Adsorption of PCDD/F on MWI fly ash

The formation of dioxins in combustion systems

“…The use of external surface for reaction analysis is consistent with the results for MSW ash of Mätz-ing et al [77]; they found that the global area was similar to the BET area, suggesting that the particles had negligible porosity. Hinton and Lane [145] after extensively characterising the ashes from 13 MSW incinerators concluded that "comparing the electron micrographs, mercury porosimetry and surface area data suggests that the majority of the surface area is found on the exposed surfaces of the flyash rather than the internal pores."…”

“…Great affinity by PCDD/F for the ash surface of ESP dust taken from an iron ore sinter strand is reported by Wang et al [76]. Mätzing et al [77] carried out equilibration tests between flyash entrained in a gas stream and HCDD added as vapour. The residence time was 1.5 s and the temperature ranged from 25 to 135 • C. They report findings similar to those of Birat et al [15], with the gas/particle partitioning at low temperatures corresponding to the sublimation equilibrium.…”

“…The rate constant for the decomposition of OCDD at 300 • C was 1.5 × 10 −3 s −1 in the presence of water vapour [78], which should be compared with a formation rate constant from PCP [77] of 1 × 10 −4 s −1 . The latter rate relates to the concentration of PCP in the gas phase, which is generally orders of magnitude higher than the surface concentration of PCDD/F.…”

“…Mätzing et al found [77] that only about one-third of the PCDD/F originally present on a flyash could be removed by solvent extraction, leading them to conclude that the strongly bound material may not vaporise in their tests. It appears that significant amounts of PCDD/F are held on the surface of flyash particles, and do not participate in gas/solid partitioning.…”

“…Alternatively, CuCl 2 may be preferentially converted to the sulfate, which is inactive. Mätzing et al [77] found that urea was an effective inhibitor when added to a pilot-scale furnace. Ruokojärvi et al [143] performed similar tests in a pilot furnace burning synthetic MSW, and found a diminution in PCDD/F by three quarters when 1 wt% urea was added.…”