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 fo und to be 0.089 ng/m(3) (in terms of toxicity equivalents (TEQs)). The se levels are well within the guideline of 0.5 ng/m(3) recommended for municipal solid waste incinerators by the Canadian Council of Ministe rs for Environment. Stack emissions accounted for less than 1% of all dioxin TEQs generated by the power boiler. While some dioxins appear t o have been generated within the particulate collection devices, the e xcellent TEQ removal efficiency of these units confirms their essentia l role in controlling stack dioxins emissions. The TEQ contribution fr om high temperature (>600 degrees 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 cou ld be relatively effective as a potential control strategy. (C) 1997 E lsevier Science Ltd.