Relationship Between Coal Ash Chemistry and Electrostatic Precipitator Opacity
Title:
Relationship Between Coal Ash Chemistry and Electrostatic Precipitator Opacity
Author:
Gentzis, Thomas Goodarzi, Fariborz
Appeared in:
Energy sources. Part A, Recovery utilization and environmental effects
Paging:
Volume 18 (1996) nr. 5 pages 585-600
Year:
1996-07-01
Contents:
Results of ash chemistry composition on highwall channel samples, coal seams 1-6, cut W86, Whilewood Mine, reveal that low SiO2 / Al2O2 ratios are associated with high electrostatic precipitator (ESP) opacity. This ratio varies from 2·26 in seam 3 to 5·81 in seam 4, and is a good indicator of the clay minerals present in the coal. A low ratio (<2·0) indicates the predominance of kaolinite clays, while a higher ratio (∼5·0) is indicative of montmorillonite clays. In the latter case there is less SiO2 available to form free quartz. The average Na2O content in seam 3 and seam 6 is 0·94% and 0·90%, respectively, much higher than in the remaining seams (0·38-0·55%). Poor ESP performance at the Wabamun power station is linked to low sodium content in coal and low Na2O content in coal ash; the problem has been rectified with the addition of Na2SO4 to the feed coal. Sodium is present mainly in an “inactive” form, in aluminosilicate minerals, this form being non-leacheable. The same is true of K2O, the inactive form of which is less effective in reducing ash resistivity. The “active” alkalis of sodium and potassium are organically or salt bound; are leacheable following extraction with water, ammonium acetate, and hydrochloric acid; vary laterally in the mine site; and contribute to ESP performance. The CaO content is highest in seam 3 (17·11%), and its significance in affecting ash resistivity increases due to the low Na2O and K2O contents in the Whitewood Mine coals. Anomalous values of CaO, Fe2O3, K2O, and SO2 at various locations in the mine may be the result of recent deposition of gypsum on the coal seam faces due to groundwater discharge. These values are not indicative of the coal ash chemistry away from the face of the exposed coal, and thus are unlikely to contribute to ESP performance. The average Alkaline Sulfate Index (ASI) is highest in seam 3 (3·17), followed by seam IL (2·56). The same index for seams IU and 4 is about 1·50. Based on studies conducted at the nearby Keephills power station, ESP opacity is expected to be higher than 15% when the ASI is less than 4·0. No significant lateral trends within the Whitewood Mine coals seams in a north to south direction are observed. Variations in ash chemistry of coal seams in Cut W86 relative to those in Cut W83 are attributed to the natural heterogeneous nature of the coal rather than “real trends.” However, these differences may affect ESP efficiency at Wabamun.
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