Abstract: During the presulfiding period of the hydrotreating unit, the SO₂ concentration in the flue gas of the heating furnace has increased abnormally or even exceeded the standard, and enterprise was forced to stop the recovery of torch gas. By analyzing the sulfur types and content of circulating hydrogen, low separation gas and flare gas during the start-up of presulfiding period, it is speculated that the methyl mercaptan and methyl sulfide produced by the step-by-step decomposition of the sulfurizing agent enter the fuel gas system with the flare gas. The SO₂ produced by the combustion of methyl mercaptan and methyl sulfide causes the concentration of SO₂ in the flue gas of the heating furnace to exceed the standard. This problem can be solved by optimizing the desulfurization solvent of torch gas, using ex-situ true sulfidization catalyst and using new sulfiding agents.

Key words: hydrotreating unit, presulfiding, flue gas of the heating furnace, SO2, desulfurization solvent, ex-situ true sulfidization, new sulfiding agent