During the startup of an air separation unit with expanded air fed into the lower column and internal compression, could overpressure occur in the lower column when starting the booster expander?
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When the internal compression air separation unit for feeding expanded air into the lower column is shut down, after pressurizing the lower column to equilibrium using the low-pressure air exchange valve, this valve is already partially open (or fully open), while the liquid throttle valve for feeding air into the upper column has not yet been opened. Will the lower column experience overpressure when the booster expander is started? How should the liquid throttle valve be operated from the lower tower to the upper tower? This is my first time dealing with internal compression air separation; I don’t understand it, so I’m seeking advice here. Thank you!
First of all, since your expander feeds into the lower column, it’s certain that the outlet pressure of your expander corresponds to the pressure in the lower column!
I’m not familiar with your process, so it’s hard to say. We control the tower pressure at levels V1, V2, and V3, ensuring that the pressure does not exceed limits, and we proceed slowly. Activate the lower tower air return valve in a timely manner to stabilize the pressure in the lower tower.
Overpressure generally does not occur. Before starting the expander, the valve connecting the lower tower to the upper tower should be open; usually, an automatic valve is installed at the outlet of the upper tower to control the pressure and prevent overpressure in both towers
Overpressure generally does not occur. Before starting the expander, the valve connecting the lower tower to the upper tower should be open; usually, an automatic valve is installed at the outlet of the upper tower to control the pressure and prevent overpressure in both towers
When the expanded air enters the lower column, only a few of the throttle valves for liquid air and liquid nitrogen flow from the lower column to the upper column are opened. Meanwhile, the liquid level in the lower column is returned to the upper column through the argon purification column condenser, thus creating a cycle. Once we return to the upper tower, the cooling capacity naturally increases and the liquid level rises. At this point, whether it is contaminated nitrogen or clean nitrogen that is used, it’s important to ensure a continuous flow of in and out of material, so as to avoid overpressure; this is how our equipment is operated.
As the poster mentioned, in such a situation, the lower tower will not experience overpressure, because your valve for allowing air to enter the lower tower is already partially open (or fully open). As a result, even if you don’t open the valve leading to the upper tower, the pressure can only rise up to the outlet pressure of the air compressor. If the pressure in the lower tower becomes too high, the compressor’s relief valve will take care of regulating it, so overpressure will not occur. However, if you set the valve to only that position to allow low-pressure air to enter the lower tower for pressure equalization, then the safety valve at the outlet of your expander and the safety valve in the lower tower might have to activate. Gradually increase the valve opening to the tower; just be careful not to cause overpressure in the tower!
My humble opinion: if the vehicle is started while hot, the valve leading to the tower should already be open before you start the engine； Or the valve for pressurized nitrogen has been opened ； When starting the machine in cold conditions, we usually open the upper tower first before starting the expander ； Dear seniors, I hope you will share the correct ways of driving, otherwise it will mislead the younger generation!
This post was last edited by Air Separation Main Cooler on January 8, 2011, at 17:06. Reply to post #8 by YouYou: You’re right; when the expander was started, gas had already been introduced into the upper column. Air compressors are equipped with check valves, but it is possible to adjust the pressure in the lower tower; otherwise, how could that pressure be adjusted? But I think the original poster had better study *your methods of operation carefully!
Overpressure will not occur; once the expanded air enters the tower, with the main valves remaining unchanged, the forward-flowing air from the low-pressure heat exchanger will automatically reduce the amount of air entering the tower.
This post was last edited by Air Separation Main Cooler on 2011-1-8 at 17:06. Reply to 8# YouYou: Hehe! The post above is misleading! I'm talking about adjusting the tower pressure, not the check valve.