Nitrous oxide (n ɑ o, commonly known as laughing gas) is a hidden safety hazard of air separation unit. Its boiling point is 185K, which is much higher than that of oxygen, nitrogen and argon. Ordinary molecular sieves can only remove about 90%. When CO ɑ penetrates, it will replace the adsorbed n ɑ o into the cold box, and eventually all of it will be enriched in liquid oxygen. Although it is not combustible, it will induce explosion, block equipment, reduce production capacity and pollute products.
1、 Block the heat exchange and rectification channels. N ɑ o condenses into solid particles before air in the main heat exchanger, blocking the plate fin channel, resulting in a sudden drop in heat exchange efficiency and an increase in cold loss. In the main condensing evaporator, when the concentration of liquid oxygen n ɑ o exceeds 50ppm, solid crystals are precipitated, blocking the fin channel, resulting in stagnation of liquid oxygen flow, formation of dry evaporation dead zone, abnormal fluctuations of main cooling temperature difference, liquid level and resistance, and serious instability of working conditions. The krypton xenon extraction system was blocked synchronously, and the production of rare gas was interrupted.
2、 Induce main cold explosion. N ɑ o is a strong combustion promoter. After the channel is blocked, acetylene and total hydrocarbon continue to enrich in the dead zone, far exceeding the safety threshold; The high-speed erosion and friction of solid crystal particles produce static electricity and local hot spots, which become the ignition source. Several accidents have confirmed that when the environmental n ɑ o is high, deflagration may occur even if acetylene meets the standard, which is the most serious safety risk of air separation.
3、 Reduce operation efficiency and product purity. The blockage of heat exchanger and main cooling leads to the reduction of unit load, the increase of power consumption, and the reduction of oxygen extraction rate. In serious cases, the whole line needs to be heated and thawed, and the loss of single shutdown is huge. At the same time, n ɑ o is carried out with oxygen and argon products, which pollutes the gas purity and affects the quality of high-purity gas.
