Abstract: In view of heat exchange efficiency reduction of the high pressure heat exchangers of VGO hydrocracking and the pressure drop continuously rise，the high pressure exchangers were cleaned and the scale samples were analyzed. The X-ray fluorescence spectrometer（XRF），scanning electron microscope（SEM）and X-ray diffractometer（XRD） and other analysis techniques were used to analyze the sample after toluene extraction. The results showed that the main inorganic components in scale sample were Fe2P4O12 and FeS. In addition, it also contained a small amount of inorganic materials containing Si and Na and a small amount of organic scales. In view of this, it is suggested that refineries strictly control the carrying of phosphorus-containing substances in hydrocracking feed oil, and protect equipment and pipelines from corrosion by naphthenic acid as much as possible.

Key words: hydrocracking, high pressure heat exchanger, scaling, ferric phosphate, ferrous sulfide