Performance on desulfurization and denitrification of one-step produced activated carbon for purification of sintering flue gas

An innovative one-step process for activated carbon production from low-rank coal is proposed in this research by applying oxidized pellets as activator. The new process can realize synchronous production of the activated carbon and direct reduction iron through combination of carbonization and activation of low-rank coal in one step while no solid wastes were discharged. The desulfurization and denitrification performance of the obtained activated carbon was also evaluated on the simulative sintering flue gas in comparison with one type of commercial activated carbon. The results indicated that a superior activated carbon with high specific surface area of 370.42 m² g^-1, iodine sorption value of 695.13 mg g^-1, compressive strength of 315 N·per^-1and abrasive resistance of 96.61%, can be prepared under suitable conditions of activation temperature at 850 °C for 140 min with C/Fe mass ratio of 2.5. Meanwhile, the direct reduction iron has a metallization ratio of 88.31%. The activated carbon has a preferable desulfurization performance with the breakthrough sulfur capacity of 5.463 mg/g and breakthrough time of 46.33 min, and single denitrification performance with the breakthrough nitric capacity of 1.935 mg/g and breakthrough time of 90.17 min at flue gas temperature of 80 °C, airspeed ratio of 8370 h^-1, gas flow of 1.8 m³/h, and oxygen concentration of 16%. The denitrification of activated carbon in the simultaneous desulfurization and denitrification process can be improved by catalytic reduction via the transformation from NO to N₂. The good results show that this process has a bright future with high technical and economic feasibility.

Air pollutant emission and reduction potentials from the sintering process of the iron and steel industry in China in 2017

The iron and steel industry (ISI) is one of the most energy-intensive industries in China, which makes a substantial contribution to the emissions of air pollutants. Among the various manufacturing processes, sintering is the major emitting process, which shares over half of the emissions of sulfur dioxide (SO₂), nitrogen oxide (NO_x) and particulate matter (PM) for the entire industry. In this study we made a comprehensive evaluation of the air pollutant emissions from the sintering process of China's ISI in 2017 based on the Continuous Emission Monitoring System (CEMS) database and estimated the future reduction potentials. We found that there was a general decreasing trend of emission concentrations in the sintering flue gas in response to the strengthened emission control policies, but the mild increase of the oxygen content in the second half of the year flattened the decreasing trend, indicating the necessity for simultaneous control of the oxygen content in the flue gas. Despite the relative high standard-reaching rates of 90% to the emission concentration limits in GB 28662-2012, the standard-reaching rates to the ultra-low emission standards were only 12%, 40% and 27% for NO_x, SO₂ and PM respectively, with the lowest value mostly occurred in the western provinces. In 2017, the NO_x, SO₂ and PM emissions from the sintering process were 378.6 kt, 169.0 kt and 51.9 kt, respectively. If the ultra-low emission standards were met, the corresponding NO_x, SO₂ and PM emissions would decrease by 69.9%, 52.9%, and 56.4% respectively, illustrating large emission reducing potentials by achieving the ultra-low emission standards.

Influence of H2O and SO3 on fine particles coagulation for sintering flue gas after desulfurization in an alternating electric field

Electric coagulation of fine particles has been studied in the simulated sintering flue gas after semi-dry desulfurization to quantify the influence of H₂O and SO₃. The electric coagulation platform has a DC charging zone and an AC coagulation zone. Fine particles were divided into different diameter intervals to deeply explore the impact of H₂O and SO₃, including less than 0.15 μm (PM_0.15), 0.15-0.5 μm (PM_0.15-0.5) and 0.5-1 μm (PM_0.5-1). The particle charge, mass fractions of fine particles, and the mean diameter are measured and compared under water and SO₃ atmosphere. The experiments showed that the increasing AC voltage helps particles larger than 0.5 μm to coagulate but has little effect on the rest particles without H₂O or SO₃. Both H₂O and SO₃ enhance the PM_1.0 AC coagulation. When flue gas relative humidity went up from 20 to 80%, the charge per particle maximally increased by 120%, as well as the mass fraction of PM_0.5-1, PM_0.15-0.5, and PM_0.15 decreased by 83.2%, 64.5%, and 66.6%, respectively. When the SO₃ concentration rose up from 0 ppm to 12.3 ppm, the charge per particle maximally increased by 100%, as well as the mass fractions of PM_0.5-1, PM_0.15-0.5, and PM_0.15 decreased by 54.5%, 28.6%, and 33.3%, respectively. The impact of water and sulfuric mist on the particle intervals was sequenced as: PM_0.5-1 > PM_0.15 > PM_0.15-0.5. The influence on PM_1.0 AC coagulation was sequenced as H₂O > sulfuric mist > AC voltage. Through data regression, H₂O had approximate linear correlation with the particle mass fractions while the impact of sulfuric mist was non-linear. The interparticle forces were calculated to analyze the dominant force of particle AC coagulation with water: liquid bridge force > Coulomb force >  > van der Waals force. The liquid bridge force indicated that liquid film was form on the surface of fine particles when water or sulfuric mist was added into the system which was the main reason enhancing the AC coagulation.

Trends in air pollutant emissions from the sintering process of the iron and steel industry in the Fenwei Plain and surrounding regions in China, 2014-2017

China is the largest iron and steel producer and consumer in the world. The iron and steel manufacture, especially the sintering process, is energy-intensive, and contributes substantially to air pollutant emissions in China. Compared with other regions, the Fenwei Plain, a coal base, has a heavy industry concentration, and high pollutant emission total amount. In addition, urban air pollution has rebounded, and the pollutants concentrations in many cities have increased rather than decreased. In this study, we investigated the inter-annual trends of particulate matter (PM), sulfur dioxide (SO₂) and nitrogen oxide (NO_x) from the sintering process of iron and steel industry (ISI) in the Fenwei Plain and the surrounding regions in China from 2014 to 2017 based on the Continuous Emission Monitoring System (CEMS). We found that the oxygen content of the flue gas is the key to judge whether the sintering flue gas air pollutant emission concentration can meet the standard. Therefore, we adopted the converted concentration by the reference oxygen content in the final analysis. Overall, the SO₂ and PM emission concentrations exhibit a downward trend from 2014 to 2017, in response to the strengthening of the emission control policies and standards in the ISI, whereas the NO_x emission concentration did not change significantly during the same period The emission factors (EFs) of PM, NO_x and SO₂ obtained in this study are lower than previous estimates. In 2017, the SO₂ and PM emissions were 27% and 32% lower than the levels in 2014.While NO_x was 22% higher than the level in 2014. Our study confirmed the effectiveness of current emission control policies and standards in the iron and steel sector. However, the levels of NO_x emissions were still high until 2017, illustrating the urgent need for more advanced emission control technologies to further reduce NO_x emissions from the sintering flue gas in China.

Emission characteristics of PM, heavy metals, and dioxins in flue gases from sintering machines with wet and semi-dry flue gas desulfurization systems

In iron and steel industry, sintering process releases large amount and different kinds of pollutants. Most sintering plants had applied the dust removal system and the flue gas desulfurization (FGD) system for exhaust treatment in China. Previous studies of FGD systems were focused on the removal of air pollutants from coal-fired boiler, rather than in the iron ore sintering process. In this study, PM, heavy metals, and dioxins were sampled at a China typical sintering plant with both wet and semi-dry FGDs. The results showed that the PM removal efficiencies of the wet and semi-dry FGDs were 29.44% and 22.28%, respectively. The size distributions of PM were at the range of 0.7~4.7 μm in the inlet flue gases of both FGDs. The overall removal efficiencies of heavy metals were above 65%. In both outlet flue gases, Pb as the most elements accounted for 93.33% of total at the wet FGD, while Pb, Cr, and Zn accounted for 76.34% at the semi-dry FGD. The proportions of gaseous heavy metals in the inlets of both FGDs were improved than those in the outlets. Furthermore, the total emission amounts of dioxins in both inlets and outlets of the flue gases were 0.0385 ng-TEQ/m³ and 0.0248 ng-TEQ/m³ at the wet FGD and 0.0078 ng-TEQ/m³ and 0.0050 ng-TEQ/m³ at the semi-dry FGD, respectively. The overall removal efficiencies of dioxins were all above 35%. The polychlorinated dibenzofurans (PCDFs) ratio in the dioxins lightly increased from 84.46 to 88.80% through wet FGD, while it decreased from 80.83 to 44.35% in semi-dry FGD.

Life cycle assessment of ultra-low treatment for steel industry sintering flue gas emissions

The largest contributor to pollutant emissions is the sintering process in steel industry. Ultra-low emission policy for the Chinese steel industry states that emission concentrations of particulate matter, SO₂ and NO_x should not exceed 10, 35 and 50 mg/m³ respectively. The emission concentrations of the steel industry are the same as the ultra-low emission policy for the coal-fired power industry, but the pollutant control technologies of the two industries are different. Life cycle assessment method is applied to analyze the latest ultra-low treatment process for sintering flue gas emissions which includes electrostatic precipitation, ozone oxidation, wet desulfurization, wet denitration, condensation dehumidification and wet electrostatic precipitation. Following this novel ultra-low emission treatment, the concentrations of particulate matter, SO₂, NO_x, and PCDDs in the sintering flue gas decreased very significantly, attaining the new emission standard. With 1 ton of sinter as the functional unit and "cradle to gate" as the system boundary, the environmental impact of the process is 0.1811 and the total economic cost is 172.79 RMB, of which internal cost is 34.64 RMB and external cost is 138.15 RMB. The main environmental impacts result from applying the wet denitration and ozone oxidation processes. Sodium sulfite in the wet denitration process, and electricity and liquid oxygen in the ozone oxidation process are the key inputs that cause environmental impact. These findings are useful for a further optimization of the ultra-low emissions process from both the environmental and economic perspective, which is applicable in other regions of the world.

Effects of slurry properties on simultaneous removal of SO2 and NO by ammonia-Fe(II)EDTA absorption in sintering plants

Simultaneous removal of SO₂ and NO by ammonia-Fe(II)EDTA absorption has become a research focus in recent years. In order to get useful data for further industrialization, in this work the practical operating conditions of the sintering plant were simulated in a pilot-scale reactor in order to explore the effects of slurry properties on simultaneous removal of SO₂ and NO. It was not conducive to the absorption of NO when (NH₄)₂SO₄ concentration and slurry temperature had been increased. The initial NO removal efficiency decreased from 90.63% to 44.12% as the (NH₄)₂SO₄ concentration increased from zero to 3.5 mol/L. With the increasing of Fe(II)EDTA concentration, SO₃^2- concentration and pH value of absorption liquid and the absorption capacity of NO by Fe(II)EDTA solution increased. Especially the existence of SO₃^2- ions in slurry had significantly improved the service life of chelating agents. The NO removal efficiency only decreased by 16.46% with the SO₃^2- concentration of 0.3 mol/L after 30-min of operation. The chloride ions had no effects on the absorption of SO₂ and NO. The results indicated that changes of slurry properties had different effects on simultaneous removal of SO₂ and NO by ammonia-Fe(II)EDTA solution. The basic data offered by the experiments could effectively contribute to further industrial applications.

Selective autocatalytic reduction of NO from sintering flue gas by the hot sintered ore in the presence of NH3

In this paper, the selective autocatalytic reduction of NO by NH3 combined with multi-metal oxides in the hot sintered ore was studied, and the catalytic activity of the hot sintered ore was investigated as a function of temperature, NH3/NO ratio, O2 content, H2O and SO2. The experimental results indicated that the hot sintered ore, when combined with NH3, had a maximum denitration efficiency of 37.67% at 450 °C, 3000 h(-1) gas hourly space velocity (GHSV) and a NH3/NO ratio of 0.4/1. Additionally, it was found that O2 played an important role in removing NOx. However, high O2 content had a negative effect on NO reduction. H2O was found to promote the denitration efficiency in the absence of SO2, while SO2 inhibited the catalytic activity of the sintered ore. In the presence of H2O and SO2, the catalytic activity of the sintered ore was dramatically suppressed.