Propylene cooling in low-temperature methanol washing
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Why is the temperature at the cryogenic station for low-temperature methanol washing -20 degrees, while the gaseous propylene coming out of the low-temperature methanol washing process is at -40 degrees? According to the law of conservation of energy, liquid propylene absorbs heat and turns into gas; therefore, the gaseous propylene coming out of the low-temperature unit should have a temperature higher than -20 degrees, right? So why is it -40 degrees?
Only temperature; the pressure is high, please maintain composure
For example, when propylene enters the propylene cooler at 20 degrees Celsius, the vapor pressure is very low, causing a large amount of propylene to vaporize; as a result, its temperature drops significantly, with the boiling point being determined by the vapor pressure
Depending on the state of propylene, vaporizing liquid propylene absorbs heat; what results is gaseous propylene, as a phase change has taken place.
This is phase-change refrigeration, which relies on the latent heat of vaporization of propylene; moreover, as propylene evaporates, the pressure decreases, causing the overall temperature to drop