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Effects of varying combustion conditions on PCDD/F emissions and formation during MSW incineration
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Waste & Energy)
Umeå University, Faculty of Science and Technology, Department of Chemistry. (Waste & Energy)
2009 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 75, no 5, 667-673 p.Article in journal (Refereed) Published
Abstract [en]

Process, combustion and fuel parameters were varied to elucidate factors that substantially affect the formation and emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) arising from municipal solid waste (MSW) incineration. The combustion conditions were varied by changing the: freeboard temperatures; quench time in the post-combustion zone; fuel load; chlorine and copper levels in the fuel; and the water, sulfur dioxide, carbon monoxide and oxygen levels in the combustion gases. The study was performed using a 5 kW laboratory-scale fluidized-bed reactor and PCDD/Fs were sampled at a point at 300 °C in the post-combustion zone. The results showed that increasing the SO2 level (from 0 to 130 ppm) substantially reduced the PCDD/F emissions, by up to 60%. In contrast, increasing the CO levels (due to transient combustion conditions), raising the Cl level (from 0.7% to 1.7%) and reducing the freeboard temperature (from 800 °C to 660 °C) all substantially increased the emission levels (more than 3-fold). Changes in PCDD/F profiles associated with increases in Cl, SO2 or CO levels and increasing the freeboard temperature (from 800 °C to 950 °C) indicate that the PCDFs were mainly formed by chlorination. In addition, increasing the Cl level increased the chlorination activity in the formation of PCDDs. Increasing the SO2 level appeared to be less effective in reducing the amount of PCDDs formed via the precursor pathway. While increased CO levels induced PCDD formation via the precursor pathway, although this was found to depend on the O2 level in the flue gas.

Place, publisher, year, edition, pages
Elsevier, 2009. Vol. 75, no 5, 667-673 p.
Keyword [en]
PCDD/F, SO2, Chlorine, Quench time, NO, N2O
National Category
Chemical Sciences
URN: urn:nbn:se:umu:diva-18474DOI: 10.1016/j.chemosphere.2008.12.038OAI: diva2:159826
Available from: 2009-02-10 Created: 2009-02-10 Last updated: 2013-11-29Bibliographically approved
In thesis
1. Effects of Varying Combustion Conditions on PCDD/F Formation
Open this publication in new window or tab >>Effects of Varying Combustion Conditions on PCDD/F Formation
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are by-products emitted from combustion sources such as municipal solid waste (MSW) incineration plants. These organic compounds are recognized as toxic, bioaccumulative and persistent in the environment. PCDD/Fs are removed from flue gases before released from MSW incineration. However, the PCDD/Fs are not destroyed but retained in the residues, thus in the environment. Understanding the pathways that lead to their formation is important in order to develop ways to suppress their formation and prevent their release into the environment. Suppressing the formation can also allow less expensive air pollution control system to be used, and/or the costs of thermally treating the residues to be reduced. The main objective of the studies underlying this thesis was to elucidate process, combustion and fuel parameters that substantially affect the emission levels and formation of PCDD/Fs in flue gases from MSW incineration. The experiments were conducted under controllable, realistic combustion conditions using a laboratory-scale reactor combusting artificial MSW.

The parameter found to most strongly reduce the PCDD/F emissions, was prolonging the flue gas residence time at a relatively high temperature (460°C). Increasing the sulfur dioxide (SO2) to hydrogen chloride (HCl) ratio to 1.6 in the flue gas was also found to reduce the PCDF levels, but not the PCDD levels. Fluctuations in the combustion process (carbon monoxide peaks), high chlorine levels in the waste (1.7%) and low temperatures in the secondary combustion zone (660°C) all tended to increase the emission levels. The PCDD/PCDF ratio in the flue gas was found to depend on the chlorine level in the waste, fluctuations in the combustion process and the SO2:HCl ratio in the flue gas. The formation pathways were found to be affected by the quench time profiles in the post-combustion zone, fluctuations in the combustion process and addition of sulfur. In addition, increased levels of chlorine in the waste increased the chlorination degrees of both PCDDs and PCDFs. A tendency for increased SO2 levels in the flue gas to increase levels of polychlorinated dibenzothiophenes (sulfur analogues of PCDFs) was also detected, however the increases were much less significant than the reduction in PCDF levels.

Place, publisher, year, edition, pages
Umeå: Kemi, 2008. 74 p.
dioxin, formation, PCDD, PCDF, MSW incineration, transient combustion, sulfur, memory effects, quench time, chlorine, combustion, polychlorinated dibenzothiophenes, NO, water
National Category
Environmental Sciences
urn:nbn:se:umu:diva-1795 (URN)978-91-7264-617-9 (ISBN)
Public defence
2008-09-22, KB3A9, KBC, Umeå, 13:00 (English)
Available from: 2008-09-01 Created: 2008-09-01 Last updated: 2009-06-18Bibliographically approved

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