Helium recovery apparatus in an ammonia synthesis loop system

Abstract

The application discloses a helium recovery device in an ammonia synthesis loop system, which comprises a membrane separation device; the outlet of permeation gas of the membrane separation device is communicated with a gas inlet pipeline of a synthesis gas compressor; the outlet of non-permeation gas of the membrane separation device is communicated with the inlet of a first plate bundle channel of a plate-fin heat exchanger A, and the outlet of the first plate bundle channel of the plate-fin heat exchanger A is communicated with the inlet of a liquid ammonia separator. Advantages: according to the application, the circulating gas before entering the synthesis gas compressor is cooled by heat exchange, ammonia gas is liquefied and separated out; helium in the circulating gas is separated out through cooling and rectification, a helium product with a purity of 99.99% is produced, meanwhile, the inert gas content in the ammonia synthesis loop is reduced, and the influence on the ammonia synthesis reaction is reduced; in addition, the gas amount of the circulating gas returned to the synthesis gas compressor is reduced through the application, and the energy consumption of the synthesis gas compressor is reduced.

Description

Technical fields:

[0001] This invention relates to the field of ammonia synthesis technology, and in particular to a helium recovery device in an ammonia synthesis loop system. Background technology:

[0002] The ammonia synthesis loop system used for ammonia production includes a syngas compressor, an ammonia synthesis tower, heat exchange and separation equipment, etc. After treatment, hydrogen and nitrogen are used as raw materials. After being compressed by the syngas compressor, they are mixed with circulating gas and sent into the ammonia synthesis tower. Under the action of a catalyst, they react to synthesize ammonia. After the heat of the reaction is recovered, the syngas is cooled by a series of heat exchange equipment and then condensed by the separation equipment to separate ammonia. The separated liquid is the product ammonia, while the separated gas (i.e., circulating gas) recovers its cooling capacity through a cold exchanger. Part of it is sent out of the loop as purge gas, and the other part is sent to the syngas compressor as circulating gas to mix with fresh raw materials.

[0003] The current design composition of the circulating gas entering the synthesis tower is 68.86% hydrogen, 24.49% nitrogen, 2.74% ammonia, 0.06% argon, 3.75% helium, and 0.1% neon, with a gas flow rate of 2.5 t / h. In addition to hydrogen and nitrogen, it contains a relatively large amount of helium, about 4%. As production progresses, some inert gas accumulates in the ammonia synthesis loop and is then vented into the flare system after passing through the synthesis tower.

[0004] In the ammonia synthesis process, helium does not participate in the synthesis reaction and is an inert gas that inhibits the reaction. This not only affects the ammonia synthesis reaction, but the presence of high helium content also increases the amount of circulating gas entering the syngas compressor, thereby increasing the energy consumption of the syngas compressor. Helium has many uses, such as being used as a pressurizing agent and booster for rocket liquid fuel, as a protective gas in smelting and welding, and as an ideal gas for balloons and airships, making it commercially valuable. If helium from the ammonia synthesis loop is directly discharged into the flare system, it will result in a waste of resources. Summary of the Invention:

[0005] The purpose of this invention is to provide a helium recovery device in an ammonia synthesis loop system that is beneficial for reducing the energy consumption of the syngas compressor and effectively recovering helium.

[0006] This invention is implemented by the following technical solution: a helium recovery device in an ammonia synthesis loop system, which includes a membrane separation device, a plate-fin heat exchanger A, a plate-fin heat exchanger B, a plate-fin heat exchanger C, and a negative pressure device;

[0007] The inlet of the second plate bundle channel of the plate-fin heat exchanger C is connected to a liquid nitrogen pipeline, the outlet of the second plate bundle channel of the plate-fin heat exchanger C is connected to the inlet of the third plate bundle channel of the plate-fin heat exchanger B, the outlet of the third plate bundle channel of the plate-fin heat exchanger B is connected to the inlet of the third plate bundle channel of the plate-fin heat exchanger A, and the outlet of the third plate bundle channel of the plate-fin heat exchanger A is connected to the negative pressure device.

[0008] The inlet of the membrane separation device is connected to a circulating gas inlet pipeline, and the outlet of the permeate gas of the membrane separation device is connected to the inlet pipeline of the syngas compressor; the outlet of the non-permeate gas of the membrane separation device is connected to the inlet of the first plate bundle channel of the plate-fin heat exchanger A, the outlet of the first plate bundle channel of the plate-fin heat exchanger A is connected to the inlet of the liquid ammonia separator, the bottom drain port of the liquid ammonia separator is connected to a drain pipeline, the top exhaust port of the liquid ammonia separator is connected to the inlet of the first plate bundle channel of the plate-fin heat exchanger B, and the outlet of the first plate bundle channel of the plate-fin heat exchanger B is connected to the inlet of the liquid nitrogen separator;

[0009] The bottom drain of the liquid nitrogen separator is connected to the inlet of the second plate bundle channel of the plate-fin heat exchanger B, the outlet of the second plate bundle channel of the plate-fin heat exchanger B is connected to the inlet of the second plate bundle channel of the plate-fin heat exchanger A, and the outlet of the second plate bundle channel of the plate-fin heat exchanger A is connected to the inlet pipeline of the synthesis gas compressor.

[0010] The top exhaust port of the liquid nitrogen separator is connected to the inlet of the first plate bundle channel of the plate-fin heat exchanger C. The outlet of the first plate bundle channel of the plate-fin heat exchanger C is connected to the bottom inlet of the helium distillation column through a pressure reducing pipeline. A pressure reducing valve is installed on the pressure reducing pipeline. The top exhaust port of the helium distillation column, the inlet and outlet of the third plate bundle channel of the plate-fin heat exchanger C, the inlet and outlet of the fourth plate bundle channel of the plate-fin heat exchanger B, and the inlet of the fourth plate bundle channel of the plate-fin heat exchanger A are connected in sequence. The outlet of the fourth plate bundle channel of the plate-fin heat exchanger A is connected to the pressure swing adsorption device.

[0011] The bottom outlet of the helium distillation column is connected to the inlet of the reflux pump, and the outlet of the reflux pump is connected to the upper part of the helium distillation column through a reflux pipe, on which a reflux valve is installed.

[0012] Furthermore, a liquid nitrogen buffer tank is provided on the liquid nitrogen pipeline.

[0013] Furthermore, the outlet of the reflux pump is connected to the inlet of the fourth plate bundle channel of the plate-fin heat exchanger C, the outlet of the fourth plate bundle channel of the plate-fin heat exchanger C, the inlet and outlet of the fifth plate bundle channel of the plate-fin heat exchanger B, and the inlet of the fifth plate bundle channel of the plate-fin heat exchanger A are connected in sequence, and the outlet of the fifth plate bundle channel of the plate-fin heat exchanger A is connected to the inlet pipeline of the synthesis gas compressor.

[0014] The advantages of this invention are as follows: By cooling the circulating gas before it enters the syngas compressor through heat exchange, ammonia is liquefied and separated, and nitrogen is liquefied and used as a partial cold source to cool the mixed gas. At the same time, the reheated nitrogen is recovered and reused. Helium is separated from the circulating gas through cooling and distillation to produce a helium product with a purity of 99.99%. This also helps to reduce the content of inert gases in the ammonia synthesis loop and reduce the impact on the ammonia synthesis reaction. In addition, this invention reduces the amount of circulating gas returning to the syngas compressor, which helps to reduce the energy consumption of the syngas compressor. Attached image description:

[0015] Figure 1 This is a flowchart of the process flow of the present invention. Detailed implementation method:

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, this embodiment provides a helium recovery device in an ammonia synthesis loop system, which includes a membrane separation device, a plate-fin heat exchanger A, a plate-fin heat exchanger B, a plate-fin heat exchanger C, and a negative pressure device.

[0018] The inlet of the second plate bundle channel of plate-fin heat exchanger C is connected to a liquid nitrogen pipeline, on which a liquid nitrogen buffer tank is installed. The outlet of the second plate bundle channel of plate-fin heat exchanger C is connected to the inlet of the third plate bundle channel of plate-fin heat exchanger B. The outlet of the third plate bundle channel of plate-fin heat exchanger B is connected to the inlet of the third plate bundle channel of plate-fin heat exchanger A. The outlet of the third plate bundle channel of plate-fin heat exchanger A is connected to a negative pressure device, which can be either a vacuum pump or an induced draft fan. Liquid nitrogen with a pressure of 0.6 MPaG and a temperature of -192℃ from the air separation unit is buffered and stabilized by the liquid nitrogen buffer tank. Under the suction of the negative pressure device, the pressure drops to -70 to -80 kPaG, allowing the liquid nitrogen to flow sequentially through plate-fin heat exchanger C, plate-fin heat exchanger B, and plate-fin heat exchanger A. This serves as the cold source for the helium recovery device. After providing cooling through depressurization flash evaporation, the liquid nitrogen is vented.

[0019] The inlet of the membrane separation unit is connected to a circulating gas inlet pipeline, and the outlet of the permeate gas from the membrane separation unit is connected to the inlet pipeline of the syngas compressor. The outlet of the non-permeate gas from the membrane separation unit is connected to the inlet of the first plate bundle channel of the plate-fin heat exchanger A. Circulating gas drawn from the inlet of the circulating section of the syngas compressor is sent into the membrane separation unit through the circulating gas inlet pipeline. The circulating gas includes hydrogen, nitrogen, ammonia, argon, helium, and neon, with a pressure of 13 MPa and a temperature of 30°C. Most of the hydrogen is separated by the membrane separation unit, and the separated permeate gas contains 80% to 90% hydrogen. This part of the gas enters the inlet pipeline of the syngas compressor and returns to the syngas compressor as feed gas for recycling. The helium content in the non-permeate gas separated by the membrane separation unit is increased from 4% to about 15%, and the non-permeate gas enters the plate-fin heat exchanger A.

[0020] The outlet of the first plate bundle channel of plate-fin heat exchanger A is connected to the inlet of the liquid ammonia separator. The bottom drain port of the liquid ammonia separator is connected to the drain pipe, and the top exhaust port of the liquid ammonia separator is connected to the inlet of the first plate bundle channel of plate-fin heat exchanger B. The circulating gas after heat exchange in plate-fin heat exchanger A is cooled to -70℃ and enters the liquid ammonia separator, where the ammonia gas is cooled into liquid ammonia. The liquid ammonia separated by the liquid ammonia separator is sent to the medium-pressure ammonia separator in the ammonia synthesis loop for recovery, while the separated mixed gas (containing hydrogen, nitrogen, argon, helium, and neon) is sent from the top of the liquid ammonia separator into plate-fin heat exchanger B.

[0021] The outlet of the first plate bundle channel of plate-fin heat exchanger B is connected to the inlet of the liquid nitrogen separator, the bottom drain of the liquid nitrogen separator is connected to the inlet of the second plate bundle channel of plate-fin heat exchanger B, and the top exhaust port of the liquid nitrogen separator is connected to the inlet of the first plate bundle channel of plate-fin heat exchanger C. The mixed gas after heat exchange in plate-fin heat exchanger B is cooled to -180°C and enters the liquid nitrogen separator, while the nitrogen in the mixed gas is cooled into liquid nitrogen. The liquid nitrogen separated by the liquid nitrogen separator is sent into the second plate bundle of plate-fin heat exchanger B, while the separated mixed gas enters the plate-fin heat exchanger C from the top of the liquid nitrogen separator.

[0022] The outlet of the second plate bundle channel of plate-fin heat exchanger B is connected to the inlet of the second plate bundle channel of plate-fin heat exchanger A, and the outlet of the second plate bundle channel of plate-fin heat exchanger A is connected to the inlet pipeline of the syngas compressor. The liquid nitrogen separated by the liquid nitrogen separator is reheated by plate-fin heat exchanger B and plate-fin heat exchanger A in sequence, and then enters the inlet pipeline of the syngas compressor and returns to the syngas compressor as raw material gas for recycling.

[0023] The outlet of the first plate bundle channel of plate-fin heat exchanger C is connected to the bottom inlet of the helium distillation column via a pressure reducing pipeline. A pressure reducing valve is installed on the pressure reducing pipeline. The top exhaust port of the helium distillation column, the inlet and outlet of the third plate bundle channel of plate-fin heat exchanger C, the inlet and outlet of the fourth plate bundle channel of plate-fin heat exchanger B, and the inlet of the fourth plate bundle channel of plate-fin heat exchanger A are connected in sequence. The outlet of the fourth plate bundle channel of plate-fin heat exchanger A is connected to the pressure swing adsorption device. The bottom outlet of the helium distillation column is connected to the inlet of the reflux pump. The outlet of the reflux pump is connected to the upper part of the helium distillation column via a reflux pipe. A reflux valve is installed on the reflux pipe.

[0024] The mixed gas separated by the liquid nitrogen separator is cooled by plate-fin heat exchanger C, and then depressurized to 5.4 MPa by a pressure reducing valve. After the temperature drops to -230℃, it enters the helium distillation column. Inside the helium distillation column, the bottom liquid (liquid nitrogen and liquid hydrogen) is pressurized by a reflux pump, and a portion is returned to the helium distillation column for repeated distillation and purification of helium. After purification, 99.9% pure helium is discharged from the top of the column, and then reheated sequentially by plate-fin heat exchanger C, plate-fin heat exchanger B, and plate-fin heat exchanger A before entering the pressure swing adsorption unit to remove trace amounts of hydrogen and neon, resulting in a pure helium product with a purity of 99.99%.

[0025] The outlet of the reflux pump is connected to the inlet of the fourth plate bundle channel of plate-fin heat exchanger C. The outlet of the fourth plate bundle channel of plate-fin heat exchanger C, the inlet and outlet of the fifth plate bundle channel of plate-fin heat exchanger B, and the inlet of the fifth plate bundle channel of plate-fin heat exchanger A are connected in sequence. The outlet of the fifth plate bundle channel of plate-fin heat exchanger A is connected to the inlet pipeline of the synthesis gas compressor.

[0026] After the bottom liquid of the helium distillation column is pressurized by the reflux pump, another part is reheated in sequence through plate-fin heat exchanger C, plate-fin heat exchanger B, and plate-fin heat exchanger A and vaporized into hydrogen and nitrogen. These gases then enter the inlet pipeline of the syngas compressor and return to the syngas compressor as feed gas for pressurization and recycling.

[0027] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A helium recovery apparatus in an ammonia synthesis loop system, characterized by, It comprises a membrane separation device, a plate-fin heat exchanger A, a plate-fin heat exchanger B, a plate-fin heat exchanger C, and a negative pressure device. The inlet of the second plate bundle passage of the plate-fin heat exchanger C is communicated with a liquid nitrogen pipeline, the outlet of the second plate bundle passage of the plate-fin heat exchanger C is communicated with the inlet of the third plate bundle passage of the plate-fin heat exchanger B, the outlet of the third plate bundle passage of the plate-fin heat exchanger B is communicated with the inlet of the third plate bundle passage of the plate-fin heat exchanger A, and the outlet of the third plate bundle passage of the plate-fin heat exchanger A is communicated with the negative pressure device. The inlet of the membrane separation device is communicated with a circulating gas inlet pipeline, the outlet of the permeated gas of the membrane separation device is communicated with a syngas compressor inlet pipeline, the outlet of the non-permeated gas of the membrane separation device is communicated with the inlet of the first plate bundle passage of the plate-fin heat exchanger A, the outlet of the first plate bundle passage of the plate-fin heat exchanger A is communicated with the inlet of a liquid ammonia separator, the bottom liquid outlet of the liquid ammonia separator is connected with a liquid outlet pipeline, the top gas outlet of the liquid ammonia separator is communicated with the inlet of the first plate bundle passage of the plate-fin heat exchanger B, and the outlet of the first plate bundle passage of the plate-fin heat exchanger B is communicated with the inlet of a liquid nitrogen separator. The bottom liquid outlet of the liquid nitrogen separator is communicated with the inlet of the second plate bundle passage of the plate-fin heat exchanger B, the outlet of the second plate bundle passage of the plate-fin heat exchanger B is communicated with the inlet of the second plate bundle passage of the plate-fin heat exchanger A, and the outlet of the second plate bundle passage of the plate-fin heat exchanger A is communicated with the syngas compressor inlet pipeline. The top gas outlet of the liquid nitrogen separator is communicated with the inlet of the first plate bundle passage of the plate-fin heat exchanger C, the outlet of the first plate bundle passage of the plate-fin heat exchanger C is communicated with the bottom inlet of a helium rectification tower through a pressure reduction pipeline, a pressure reduction valve is installed on the pressure reduction pipeline, the top gas outlet of the helium rectification tower, the inlet and outlet of the third plate bundle passage of the plate-fin heat exchanger C, the inlet and outlet of the fourth plate bundle passage of the plate-fin heat exchanger B, and the inlet of the fourth plate bundle passage of the plate-fin heat exchanger A are sequentially communicated, and the outlet of the fourth plate bundle passage of the plate-fin heat exchanger A is communicated with a pressure swing adsorption device. The bottom outlet of the helium rectification tower is communicated with the inlet of a reflux pump, the outlet of the reflux pump is communicated with the upper part of the helium rectification tower through a reflux pipeline, and a reflux valve is installed on the reflux pipeline.

2. A helium recovery apparatus in an ammonia synthesis loop system according to claim 1, characterized in that, A liquid nitrogen buffer tank is arranged on the liquid nitrogen pipeline.

3. A helium recovery unit in an ammonia synthesis loop system according to claim 1, characterized in that, The outlet of the reflux pump is communicated with the inlet of the fourth plate bundle passage of the plate-fin heat exchanger C, the outlet of the fourth plate bundle passage of the plate-fin heat exchanger C, the inlet and outlet of the fifth plate bundle passage of the plate-fin heat exchanger B, and the inlet of the fifth plate bundle passage of the plate-fin heat exchanger A are sequentially communicated, and the outlet of the fifth plate bundle passage of the plate-fin heat exchanger A is communicated with the syngas compressor inlet pipeline.

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