The formation and emission of dioxins in large scale thermal processes.

The paper assesses extensive data of PCDD/F measurements on flue gas emissions from thermal processes, including, e.g. municipal solid waste incinerators (MSWIs), combustors of wood and industrial waste, coal fired powerplants and boilers, ferro and non-ferro processes. Numerous investigators have conducted laboratory experiments to assess the formation mechanisms of PCDD/F. The results, obtained from fixed-bed experiments, have been critically evaluated and indicate that de novo synthesis is the dominant mechanism in actual thermal processes where conditions that favour the precursor formation are not experienced. The analysis of PCDD/F profiles from the large scale thermal processes in general, and MSWIs in particular, supports the dominant role of the de novo synthesis, irrespective of the type of thermal process considered. The PCDF/PCDD ratio exceeds 1 and the degree of chlorination points towards the dominant presence of HpCDD and OCDD within the dioxin group, and of PeCDF, HxCDF and HpCDF within the furan group. Since real-time measurement of PCDD/F is impossible, the correlation of PCDD/F emissions with operating parameters and/or emission levels of other more easily measured pollutants could be a tool in predicting the PCDD/F formation levels. Data of Flemish MSWIs were used to statistically assess such correlations. From an evaluation of the data at a given operating temperature, misleading conclusions can be drawn. Only the effect of temperature is evident. After converting all data at a reference temperature of, e.g. 230 degrees C, PCDD/F concentrations achieve nearly constant values, irrespective of the values of other parameters, thus stressing that the major controlling parameter for the PCDD/F emission is the temperature of the ESP. The PCDD/F concentrations increase with temperature in the range up to 280 degrees C. The ESP temperature should be kept preferably between 180 degrees C and 200 degrees C, where de novo synthesis is reduced and where PCDD/Fs are increasingly adsorbed on the fly ash, in line with the standard temperature dependence of adsorption isotherms.

[1]  H. Vogg,et al.  On formation conditions of PCDD/PCDF in fly ash from municipal waste incinerators , 1987 .

[2]  H. Hagenmaier,et al.  Catalytic effects of fly ash from waste incineration facilities on the formation and decomposition of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans , 1987 .

[3]  F. Karasek,et al.  Model studies of polychlorinated dibenzo-p-dioxin formation during municipal refuse incineration. , 1987, Science.

[4]  A. Buekens,et al.  Influence of combustion conditions on dioxin in an industrial-scale fluidized-bed incinerator: experimental study and statistical modelling , 1997 .

[5]  J. Ruuskanen,et al.  Formation of polychlorinated dioxins and dibenzofurans in incineration of refuse derived fuel and biosludge , 1993 .

[6]  M. Milligan,et al.  The relationship between de novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans and low-temperature carbon gasification in fly ash , 1993 .

[7]  Michael Metzger,et al.  Recent Findings On the Formation and Decomposition of PCDD/PCDF in Municipal Solid Waste Incineration: , 1987 .

[8]  Peter Mulder,et al.  Fly ash mediated reactions of phenol and monochlorophenols: oxychlorination, deep oxidation, and condensation , 1993 .

[9]  F. Karasek,et al.  Mechanism of formation of PCDD/PCDF in industrial waste incineration and a method of prevention of their formation , 1993 .

[10]  B. Gullett,et al.  Effect of sulfur dioxide on the formation mechanism of polychlorinated dibenzodioxin and dibenzofuran in municipal waste combustors , 1992 .

[11]  Kevin R. Bruce,et al.  Mechanistic steps in the production of PCDD and PCDF during waste combustion , 1992 .

[12]  K. Olie,et al.  The formation of coplanar PCBs, PCDDs and PCDFs in a fly ash model system. , 1995 .

[13]  H. Bautz,et al.  Investigation of precursor reactions in the De-Novo-synthesis of PCDD/PCDF on fly ash , 1997 .

[14]  Dieter Lenoir,et al.  Quantitative comparison of de novo and precursor formation of polychlorinated dibenzo-p-dioxins under simulated municipal solid waste incinerator postcombustion conditions , 1992 .

[15]  K. Froese,et al.  Polychlorinated benzene, phenol, dibenzo-p-dioxin, and dibenzofuran in heterogeneous combustion reactions of acetylene , 1996 .

[16]  F. Kapteijn,et al.  Mechanism of formation of polychlorinated dibenzo-p-dioxins and dibenzofurans in the catalyzed combustion of carbon. , 1994, Environmental science & technology.

[17]  H. Vogg,et al.  On formation conditions of organohalogen compounds from particulate carbon of fly ash , 1991 .

[18]  D. Lenoir,et al.  Influence of operating parameters and fuel type on PCDD/F emissions from a fluidized bed incinerator , 1991 .