Issues related to crude oil properties
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I’m a beginner. If we compare the properties of crude oil to those of water, then if the properties of crude oil become lighter, it means there are more light components in it. Does that mean the water becomes cooler? If the properties of crude oil become heavier, does that mean the water turns into hot water? If the properties of the crude oil fed into the tower become lighter, then, with all operating conditions remaining unchanged, the bottom temperature of the tower decreases, the vaporization rate at the top increases, the top temperature of the tower drops, the pressure at the top rises, the quality of the product deteriorates, and the distillation temperature of the side streams decreases as well, resulting in a lower quality of the material flowing out from those side streams. Is that what it means? If there’s anything wrong, please point it out to me, senior
Why is lightness and heaviness distinguished by cold and hot?
The difference between light crude oil and heavy crude oil lies in their density. Crude oil with a relative density of 0.9 to 1.0 is referred to as heavy crude oil ； If the relative density is less than 0.9, it is called light crude oil.
Atmospheric and vacuum distillation do not have such strict control over the boiling range; whereas in distillation, in order to ensure product quality, it is necessary to control the amount of distillate sent out from the tower. This is just my personal opinion for reference only.
It can be understood in this way: crude oil is composed of non-condensable gases, gasoline, diesel, and residue. If the crude oil becomes lighter, it indicates an increase in the light components within it (non-condensable gases, gasoline, diesel); if it becomes heavier, it means there is more residue in the crude oil. If the properties of the crude oil fed into the tower change to be lighter, then, with all operating conditions remaining unchanged, the bottom temperature of the tower decreases, the vaporization rate at the top increases, the top temperature of the tower drops, and the pressure at the top rises. As a result, the quality of the product deteriorates, the distillation temperature of the side streams decreases, and the quality of the materials coming from these side streams also declines. You’ve mentioned too many operating conditions here; yet you say that all of them remain unchanged, which seems a bit contradictory, doesn’t it? If the feed becomes lighter while the bottom temperature remains unchanged, the upward gas load will definitely increase. If the gas-phase load is to be kept constant, it is necessary to lower the bottom temperature of the tower; as a result, the properties of the material at the bottom of the tower become lighter. When the gas-phase load increases, if the top temperature of the tower is kept unchanged, the pressure at the top of the tower will definitely rise ； If the gas-phase load increases, in order to ensure product quality, it is necessary to increase the reflux flow rate for each line, that is, to maintain a relatively stable reflux ratio. Therefore, when the properties of crude oil become lighter, it is necessary to adjust the flow rates of various side streams appropriately in order to maintain product quality and yield. And adjust the extraction temperatures of each side stream appropriately according to changes in product quality. When using top cooling reflux to control the top temperature, it is necessary to ensure stable top pressure.
This post was last edited by qugd on 2020-6-27 21:02. First of all, crude oil is a mixture, while water is essentially a pure substance. The physical properties of a mixture are related to its constituent components through partial molar functions, whereas water has fixed physical properties. The poster’s analogy stems from a lack of understanding of the characteristics of mixtures and pure substances; therefore, such an analogy is inappropriate. The crude oil distillation process is a process of fractionating mixtures, whereas the boiling point of water is fixed. The distillation process is closely related to the composition of the material being distilled.