Study On Heavy Metal Transfer Characteristics Of Municipal Solid Waste In The Incineration Process Under O₂/CO₂ Atmosphere

In recent years,with the rapid development of economy in China,people’s life has been greatly improved and the consumption level has risen sharply,resulting in an ever-increasing amount of municipal solid waste（MSW）.Compared with other MSW treatment methods,incineration has the unparalleled advantages of volume reduction,high efficiency and small footprint compared with other treatment methods.Therefore,it has been popularized both at home and abroad.At the same time,the rapid economic development in China has brought about a dramatic increase in carbon emissions.Oxy-fuel combustion is an important CO₂emission reduction technology.Its application is receiving more and more attention from all walks of life.Therefore,the combination of oxy-fuel combustion technology and waste incineration technology is very promising.In this paper,we study the transfer characteristics of heavy metals under the typical components of MSW（sawdust and PVC）combustion process by using tube furnace and inductively coupled plasma atomic emission spectrometry.Firstly,the transfer characteristics of three heavy metals Zn,Pb and Cr during the combustion and mixed combustion of sawdust and polyvinyl chloride（PVC）under oxygen-fuel combustion and the effects of organic chlorine（PVC）and inorganic chlorine（NaCl）on the transfer characteristics of three heavy metals Zn,Pb and Cr were studied.The results showed that he determining factors of the transfer behavior of heavy metals under oxy-fuel combustion are still boiling point and temperature.Compared with convention combustion,oxy-fuel combustion increase the volatilization of Pb and Zn,but reduce that of Cr.The co-firing promotion of the volatilization of heavy metals is lowest when the mass ratio of wood to PVC is 1 to 1,compared with that is 7 to 3 or 3 to 7.Under oxy-fuel combustion,the promotion of volatilization of Pb by adding organic chlorine is greater than by adding inorganic chlorine.Then,the effects of temperature and dosing ratio on the adsorption of heavy metals such as Cr,Cu,Pb and Zn by limestone under oxygen-fuel combustion conditions were studied.The experimental results were analyzed by two-way ANOVA.The results showed that the average capture efficiency of natural limestone for Cr,Cu,Pb and Zn in descending order under oxy-fuel combustion was Cu>Zn>Pb>Cr.Cu have a greater capture efficiency at700℃and 900℃;the capture efficiency of Zn reached its maximum at 700℃;the capture efficiency of Cr and Pb increased with increasing temperature between 600℃and 900℃.The adsorption efficiency of Pb increased with the increase of the dosing ratio of adsorbent;Cr was less affected by the additive amount of limestone at low temperature;the addition efficiency did not increase the capture efficiency of Zn;the capture efficiency of Cu always increased with the increase of the dosing ratio of adsorbent whether at low temperature or high temperature.Analysis of variance showed that the temperature had a significant effect on the capture efficiency of all heavy metal elements.However,the sorbent dosing ratio had a significant effect on the capture efficiency of Cu and Pb,but had no significant effect on the capture efficiency of Cr and Zn.Finally,the natural limestone was modified with modifying agent（NaCl,K₂CO₃,Al₂（SO₄）₃）to study the effect of the ion ratio(γ=Ca²⁺/other added metal ions),temperature and heavy metal species on modified limestone adsorption efficiency.The results showed that the effect of adding NaCl on capture of Pb was always inhibited,the effect on Cu and Zn capture was first inhibited and then promoted with the increase of temperature,and the effect on the capture of Cr was mild.For all heavy metals,as the temperature increases,the inhibition of NaCl on limestone decreased,the promotion effect of NaCl on limestone increases.Effects of modification on the capturing performance of limestone in wood combustion under oxygen-fuel combustion vary on different heavy metal species.After limestone was modified by K₂CO₃,the capture efficiency of Cr and Cu was improved.The capture efficiency of Pb was inhibited,while the capture efficiency of Zn was not much affected.After the modification of Al₂（SO₄）₃,the capture performance of the four heavy metals was improved.For Cr,the best modification method of limestone is K₂CO₃（γ=10）,the capture efficiency is 83.20%;for Cu,the best modification method of limestone is Al₂（SO₄）₃（γ=15）,the capture efficiency is 82.14%;for Pb,the optimum modification method of limestone is Al₂（SO₄）₃（γ=10）,the capture efficiency is 32.13%;for Zn,the optimum modification method of limestone is Al2（SO4）3（γ=10）,the capture efficiency is 55.91%.