-lean liquid heat exchanger is connected to the lean liquid outlet of the first medium-pressure cylinder, and the lean liquid outlet of the first rich-lean liquid heat exchanger is connected to the lean liquid inlet of the first low-pressure cylinder.

[0130] The second waste heat refrigeration unit (such as Figure 4 shown) include:

[0131] A second intermediate-pressure cylinder, wherein the second intermediate-pressure cylinder is provided with a low-pressure steam inlet, an ammonia steam outlet, a condensate outlet, a lean liquid outlet, and a rich liquid inlet;

[0132] A second condenser, wherein the second condenser is provided with an ammonia vapor inlet and a liquid ammonia outlet; the ammonia vapor inlet of the second condenser is connected to the ammonia vapor outlet of the second intermediate-pressure cylinder; the liquid ammonia outlet pipeline of the second condenser is connected to the liquid ammonia inlet of the second ammonia cooler through the second shell side of the cold recovery heat exchanger;

[0133] A second low-pressure cylinder, wherein the second low-pressure cylinder is provided with a gas ammonia inlet, a lean liquid inlet, and a rich liquid outlet; the liquid ammonia inlet of the second low-pressure cylinder is connected to the gas ammonia outlet of the second ammonia cooler 11;

[0134] The second rich-lean liquid heat exchanger (second GAX), the second rich-lean liquid heat exchanger is provided with a rich liquid inlet, a rich liquid outlet, a lean liquid inlet and a lean liquid outlet; the rich liquid inlet of the second rich-lean liquid heat exchanger is connected to the rich liquid outlet of the second low-pressure cylinder, and the rich liquid outlet of the second rich-lean liquid heat exchanger is connected to the rich liquid inlet of the second medium-pressure cylinder; the lean liquid inlet of the second rich-lean liquid heat exchanger is connected to the lean liquid outlet of the second medium-pressure cylinder, and the lean liquid outlet of the second rich-lean liquid heat exchanger is connected to the lean liquid inlet of the second low-pressure cylinder.

[0135] A first solution pump is arranged on the pipeline between the first low-pressure cylinder and the first lean-rich liquid heat exchanger for conveying the rich liquid in the first low-pressure cylinder to the first lean-rich liquid heat exchanger.

[0136] A second solution pump is arranged on the pipeline between the second low-pressure cylinder and the second lean-rich liquid heat exchanger, for conveying the rich liquid in the second low-pressure cylinder to the second lean-rich liquid heat exchanger.

[0137] Two paths are arranged on the pipeline of the low-pressure steam outlet of the drum 7, the first path is connected to the low-pressure steam inlet of the first intermediate-pressure cylinder, and the second path is connected to the low-pressure steam inlet of the second intermediate-pressure cylinder. The distribution of the low-pressure steam is determined according to the cooling load required by the first ammonia cooler 10 and the second ammonia cooler 11.

[0138] The gas ammonia outlet of the first ammonia cooler 10 is connected to the gas ammonia inlet of the first low-pressure cylinder of the waste heat refrigeration unit, and the gas ammonia outlet of the second ammonia cooler 11 is connected to the gas ammonia inlet of the second low-pressure cylinder of the waste heat refrigeration unit.

[0139] Use Figure 2 The waste heat refrigeration system shown is adapted to the waste heat refrigeration method of dynamically synthesizing green ammonia:

[0140] 1. The raw gas is pressurized to 14.5 MPaG by a compressor to obtain raw compressed gas, which is preheated to 145°C by an inlet and outlet heat exchanger 1 and enters an ammonia synthesis tower 5 for an ammonia synthesis reaction to obtain synthesis gas;

[0141] 2. subjecting the preheated raw compressed gas to an ammonia synthesis reaction in an ammonia synthesis tower to obtain synthesis gas; the catalyst in the ammonia synthesis tower is an iron-based catalyst Amomax-10;

[0142] The synthesis gas is transported to the waste heat boiler to provide waste heat for the waste heat boiler, and the waste heat boiler produces low-pressure steam as a by-product; the pressure of the low-pressure steam is adjusted to 1 MPaG; the temperature of the low-pressure steam is 159°C; the low-pressure steam enters a steam drum connected to the waste heat boiler;

[0143] The synthesis gas is cooled by a boiler feed water heater after the reaction heat is recovered by the waste heat boiler to obtain a cooled synthesis gas with a temperature of 165°C; the boiler feed water is preheated by the boiler feed water heater and then enters the waste heat boiler;

[0144] 3. Cool the synthesis gas after step 2 through a multi-stage cooler system:

[0145] The synthesis gas treated in step 2 is cooled in turn through the inlet and outlet heat exchangers, the water cooler and the cold exchanger; the temperature of the synthesis gas after cooling through the inlet and outlet heat exchangers is 76°C; the temperature of the synthesis gas after cooling through the water cooler is 40°C; the synthesis gas after cooling through the water cooler is heat exchanged with its shell side cold air in the cold exchanger, and the temperature of the synthesis gas after cooling through the cold exchanger is 31°C;

[0146] Then cool down through the cooling condenser system:

[0147] The synthesis gas cooled by the cold exchanger is cooled to 12°C by the first ammonia cooler and then cooled to -8°C (tube outlet temperature) by the second ammonia cooler to liquefy the ammonia.

[0148] The synthesis gas cooled by the second ammonia cooler enters the ammonia separator to separate the liquid ammonia;

[0149] The gas separated by the ammonia separator enters the shell side of the cold exchanger to recover the cold, and then enters the circulation section of the synthesis gas compressor (i.e., circulating gas) for the next cycle;

[0150] The liquid ammonia separated by the ammonia separator is depressurized to 1.6 MPaG, preheated to 0°C by the cold recovery heat exchanger, and sent to the product tank area; the flash gas (high-temperature and high-pressure gas, when the pressure drops rapidly, the gas flashed out is flash gas) is sent to the low-pressure section of the fresh gas compressor for reuse;

[0151] The liquid ammonia discharged from the waste heat refrigeration unit recovers cold in the cold recovery heat exchanger, and then is transported to the first ammonia cooler and the second ammonia cooler for heat exchange and then vaporized. The gaseous ammonia enters the waste heat refrigeration unit for recycling.

[0152] Taking 100% production load as an example, the first ammonia cooler (ammonia cooler) requires 4331.5 kW of cooling capacity and 7.3℃ of cooling temperature, and the second ammonia cooler (ammonia cooler) requires 3317.8 kW of cooling capacity and -13℃ of cooling temperature (shell side operating temperature); at this time, the maximum steam production of process byproducts is 28.38 t / h, and the average is 16.5 t / h. After using waste heat refrigeration, the first ammonia cooler (ammonia cooler) requires 4331.5 kW of cooling capacity and 9.2 t / h of waste heat, and the second ammonia cooler (ammonia cooler) requires 3317.8 kW of cooling capacity and 11.9 t / h of waste heat; there is still 7.28 t / h of excess steam for the maximum steam surplus. Considering the operation safety of the unit, it can be used for the cooling output of ammonia cooler in summer or for heating in winter.

[0153] The specific parameters are shown in Table 1.

[0154] Table 1 Specific parameters involved in 100% production load

[0155]

[0156] The relationship between the amount of by-product low-pressure steam as a heat source and the ammonia synthesis production load is close to linear, as shown in the following example: Figure 5 shown. Figure 5 This is a graph showing the relationship between the amount of by-product low-pressure steam used as a heat source and the ammonia synthesis production load in Example 1 of the present invention. Figure 5 It can be seen that the by-product steam output is basically linearly related to the production load.

[0157] The specific relationship between the cooling capacity required by the first ammonia cooler and the ammonia synthesis production load is as follows: Figure 6 shown. Figure 6 The relationship between the cooling capacity required for refrigeration of the first ammonia cooler and the ammonia synthesis production load of the present invention is shown in FIG. The relationship between the cooling capacity required for refrigeration of the second ammonia cooler and the ammonia synthesis production load is shown in FIG. Figure 7 shown. Figure 7 This is a graph showing the relationship between the cooling capacity required by the second ammonia cooler of the present invention and the ammonia synthesis production load. Figure 6 and Figure 7 It can be seen that ammonia refrigeration also basically shows a linear relationship under low load, but as the production load further increases, the growth rate of required cooling capacity decreases and the curve tends to be flat.

[0158] Under different loads, the required amount and surplus amount of by-product low-pressure steam of the waste heat refrigeration unit are shown in Table 2.

[0159] Table 2 Steam relationship under different production loads

[0160]

[0161] Note: The above takes into account 10% cooling loss.

[0162] From Table 2, we can see that, taking 100% working condition as an example, the total amount of by-product steam is 28.38t / h, the first ammonia cooler requires a cooling capacity of 4331.5 kW, corresponding to the required steam consumption of 9.2t / h; the second ammonia cooler requires a cooling capacity of 3318 kW, corresponding to the required steam consumption of 11.9t / h; there is still 7.28t / h left for winter heating or use in the deaeration tank of the whole plant process.

[0163] Although by-product steam and cooling demand fluctuate according to production load, waste heat refrigeration technology can achieve cooling and heat coupling under different operating conditions, and there is still surplus steam to support the safe operation of the unit.

[0164] The load fluctuation of the synthetic green ammonia unit is relatively strong, and there are conditions of long-term continuous low-load operation. The waste heat refrigeration unit uses the by-product low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system, and uses the waste heat refrigeration unit to replace the ammonia ice machine. The annual electricity consumption of the waste heat refrigeration unit is: (53+57.4)×8000×0.4=353,300 yuan, and the operating cost is relatively low.

[0165] Green ammonia coupled waste heat power generation technology in existing technology: When synthetic ammonia is produced at full load, the by-product steam volume is 23.26t / h, so this steam volume needs to be used as the design basis for the rated load of the saturated steam generator set; when the synthetic ammonia production load is 20% in summer, the by-product steam volume is 4.65t / h. At present, the minimum operating load requirement of the saturated steam generator set must be greater than 30% of the rated load, and the steam volume generated by the minimum load of the whole plant is 4.65t / h≤7t / h (23.26t / h×30%), which cannot guarantee that the saturated steam generator set can operate under the lowest operating conditions. Therefore, it is necessary to add accumulators as auxiliary facilities to help the saturated steam generator set to operate normally under the lowest load conditions. In extreme cases, the steam generator set will not be able to continue to operate normally, and the steam will be forced to vent. If the accumulator is added (taking the shortest 18 hours as an example, an additional 7 100 m 3 Accumulator), which will greatly increase investment and floor space.

[0166] Compared with the existing green ammonia coupled waste heat power generation technology, the waste heat refrigeration technology adopted in the present invention has the following advantages:

[0167] 1. Strong dynamic matching:

[0168] Combined with the new energy output curve, energy storage and hydrogen storage tank configuration, the green ammonia synthesis unit often operates at a production load of 20% for thousands of hours throughout the year, including dozens of hours of continuous extreme low-load conditions. A single waste heat generator set cannot maintain normal operation, and additional steam accumulators are required to meet the normal operation of the unit at a long-term production load of 20%.

[0169] Through waste heat refrigeration technology, by-product steam can be effectively utilized, dynamically matching the cooling capacity required for ammonia synthesis, completing the direct conversion between the cold and hot ends, and achieving the goal of adapting to fluctuations with fluctuations.

[0170] 2. Low operating cost:

[0171] The above green ammonia coupled waste heat power generation technology is used to generate electricity: when the synthetic ammonia unit operating load is more than 30%, the waste heat power generation unit can operate continuously, and the annual power generation is: 10506000KW; the annual power consumption of the two ammonia ice machine units is: (1400+1100)×8000=20000000KW; the annual electricity fee is: (20000000-10506000)×0.4 yuan / KW=3.7976 million yuan;

[0172] The system and method provided by the present invention are used for refrigeration: at this time, the waste heat refrigeration unit replaces the ammonia ice machine, and the annual electricity consumption of the waste heat refrigeration unit is: (53+57.4)×8000×0.4=353,300 yuan.

[0173] The annual electricity saving is 379.76-35.33=344.43 million yuan.

[0174] In summary, the fluctuation of upstream raw material input leads to changes in production load, and the reaction heat generated is different. The waste heat after the reaction can produce 0.3~2.5 MPaG saturated steam. The saturated steam output is basically linearly distributed with the production load. Although the total cooling demand is not linearly distributed with the production load, the growth rate of cooling demand decreases with the increase of production load. The by-product steam can fully meet the demand for waste heat refrigeration, and there is still a certain margin, which is enough to maintain the overall safe operation.

[0175] The present invention utilizes waste heat refrigeration technology to achieve coupling between the fluctuating by-product steam output and the fluctuating cooling demand of the green ammonia project, and completes the direct conversion between the cold and hot ends, which is in line with the concept and production principles of green hydrogen and green ammonia.

[0176] The description of the above embodiments is only used to help understand the method of the present invention and its core idea. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest range consistent with the principles and novel features disclosed herein.

Claims

1. A waste heat refrigeration method adapted to the dynamic synthesis of green ammonia, comprising the following steps: S1, exchanging heat between the raw compressed gas and the synthesis gas after the ammonia synthesis reaction in a multi-stage cooler system to achieve preheating; S2, subjecting the preheated raw compressed gas to an ammonia synthesis reaction in a synthetic ammonia reaction system to obtain synthesis gas; the synthesis gas is passed through a waste heat boiler to recover reaction heat and produce low-pressure steam as a by-product; S3, cooling the synthesis gas after the treatment in step S2 in a multi-stage cooler system and a cooling condenser system in sequence to liquefy the ammonia, and separating the liquid ammonia in a product recovery system; The product recovery system includes an ammonia separator and a cold recovery heat exchanger connected to the liquid ammonia outlet of the ammonia separator; The waste heat refrigeration unit utilizes the low-pressure steam to dynamically match the cooling capacity required by the cooling condenser system; The waste heat refrigeration unit comprises a first waste heat refrigeration unit and a second waste heat refrigeration unit; The first waste heat refrigeration unit comprises: The first intermediate pressure cylinder; The first condenser; the ammonia vapor inlet of the first condenser is connected to the ammonia vapor outlet of the first intermediate pressure cylinder; the liquid ammonia outlet pipeline of the first condenser is connected to the liquid ammonia inlet of the first ammonia cooler through the first shell side of the cold recovery heat exchanger; First low-pressure cylinder: the gas ammonia inlet of the first low-pressure cylinder is connected to the gas ammonia outlet of the first ammonia cooler; A first lean-rich liquid heat exchanger; the rich liquid inlet of the first lean-rich liquid heat exchanger is connected to the rich liquid outlet of the first low-pressure cylinder, and the rich liquid outlet of the first lean-rich liquid heat exchanger is connected to the rich liquid inlet of the first intermediate-pressure cylinder; the lean liquid inlet of the first lean-rich liquid heat exchanger is connected to the lean liquid outlet of the first intermediate-pressure cylinder, and the lean liquid outlet of the first lean-rich liquid heat exchanger is connected to the lean liquid inlet of the first low-pressure cylinder; The second waste heat refrigeration unit comprises: A second intermediate pressure cylinder; The second condenser; the ammonia vapor inlet of the second condenser is connected to the ammonia vapor outlet of the second intermediate pressure cylinder; the liquid ammonia outlet pipeline of the second condenser is connected to the liquid ammonia inlet of the second ammonia cooler through the second shell side of the cold recovery heat exchanger; Second low-pressure cylinder: the gas ammonia inlet of the second low-pressure cylinder is connected to the gas ammonia outlet of the second ammonia cooler; The second lean and rich liquid heat exchanger; the rich liquid inlet of the second lean and rich liquid heat exchanger is connected to the rich liquid outlet of the second low-pressure cylinder, and the rich liquid outlet of the second lean and rich liquid heat exchanger is connected to the rich liquid inlet of the second intermediate-pressure cylinder; the lean liquid inlet of the second lean and rich liquid heat exchanger is connected to the lean liquid outlet of the second intermediate-pressure cylinder, and the lean liquid outlet of the second lean and rich liquid heat exchanger is connected to the lean liquid inlet of the second low-pressure cylinder.

2. The waste heat cooling method according to claim 1, characterized in that: In step S1, the multi-stage cooler system includes an inlet and outlet heat exchanger, a water cooler and a cold exchanger connected in sequence; The raw compressed gas is heat exchanged with the synthesis gas after the ammonia synthesis reaction in the inlet and outlet heat exchangers to achieve preheating; the temperature of the raw compressed gas after preheating is 140-150°C.

3. The waste heat cooling method according to claim 1, characterized in that: In step S2, the synthetic ammonia reaction system includes an ammonia synthesis tower, a molten salt heater, a molten salt heat storage unit and an electric heater; The preheated raw compressed gas undergoes an ammonia synthesis reaction in an ammonia synthesis tower; The electric heater is used to heat the raw compressed gas entering the ammonia synthesis tower; the temperature of the heated raw compressed gas is 350-500°C.

4. The waste heat cooling method according to claim 1, characterized in that: In step S2, the pressure adjustment range of the low-pressure steam is 0.3~2.5 MPaG; the temperature of the low-pressure steam is 143.6~226°C; the low-pressure steam enters the steam drum connected to the waste heat boiler; The synthesis gas is cooled by a boiler feed water heater after the reaction heat is recovered by a waste heat boiler; the temperature of the synthesis gas after cooling is 160-170°C.

5. The waste heat cooling method according to claim 1, characterized in that: Cooling the synthesis gas after the treatment in step S2 through a multi-stage cooler system comprises: The synthesis gas treated in step S2 is cooled in turn through the inlet and outlet heat exchangers, the water cooler and the cold exchanger; the temperature of the synthesis gas after cooling through the inlet and outlet heat exchangers is 70-80°C; the temperature of the synthesis gas after cooling through the water cooler is 37-43°C; the temperature of the synthesis gas after cooling through the cold exchanger is 28-33°C.

6. The waste heat cooling method according to claim 1, characterized in that: In step S3, the cooling condenser system includes a first ammonia cooler and a second ammonia cooler connected in sequence; the synthesis gas cooled by the cold exchanger is cooled to 10-14°C by the first ammonia cooler; and cooled to -10--6°C by the second ammonia cooler.

7. The waste heat cooling method according to claim 6, characterized in that: In step S3, the gas separated by the ammonia separator enters the multi-stage cooler system to recover cold energy; The liquid ammonia separated by the ammonia separator is depressurized to 1.4~1.8 MPaG.

8. The waste heat cooling method according to claim 7, characterized in that: In step S3, the liquid ammonia separated by the ammonia separator is preheated to 0-3°C by a cold recovery heat exchanger and sent to the product tank area.

9. The waste heat cooling method according to claim 8, characterized in that: In step S3, low-pressure steam provides the heat source required for evaporation of liquid ammonia in the waste heat refrigeration unit; The liquid ammonia discharged from the waste heat refrigeration unit recovers cold in the cold recovery heat exchanger, and then is transported to the first ammonia cooler and the second ammonia cooler for heat exchange and then vaporized, and the gaseous ammonia enters the waste heat refrigeration unit for recycling.

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