Comparative study on formations of polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran and related compounds by pyrolysis of some precursors on unused sand for fluidized bed incinerator and long term used sand

The effect of wearing of sand in the furnaces of fluidized bed incinerators (FBIs) on the formation of polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF) and their related compounds from polychlorinated biphenyl (PCB) and 1,2,3-trichlorobenzene (1,2,3-T3CBz) was studied experimentally using a pyrolysis apparatus consisting of an injection unit; a stainless steel tube, in which packed was either unused sand (virgin sand) or used for two months in FBI (worn-out sand), heated to 650°C by an electric furnace; and a sampling unit. Furthermore, polychlorinated diphenyl ether (PCDE) was pyrolyzed on worn-out sand in order to compare the formation mechanisms of PCDD and PCDF with those from PCBs. Besides the generation of PCDD and PCDF, the hydroxylation of the starting compounds occurred. PCB was detected in the pyrolyzed samples of 1,2,3-T3CBz on both types of sand. In all cases, PCDF was in much higher yield than PCDD and pyrolysis on worn-out sand was more favorable for the formation of PCDD, PCDF and their relatives than pyrolysis on virgin sand. There was marked difference in metal concentrations between virgin and worn-out sand, implicating that the increased metal concentrations in sand would promote the formation of PCDD, PCDF and their related compounds in FBIs.