Nitrogen air separation membrane Principle for raw materials to the air, after compression, purification, air heat exchange with a liquefaction of liquid air. Air Liquide is mainly a mixture of liquid oxygen and liquid nitrogen, the use of liquid oxygen and liquid nitrogen different boiling point through distillation, enabling them to obtain nitrogen separation.

1. Typical cryogenic nitrogen plant process

The entire process from air compression and purification, air separation, evaporation of liquid nitrogen.

1.1 compressed air purification and

Air through the air filter dust and mechanical removal of impurities into the air after the compressor, compressed to the required pressure, and then into the cooler air, reducing the temperature of the air. Re-enter the air dry cleaner, to remove moisture in the air, carbon dioxide, acetylene and other hydrocarbons.

1.2 air separation

Purified air into the space in the tower at the main heat exchanger, the regurgitation of gas (nitrogen products, exhaust) cooled to saturation temperature, into the distillation column at the bottom, the top by nitrogen in the tower, cutting expenditure by Air Liquide After the evaporator into the condensate evaporation condensation from the distillation column at the same time sent some of nitrogen, after the condensation liquid nitrogen as part of the return of distillation, another part of a product as a liquid nitrogen air separation column.

Condensation from the evaporator out by the exhaust heat-exchanger to about 130 K-expander expansion refrigeration for the cooling of air separation Dadi, the expansion of gas as part of the regeneration and molecular sieve with cold winds, and then discharged into the Mufflers atmosphere.

1.3 vaporization of liquid nitrogen

From the air separation column by liquid nitrogen into the liquid nitrogen storage tank, when ASU overhaul, the liquid nitrogen storage tank is heated into the carburetor, the product of nitrogen into the pipeline.

Nitrogen cryogenic system can be admitted ≧ 99.999% purity nitrogen.

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2. Major equipment Profile

2.1 air filters

To reduce air compressor internal mechanical movement of the surface wear to ensure that air quality, air compressor in the air before entering, must first be subjected to air filters to remove dust contained therein and other impurities. At present air compressor inlet to use coarse filter or effect of efficiency filters.

Air Compressor 2.2

According to principle, air compressors can be divided into volume-and speed-two categories. At present more than a reciprocating air compressor piston air compressors, centrifugal air compressor and screw-type air compressors.

2.3 air cooler

Is used to lower into the air purifier and air drying tower minutes before the compressed air temperature, inlet temperature to avoid large fluctuations, and precipitation in most of compressed air moisture. Commonly used nitrogen water cooler (from the water cooling towers and air-cooling tower components: a water tower with an empty-tower emissions have circulating water cooling, air cooling tower water tower is used by the circulating water cooling air), air-cooled Freon for.

2.4 drying air purifier

Compressed air cooler air will still contain water, carbon dioxide, acetylene and other hydrocarbons. Been frozen water and carbon dioxide in the air deposition at the tower will be blocked channel, and pipelines and valves, acetylene have accumulated in the liquid oxygen in the risk of explosion, dust will wear operate machinery. In order to ensure the long-term air separation plant safety operation, we must set up special decontamination equipment to remove these impurities. Air purification is the most common method for freezing and adsorption method. Domestic small and medium-sized nitrogen plant is widely used in molecular sieve adsorption method.

2.5 air separation column

Air Separation Column includes a main heat exchanger, liquefaction, distillation, condensate evaporator. The main heat exchanger, condensate and liquefied evaporator plate for the Alice-aluminum heat exchanger is a metal structure septal new modular heat exchanger, the average temperature small, heat exchanger efficiency as high as 98-99%. Distillation equipment for air separation, and Tajikistan, according to the type of equipment within a division, said the board set up sieve sieve column, said the board set blister bubble tower, dumps fill that packed tower. Sieve plate structure simple and easy to manufacture, tray efficiency high, in the air-are widely used in the distillation column. Packed Tower mainly for less than 0.8 m in diameter, height is not more than 7 m of the distillation column. Blister tower because of structural complexity, manufacturing difficulties have been rarely used.

2.6 Turboexpander

Nitrogen plant is used to produce cold rotary blade machinery, is a low-temperature conditions for the gas turbine. Turboexpander by gas in the impeller flow into the axial-flow to the heart and runoff-axial-flow to the heart Drive; by gas in the impeller in the continued expansion and is divided into counter-impulse to counterattack for expansion - not for the continued expansion of impact. ASU widely used in the single-stage axial flow to the heart Drive counter-turbo-expander.

Nitrogen air separation membrane Principle equipment complex area, the high cost of infrastructure, equipment, one-time investment, operating costs, slow gas production, installation requirements and long life cycle. Nitrogen air separation membrane Principle devices suitable for large-scale industrial nitrogen production in the small and medium-scale nitrogen plant it is not economical. In 3500 Nm3 / h following equipment, devices the same size of the investment scale PSA than cryogenic air separation plant by 20% to 50%.