Unexpectedly Increased Particle Emissions from the Steel Industry Determined by Wet/Semidry/Dry Flue Gas Desulfurization Technologies.

"Ultralow-emission" standards have started to be implemented for steel plants in China. Flue gas desulfurization (FGD) systems integrating desulfurization and dedusting, common end-of-pipe technologies before the stacks, have been a key process for controlling the complexity of sintering flue gas to meet ultralow-emission requirements. This study reports comprehensive analysis of the influence of wet/semidry/dry FGD systems on particulate emissions via a field investigation of five typical sinter plants equipped with various FGD devices. The size distribution and mass concentration of particulate matter (PM) are adjusted to different ranges by these FGD systems. Chemical analysis of the PM compositions shows that 20-95% of the mass of inlet PM is removed by FGD systems, while it is estimated that approximately 17, 63, 59, and 71% of the outlet PMs are newly contributed by desulfurizers and their byproducts for the tested wet limestone, wet ammonia, semidry circulating fluidized bed, and activated coke FGD systems, respectively. The newly contributed compositions of PM2.5 emitted from these FGD systems are dominated by CaSO4, (NH4)2SO4, CaSO4 + CaO, and coke carbon, respectively. These results suggest that the deployment of FGD technology should be comprehensively considered to avoid additional negative impacts from byproducts generated in control devices on the atmosphere.