This project is an acid-making tail gas desulfurization system of CNOOC Hubei Dayukou Chemical Co., Ltd. The company currently has a set of 800,000 tons/year and two sets of 310,000 tons/year sulfuric acid production units. The 800,000-ton/year sulfuric acid plant was completed and put into operation in 2012, using a 3+2 two-turn two-suction process. In this project, a new set of tail gas desulfurization system is built in the boundary of the existing C series 800kt/a sulfuric acid plant to treat the flue gas at the exit of the secondary suction tower. The amount of flue gas is 170,000 standard square meters, and the SO2 concentration is 800mg/Nm3. The ammonia desulfurization process is used to make the SO2 concentration below 30mg/Nm3. It is discharged through the top chimney, and the by-product ammonium sulfate solution is sent to the original system for treatment. The project was signed in February 2019 and started operation in November 2019.