The boiling range of the low-end tail oil from the fractionation tower is not within the specified limits
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The cracking zone side stream is drawn off to a fractionation tower, while the diesel obtained from this side stream enters a stripping tower. Recently, the initial boiling point of the bottom residue oil has been low, with 4% of the material distilling at 365 degrees. Adjusting the steam supply to the bottom of the tower did not result in any changes; however, increasing the reflux at the middle section led to a significant increase in the initial boiling point, with only 2% of the material distilling at 365 degrees. I would appreciate it if you could help analyze the impact of reflux at the middle section on the boiling range of the bottom residue oil
Ensure that the diesel recovery is of satisfactory quality; increase the draw rate from the side line, while keeping the mid-section reflux unchanged. The initial boiling point will rise.
This is easy to understand, but what causes the increase in the initial boiling point due to increased backflow in the middle section?
In your company’s gas tower, the vapor phase stream returns to the side extraction column; with the heat load of the gas tower remaining unchanged, less heavy components enter the column for distillation, resulting in more vaporization in the vapor phase. Now that the gas phase volume in the stripping tower has increased and there are fewer light components, the initial boiling point has risen.
The circulation volume in the middle section has increased; why is there less overlap between the bottom residue oil and diesel at 365°C?
The circulation rate in the middle section of the distillation column was originally 175 t/h; after it was increased to 198 t/h, the proportion of the tail oil product distilled at 365°C decreased from 4% to 2%
After increasing the mid-stage circulation, does the temperature entering the tower after circulation increase?
No, the temperature returning to the tower remains essentially constant at 176°C
Has your fuel reserve increased then?
Increasing the mid-section reflux improves the separation efficiency of the distillation column, resulting in less overlap between the tail oil and diesel