Questions about diesel freezing point

For a fractionation tower, the diesel dry point is adjusted to control the freezing point.

But in practice, it is usually the temperature of the product taken from the side stream that is used to indicate the dew point of diesel. A higher temperature of this side-stream product indicates a reduction in light components, which in turn raises the initial boiling point; it has little effect on the dry point

For a multi-side-line fractionation tower, it is one-sided to isolate and discuss separately any single quality control scheme for a particular product. Analyzing it in terms of diesel freezing point: Controlling the diesel freezing point using the temperature of the diesel extraction layer is possible only on the premise that both the bottom and top temperatures of the tower are within the specified ranges, that the reflux rates at various stages are appropriate, and that the tower pressure remains stable. Any change in any of these prerequisites can lead to deviations in the diesel freezing point ； For example, the temperature of the diesel extraction layer remains stable, but the top temperature of the tower decreases due to changes in the feed composition; if the original control parameters are still used in such a situation, the freezing point of the diesel will decrease. In other words, both the top temperature and the bottom temperature of the tower have a significant impact on the freezing point of diesel. Regarding the relationship between diesel’s freezing point and its boiling range, I believe that, when the properties of the raw material remain constant, a lower initial boiling point of the diesel corresponds to a lower freezing point, while a higher final boiling point leads to a higher freezing point; the reverse is also true. It is possible to compare these two quality indicators during normal operational control, and through extensive data analysis, one can arrive at the correct conclusions.

Thank you for your helpful answer. For fixed raw materials, both the initial boiling point and the final boiling point certainly affect the dew point of diesel; but which one has a more direct impact on the dew point? In other words, if a certain straight-run diesel has a boiling range of 180–355°C and this distillation column has only one side stream corresponding to diesel, then in order to lower the freezing point of this diesel, with all other operating conditions remaining unchanged, should the initial boiling point or the final boiling point be reduced? I hope you can kindly offer your guidance.

Or, setting aside practical operations, we can analyze only a certain amount of diesel, considering solely its boiling range, as the ultimate goal of such operations is to adjust the composition of the oil, that is, its boiling range. So, for a bottle of diesel with a temperature range of 180–355°C, if one wants to lower its freezing point, should one add distillate oil with a boiling range of 170–180°C in order to reduce its initial boiling point, or should the dry point of the diesel in that bottle be adjusted to 345°C? Considering it from a purely theoretical perspective.

Is it a atmospheric and vacuum distillation unit, a catalytic unit, or some other type of facility? It depends on whether the production scheme for this device involves deep drawing or shallow drawing, and whether it is a gasoline-based or diesel-based scheme. A deeper distillation reduces the initial boiling point, while a shallower distillation reduces the final boiling point. A scheme aimed at producing more diesel lowers the initial boiling point, whereas a scheme aimed at producing more gasoline lowers the final boiling point. If high requirements are placed on the final boiling point of diesel, lower it. While reducing the initial boiling point, it is necessary to ensure that the flash point remains within acceptable limits ； It is also necessary to take into account the analysis results of the bulk product; if the final boiling point determined by that analysis is already quite high, continuing to produce diesel with a high final boiling point may result in the bulk product failing to meet the required standards, which would be counterproductive... I am not able to determine whether the initial boiling point or the final boiling point has a greater impact on the freezing point of diesel.

Taking atmospheric and vacuum distillation as an example, what about the diesel option? What is deep extraction and shallow extraction? This tower has only one diesel side stream; naphtha at the top and wax oil at the bottom.

This post was last edited by altpage on 2017-12-8 at 10:38. Shallow drawing: When there are further processing steps for the material at the bottom of the tower, and when some of the heavier diesel fractions, after being sent to the bottom of the tower, do not result in significant waste (for example, when diesel from the atmospheric and vacuum distillation units is sent to the wax oil fraction, and this wax oil is then used as feed for the catalytic reactor; due to its low carbon residue content, it helps to reduce the carbon residue level in the catalytic feed, which is beneficial for the operation of the catalytic unit), shallow drawing is considered an appropriate option. Deep extraction: When the material at the bottom of the tower is a product with low added value or an extract, and there are subsequent refining methods available (such as hydrodesulfurization). To increase diesel production in atmospheric and vacuum distillation, reducing the initial boiling point is the preferred approach, while the control of the final boiling point can be adjusted according to the requirements of subsequent processes. Of course, these methods can only be used for fine-tuning.

Thank you for your answer; I’ve learned something. In my opinion, the most direct effect of adjusting the freezing point of oil is on its final boiling point; this is due to the heavier components in the oil, as it is these heavier components that start to solidify first. The mixing of lighter components, on the other hand, helps to lower the overall freezing point.

Thank you for your answer; I’ve learned something. In my opinion, the most direct effect of adjusting the freezing point of oil is on its final boiling point; this is due to the heavier components in the oil, as it is these heavier components that start to solidify first. The mixing of lighter components, on the other hand, helps to lower the overall freezing point.