|
Municipal solid waste incineration due to the volume reduction weight loss ratio, fastprocessing speed, energy recovery and occupied the small land area, etc., by the widespreadconcern at home and abroad. However, municipal solid waste incineration has also broughtserious secondary pollution substances such as heavy metals, dioxins and other emissions.This paper describes the characteristics of migration of heavy metals in municipal solid wasteincineration process, analyzes the factors influencing the migration of heavy metals, heavymetal emissions from municipal solid waste incineration process control, reduceenvironmental pollution caused by municipal solid waste incineration, the the necessaryexperimental evidence and theoretical basis.Through the tube furnace experiments under different conditions of municipal solidwaste incineration digestion study the migration of heavy metals. The results show that above600°C, the weight loss process of the municipal solid waste mainly occurred in less than1min, which is quite high due to the volatile content of the MSW dried. The impact oftemperature on municipal solid waste heavy metal migration is significant when thetemperature increases above600°C will greatly promote Pb, Zn, Cu, Cd to the gas phasemigration, attached to the fly ash into the atmosphere. Atmosphere of municipal solid wastemigration of heavy metals was relatively small, the temperature will increase the evaporationrate of heavy metals at low temperatures, oxygen and nitrogen than improve, rather than theimprovement of the nitrogen and oxygen at high temperature have little effect on the heavymetal evaporation rate. Residence time on the characteristics of migration of heavy metals isalso very significant migration of heavy metals occurs mainly in5min before incineration,volatile slowly thereafter until it reaches the maximum volatile value.The additive migration impact of heavy metals in municipal solid waste incinerationprocess is also different.700°C under air atmosphere, chloride will contribute significantlyto the heavy metals Pb, Zn, Cu, Cd metal chloride to the high evaporation pressure conversion,thereby enhancing the evaporation rate of heavy metals due to the relatively low boiling point,melting metal chlorides, Cl growth will significantly reduce the content of heavy metals in thebottom ash. Oxide opposite, in the700°C under air atmosphere, on the one hand, the oxidehaving a certain the sorption constant heavy metals, on the other hand, the oxide to be addedwill form a melt having a higher boiling point heavy metal oxide, thereby residue in thebottom ash. And sulfide add different migration characteristics of different heavy metals,sulfides at600℃addition causes Pb migration to the fly ash, a result of Cd residues into the bottom ash.Equilibrium phases of the composition of the heavy metal compounds and compounds inmunicipal solid waste incineration process the Factsage software simulation results show thatthe main form of Pb in the incineration: PbO （g）, PbCl2（g）, PbCl2（s） PbSO4（s）; mainlyexists in the form of heavy metals Cd incineration: Cd （g）, the CdO （g）, Cd （OH）2（g） theCdO （s）, CdCl2（g） and CdCl2（s）; mainly exists in the form of heavy metals Zn incineration:ZnCl2（g）（s）, ZnSO4, ZnCl2（s）. Heavy metals Zn at200°C before ZnCl2（s）; heavy metalsCu incinerated main form: CuCl （g）, Cu3Cl3（g）, CuSO4（s）, CuCl （s） when the temperature isabove600℃on the migration of volatile heavy metals as a strong positive impact that thehigher the temperature, the higher the rate of volatilization of heavy metals, heavy metal togas migration more. With the reduced oxygen concentration, is not conducive to the migrationof heavy metals in the gas phase, reduced volatilization of heavy metals, heavy metalvolatilization products curve to the right, under the same temperature, evaporation rate ofheavy metals decreased. As the oxygen concentration increased, the heavy metals Pb, Cdvolatile impact, will promote two kinds of heavy metals to the gas phase migration of heavymetals Zn, Cu impact was not significant.
|