| OCR Text |
Show Mass Mean Diameter = 200 I (microns) For the two different nozzles used in our experiments, plots of combustion efficiency versus droplet diameter are shown in Figure 5-3. The trends indicate larger droplet diameters for all the steam atomization cases which resulted in lower combustion efficiency. The marked difference in the trends of the two different atomizers indicate that poorer droplet spray formation resulted from the modified North American nozzle effecting poorer combustion efficiency. This was comfirmed by head-on and lateral visual observation of the PETCOM flame, along with thermocouple measurements which indicated differing flame patterns with the two nozzles. In conclusion, although steam atomization resulted in poorer combustion efficiency, lower atomization energy due to low steam pressure and flow rates account for this poorer performance. Steam conditions were typical of those used with this burner for much lower viscosity residual fuel oils and thus indicate the requirement to either provide higher fuel preheat or higher steam pressures and flow rates for PETCOM. From an overall system efficiency point-of-view, additional fuel preheat would best achieve more efficient atomization by lowering fuel viscosity. As seen in later discussion, excessive steam atomization flow rates may impose burning rate limitations on coke particles by lowering flame temperatures and competing with oxygen for reaction sites. Droplet, Particle, and Slurry Combustion Once properly atomized, the PETCOM slurry must burn with a short compact flame to ensure good performance in oil-designed boiler applications. It is therefore desirable to achieve rapid burnout of the petroleum coke particles to minimize or eliminate any boiler derating. As will be shown in the following discussion, achieving an ultrafine grind of coke particles in the PETCOM is the key to this goal. 19-23 |
