Study of the Memory Effect of PCDD/F During the Combustion of Several Biomasses in A Moving Grate Boiler

Abstract

The objective of this work was to study the influence of temperature on the PCDD/Fs behavior stored in biomass ashes issued from an automatic pilot-scale wood boiler. A mixture of these ashes with a dioxin mass ratio dry based of 5.9 µg.kg−1 was used for thermal treatment at temperatures ranging between 200 and 500°C. First tests were carried out in a macro thermogravimetric analysis instrument while couple of other tests were carried out in a quartz-lined crossed fixed-bed reactor. These treated ashes were afterwards analyzed and their dioxin mass ratio was determined. Results obtained from these both experiments are radically different: ashes treated in macro-TGA significantly contain more dioxins than the initial non-treated ashes while those from the reactor are extremely less concentrated. 91% of stored dioxins in the initial ashes were eliminated after 1h at 400°C in crossed fixed-bed reactor. Macro-TGA experiments are a representation of what happens during the shut-down and cooling phase of the boiler, some areas reaching temperatures for which the PCDD/Fs formation is optimal. Without cleaning the boiler, a memory effect on further tests is observed.