Cryogenic air separation technology, also known as cryogenic air separation, is one of the key methods used in modern industry to produce high-purity gases on a large scale, especially for the preparation of liquid nitrogen. Due to its extremely low temperature and widespread use, liquid nitrogen plays an irreplaceable role in medicine, chemical industry, food cryopreservation, metal treatment and other fields. This article uses cryogenic air separation technology to produce liquid nitrogen, and explains it to you in combination with relevant data.
Air compression and purification
First, air in the environment is sucked in and pressurized through a series of compressors. In the equipment system, the air pressure can be increased to 5-8 bar, a step mainly to increase the oxygen and nitrogen content per unit volume, preparing for the subsequent separation process. The compressed air contains impurities such as moisture and carbon dioxide, which will condense into solids under low temperature conditions, thereby blocking the equipment. Therefore, moisture and carbon dioxide must be removed through the cooler and adsorbent bed to ensure that the air quality entering the next stage of treatment is pure.
Air cooling and liquefaction
The purified high-pressure air then enters the heat exchanger, where it is pre-cooled to a temperature close to the liquid state. Depending on the specific design, the temperature at this stage usually drops to around -170°C. This portion of the air will then be directed into the expander or throttle valve, further cooled down and partially liquefied by reducing the pressure. During this process, about 30%-40% of the air can be converted into liquid state.
Distillation process in separation tower
The liquefied air is sent into a device called a "low temperature separation tower", where the boiling point difference of different components is used for precise separation. The boiling point of nitrogen is about -196°C, while the boiling point of oxygen is -183°C, which means that under the same conditions, nitrogen becomes more likely to become a gas than oxygen. Through bottom heating and top cooling, nitrogen gradually evaporates from the liquid mixture and is collected in the top area. In contrast, the oxygen-rich part stays at the bottom of the tower and is collected as a by-product.
Purification and storage of liquid nitrogen
The preliminary nitrogen obtained from the top of the separation column also requires an additional purification step to achieve the desired purity standard. Generally speaking, the purity requirement for industrial grade liquid nitrogen is at least 99.99%, while in certain special applications, such as the electronics industry, ultra-high purity of up to 99.999% may be required. After purification, liquid nitrogen will be stored in a specially made insulated container. This type of container can effectively reduce heat transfer and ensure that liquid nitrogen can remain in a low temperature state for a long time without significant volatility.
The cryogenic air separation method is actually a complex but efficient process flow, which involves precision control of multiple links. According to relevant data, a typical cryogenic air separation equipment can produce tens of thousands or even hundreds of thousands of tons of liquid nitrogen products every year, meeting the needs of all walks of life. With the advancement of technology and the improvement of environmental protection requirements, the future cryogenic air separation system is expected to achieve higher energy efficiency ratios and lower operating costs, providing more economical and reliable services to users around the world.
