How to maintain cold balance inside the liquid nitrogen cooling tank during normal production?

This is a rather complex issue, as there are many factors that affect the balance of the cryogenic box. The aspects that I pay attention to usually are as follows: 1. The flow rate of syngas sent back to the low-temperature methanol wash for re-warming; generally, the ratio of the flow rate of the gas being re-warmed to that of the cooled high-pressure nitrogen is 3:1. 2. The liquid level of the tail liquid at the bottom of the tower should be kept stable, as well as the evaporation pressure of this tail liquid. 3. The flow rate of nitrogen used in the washing process is controlled using cascade control based on the load (automatic control is also used in some cases). 4. In some plant designs, it is necessary to supply additional cooling capacity, which requires the use of liquid nitrogen. Our setup’s cryostat is somewhat well-provided, so normal temperature nitrogen is used for temperature regulation.

I would like to ask how exactly temperature control using nitrogen works, as you mentioned. Is it done during normal production?

Before entering the washing tower, high-pressure nitrogen represents heat for the system; it absorbs cold energy and turns into liquid nitrogen before entering the nitrogen washing tower. The roughly conditioned nitrogen gas between the heat exchangers, once it enters the process gas, acts as a source of cooling for the system due to throttling expansion.

The device is designed with a 2-inch temperature control pipeline that directly supplies nitrogen at normal temperature and high pressure behind the nitrogen adjustment valve. After mixing, return it to the cold box for rewarming.

Our device does not use high-pressure nitrogen for temperature control, as you mentioned. Also, is it easy to control the liquid level in the separation tank at your facility?

The process on our end might be relatively simple. We do not recycle the tail liquid. So there is only a simple flash tank, which keeps the flashing pressure constant and the liquid level stable as well.

The separation pressure in the hydrogen separation tank on our side is stable, but the liquid level fluctuates.

This post was last edited by *aoyan*ao on 2016-3-24 00:01. Also, does the fluctuation in the liquid level of the hydrogen separation tank indicate a change in the cooling capacity of the system?

Yes, the level of the separation tank is closely related to the system cryogenic tank. In our unit, the bottom height of the separation tank is almost the same as the bottom height of the main heat exchanger. When a liquid level is formed in the separation tank, it indicates that there is also a liquid level on the exhaust gas side of the heat exchanger. In such cases, the heat exchange between the liquid and other flow channels takes place in a gas-liquid form. Since the latent heat of vaporization for liquids is generally high, heat exchange is significant when the liquid level fluctuates.

Well, that’s right. So, is the cold energy inside your cold box needs to be discharged during normal production?