Abstract
ABSTRACT Iron and steel industry is crucial for economic development. However, large exhaust volume and complex feeding of the steel-making process results in enormous emissions of air pollutants such as particulate matter (PM), sulfur oxides (SOx), nitrogen oxides (NOx), polycyclic aromatic hydrocarbon (PAHs) and carbon monoxide (CO). This study sampled and analyzed the concentrations of PM, PAHs, SOx, NOx and CO at the inlet and outlet of the air pollution control devices (APCDs) adopted in sintering process (SP) and electric arc furnaces (EAF), respectively, to evaluate the performance of APCDs and emission characteristics of these air pollutants. The results show that filterable PM (FPM) concentrations measured at stacks of SP and EAF are 8.2 ± 1.3 and 13.6 ± 2.2 mg Nm–3, respectively. The FPM2.5 concentrations emitted from SP and EAF are 1.8 ± 0.5 and 3.2 ± 1.1 mg Nm–3, respectively, while the condensable PM (CPM) concentrations emitted from SP and EAF are measured as 37.7 ± 1.3 and 3.4 ± 0.8 mg Nm–3, respectively. Moreover, the flue gas desulfurization (FGD) and selective catalytic reduction (SCR) equipped in SP removed 82% and 58% of SOx and NOx, respectively, whereas SOx and NOx emitted from EAF are relatively low (< 1 ppm). The overall PAH removal efficiencies achieved with the APCDs adopted by SP and EAF are 72% and 26%, respectively. For total toxicity equivalency quantity (TEQ) PAH concentrations, similar results for SP (5.45 µg-BaPeq Nm–3) and EAF (4.74 µg-BaPeq Nm–3) are obtained. Moreover, the diagnosis ratios of FL/CHR, FL/(BaA + CHR), Pyr/5-MC and Pyr/(BaA + CHR) are suggested as the indicators for EAF. The emission factors calculated indicate that operating conditions of the APCDs in the SP investigated are well controlled. The concentrations of air pollutants emitted from SP investigated are lower than other studies. On the other hand, the concentrations of FPM and PM2.5 emitted from EAF are higher than other studies. However, NOx, SOx and PAHs are well controlled. Moreover, the CO emission factors calculated from these two steel-making processes are higher than most reports. Overall, the operation of APCDs should be improved to reduce air pollutants emitted from these two steel-making processes.
Highlights
Iron and steel industry is crucial for economic development
The moisture, oxygen, and CO2 contents measured at the sintering process (SP) stack are 20%, 13.9%, and 7.2%, respectively, which are close to that measured at the air pollution control devices (APCDs) inlet
The carbon monoxide (CO) concentrations measured at the APCD inlet and stack are 5,857 and 5,208 ppm, respectively, confirming that CO removal achieved with existing APCDs is insignificant
Summary
According to the statistics released by the World Steel Association, annual global crude steel production reached 1,869 million tonnes in 2019, and the output has been increasing since 1950 (Association 2020). The crude steel production in Taiwan (22.4 million metric tons in 2017) ranked eleventh in the world, accounting for 1.33% of global output, of which crude steel produced by SP and EAF accounted for 61% and 39%, respectively. According to the statistical data released by the Taiwan EPA, PM, PM2.5, SOx, NOx and CO emitted from the steel-making process accounted for 15.9%, 17.5%, 16.7%, 13.0%, 8.31% and 82.1% of industrial emissions (TEDS 10.0, 2016) in Taiwan, respectively, confirming the importance of the steel-making process as a source of air pollutants. Previous studies indicate that iron and steel industries are major contributors of PM and persistent organic pollutants (POPs) in the vicinity (Amodio et al, 2012; Van Thuong et al, 2014; Xiao et al, 2013)
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