LNG mixed refrigerant
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It is a cryogenic chamber cooled by a combination of nitrogen, methane, ethylene, propane, and isopentane; the exit temperature of this chamber is around 15 degrees, with a pressure of 2.7 kilograms. So why remains isopentane in gaseous state under such conditions, given that its boiling point is only 27.8 degrees? Which sea friend can help analyze this? Thank you
The cold box outlet is the throttling element, right? It needs to be in gas form in order to easily enter the mixed refrigerant compressor.
Thank you for your answer. The material coming out of the cryogenic tank is indeed in gaseous form; there are no throttling elements. The inlet to the cryogenic tank has a 6-inch pipe for the gas phase and a 3-inch pipe for the liquid phase, while the outlet has a 12-inch pipe. Could this be related to the diameter changes of the pipes?
The key to mixed refrigerants lies in their mixing; the pressure you mentioned is the total pressure. In fact, isopentane is just one of the components in such mixed refrigerants, and under ideal conditions, its partial pressure is proportional to the amount of that component present. The partial pressure of isopentane is relatively low, so it naturally does not appear in a liquid state. It’s a good idea to spend more time studying the basic knowledge related to the properties of substances.
Even if the partial pressure is very low, there is still pressure. And the boiling point occurs at standard atmospheric pressure – isn’t boiling point proportional to pressure? It should be higher than the original boiling point. I still don’t understand! ! Thank you
The mixture is usually referred to as the bubble point and dew point; obviously, the dew point has not been reached. Based on the refrigerant components, the partial pressure of C5 is very low; the lower the pressure, the lower the boiling point, while it becomes more difficult for it to condense, so no liquid forms.
I have a simple question for the original poster: isn’t there any water vapor in the air at room temperature? ? ?
In a mixture, it is called the bubble point, while in a pure substance it is called the dew point. Please do not mislead the original poster!
Oh, there is water vapor. What’s the principle behind that? Thank you
With low water vapor content in the air, my C5 exists in a liquid state inside the cryogenic tank; it only fully vaporizes at a certain point.
The 27° you mentioned is the boiling point of pure isopentane (this is under theoretical conditions); for mixtures, it’s the bubble point that matters. You should consult a core textbook on physical chemistry, as it covers the thermodynamics of multi-component systems! ! ! Once any substance in the mixture no longer reaches a critical state, it will exist in both states; it’s just a matter of to what extent!