| OCR Text |
Show - 11 - Initial and boundary conditions: - particle diameter 0.1 mm - initial moisture content (water/dry) 0.05 - gas temperature 1073 K - radiation (wall) temperature 1073 K - oxygen mass fraction of the atmosphere 0.1 Some parameters used in the calculations: - particle emissivity 0.9 - particle initial temperature 293 K - ignition temperature 623 K The combustion model - the pyrolysis is assumed to be limited by the heat transport, the yield of volatiles is calculated by using the temperature dependent asymptotic yield of volatiles, (DTG-curve, Fig. 1, is taken into account, but the kinetic reactions are assumed to be infinitely fast) - char combustion model 3 - the char combustion is assumed to be diffusion controlled The fuel properties used in the calculations - initial (dry) density 1300 kg/m 3 - heat of pyrolysis 100 kJ/kg - heating value of dry ash free fuel 25 MJ/kg - heating value of dry ash free char 33 MJ/kg - specific heat of dry solid 1.8 kJ/kg - heating value of pyrolysis products 21.2 MJ/kg - ash content 7% Table 1. The standard conditions from which perturbations are made in the calculations. So far no comparisons of the model calculations for the transient mass to own measurements with coal have been made. Our entrained-flow reactor has just been built. The reactor will be used to investigate the reaction mechanisms and kinetical constants by comparisons to model calculations. The comparison of the calculations to measurements with the entrained-flow reator presented in the literature is difficult due to the lack of the measured DTG-curve for those specific coals used in the measurements. The pyrolysis model requires the measured DTG-curves (Fig. 1) as the input data for different coals. Some calculated examples are presented in Fig. 6, 7 and 8. The normalized (dry) mass m/mo and the normalized particle temperature (T - 273K)/(Tmax- 273K) are presented in the figures. |
