Cryogenic air separation nitrogen production is a traditional nitrogen production method with a history of several decades. It uses air as raw material, compresses and purifies it, and then uses heat exchange to liquefy the air into liquid air. Liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. Using the different boiling points of liquid oxygen and liquid nitrogen, nitrogen is obtained by separating them through the distillation of liquid air.
Typical process flow
The entire process consists of air compression and purification, air separation, and liquid nitrogen vaporization.
1. Air compression and purification
After the air is cleaned of dust and mechanical impurities by the air filter, it enters the air compressor, is compressed to the required pressure, and then sent to the air cooler to reduce the air temperature. Then it enters the air drying purifier to remove moisture, carbon dioxide, acetylene and other hydrocarbons in the air.
2. Air separation
The purified air enters the main heat exchanger in the air separation tower, is cooled to the saturation temperature by the reflux gas (product nitrogen, waste gas), and is sent to the bottom of the distillation tower. Nitrogen is obtained at the top of the tower, and the liquid air is throttled and sent It enters the condensation evaporator to evaporate, and at the same time, part of the nitrogen sent from the rectification tower is condensed. Part of the condensed liquid nitrogen is used as the reflux liquid of the rectification tower, and the other part is used as liquid nitrogen product and leaves the air separation tower.
The exhaust gas from the condensation evaporator is reheated to about 130K by the main heat exchanger and enters the expander for expansion and refrigeration to provide cooling capacity for the air separation tower. Part of the expanded gas is used for regeneration and cooling of the molecular sieve, and is then discharged through the silencer. atmosphere.
3. Liquid nitrogen vaporization
The liquid nitrogen from the air separation tower is stored in the liquid nitrogen storage tank. When the air separation equipment is inspected, the liquid nitrogen in the storage tank enters the vaporizer and is heated before being sent to the product nitrogen pipeline.
Cryogenic nitrogen production can produce nitrogen with a purity of ≧99.999%.
purity
Cryogenic nitrogen production can produce nitrogen with a purity of ≧99.999%. Nitrogen purity is limited by nitrogen load, number of trays, tray efficiency and oxygen purity in liquid air, etc., and the adjustment range is small.
Therefore, for a set of cryogenic nitrogen production equipment, the product purity is basically certain and is inconvenient to adjust.
Main equipment included in the cryogenic nitrogen generator device
1. Air filtration
In order to reduce the wear of the mechanical moving surface inside the air compressor and ensure the air quality, before the air enters the air compressor, it must first pass through the air filter to remove dust and other impurities contained in it. The air intake of air compressors mostly uses coarse-efficiency filters or medium-efficiency filters.
2. Air compressor
According to the working principle, air compressors can be divided into two categories: volumetric and speed. Air compressors mostly use reciprocating piston air compressors, centrifugal air compressors and screw air compressors.
3. Air cooler
It is used to reduce the temperature of the compressed air before entering the air drying purifier and air separation tower, avoid large fluctuations in the temperature entering the tower, and can precipitate most of the moisture in the compressed air. Nitrogen water coolers (composed of water cooling towers and air cooling towers: the water cooling tower uses the waste gas from the air separation tower to cool the circulating water, and the air cooling tower uses the circulating water from the water cooling tower to cool the air), Freon air cooler .
4. Air dryer and purifier
Compressed air still contains a certain amount of moisture, carbon dioxide, acetylene and other hydrocarbons after passing through the air cooler. Frozen moisture and carbon dioxide deposited in the air separation tower will block the channels, pipes and valves. Acetylene accumulates in the liquid oxygen and there is a risk of explosion. Dust will wear out the operating machinery. In order to ensure the long-term safe operation of the air separation unit, special purification equipment must be set up to remove these impurities. The most common methods of air purification are adsorption and freezing. Molecular sieve adsorption method is widely used in small and medium-sized nitrogen generators in China.
Nitrogen Production Manufacturers - China Nitrogen Production Factory & Suppliers (xinfatools.com)
5. Air separation tower
The air separation tower mainly includes main heat exchanger, liquefier, distillation tower, condensing evaporator, etc. The main heat exchanger, condensing evaporator and liquefier are plate-warped heat exchangers. It is a new type of combined partition heat exchanger with an all-aluminum metal structure. The average temperature difference is very small and the heat exchange efficiency is as high as 98-99%. The distillation tower is an air separation equipment. The types of tower equipment are divided according to the internal parts. A sieve plate tower with a sieve plate is called a sieve plate tower, a bubble cap tower with a bubble cap plate is called a bubble cap tower, and a packed tower with stacked packing is called a sieve plate tower. The sieve plate has a simple structure, is easy to manufacture, and has high plate efficiency, so it is widely used in air fractionation distillation towers. Packed towers are mainly used for distillation towers with a diameter less than 0.8m and a height not greater than 7m. Bubble cap towers are now rarely used due to their complex structure and manufacturing difficulties.
6. Turboexpander
It is a rotating blade machine used by nitrogen generators to generate cold energy. It is a gas turbine used under low temperature conditions. Turboexpanders are divided into axial flow type, centripetal radial flow type and centripetal radial flow type according to the flow direction of the gas in the impeller; according to whether the gas continues to expand in the impeller, it is divided into counterattack type and impact type. Continued expansion is counterattack type. type, it does not continue to expand and becomes impact type. Single-stage radial axial flow impact turbine expanders are widely used in air separation equipment. The cryogenic air separation nitrogen generator has complex equipment, a large area, high infrastructure costs, high one-time investment in equipment, high operating costs, slow gas production (12 to 24 hours), high installation requirements, and a long cycle. Taking into account equipment, installation and infrastructure factors, the investment scale of PSA equipment with the same specifications for equipment below 3500Nm3/h is 20% to 50% lower than that of cryogenic air separation equipment. The cryogenic nitrogen generator device is suitable for large-scale industrial nitrogen production, but medium and small-scale nitrogen production is uneconomical.
Post time: Feb-27-2024
