The outlet temperature of the distillation tower is negative
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I built a distillation column with ethylene flowing upward and propylene flowing downward; however, after it started operating, the temperature at the upper part became negative. I need help from experts
If Aspen can run, there shouldn’t be any problems; it must be that you set the conditions incorrectly
The pressure design is too low; it is recommended to increase the pressure so that, under conditions where the ethylene at the top of the tower reaches the specified purity, the dew point temperature is 40–50°C, thereby enabling condensation using condensate water. This system needs at least 10–15 bar.
This post was last edited by zhxbkofkyo on 2017-10-23 at 15:58. It’s too difficult to try to use condensate water for condensation; it’s more reliable to use an ice machine for cooling. Also, there must be an issue with the pressure setting – it’s vacuum on the lower side. If the propylene temperature is over 100 degrees, the pressure is too low
In Aspen simulations for distillation, it is assumed by default that the vapor at the top of the tower is condensed into a saturated liquid phase. At atmospheric pressure, ethylene has a very low boiling point; therefore, extremely low temperatures are required to cool it down, resulting in high costs in terms of cooling energy.
Increasing pressure has little effect on temperature
Are there any other low-boiling non-condensable gases in the system besides ethylene and propylene?
Ethylene has a relatively low boiling point at atmospheric pressure; if there are other non-condensable gases in your system with even lower boiling points, then using a total condenser will result in a very low temperature at the top of the tower.