OCR Text |
Show The flue-gas temperature, which strongly affects the boiler efficiency, was not constant during the coal particle size tests. It increased with time because of increasing ash deposition in the boiler. The average flue-gas temperature during a 6-hour test period was higher when burning COM containing finer coal. Because of the combining effects of the carbon-conversion efficiency and the flue-gas temperature, the average boiler efficiencies ranged from 81.3 percent when firing coarse coal to 82.0 percent when firing fine coal in 40 percent COM. Effect of Coal Type Three coal types, with initial ash deformation temperatures of 2030 F (Illinois No. 6 coal), 2110 F (Montana subbituminous coal), and 2350°F (Pittsburgh seam coal), were tested. Two coal particle size consists were used in the COM: a coarse size (67 percent minus 200 mesh) using Montana and Pittsburgh coals, and a fine size (90 percent minus 200 mesh) using Illinois and Pittsburgh coals. No serious problems due to slagging or fouling were experienced during these 6-hour duration tests. For full load tests with 50 percent COM, the carbon-conversion efficiencies were 99.7 percent for Montana coal, 96.7 and 99.0 percent for Pittsburgh coarse and fine coal, respectively, and 99.4 percent for Illinois coal. The corresponding boiler efficiencies were 82.6, 81.1, 82.4, and 82.3 percent for Montana, coarse Pittsburgh, fine Pittsburgh, and Illinois coal, respectively. Pollutant Emissions With a similar set of boiler operating conditions and a particular coal type, the fly-ash emissions increase with increasing the coal concentration and with increasing the coal particle size consist in the COM. The fly-ash emissions were also found to be higher when unwashed Pittsburgh seam coal was used than when washed coal was used. The average fly-ash particle size also increased with increasing coal particle size in the 14-5 |