Dioxin and fly ash free incineration by ash pelletization and reburning

Dioxins (DXNs) in municipal waste incinerator fly ash were effectively redu ced by pelletizing the mixture of ash, cement, and sodium phosphate and reb urning the pellets in a laboratory scale bubbling fluidized bed (BFB) furna ce. Three types of pellets-A, B and C, of various sizes and compositions we re used in the experiments. The efficiency of DXN reduction in the pellet m atrix was proportional to the incineration time, temperature, and degree of pellet incineration. At 700 degreesC and incineration time sufficient for a complete burnout, the efficiency of DXN reduction in the pellets of type A and C was found to be 99.9% and 99.7%, respectively. Correspondingly, the DXN concentration in the pellets decreased from 862 ng TEQ/kg to 0.9 ng TE Q/ kg for pellets A and 2.2 ng TEQ/kg for pellets C. The residual concentra tion of coplanar polychlorinated biphenyls (coplanar PCBs) was below 0.2 ng TEQ/kg and 0.4 ng TEQ/ kg, respectively. Assuming a tortuosity factor of t au = 3 and the reaction rate constants of 0.013 m/s (at 700 degreesC) and 0 .025 m/s (at 800 degreesC), the experimental pellet incineration times were reasonably predicted by using the shrinking core model. Possible DXN evapo ration from the pellets was also studied. The amount of DXNs in the flue ga s captured by an impinger trap was less than 3% when the reactor was operat ed at 700 and 800 degreesC. The described method of fly ash pelletization a nd reburning seems to be a relatively easy and inexpensive way to reduce bo th the emission of DXNs and the amount of fly ash.