Abstract: During the operation of the residue hydrotreating unit, it was found that the sulfur content of the hot low-pressure separator oil increased abnormally and the quality of the hydrotreated residue was unqualified. Based on impurity removal rate analysis, heat analysis of heating furnace and FT-ICR MS analysis, it was determined that there was internal leakage in the high-pressure heat exchanger, and the estimated leak at the end of the run was close to 15%. After the shutdown, a water pressure test was conducted on the heat exchanger, and it was judged that the cause of the leakage was due to the small pre-tightening force of the top pressure bolt. In the early stage of operation, the pressure drop of the reactor was relatively small, and the heat exchanger operated normally. As the operating time increased, the pressure drop between the tube side and the shell side increased, the pressure on the shell side exceeded the rebound force of the metal coating pad, and the leakage occurs at the sealing point between the tube side and the shell side of the heat exchanger. The feed oil with high impurity content directly leaked into the hydrotreated product, resulting in the increasing impurity content of the product. It is suggested that the structure of metal toothed gasket and steel ring should be used to replace the metal cover cushion, and the pre-tightening force of heat exchanger should be re-calculated to ensure long-term efficient operation of the high-pressure heat exchanger.

Key words: residue hydrotreating, high-pressure heat exchanger, internal leakage