The production of industrial nitrogen is obtained by separating oxygen and nitrogen from air. The main methods are cryogenic method, pressure swing adsorption method and membrane separation method.

1. Cryogenic method

Industrial large-scale nitrogen production usually adopts the traditional cryogenic method. The cryogenic method uses air as the raw material. In the cryogenic air separation unit, the air is cryogenically liquefied and obtained by rectifying and separating using the different boiling points of oxygen and nitrogen.

As a traditional air separation technology, cryogenic method has served mankind for decades, and it is still the main source of nitrogen supply in my country's industry. Because the cryogenic method has been industrialized for a long time, people's understanding of it is relatively mature, and it has advantages that cannot be replaced by other methods, such as large gas production, high purity of product nitrogen, stable operation, and oxygen, argon, etc. can be obtained while extracting nitrogen. other gases, this is also a unique advantage of cryogenics over other methods. Therefore, the cryogenic method still occupies a dominant position in large and medium-sized air separation.

However, its technological process is complex, the requirements for equipment manufacturing, installation and commissioning are high, the one-time investment is large, the infrastructure cost is high, the area is large, and the gas production is slow (12~24 hours). The cryogenic method is suitable for large-scale industries. Nitrogen production is not very economical in small and medium-scale production.

2. Pressure swing adsorption

Pressure Swing Adsorption (PSA) is an important branch of non-low temperature gas separation technology in gas separation technology. Since the late 1960s and early 1970s, it has developed rapidly abroad. Pressure swing adsorption nitrogen production uses air as raw material, carbon molecular sieve as adsorbent, using the principle of pressure swing adsorption, using carbon molecular sieve to selectively adsorb oxygen and nitrogen, and separate oxygen and nitrogen to obtain nitrogen.

Compared with the traditional cryogenic nitrogen production, pressure swing adsorption nitrogen production has remarkable characteristics: adsorption is carried out at room temperature, no thermal insulation problem is involved, the process flow is simple, the equipment is easy to manufacture, the device is small, and the area is small, and ready-made It can be installed in empty space, easy to start and stop, quick to start, fast gas production (15~30 minutes), low energy consumption, low operating cost, low investment, simple operation and maintenance, convenient skid installation, good device adaptability, product gas Purity adjustment, etc., can be performed upon request. From the perspective of technical and economic benefits, pressure swing adsorption is better than cryogenic in nitrogen generators with a capacity of less than 3000Nm3/hr. In the market, nitrogen generators below 1000Nm3/hr are quite competitive, and are welcomed by small and medium-sized users.

3. Membrane separation method

Membrane separation air separation is a high-tech emerging abroad in the 1980s. It belongs to polymer material science. It is one of the top ten high-tech industries in the 21st century. Internationally, there is a saying that "whoever masters membrane technology will master the future of chemical industry". statement. Although the technology started late, it has developed rapidly, and its promotion and application in China is a matter of recent years.

The basic principle of membrane separation is to use air as the raw material, under a certain pressure, to separate oxygen and nitrogen by using different permeation rates of gases with different properties such as oxygen and nitrogen in the hollow fiber membrane. Compared with the above two nitrogen production methods, membrane separation nitrogen production has the advantages of simpler device structure, smaller volume, no switching valve, more convenient operation and maintenance management, faster gas production speed, and convenient expansion and expansion. However, the hollow fiber membrane has higher requirements on the cleaning of compressed air, and the filter element of the membrane is prone to aging and corrosion and fails, which is often difficult to repair, and needs to be replaced with a new membrane. Moreover, at present, hollow fiber membranes need to be imported from abroad, which is expensive.

Membrane separation nitrogen production is more suitable for small and medium-sized nitrogen users who require nitrogen purity ≤98%, and has a functional price ratio. However, when the nitrogen purity is required to be higher than 98%, its price is about 30% higher than that of the pressure swing adsorption device of the same specification.

To sum up, from the comparison of production method, installation, operation, maintenance difficulty, manufacturing and use cost, etc., PSA nitrogen generator has the advantages of small investment, simple use, convenient maintenance and low energy consumption. It is especially advantageous for customers with small and medium nitrogen consumption (less than 3000Nm3/hr).