Abstract: An industrial practice of blending feedstock for FCC unit with vacuum gas oil from the fourth side-line has carried out in CNOOC Huizhou Petrochemical Company, which can optimize the product structure of the whole plant and improve economic benefits. The results showed that after blending ratio of the vacuum gas oil to 8.59%, the total liquid yield was decreased by 0.77 percentage point, the coke yield was increased by 0.33 percentage point, and the energy consumption was increased by 116.47 MJ/t; the molar ratio of H2/CH4 of catalytic dry gas was increased slightly, the olefin content of liquefied petroleum gas and gasoline were increased by 0.21 percentage point and 1.3 percentage points, respectively, the gasoline density（20 ℃） was increased by 2.1 kg/m3 and RON was increased by 0.6 unit, the aromatics content of gasoline was increased by 1.9 percentage points, and the benzene content of gasoline was decreased by 0.08 percentage point. The contents of Ni and Ca on equilibrium catalyst were increased by 388 μg/g and 2 462 μg/g, respectively, and would continue to increase over time, which would threaten the long-term operation of FCC unit. Measures should be taken to ensure long-term operation of FCC unit, such as optimizing crude oil varieties, intensifying crude oil desalination, increasing catalyst replacement speed, and adding multi-functional metal passivator.

Key words: FCC, MIP, HVGO, nickel, calcium