I. Technical basis of oil content limit
the pipes, valves, heat exchanger and other components through which oxygen flows in the air separation cold box are extremely sensitive to lubricating oil residues. Excessive oil content may lead to the risk of combustion or explosion, so it is necessary to strictly control the oil content in compressed air and liquid oxygen system.
II. Core standards and grade requirements
widely adopted in ChinaGB/T 13277.1 -2018 compressed air Part 1: Pollutant purification level, which corresponds to the international standardISO 8573-1:2010. This standard takes “oil content” (oil mist and oil vapor) as the key index, and according to the mass concentration (mg/ m³) and granular oil (mg/ m³) grading.
- Compressed air used for instrument air source of air separation unit is usually required to reach ISO in 8573-1 Class 1 or Class 2 grade;
- for systems that directly contact liquid oxygen or high pressure oxygen, the oil content limit should be ≤ 0.01 mg/ m³ (I. E. Class 1 level);
- if there is a risk of oil accumulation in the low temperature area of the cold box, comprehensive evaluation should be carried out in combination with material compatibility and condensation precipitation characteristics.
III. Key points of Oxygen safety
the autoignition point of oil substances in oxygen-enriched or pure oxygen environment is significantly reduced, and it is easy to adhere and deposit at low temperature, forming local hot spots. Therefore, oil content control is not only the purification index, but also the basic premise of the intrinsic safety of oxygen system. In the design and operation and maintenance phase, oil content detection and filter selection verification must be carried out according to the above standards.