Dioxins formation in salt-laden power boilers: A mass balance

Stack dioxins emissions at a coastal pulp mill burning salt-laden wood waste in its power boiler, at typical steam production rates, were found to be 0.089 ng/m3 (in terms of toxicity equivalents (TEQs)). These levels are well within the guideline of 0.5 ng/m3 recommended for municipal solid waste incinerators by the Canadian Council of Ministers for Environment. Stack emissions accounted for less than 1 % of all dioxin TEQs generated by the power boiler. While some dioxins appear to have been generated within the particulate collection devices, the excellent TEQ removal efficiency of these units confirms their essential role in controlling stack dioxins emissions. The TEQ contribution from high temperature (>600°C) dioxins formation appears to have been minimal, less than 15% of the total. This suggests that in power boilers fuelled with salt-laden wood waste, dioxins formation occurs primarily at low temperatures. Consequently, temperature quenching could be relatively effective as a potential control strategy.