Is a temperature of “-38 degrees” in the distillation section of the designed plate tower normal?
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It’s a plate column used for distillation; the temperature in the distillation section reaches negative values, specifically minus 38 degrees. Is this normal? The feed temperature is +76 degrees, and all other settings are normal; yet the result turned out to be negative. The temperature difference across each tray is about 20 degrees, and I really can’t find any errors. Please help me figure this out. Thank you. Additional note: It seems to be related to pressure; when the pressure is 4 MPa, the temperature at the top of the tower can reach -15 degrees. But my previous pressure was 0.6 MPa – increasing the pressure by so much just to raise the temperature by 50 degrees doesn’t seem reasonable, does it? Solve.
In actual production, I’ve never heard of such operating conditions – a temperature difference of 20 degrees per tray is quite exaggerated. The specific details aren’t clear, so it’s hard to determine whether there’s a calculation error
Temperature is mainly related to the composition of the material, and generally increases as pressure rises
It can be said that it’s almost certainly wrong. You can first estimate the temperature at the top of the tower.
Temperature is related to physical properties and pressure; I wonder what system you are using? Even if it is a negative value, it isn’t necessarily a problem; in industry, the separation of ethylene and ethane is carried out at an operating pressure of around 20 kilograms, with the top temperature being several degrees below zero.
Could the poster consider not allowing complete condensation at the top of the tower, and instead allowing an appropriate amount of non-condensable vapor to escape? This way, the temperature at the top of the tower can be reduced somewhat.
Wrong, it’s to increase it appropriately; my apologies.
Wrong, it’s to increase it appropriately; my apologies.
If the run converges, then there will be no problem with ASPEN itself. In actual production, it is not unusual for the top temperature of the tower to be as low as minus 40°C; in the deep cryogenic separation of ethylene, the temperature can be even lower than that. I don’t know what the components of the owner’s material are, so I can’t give a specific judgment.
Thank you all for your enthusiastic responses; I’m very touched. I work on CO2 separation towers; previously, ammonia water was used for absorption, so the main components are ammonia water and CO2. I thought about it carefully again: since both ammonia and CO2 are light key components, with only water being a heavy key component, then when setting up the condensation process, as I want ammonia to flow back, it is necessary to reach -38 degrees (at the corresponding pressure) for ammonia to turn into a liquid state and thus be able to flow back. Therefore, it seems that Aspen must have handled things in this way in order to obtain such a negative tower top temperature. Although that’s what I said, I still don’t know how to solve it. I hope everyone can help me again; thank you :)
Generally, when ammonia water is used as the absorbent, regeneration is not considered, just like in desulfurization. . . For regeneration, it is recommended to use the ethanolamine series.