Maybe a simple problem with a simple tower
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This post was last edited by dongliangsir on 2010-7-26 22:40. A naphtha separation tower, gasoline is fed, light naphtha comes out from the top, heavy naphtha comes out from the bottom. The bottom reboiler is reboiled. The reboiler is now stopped for some reason. The feed temperature is maintained at 110 to 120 degrees. The tower top temperature was originally controlled at 80 degrees. Now only a small amount of reflux is made, and the tower ejection device is stopped. Because there is no bottom heat source, the upper load becomes smaller. Now the tower top temperature is only about 50 degrees, and the temperature after the tower top is cooled is 25 degrees. The problem is: 1. The tower pressure has increased from about 0.18 MPa in normal operation to 0.22. The liquid level in the reflux tank at the top of the tower is normal. The above operating conditions mean that the tower pressure cannot be controlled, so we have to increase the gas discharge at the top of the tower. The discharge volume rises from about 50 cubic meters to more than 200 cubic meters. Only then can the tower pressure be controlled from rising further. There is not much gas phase load at the top, so where does so much gas come from? The temperature after cooling is 26 degrees. Even if there is gas rising in the tower, it should have turned into liquid phase when it comes out of the air cooler? 2 Later, when the reflux at the top of the tower was stopped, the tower pressure began to drop to 0.16. It turned out to be the cause of the reflux at the top of the tower. But I still don't understand that the reflux components should be condensed back to the reflux tank again at 26 degrees. How could there be so much "non-condensable gas" that raised the tower pressure? Please give me some advice.
The last post of this post was edited by dongliangsir on 2010-7-27 10:40. The tower pressure of our gas separation deethanizer tower is mainly related to the partial pressure of non-condensable gas. The higher the non-condensable gas content at the top of the tower, the higher the top pressure will be. The composition of the top of the tower is controlled by reflux and bottom temperature, so our phenomenon is that when the reflux is increased or the bottom temperature is lowered, the pressure at the top of the tower rises. I don’t know if there are any similarities.
Very similar, but how to explain it from the principle of fractionation?
If the top reflux components are light and will still vaporize at 0.22MPa and 50 degrees, then the greater the amount of top reflux, the more vaporized, and the higher the tower pressure. On the contrary, the lower it is. Personal opinion, for reference only.
This is still related to naphtha. You mainly think about the initial boiling point. This temperature should not be high.
There is no heat source at the bottom, and the components at the top of the tower become relatively lighter and are less likely to be completely condensed, causing the tower pressure to rise. It is correct that the tower pressure dropped after the top reflux was stopped~
When cooling and refluxing, the liquid phase returns to the tower to absorb the heavier components in the gas phase (due to the low top temperature, the absorbed components are lighter than under normal operating conditions), resulting in a gradual increase in the content of light components in the gas phase (lighter components than during normal operation), and the pressure at the top of the tower increases.； After stopping the cold reflux, it is equivalent to the top of the tower becoming a dead zone, and the pressure at the top of the tower at the corresponding temperature is lower than normal operation. This is my personal analysis, please give me your advice. . .
I agree with you upstairs, your feed temperature is relatively high, but I don’t know which layer the feed is at. The feed at 120 degrees is mostly steamed for naphtha. When there is cold reflux, it is basically the same as opening the tower normally, and you cannot produce light naphtha. As mentioned above, cold reflux presses down the heavier components, while the light components continue to come up. The light components at the top of the tower accumulate more and more, and can only be balanced by increasing the pressure. When the pressure at the top of the tower is high, the light components will decrease as they rise. ； In addition, the operation of cold reflux and tower top cooling systems only increases the total circulation amount of light components at the top of the tower. Therefore, if you stop the cold reflux, the above situation will not occur. The gas-liquid balance in the tower is basically broken, forming a dead balance. The final tower top pressure is the equilibrium pressure in the tower corresponding to the feed temperature.