Inhibition of PCDD/F by adding sulphur compounds to the feed of a hazardous waste incinerator
ABSTRACT Sulphur compounds, including (NH(4))(2)SO(4) and pyrite, were tested as suppressants in a hazardous waste incineration facility. The test results suggested that adding sulphur compounds only slightly reduced PCDD/F stack emissions; this restricted effect was attributed to the release of fly ash in large amounts during the sulphur adding experiments, i.e., it was due to a malfunctioning of the baghouse filter. Nevertheless, for the combined flow of flue gas+fly ash a reduction of more than 50% was achieved for the total PCDD/F concentrations and the total toxic concentrations, and an even higher inhibition capability was observed for PCDD. Also, a simulation of the thermodynamic equilibrium conditions by sulphur dioxide was conducted in the domain of experimental interest. Deactivation of catalysts, which promote PCDD/F formation, was found to be the dominant inhibition mechanism in low temperature PCDD/F formation. SO(2) could also inhibit the formation of molecular Cl(2) via the Deacon reaction, but that was not the main reason for inhibition.
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ABSTRACT: “Dioxins” (or PCDD/F) are persistent organic pollutants (POP) which are emitted in the atmosphere by several combustion and thermal processes. Many studies concern the formation of dioxins, but very few thermal destruction. The present study concerns the oxidation and the pyrolysis of dibenzofuran which is chosen as a model molecule of “PCDF” (polychrorodibenzofurans). The reaction is studied at very low concentration of dibenzofuran (i.e. near 2 ppm) in a continuous perfectly stirred reactor, at atmospheric pressure. The residence time is varying between 3 s and 5 s, whereas the temperature is ranging from 500 to 950 °C. Dibenzofuran is a solid compound in standard conditions, so a difficulty of this study is to realize a continuous gas flow of this species. During dibenzofuran decomposition, the conversion can be close to 100% and several intermediary species are formed. These species are identified by GC/MS and then quantified by GC/FID. The main byproducts are derivatives of benzofuran, polyaromatic hydrocarbons and other volatile organic compounds. These experimental data are used to improve a kinetic mechanism and previously validated with experimental data obtained with higher ranges of DBF concentration.Journal of Environmental Chemical Engineering 01/2013; DOI:10.1016/j.jece.2013.11.030
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ABSTRACT: The use of waste wood as an energy carrier has increased during the last decade. However, elevated levels of alkali metals and chlorine in waste wood compared to virgin biomass can cause increased deposit formation and higher concentrations of organic pollutants. In this study, we investigated the effect of the ChlorOut technique on concentrations of organic pollutants. Ammonium sulfate was injected into the combustion system to inhibit formation of KCl (which causes deposits) and persistent organic pollutants, namely polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs). The results showed that concentrations of the toxic congeners of PCDD, PCDF and PCB decreased in the presence of ammonium sulfate.Chemosphere 02/2013; 91(6). DOI:10.1016/j.chemosphere.2013.01.090 · 3.50 Impact Factor
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ABSTRACT: Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are formed during waste incineration and in waste-to-energy boilers. Incomplete combustion, too short residence times at low combustion temperatures (<700°C), incineration of electronic waste and plastic waste containing chlorine are all factors influencing the formation of PCDD/Fs in boilers. The impact of chlorine and catalysing metals (such as copper and iron) in the fuel on PCDD/F formation was studied in a 12MWth circulating fluidised bed (CFB) boiler. The PCDD/F concentrations in the raw gas after the convection pass of the boiler and in the fly ashes were compared. The fuel types were a so-called clean biomass with low content of chlorine, biomass with enhanced content of chlorine from supply of PVC, and solid recovered fuel (SRF) which is a waste fuel containing higher concentrations of both chlorine, and catalysing metals. The PCDD/F formation increased for the biomass with enhanced chlorine content and it was significantly reduced in the raw gas as well as in the fly ashes by injection of ammonium sulphate. A link, the alkali chloride track, is demonstrated between the level of alkali chlorides in the gas phase, the chlorine content in the deposits in the convection pass and finally the PCDD/F formation. The formation of PCDD/Fs was also significantly reduced during co-combustion of SRF with municipal sewage sludge (MSS) compared to when SRF was fired without MSS as additional fuel.Waste Management 05/2013; 33(8). DOI:10.1016/j.wasman.2013.03.022 · 3.16 Impact Factor