Simply put, air separation processes refer to industrial equipment that separates various components from atmospheric air to produce oxygen, nitrogen, argon and rare gases including helium, neon, krypton, xenon and radon. Industrial gases such as oxygen, nitrogen, argon, neon, helium, hydrogen, carbon dioxide and acetylene are widely utilized across metallurgy, petrochemical, semiconductor, aerospace and other industries. Cryogenic rectification is the most prevalsent air separation technology. It converts air into liquid through compression cycles and deep refrigeration, then gradually separates oxygen, nitrogen, argon and other inert gases from liquefied air based on differing boiling points via low-temperature rectification. This technology is extensively adopted in traditional metallurgy, new coal chemical engineering, large-scale nitrogen fertilizer production and professional industrial gas supply.
Alternative air separation technologies including membrane separation, Pressure Swing Adsorption (PSA) and Vacuum Pressure Swing Adsorption (VPSA) are mainly applied to extract single gas components from air. Cryogenic rectification is mandatory for producing high-purity oxygen, nitrogen and argon for semiconductor manufacturing, and it also serves as the viable source of rare gases neon, krypton and xenon.
With economic growth, domestic air separation units have trended toward larger capacities, requiring supporting on-line gas analyzers. On-line gas analyzers enable direct quality control over air separation production processes, supply critical parameters for production operations, and allow operators to monitor gas composition at each process control point in real time. They act as essential equipment for boosting product output and quality, as well as a vital guarantee for safe operation of air separation units. Air separation processes are divided into nine subsystems：
1. Air Filtration System: Removes dust and solid mechanical impurities.
2. Air Compressor System: Imparts work to air to raise energy levels and enable refrigeration capacity.
3. Air Precooling System: Pre-cools air to cut energy consumption and improve economic efficiency. Single-throttle cycles with pre-cooling outperform those without pre-cooling by adding auxiliary refrigeration cycles, reducing heat exchanger loads and maximizing utilization of cold energy from finished products.
4. Air Purification System: Delivers explosion prevention and gas purification. Air is a multi-component mixture containing water vapor, carbon dioxide, acetylene and trace solid dust alongside oxygen and nitrogen. These impurities cause severe hazards when entering compressors and separation units: solid contaminants abrade compressor moving parts and block coolers to reduce cooling efficiency; water vapor and carbon dioxide freeze during air cooling, clogging equipment and pipelines and halting production; acetylene triggers explosions inside air separation units. Removal of such impurities is therefore essential for safe operation of oxygen generators. This system leverages varying adsorption capacities of solid adsorbents for mixed gas components, with an oxygen-to-nitrogen production ratio of 1:(2.5~3.5). Its core function is to adsorb airborne moisture, carbon dioxide, acetylene, propylene, propane, heavy hydrocarbons, nitrous oxide and other impurities.
5. Air Compression & Expansion System: Consists of refrigeration and heat exchange subsystems. External work is generated during expansion; gas internal potential energy rises post-expansion and consumes energy offset by kinetic energy, inevitably lowering gas temperature. The heat exchange subsystem facilitates energy transfer, enhances economic performance and sustains low-temperature operating conditions.
6. Air Separation System: Composed of main rectification towers for nitrogen-oxygen separation. A proper proportion of expanded air (20%~25% of total intake air) is directly fed into the upper rectification tower for separation. Nitrogen extracted from the top of the lower tower or beneath the condenser-evaporator cover is reheated and sent to a nitrogen turbo expander. After recovering cold energy through the expander, nitrogen is either delivered as finished product or vented.
7. Oxygen Compression Subsystem
8. Nitrogen Compression Subsystem
9. Liquid Storage & Vaporization Subsystem
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