OCR Text |
Show Coals lower in iron or alkalis would be the easiest fuels for retrofitting oil-fired steam generators by direct firing. The derating would be minimal, and deficient heat-transfer surface could be made up by adding partial division walls at the furnace exit. BENEFICIATION AND COAL BLENDING Approaches other than direct firing are being considered as a means of displacing oil with coal in oil-fired steam generators. Reducing total ash content by coal beneficiation appears to be a logical approach. Mechanical processes have been used since the early 1930s to beneficiate coal by removing large portions of extraneous ash. More recently, mechanical cleaning has been considered as a method for controlling surface emissions by removing pyrites before combustion. Deurbrouck performed extensive washability studies on 455 mine samples representing 70 percent of the total United States existing coal supply at the time.33 The investigation indicated that many of the coals tested would yield a clean fraction with less than 4 percent ash when crushed to -3/8 in. and washed at a specific gravity of 1.3. Furthermore, he indicated a pyritic sulfur reduction between 30 and 75 percent could be expected with a 90-percent yield for all coals tested. The reduction could be increased to between 55 and 88 percent if a 60-percent yield were acceptable. The washability studies were all performed on coals crushed to 1-1/2 in. x 0 and 14 mesh x 0-all within the size range that can be handled by coal cleaning plants. R. Saltzman, et al.,31* of Bituminous 1-46 |