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Show -4 2 for mass transfer control (^1.54 x 10 g C/cm s), but very close to the rate predicted by the chemical rate expression of Field et al. -5 2 (19), 2.84 x 10 " g C/cm s. The graphite rate was also similar to the Kentucky No. 9 rates for small particles burning under chemical control. Thus it appears that the graphite combustion was chemically controlled, even for such a large particle. This illustrates the tremendous influence that porosity has on Kentucky No. 9 combustion. The Combined Combustion Rate Results Figure 13 and Table 5 show the overall comparison between the experimental combustion rates from both Phase I and Phase II and the rates predicted using Eqs. (4), (7), and (13). Equations (4) and (13) were used to predict R ^ and R , and these values were then used in Eq. (7) or (8) (depending on the value of R./R.^) to estimate R .. cal Additional Information A more detailed tabulation of the data and discussion of the experimental results is presented in Daw and Krishnan (9). Those desiring more information should refer to this report. CONCLUSIONS The major conclusions of this investigation are: Kentucky No. 9 undergoes substantial swelling and plastic flow during devolatilization. The swelling can have a major impact on subsequent char combustion. The degree of swelling is strongly influenced by the combustor environment (e.g., temperature and oxygen concentration). It is likely that the effect of temperature is due to changes in the heating rate. After devolatilization, 3M x 4M coal (nominal 0.635 cm or 0.25 in. particles) burns almost completely under external diffusion control. For coal <1 mm diam, combustion becomes dominated by chemical reaction. 35 |