Abstract: The load of atmospheric distillation unit is greatly increased when the feed blends with the light crude oil or the light sump oil recycled. When the reflux of the tower is greater than or equals to 22t/h, the pressure drop between the top of the tower and the feed entering position increases from 20kPa to 40kPa with the overlap of boiling range of the top oil and the first side line oil. It is found that there are a lot of fouling deposits at the 9-16 layer trays, almost blocking the whole tray. The deposits were characterized by the elemental analysis, XRD and XRF. The results indicate that the main component of the deposit is NH4FeP2O7, confirmed by the simulation test of high temperature corrosion inhibitor. Finally, the optimization solutions for the problem are proposed.

Key words: fouling deposit, analysis, characterization, high temperature corrosion inhibitor, blockage