Effect Of Typical Metal Compounds On Dioxins In Fly Ash

The factors that affected the formation of dioxin in fly ash of MSWI were investigated from three aspects in this paper. The first study centers on establishing the physical and chemical characteristics of fly ash, firstly classified in several size fractions, and on their load of polychlorinated dibenzo-p-dioxins (PCDD), dibenzofurans (PCDF), biphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH). First two samples are considered, taken in a problematic MSWI stoker plant. The samples come from the exit of furnace and the baghouse filter. Various methods including laser particle size analysis, SEM-EDS, XRD and XRF were used to characterise the physical and chemical properties of samples. The primary purpose of this first study is verifying in how far such off-line fly ash analyses supplement the routine emission-monitoring mandatory for such plant and develop supplemental knowledge on the state of the plant and on its potential to form PCDD/F, PCB, PAH. Different particle size distributions, morphology and elementary compositions were found in samples from different positions mainly due to various operational conditions in units as well as physical settlement of fly ash and chemical reaction during the process. The volatility of elements was found to be the major factor influencing the size distribution and difference between bulk and surface concentration of elements. The contents of volatile elements like S, Cl, Zn, Cd, As, Se and Hg were found to increase markedly with decreasing particle size, which can be mainly explained by a mechanism involving high-temperature volatilization. The trends of PCDD/Fs and PCBs are similar since they can generate together via de novo synthesis, which is different with PAHs.The formation of PCDD and PCDF was explored during de novo tests designed to compare the catalytic activity of copper (II) chloride (CuCl2) with that of iron (III) oxide (Fe2O3) and to test some synergistic effect between these two catalytic compounds. Both copper chloride (CUCl2) and iron oxide (Fe2O3) were earlier proposed as catalysts to explain the PCDD/F emissions from, e.g., municipal solid waste incineration (MSWI). In addition, haematite (Fe2O3) is the main iron ore and could be responsible for the typical iron ore sintering plant fingerprint. A total of nine Model Fly Ash (MFA) samples were prepared by mixing and grinding of sodium chloride (NaCl), activated carbon, and a powder matrix of silica (SiO2) with the selected metal compound(s). The conditions of these de novo tests were 1 h duration, 350 ℃ in a flow of synthetic combustion gas (10 vol.% oxygen in nitrogen). The effect of Fe-Cu catalyst concentration on yield and distribution pattern of PCDD/F was systematically explored; three strongly differing ratios of [Fe]:[Cu] were considered (1:1,10:1 and 100:1) to study the potential interactions of Fe2O3 and CuCl2 suggested earlier. The results show some slight rise of PCDD/F formed with raising iron concentration from 0 to 10.1 wt.%(no Cu added; 0.1 wt.% Cu), as well as strong surging of both amount and average chlorination level of PCDD/F when rising amounts of copper (0 to 1.1 wt.%) are introduced. The resulting fingerprints are compared with those from sintering and from MSWI.In addition, principal component analysis (PCA) and hierarchical cluster analysis (HCA) are used to analysis the existed dioxins data to achieve mutual verification of these two methods as well as provide new idea for further study.