OCR Text |
Show The data for F-23 again demonstrate the importance of oxygen concentration in the combustion rate of the soot-like material. After an ignition delay, the rapid decrease in O2 is accompanied by a rapid rise in the C/H ratio. When the on axis oxygen concentration again rises, the sootlike material apparently is quickly oxidized and the burnout rapidly improves. In fig. 4 the C/H ratio, Tx, and the O2 concentration are shown for the two input rates tested with the Norwich Park coal. Judging from the C/H ratios during the combustion, this coal has a reduced sooting tendency when compared to the Elk Creek coal. This is perhaps not surprising for a coal of this particular rank. The amount of tar expected from the Norwich Park coal, on a percent daf of the input coal basis, would be much less than the Elk Creek coal, (see fig. 7). In fig. 5 the same burnout related parameters are shown for the 1200 and 930°C blast temperature Armco flames F-28 and F-29. For this coal the sooting tendency does not appear to be particularly strong. This rank coal could release more of its volatile matter as gaseous products than the Elk Creek coal inhibiting sooting behaviour. A greater amount of gaseous volatiles from the Armco versus the Elk Creek coal also would help account for the much earlier peak temperature produced by the Armco coal, fig. 1C. The difference in combustion behaviour found for the two high volatile bituminous coals was observed not only in the burnout and temperature measurements but also in the visual flames. The Elk Creek flame was extremely bright while the Armco coal gave a more transparent flame. This difference is also attributed to a much high soot concentration with the Elk Creek coal. Another significant and important result for blast furnace use, was the combustion behaviour at reduced blast temperatures. When the Elk Creek coal was injected in a blast temperature just below 1000°C the bright flame resulting from volatile combustion and cracking disappeared, except for random ignition of either separate or small groups of particles. As the blast temperature was reduced still further to 930°C these ignition flashes disappeared, and the combustion process took place without a visible flame, (F-42). For flame F-42 (930°C blast) the burnout at 1.5m was lower than for flame F-18 (1200°C blast) while for flame F-23 (1030 C blast) no decrease 10-17 |