Mineralogical and engineering characteristics of dry flue gas desulfurization products

Fifty-nine coal combustion products were collected from coal-fired power plants using various dry flue gas desulfurization (FGD) processes to remove SO 2. X-ray diffraction analyses revealed duct injection and spray dryer processes created products that primarily contained Ca(OH) 2 (portlandite) and...

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Bibliographic Details
Published in:Fuel (Guildford) 2005-10, Vol.84 (14), p.1839-1848
Main Authors: Bigham, Jerry M., Kost, David A., Stehouwer, Richard C., Beeghly, Joel H., Fowler, Randy, Traina, Samuel J., Wolfe, William E., Dick, Warren A.
Format: Article
Language:English
Subjects:
Air pollution caused by fuel industries
Applied sciences
Coal ash
Energy
Energy. Thermal use of fuels
Ettringite
Exact sciences and technology
Flue gas desulfurization products
Pollution reduction
Stack gas and industrial effluent processing
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Summary:Fifty-nine coal combustion products were collected from coal-fired power plants using various dry flue gas desulfurization (FGD) processes to remove SO 2. X-ray diffraction analyses revealed duct injection and spray dryer processes created products that primarily contained Ca(OH) 2 (portlandite) and CaSO 3·0.5H 2O (hannebachite). Most samples from the lime injection multistage burners process contained significant amounts of CaO (lime), CaSO 4 (anhydrite), and CaCO 3 (calcite). Bed ashes from the fluidized bed process were often dominated by CaSO 4 but also contained CaCO 3, CaO (lime), and MgO (periclase). Cyclone ashes were similar in composition to the bed ashes but contained more unspent sorbent and CaSO 4 and less MgO. Fly ash in all samples ranged from 10 to 79 wt%. Samples usually exhibited two distinct swelling episodes. One occurred immediately after water was applied due to hydration reactions, especially the conversion of CaO to Ca(OH) 2 and CaSO 4 to CaSO 4·2H 2O (gypsum). The second began between 10 and 50 d later and involved formation of the mineral ettringite (Ca 6[Al (OH) 6](SO 4) 3·26H 2O). The final pH after 112 d ranged from 10.0 to 12.1. If samples are incubated under ‘closed’ (i.e. incomplete recarbonation with atmospheric CO 2) and alkaline weathering conditions, gypsum and portlandite are initially formed followed by the conversion of the gypsum to ettringite. Closed, alkaline conditions typically can occur when FGD products are placed in confined settings such as a road embankment or buried as a discrete layer as occurs in some surface mine reclamation projects.
ISSN:0016-2361
1873-7153
DOI:10.1016/j.fuel.2005.03.018