Issue liquid nitrogen reflux valve
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I would like to ask the experts: under what conditions does the liquid nitrogen reflux valve switch between open, closed, and open states?
In the device cooling, liquid accumulation, and purification stages, a shut-off-shut-off-on operation is also used.
On the second floor, please explain the Guan Guan Kai operation again. We rarely find this downflow reflux valve on air separation units anymore; it has been removed in all of them. It can be opened without this valve; the benefits of this valve aren’t very clear. The cost of having this valve is obvious – low-temperature valves are relatively expensive; better brands can cost tens of thousands of yuan.
Why doesn’t our air separation unit have a liquid nitrogen return valve? ?
Some small and medium-sized air separation units in Kaifeng do not have this valve; I think that’s still an advantage, as it allows for better stability in adjusting the liquid level//
The liquid nitrogen reflux valve is a valve used to return the liquid nitrogen from the main condensation evaporator to the lower column; it is employed to adjust the reflux ratio of the lower column as well as the temperature difference in the main cooling system. It is generally used at the beginning of operation of the cooling column ； During the fluid accumulation phase in the upper tower ； During the purification stage, in order to increase the purity of the liquid nitrogen coming out of the lower tower, it is activated
During the cooling phase of the device, in order to ensure even cooling of all its low-temperature components, it is necessary to open up all the pipelines, thereby facilitating their cooling and preventing deformation caused by large temperature differences. Our device was provided by Sichuan Airlines, and the technicians from Sichuan Airlines insisted strongly that this valve be closed while operating the equipment; since the pipeline is relatively short, turning the valve on and off does not exert much stress on it. During the cooling phase, the blow-off valves for all low-temperature liquids are kept open until the temperature inside the tower drops to -170 degrees Celsius, after which they are closed. During the liquid accumulation phase, to ensure rapid liquid accumulation in the upper tower and reduce the reflux flow rate in the lower tower, it is required to close everything completely. During the purification stage, distillation in the lower column is established by gradually opening this valve in small increments to create reflux in the lower column, thereby enabling rapid purification. If there are any mistakes, please correct them, thank you!
Generally, it is done when the chiller tower just starts operating ； During the fluid accumulation phase in the upper tower ； During the purification stage, in order to increase the purity of the liquid nitrogen coming out of the lower tower, this valve is opened to its full extent!!! However, different main cooling systems have different requirements, and the treatment methods vary as well when cooling the tower! Some air separation units do not have this valve; the total time required for cooling the tower and for allowing liquid to accumulate is not very different, so it’s possible to skip using this valve if the material can withstand a slower cooling rate. It is sufficient to adjust the throttle valve of the liquid nitrogen going into the upper tower instead!
Generally, it is done when the chiller tower just starts operating ； During the fluid accumulation phase in the upper tower ； During the purification stage, in order to increase the purity of the liquid nitrogen coming out of the lower tower, this valve is opened to its full extent!!! However, different main cooling systems have different requirements, and the treatment methods vary as well when cooling the tower! Some air separation units do not have this valve; the total time required for cooling the tower and for allowing liquid to accumulate is not very different, so it’s possible to skip using this valve if the material can withstand a slower cooling rate. It is sufficient to adjust the throttle valve of the liquid nitrogen going into the upper tower instead!
Hello, we are also from Sichuan Airlines. But every time we turn off the liquid nitrogen valve completely, overpressure occurs during the process of turning it back on. How about you?
When this valve is opened, distillation takes place in the lower column, which inevitably leads to an increase in liquid nitrogen in that column as well as an increase in the amount of air entering it; this can easily result in overpressure. Therefore, the opening speed of this valve must be controlled properly, and the valve controlling the flow of liquid nitrogen into the upper column also needs to be adjusted accordingly~~