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

Abstract

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 ultralowemission 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 PM 2.5 emitted from these FGD systems are dominated by CaSO 4 , (NH 4 ) 2 SO 4 , CaSO 4 + 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.

Direct Observation of Sulfate Explosive Growth in Wet Plumes Emitted From Typical Coal‐Fired Stationary Sources

“…High 23 Na + , 36 (Figure 2a). These peaks indicate that the aerosols at the WFGD inlet are directly formed during combustion in the CFPP boiler (fly ash), consistent with our previous study on CFPP emissions (Ding et al, 2019). , were much higher in the negative ion spectrum at the WFGD outlet, while the signals of 17 NH 4 + and 40 Ca + slightly increased owing to the conversion of NH 3 and WFGD slurries.…”

Gaseous and Particulate Chlorine Emissions From Typical Iron and Steel Industry in China

“…Both Cl FPM and Cl CPM can contribute to the chlorine in PM (i.e., Cl PM = Cl FPM + Cl CPM ) after the flue gas is released into the atmosphere. The significant difference in the removal efficiencies of Cl FPM among the different FGD systems is primarily caused by their removal mechanisms in the dry/wet FGD systems, as detailed in our previous study (Ding et al, 2019). Cl FPM was removed with an efficiency of up to 92.8 ± 2.1% by the activated coke FGD through adsorption and filtration, whereas the limestone and ammonia WFGD processes can convert Cl Inorganic gases into particulate Cl via heterogeneous condensation with in the desulfurization slurries.…”

“…Except the steel rolling process (which produces unorganized emissions, i.e., emissions directly leaked into the atmosphere without an installed sealing equipment), emissions from most of the traditional iron and steel production processes were measured and estimated in the field. The desulfurization and dust removal facilities typically used wet/dry FGD, ESPs, and bag filters, whereas wet ESPs (WESP) were employed following wet FGD (WFGD) to further remove dusts and slurries, as detailed in our previous study (Ding et al, 2019). The three tested sintering processes (labeled as 1#, 2#, and 3#) employed limestone or ammonia WFGDs combined with WESPs and activated coke dry FGD, respectively.…”

“…Various FGD technologies have been developed for sintering flue gases, including wet FGD (such as limestone/ammonia wet FGD), semidry FGD (such as circulating fluidized bed‐FGD), and dry FGD (such as activated coke FGD) technologies. The chemical composition of PM 2.5 at the stack exit depends on the FGD technologies and desulfurizers employed (Ding et al, 2019). Chlorine‐rich materials coburn incompletely with fuel and possibly release high concentrations of organic/inorganic chlorine to the flue gases.…”

“…APCDs = air pollution control devices; ESP = electrostatic precipitator; L-WFGD or A-WFGD = lime-gypsum or ammonia wet flue gas desulfurization combined with wet electrostatic precipitator; AC-FGD = activated coke dry flue gas desulfurization; CFB-FGD = circulating fluidized bed semidry flue gas desulfurization combined with fabric filter (FF); SCR = selective catalytic reduction. a Reported byDing et al (2019).…”