Causes of "nitrogen plug" in crude argon column:
The direct cause of "nitrogen plug" in crude argon tower is that the nitrogen content of argon fraction in the upper tower exceeds the standard. Under normal working conditions, the nitrogen content shall not exceed 0.1%. The argon fraction extraction port of the upper tower is fixed. When the argon rich area of the upper tower changes up and down along the tray, the material composition of the argon fraction extraction port also changes. When the oxygen purity of the upper tower drops too low, the argon rich area of the upper tower moves down seriously, resulting in too high nitrogen content in the argon fraction, which directly causes the "nitrogen plug" accident of the crude argon tower.
Accident handling method:
(1) Gradually open the crude argon vent valve v712 to increase the extraction amount of crude argon, and the flow increases from 700m3 / h to about 1000m3 / h. However, the crude argon purity of crude argon tower II is still declining and the trend is fast. Therefore, the operator immediately closes the regulating valve V705 from crude argon to refined argon tower, stops the work of refined argon tower, and continues to open the valve v712 to vent all crude argon, The nitrogen at the top of the crude argon tower is discharged out of the tower in the shortest way. When the crude argon purity ai705 no longer has a downward trend, but has an upward trend, gradually reduce the extraction amount of crude argon until the flow under normal working conditions is about 500m3 / h to 750m3 / h.
(2) Properly reduce the extraction amount of product oxygen, turn down the liquid nitrogen regulating valve V3 according to the liquid air purity of the lower tower, reasonably control the reflux ratio of the upper and lower towers, control the liquid oxygen level of the main cooling to be stable, and make the product oxygen purity qualified as soon as possible.
(3) Properly reduce the extraction amount of argon fraction from the upper tower, but the operation range should not be too large. Reasonably control the reflux ratio of crude argon I tower to prevent excessive liquid returning to the upper tower at the bottom of crude argon I tower, resulting in further deterioration of the upper tower working condition and low reduction of oxygen purity.
(4) Appropriately reduce the amount of expansion air entering the upper tower, increase the Vapor-Liquid Ratio of the tray above the expansion air inlet, enhance the component separation capacity, increase the argon content in the argon fraction and reduce the nitrogen content.
(5) Open the return gas valve from the pressurized liquid argon storage tank to the refined argon tower, and use liquid nitrogen to enter the condenser valve v706 of the refined argon tower and the residual gas discharge valve v751 of the refined argon tower to control the pressure in the refined argon tower at 20-40kpa, so as to prevent the "blocking" accident of the refined argon tower caused by the backsuction of external wet air into the tower.
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