The nitrogen purity is insufficient

Is a nitrogen content of 95.6% also required for the upper tower? Theoretical analysis: It is normal for the pure nitrogen at the top of the tower to have a higher purity compared to that at the bottom of the tower. The most straightforward approach is to increase the amount of liquid nitrogen sent to the top of the tower, while ensuring that the purity of the nitrogen at the bottom of the tower remains unchanged.

The purity of liquid nitrogen is low; adjust it, adjust it thoroughly. . The distillation section has no impact on oxygen purity.

Reply to 1# liuiiiii: It was working fine before; did it start having problems recently? What is the oxygen content on the side draw, and what is the pressure difference at the top of the tower?

Calibrate the gauge to check whether your level gauge, differential pressure gauge, and flow meter are accurate. .

Good purity of liquid nitrogen, with the purity of the product nitrogen being the same as that of the nitrogen coming from the tower, indicates a problem related to operating conditions and parameter accuracy. If there is a difference between the product nitrogen and the nitrogen from the tower, it suggests there is an issue with the heat exchanger or subcooler

This post was last edited by you*n*nyou on 2011-8-24 at 20:20. The purity of nitrogen is not sufficient: http://bbs.hcbbs.com/thread-891638-1-2.html. Reposted: “Forum moderator, the personnel who carried out the on-site debugging last time did not provide me with the specific details. After working hard yesterday, I have recorded and organized all the information related to that debugging process. I hope to receive feedback; I welcome suggestions regarding analysis and solutions!” Since XX Steel Plant reported that the purity of our nitrogen did not meet the standards and could not satisfy Party A’s requirement to use pure nitrogen instead of argon for smelting, we used the zirconia analyzer for oxygen from XX Phase I on the morning of the 18th to adjust the purity of the nitrogen once again. We used an analyzer to measure the purity of the contaminated nitrogen gas at tower A7, which was 3.05% oxygen; thereafter, we gradually opened the contaminated nitrogen valve PVC110 to 100% ； At 11:18, the temperature at the hot end of the plate-type nitrogen treatment unit was 10.7°C (the temperature of the air entering the plate-type unit was 17.0°C), and the pressure at the outlet of the nitrogen treatment unit dropped to 7.80 KPa ； At the same time, to reduce the amount of pure nitrogen removed, the pure nitrogen valve PVC108 was gradually closed to 29.7% (with the hot-side temperature at 14.8°C). Subsequently, following the adjustment principle of lowering the tower first and then raising it, at 12:20 the nitrogen purity A3 at the top of the lower tower was measured to be 0.58–0.48% oxygen (at that time, the V2 valve was open at 43%, and the purity of the liquid air determined by manual analysis was 35.5%) ； Subsequently, the V2 valve was slowly closed to gradually increase the purity of nitrogen A3 at the top of the lower column. By 16:50, the purity of A3 reached 139–163 PPm (with the V2 valve at 42.2% open and V11 fully open). Subsequently, the instrumentation operator (XXX) connected the analyzer to A8 (the analysis point before the subcooler, where pure nitrogen exits the tower). At 17:17, the analyzer showed that the purity of A8 was 0.29–0.28% oxygen (the readings were quite volatile as soon as it was connected to the analysis system). At that time, the flow rate of pure nitrogen from the air separation unit was 8,782 cubic meters per hour, with a pressure of 23.2 KPa and a temperature of 17.1°C. At the same time, the opening degree of the dirty nitrogen valve PVC110 was 100%; the pressure of dirty nitrogen leaving the tower was 10.69 KPa, the temperature at the hot end was 7.0°C, and the temperature of the air entering the plate heat exchanger was 17.0°C. The purity of the liquid air was between 34% and… At 20:00, the flow rate of pure nitrogen exiting the air separation unit was adjusted to 7530 cubic meters per hour, with a pressure of 27.9 KPa and a temperature at the hot end of 21.5°C℃ ； At this point, the temperatures in the middle part of the plate have gradually shifted to -151.3°C, -21.5°C, and -90.4°C (with the valve V101 for air flow into the pure nitrogen heat exchanger open at less than 45%, valve V102 for air flow into the oxygen heat exchanger open at less than 40%, and valves V103 and V104 for air flow into the contaminated nitrogen heat exchangers both open at 100%) ； The reduction in the opening of V101 has already begun to affect the amount of air entering the tower); the air pressure entering the lower section of the air separation unit is -172.3, while the temperatures on both sides of the main cooler are -176.7°C and -177.8°C respectively. The resistance in the lower section of the tower is 13.2 KPa, and that in the upper section is 20.5 KPa. The pressure at the bottom of the upper section has gradually increased to 55.5 KPa (during this period, the V2 valve remained open at 42.2%). The analyzer indicated that the oxygen content in the V8 nitrogen was 0.49–0.61%. Due to the significant offset current in the plate heat exchanger and the ongoing increase in pressure in the upper tower, the valve PVC108 was gradually opened starting at 20:08, in order to increase the flow rate of pure nitrogen to 8,000 cubic meters per hour. By 1:00 on the 19th, the analyzer showed that the purity of pure nitrogen leaving the tower was between 0.40–0.51%, with oxygen content present ； At this time, the opening degree of the dirty nitrogen valve PVC110 is 100%; the temperature at the hot end is 4.9°C, the pressure is 11.92 KPa, and the air flow into the plate heat exchanger is 17.0℃ ； The opening degree of the pure nitrogen valve PVC108 is 25.6%; the temperature at the hot end is 17.6°C, the pressure is 26.9 KPa, and the flow rate is 8123 cubic meters per hour. Product oxygen: 6,084 cubic meters per hour, with a purity of 99.55%. Air Liquide provides oxygen with a purity of 32%. As of 9:00 on the 19th, the purity of contaminated nitrogen gas A7 was 3.5–3.8% oxygen; the purity of nitrogen gas A3 from the lower column was 132–151 PPm; the purity of pure nitrogen gas A8 was 0.4–0.5% oxygen, with a flow rate of pure nitrogen of 8,500 cubic meters per hour. It was later terminated as the analyzer was brought in for debugging in the first phase. Analysis: Following the adjustment principle of lowering the pressure in the tower first before raising it, and by gradually reducing the opening degree of valve V2, the nitrogen purity in the lower tower can reach 139–163 PPm when the opening degree of valve V2 is 42.2% ； Subsequently, while keeping the opening degree of valve V2 unchanged, adjusting the purity of pure nitrogen by closing the pure nitrogen outlet valve PVC108 had an impact on the pressure in the upper column; increasing the opening of the contaminated nitrogen valve could not completely eliminate this effect. When the amount of pure nitrogen removed is less than 10,000 cubic meters per hour, the pressure in the upper tower begins to increase gradually. Increasing the valve PVC110 that controls the flow of waste nitrogen out of the tower does not yield a sufficient reduction in this pressure; this is true until valve PVC110 is opened to 100% (based on the amount of air entering the tower and the amounts of oxygen and nitrogen being removed, the flow of waste nitrogen at this point should be around 18,000 cubic meters per hour) ； When the output of pure nitrogen dropped to 7,530 cubic meters per hour, the pressure at the bottom of the tower gradually increased to 55.5 KPa ； At this point, the system pressure increases significantly starting from the air compressor ； The plate-type bias flow is significant, and it cannot be adjusted without affecting the gas flow rate into the tower ； The analyzer shows that the oxygen content in pure nitrogen with purity grade A8 is 0.40–0.51% oxygen. ”——Repost the original poster’s post!

Nitrogen purity of 95.6%? It can’t be that low; it’s even purer than our ammonia nitrogen. For national standard high-purity nitrogen, the level must be less than 3PPm

Check the temperature of the liquid nitrogen entering the tower (around 187 degrees after the subcooler); it’s possible that the liquid nitrogen is a mixture of gas and liquid, so take a look. If that’s the case, reduce the emission volume, increase the amount of gas entering the lower tower, and slightly reduce the liquid nitrogen throttle valve; once the temperature is back to normal, increase it again. But when adjusting, the nitrogen product export function needs to be turned off. The above are my personal opinions

The last edit to this post was made by fhwfhwfhwfhw on 2011-8-22 at 23:55. I have little experience in operating such systems, so my thoughts might not be accurate; they’re just tentative suggestions meant to stimulate further discussion. 1. The temperature of the air entering the lower column in the air separation unit is -172.3°C, while the temperatures on both sides of the main cooler are -176.7°C and -177.8°C respectively. I think all three of these temperatures are too high. Moreover, the outlet temperature of the contaminated nitrogen remains low. 2. The nitrogen content at the top of the lower tower remains low. Logically, the amount of liquid nitrogen and nitrogen extracted from the top of the lower column should be reduced. However, according to your description, the output of low-pressure nitrogen remains insufficient (at least compared to the original design conditions); as a result, the amount of liquid nitrogen flowing from the lower column to the top of the upper column is also inadequate. These two points seem contradictory. Has the production of medium-pressure nitrogen or liquid nitrogen been increased? 3. If the O2 content at the top of the lower tower is 100–200 ppm, yet the O2 purity at the top of the upper tower is only 0.4%, then there must be no liquid nitrogen flowing into the upper tower, right? After a rough calculation, if the gas phase at the bottom of the tower is accurate, then the oxygen purity in the low-pressure nitrogen at the top of the tower isn’t that high. . . Sweat. . . Could it be, as mentioned above, that the temperature of the outlet cooler is too high? 4. Can the valve for the oxygen-enriched liquid air be opened wider? However, increasing it too much may reduce oxygen purity. I think low-pressure nitrogen is actually closely related to the liquid nitrogen that goes into the tower; the more liquid nitrogen there is, the more low-pressure nitrogen will be produced. Both the purity of the liquid nitrogen and its low temperature can increase the production of low-pressure nitrogen. It always feels like the temperature is too high and there isn’t enough cooling. I’m not sure if my thoughts are correct; I welcome everyone’s criticism and suggestions.

In my opinion, the low oxygen production and high nitrogen output result in some of the oxygen component being carried away, which leads to low nitrogen purity