Behavior of Sulfur Oxides in Nonferrous Metal Smelters and Implications on Future Control and Emission Estimation

This study jointly conducted a field investigation and thermodynamic model simulation in three nonferrous metal smelters (NFMS) to identify sulfur oxides (SOX) formation, transformation, and emissions in the flue gas. Most of SOX was released as sulfur dioxides (SO₂) at the outlet of the furnace with the molar proportion of sulfur trioxides (SO₃) of 1.0-4.1%. The formation of SO₃ in smelters depended on temperature, material composition, and flue gas components. These factors were relatively certain once the production was designed. During the use of air pollution control devices (APCDs), SO₃ removal alternated with its formation in the APCDs of the smelting/roasting step. Deep clean measures could not ensure standard emissions of SO₃ in all smelters. Under the strict production and emission requirements, we recommended the combined effort of production design, parameter optimization, and deep clean measures to control SO₃ pollution. In addition, recognizing the underestimation of the national inventory (10% at the most) due to the lack of emissions from NFMS, we suggested the attention on SOX emissions from sectors using high-sulfur raw materials in the pyroprocess. Besides, the higher potential of SO₃ on secondary particle formation highlighted the distinction of SO₃ and SO₂ emissions in inventories for better evaluation of their environmental impact.