Assessment of environmental impact of oil shale fly ash from PF and CFB combustion
Date
2011-07-22
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Abstract
Käesoleva doktoritöö eesmärgiks oli uurida põlevkivielektrijaamast pärine¬vate tahkete osakeste ehk tuha mõju keskkonnale võrreldes omavahel tolm¬põletus- ja keevkihtpõletustehnoloogiat. Töö käigus teostati uuringud, mis kirjeldavad lendtuha aerosooli käitumist atmosfääris, tuhaosakeste settimis¬kiirust ning polüaromaatsete süsivesinike (PAH) ja raskmetallide sisaldust põlev¬kivielektrijaama lendtuhas, samuti põlevkivituha käitumist veega kokku¬puutel. Tuhaproovid pärinesid AS Narva Elektrijaamad kahel erineval tehno¬loogial põhineva põletamisprotsessi tuhakogumispunktidest. Atmosfäärsete saasteainete uuringud viidi läbi suurtes atmosfääriosakeste uuringute kambrites nii USAs kui Eestis. Uuritud tuhkade fraktsioonilised jaotus¬omadused ja käitumine ajas oli suhteliselt sarnane. Mitmemodaalse jaotusega tuhaosakeste suurused olid peamiselt vahemikus 2–5 µm. Suuremad osakesed settisid väga kiiresti, enamasti paari tunniga. Väiksemad osakesed aga olid stabiilsemad.
Kogu PAH sisaldus uuritud tuhafraktsioonides jäi tolmpõletusprotsessi puhul vahemikku 82,2–152,1 µg/kg, samas kui keevkihttehnoloogiast pärineva tuha PAH sisaldus oli madalam, jäädes vahemikku 30,2–63,7 µg/kg. Teostatud leostuskatsetele vastavalt Euroopa standardile EN 12457–2, leiti et mõlema põletusprotsessi tuha vesiekstraktid olid väga leeliselised. Kõrged juhti¬vuse väärtused ja mineraalosa kontsentratsioon vesiekstraktis viitavad põlev¬kivituhas leiduvate anorgaaniliste ühendite suurele lahustuvusele. Märkimis¬väärsel hulgal leostus põlevkivituhast välja PAHe. Leostustesti kaheetapiline rakendamine tõestas, et põlevkivituhast erinevate saasteainete eraldumine vesifaasi on pidev protsess.
Raskmetallide analüüsidest leiti, et peenematel tuhaosakestel, mis pärinesid tolmpõletustehnoloogia viimastest elektrifiltritest on märkimisväärne kontsent¬ratsioon Pb ja Zn puhul. Samas aga keevkihttehnoloogia puhul on Pb ja Zn kontsentratsioonid madalamad tänu madalamale põletamistemperatuurile.
Töö tulemusena saadi väärtuslikku infot põlevkivienergeetika tahkete atmos¬fäärsete heitmete käitumise kohta keskkonnas.
Fly ash discharged by PF and CFB combustion process from Estonian PP was compared in this work. Special emphasis was addressed to polycyclic aromatic hydro¬carbons (PAH) and toxic heavy metals. Investigation of difference in atmo¬spheric behavior of the fine particles was made. Also leaching test according to European Standard EN 12457–2 was carried out. The properties and aging behavior of the fly ash aerosols from PF and CFB process had similar properties and behavior in the simulated chamber study. Initial fly ash aerosol had multimodal fractional distribution with mass mean diameters around 2 μm and 5 μm. Both the PF and the CFB fly ash formed during the aging process stable aerosol with mass median diameter around 2 μm which is prone to long-range transport. Based on the experimental results obtained in this study with oil shale fly ash aerosol, we can conclude that the new CFB technology does not provide better performance comparing to the PF technology, from an environmental point of view. The total concentration of PAH in the ash fractions was found to be in the range of 82.2-152.1 µg/kg for the PF process, whereas for the new CFB technology, the total content of PAH was lower, 30.2-63.7 µg/kg. According to the leaching test the water extracts of different ash samples were very alkaline with similar pH values. The high conductivity values and high concentration of mineral components in the water indicates a significant water solubility of inorganic ingredients of oil shale ash. Organic components, including hazardous PAH, were also found in water extracts. A continuous release of mineral and organic compounds to the water phase was detected with two-phase leaching tests. However, from leaching tests of the ash, the cumulative release of PAH, was more significant in CFB process than in the PF process. Therefore the environmental hazard of deposition of solid wastes would be more pronounced in the CFB process than in the conventional PF technology. There was a notable accumulation of heavy metals such as Pb and Zn in the oil shale fly ash collected from the last electric precipitator of the boiler operating on the PF technology. The high concentration and toxicity of the heavy metals in the fly ash can cause environmental problems and is an obstacle to the direct application without any treatment. As a result of the current study valuable knowledge of the impact of the solid waste from oil shale PPs on the environment was obtained.
Fly ash discharged by PF and CFB combustion process from Estonian PP was compared in this work. Special emphasis was addressed to polycyclic aromatic hydro¬carbons (PAH) and toxic heavy metals. Investigation of difference in atmo¬spheric behavior of the fine particles was made. Also leaching test according to European Standard EN 12457–2 was carried out. The properties and aging behavior of the fly ash aerosols from PF and CFB process had similar properties and behavior in the simulated chamber study. Initial fly ash aerosol had multimodal fractional distribution with mass mean diameters around 2 μm and 5 μm. Both the PF and the CFB fly ash formed during the aging process stable aerosol with mass median diameter around 2 μm which is prone to long-range transport. Based on the experimental results obtained in this study with oil shale fly ash aerosol, we can conclude that the new CFB technology does not provide better performance comparing to the PF technology, from an environmental point of view. The total concentration of PAH in the ash fractions was found to be in the range of 82.2-152.1 µg/kg for the PF process, whereas for the new CFB technology, the total content of PAH was lower, 30.2-63.7 µg/kg. According to the leaching test the water extracts of different ash samples were very alkaline with similar pH values. The high conductivity values and high concentration of mineral components in the water indicates a significant water solubility of inorganic ingredients of oil shale ash. Organic components, including hazardous PAH, were also found in water extracts. A continuous release of mineral and organic compounds to the water phase was detected with two-phase leaching tests. However, from leaching tests of the ash, the cumulative release of PAH, was more significant in CFB process than in the PF process. Therefore the environmental hazard of deposition of solid wastes would be more pronounced in the CFB process than in the conventional PF technology. There was a notable accumulation of heavy metals such as Pb and Zn in the oil shale fly ash collected from the last electric precipitator of the boiler operating on the PF technology. The high concentration and toxicity of the heavy metals in the fly ash can cause environmental problems and is an obstacle to the direct application without any treatment. As a result of the current study valuable knowledge of the impact of the solid waste from oil shale PPs on the environment was obtained.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
põlevkivienergeetika, elektrijaamad, põlevkivituhk, keskkonnamõjud, oil-shale energetics, power plants, oil-shale ash, environmental impacts