OCR Text |
Show An interesting finding in this connection, which has been described in Ref. 7, was that on one occasion we evaluated successively, for overfeed firing an Australian and and Indian coal, with very similar analyses - both with approximately 8% ash content. The combustion of the Australian coal was very satisfactory with carbon in ash losses below 1%; the performance with the Indian coal was wholly unsatisfactory with carbon in ash losses over k% even after a burn out equivalent to over 50$ of the grate areaI The difference was that the ash in the Indian coal was highly disseminated through the coal structure and the burning of the outer layers of a coal particle resulted in the formation of a powdery, but coherent, ash shell which prevented access of the combustion air to the core of particles; grading size reduction produced little improvement. The Australian coal ash was largely adventitious and did not interfere with combustion. r- ---- The value of the pot furnace testing in discovering the problems with an apparently suitable fuel is obvious. Ash Condition The aspect evaluated is ash clinkering. With few exceptions because of the thinner, cooler active bed the ash from spreader firing is rarely clinkered. Travelling grate combustion ashes from certain fuels, however, have been found to clinker to an unacceptable extent - at worst forming a molten "pancake" on the grate, disrupting air access with consequent undesirable effects on burn out and presenting possible handling difficulties. The effect of air temperature can be important. Pot furnace testing can discover and explore potential remedial actions to alleviate the problem. 24-14 |