Abstract
ABSTRACT The purpose of this study was to reduce the dioxin content of fly ash from an incinerator by thermal treatment. To increase the residence time of fly ash in the incinerator, the fly ash was mixed with different amounts of coal and clay and then pelletized. All experiments were conducted in a bench-scale fluidized bed combustion system. The polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs) content of the fly ash were investigated following combustion. The results showed that the I-TEQ (Toxic Equivalents Quantity of 2,3,7,8-tetrachlorinated dibenzo-p-dioxin) values of the ash collected from the cyclone met Taiwan's regulatory standards (< 1 ng g–1). The total toxicity of dioxin, including those in the fly and bottom ash, can be reduced by 88–95% after combustion. The strength of the pellets is enhanced by the addition of clay, resulting in their aggregation in the bed and discharge as bottom ash. The distribution profiles of the PCDD/Fs homologs in the fly ash collected from the baghouse in each experiment were similar. The most prevalent congeners in the ash were 1,2,3,4,6,7,8-HpCDF, OCDD, and OCDF. The predominant contributor to the total I-TEQ values was 2,3,4,7,8-PeCDF. The amount of residual carbon in the fly ash is strongly correlated with the dioxin content of the fly ash collected from the baghouse.
Highlights
The incineration of municipal solid or medical waste is prone to high dioxins emissions
Concentration of polychlorinated dibenzodioxins (PCDDs)/Fs in the Fly Ash after Burning After burning, the concentration of PCDD/Fs in the fly ash collected from the cyclone and the baghouse ranged from 9.99 to 26.67 ng g–1 (0.326 to 0.926 ng I-TEQ g–1), and 1121.07 to 2163.79 ng g–1 (50.3 to 76.3 ng I-TEQ g–1), respectively, as shown in Table 4 and Fig. 4 The results showed that the I-TEQ values of the ash collected from the cyclone meet Taiwan’s regulatory standards (< 1 ng g–1), which agrees with previous work (Shen et al (2019)
Shin and Chang (1999) investigated the distribution characteristics of fly ash homologs produced by a waste incinerator in Korea, and the results showed that both PCDD and PCDF existed with a higher degree of chlorination
Summary
The incineration of municipal solid or medical waste is prone to high dioxins emissions. The operating conditions and pollution control devices are key factors for controlling dioxin emissions. The emissions of dioxins to the atmosphere from incineration systems must be decreased, and, typically, the dioxins produced from incinerators are captured by the air pollution control division (APCD) and remain in the fly ash. De novo synthesis is catalyzed by a heterogeneous gas-phase reaction between the fly ash particles and flue gas (Vogg and Stieglitz, 1986; Stieglitz et al, 1989). A theory proposed by Griffin (1986) and tested by Hagenmaier et al (1987) demonstrated that formation occurs through the de-novo synthesis of compounds within the flue gas and fly ash.
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