| OCR Text |
Show 5 the furnace where pulverized coal was supplied with N2 gas added NO of a known quantity. Table 1 Characteristics of the Coals used Coal A B C D E F Gross calorific value (kcal/kg) 6,520 5,690 6,980 6,620 6,830 6,050 Proximate analysis: Moisture (wt%) 4.4 6.2 1.3 3.2 2.8 3.2 Volatile matter (wt%) 42.1 33.0 27.5 16.5 12.9 6.9 Fixed carbon (wt 0/0) 45.3 47.5 58.5 64.8 72.5 78.4 Ash (wt%) 12.6 19.5 14.0 18.8 14.6 14.7 Fuel ratio (-) 1.1 1.4 2.1 3.9 5.6 11.3 Ultimate analysis: Carbon (wt % ) 69.5 62.2 72.5 69.9 75.6 78.9 Hydrogen (wt 0/0) 3.9 4.1 4.2 3.5 3.7 1.2 Oxygen (wt%) 12.3 11.9 7.6 5.7 3.9 4.5 Nitrogen (wt%) 1.4 1.2 1.5 1.6 2.0 0.6 Sulfur (wt % ) 0.7 1.4 0.5 0.8 0.8 0.1 Fuel ratio = Fixed carbon/Volatile matter 4. Results and Considerations (1) Rate of volatile evolution In this paper, the rate of volatile evolution was estimated from the data of DTF as follows. Figure 4 shows the variation of the mass fraction of unbumt fuel, (1-V) with the residence time for coal B. We divide the coal combustion process into three zones, i.e., the volatile evolution zone, the transition zone where both volatile matter and char combust at the same time, and the char combustion zone in the latter stage. From the slope of volatile evolution zone shown in Figure 4, the' rate of volatile evolution (KyM) is calculated as follows ; KYM = -(dV/dt)/(VYM-V) = {(V2-Vl)/(t2-tl)}/{VYM-(Vl+Vi)/2} (4) where, V is the mass fraction of volatile evolved, t is the residence time, subscripts 1 and 2 correspond to points 1 and 2 in Figure 4, respectively, and VYM is the mass fraction of volatile evolution at an endless time. As shown in Figure 4, the value of V YM is assumed by the intersecting point of the two lines ; the maximum volatile evolution line and the char combustion line, being V VM = 0.86 in this case. Figure 5 shows Arrhenius plots of the rate of volatile evolution (KyM) for all coals tested. Although data of KVM for each coal are a little dispersed, the log KYM value |
