A field test of paper mill sludge and coal co-firing was conducted on a 600 MW unit boiler to explore the effect of mix-firing sludge on the formation and emission of dioxins(PCDD/Fs). Under the conditions with and without sludge co-firing

flue gas samples at the inlet and outlet of drying-charring machine

the inlet of selective catalytic reduction(SCR) equipment

the outlet of air preheater and chimney as well as solid samples including raw sludge

dried and partly charred sludge

slag and fly ash were collected

and the PCDD/Fs were analyzed by a highresolution gas chromatograph combined with high-resolution mass spectrometer. The obtained results indicated that

co-firing sludge(accounted for about 1%(weight percent) of pulverized coal) did not result in the formation of PCDD/Fs via high-temperature gas-phase homogeneous formation mechanism and medium-and low-temperature catalytic formation mechanism

and did not increase the emission of PCDD/Fs to atmosphere. The international toxic equivalence quantity(I-TEQ) concentrations of 6 chimney gas samples collected under the condition with sludge co-firing were in the range of 0.008～0.013 ng/m~3(average value: 0.010 ng/m~3)

which did not significantly differ from that(0.008～0.015 ng/m~3

average value: 0.012 ng/m~3) of the 6 chimney gas samples collected under the condition without sludge co-firing. It was found that

a small quantity of PCDD/Fs was formed during sludge dryingcharring process. The newly-formed and original PCDD/Fs in sludge could be completely destroyed by high temperature in coal combustor. The SCR catalyst induced the catalytic degradation of PCDD/Fs

especially the highly-chlorinated dioxins. The concentration of the PCDD/Fs in fly ash samples were lower than 0.2 ng/m~3

indicating its resource utilization could not pose dioxin pollution risk to ambient environment.