The top temperature of the distillation tower is 110°C; why can the dry point of the crude vapor reach 200℃
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The top temperature of the fractionation tower is 110°C; why can the dry point of the crude vapor reach 200°C? And the 50% point for the crude steam is exactly 100°C; could any teacher give some guidance? Thank you
How does the high-temperature component rise to 200°C?
Distillation is simply the process of distilling until reaching the boiling point of the heaviest fractions. It is impossible for the tray to achieve 100% separation; there will always be recombined components carried to the upper layer, while light components are carried to the lower layer
The tower top temperature is the dew point temperature of the oil under the tower top pressure; it is something different from the dry point of the oil.
This is related to the vapor pressure of oil and gas in the fractionation tower, and it is different from determining the dry point at atmospheric pressure.
The operating temperature at the top of the tower is the dew point temperature of the product at that level, under its vapor pressure. The percentage of gasoline in the vapor stream is less than half of the total vapor volume; due to the low vapor pressure, some of the vapor with a boiling point higher than the temperature at the tower top remains in the gaseous state and is carried away along with the product distilled from the top of the tower. Enthalpy distillation, on the other hand, is carried out at atmospheric pressure, so the vapor pressure equals 1 atmosphere. As a result, the temperature at the top of the distillation column is much lower than the dry point of the crude gas!
In simple terms, the vapor at the top of the tower contains both light components and heavy components. The temperature at the top of the tower is the dew point temperature of these mixed components under the vapor pressure present there. This dew point temperature is higher than the boiling point of the light components under that vapor pressure (for a single component, the boiling point and the dew point are the same), but it is lower than the boiling point of the heavy components.
The temperature during operation is different from the temperature used in distillation; partial pressure needs to be taken into account during operation, and the 50% point is probably just a coincidence
It can also be approximated as the equilibrium evaporation rate of the oil at that operating pressure, which is also an indicator of the average evaporation rate of gasoline. This is also not just a coincidence.