Experimental study of dioxin formation and emissions from power boilers burning salt-laden wood waste

Dioxins (PCDDs) and furans (PCDFs) are groups of substances known to be toxic. The Canada Wide Standard (CWS) has set a stack emission limit of 0.1 and 0.5 ng TEQ/m³, respectively, for new and existing facilities. To help the affected Canadian mills meet these limits, an extensive research project was carried out between 2000 and 2003. The investigations involved experimental and survey studies on nine full-scale power boilers. This report presents the survey results obtained from eight coastal mill boilers and one interior boiler. In addition to stack PCDD/F emissions, many other stack emissions and ash analyses were also tested. A total of 112 stack dioxin tests were reported. Dioxin emissions varied significantly between individual tests on a given boiler and between boilers at different pulp mills. Stack dioxin emissions for the power boiler at the interior mill are 2 to 3 orders of magnitude lower than typical emissions from a coastal mill. However, a lower hog salt content does not mean lower dioxin formation and emissions. The average emission levels tested in 2002 were generally lower than those tested in the previous two years. Measures taken to control PCDD/F emissions include improved boiler operations, minimized gas/oil firing, adding coal and TDF, and successful trials of other dioxin control techniques.