Abstract:  This paper introduces the feeding process of sulfur transfer agent injection system in FCC unit and its effect on the products. After the injection of sulfur transfer agent, the removal rate of SO₂ in flue gas reaches 50.1%, and the proportion of flue gas sulfur in feed sulfur decreases from 2.81 wt% to 2.27 wt%. Meanwhile, the test run results of industrial tests show that the sulfur contents of dry gas and LPG increase significantly after adding sulfur transfer agent, and no adverse effects are found on the properties of LPG, gasoline and light diesel products. In addition, sulfur transfer agent has no significant negative effects on the particle size distribution, activity or selectivity of the catalysts in FCC unit. However, the use of sulfur transfer agent leads to changes in the process gas of sulfur recovery unit, and the latent sulfur in acidic gas reaches 107.5% of the normal value, so the sulfur recovery unit should be designed to have higher operating flexibility. When the SOx concentration in flue gas is high, the combination process of sulfur transfer agent and wet desulfurization can be adopted. The NaOH consumption can be reduced from 1217 kg/h to 486.8 kg/h, the saline sewage can be reduced from 19.06 t/h to 17.1 t/h, and the salt content can be reduced to 4.87%, so it can be discharged directly without installing sulfate crystallization facilities, thus reducing the unit cost.

Key words: sulfur transfer agent, fluid catalytic cracking/FCC, sulfur recovery