Problems with the top pressure in distillation columns
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It does increase the boiling point of the oil, but does it reduce the speed of the vapor that rises? After all, higher pressure means a higher boiling point; as a result, less vapor rises. With less vapor present, the static pressure is lower, and thus the kinetic energy generated is also lower, which leads to a reduced speed. Am I correct in my analysis? ? ? ?
I don’t agree with your view. You should keep in mind that when the pressure at the top increases, the pressure at the bottom will also increase accordingly; therefore, I’m not in agreement with your opinion. According to your analysis, the vapor rising in the gas phase does so more slowly; consequently, more liquid moves downward. Wouldn’t that make the top of the tower lighter? I don’t think that’s correct!
The top pressure is high, and so is the low pressure. That’s right; because the pressure throughout the tower is high, the volatility of the oil, or its boiling point, is also high. With the feed temperature and top temperature remaining unchanged, the thermodynamic driving force in the gas phase decreases. That’s why I believe the kinetic energy is low and the velocity is low. Increasing the top pressure will result in a product stream from the middle section that is heavier at the beginning and lighter towards the end, but the product at the top of the tower is light. The top temperature is also controlled by the reflux rate; if the top temperature is to remain constant, the reflux rate must be low
According to Dalton’s law, as the top pressure increases, the vapor pressure of the oil and gas rises; as a result, the dry point of the product decreases. Conversely, an increase in top temperature leads to an increase in the dry point, causing the oil to become heavier. It is also necessary to take into account the dew point temperature of water vapor when it is present, and the top temperature must be kept above this dew point； In principle, the higher the top temperature, the higher the dry point; the higher the top pressure, the lower the dry point. .