Abstract: In order to reduce the SO₂ mass concentration in the emitted flue gas of sulfur recovery unit, the process and technical transformation of the unit were carried out. The waste gas from liquid sulfur pool was introduced into Claus furnace and hydrogenation reactor respectively. The comparison and analysis of the two processes were carried out from the aspects of process principle, technical transformation input, operation effect and energy consumption. The results showed that: (1) although the operation energy consumption of waste gas from liquid sulfur pool into Claus furnace was high, the emission reduction effect was obvious, the process operation was stable, and the quality of liquid sulfur products could be guaranteed; (2) the process of liquid sulfur pool waste gas into hydrogenation reactor also had the effect of emission reduction and low energy consumption. However, due to the limitation of hydrogen content at the outlet of quench tower, the energy-saving effect of oxygen resistant low-temperature hydrogenation catalyst could not be fully utilized, and the ability to resist upstream fluctuation and prevent SO₂ penetration decreased.