Working principle of a small liquid nitrogen machine

SmallLiquid nitrogen equipmentUsing an adsorbent called carbon molecular sieve, nitrogen and oxygen are selectively adsorbed to separate nitrogen from the air. The separation of nitrogen and oxygen by carbon molecular sieve is mainly based on the different diffusion rates of nitrogen and oxygen molecules on the surface of the molecular sieve. Oxygen molecules with smaller diameters diffuse faster and enter the solid phase of the molecular sieve more. Nitrogen molecules with larger diameters diffuse slower and enter the solid phase of the molecular sieve less, causing nitrogen to be enriched in the gas phase.

After a period of time, the molecular sieve adsorbs a certain amount of oxygen, and the gas adsorbed by the carbon molecular sieve is released under reduced pressure, and the molecular sieve is regenerated. This is based on the different adsorption capacities of the molecular sieve for adsorbed gases under different pressures. Small liquid nitrogen equipment usually uses two parallel adsorbers, alternately performing pressure adsorption and vacuum regeneration, with a cycle of about 2 minutes.

Using air as a raw material and carbon molecular sieve as an adsorbent, small liquid nitrogen equipment uses the pressure swing adsorption principle to utilize the selective adsorption of carbon molecular sieve on oxygen and nitrogen to separate nitrogen from oxygen, generally called PSA nitrogen generation. This method is a new nitrogen generation technology that rapidly developed in the 1970s. Compared with traditional nitrogen generation methods, it has the advantages of simple process flow, high degree of automation, fast gas production (15 ~ 30 minutes), low energy consumption, product purity can be adjusted in a wide range according to user needs, convenient operation and maintenance, low operating costs, and strong adaptability of the equipment. Therefore, it is very competitive in liquid nitrogen equipment below 1000Nm3/h and is becoming increasingly popular among small and medium-sized nitrogen generation users.

Small liquid nitrogen equipment is a traditional nitrogen generation method with a history of several decades. It uses air as a raw material, which is compressed and purified, and then liquefied into liquid air through heat exchange. Liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. Utilizing the different boiling points of liquid oxygen and liquid nitrogen (at 1 atmospheric pressure, the boiling point of liquid oxygen is -183℃, and the boiling point of liquid nitrogen is -196℃), liquid air is rectified and separated to obtain nitrogen. Cold air separation nitrogen generation equipment is complex, occupies a large area, has high infrastructure costs, large one-time investment, high operating costs, slow gas production (12 ~ 24h), high installation requirements, and a long cycle. Considering equipment, installation, and infrastructure factors, the investment scale of PSA equipment with the same specification below 3500Nm3/h is 20% ~ 50% lower than that of cryogenic air separation equipment. Deep cryogenic air separation nitrogen generation equipment is suitable for large-scale industrial nitrogen generation, but it is not economical for small and medium-scale nitrogen generation.