The Characteristics Of Heavy Metals Transfer And Distribution During Sewage Incineration Process

By using tubular furnace, the characteristics of heavy metals distribution and migration were studied. Based on the study of the current situation of sewage sludge incineration, the hazard of heavy metals during sludge incineration, and through sludge composition and thermogravimetric analysis and the selection of optimal wet digestion methods of sludge, fly ash and residue, the influences of incineration temperature, the concentration of initial sludge, the sludge blending ratio, different sulphur compounds, different chlorine compounds and different inert substances on the distribution and migration of Pb, Cd, Ni during sewage sludge incineration were studied, the results are shown below:(1) With the analysis of the characteristics of sludge, it can be found that sludg is rich in volatile and ash content, while the content of fixed carbon is low, because of he high air dried basis calorific value, sludge is suitable for incineration treatment; through the thermal analysis, the main reason for the weightlessness is the devolatilization and volatile combustion; the ignition temperature and burnout temperature of sludge are lower than coal, while the comprehensive combustion characteristics of sludge is better.(2) The digestin method of sludge, fly ash and residue can be determined by the selection of the kinds of acids, the amount of acids and the digestion time of different stages. The best digestion method of sludge and fly ash is HNO3+(1:4)HNO3:HC1O4+HF, while using HNO3+HF to digest residue is better; incrasing the amount of acids or extending the stage time of mixed acid digestion stage is good for digestion the samples completely.(3) In850℃, Pb and Cd mainly distributed in fly ash and residue, the content in gas is little, Ni is mainly distributed in residue, very few existed in flue gas; the increase of incineration makes Pb, Cd, Ni enriched in flue gas, while increase the sludge blending ratio or the initial concentration of heavy metals had little influence on the distribution ratio of heavy metals.(4) For different heavy metals, the addition of different sulphur compounds has different effect on heavy metals transfer and distribution, in the whole, the effect of sulphur compounds upon Pb, Cd and Ni distribution in flue gas was successively in the order of Na2SO4> Na2SO3>S>Na2S.(5) With the addition of chlorine compounds, Pb, Cd and Ni tended to distribute in flue gas, under the same adding amount, for Pb and Ni, NaCl is superior to PVC, while for Cd, just the reverse. (6) the adding of inert substances was beneficial to the heavy metals enrichment in residue, as for quartz sand, zeolite and CaO, CaO and quartz sand had larger effect on Pb and Ni distribution in residue, while zeolite had more influence on Cd.The results in this paper provides basic data support on the further studies of heavy metals transfer and distribution, and offer the reference of the selection of heavy metals control technologies during sludge incineration process.