Study On PCDD/F And Heavy Metal Emission Characteristics And Control Technology During Municipal Solid Waste Incineration

The incineration technology is playing an increasingly important role in treatingmunicipal solid waste (MSW) in large-and-medium size cities due to its advantages includingvolume and mass reduction, detoxification, and energy recovery. Based primarily on fieldmeasurements, much detailed research work was conducted to investigate emission andcontrol of PCDD/F and heavy metal in municipal solid waste incinerators (MSWI). The maintopics of this dissertation are as follows:(1) According to the survey about MSWI basic information in China, the representativePCDD/F emission levels ranged between0.0042and7.90ng I-TEQ/Nm~3, with a mean valueof0.561ng I-TEQ/Nm~3.85%emission values can meet Chinese dioxin emission standard(1.0ng I-TEQ/Nm~3), however, only42%under EU standard (0.1ng I-TEQ/Nm~3). Then theexhaustive research and monitoring were carried out in8typical MSWIs in China. Based onregional distribution, incineration technology and management level, the PCDD/F and heavymetal emission levels and characteristics were totally elaborated from Chinese typicalMSWIs.(2) The important factors that affected PCDD/F and heavy metal emissions weresystemtically investigated. First, the influence of different incineration technology,conditions(normal and abnormal), and management level on PCDD/F and heavy metalemission were examined. It can be obtained that abnormal operating conditions resulted in thehighest PCDD/F emission concentrations under bad management, ranging from8.01to181.69ng I-TEQ/Nm~3with78.18ng I-TEQ/Nm~3on average, but abnormal conditions didn’tnecessarily lead to increasing heavy metal emission. Second, the effects of the key ingredientin MSW, such as moisture content, calorific value, sulphur and chlorine content, and heavymetal input, were analyzed. Third, the influence of key technologies in pollution control, suchas quencher and activated carbon injection(ACI), on PCDD/F and heavy metal formation andemissions were studied. Results indicated that the quencher resulted in lower PCDD/Femissions through inhibiting the formation of lower chlorinated PCDD/F, and ACI alsomainly removed lower chlorinated PCDD/F. Although no activated carbon was injected priorto bag filter in a short time, the high removal efficiency can be obtained. Last, PCDD/F andheavy emissions were investigated in different stages during incinerator start-up period.Results indicated that PCDD/F emissions during start-up period were higher than duringnormal operation. After waste was feed dioxin emissions reached the highest concentrations.Due to memory effect, PCDD/F emissions cannot immediately drop to normal values. (3) The relationship between operation conditions, as well as regular parameters andPCDD/F emissions was studied in order to find the optimal conditions for minimizingPCDD/F emissions. Based on a normal operating MSWI, the change law of PCDD/Femission with different conditions and parameters was analyzed, and the correlativefeasibility was explored. So a significant linear correlation between partial conditions, as wellas parameters and PCDD/F emissions was established. Then through conducting a multipleregression analysis, the correlation between dioxin emission and multiple variables wasobtained. Thus a control model can be constructed and serve the purpose of determining howto reduce dioxin emissions.(4) PCDD/F and heavy metal emissions were investigated under abnormal conditions.First, according to the related literatures and monitoring data, the representative dioxinemission factors were provided under normal conditions (range:0.0154–10.720μgI-TEQ/t-waste, average:1.602μg I-TEQ/t-waste). Second, different abnormal conditionswere classified, and PCDD/F formation and emission characteristics were studied in differentsorts of abnormal conditions. Results indicated that abnormal conditions of the MSWI werefound to considerably increase PCDD/F emission, and PCDD/F emissions increased withincreasing abnormal condition sorts. The PCDD/F congener profiles presented greatsimilarities for different abnormal conditions. The emission factors in abnormal conditionswere23order of magnitude than that in normal conditions. Then according to StandardizedToolkit for Identification and Quantification of Dioxin and Furan Releases, emission factorswere regulated and estimated in different sorts of abnormal conditions. Finally, heavy metalemission factors were examined under abnormal conditions. It can be obtained that heavymetal emission factors didn’t show regularity with the changes of conditions.(5) The emission, mass balance, and distribution characteristics of PCDD/Fs as well asthose of heavy metals (Hg, Cd, Pb, Cr, and Cu) were investigated during the co-combustionof5%,10%,15%, and20%sewage sludge (SS) in a pulverized coal power plant. ThePCDD/F emissions increased from7.00pg I-TEQ/Nm~3to32.72pg I-TEQ/Nm~3as the amountof SS in the mixed fuel (MF) increased. High sulfur content and relatively low chlorine levelsin MF resulted in lower PCDD/F emissions. SS exhibited a remarkable difference in congenerprofiles compared with flue gas, bottom ash, and fly ash. The negative dioxin mass balanceindicated that the co-firing of SS with coal in power plants was not a source but a sink ofdioxins. The concentrations and emission factors of heavy metals in flue gas and bottom ash,as well as fly ash, all exhibited a tendency to increase with increasing input values of heavymetals in MF. The distribution characteristics of the investigated heavy metals were primarily dependent on the evaporative properties of these metals. The availability of chlorine couldalter the heavy metal distribution behavior.