How does the oil in the atmospheric leg of a vacuum distillation unit get out?
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The atmospheric leg of the vacuum system extends into the water seal, and the condensate (water + oil) in the condenser flows down through the atmospheric leg. My question is: inside the air leg, there will be a column of liquid due to the pressure difference. The water and oil that condense and enter the atmospheric leg are also added to this liquid column; to maintain pressure balance, any excess water at the bottom of the column is pressed back into the tank. Well, since oil has a low density, it floats on the surface of the water column; so doesn’t it remain trapped there the whole time? How do I get inside the tank? Isn’t it all oil towards the end? Then wouldn’t some designs with 10.5-meter atmospheric legs be insufficient? Please give me your guidance.
The atmospheric leg extends into the water seal, which is divided into two parts by a baffle; oil overflows from above the baffle, enabling separation of oil and water.
"What is an atmospheric leg? Could you show a picture?
I know that. The key question is: how does the oil at the upper layer of the liquid column in the atmospheric leg penetrate through the water layer and enter the tank?
You are right. In the end, the upper part or even the entire area above the liquid column in the air leg is filled with oil; a height of 10.5 meters for the air leg is not sufficient.
Is that so? Thank you. I infer that the final result will be basically all oil. But I saw that the relevant information states the atmospheric leg is designed to be only 10.5m long, which seems insufficient; therefore I’m posting this question to ask whether the oil inside the atmospheric leg can be removed.
The atmospheric leg contains a mixture of oil and water, with the water content being much higher than that of oil (this can be determined by comparing the amount of steam used during vacuuming, the steam used at the bottom of the tower, and the amount of contaminated oil sent out). Therefore, during the condensation process, almost everything in it is water； Secondly, during the vacuuming process, steam serves as the driving force, and there is always a tendency for flow. The discharge of non-condensable gases and the removal of wastewater create a liquid level difference and pressure difference between the vacuum side and the wastewater side. This results in a flow inward (after vacuuming, through condensation and cooling); during this flow, the mixture consists of oil and water (it is the high pressure in the atmospheric leg that causes the flow toward the condenser). In the condenser, the space available for the water seal and the atmospheric leg is very small, so there is no time for the oil and water to separate after they enter; thus, they pass together through the partition of the water seal into the oil-water separation area, where separation takes place – the oil is sent away and the wastewater is also sent away.
It is a displacement process: the mixture of oil and water (which is mostly water) at the back pushes out the substance at the front. This mixture of oil and water (primarily water) then flows into the water seal area of the separation tank. Due to its small volume, it doesn’t have time to separate before quickly flowing into the oil-water separation area where separation takes place.
This post was last edited by qhhqhh on 2019-6-26 at 14:55 :handshake Thanks:D. If there’s no time to separate them, 10.5m is generally sufficient as well. Some of these large legs are designed with a length of not less than 15 meters – is it to prevent oil from accumulating over time? Or is it a fear that when water is released, the water level will be too low and oil might get in?
It’s just to discuss problems together! I hope to ask more questions; only by thinking can one gain something!
Mm. I’m happy to answer more questions when I see hope:D