Application of surface fuel addition coupled with pulsed-step natural gas injection in iron ore sintering: heat distribution and process optimization

Hydrogen-rich gas injection technology represents a critical area of research in low-carbon sintering for countries and regions where sinter serves as the primary raw material for blast furnaces. However, the surface sinter index is insufficient, rendering even high concentrations of gas injection inadequate to address this issue, which poses an urgent challenge for current sintering plants. Therefore, this paper introduces a novel approach, surface fuel addition technology, to enhance gas injection sintering in response to this problem, the results indicate that the addition of 5 wt% fuel to the surface of the sintering bed enhances the surface yield from 43.05% to 54.57% while the total yield increases from 69.11% to 76.03%. This improvement is attributed to an increased residence time in the red zone and an optimized thermal state in the upper layer, but results in a postponement of the gas injection interval. After injecting natural gas with a concentration of 0.8 vol% in 8–16 min, the sintering indexes are similar to the benchmark but the bed temperature is greatly changed, the melt holding time of surface and upper layer increased while that of middle and lower layer decreased. Therefore, the pulsed-step injection mode is proposed to strengthen the heat supply in the middle and lower layers and further reduce the coke breeze usage by 15 %. Furthermore, the CO in flue gas in the early stage of sintering increases from 1.20% to 1.90%–2.03% because of the proportion of surface fuel is high while the average CO and NO emission concentration decrease by 8.96% and 30.66%. For a 360 m² sintering machine (annual output of 3.2 million tons), 27680 tons of coke breeze and about 66208 t CO₂ can be reduced per year, which is beneficial to the sustainable development of iron and steel making and protection of environment.