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Why does DEAR air separation units extract dirty liquid nitrogen and dirty gas nitrogen in the fractionating column of a fully low-pressure oxygen generator that manufactures dual-high-purity products?
2022-01-06

The greater the pressure difference of molecular sieve switching, the greater the pressure on the sieve bed, which will be detrimental to the safety of molecular sieve bed. Therefore, we should pay close attention to the molecular sieve heating, cold blowing and other processes. It is disadvantageous to take too long and too short time to equalize and relieve pressure.Due to the increase of air velocity, pressure, backwater volume and spray volume, a large amount of water will be brought into the DEAR air separation tower. When the purifier was switched over, water was carried out due to the impact of air flow due to too fast speed. In order to prevent water carrying accident, careful management and operation of nitrogen water precooler should be strengthened.When the power supply of the DEAR air separation unit in the molecular sieve adsorption purification process is restored after the power failure, the operation should be carried out according to the following steps: the possible impact on the air compressor and other mechanical equipment should be judged in case of sudden power failure. If there is no influence, start the air compressor according to the operating procedures of the air compressor;
The automatic valve is actually a kind of one-way valve, which is installed at the cold end and central extraction of the switching heat exchanger. It is matched with the forced valve. When the positive flow air is used, the air (and intermediate air extraction) automatic valve will open and the sewage nitrogen (or oxygen, nitrogen) automatic valve will close; when the backflow air is used, the sewage nitrogen automatic valve will open and the air automatic valve will close.Generally, the qualified standard for degreasing of inner surface is that the relative increase of oil content in degreasing agent is not more than 20mg / L when cleaning again. The degreasing qualification standard of the exposed surface is: wipe the degreasing surface with white filter paper, and no oil stains can be seen on the paper.If the automatic valve cannot be opened (or not fully opened), the resistance will increase and the material flow between the heat exchange units will be unbalanced. If the middle extraction valve fails to open, the air extraction will be interrupted and the self cleaning condition will be destroyed. If the automatic valve is not closed tightly, the air will run away from the heat exchanger, which will reduce the amount of air into the tower and the output of oxygen and nitrogen. At the same time, due to the increase of backflow, the cold loss of the hot end will increase, and in severe cases, the temperature of the hot end will decrease sharply. In addition, when the automatic valve falls, it is possible that the overpressure accident of the low pressure system will occur.
Nitrogen and a small amount of excess hydrogen are in the top of the tower after several times of partial condensation of the rising steam (the liquefaction temperature of hydrogen is lower than that of nitrogen, so it is impossible to condense), and there is still about 40% argon in it. Part of the rising gas required for distillation comes from the argon evaporated at the bottom of the column. Gas nitrogen from the lower tower is used as heat source for evaporation of liquid argon.If there is too much reflux liquid in the lower tower, not only the purity of liquid air will be too low, but also the flooding of the lower tower may be caused. Therefore, the valve-1 should be opened at this time to improve the purity of liquid air and liquid oxygen. While the liquid level continues to rise, the distillation conditions of upper and lower columns gradually tend to be normal. When accumulating liquid oxygen, it is an important way to speed up the rise of liquid oxygen level to grasp the opening and closing time of several valves and cooperate with each other.