Abstract
The new process of flue gas recirculation, which reduces coke consumption and reducing NOx emissions, is now extensively used. Compared with traditional sintering, the characteristics of circulating flue gas and coke parameters significantly affect the combustion atmosphere and coke combustion efficiency. Based on the actual complex process of sintering machine, this study proposes a relatively comprehensive one-dimensional, unsteady mathematical model for flue gas recirculation research. The model encompasses NOx pollutant generation and reduction, as well as SO2 generation and adsorption. We focus on the effects of cyclic flue gas characteristics on the sintering-bed temperature and NOx emissions, which are rarely studied, and provide a theoretical basis for NOx emission reduction. Simulation results show that during sintering, the fuel NOx is reduced by 50% and 10% when passing through the surface of coke particles and CO, respectively. During flue gas recirculation sintering, the increase in circulating gas O2 content, temperature, and supply-gas volume cause increased combustion efficiency of coke, reducing atmosphere, and NOx content in the circulating area; the temperature of the material layer also increases significantly and the sintering endpoint advances. During cyclic sintering, the small coke size and increased coke content increase the char-N release rate while promoting sufficient contact of NOx with the coke surface. Consequently, the NOx reduction rate increases. Compared with the conventional sintering, the designed flue gas recirculation condition saves 3.75% of coke consumption, i.e., for 1.2 kg of solid fuel per ton of sinter, the amount of flue gas treatment is reduced by 21.64% and NOx emissions is reduced by 23.59%. Moreover, without changing the existing sintering equipment, sintering capacity increases by about 5.56%.
Highlights
Since NOx is the root cause of photochemical smog and acid rain, it causes serious environmental and ecological problems
The flue gas produced by coke combustion stays longer in the pore and coke-surface powder than does that produced by pulverized coal combustion, and the former is more conducive to NOx reduction
The reliability of the model is verified by comparing the simulated values with the experimental one
Summary
Since NOx is the root cause of photochemical smog and acid rain, it causes serious environmental and ecological problems. New technologies for reducing NOx emission during sintering mainly include flue gas recirculation sintering (FGRS), selective catalytic reduction [2], biomass fuel [3,4,5,6], gas injection [7], and parameter control [8,9]. SO2 is absorbed and filtered by the mixed layer, CO is reused as fuel, and the production of iron ore per ton can reduce NOx by 20%–45%, dioxins by 60%–70% and SO2 by 20%–45% [16], which proves that flue gas recycling can effectively reduce pollutant emissions. Many studies have focused on the combustion behavior and heat transfer in iron-ore sintering, the influences of fuel ratio, gas supply, coke size, limestone particle size, and different exhaust-gas cycle schemes on sintering [17,18,19,20]. The effects of the main operating parameters on NOx emission during recirculation sintering is explored, and a theoretical basis for the optimization of flue gas recirculation is provided
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