Adjustment of the diesel cut point
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Currently, the dry point of gasoline at the distillation unit is controlled at 205 degrees; it was previously set at 200 degrees. However, recently the initial boiling point of diesel has decreased, dropping from 175 degrees to 165 degrees. What is the cause of this, and how can it be optimized and adjusted better?
This post was last edited by Zhongyuanren on 2020-9-26 at 10:26: adjustments were made to the operation of the distillation column, the reflux rate was reduced, and more light components entered the top of the column. If there are no requirements for the gasoline components, there is no need to make any adjustments ； If the gasoline composition is required to remain the same, you need to have a lower initial boiling point for the feedstock in the upstream units.
It indicates that you have pushed the light components too far downward; it’s necessary to reduce the reflux rate and increase the temperature in order to vaporize the light components!
The dry point of crude gasoline has increased, while the initial distillation point of diesel has decreased; as a result, the overlap between the two fractions has increased. There is clearly a problem with the operation; it is recommended to compare the parameters before the adjustment with those after the adjustment, make fine tweaks, and observe the changes. The recommended measures include: appropriately increasing the steam supply to the stripping tower ； Reduce the mid-stream circulation flow rate; increase the temperature of the diesel extraction layer provided that the diesel’s freezing point is within acceptable limits.
There is no room for further increase in the 95% point for diesel; it has already reached the upper limit required by regulations. How should we understand improving diesel to make adjustments?
Oh, in that case, we can’t mention the diesel extraction layer temperature. The backflow at the top should be reduced. Furthermore, a high 95% diesel point indicates that some heavy oil has entered the middle section; this can be controlled by increasing the flow rate of the bottom circulation reflux and the reprocessed oil returning to the tower.
Is the mid-stream backflow forcing gasoline into the diesel?
By raising the temperature, the light components evaporate, and 95% of the diesel is removed. This is exactly what happens here: the initial boiling point is around 185 degrees, while 95% of the diesel is removed at 365 degrees
Generally, there are two outlets for light diesel that can be adjusted; isn’t such a procedure available where you are?
It should mainly be a problem with the operation at the top of the distillation column
Control a return tower temperature! Maintain the temperature gradient in the fractionation tower to control the amount of rich absorbent oil returning to the tower! Under the requirements for dry gas! Keep it as low as possible; by increasing the temperature at which the vapor is extracted, the dew point of diesel increases! Maintain the amount of diesel stripping steam