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Mercury and dioxins in a MercOx-scrubber
Örebro University, Department of Natural Sciences.
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
Keywords [en]
waste incineration, flue gas cleaning, PCDD/PCDF, PBDD/PBDF, wet scrubber
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:oru:diva-825ISBN: 91-7668-519-5 (print)OAI: oai:DiVA.org:oru-825DiVA, id: diva2:137327
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
List of papers
1. Mercury speciation in flue gases after an oxidative acid wet scrubber
Open this publication in new window or tab >>Mercury speciation in flue gases after an oxidative acid wet scrubber
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2007 (English)In: Chemical Engineering & Technology, ISSN 0930-7516, E-ISSN 1521-4125, Vol. 30, no 1, p. 131-138Article in journal (Refereed) Published
Abstract [en]

Flue gases from a hazardous waste incinerator have been sampled in three campaigns, before and after, an oxidative acid wet scrubber working with the MercOx-process. A continuous emission monitor for mercury speciation was used before the scrubber in the first campaign. In all campaigns, impingers with KCl and KMnO4 were used. A solid adsorption method was used in the last campaign. The mercury leaving the scrubber is oxidized at > 90 % efficiency (independent of the inlet speciation). A substantial decrease in the redox potential of the scrubber liquid caused an increased fraction of elemental gaseous mercury to be present in the clean gas. The measurements also show that the scrubber has the ability to readily absorb mercury peaks. During one extreme peak of 3,600 μg/m3 (dry gas) in the raw gas, the removal efficiency was above 99.9 %.

National Category
Engineering and Technology Chemical Engineering
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3203 (URN)10.1002/ceat.200600172 (DOI)
Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2017-12-14Bibliographically approved
2. Equilibrium calculations of mercury in a MercOx scrubber
Open this publication in new window or tab >>Equilibrium calculations of mercury in a MercOx scrubber
(English)Manuscript (Other academic)
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3204 (URN)
Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2017-10-18Bibliographically approved
3. Dioxin emissions after installation of a polishing wet scrubber in a hazardous waste incineration facility
Open this publication in new window or tab >>Dioxin emissions after installation of a polishing wet scrubber in a hazardous waste incineration facility
2005 (English)In: Chemosphere, ISSN 0045-6535, E-ISSN 1879-1298, Vol. 61, no 3, p. 405-412Article in journal (Refereed) Published
Abstract [en]

Dioxin levels measured after wet scrubbing systems have been found to be higher than levels measured before the scrubber. It is believed that there is an adsorption of PCDD/Fs on plastic materials in the scrubber. The PCDD/F levels after a polishing wet scrubber were followed continuously for 18 months using long-time sampling equipment at a hazardous waste incineration facility in Sweden. Each sampling period lasted two weeks. It was found that the levels during and shortly after start-up periods were elevated. The decline was very slowly, which supports a memory effect in the scrubber. Further, a multivariate model showed that the relation between different homologues changed over time, which is in agreement with a desorption model, taking into account the vapour pressures for different congeners.

National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3205 (URN)10.1016/j.chemosphere.2005.02.015 (DOI)
Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2017-12-14Bibliographically approved
4. Numerical modelling of the memory effect in wet scrubbers
Open this publication in new window or tab >>Numerical modelling of the memory effect in wet scrubbers
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.

National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3206 (URN)10.1016/j.chemosphere.2007.06.095 (DOI)
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
5. Comparison of PBDD/Fs and PCDD/Fs in flue gases and fly ash from a MSW incinerator
Open this publication in new window or tab >>Comparison of PBDD/Fs and PCDD/Fs in flue gases and fly ash from a MSW incinerator
2006 (English)In: Organohalogen Compounds, ISSN 1026-4892, Vol. 68, p. 1800-1803Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Vienna: Federal Environmental Agency, 2006
National Category
Environmental Sciences
Research subject
Environmental Chemistry
Identifiers
urn:nbn:se:oru:diva-3207 (URN)
Available from: 2006-12-29 Created: 2006-12-29 Last updated: 2017-10-18Bibliographically approved

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