Effect of liquid inhibitors on PCDD/F formation, prediction of particle-phase PCDD/F concentrations using PLS modelling with gas-phase chlorophenol concentrations as independent variables

Emissions of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (P CDFs) from municipal waste incineration are currently a subject of consider able public concern because of their extreme toxicity. PCDD/F formation in incineration processes is being studied widely, but little work has been do ne on their inhibition. We studied the effect of two liquid inhibitors, sod ium ammonium hydrogen phosphate (NAHF) and urea (H2NCONH2), on PCDD/F. form ation in the combustion of liquid fuel doped with copper and chlorine using a pilot-scale plant. The inhibitors were injected into the flue gas stream at a temperature of 725 degrees C, whereupon both the chlorophenol and PCD D/F concentrations decreased. Particle-phase PCDD/F concentrations in parti cular decreased by up to 90 % with NAHF and 70 % with urea, but gas phase r eduction took place only with urea. The results suggest that the formation of PCDD/Fs is hindered in the particle phase a: the early stages of the PCD D/F formation chain, probably even before precursors such as chlorophenols have been formed. As a consequence, particle-phase PCDD/F concentrations ca n be predicted by a PLS (partial least-squares) approach with the gas-phase chlorophenol concentrations as independent variables. The structure and pa rtial charges of Cu+-urea complex were calculated by the HF/3-21G basis set . (C) 1999 Elsevier Science Ltd. All rights reserved.