Fate and Distribution of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in a Woodchip-fuelled Boiler

Abstract

As yet, very little is known about the PCDD/F fate and distribution in the woodchip-fuelled boilers. In this study, the feeding woodchips, stack flue gases and the ashes in different units of a woodchip-fuelled boiler are sampled to investigate their PCDD/F characteristics. The PCDD/F contents in the bottom residues and fly ashes ranged from 18.9 to 66.3 ng I-TEQ/kg, which are below the Taiwanese PCDD/F regulation for reutilization of bottom residues, but still higher than PCDD/F limitations on soils for agricultural use (10 ng I-TEQ/kg), which are adopted by several countries. From the PCDD/F output/input ratios, we found that combustion of woodchips in the boiler system is more favourable for the formations of PCDFs by de novo syntheses, especially for lower chlorinated PCDF congeners. Although about half of the input PCDD/Fs mass are destroyed in the combustion, the output PCDD/Fs toxicity are 6.9 times higher than the inputs. Fly ashes exhibited the highest PCDD/F distributions among the woodchip-fuelled boiler. Still 21.4% of total PCDD/F mass and 18.0% of total PCDD/F toxicity were emitted from the stack flue gases due to the lack of control devices for gaseous phase PCDD/Fs. Decreasing de novo syntheses among the boiler systems, deploying control devices for gaseous phase PCDD/Fs, and proper management on the reutilization of fly ashes will ensure woodchip-fuelled boilers as a sustainable and renewable biomass energy.

An Overview of PCDD/F Inventories and Emission Factors from Stationary and Mobile Sources: What We Know and What is Missing

“…In the study of PCDD/F output/input ratio related to power plants and boilers, Zhang et al (2013) found out that PCDD/Fs were destroyed during co-combustion of coal and sewage sludge, since the PCDD/F inputs were in the range of 1.17-4.69 µg I-TEQ tonne-MF . On the other hand, Chen et al (2011b) found out that the output PCDD/Fs toxicity was about 7 times greater than that contained in the input woodchip feedstock, indicating that PCDD/Fs were formed in the woodchip-fueled boilers rather than destroyed. The formations of PCDD/Fs in the boilers may be as a result of lower efficiency on combustion and heat exchange system, which may increase retention time of flue gases at PCDD/F de novo formation window.…”

“…Emissions from this particular woodchip-fueled boiler were compounded by the fact that there were no active control devices for gaseous phase PCDD/Fs. There were about 21.4% of total PCDD/F mass and 18.0% of total PCDD/F toxicity emitted from the stack flue gases of the woodchip-fueled boiler, because only cyclone and bag filter were deployed (Chen et al, 2011b).…”

Distribution of Polybrominated Dibenzo-p-dioxins and Dibenzofurans and Polybrominated Diphenyl Ethers in a Coal-fired Power Plant and Two Municipal Solid Waste Incinerators

“…The structural similarity also occurred between PCDD/Fs and PBDEs; similar characteristics were also found, such de novo synthesis (Artha et al, 2011). It is known to us that PCDD/Fs have been found in various sources, such as crematories, sinter plants and so on (Wang et al, 2003a;Wang et al, 2003b;Lee et al, 2004;Lee et al, 2005;Chen et al, 2011;Huang et al, 2011;Lin et al, 2011). PCBs and PCDD/Fs are known to entering soils via dry and wet disposition (Lee et al, 1996), and accumulate in animals (Lee et al, 2009); these are the characteristics PBDEs also possess.…”

Identification the Content of the Windbox Dust Related to the Formation of PCDD/Fs during the Iron Ore Sintering Process

“…Fax: +886-6-2752484 E-mail address: pjtsai@mail.ncku.edu.tw Chen et al, 2011). Among them, the iron ore sintering process is considered as the most important PCDD/F emission source in many countries (Lahl, 1993(Lahl, , 1994Alcock et al, 1999;Anderson and Fisher, 2002;Aries et al, 2006;Shih et al, 2006Shih et al, , 2008Shih et al, , 2009Chen et al, 2010).…”