The Research On Formation Inhibition And Increased Re-Moval Technologies Of Dioxins During Solid Waste Incineration

Incineration treatment has the advantages of capacity reduction,quantity reduction and resource utilization,etc.,and it has become the main measure to treat municipal solid waste(MSW)and medical waste(MW)in China.However,dioxins(PCDD/Fs)and other uninten-tional persistent organic pollutants(POPS)are easily produced during the incineration.These compounds are highly toxic,very stable and easily accumulated by organisms,and thus ex-hibit adverse effects on the ecological environment and human health.Most of solid waste incinerators have adopted strict control measures to minimize dioxin emissions.Nevertheless,the excessive emission of dioxins is still often happened.In order to fully ensure that the emission of dioxins from solid waste incineration facilities PCDD/Fs meets the established emission standard,we selected 1 municipal solid waste incineration power plant and 1 medi-cal waste incineration plant as experiment bases,and explored the effects of three technical measures,spraying recycling water,decreasing flue gas temperature at the boiler outlet and spraying chemical agglomeration agent,on dioxin emission.The obtained results are as fol-lows.The formation of PCDD/Fs was significantly inhibited by spraying recycling water into flue gas at the top of secondary combustion chamber of the MSW incineration system.Com-pared with the control treatment,the total concentration of tetra-to octo-chlorinated dioxins(?PCDD/Fs)and their international toxic equivalent(I-TEQ)in flue gas at the boiler outlet under the condition of spraying recycling water treatment were decreased by 38.0%and 43.1%,respectively.Spraying recycling water treatment induced a higher inhibition rate for the formation of penta-to octo-chlorinated dioxins,but only a lower inhibition rate for the formation of tetra-chlorinated dioxins.Under the condition of control treatment,the ratio of PCDFs/PCDDs in flue gas at the boiler outlet was 2.3,whereas the ratio of PCDFs/PCDDs was increased to 2.7 under the condition of spraying recycling water.indicating that Spray-ing recycling water treatment exhibited a stronger inhibition effect on the formation of PCDDs.Decreasing flue gas temperature at the boiler outlet is an effective measure to suppress the generation of PCDD/Fs.In the test waste incineration system,decreasing the average temperature of flue gas at the boiler outlet from 276? to 198? induced 66.5%and 67.2%reduction in the concentrations of ?PCDD/Fs and their I-TEQ in the flue gas at the reaction tower inlet,respectively.The temperature reduction of flue gas at the boiler outlet exhibited a strong inhibition effect on the formation of tetra-to octa-chlorinated PCDFs and penta-to octa-chlorinated PCDDs homologues in flue gas,with inhibition rates of 51.5-77.0%.However,the inhibition rate for the formation of tetra-chlorinated dibenzo-p-dioxins(TeCDDs)was 15.5%.Polyacrylamide was adopted as a chemical agglomeration agent,which was dissolved and then sprayed into the flue gas in the cooling reactor tower.When the mass concentrations of polyacrylamide in the spray solution were 0.005%and 0.01%,the average concentrations of dust in stack gas of MSW incineration system was 4.4 mg/m3 and 3.6 mg/m3,and the I-TEQ concentration of dioxins was 0.015 ng/Nm3 and 0.010 ng/Nm3,respectively.Compared with the control treatment,the average concentrations of dust in stack gas were decreased by 8.7%and 25.2%,and the I-TEQ concentrations of dioxins in stack gas were decreased by 21.6%and 47.0%,respectively.In addition,compared with the control treatment,the I-TEQ concentrations of dioxins in bag filter ash were increased by 21.0%and 50.9%when spraying chemical agglomeration agent solutions with the mass concentration of 0.005%and 0.01%,respec tively.These results indicated that the spraying of chemical agglomeration agent pro-moted the aggregation of particulate matters in flue gas and enhanced the removal efficiency of dioxins in flue gas by bag filter.