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The relationship between fly ash chemistry and the thermal formation of polychlorinated pollutants during waste incineration
Umeå University, Faculty of Science and Technology, Department of Chemistry.
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 [en]
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: urn:nbn:se:umu:diva-80186ISBN: 978-91-7459-719-6 (print)OAI: oai:DiVA.org:umu-80186DiVA: diva2:647313
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
List of papers
1. Accurate sampling of PCDD/F in high temperature flue-gas using cooled sampling probes
Open this publication in new window or tab >>Accurate sampling of PCDD/F in high temperature flue-gas using cooled sampling probes
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2012 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 88, no 7, 832-836 p.Article in journal (Refereed) Published
Abstract [en]

In a laboratory-scale combustion reactor, flue-gas samples were collected at two temperatures in the post-combustion zone, 700 °C and 400 °C, using two different water-cooled sampling probes. The probes were the cooled probe described in the European Standard method EN-1948:1, referred to as the original probe, and a modified probe that contained a salt/ice mixture to assist the cooling, referred to as the sub-zero probe. To determine the efficiency of the cooling probes, internal temperature measurements were recorded at 5 cm intervals inside the probes. Flue-gas samples were analyzed for polychlorinated dibenzo-p-dioxin and dibenzofurans (PCDD/Fs). Samples collected at 700 °C using the original cooling probe showed higher concentrations of PCDD/Fs compared to samples collected using the sub-zero probe. No significant differences were observed between samples collected at 400 °C. The results indicated that artifact formation of PCDD/Fs readily occurs during flue-gas sampling at high temperatures if the cooling within the probe is insufficient, as found for the original probe at 700 °C. It was also shown that this problem could be alleviated by using probes with an enhanced cooling capacity, such as the sub-zero probe.

Although this may not affect samples collected for regulatory purposes in exit gases, it is of great importance for research conducted in the high-temperature region of the post-combustion zone. 

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Polychlorinated dibenzo-p-dioxins, Polychlorinated dibenzofurans, Quenching, Sub-zero cooling probe, Waste combustion
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-54601 (URN)10.1016/j.chemosphere.2012.03.090 (DOI)
Note

Available online 28 April 2012

Available from: 2012-05-02 Created: 2012-05-02 Last updated: 2017-12-07Bibliographically approved
2. Effects of regional differences in waste composition on the thermal formation of polychlorinated aromatics during incineration
Open this publication in new window or tab >>Effects of regional differences in waste composition on the thermal formation of polychlorinated aromatics during incineration
2013 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 93, no 8, 1586-1592 p.Article in journal (Refereed) Published
Abstract [en]

Two artificial wastes (A and B) whose contents reflect regional differences in municipal solid waste composition, were used to investigate the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) during incineration. Flue gas samples were simultaneously collected at three ports in the post-combustion zone corresponding to flue gas temperatures of 400, 300, and 200 °C. The combustion of Waste B, which had a higher chlorine and metal content than Waste A, produced greater levels of highly-chlorinated homologues, as demonstrated by a higher degree of chlorination. The total concentrations of PCDDs, PCDFs, PCBs, and PCNs formed in the combustion of both wastes increased as temperature decreased along the convector. There were no significant differences in total concentrations between Waste A and Waste B combustion at specific temperatures, with exception of PCDFs at 400 °C. Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) modeling, used to evaluate the data for all compound groups, suggest that during flue gas quenching at temperatures of 400 °C low-chlorinated homologues are preferentially formed in the presence of copper, which is known to be a very active catalyst for this process. At 300 and 200 °C, the formation of highly-chlorinated homologues is favored.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Polychlorinated dibenzo-p-dioxin, Polychlorinated dibenzofuran, Polychlorinated biphenyl, Polychlorinated naphthalene, Chlorination, OPLS-DA
National Category
Chemical Sciences Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-80179 (URN)10.1016/j.chemosphere.2013.08.012 (DOI)
Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2017-12-06Bibliographically approved
3. Physicochemical properties of fly ash particles formed during municipal solid waste combustion
Open this publication in new window or tab >>Physicochemical properties of fly ash particles formed during municipal solid waste combustion
(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
Waste incineration, fly ash characterization, XPS, SEM/EDX, XRD
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-80183 (URN)
Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2014-02-19Bibliographically approved
4. A link between fly ash chemistry and the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during waste incineration
Open this publication in new window or tab >>A link between fly ash chemistry and the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during waste incineration
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The relationship between the properties of fly ash generated during waste incineration and the thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) was investigated using a laboratory incinerator and two artificial wastes that were designed to reflect regional differences in municipal solid waste composition. Flue gas and fly ash samples were collected isokinetically via a sampling port in the post-combustion zone at a flue gas temperature of 300 °C. The mineralogical properties, morphology and sub-surface composition, surface composition and elemental oxidation states of the fly ash samples were determined. The flue gas samples were analyzed for Mo-OCDDs, Mo-OCDFs, Tri-DCBs, and Di-OCNs. Orthogonal Projections to Latent Structures (OPLS) modeling was used to study the relationship between the properties of the fly ash and the post-combustion formation of polychlorinated aromatics. The presence of high levels of ash-forming elements (i.e. Na, Mg, Fe, Ti, etc…) in the waste reduced the S content of the flue gas and thereby promoted the production of Cl2 via the Deacon process. Because this process is vital for the formation of polyaromatic species, wastes with depleted levels of fly ash-building elements should be favored to minimize the release of toxic PCDDs, PCDFs, PCBs, and PCNs during incineration.

Keyword
Waste incineration, Deacon reaction, formation, particle characterization, OPLS
National Category
Chemical Sciences
Identifiers
urn:nbn:se:umu:diva-80185 (URN)
Available from: 2013-09-11 Created: 2013-09-11 Last updated: 2014-02-19Bibliographically approved

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