NO _x Reduction in the Iron Ore Sintering Process with Flue Gas Recirculation

Abstract

Flue gas recirculation (FGR) has been implemented for exhaust gas emissions reduction in iron ore sintering. However, the mechanism of NO _x reduction through FGR is still unclear. In this paper, the laboratory pot-grate sintering test showed a 30% reduction in gas flow and 15.51% reduction in NO _x emissions achieved with a 30% FGR ratio, and the sinter indexes almost matched those of the conventional process. In the sinter zone, NO-CO catalytic reduction occurs in the range of 500–900°C. When the sinter temperature is 700°C, the highest nitrogen reduction ratio (NRR) achieved is 8%; however, the NO _x reduction is inhibited as the post-combustion of CO starts when the temperature increases beyond 700°C. NO _x in the flue gas is mainly a product of the fuel combustion in the combustion zone, as the nitrogen conversion rate reaches 50–60%, because the N-containing intermediates exist during the fuel combustion. The existence of NO in the FGR gas inhibits the NO _x generation from the fuel combustion, and the NO elimination—through the NO-carbon reaction—is significant in the combustion zone. The NRR in the combustion zone reaches a range of 18–20%.