Abstract: Unit A was the first fixed bed residue hydrogenation unit for processing low sulfur and high nitrogen residue in China. Its mass fraction of sulfur(1.38%) was lower and mass fraction of nitrogen(0.68%) was higher. The feedstock properties of the fixed-bed hydrogenation unit for high sulfur residue were significantly different from those in the past. In order to analyze the hydrogenation reaction characteristics of low sulfur and high nitrogen residue, a comparative experiment was carried out in the laboratory with the hydrotreating of high sulfur residue, and the operating data of industrial units of processing low sulfur and high nitrogen residue and high sulfur residue were also be compared. In the pilot test, the same catalyst gradation was used under the conditions of reaction temperature 375.5 ℃, H2 partial pressure 15.0 MPa, liquid volumetric space velocity 0.23 h^-1, and volume ratio of H2/oil 700. The results showed that the reduction rate of carbon residue was 49.83% for low sulfur and high nitrogen residue, and 69.10% for high sulfur residue. In commercial application, the carbon residue reduction rate was 48.14% for low sulfur and high nitrogen residue with 11.32% of carbon residue in unit A, and 55.39% for high sulfur residue with 11.50% of carbon residue in unit B. The results of both laboratory and commercial application showed that it was difficult to hydrogenation the carbon residue precursors in low sulfur and high nitrogen residual oils. Unit A has completed 6 cycles of operation since it was built. The average sulfur content in the feedstock in each cycle was no more than 1.51%, and the average nitrogen content in the feedstock was no less than 0.62%. By analyzing the operation of Unit A, it was found that the scaling of the high-pressure heat exchanger made it difficult to increase the reaction temperature in the middle and end of run. The proportion of vacuum residue in the feedstock had a significant impact on the length of the operating cycle. The operating cycle was short when the proportion of vacuum residue was high, and vice versa. The measure to eliminate the operation bottleneck of the unit is to retrofit the high-pressure heat exchanger and reactor system.

Key words: low sulfur and high nitrogen, residue, fixed-bed hydrotreating, operation analysis, eliminating bottlenecks