Abstract: The flue gas desulfurization unit of a 2.8 Mt/a catalytic cracking unit in a domestic refining and chemical enterprise has successfully put into operation the "sodium-based desulfurization extracting sodium bisulfite" green circular process demonstration project. This article briefly introduces this process, analyzes common problems based on actual on-site operation conditions, and provides effective solutions.This innovative process achieves efficient removal and resource utilization of SO₂ through a dual-tower system. While meeting the ultra-low emission standards for flue gas (the mass concentration of SO₂ is not grater than 25 mg/m³, the mass concentration of dust is not grater than 10 mg/m³), it converts the desulfurization products into industrial-grade anhydrous sodium bisulfite products. The unit adopts a "concentration tower-absorption tower" collaborative operation mode, combined with salting-out crystallization technology, achieving the dual environmental protection goals of near zero discharge of salt-containing wastewater and commercialization of by-products. After one year of continuous operation verification, the system emission indicators have stably reached the design values, the purity of the post-treatment unit products has been maintained at over 80%, and the overall operating pressure drop has been controlled within the range of 1200—1500Pa, verifying the technological progressiveness and engineering feasibility of this process in the field of catalytic cracking flue gas treatment.

Key words: catalytic cracking, flue gas desulfurization, sodium sulfite, near zero wastewater discharge