Feasibility of a monitoring system for detecting changes in dioxin concentrations of both in flue gas and fly ash in incineration plants

Surrogate measurements should be low in cost and quick to perform. To examine its feasibility, continuous surrogate monitoring was performed using an organic halogen compound (OHC) analyzer. Surrogates for dioxins (DXNs) from waste incinerators were examined by changing the operating conditions such as the atomized volume of activated carbon added and the temperature at the inlet of the dust collector. OHCs were measured along with DXNs in flue gas at the inlet and the outlet of the dust collector of two waste incinerators over five runs; the fly ash was sampled at the same time. Although the final flue gas concentration of DXNs at the incineration plants was below the regulation criteria, this does not mean complete reduction of DXNs. In addition, the de novo synthesis of DXNs inside the dust collectors was studied by analyzing the mass balance for DXNs concentrations in flue gas and fly ash. Semivolatile chlorinated organic compound concentrations at the outlet of the bag filter were basically well correlated with DXNs levels at the inlet of the bag filter in the test runs. When advanced flue gas treatment is applied by using a bag filter and lime/activated carbon adsorbent, DXNs that may be generated during flue gas cooling processes move to the fly ash, and this amount determines the mass balance of the entire system. It may be useful to monitor surrogate organic halogens for detecting changes in DXN concentrations of both flue gas and fly ash in incineration plants.     

Adsorption characteristics of carbonaceous adsorbents for organic pollutants in a model incineration exhaust gas

Adsorption characteristics of carbonaceous adsorbents were examined using 1,2,3,4-tetrachlorobenzene, naphthalene and 2,4,6-tribromophenol as adsorbates. The breakthrough and equilibrium adsorption characteristics were evaluated using laboratory-scale adsorption test equipment. A micropore volume of diameter less than 2 nm is the most important factor governing the adsorption capacity of all adsorbates. A kinetic analysis was performed and the adsorption behavior of the adsorbates was analyzed. Diffusion within porous particles controls the adsorption rate in this system, and the diffusion process is a function of pore diffusion. The operating conditions in working incineration facility adsorbers were reviewed and the breakthrough time of these adsorbents in actual adsorbers was estimated using the mass transfer zone method. Information on the optimal operating conditions of adsorbers was derived from the adsorption breakthrough characteristics.     

Polyethylene conversion by partial oxidation in supercritical water

This paper gives the results of partial oxidation experiments of polyethylene (PE) in supercritical water (SCW). The experiments were carried out at a reaction temperature of 693K and a reaction time of 30 min using 6 cm³ of a batch-type reactor. The loaded sample weight was 0.3 g and there was 2.52 g water (0.42 g/cm³). The ratio of oxygen atoms to carbon atoms was 0.3. The results show a significant CO formation in O₂–SCW, and the 1-alkene/n-alkane ratio in partial oxidation was higher than that in SCW pyrolysis. These results suggest the possibility of the hydrogenation of hydrocarbon through partial oxidation followed by a water–gas shift reaction. Received: July 19, 2000 / Accepted: September 28, 2000     

Modification of UNIFAC parameter table Revision 5 for representation of aqueous solubility and 1-octanol/water partition coefficient for POPs

In order to represent aqueous solubility and 1-octanol/water partition coefficient for POPs (persistent organic pollutants) by the UNIFAC model, two pairs of group interaction parameters in Revision 5 of the UNIFAC parameter table were modified. First, the pair of interaction parameters between the aromatic carbon-chloride (ACCl) and water (H2O) groups were corrected by minimizing the deviation between the experimental and calculated values of these properties for chlorinated benzenes, polychlorinated biphenyls, and polychlorinated dibenzo-p-dioxins and dibenzofurans. The corrected interaction parameters provided a better representation of both properties than the calculation results obtained in early works using the UNIFAC model. Second, the unknown pair of interaction parameters between the chloroalkene (Cl(C=C)) and H2O groups, which are required for calculating those properties of the other five POPs (aldrin, chlordane, endrin, dieldrin, and heptachlor), were newly determined from the experimental data on their properties. Finally, this study shows that Revision 5 could also predict solubility of POPs in some organic solvents. The modified parameter table is first suggested as the UNIFAC parameter table applicable to various phase equilibria including aqueous or nonaqueous solubility and partition coefficient of POPs.