How to Produce High-Purity Nitrogen and Oxygen by Cryogenic Air Separation？
1. Basic Principles of Cryogenic Air Separation
Cryogenic Air Separation (Cryogenic Air Separation) is a process that separates the main components of air by lowering the temperature. Air mainly consists of nitrogen, oxygen, and a small amount of argon. By compressing and cooling the air to extremely low temperatures, it becomes liquefied. Then, using the different boiling points of each gas, distillation is carried out to separate nitrogen and oxygen. The boiling point of nitrogen is -195.8℃, and that of oxygen is -183℃. Therefore, they can be purified separately through staged distillation.
2. Pre-treatment Stage: Air Purification
In the process of cryogenic air separation, the pre-treatment of air is a crucial first step. Air contains impurities such as dust, carbon dioxide, and moisture, which will freeze in the low-temperature environment, causing equipment blockage. Therefore, air is first filtered, compressed, and dried to remove impurities and moisture. Usually, dryers and molecular sieve adsorbers are important equipment for removing impurities in the air to ensure the stability and efficiency of the subsequent cryogenic separation process.
3. Air Compression and Cooling
The purified air needs to be compressed, usually through multi-stage compressors, to a pressure of 5-6 megapascals. The compressed air is then cooled by heat exchange with the returned low-temperature gas, gradually reaching the liquefaction temperature. In this process, heat exchangers play a crucial role, as they can effectively reduce energy consumption and improve cooling efficiency, ensuring that the air can be liquefied under low-temperature conditions, providing conditions for subsequent distillation separation.
4. Air Liquefaction and Distillation
In the cryogenic separation tower, the compressed and cooled air is further cooled to a liquefied state. The liquefied air is sent to the distillation tower for separation. The distillation tower is divided into two parts: the high-pressure tower and the low-pressure tower. In the high-pressure tower, the air is separated into crude oxygen and crude nitrogen, and then in the low-pressure tower, the crude oxygen and crude nitrogen are further distilled to obtain high-purity oxygen and nitrogen. The separation of nitrogen and oxygen mainly utilizes their different physical properties of boiling points, so efficient separation can be achieved in the distillation tower.
5. Purification Process
The oxygen and nitrogen separated in the distillation tower still contain a small amount of impurities, so they need to be further purified to meet industrial and medical standards. The purity of nitrogen can be improved by using hydrogen deoxygenation catalysts, while the purity of oxygen can be achieved by the re-distillation process to the required level. To improve the purity of the product gas, equipment such as nitrogen purifiers and oxygen purifiers are usually used, ultimately obtaining high-purity oxygen and nitrogen products.
6. Applications of Nitrogen and Oxygen
High-purity nitrogen and oxygen produced by cryogenic air separation technology have wide applications in various industries. High-purity nitrogen is used as a protective gas and carrier gas in the chemical industry, for preservation and packaging in the food industry, and is widely used in the medical and welding industries. In the metallurgical industry, oxygen is also used to improve combustion efficiency and reduce carbon emissions. In these applications, the purity of the gas is the key to determining its applicability. Cryogenic air separation technology has gained wide recognition due to its efficient separation and high-purity output.
7. Advantages and Challenges of Cryogenic Air Separation Technology
Cryogenic air separation technology is favored in the industrial sector due to its high purity and high efficiency. However, this technology also faces some challenges, such as high energy consumption and high equipment maintenance costs. To reduce energy consumption, modern cryogenic air separation equipment is usually equipped with advanced energy-saving systems, such as heat recovery devices and multi-stage compression cooling systems. In addition, the application of automation control technology has greatly improved the operation efficiency and safety of cryogenic air separation devices.
Through technological optimization and equipment improvement, the energy efficiency and stability of cryogenic air separation have continuously improved, further promoting its application in various industries. Deep cryogenic air separation is currently one of the most effective methods for producing high-purity nitrogen and oxygen. It effectively separates and purifies oxygen and nitrogen from the air through multiple steps such as pre-treatment, compression, cooling, liquefaction, and distillation. Although the deep cryogenic air separation process has high energy consumption and complex equipment, its efficient separation effect and high-purity product output make this technology indispensable in multiple industries.
