Catalytic NO Reduction by CO over Ca–Fe Oxides in the Presence of O2 with Sintering Flue Gas Circulation

Emission reduction of PCDD/Fs by flue gas recirculation and activated carbon in the iron ore sintering

One of the main sources of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the environment is the sintering of iron ore. Both flue gas recirculation (FGR) and activated carbon (AC), which have the impact of decreasing both PCDD/Fs and conventional pollutants (NOx, SO2, etc.), are significant technologies for the abatement of PCDD/Fs from the sintering exhaust gas. This work involved the first measurement of PCDD/Fs emissions during FGR and a thorough analysis of the impact of PCDD/Fs reduction following the coupling of FGR and AC technologies. According to the measured data, the ratio of PCDFs to PCDDs in the sintered flue gas was 6.8, indicating that during the sintering process, the PCDD/Fs were primarily produced by de novo synthesis. Further investigation revealed that FGR initially removed 60.7% of PCDD/Fs by returning it to the high temperature bed, and AC further removed 95.2% of the remaining PCDD/Fs through physical adsorption. While AC is better at removing PCDFs and can efficiently remove tetra-to octa-chlorinated homologs, FGR is more effective at removing PCDDs and has higher removal efficiency for hexa-to octa-chlorinated PCDD/Fs. Together, they complement each other with a removal rate of 98.1%. The study's findings are instructional for the process design of combining FGR and AC technologies to reduce PCDD/Fs in the sintered flue gas.

Investigation on the application of by-product steam in iron ore sintering: performance and function mechanism

The combustion-supporting effect of steam to coke breeze in sintering has the potential to improve sinter quality and reduce pollutants emissions. The results show that increasing the by-product steam injection concentration (0.32-0.47vol%) and prolonging the injection time (5 min) within a proper range (10-15 min) can improve sinter quality. 2.13kgce/t_-sinter of the fuel consumption was decreased by reducing coke breeze usage from 5.60 to 5.45% under the recommended parameters, with 15.16% decrease of CO in sintering waste gas. By comparing experimental data with thermodynamic calculations, although the reaction between CO and steam can reduce CO emission and generate H₂, steam tends to react with coke breeze to generate H₂ and CO (react at 674℃), and OH radical produced by H₂ which can reduce the activation energy of CO oxidation reaction is the key to reducing pollutant emissions. The potential economic benefit of steam injection technology was calculated based on a 360m² sintering machine (the annual sinter output is 3.2million tons), excluding the equipment modification and steam injection cost of $300,000; a profit of $737491.2 per year or 0.23 dollars per ton sinter can be achieved. Therefore, low-carbon and cleaner iron ore sintering production can be realized through applying by-product steam.

NO reduction with CO over a highly dispersed Mn/TiO2catalyst at low temperature: a combined experimental and theoretical study

A highly dispersed Mn/TiO₂catalyst, which has high efficiency for NO conversion with CO and almost completed N₂selectivity at a low-temperature range (350-550 K), was investigated using experimental and DFT theoretical calculation. The characterization results illustrated that the catalyst assembled with nanoparticles and the Mn doping into the TiO₂surface lattice led to the formation of Mn-O-Ti configuration, which enhanced the dispersion of Mn on the body of TiO₂. The DFT study mapped out the complete catalytic cycle, including reactants adsorption, oxygen vacancy generation, N₂O intermediates formation, N₂formation in Eley-Rideal (ER), Langmuir-Hinshelwood, and termolecular Eley-Rideal mechanisms. With thermodynamic and kinetic analysis combined with experimental results, the ER reaction process was considered to be the fundamental mechanism over the highly dispersed Mn/TiO₂catalyst. The calculation results indicated that N₂O was a significant intermediate. However, the rapid N₂O reduction process led to high N₂selectivity. The rate-limiting step was the deoxygenation step of NO-MnO_v/TiO₂from N-O bond scission. The active site Mn-O_vpair embedded in Mn/TiO₂was responsible not only for the formation of N-Mn/TiO₂in the ER-1 step but also for the N₂O deoxygenation process to make the final product N₂in the ER-2 step. The synergetic effect between Mn 3d electron and the oxygen vacancy of TiO₂were responsible for the catalytic activity of Mn/TiO₂.