Abstract: Because of the shutdown of the fixed-bed residue hydrotreating unit in an 8.0 Mt/a refinery, the cost of clean gasoline production increased remarkably. Based on the four-year turnaround cycle of the refinery, analyzing the main factors influencing the running time of fixed-bed unit, the relationship between the operating period and feedstocks CCR, the catalyst grading scheme and the activity stability. Furthermore, the optimal methods were suggested. The main factors influencing the operating period of fixed-bed unit are feedstock properties and catalyst grading scheme. From the overall trend, the higher CCR in the feedstocks, the shorter the operating time of the unit, indicating that the higher the proportion of vacuum residue, the shorter the operating cycle. The catalyst grading scheme affects the hydrotreating activity stability of grading catalysts. The optimal of catalyst grading scheme must balance the ability of contain metals and the hydrotreating activity stability of grading catalysts. To achieving a 2-year operating period of fixed-bed residue hydrotreating unit, the optimal following measures are proposed,i.e. maintaining the proportion of vacuum residue about 50% in its feedstocks,adding an appropriate amount of FCC light cycle oil to the feedstocks,operating at lower reaction temperature and higher hydrogen partial pressure. In addition, refining enterprises should select a suitable catalyst licensor, and licensors should also continue to carry out research and development of catalysts and their grading technologies.

Key words: fixed-bed, residue hydrotreating, cycle-length, optimization