Characteristics of Fly Ashes from Full-Scale Coal-Fired Power Plants and Their Relationship to Mercury Adsorption

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• 作者：Yongqi Lu ; Massoud Rostam-Abadi ; Ramsay Chang ; Carl Richardson ; Jennifer Paradis
• 刊名：Energy & Fuels
• 出版年：2007
• 出版时间：July 2007
• 年：2007
• 卷：21
• 期：4
• 页码：2112 - 2120
• 全文大小：654K
• 年卷期：v.21,no.4(July 2007)
• ISSN：1520-5029

文摘

Nine fly ash samples were collected from the particulate collection devices (baghouse or electrostaticprecipitator) of four full-scale pulverized coal (PC) utility boilers burning eastern bituminous coals (EB-PCashes) and three cyclone utility boilers burning either Powder River Basin (PRB) coals or PRB blends (PRB-CYC ashes). As-received fly ash samples were mechanically sieved to obtain six size fractions. Unburnedcarbon (UBC) content, mercury content, and Brunauer-Emmett-Teller (BET)-N₂ surface areas of as-receivedfly ashes and their size fractions were measured. In addition, UBC particles were examined by scanning electronmicroscopy, high-resolution transmission microscopy, and thermogravimetry to obtain information on theirsurface morphology, structure, and oxidation reactivity. It was found that the UBC particles contained amorphouscarbon, ribbon-shaped graphitic carbon, and highly ordered graphite structures. The mercury contents of theUBCs (Hg/UBC, in ppm) in raw ash samples were comparable to those of the UBC-enriched samples, indicatingthat mercury was mainly adsorbed on the UBC in fly ash. The UBC content decreased with a decreasingparticle size range for all nine ashes. There was no correlation between the mercury and UBC contents ofdifferent size fractions of as-received ashes. The mercury content of the UBCs in each size fraction, however,generally increased with a decreasing particle size for the nine ashes. The mercury contents and surface areasof the UBCs in the PRB-CYC ashes were about 8 and 3 times higher than UBCs in the EB-PC ashes,respectively. It appeared that both the particle size and surface area of UBC could contribute to mercurycapture. The particle size of the UBC in PRB-CYC ash and thus the external mass transfer was found to bethe major factor impacting the mercury adsorption. Both the particle size and surface reactivity of the UBC inEB-PC ash, which generally had a lower carbon oxidation reactivity than the PRB-PC ashes, appeared to beimportant for the mercury adsorption.