Experimental Study On Inhibitory Effect Of Sulfur On The Formation Of Poly-chlorinated Dibenzo-p-dioxins And Polychlorinated Dibenzofurans During Waste Incineration Process

Incineration technology is one of the main municipal solid waste (MSW) disposal methods adopted in the world. Study for formation mechanism and control technology of dioxins in MSW incineration is one of the very active issues among environmental researches.First of all, the physical and chemical characteristics, origin and risk of dioxins is reviewed in the paper. And then formation and control of dioxins in MSW incineration is introduced systematically.This paper focuses on the role of element sulfur and SO₂ on the formation of PCDD/Fs. The effect of SO₂ on the formation of dioxin is investigated in the experiment of MSWI fly ash. Results reveal that the dioxin emission concentration decreases with the increase of SO₂ concentration. When SO₂ concentration is up to 400 ppm, the emission of dioxin almost is kept stable. This phenomenon shows that the inhibiting effect is unconspicuous with further increase of SO₂ concentration, up to 400 ppm.The results from heating of PCP and element sulfur under different temperatures showed that, the toxic lag phenomenon could be observed about 500℃, sulfur could inhibit dioxin formation when heating temperature was set over 500℃ and on the contrary more dioxin formed when heating temperature is less than 500℃. The S/Cl in fuel also has a great influence on dioxin formation from precursors. In the experiment of SO₂ injection, the lower rate of S/Cl can also efficiently inhibit the formation of PCDD/Fs with the same quantity of PCP. This phenomena show that inhibitong ability of SO₂ is better than element sulfur. When a standard coal according to different sulfur content and PCP were co-fired, the dioxin inhibition efficiency was over 80% and even over 99%.In the studies of the memory effect of SO₂ on the formationg, we can find that with the addition of SO₂, the formation of PCDD/Fs increased firstly and then decreaced. Because residual PCDD/Fs or the precursor desorbs slowly to the flue gas and increases the PCDD/Fs concentration, then the formation of PCDD/Fs does not decrease though the addition of SO₂. With the further addition of SO₂ to 200ppm, we can find the inhibition effect of SO₂. In the repeated experiment, when decreasing the addition of SO₂, the formation of PCDD/Fs does not increase contrast to the formationcondition with 200ppm SO2 addition. This phenomena apperad that the decreased PCDD/Fs formation is attributed to the co-effect of residual SO2 and added SC>2.We can observe the phenomena of memory effect of SO2 during the experiment.