In 1978, Chinese air separation industry successfully developed and produced the first set of high-purity nitrogen air separation plant. Up to now, the research and development and manufacturing of nitrogen production equipment have achieved leapfrog development in recent decades, and the production technology of high-purity nitrogen equipment has become increasingly mature and has fully realized localization.
The demand areas of nitrogen products mainly include oilfield nitrogen injection, petrochemical industry, synthetic fiber, synthetic ammonia, glass, steel rolling, high-tech materials and electronic industry. Large scale high-purity nitrogen equipment is mainly used in oil field nitrogen injection; large and medium-sized high-purity nitrogen equipment is mainly used in petrochemical, float glass, synthetic fiber, synthetic ammonia, steel rolling and other industries; small-scale nitrogen production equipment is mainly used in electronic industry.
The basic process forms of high purity nitrogen are as follows:
1.The reflux expansion process is suitable for the occasion of high nitrogen product pressure. This process can effectively utilize the exhaust gas with pressure, which can be divided into two processes: full expansion and partial expansion. The liquid volume produced by full expansion is larger than that by partial expansion, but the investment of expander will be increased.
2.The process of positive flow air expander is suitable for the situation where the nitrogen product pressure is low. The flow form is that the expansion air is directly expanded after being pressurized at the booster end of the expander, and then directly vented when the expansion is close to the normal pressure. When the scale of the plantis large, the booster is set separately to pressurize the expansion air to improve the product output.
3.Pressure swing adsorption (PSA) is suitable for low purity nitrogen. Generally, PSA can't produce liquid. If liquid product is needed, it should be equipped with external liquefaction device.
Compared with the above processes, PSA can reduce energy consumption, but the investment is large.
At present, the most widely used process is the reflux expansion process and the positive flow air expansion process. The positive flow expansion process is suitable for users with large liquid consumption. The reflux exhaust gas expansion process has the advantage of low energy consumption and is widely used.