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.

Influence of flue gas recirculation on the performance of incinerator-waste heat boiler and NOx emission in a 500 t/d waste-to-energy plant

The flue gas composition and the flue gas temperature at outlet of the economizer were tested, and the influence of flue gas recirculation (FGR) on the efficiency of the incinerator-waste heat boiler and NOx emission in a waste incineration power plant with a waste disposal capacity of 500 t/d was explored experimentally. The results indicate that the largest proportion of the total heat loss is the exhaust heat loss under different loads, and the next is the heat loss of slag. Within the test range, the efficiency of the incinerator-waste heat boiler increases from 80.26% to 80.42% as the ratio of the recirculating flue gas increases from 0 to 16.43%. The oxygen content in the flue gas and FGR have significant influence on NOx emissions. The NOx concentration at outlet of the economizer increases from 209.54 mg/m³ to 307.30 mg/m³, that is an increase of 46.65%, when the oxygen content at outlet of the economizer increases from 4.52% to 8.00%. Compared with the shutdown of FGR system, the NOx concentration at outlet of the economizer decreases from 209.54 mg/m³ to 126.15 mg/m³ when the FGR valve is fully opened. The results have important reference significance for the design of incinerator-waste heat boiler and the optimal operation of power plant.