Urgent issue with liquid nitrogen washing! ! ! ! !
Thread Content
Vaporization reduces the volume; the pressure of the purified gas entering the cold box drops from around 85,000 to around 81,000, while the outlet pressure decreases from 5.1 to 4.9； The temperatures at various points in the cold box are all within the specified limits, but the carbon monoxide level at the outlet exceeds the limit by reaching 3.6 ppm. What could be the reason for this? ? ?
The control of temperatures at various points in the cold box is within the specified limits; under such conditions, carbon monoxide levels should not exceed the allowed limits. It is likely that insufficient cooling capacity is the result of reduced gas supply or other similar reasons.
Agree with what was said above: as long as the temperatures at various points inside the cold box are normal, the CO level will not exceed the permissible limits. It is recommended to check the temperature of the hydrogen-rich gas – it should increase somewhat.
Thank you, both of you. After making adjustments to the instruments, the CO level was around 0.8. I have another question: if the medium-pressure nitrogen supplied from the air separation unit contains a certain amount of oxygen, could that cause the CO level to exceed the acceptable limit? ? ?
If the CO concentration in the environment surrounding the air separation unit increases, the CO concentration in the medium-pressure nitrogen produced by the unit will exceed the permissible levels. In our plant, there was an incident in which the CO concentration in the environment of the air separation unit exceeded 100 ppm (the upper limit of the measurement range being 100 ppm); the CO concentration in the medium-pressure nitrogen produced by the air separation unit was as high as 6 ppm, which resulted in a CO concentration of 3 ppm in the product gas after treatment with liquid nitrogen.
I don’t know how long the CO level mentioned by LZ stayed at 3 ppm? A common phenomenon here is that when the load upstream drops suddenly, the system pressure also drops; online analysis shows an increase in CO concentration, which can sometimes rise to 5 ppm, yet the CO level in the tower remains within acceptable limits. And once the pipeline pressure stabilizes, the online CO concentration in the product will drop rapidly to around 0. Therefore, we have always believed that when there are fluctuations in the pipeline pressure, as long as the CO level in the tower does not exceed the limit, any excess levels detected in the product must be false readings caused by the pressure fluctuations in the analyzer.
If the pressure decreases, it makes sense for CO levels to rise as well; with lower pressure, the partial pressure of CO in the gas phase is reduced, and liquid nitrogen’s ability to absorb CO decreases, or in other words, its solubility drops