Abstract
The inhibition effect of calcined lime (CaO) and limestone (CaCO3) on the formation of dioxins during iron ore co-sintering with fly ash was investigated in a sinter pot in the present work. Experimental results indicated that international total toxicity equivalent concentration of dioxins decreased from 1.4335 to 0.2922, 0.1048, 0.4562, and 0.3098 ng I-TEQ Nm−3 under four different experimental conditions. It can be concluded that 5 wt.% calcined lime with 3 wt.% limestone is the optimal addition to reduce the concentration of dioxins in flue gas, with 92.70% inhibition efficiency. Effects on dioxin distribution was also analyzed. The distribution proportion of low-chlorinated dioxins was found to increase, while that of high-chlorinated dioxins decreased, except for octachlorianted dibenzo-p-dioxins (OCDD). The reason is that the consumption of HCl not only inhibits the de novo synthesis, but also dramatically promotes the condensation and dechlorination to produce more tetrachlorianted dibenzo-p-dioxins and octachlorianted dibenzo-p-dioxins through precursors. Finally, condensation, dichlorination, and inhibition mechanisms of dioxins during co-sintering with municipal solid waste incineration (MSWI) fly ash are proposed.
Highlights
Municipal solid waste incineration (MSWI) [1] has developed rapidly in recent years, and controversy on MSWI’s safety to human health and the ecological environment is increasingly fierce, and the public has aroused great concern around the world, especially regarding MSWI fly ash (FA) [2]
(>1000 ◦ C) supplied by the combustion of fuels [14], and reformed in the preheat-dry zone, exhibiting a remarkable de novo synthesis pathway [15,16] A great deal of coke, chlorine, and catalytic metals contribute to the de novo synthesis [17,18] since the temperatures range between 200–650 ◦ C [19,20], and fly ash is abundant in these necessary elements in the form of carbon and chlorides [21,22]
After 1 wt.% Washed FA (WFA) was added to the sinter raw mix (FG2), the I-TEQ concentration of dioxins in flue gas increased to 1.4335 ng I-TEQ/Nm3, which was twice as much as that of FG1, showing a significant facilitation in the formation of PCDD/Fs
Summary
Municipal solid waste incineration (MSWI) [1] has developed rapidly in recent years, and controversy on MSWI’s safety to human health and the ecological environment is increasingly fierce, and the public has aroused great concern around the world, especially regarding MSWI fly ash (FA) [2]. Landfill after cement solidification/stabilization with a chelating agent is the most widespread disposal method, which barely decomposes dioxins, but increases the volume of the waste, causing the consumption of land resources [4,5] Thermal treatment such as sintering [6,7], melting [8], and vitrification are being developed to dispose MSWI fly ash [9,10] by decomposing dioxins and synergistically solidifying heavy metals. This thermal disposal method conforms with the principle of “reducing quantity”, “harmless”, and that products are environmentally friendly materials that can be reutilized.
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