Combustion dioxin formation

Nestrick TJ, Lamparski LL. 1983. Assessment of chlorinated dibenzo-p-dioxin formation and potential emission to the environment from wood combustion. Chemosphere 12 617-626. 

Mere destruction of the original hazardous material does not adequately measure the performance of an incinerator. Products of incomplete combustion can be as toxic as, or even more toxic than, the materials from which they evolve. Indeed, highly mutagenic polycyclic aromatic hydrocarbons are generated in the fuel rich regions of most hydrocarbon flames [48]. Dioxin formation in the combustion of chlorinated hydrocarbons has also been reported [49],... 

Fangmark I (1993), Formation of chlorinated aromatic compounds during incineration - an application of statistical experimental design", Dissertation, Universitat Ume3, Schweden Griffin RD (1987), Chemosphere 15 1987-1990. A new theory of dioxin formation in municipal solid waste combustion"... 

These techniques are applied in other industrial sectors, such as steel and non-ferrous metal production and waste incineration. Judging on a technical basis, they may be transposed to foundry furnace types that show a risk of dioxin formation cupola, rotary and electric arc furnaces melting iron and steel (Section 3.8.2). For new and existing installations primary dioxin reduction measmes, such as efficient combustion, furnace design modifications and scrap quality control have to be taken into consideration on a case-by-case basis, before turning to secondary measures. 

The application of an afterburner allows the reduction of organic carbon emissions and combustible particles. This technique may also be effective in reducing the risk of dioxin formation upon cooling of the gases. The afterburner is installed after the furnace and before the heat-exchanger. One of the following afterburner types may be used thermal incinerator combustion in an open flame... 

A further development in incinerator technology is the use of chemical waste as a supplementary fuel for use in cement of lime kilns. These processes operate at extremely high temperature sufficient for complete combustion of hydrocarbon waste. An extension to the disposal of halogenated materials may be possible providing the temperature and residence times required for elimination of dioxin formation can be consistently established within the kiln. 

Huang H, Buekens A. On the mechanisms of dioxin formation in combustion processes. Chemosphere 1995 31 (9) 4099-4117. 

Some PBBs are considered possible precursors of toxic poly-brominated dibenzo-p-dioxins (12-138) and dibenzofurans (12-139), which are formed during combustion. The formation of degradation products of PBBs depends generally on the temperature, the amount of oxygen present and certain other factors. A study of the pyrolysis of the commercial mixture FireMaster BP-6 in the absence of oxygen at 600-900 °C showed the formation of bromobenzenes and lower brominated biphenyls, but polybromi-nated furans did not result. Pyrolysis in the presence of oxygen at 700-900 °C, however, yielded di- to heptabromodibenzofurans. 

In the post-combustion chamber temperatures of 900 °C to 1200 °C are reached. The kiln can - like any rotary kihi - handle solid, fluid and gaseous waste streams. Based on the heat capacity of the waste, halogen content, and potential slag formation, an optimal mixture of wastes is determined. By choosing the feed carefully, production of high-quality HCl can be assured. Furthermore, in this way a minimum formation of dioxins and furans can be ensured. 

Combustion of wood or paper treated with pentachlorophenol resulted in no increase and more probably a decrease in octachlorodi-benzo-p-dioxin concentrations while octachlorodibenzo-p-dioxin increased slightly in paper treated with sodium pentachlorophenate. The pho-tolytic degradation of sodium pentachlorophenate at pH 8 is very rapid. Under these controlled conditions formation of no more than 0.03% octachlorodibenzo-p-dioxin was observed. The 2,3,7,8 isomer, one of the most active chloracnegens is seemingly stable towards air oxidation but... 

Heating of houses with wood, charcoal or mazut also results in formation of trace amounts of dioxins. Hazardous source of PCDD and PCDF constitutes the combustion of engine oil and gasoline with chlorine- or bromine-organic additives. Over the long period of time, pesticides containing dioxins (2,4,5-T, copper trichlorophenolate etc.) [4] were used in agriculture. 

Furthermore, if the syngas is combusted in a gas turbine where excess oxygen is present, the high combustion temperature does not favor formation of free chlorine. In addition, post-combustion formation of dioxin or furan is not expected to occur because very little of the particulates that are required for post-combustion formation of these compounds are present in the flue gas. 

There are 210 different isomeric possibilities, 75 of which are PCDDs and 135 are PCDFs. The toxicity of these isomers varies greatly, and only 15 exhibit extreme toxicity, the most toxic of which is 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). The toxicity of the other isomers is therefore expressed as a toxicity equivalent of 2,3,7,8-TCDD. The PCDDs and PCDFs are poorly water soluble but are fat soluble and are therefore able to accumulate in tissue fat, thus allowing them to bio-accumulate in living organisms. The origin of dioxins in the pulp and paper industry is not entirely clear. They may be produced from the chlorination of dibenzodioxin which may be present in recycled oils used to make defoamers, but they may also arise from wood chips which have been treated with polychlorophenol to prevent sap stain formation. It is also possible that they are derived from lignin by chlorination. Dioxins are also known to be formed naturally by combustion of material such as wood, and forest fires have been particularly identified as a likely major cause of dioxin emissions. 

The carbon content of MSW cannot be converted into C02 entirely, and due to incomplete combustion, minor amounts of CO and soot particles are found in the flue gases. The particulate carbon is known to be involved in the formation of volatile and toxic compounds especially poly-chlorodibenzo-dioxins and -furanes. Tests in the fully working incinerator plants revealed the presence of particulate carbon, chlorides, and Cu compounds as catalysts in the fly ash (see also Table 3). 

Formation of polychlorinated dibenzo(p) dioxins and furans (PCDD/PCDF) in waste combustion has received considerable attention, because dioxins even in very small concentrations are believed to be harmful to humans. Sources of PCDD/PCDF include the waste itself, gas-phase and heterogeneous reactions within the combustion zone, and catalyzed reactions in the low-temperature region downstream [352],... 

Ahling B, Liondskog A, Jansson B, et al. 1977. Formation of polychlorinated dibenzo-p-dioxins and dibenzofurans during combustion of a 2,4,5-T formulation. Chemosphere 6 461-468. 

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