Since operations started, the catalytic diesel has not been functioning properly
Thread Content
Our unit was shut down for maintenance in January and has been restarted recently. But diesel has always been as dark as reprocessed oil, and even the color intensity of the intermediate fraction is abnormal. I’ve changed shifts several times, but there’s been no improvement. I am now turning to all the experts for help. We have checked the mid-stream and diesel system processes, so it should be possible to rule out oil crossover. At the start of operation, the liquid levels in the crude oil buffer tank and the bottom of the distillation tower were too high, which could have led to overflow onto the middle and upper tray levels; however, in our case it even reached the diesel stripping tower, and it took only one shift to resolve the issue. In the case of tower flooding, there are temperature differences between various sections, and these differences are similar to those observed before. There were also no abnormalities in the reflux and reboiler temperature at each section. It was removed and cleaned during the tray maintenance, so there should be no problem. Everyone, have any of you masters encountered similar situations? Do you have any suggestions? Please help everyone. Thank you.
The darkening of the diesel color is likely due to the heavier components from the lower part of the distillation tower being carried up to the middle section. It is possible to check whether the flow rate of the circulating slurry, the flow rate in the second section, the vapor phase temperature, and the temperature in the second section are within normal ranges, in order to determine whether the operation in the lower part of the distillation tower is proper.
It is very likely that carelessness during the initial operation led to heavier components entering the diesel outlet, contaminating the entire diesel pipeline system； I think as long as this portion of diesel is completely replaced, the color of the diesel distilled from your plant will definitely improve!
Check whether the heat exchanger for diesel and raw materials has internal leaks; if there are leaks, the diesel returns to the distillation tower via the rich absorption oil； If there is any heat exchange with the raw material or slurry, check as well the distillation range analysis of oil samples before and after passing through the heat exchanger; although the color is dark, the reformed fraction will be high in the case of a leak. If the gasoline dry point is normal and the pressure drop in the fractionating tower is normal, it might be a leak in the heat exchanger. If the tray is turned over, the pressure drop will decrease, and the re-refining will be light. Blowing over just a few layers generally won’t have a significant impact. Check the heat exchanger.
Thank you all; everything is back to normal now. The equipment should be fine. After we increased the outlet of the reprocessed oil, we started using the reprocessed oil for refining, and the quality of diesel improved gradually. Prior to this, the reprocessed oil would go directly into the distillation tower via the return line. Please discuss theoretically why this is the case. Thank you again.
I see. Is there a problem with the trays in the distillation column, since the column was flooded earlier?
By increasing the amount of reflux in the refining process, the thickness of the liquid phase in the upper and middle layers is reduced, which helps to improve the situation regarding tower flooding; as a result, the separation efficiency improves and the product meets the required standards.
The reprocessed oil was not completely extracted; the oil that was extracted was returned to the distillation column via the emergency bypass. A large amount of components from the reprocessed oil accumulated within the column, resulting in very high loads above and below the extraction stage, which caused entrainment and affected the quality of the diesel. All the fluids that need to be extracted from each measurement line in the fractionation system must be extracted; otherwise, problems will definitely arise.
I personally think the analysis on floor 8 makes quite a lot of sense! ! ! ! ! !