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Physicochemical properties of fly ash particles formed during municipal solid waste combustion
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Chemistry.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Fly ashes generated from two artificial wastes were investigated with regard to physicochemical properties of importance for thermal formation of persistent organic pollutants (POPs). The ash samples were collected in the post-combustion zone at approximately 300 °C and were characterized using complementary techniques: X-ray diffraction (XRD), scanning electron microscopy/energy dispersive X-ray (SEM/EDX), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. The results showed a strong correlation between ash chemistry and waste composition. The waste containing higher levels of Al resulted in more abundant Al-bearing minerals, as well as the element Al, in the fly ash. In the case of Fe, no such correlation was found. Copper, an especially important reaction catalyst, was not detected by in the top 10-nm layer of ash but rather occurred within the top 2-µm, indicating that POPs formation reactions may have depleted the available surface Cu. The possibly inaccessible buried forms of Cu may also be a limiting factor in the production of POPs. Furthermore, organic forms of carbon were present at fly ash surfaces, although not significantly in their chlorinated forms. Taken collectively, these results contribute to understanding the correlations between fly ash chemistry and the thermal formation of POPs.

Keyword [en]
Waste incineration, fly ash characterization, XPS, SEM/EDX, XRD
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:umu:diva-80183OAI: oai:DiVA.org:umu-80183DiVA: diva2:647300
Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2014-02-19Bibliographically approved
In thesis
1. The relationship between fly ash chemistry and the thermal formation of polychlorinated pollutants during waste incineration
Open this publication in new window or tab >>The relationship between fly ash chemistry and the thermal formation of polychlorinated pollutants during waste incineration
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) is a major problem in waste incineration. Ideally, rather than relying on air cleaning systems and treatment techniques, their formation should be minimized or, if possible eliminated. The work presented in this thesis was conducted to obtain a deeper understanding of the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during incineration using a 5 kW laboratory scale incinerator and two artificial wastes that were designed to reflect regional differences in waste composition.

The first part of the thesis focuses on the validation of a recently-developed flue-gas sampling probe with enhanced cooling capabilities. Artifact formation of PCDDs and PCDFs can occur during the sampling of hot flue gases if the cooling is insufficient. The new probe was successfully used to collect samples at 700 °C without biasing the measured POP levels. The thermal formation of PCDDs, PCDFs, PCBs, and PCNs in the post-combustion zone of the incinerator was then studied by collecting flue gas samples at 400 °C, 300 °C, and 200 °C during the incineration of the two artificial wastes. Highly chlorinated POPs were formed in larger quantities when burning the waste with the higher content of metals and chlorine, which suggests that high metal levels in the waste favor the chlorination of less chlorinated POPs or otherwise facilitate the formation of highly chlorinated polyaromatics, possibly via the condensation of highly chlorinated phenols. The concentrations of these pollutants and the abundance of highly chlorinated homologues increased as the flue gas cooled. Fly ash particles play an important role in thermal POP formation by providing essential elements (carbon, chlorine, etc.) and catalytic sites. The chemical and mineralogical properties of fly ash samples were studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX), and X-ray photoelectron spectroscopy (XPS) to determine their impact on thermal POP formation. Orthogonal Partial Least Squares (OPLS) modeling was used to identify correlations between the observed POP distributions and the physicochemical data. This investigation provided new insights into the impact of fly ash chemistry on thermal POP formation.

In addition, the POP isomer distribution patterns generated during waste combustion were examined. These patterns are used to “fingerprint” mechanisms of POP formation. It was found that wastes containing large quantities of metals and chlorine favored the formation of highly chlorinated homologues including the very toxic 2,3,7,8-congeners. The data suggest that reducing fly ash emissions might increase the SO2 content of the flue gas and thereby suppress the Deacon process and the formation of harmful highly chlorinated aromatic species.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2013. 71 p.
Keyword
Incinerations, dioxins, PCDD/Fs, PCBs, PCNs, flue gas, fly ash, sampling, particle characterization, XPS, XRD, SEM/EDX, formation, chlorination, PCA, OPLS, OPLS-DA
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-80186 (URN)978-91-7459-719-6 (ISBN)
Public defence
2013-10-03, KBC-huset, KB3A9, Umeå universitet, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2013-09-12 Created: 2013-09-11 Last updated: 2013-09-13Bibliographically approved

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