Behavior of sulfur oxides (SOX) in nonferrous metal smelters and implications on future control and emission estimation.
This study jointly conducted 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 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 component. These factors were relatively certain once the production was designed. During 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 national inventory (10% at the most) due to the lack of NFMS, we suggested the attention on SOX emissions from sectors using high-sulfur raw materials in pyro-process. 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.