Vigorously promoting the progress and development of China's gas separation industry, not only can meet the national production demand, but also has great significance to enhance China's comprehensive competitive strength. Since 1978, China's nitrogen production market has been on the rise year by year, and the demand for nitrogen product volume and product purity has been further improved.
At present, the equipment in the common nitrogen market can be fully localized, while the market of ultra-high purity nitrogen equipment is controlled by foreign countries. Domestic air separation manufacturers have not yet entered this field, which is also a new challenge faced by the gas separation industry. At present, pure nitrogen is mainly used in oil field nitrogen injection, petrochemical industry, synthetic fiber, synthetic ammonia, float glass, steel rolling and electronic industry
The scale of nitrogen production device for nitrogen injection in oil field is the largest, and the largest one in foreign countries is 310000 nm / h. The purity of nitrogen product requires oxygen content less than 10ppm, and the product pressure is generally between 300 and 400bar. The production process is allowed to be interrupted for a short time, and a small amount of liquid nitrogen is required. The scale of nitrogen production device for petrochemical industry, synthetic fiber, synthetic ammonia, float glass, steel rolling, etc. is generally from thousands to tens of thousands, The purity of the product is required to contain 2-100ppm oxygen, and the product pressure is generally 1.35-31bar. Some equipment needs to have standby liquid nitrogen, so it is required to ensure uninterrupted product supply.
In the electronic industry, the scale of nitrogen making filtration device is small, generally from hundreds to thousands, but the purity of the product is the highest, usually the oxygen content is less than 1ppm, and the content of CO and H2 in the product is higher. The pressure of the product is between 3 and 10 bar. It is required that the product supply is uninterrupted and there is standby liquid nitrogen.
After decades of vigorous development, the nitrogen industry has stepped up to a higher level in terms of scale and product requirements. For products of different specifications, the nitrogen production process has been developed at home and abroad, and the author summarizes the process organization and selection of nitrogen filtration device in combination with the development at home and abroad
There are two schemes for high-purity nitrogen energy-saving process:
The first scheme: high purity nitrogen return flow full expansion energy-saving process: full expansion is adopted, and the excess cooling capacity is to pump a stream of low-temperature gas after the expander and mix it with waste nitrogen to about - 20 ℃, and then to the aluminum plate fin heat exchanger for heat exchange, eliminating the water chiller.
The second scheme: high purity nitrogen positive flow full expansion energy-saving process: adopt full expansion, which can reduce the air compressor exhaust pressure and save energy, but the diameter of the expander impeller will increase, and the investment will increase accordingly
There are two options for PSA:
The first scheme: crude nitrogen, purity up to 99.99%, refined nitrogen, purity up to 99.999%, single set can achieve about 3000Nm / h, multiple sets can be combined, according to the need to stop or open, do not need liquid products.
The second scheme: crude nitrogen, purity of 99.99%, refined nitrogen, purity of 99.999%, a single set can achieve about 3000Nm / h, can be combined with multiple sets, according to the need to stop or open, need liquid products, adopt supporting external liquefaction filter device, can stop or start freely, the advantage is to save energy consumption, the disadvantage is large investment.
Ultra high purity nitrogen
Ultra high purity nitrogen is mainly used in the electronic industry. In the production process of integrated circuits, chips (chips) and related components, ultra-high purity nitrogen has strict requirements for the following conditions compared with ordinary nitrogen. At present, the general requirements for the total impurity content of integrated circuits are 4ppm and 1ppm or higher for chips. At the same time, when designing high purity nitrogen devices for the electronic industry, attention should be paid to the devices The measurement of the atmospheric composition, and the design must leave a margin. The difficulties and key points are to meet the standards of carbon monoxide, hydrogen and water. Therefore, different methods should be adopted to remove carbon monoxide, hydrogen and water
(1) net removal of CO: with the help of catalyst and the compression heat of compressor, the CO in the product can be reduced to less than 0.1ppm by catalytic reaction.
(2) CO2 removal: adsorption through molecular sieve bed.
(3) net removal of low boiling point components such as hydrogen: hydrogen, helium and neon are components with lower boiling point than nitrogen. In carbon monoxide converter, hydrogen in air generates water, and then the non condensable gas is discharged from the condensing evaporator and vented to remove the low boiling point components. However, the purity is still not enough, and special process organization is still needed, such as adding auxiliary distillation tower of pure nitrogen, in liquid nitrogen A condenser is arranged at the top and a reboiler is arranged at the bottom to increase the circulation ratio to remove impurities such as hydrogen with low boiling point.
(4) net removal of components with high boiling point such as methane: the boiling points of hydrocarbon gases such as methane and rare gases such as krypton and xenon are much higher than that of nitrogen. They will all be concentrated in the oxygen enriched liquid air at the bottom of the tower, and there is no problem in reaching the standard.
(5) water removal: adsorbed by molecular sieve bed, and the water has the highest boiling point, so it is OK to meet the requirements.
(6) particle size: it is satisfied by precision filter.