Analysis of nitrogen production by pressure swing adsorption (PSA)
working principle
The current nitrogen supply methods on the market mainly include liquid nitrogen, bottled nitrogen, and on-site nitrogen production. Integrating three nitrogen supply methods, on-site nitrogen production is currently the most economical, efficient and energy-saving nitrogen supply method. On-site nitrogen production is suitable for users with a gas consumption below 1000 Nm 3 /h. One of the main methods of on-site nitrogen production is the Pressure Swing Adsorption (PSA) nitrogen generator. The principle of PSA nitrogen production is mainly based on the difference in the adsorption rate of oxygen and nitrogen by Carbon Molecular Sieving (CMS). The carbon molecular sieve preferentially adsorbs oxygen, while the nitrogen is mostly enriched in the non-adsorbed phase. CMS is a kind of semi-permanent adsorbent (recyclable) which is specially processed with coal as the main raw material. The black surface is filled with microporous particles. Its separation of oxygen and nitrogen is mainly based on the different diffusion rates of the two gases on the surface of the carbon molecular sieve. The O 2 kinetic diameter is smaller, the gas molecules diffuse faster, and more enter the molecular sieve solid phase (micropores). The N 2 kinetic diameter is larger, the gas molecules diffuse slowly, and the solid phase entering the molecular sieve is less, so that the rich fraction of nitrogen can be obtained in the gas phase. Therefore, using CMS to distinguish the difference in the amount of adsorption between O 2 and N 2 in a certain period of time, according to a specific procedure, combined with a rapid cycle of pressure adsorption and decompression desorption (pressure swing adsorption), the completion of oxygen-nitrogen Separation to obtain high purity N 2 in the gas phase. PSA nitrogen has the characteristics of economy, high efficiency, low operating cost, strong adaptability, easy operation, safety and convenience. Since CMS has a certain adsorption capacity, it needs to be regenerated when the adsorption is saturated. Therefore, the adsorption of the single adsorption tower is intermittent. To ensure continuous gas supply, the double adsorption tower is used in parallel to alternately adsorb, and one tower works and one tower is regenerated continuously. Generate N 2 .
Adsorption Characteristics of CMS for O 2 and N 2
Note: As the adsorption pressure increases, the adsorption amount of O 2 and N 2 increases, but the adsorption increase of O 2 is much higher than that of N 2 .
Process flow
After the air is removed by air filter to remove dust and mechanical impurities, it enters the air compressor and is compressed to the required pressure. After strict degreasing, water removal, dust removal and purification treatment, the clean compressed air is output to ensure the use of molecular sieve in the adsorption tower. life. There are two adsorption towers equipped with carbon molecular sieves. When one tower is working, the other tower is decompressed under reduced pressure. Clean air enters the working adsorption tower. Oxygen, carbon dioxide and water are adsorbed by the molecular sieve, and the gas flowing to the outlet end is N 2 and a small amount of argon and oxygen. Another column (desorption column) causes the adsorbed O 2 , carbon dioxide and water to escape from the molecular sieve micropores to the atmosphere. Thus, the two towers are carried out in turn to complete the separation of nitrogen and oxygen, and continuously output N 2 . The purity of N 2 prepared by PSA adsorption is 95%-99.9%. If higher purity N 2 is required, it is necessary to increase the N 2 purification equipment. 95%-99.9% N 2 output from the pressure swing adsorption nitrogen generator enters the N 2 purification equipment, and a proper amount of hydrogen is added through a flow meter to catalytically react hydrogen and a trace amount of oxygen in the N 2 in the deoxidation tower of the purification equipment. In order to remove oxygen and then be cooled by a water condenser, the steam separator is dehydrated and then dried by a dryer (two adsorption drying towers are used alternately: one adsorption drying water removal, the other heating desorption drainage) to obtain high purity N 2 , the purity of N 2 at this time can reach 99.9995%. At present, the maximum production capacity of PSA nitrogen is 3000 Nm 3 /h.
Application field
The N 2 with a purity greater than 99.5% obtained by the PSA nitrogen production mechanism can be obtained by the combined treatment with the N 2 purification equipment to obtain a high quality N 2 having a purity greater than 99.9995% and a dew point lower than -65 ° C, mainly for annealing protection. , sintering protection, nitriding treatment, washing furnace and purging gas, etc., metal heat treatment, powder metallurgy, magnetic materials, copper processing, wire mesh, galvanizing line, semiconductor, powder reduction and other fields are widely used; purity is greater than 98% Or the required purity of N 2 , mainly used in chemical raw materials, pipeline purging, gas protection, product transportation, etc., mainly used in chemical, biotechnology and other industries; N 2 with purity greater than 98% or purity of 99.9%, main application For food packaging, food preservation, pharmaceutical packaging, pharmaceutical replacement gas, pharmaceutical delivery; N 2 with a purity greater than 99.9% or 99.99%, or a high quality with a purity greater than 99.9995% and a dew point below -65°C through N 2 purification equipment N 2 is mainly used for encapsulation, sintering, annealing, reduction, storage, etc. of electronic products.
Security
Nitrogen is used as an inert gas for isolating oxygen, and it is easy to cause hypoxia and suffocation at high concentrations. When using, the personnel must be in a well-ventilated environment. If a suffocation accident occurs, the injured person should be promptly sent to the place where fresh air is circulated for artificial respiration. The gas in the PSA nitrogen system is pressurized, and the slag impact of the gas should be prevented. It is strictly forbidden to stand at the exhaust port of equipment such as air compressor, nitrogen generator, nitrogen purification device, etc. The link of each equipment must be firm and reliable. The system must perform the corresponding safety test before the system is running. The exhaust gas discharged from the PSA nitrogen generator is concentrated oxygen. In view of the combustion-supporting effect of oxygen, the nitrogen system must be strictly controlled to prevent fire.
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