There are different opinions on whether liquid oxygen explosion-proof system should be set in the air separation plant of molecular sieve purification process. This kind of process introduced from Germany and made in China no longer sets explosion-proof system. But the liquid oxygen self-circulation adsorption system is still set in the air separation plant of large molecular sieve purification process introduced from America and France. The reason for setting this system is:
1) from the perspective of liquid oxygen explosion-proof, setting is safer than not setting. Because in the molecular sieve purifier, the molecular sieve can co-adsorb the impurity moisture, carbon dioxide and acetylene in the air. The adsorptive capacity of polar water molecules is relatively large, followed by the adsorption of unsaturated hydrocarbon acetylene, and then carbon dioxide. Although the molecular sieve can absorb and remove the acetylene and some hydrocarbon in the air relatively thoroughly, the molecular sieve does not absorb some hydrocarbon contained in the air, for example: molecular sieve does not adsorb methane at all, but only partially adsorbs ethylene, ethylene and propylene. These unadsorbed hydrocarbon enter into the lower tower of the distillation tower along with the air, dissolve in the liquid air, enter into the upper tower along with the liquid air, flow back with the upper tower, and accumulate in the liquid oxygen at the bottom of the upper tower. Due to the accumulation of these hydrocarbon, it is possible to cause the explosion accident of the oxygen generator, and this kind of accident has also happened. Therefore, in order to ensure the safe operation of the oxygen generator, liquid oxygen cyclic adsorber is also set in the purification process of the molecular sieve, which can remove all kinds of hydrocarbon in the way of liquid adsorption.
2) after accumulating in the liquid oxygen for a long time, the micro acetylene in the liquid oxygen may gradually increase, or even reach the dangerous concentration. With the liquid oxygen self-circulation adsorption system, it can ensure that acetylene will not increase concentration.
3) considering that the molecular sieve adsorption system may also work abnormally. For example, the regeneration is not complete, the air cooling tower with water and other factors will also make dangerous impurities into the liquid oxygen, with the self-circulation adsorption system can be more assured.
Because the air volume that large air separation plant enters into the unit is very large per hour, such as acetylene and carbon dioxide
Because of the uneven adsorption of molecular sieve, it will be brought into the tower more or less. There is no liquid-air adsorber in the process, and it is more reliable to add liquid oxygen self-circulation adsorption system. In addition, after the liquid oxygen self-circulation adsorption system is installed, the heat transfer area of the main condensing evaporator can be reduced accordingly.
