Large-scale integrated circuit, television tube, laser communication optical fiber, analysis and test and other high-tech fields require the purity of oxygen to reach 99.995%, even 99.99999%. The national standard of high purity oxygen in our country stipulates: the purity of oxygen is not less than 99.999%, among which the content of argon is not more than 2×10-6, and the content of nitrogen is not more than 5×10-6, the content of methane and carbon dioxide is not more than 1×10-6, and the content of water is not more than 2×10-6 (all are volume fraction ).
The usage of high-purity oxygen is not large, and the high-purity oxygen tower attached to large and medium-sized air separation towers is usually used to produce. High purity oxygen can use liquid oxygen as raw material and gas oxygen as raw material.
1) use liquid oxygen as raw material. Liquid oxygen is extracted from the main cooling of the main tower, and its liquid oxygen purity is 99.5% ~ 99.7%, the others are nitrogen, argon, KR, xenon and hydrocarbon. Liquid oxygen is the reflux liquid of high purity oxygen tower. The condensing evaporator at the bottom of the tower uses the medium pressure nitrogen from the top of the main condensing evaporator of the main tower as the heat source. From the low pressure side of the condensing evaporator at the bottom of the tower, high purity oxygen or liquid oxygen can be obtained, its content can reach 99.995%, then enter into the oxygen terminal purifier, use molecular sieve to adsorb and remove carbon monoxide, methane, carbon dioxide and other micro impurities, and obtain more than 99.999% of high purity oxygen products, finally, the membrane compressor is adopted to fill the processed steel cylinder.
2) use gas and oxygen as raw materials. There are two processes: one is to use two additional high-purity oxygen towers. 99.5% of the gas and oxygen extracted from the main cooling of the main tower enters the lower part of the first distillation tower. There is a condenser on the top of the tower, which uses the liquid air from the main tower as the cold source and condenses the rising steam as the recirculation liquid. The gas (without impurities higher than the boiling point of oxygen) from the top of the tower enters the middle of the second distillation column. The second distillation column is equipped with upper and lower condenses. The upper condenser uses the main cooling as the cold source; the lower condenser uses oxygen-enriched vapour as the condensate to remove impurities such as argon and nitrogen which are lower than the boiling point of oxygen through rectification. The top of the tower leads exhaust gas, Tower Bottom get gao chun qi oxygen, finally, the diaphragm compressor compression charger bottle.
The second process is to use pre-purification equipment and a high-purity oxygen tower. Lead from the main cold Tower 99.5% ~ 99.6% of the gas and oxygen enter into the catalytic reactor, and use the normal temperature catalytic method to remove the hydrocarbon compounds. The catalyst is palladium or platinum, and the reaction temperature is 450 ℃; if the catalyst is AG-aluminum, the reaction temperature is 550 ℃. The carbon dioxide and water generated after the reaction are cleaned with 5A Molecular sieve. Then it enters the bottom of the pure oxygen tower after being cooled down by the heat exchanger. Liquid nitrogen is supplied outside the tower top condenser as cold source. In the tower bottom condenser, liquid oxygen containing helium, xenon and hydrocarbon is discharged; impurities such as neon, helium and hydrogen are introduced from the top of the lower condenser; remove nitrogen and argon gas and oxygen from the top of the upper condenser. Lead out high purity oxygen on the tower plate at the bottom of pure oxygen tower.
The comparison between the two methods of producing high purity oxygen from liquid oxygen and gas oxygen shows that the process of producing high purity oxygen from liquid oxygen is simple and feasible. In addition, when using liquid oxygen to produce 99.999% high-purity oxygen, only a single high-purity tower is used, and a terminal purifier needs to be set up.
