Abstract: The major problems of FCCU flue gas in wet purification process were analyzed and the countermeasures were proposed. The problems included blue smoke tail, ammonia escape of SCR, complex acids and high salt content in scrubbing solution, and visual white smoke from purified flue gas. The sulfur transfer agent to recover SO_x from source was recommended as the main measures. After using the sulfur transfer agent, the SO_x removal rate of the flue gas was 50% to 95%, the blue smoke tail disappeared and the ammonia escape of SCR was reduced by using automatic precise control technology of ammonia injection. Temperature should be considered for pH control of the scrubbing tower. It is necessary to consider the recovery of particulate matter from the source to reduce the wet recovery

Key words: catalytic cracking, flue gas, purification, measures, pollutant