Regulations on oil content in air separation cryogenic tanks and their sources

Specifications and Sources for Oil Content in Air Separation Cryogenic Boxes

In air separation units, cryogenic boxes serve as core low-temperature equipment, containing numerous low-temperature heat exchangers, distillation columns, and liquid oxygen/liquid nitrogen pipelines. To prevent lubricating oils or hydrocarbon impurities from precipitating, depositing, or even posing explosion risks at low temperatures, the industry imposes strict limits on the oil content of process media entering these boxes, especially process air, instrument air, and seal gas.

Primary Sources of Specifications

• GB/T 13308 —2011 “Technical Conditions for Air Separation Equipment”: It explicitly requires that the total hydrocarbon content in process air before entering the cryogenic box be ≤100×10⁻⁶ (v/v), with non-methane total hydrocarbons needing to be kept at an even lower level. Although it does not directly specify an “oil content” limit, it mandates that compressed air undergo efficient oil removal purification to ensure no visible oil mist or free oil is present.
• JB/T 13795—2020 “Molecular Sieve Adsorbents for Low-Temperature Liquid Storage and Transportation Equipment”and related adsorption purification system standards indirectly require that the oil content in gases entering the cryogenic box meet molecular sieve protection requirements, typically recommending ≤0.01 mg/ m³ (based on mineral oil).
• Corporate design specifications and operating procedures(such as technical agreements from major air separation manufacturers like Hangyang and Chuan Kong): These generally set an upper limit for oil content in air entering the cryogenic box at ≤0.003 mg/ m³ (ISO 8573-1:2010 Class 1 level) and require a three-stage filtration combination (coalescing + adsorption + activated carbon) for purification.

It should be noted that oil content refers not only to liquid lubricating oils but also to light hydrocarbons produced by the cracking of compressor lubricants, oil vapors, and aerosolized oil particles. Continuous monitoring must be carried out using online oil content analyzers such as photoionization detection (PID) or infrared methods during actual operation.