Atmospheric chamber study of oil shale fly ash particles from circulating fluidized bed and pulverized firing processes

Oil shale combustion fly ash collected to electric precipitators from pulverized firing (PF) and circulating fluidized bed combustion (CFB) processes was investigated in atmospheric chamber experiments. The aim of the work was to detect differences in the atmospheric behaviour of the fine particles from CFB and PF boilers of the Estonian Power Plant (PP), located close to Narva, Estonia. One series of experiments was performed in a dual outdoor Teflon film smog chamber (270 m3) at the University of North Carolina at Chapel Hill (USA) under normal weather conditions (temperature, humidity, sunlight). Parallel tests were carried out in an outdoor smog chamber (108 m3) at Tuulna, Harju County, Estonia, where the experiment was made under meteorological conditions similar to those at the location of the PP. The size distribution and number concentration of particles in the chamber were monitored during the experiment. The fractional distribution results demonstrate that the CFB aerosol in the chamber air had more fine particles than the PF aerosol. Approximately 2 h after injection the fly ash particles larger than 4 μm had settled out from both samples. The initial fly ash aerosol had a trimodal fractional distribution. Both PF and CFB fly ash formed stable aerosols 1–3 μm in diameter during the 6 h experiment and are therefore prone to long-range transport

Elektri tootmisel tekkiva põlevkivituha keskkonnamõju – keevkiht- ja tolmpõletustehnoloogia

Väitekirja elektrooniline versioon ei sisalda publikatsioone.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