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Show 3. PERFORMANCE CHARACTERISTICS OF THE EXPERIMENTAL COAL-IN-OIL FUELS 3.1 Comparison of COM and COD These experiments concerning the effect of coal particle size in the coal-in-oil fuels were made using the furnace number 1, fired at 4.5 MW using the nominal 4 MW burner with appropriate atomisers and using ambient temperature combustion air. Neither fuel was found to be particularly difficult to handle in terms of pumping and preheating although it must be emphasized that the period of the trials was insufficient to allow any real comparison for example in terms of abrasion effects upon pumps etc. A further point is that the COM was as noted above, prepared continuously and fired immediately which in the event successfully precluded the possibility of sedementation. Significant differences in the fuels, which could be related to the coal particle size, were experienced in the fuel gun itself. It was found that the COD could be fired successfully with either atomizer to produce acceptable flames but with the COM it was necessary to have a larger minimum passage diameter in the atomizer in order to avoid gun blockage. In the event it was impossible to employ successfully the Y-jet atomizer for COM combustion but acceptable flames were produced with the internal mix atomizer. Within these limits acceptable flames could be produced for apparant-ly ultimated periods with either fuel although in general the COD could be fired successfully within a significantly greater range of atomizer and burner variables than could the COM. Concerning "acceptability" in relation to the flames, important criteria were naturally ignition stability, the avoidance of flame impingement upon the quarl or furnace walls and the formation of smoke and the minimization of sparklet emission from the flame tail. Within these criteria there were however differences in the characteristics of the flames produced by the two coal-in-oil fuels. COD could be fired to give flames which were well formed with no apparent sparklet emission at the flame tail. Their appearance was generally similar to the reference oil flames as were their dimensions for equivalent thermal input. The COM flames were also well formed but had somewhat different general characteristics. The visible flame region was significantly shorter but sparklet emission from the flame tail could not be completely eradicated. In addition, the visible flame region itself tended to be more intense than that of the COD flames. Particular importance in these experiment, was placed upon total level of burn out, Cx, in the furnace flue. To evaluate this parameter, samples of the ash in the flue gas were extracted isokinetically at a point in the exhaust duct, 1.8 m after the furnace end. These samples were subsequently analysed for remaining combustible matter and based on the assumption the coal ash may be used as a tracer, the total burn out Cx was calculated according to: 15-8 |