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Numerical modelling of the memory effect in wet scrubbers
Örebro University, Department of Natural Sciences.
2008 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 73, no 1, p. S101-S105Article in journal (Refereed) Published
Abstract [en]

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) can be absorbed in and desorbed from polypropylene (PP) tower packings in wet scrubbers utilized in waste incineration lines. This behaviour, also known as the memory effect, has been modelled using a gas phase – PP surface equilibrium and a numerical solid phase diffusion model describing the transport of PCDD/Fs inside the PP. The diffusivities and gas – PP partition coefficients of TCDD/F to HxCDD/Fs in PP have been estimated using the numerical model. Two incineration lines were modelled. In the first line, the absorption and desorption in PP test rods was followed before and after installation of a fabric filter that was placed before a wet scrubber. In the second incineration line, the accumulation of PCDD/Fs in a wet scrubber during start up periods and the subsequent decline during the following three months was modelled and compared to continuous two-week gas measurements after the scrubber. The obtained diffusivities in PP range from 10−13 m2/s for TCDD to 10−16 m2/s for HxCDD. Lower chlorinated homologues with a distinctive change in concentrations during the desorption period (e.g. TCDF) are easier to model, and show the best agreement between the two incineration lines.

Place, publisher, year, edition, pages
2008. Vol. 73, no 1, p. S101-S105
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:oru:diva-3206DOI: 10.1016/j.chemosphere.2007.06.095OAI: oai:DiVA.org:oru-3206DiVA, id: diva2:137325
Note
Supplement 1. Halogenated Persistent Organic Pollutants Dioxin 2005 - Selected Papers from the 25th International Symposium on Halogenated Environmental Organic Pollutants and POPs held in Toronto, Canada, August 2005Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Mercury and dioxins in a MercOx-scrubber
Open this publication in new window or tab >>Mercury and dioxins in a MercOx-scrubber
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The removal of mercury and the absorption of dioxins in an acid wet scrubber have been studied in industrial scale. Hydrogen peroxide is added as an oxidizing agent to the scrubber liquid with the purpose to remove SO2 and enhance the removal of mercury. The scrubber is operating as the final flue gas cleaning stage at the SAKAB plant, a hazardous waste incinerator in Sweden.

Mercury speciation was measured in flue gases upstream and downstream of the scrubber with three different techniques: Impingers, solid phase absorbents and a continuous emission monitor. During the flue gas sampling periods also the scrubber liquid was sampled. It was found that mercury entering the scrubber is efficiently oxidized at normal operating conditions. An increased fraction of elemental gaseous mercury was found in flue gases after the scrubber at redox potentials below 700 mV and pH below 1. The mercury emissions were more dependent on the scrubber liquid composition than on the inlet concentrations.

Equilibrium calculations of the mercury speciation in the scrubber liquid and flue gases after the scrubber showed that mercury is normally emitted as HgBr2 or HgCl2. Elemental bromine and chlorine are formed in the scrubber. Both species probably take part in the mercury oxidation process.

Results from 18 months of dioxin sampling, using a continuous long term sampling device (the AMESA system) were evaluated by multivariate data analyses. It was shown that the elevated emissions observed were caused by a memory effect in the scrubber due to high start-up concentrations. The memory effect was modelled in a diffusion model where the dioxins were considered to be physically absorbed in and desorbed from the polypropylene fillings of the scrubber. From the diffusion model, the diffusivities for tetra to hexa chlorinated dioxins in polypropylene were calculated. The diffusivity of tetra chlorinated dioxins was calculated to be 10-14 m2/s. The diffusivity decreases with increasing chlorination. For hexa chlorinated dioxins it was calculated to be 10-16 m2/s.

Brominated dioxins were measured before and after a fabric filter. The fraction of brominated dioxins increased after the filter. Di brominated furans were the most abundant homologue.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek, 2006. p. 54
Series
Örebro Studies in Chemistry, ISSN 1651-4270 ; 7
Keyword
waste incineration, flue gas cleaning, PCDD/PCDF, PBDD/PBDF, wet scrubber
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-825 (URN)91-7668-519-5 (ISBN)
Public defence
2007-01-19, Hörsal 1, Prismahuset, Örebro universitet, Örebro, 10:15
Opponent
Supervisors
Available from: 2006-12-29 Created: 2006-12-22 Last updated: 2017-10-18Bibliographically approved

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Löthgren, Carl-Johan

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