OCR Text |
Show SO« removal efficiency increased with increasing baghouse temperature and Na2/S ratio. The SO« removal efficiency was about 70 percent when the Na2/S ratio was 1 and the baghouse temperature was 475°F. This corresponds to a sorbent utilization of 70 percent. Removal efficiencies as high as 90 percent were achieved at higher Na2/S ratios but with lower sorbent utilization. Ash Deposition The 700-hp boiler was not equipped with furnace ash removal equipment. Ash carried into the boiler by the fuel was either emitted as fly ash or left within the boiler as deposits. Coal concentration and the coal particle size consist in COM affect not only the fly-ash emissions but also the ash deposition in the boiler. During the combustion tests with different coal particle size consists, it was observed that contrary to what one would intuitively expect, the amount of ash deposition increased with increasing the fineness of coal particle size. The structure of the ash deposits also depended on the coal particle size consists in the COM. The coal type did not produce any significant difference in ash deposition nor on slagging during the 6-hour short-duration tests, although the initial ash deformation temperatures were different for these coals. During the 500-hour duration test with the 40 percent COM and Pittsburgh seam coal, a total of 4830 pounds of ash, or 0.76 percent of the total COM fuel input, accumulated in the furnace after 370 hours of operation. This ash accumulation blocked a large portion of the entrance to the convection bank of the boiler. As a result, a steady furnace pressure could not be maintained, and the boiler was shut down for ash removal. Subsequently, a set of two retractable furnace soot blowers was developed. The soot blowers were inserted from the two viewports at the rear wall of the boiler and positioned approximately 3 ft above the furnace floor and l£ ft from each of the two side walls. To determine the effectiveness of the furnace soot blowers, 14-7 |