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Show F-15, F-25, F-22 and F-40 the degree of burnout at 1.5 m ranges from 59% to 64%). However, when the coal rate was halved (SR = 2) the burnout was significantly higher than for the full rate condition, (72% to 81% for flames F-18, F-26, and F-23). The only exception to this was for the 930 C blast temperature, flame F-42, where in spite of a stoichiometric ratio of 2 the burnout was only 61%. The other bituminous coal tested at two stoichiometric ratios, the Norwich Park, also showed a significant improvement in burnout at a reduced coal input rate, (F-36 and F-35). The other test parameter that showed a large influence on the combustion rate was the coal rank. The rank order of the coals is from highest to lowest; Preussag, Norwich Park, Elk Creek and Armco. The burnout levels for the coals inversely follow that order, with the Armco coal giving the best performance and the Preussag the worst. A complete explanation for these results is quite complex, but significant insight into the combustion process for these coals can be acquired from an analysis of fig. 1. Here fuel burnout quantities (Zx and Tx) and local gas temperatures have been plotted versus axial distance, first for various flames obtained by changing input parameters with the Elk Creek coal in 1A and IB and then for the four coals and heavy fuel oil in 1C and ID. Tx is the total burnout level of the fuel while Zx is the degree of devolatilization of the sampled char, calculated from the percent volatile matter remaining in the solid material. On the left hand figs. A and C the approximate particle residence times in the furnace are shown, while in the right hand figs. B and D the axial position in the flame where the measurements were taken is indicated These two scales are directly interchangeable as shown in fig. 6. Based on results generated by various investigators and the general burnout trends measured in this trial, the following interpretation of the on axis coal burnout curves shown in fig. 1 seems probable. The burnout levels measured for distances less than 1.0 m (9 ms) probably result primarily from a loss in volatile matter. In figs. IB and ID the burnout curves for the bituminous coals show little or no increase in Tx between 0.25 and 1.0 m. This flat region is consistent with the very high degree of devolatilization measured for these coals, typically about 90% at the first measurement point (0.25 m), combined with the extreme lack of oxygen measured between 10-8 |