Prevention of polychlorinated dibenzo-p-dioxins/dibenzofurans formation on municipal waste incinerator fly ash using nitrogen and sulfur compounds

Formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans on incinerator fly ash can be reduced under laboratory conditions by the addition of ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), or Na2S. With these compounds (inhibitors), a reduction in formation of ca. 80-90% is achieved. The inhibitors reduce the ratio of [PCDD]:[PCDF] formed, suggesting that more than one pathway for the formation from carbon exists. EDTA and Na2S reduce the degree of chlorination of PCDD; for PCDF, the same effect is seen with Na2S. No change was ever seen in the isomer distribution within homologues as a result of the inhibitors added, in accordance with the theory that these isomer distributions are thermodynamically controlled. In additional experiments, NTA gave a good reduction with reaction times of 30-60 min, at temperatures between 300 and 400 degrees C, and with concentrations in the reaction mixture of 2-10%. With HCl as a chlorinating agent, the inhibition by NTA is >50% for both PCDD and PCDF. These inhibitors show promising results to achieve the reduction of PCDD/F formation. The additional experiments with NTA show that this compound can reduce formation under various conditions, making it suitable for use in the post-combustion zone of an incinerator, where reaction conditions will vary.