Web Release Date: July 19,
Emission of PCDD/F, PCB, and HCB from Combustion of Firewood and Pellets in Residential Stoves and Boilers
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Unit of Biomass Technology and Chemistry, Swedish University of Agricultural Sciences, P.O. Box 4097, SE-904 03 Umeå, Sweden, and Chemistry Department, Environmental Chemistry, Umeå University, SE-901 87 Umeå, Sweden
Received for review December 1, 2005
Revised manuscript received May 12, 2006
Accepted May 17, 2006
Abstract:
To assess potential emissions of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), and hexachlorobenzene (HCB) from residential combustion of biofuels, experiments were performed in which various types of pellets and firewood were combusted in four types of stoves and boilers, with both full and reduced rates of air supply. Intermittent combustion of wood pellets resulted in emissions of 11 ng(WHO-TEQ)/kg combusted fuel (dry weight). A modern, environmentally certified boiler yielded somewhat lower emissions of PCCD/F and PCB than a wood stove. Both gave <0.1 ng(WHO-TEQ)/m3n (1.3-6.5 ng(WHO-TEQ)/kg) and considerably lower emissions than an old boiler (7.0-13 ng(WHO-TEQ)/kg). No positive effect on emissions could be observed in full air combustion (simulating the use of a heat storage tank) compared to combustion with reduced air. Two of the wood combustion experiments included paper and plastic waste fuels. Chlorine-containing plastic waste gave rise to high emissions: ca. 310 ng(WHO-TEQ)/kg over the whole combustion cycle. The homologue profiles of PCDD/Fs show characteristic differences between ashes and flue gas from combustions with different levels of air supply. These differences do not, however, seem to have any correlation to the relative amount of toxic congeners.
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