Study On Controlling Of Dioxin Emissions From Iron Ore Sintering Process

The iron ore sintering process is the biggest source of dioxin in steel and iron industry, which makes it extremely urgent to control its emission. Adding inhibitors into the sintering mixture is not only a cost-efficient technology to control dioxin emission but also a technology that can reduce the formation of dioxin essentially. The inhibition effect of inorganic S-and N-compounds on dioxin emission from iron ore sintering process was studied. Three inhibitors-thiourea, sulfamic acid and ammonium sulfate-and three different inhibitor mass ratios-0.05%,0.1%and0.5%-were chosen.Satisfactory emission reduction of dioxin was found when adding thiourea and sulfamic acid into the sintering mixture and the more the inhibitors were adding, the more the dioxin emission was reduced. The dioxin mass and TEQ concentration was both reduced by78%when adding0.5%(w) thiourea and was reduced by69%and76%respectively when adding0.5%(w) sulfamic acid. However, ammonium sulfate inhibited the dioxin formation only when its dosage was0.05%(w), which made the dioxin mass and TEQ concentration be reduced by40%and52%respectively. Therefore, thiourea is the most efficient inhibitor on dioxin formation.All the three inhibitors showed better inhibition effect on PCDFs than on PCDDs, which indicated that reducing the de novo synthesis reactions was the main way. The nitrogen-containing compounds and oxysulfides released from inhibitors cound not only reduce the chlorine source but also deactivate the Cu catalyst which was essential in the de novo synthesis reactions. The possible reason why more dioxin was emitted when adding0.1%and0.5%(w) ammonium sulfate into the mixture was that ammonium sulfate absorbed too much heat from the sintering for decomposition, which led to the slowdown of temperature rise in the sinter bed thus resulted in more dioxin emission.