Regarding the control of dry spots
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First, we know that reducing the pressure at the top of the tower can increase the dry point, but what is the principle behind this? Generally, the higher the pressure, the higher the boiling point; and with a higher boiling point, doesn’t the dry point also increase? Aren’t there contradictions between these two places? The more I think about it, the less I understand it; please provide an explanation
You’re referring to that aspect, right? The reason why reducing pressure increases the dry point is that, with constant temperature, lowering the pressure causes the heavier components at the bottom of the tower to move into the tank, which in turn raises the dry point. If the pressure is increased, it means that the heavy components can’t rise; and if those heavy components can’t rise, then the level doesn’t go up either. Try to find out what the raw materials are; in the case of naphtha and similar substances, it is mainly the upstream processing units that control them. Different raw materials require different drying methods
The operating pressure in a conventional distillation tower is relatively low, at only 0.015 MPa; the main purpose of this is to lower the boiling point of the oil during operation. Therefore, towers used for diesel production operate under negative pressure. As for the issue of the dry point you mentioned, it should be considered on this basis – don’t get it backwards
Tower pressure is the total pressure; what you’re referring to is partial pressure. Tower pressure affects the load on the entire tower – when the pressure is high, the load on the tower increases, and the dry point decreases
You have misunderstood this. Firstly, the reason why liquids or oils vaporize is that their saturated vapor pressure is higher than the external pressure. The saturated vapor pressure is related to temperature. First, with the temperature and saturated vapor pressure remaining constant, reducing the tower pressure makes it easier for the oil to vaporize, or in other words, to reach the top of the tower. So the components that are extracted will be heavier and are different components. . Similarly, if you increase the pressure, you need to raise the temperature in order to obtain the same components, keeping in mind that it is the same components that are desired. By increased pressure leading to an increased boiling point, you mean the same component. It’s not that the product has become heavier. If you want to increase the tower pressure and obtain products with higher boiling points, you need to raise the temperature even further! So these two points are not contradictory; I’m not sure if you can understand that.