While driving the machine, should the liquid be discharged first from the upper tower or from the lower tower?

Yours is a large-scale air separation unit, right? Generally, large-scale air separation units take longer to cool down and to become operational due to their large size. Therefore, in small air separation units, liquid backflow is used, and the refrigerant fluid is produced through expansion refrigeration. And it’s the lower tower where fluid accumulates first

We generally use turbine expansion for cooling the accumulated liquid, especially during the first startup; we only resort to the method of pouring in low-temperature liquid if there are time constraints

When using expansion mechanism cooling exclusively, it seems that both situations of liquid accumulating first in the upper column and first in the lower column can occur. It is estimated to be related to the cooling method.

When using expansion mechanism refrigeration, depending on the process, it is possible for liquid to accumulate first in the upper column or in the lower column. But in most cases, fluid accumulates first in the lower tower.

The process is different; the location where the first drop of liquid appears is different, but it can be clearly stated to the original poster that the liquid is seen first at the bottom of the tower.

Currently, liquid oxygen and liquid nitrogen are fed back into the upper tower while driving the process; it seems that not much liquid level buildup occurs as a result of cooling generated by the turbines. Feeding back liquid helps to accelerate the establishment of the distillation conditions； Whether large or small air separation units, they can all independently handle liquid accumulation. Regarding what you mentioned about \"whether liquid comes out first from the upper tower or from the lower tower during operation,\" the area where no liquid comes out is the place where liquid accumulates. When the device is started and liquid begins to accumulate, the first drop of liquid appears as well as the main area from which liquid comes out, and these are located at the cold end of the main heat exchanger. Furthermore, the claim that \"currently, when driving the process by feeding liquid oxygen and liquid nitrogen into the upper tower, it seems that little liquid level accumulation occurs through turbine cooling\" is incorrect; a system that does not have the basic equipment for independent liquid level accumulation cannot be approved. I wonder if the original poster received a kickback, hehehe;P Sorry, it was just a joke. But one really needs to be careful during the evaluation and inspection process. (For reference)

Air separation processes that rely entirely on expansion refrigeration, high-pressure throttling refrigeration, or chiller refrigeration can have the liquid formed either in the upper column or in the lower column, depending on the startup method. When the liquid-air throttle valve is fully open while driving, liquid is first generated in the upper column; thereafter, the liquid-air throttle valve is reduced in size, and liquid accumulation begins in the lower column. Whether liquid is produced first in the upper column or in the lower column, as long as the operations are carried out properly during startup, it will have no impact on the entire startup process; it basically does not affect the speed at which the product is produced nor the time required for the product to meet quality standards.

Generally, liquid should first accumulate in the lower column. If the throttle valve is opened too wide, all the liquid from the lower column gets blown into the upper column, resulting in liquid accumulating in the upper column first!

Hehe, in our medium-sized units, driving is entirely dependent on expanders, and two of them are used at the same time… Depending on the process, either the main cooler or the lower column may accumulate liquid first, but generally it’s the lower column that develops liquid first

In air separation, the air that enters the lower column contains liquid; the amount of liquid in the lower column keeps increasing in order to establish the operating conditions for air separation. Therefore, I believe it should be the lower column that releases liquid first.

After driving air into the column, the gas in the column gradually cools down. As the temperature drops, liquid begins to form at the bottom of the column. If the control valves that send fluid to the upper part of the column are closed at this point, liquid will accumulate at the bottom of the column. If the control valve is opened to full, liquid will first accumulate in the upper tower. Either one of these will work! Here too, some people prefer to accumulate fluid first at the lower tower, while others prefer to do so at the upper tower. Personally, I think accumulating liquid first at the tower speeds up the purification of liquid oxygen a bit!