PURPOSE: A liquid-phase hydrogenation column and a gas-phase hydrogenation column are connected in series, crude heavy oil is catalytically hydrogenated in liquid phase into light and medium fractions, then, the formed gas is subjected to gas-phase catalytic hydrogenation, thus enabling the use of the catalyst in high concentration and the prolongation of catalyst life and increasing the efficiency.
CONSTITUTION: At first, a heavy oil containing suppended catayst such as MoS2 in high concentration is provided and sent from the line 34 to the feed tank 12 where it is mixed with the starting oil. Then, the mixture is heated with the heat exchanger 15 and the preheater 16 and fed together with an excessive amount of hydrogen into the liquid-phase hydrogenation column 17 continuously where the heavy oil is catalytically hydrogenated, e.g., at 390-460oC and 130- 300 atmospheric pressure. The resultant gas stream mainly consisting of vapors of crude light and medium fractions and unreacting hydrogen is continuously taken out from the top of the column 17 and sent into the gas-phase hydrogenation column 19 for catalytic hydrogenation. Then, the vapor containing the formed light fractions and unreacting hydrogen is cooled with the heat exchanger 15 and separated in the low-temperature separation column 21 and the former is taken out of the line 22, the latter is circulated through the line 14 into the reaction system.